lesson 15: sludge treatment in jordan · planted drying bed this page considers the general generic...

29.10.18, 13*07How Treatment Technologies Impact the Climate: Overview

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Lesson 15: Sludge Treatment inJordan

This first lesson in our e-Learning course 2 («How TreatmentTechnologies Impact the Climate») describes the treatment technologiesthat are used in the ACC project in Jordan for dewatering andstabilizing the sludge.

Lesson 15 mentions some of the technologies, such as:

Unplanted Drying Beds

An unplanted drying bed is a simple, permeable bed that, when loadedwith sludge, collects percolated leachate and allows the sludge to dry byevaporation.

Planted Drying Beds

The key improvement of the planted bed over the unplanted bed is that thefilters do not need to be desludged after each feeding/drying cycle.Fresh sludge can be directly applied onto the previous layer. This pagedescribes the technology, while the next page on SDRBs goes into detail.

Sludge Drying Reed Beds (SDRB)

Domestic sludge is dispersed onto reed beds for dewatering. The reed plantsgrow through the overlying sludge and develop numerous roots in the

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substrate. This leads to a forced dewatering and mineralization of thesludge.

The section describes the SDRB technology in practice and in greater detailand gives examples from Jordan (Wadi Hassan) as well as from other partsof the world.

Exercise for Participants

The chapter finishes with a short exercise for the participants of the e-Learning course on how to dimension a SDRB.




29.10.18, 13*07How Treatment Technologies Impact the Climate: Unplanted Drying Bed


Unplanted Drying Beds

An unplanted drying bed is a simple, permeable bed that, when loaded with sludge, collects percolated leachate and allows the sludge to dry by evaporation. Approximately 50% to 80% of the sludge volume drains off as liquid or evaporates. The sludge, however, is not effectively stabilized or sanitized.

The bottom of the drying bed is lined with perforated pipes to drain the leachate away that percolates through the bed. On top of the pipes are layers of gravel and sand that support the sludge and allow the liquid to infiltrate and collect in the pipe.

It should not be applied in layers that are too thick (maximum 20 cm), or the sludge will not dry effectively. The final moisture content after 10 to 15 days of drying should be approximately 60%. When the sludge is dried, it must be separated from the sand layer and transported for further treatment, end-use or final disposal.

The leachate that is collected in the drainage pipes must also be treated properly, depending on where it is discharged.

Design Considerations

The drainage pipes are covered by 3-5 graded layers of gravel and sand. The bottom layer should be coarse gravel and the top fine sand (0.1 to 0.5 mm effective grain size). The top sand layer should be 250 to 300 mm thick because some sand will be lost each time the sludge is removed.

To improve drying and percolation, sludge application can alternate between two or more beds. The inlet should be equipped with a splash plate to prevent erosion of the sand layer and to allow for even distribution of the sludge.



Designing unplanted drying beds has to consider future maintenancebecause ensuring access to people and trucks for pumping in the sludge andremoving the dried sludge is essential.

If installed in wet climates, the facility should be covered by a roof andspecial caution should be given to prevent the inflow of surface runoff.

Appropriateness

Sludge drying is an effective way to decrease the volume of sludge, which isespecially important when it has to be transported elsewhere for furthertreatment, end-use or disposal. The technology is not effective at stabilizingthe organic fraction or decreasing the pathogenic content. Further storageor treatment (e.g. Co-Composting) of the dried sludge might be required.

Unplanted drying beds are appropriate for small to medium communitieswith populations up to 100,000 people, but larger ones also exist for hugeurban agglomerations. They are best suited for rural and peri-urban areaswhere there is inexpensive, available space situated far from homes andbusinesses. If designed to service urban areas, unplanted drying bedsshould be at the border of the community, but within economic reach formotorized emptying operators.

This is a low-cost option that can be installed in most hot and temperateclimates. Excessive rain may prevent the sludge from properly drying.

Health Aspects & Acceptance

Both the incoming and dried sludge are pathogenic; therefore, workersshould be equipped with proper protection (boots, gloves, and clothing).

The dried sludge and effluent are not sanitized and may require furthertreatment or storage, depending on the desired end-use.

The drying bed may cause a nuisance for nearby residents due to badodours and the presence of flies. Thus, it should be located sufficiently away



from residential areas.

Operation & Maintenance

Trained staff for operation and maintenance is required to ensure properfunctioning.

Dried sludge can be removed after 10 to 15 days, but this depends on theclimate conditions. Because some sand is lost with every removal of sludge,the top layer must be replaced when it gets thin. The discharge area must bekept clean and the effluent drains should be regularly flushed.

29.10.18, 13*11How Treatment Technologies Impact the Climate: Planted Drying Bed


Planted Drying Bed

This page considers the general generic aspects of this technology, whilethe next page concentrates on the practical use of sludge drying in reedbeds.

A planted drying bed is similar to an Unplanted Drying Bed, but has theadded benefit of transpiration and enhanced sludge treatment due to theplants. The key improvement of the planted bed over the unplanted bed isthat the filters do not need to be desludged after each feeding/dryingcycle. Fresh sludge can be directly applied onto the previous layer; theplants and their root systems maintain the porosity of the filter.

This technology has the benefit of dewatering and stabilizing the sludge.Also, the roots of the plants create pathways through the thickening sludgethat allow water to easily escape.

The appearance of the bed is similar to a Vertical Flow Constructed Wetland(T.9). The beds are filled with sand and gravel to support the vegetation.Instead of effluent, sludge is applied to the surface and the filtrate flowsdown through the subsurface where it is collected in drains.






Ventilation pipes connected to the drainage system contribute to aerobicconditions in the filter. A general design for layering the bed is:

250 mm of coarse gravel (grain diameter of 20 mm);250 mm of fine gravel (grain diameter of 5 mm); and100 to 150 mm of sand

Free space (1 m) should be left above the top of the sand layer to account forabout 3 to 5 years of accumulation.

Reeds (Phragmites sp.), cattails (Typha sp.) antelope grass (Echinochloasp.) and papyrus (Cyperus papyrus) are suitable plants, depending on theclimate. Local, non-invasive species can be used if they grow in humidenvironments, are resistant to salty water and readily reproduce aftercutting.

Sludge should be applied in layers between 75 to 100 mm thick andreapplied every 3 to 7 days, depending on the sludge characteristics, theenvironment and operating constraints. Sludge application rates of 100 to250 kg/m2/year have been reported in warm tropical climates. In colderclimates, such as northern Europe, rates up to 80 kg/m2/year are typical.Two or more parallel beds can be alternately used to allow for sufficientdegradation and pathogen reduction of the top layer of sludge before it isremoved.

The leachate that is collected in the drainage pipes must be treatedproperly, depending on where it is discharged.

Appropriateness

This technology is effective at decreasing the sludge volume (down to 50%)through decomposition and drying, which is especially important when thesludge needs to be transported elsewhere for end-use or disposal.



Because of their area requirements, planted drying beds are mostappropriate for small to medium communities with populations up to100,000 people, but they can also be used in bigger cities. If designed toservice urban areas, planted drying beds should be at the border of thecommunity, but within economic reach for motorized emptying operators.


Because of the pleasing aesthetics, there should be few problems withacceptance, especially if located sufficiently away from dense housing.Undisturbed plantations can attract wildlife, including poisonous snakes.

Faecal sludge is hazardous and anyone working with it should wearprotective clothing, boots and gloves. The degree of pathogen reduction inthe sludge will vary with the climate.

Depending on the desired end-use, further storage and drying might berequired.


Trained staff for operation and maintenance is required to ensure properfunctioning. The drains must be maintained and the effluent properlycollected and disposed of.

The plants should have grown sufficiently before applying the sludge. Theacclimation phase is crucial and requires much care. The plants should beperiodically thinned and/or harvested.

After 3 to 5 years the sludge can be removed.

29.10.18, 13*13


Sludge Drying Reed Bed – General Concept

(uploads/pics/sdrb.jpg)[SRDB, Source: BORDA]

This page introduces the practical use of sludge drying in reed beds in Jordan.The generic technology is described on the previous page (index.php?id=3984)

Domestic sludge is dispersed onto reed beds for dewatering. The reed plants growthrough the overlying sludge and develop numerous roots in the substrate. Thisleads to a forced dewatering and mineralization of the sludge. The dewatering isdriven by evapotranspiration and particularly by a drainage system on the bottomof the sealed reed beds (polythelene liner). The sludge volume declines to about10% of the initial volume. Usually, reed beds work for a period of 8-12 yearswithout sludge removal. The resulting product of the dewatering is earthy organicmaterial. The sludge humus can be used for further reuse such as composting,fertilisation, thermal recycling, recultivation, gardening and landscaping.

The reed bed dewatering contributes new ways of medium- and long-term disposalpossibilities giving the municipalities and other stakeholders/operators certaintyconsidering growing restrictions by legislations for reuse, however the application isoften restricted according to laws and regulations (same applies for the Jordaniancontext).

This natural sludge processing method offers ecological advantages like gravitydewatering, reed induced mineralization and evapotranspiration, which positivelyinfluence the energy balance. The method works without chemical additives likepolymers as conditioner.

The reed bed treatment is economically efficient compared to conventional mechanicaltechnologies. In addition, wildlife enhancement is an important secondary goal of SDRBwhich create habitat for birds, amphibians and invertebrates.

The operational procedures for SDRB within an interval of 7 – 12 years is described inthe image below:

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29.10.18, 13*13How Treatment Technologies Impact the Climate: Sludge Drying Reed Beds (SDRB)


Treatment schedule over years of operation (intermittent sludge loading, dewatering and mineralization of organics). Source: BORDA]

Starting up ½ - 1 year | Loading 6 – 8 years | Drying ½ - 1 year

Interval of use: ca. 7 – 10 years | Useful life: 25 years

3 times sludge removal

Description of the Dewatering Process

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The domestic sewage sludge gradually underlies a fundamental and constantconversion into earthy substances. The following processes in the rhizosphere of thereeds are responsible for this conversion:

The reed plants transport oxygen via the culm into the root space, including arich bacteria community. Bacteria are responsible for a partial mineralization oforganic substances. The reed planting doubles the microbiological activity(degradation and conversion of organic substances) compared to unplantedsludge dewatering beds.The plants are able to dewater the sludge due to high osmotic pressures andtranspire water by their leaves.The reed increases the water conductivity of the rooted sludge thus supportingis self dewatering to the drainage system.The permanently growing rhizomes and roots lead to a continuous conditioningand restructuring of the settled sludge. While the overlying sludge layer is stillblack by precipitated iron sulphide and is still of a muddy consistence theunderlying layer already has turned into brown non-smelling sludge humus. Is iswell dewatered and has a crumbly structure.

The result is a «high value» endproduct. The water content is 40 - 75% and the sludge is carrier of nutrients with slowly nutrientsdelivery. It has a stable structure and high waterstorage capacity (like humus).

Different reuse options are possible depending on regulations: among others in agriculture, landscaping or humus-production.

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(uploads/pics/humus1.jpg)[Source: Blumberg Engineers] (uploads/pics/humus2.jpg)

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(Source: Blumberg Engineers)

Examples of SDRBs worldwide

Germany

The technology of SDRB is known and implemented worldwide. In Germany > 100SDRB are running with a complete capacity of more than 1 Mio PE.

Bahrain

Tests in hot climate such as the Middle East (Egypt, Jordan and U.A.E.) have proved that the SDRB technology has a much higherefficiency under hot climate conditions than in Europe, because of:

Higher evapotranspiration,Faster microbial dismantling,Longer period of vegetationFaster and stronger growth of the reeds

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29.10.18, 13*17How Treatment Technologies Impact the Climate: SRDB worldwide


In Bahrain, SDRB are implemented to treat the excess sludge from a MBBR system.


Oman

Sludge mineralization reed bed for Six Senses Resort in Zighy Bay, Oman (treating 300 m sewage/day)


Jordan (Salt)

In Jordan, in the WWTP of Salt, 4 normal (unplanted) drying beds were modified to SDRBs as a pilot and testing site together with theUniversity of Jordan. Pilot System 4 x 160 m² (constructed 2011-2013).

(Source: Bauer Group

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29.10.18, 13*17How Treatment Technologies Impact the Climate: SRDB worldwide


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29.10.18, 13*30How Treatment Technologies Impact the Climate: Dimensioning Exercise


EXERCISE: Dimensioning thearea required for SDRBsAfter having read the explanations on the construction of the SDRBs in theWadi Hassan Wastewater Treatment Plant, we would like to present to youa short example how to calculate the area required for SDRBs based on thesludge load and on the expected duration of operation.

Example calculationPlease find following an example that shows how to calculate the totalarea and the number of basins required for the SDRB’s in WadiHassan:

Data given:

Duration of operation: 6 months (only during winter time; duringsummer time unplanted beds can be used)Expected amount of sludge: 9150 m3/6 monthsDry sludge percentage: 3%Sludge load on SDRB´s: 70 kg/m2

Solution:

Step 1: Calculation of the dry sludge content [kg/6 months]Dry sludge [kg/6months] = (amount of sludge [m3/6 months] xDry sludge [%]) x 1000 [kg/m3]Dry sludge [kg/6 months] = (9150 x 0.03) x 1000 = 274500[kg/6 months]

Step 2: Calculation of the required net area [m2] for the SDRB’s.Hence, the next step is to divide the Dry sludge amount in Kg over thesludge load of SDRB. [Note: for the climatic conditions in Jordan, a

29.10.18, 13*30How Treatment Technologies Impact the Climate: Dimensioning Exercise


Sewage Sludge loading of 70 kg/m2 is chosen. For European climaticconditions (such as Germany) a loading of 25 kg/m2 is used].

Net area required: 274500 [kg/6 months] / 70 [kg/m2] = 3921[m2/6 months]

Step 3: Calculation of the appropriate number of SDRB basins. [Hint: as a suitable size for operation and maintenance of the SDRB´s, an area of 1000 m2 per basin can be assumed. The basins areoperated in sequence, that means one bed is loaded with the sludgefrom one day, the next day another bed is loaded so that there isenough time for the initial drying process on each bed].

Required area m2 / The recommended basin size in m2

Number of basins= 3921 [m2/6 months] / 1000 [m2] = 3.92 = 4basins

Step 4: The final step is to calculate the total gross area required(including dams and ways between the basins). Thereforethe formula has to multiply the net are with 1.5. [Note: Gross area =1.5 * net area]

Total gross area= 3921 m2 x 1.5= 5881 m2

5 tips for NGOs working in sanitation, private players, Governments and ULBs to set up

their own Faecal Sludge Treatment Plant (FSTP).

EAWAG (2017): lntroduction to Faecal Sludge Management. 9:00min

Description how «Unplanted drying beds» work and what to consider when constructing

them.

Sludge mineralisation as a possibility for the minimisation

of sewage sludge in rural areas

Dr.-Eng. Noama Shareef

Definition

The treatment of sewage sludge in constructed wetlands is a

process of dewatering and advanced mineralisation of sludge

(Sludge Mineralisation)

First experience with this process in Germany about 1960

Application: rural areas 300 – 800.000 PE in Germany More than 80 plants ( > 1 million PE) in Germany

Types of process Bed planted with common reed (Phragmatis australis)

Bed planted with grass (Lolium perenne) [German Patent BP19700434)

Emden 90,000 PE

Reed (Fa. Eco-Plant)

WTP 4,000 E

Growth with reed

Aschersleben 48,000 PE

Growth with grass

Buffer tank for the input is usually required

Construction

Removable concrete slab

Earth bank Seal system (Foil or clay)

System for sludge distribution

Regular and careful distribution to protect stalks Radius of distribution about 4 - 6 m

Special layer of substrate for the growth of plant

Drainage with filter layer

The particle size should increase from the top to the bottom

Mechanical and hydraulical effectiveness

Ramp or paved path for the removal of treated sludge

Details of construction

Buffer tank for the input is usually required Construction

Removable concrete slab Earth bank Seal system (Foil or clay)

System for sludge distribution Regular and careful distribution to protect stalks Radius of distribution about 4 - 6 m

Special layer of substrate for the growth of plant Drainage with filter layer

The particle size should increase from the top to the bottom Mechanical and hydraulical effectiveness Ramp or paved path for the removal of treated sludge

Construction Different methods of sludge distribution

l General

Loading with sludge, which is free of screening

Equal distribution across the surface of the bed

Operates through the whole year (except during extreme frost)

Seed or plantation outside the frost period

Beginning of operation (e.g. a young reed must not be broken)

Reedbeds Sludge loading in period of 5 to 10 years; the last year

feeding break Minimised times with stormwater treatment Irrigation if necessary, overdming Remove foreign plants Dead reeds remain in the sludge Application of moveable footbridges etc.

l General

Input: quantity of sludge p.a.; DS and oDS- Content

Subdivided into at least three or four units

Active surface of the bed about 0,5 m2/PE (without slopes, ramps etc.)

Reed beds

Height of layer per year: 10 to 20 cm

Load of solid matter depending on stabilisation degree (VS 55 - 65%):

30 - 70 kg DS/(m²·a)

Depth of the bed about 1.5 -1.7 m

Sludge-Qualities

According to German law = sludge

Nutrients, mainly phosphorus, remain in the sludge. Nitrogen can be nitrified and denitrified

Heavy metals remain in the sludge

Positive effect on physical qualities

Crumbly structure; easily processed

Increase of the DS from 3 - 4% up to 20% (literature 30 – 50%)

Decrease of the Volatile solids to 45 - 55% (literature 30 – 45%)

Earthy smell

Advantages

Decreases the sludge amounts by 80% and more (dewatering and mineralisation)

„Win of time “

Few moving parts

Relatively low expenditure of human labour

Low energy demand( Feeding; removal)

Reduction and equalisation of the re-load

No use of f locculants

Increase of application in agriculture and landscaping

Disadvantages

Large space demand ( 0,25 –1,5m²/PE)

Difficult operation while starting the process and during winter time

Disposition of the heavy metals and the organic pollution

The care for the plants is often underestimated (Water management)

Handling of extreme loads of pollution (e.g. damage)

Reed Bed Contracting L.L.C. / [email protected] / www.reedbed.ae PO box 43157 / Abu Dhabi – United Arab Emirates / License CN-1934649 / Al Saman Tower 3, Block A, Office 1303 Page 1 of 6

FREQUENTLY ASKED QUESTIONS ABOUT REED BED - FAQ MANUAL -


TABLE OF CONTENT

1. What about smell?

2. What about mosquitoes?

3. What about rats?

4. Is a pre-treatment required?

5. What about the sewage sludge?

6. Must the reed plants be harvested?

7. Can other plants be used?

8. Must the plants be replanted?

9. Do reed plants match with the local flora and fauna?

10. What effect has the local temperature on the system?

11. How much water is used by the reed plants?

12. Do the system needs a constant inflow (low season) ?

13. Will the reed plants invade other landscaping areas?

14. What is the life time of the system?

15. What operation and maintenance is required?

16. Time between design and functional system?

17. References in the Middle East?

18. Scientific Researches about Reed Beds?


1. What about smell? The treatment process in the upper bio activator filter layers is an aerobic process. The Oxygen will be supplied by the Reed plants through intermittent loading. As smell is only created by anaerobic processes, no smell will occur at the reed beds. Therefore the system is directly built near the villas compounds. Since years of operation, reed beds have guaranty a zero smell.

2. What about mosquitoes? In comparison to waste water lagoons, reed beds do not have constant open water areas. The reed bed is a planted filter, through which the waste water percolates vertically or horizontally with only short or even no contact to the surface, depending on the design. Without any open water no mosquitoes can breed. Even other insects like flies, in the reed bed and the adjacent areas, are reduced by the high biodiversity of the system to a minimum (food chain: insects > dragon flies > birds)

3. What about rats?

Rats do not find any food in the pre-treated or totally shredded sewage which is fed into the reed beds (depending on the design) therefore they are not attracted by the wetlands as food supply. As any other plantation red beds give a shelter only for birds. As the filter bed is temporary charged with water and there is always a water level in the lower substrate layers rats or rabbits can not build burrows in the reed beds. A pest control as usual for plantation areas in urban landscaping is sufficient to control the rat population, however additional measures especially for the reed beds are not required.

4. Is a pre-treatment required? That depends on the design; there are reed bed systems (Stage B reed bed) which require a pre-treatment in form of a screen, septic tank or even an aerobic biological process (SBR, trickling filter, fixed bed). But there are also systems which can be charged with raw sewage. These systems have a special reed bed filtration stage (Stage A reed bed) which removes and convert the suspended solids prior to a second biological red bed treatment stage (Stage B reed bed). Which reed bed technology will be chosen depends on the project and client.

5. What about the sewage sludge? If a reed bed system with a pre-treatment in the form of sedimentation is chosen, the accumulated sludge in the sedimentation stage can either be discharged by tankers or converted into humus in a special sludge composting reed bed. The produced volume of sewage sludge, if any, depending on the chosen reed bed system, is always less than in any other STP system. In a raw sewage reed bed the mineralized sludge in the first filtration stage must be removed only after 30 – 50 year depending on the design.

6. Must the reed plants be harvested? Yes, every 5 years the reed plants should be harvested to avoid a too high accumulation of reed mulch and litter on top of the systems, monthly the plants can be trimmed at the sides of the system. If required the plants can frequently be harvested and used as Biomass for wood fire, biogas production or eco-friendly construction materials without any negative effects on the treatment process.

7. Can other plants be used? Because of the high oxygen supply into the Rootzone and the strong growth of the roots Phragmites Communis is the best marsh plant for reed beds. But there are several other native marsh plants which can be used in the reed bed. We would propose to use these other native plants as well in the system to preserve these plants which are


reducing in numbers at present in the U.A.E. due to the lowering ground water levels and thereby drying of natural oasis's, wadis and wetlands. Therefore each artificial wetland equipped with different marsh plants will preserve the native fauna.

8. Must the plants be replanted? No, never, once the marsh plants are established they will self generate until the system will be removed.

9. Do reed plants match with the local flora and fauna? Yes, Phragmites communis is a native wide spread species in the region. Wherever brackish or freshwater moisturise the soil or is appearing at the surface (wadis, oasis, sewage and irrigation water spills), reeds will grow naturally. Reed plants could also be used to link fresh water wetlands with salt water wetlands like sabkhas, mangroves and sea grass fields.

10. What effect has the local temperature on the system? The higher the better, in contrast to technical sewage treatment plants, the reed bed technology has its optimum performance under hot climate as more energy is feed to the reeds to grow, higher sunlight improves photosynthesis and therefore the Oxygen transfer into the root system and the sludge humifies much better.

11. How much water is used by the reed plants? The water is not lost, as it is used to create greenery with the reed plants. If the reed bed is integrated into the landscaping its footprint replaces area of the normal soft landscaping which would otherwise consume water for irrigation. The reed plants do not consume more water per m² as spray irrigated turf. According to the design a minimum of 15 % and up to 100% of the sewage can be consumed by the reed plants. 100% consumption is helpful if the sewage can not be reused and would otherwise pose a problem to the client to get rid of.

12. Do the system needs a constant inflow (low season) ? No, only during the initial 'rooting' period it is important to have a constant inflow to prevent the young plants dying (the first half year). Once the reed plants are established and have developed their Root zone (Rhizomes are like a flower bulb) it is nearly impossible to kill the complete stock. A longer period without sewage inflow (3 – 4 month) will lead a hibernation of the reeds; the above ground biomass will dry off, but the Rhizomes will immediate sprout new shoots if water is available again. The dried biomass can be harvested before new sewage is filled into the system. A start up period (like with a technical treatment plant) is not required.

13. Will the reed plants invade other landscaping areas? The seeds of the reed plants are already natural spread over all areas in the Middle East from natural stocks of reed plants, as the seeds can fly over hundreds of kilometres. Precautions should only be taken against the spread of the Root system of the established reed stock in a reed bed, but this is already done by the PVC or HDPE liner which divides the root system from the surrounding soils. Only horizontal off-shoots of the stalks can invade surrounding areas. As these horizontal off-shoots grow roots very slowly a monthly removal of these shoots is sufficient to prevent invading of the reed stock into adjacent areas and is considered as normal landscaping or gardening maintenance

14. What is the life time of the system? As the reed stock is a self generating system and all sewage solids will be totally broken down by the micro organisms into minerals, there is no wear in the system and there is an increase of solids in the system, which has no impact on the performance. The oldest systems in France and Germany are over 50 years without any


weakening of the performance. The only mechanical part of the system is a lift station, which must be calculated with a life time of around 10 years according to pumps used.

15. What operation and maintenance is required? Depending on the size of the system a weekly visual check and a monthly trimming of the reed shoots is enough.

16. Time between design and functional system? As there are no delivery times for foreign materials and equipments a reed bed treatment system for a single household can be build within a few days after the design and approval period. The installation time of larger system depend mainly on the capability of the contractor.

17. References in the Middle East? In Middle East the construction of Reed Beds Sewerage Treatment Plant have started 10 years ago. Today there are more than 30 major Reed Beds system running. The most recent ones have been built for the Ministry of Presidential Affairs in United Arab Emirates.

Use of Reed Beds for FaecalSludge Dewatering

Udo Heinss* and Thammarat Koottatep**

A Synopsis of Reviewed Literatureand

Interim Results of Pilot Investigations with Septage Treatmentin Bangkok, Thailand

1998

* EAWAG, Swiss Federal Institute for EnvironmentalScience & TechnologySANDEC, Dept. for Water and Sanitation in Developing Countries

** AIT, Asian Institute of TechnologySchool of Environment, resources and DevelopmentEnvironmental Engineering Program

Asian Institute of TechnologyBangkok, Thailand –

Urban Env. Engineering &Managament Program

Acronyms and Abbreviations

AIT Asian Institute of Technology, BangkokBMA Bangkok Metropolitan AdministrationEAWAG Swiss Federal Institute for Environmental Science &

Technology, ZurichEEP Environmental Engineering Program (AIT)SANDEC Dept. of Water & Sanitation in Developing Countries

(EAWAG)

AG-WSP Attached-Growth Waste Stabilisation PondsCW Constructed WetlandsFS Faecal SludgeHRT Hydraulic retention timeSLR Solids loading rateSTP Sewage Treatment Plants

BOD Biochemical Oxygen DemandCOD Chemical Oxygen DemandSS Suspended SolidsTKN Total Kjeldahl NitrogenTS Total Solids

Contents

Preface i

1 Rationale and Introduction 1

Part A

2 Findings from the Literature.2.1 Comparative Performance of Planted vs. Unplanted Beds 22.2 Hygienic Quality of the Percolating Water 22.3 Need for Bottom Ventilation 32.4 Reeds 32.5 Close-Up View 3

3 Conclusions 5

4 Recommended Design for a Pilot Reed Bed 6

Part B

5 Interim Results of Pilot Cattail Bed (Constructed Wetlands)Operations at AIT, Bangkok

5.1 Introduction 75.2 Operations 75.3 Evaluation 10

Table 1 Summary of Reed Bed PerformanceData for Sludge Dewatering/Drying 14

Table 2 Reviewed Publications 15

Preface i

Preface

Most urban dwellers in developing countries use on-site excreta disposal systems,such as public and family latrines, aqua privies and septic tanks. Contrary towastewater collection and treatment, improvements in faecal sludge managementhave received little attention until very recently. To date, in the majority of cases,faecal sludges collected from on-site disposal systems are still disposed of untreated,mainly for lack of affordable treatment options. Therefore, SANDEC has embarkedon practice-oriented R+D of faecal sludge (FS) treatment options, with the objectiveto develop guidelines for the design and operation of sustainable treatmenttechnologies based mainly on practical field research.

So far, SANDEC mainly examined the use of pond systems for FS treatment throughcollaborative field research carried out with Ghana's Water Research Institute.Results of these investigations and recommendations for practitioners have beenpublished in "Solids Separation and Pond Systems for the Treatment of FaecalSludges in the Tropics" by Heinss, Larmie and Strauss (SANDEC report no.05/98).Another focus project was on the use of septage for land reclamation of Lahar(volcano ash) stricken areas. In a new collaborative field research project with AIT(Asian Institute of Technology), reed beds will be tested for their ability to treatseptage.

Rationale and Introduction 1

1. Rationale and Introduction

Sludge drying beds may be classified as a solids-liquid separation process,producing a dewatered or dried solids product and a liquid (percolate) requiringfurther treatment prior to discharge or use. Mostly unplanted drying beds havebeen used to date to handle sludges from sewage treatment plants (STP).However, in Europe and in the United States, planted sludge drying beds arefinding increasing use. Reeds normally are the plants-of-choice for such beds thatare therefore also designated “reed beds”. They require substantially less operatingcare than unplanted beds as they need to be emptied every few years, only.SANDEC hypothesizes that reed beds might prove a feasible option for treatingfaecal sludge.

Part A contains the literature review. Experience gained with the use of reed beds fordewatering/drying sewage treatment plant or excess activated sludge in mostlytemperate climate is summarised. The purpose of the review was to make theinformation available to persons dealing with faecal or STP sludge management.Further to this, SANDEC needed hints as to the possible design of planted dryingbeds to carry out pilot or demonstration schemes for FS dewatering/drying. Thefindings from the literature review are discussed in Chpt. 2 below. Table A1 in theAnnex is a synopsis of the reported design and operating parameters. Fig. 1 showsthe schematic design of a ventilated reed bed. Table A2 of the Annex provides thelist of reviewed publications.

In Part B, interim results of AIT/SANDEC collaborative field research conducted inBangkok, Thailand, are presented. Three pilot reed beds (“constructed wetlands”)treating septage have been in operation and subjected to intensive monitoring sinceearly 1997.

Findings from the Literature 2

Part A

2. Findings from the Literature

2.1 Comparative Performance of Planted vs. Unplanted Beds

Three experiments compare the performance of planted and unplanted dryingbeds (4,7,8). The results obtained show the advantages of reed beds as over theconventional sludge drying beds.

Drying

- The average reported solids content in planted beds amounts to 40%compared to 32% in unplanted beds.

- According to the authors, the lower sludge layer in a planted bed isaerobic and brown in colour whereas the sludge in unplanted beds isanaerobic and black.

BOD and COD

- BOD and COD concentrations in the percolating water of reed beds are35-55% and 50-60%, respectively, lower than in unplanted beds.

Nitrification

- The ammonium in the percolating water of reed beds is 70-80% lowerthan in the liquid of conventional beds. Nitrate levels in the effluent of reedbeds are, in turn, 3-10 times higher than in other beds. It can therefore beconcluded that nitrification in reed beds is greater than in conventionalunplanted beds.

Ventilated vs. Non-Ventilated Beds

- The difference in quality between the percolating waters of planted andunplanted beds becomes smaller when the beds are equipped with aventilation system inducing an air current along the bottom of the bed (7)(see Fig.1). As a result, oxidising reactions also tend to occur in unplantedbeds.

2.2 Hygienic Quality of the Percolating Water

- Hygienic quality improvement was also investigated (8,9). Concentrationsof enterobacteria (mainly E. coli) were reduced during percolation throughthe reed beds by 2-3 orders of magnitude. According to one author, anunrestricted agricultural use of the sludge from reed beds is possible after14 months of storage and drying of the sludge (8).


2.3 Need for Bottom Ventilation

- Loading rates for anaerobically stabilised sludges should be kept small inreed beds without bottom ventilation (4). Planted reeds died in non-ventilated beds when loaded with activated sludge from an oxidation ditch(7). However, in a ventilated bed the reeds survived and the averagedrying rate was significantly higher than in a non-ventilated bed. Reedsgrew very well when aerobic stabilised sludge was applied in a non-ventilated bed (8). However, if the beds were loaded with a fresh excesssludge or digested sludge, the stock of reed plants decreased.

2.4 Reeds

- All reed beds were planted with Phragmites. In beds where also otherHelophytes were planted, Phragmites was the only plant that developed apermanent plant stock and supplanted all other plants.

- Newly planted reeds reportedly formed a dense standing crop several

months later (9).

- As regards cutting, different opinions prevail: from no cutting to cuttingevery year or after several years.

2.5 Close-Up View

- It is assumed that reeds influence the sludge dewatering andmineralisation process in different ways. Bacteria may thrive on theextensive root system as attached biofilm. The hollow roots possibly allowtransport and supply of O2 to attached aerobic bacteria. Since the rootsystem is continuously growing, the sludge/soil layer remains permeableeven through the increasing sludge layer.

- Compared to unplanted drying beds, higher TS contents but lowerpercolating water were obtained in planted beds (4,8). This can beattributed to the high suction pressure exerted by the root system and theleaves which evapotranspirate high quantities of water (15-25 mm/d (1,2)).

3. Conclusions

Use of reed beds for faecal sludge dewatering in tropical countries may constitute apromising alternative to conventional sludge dewatering beds. Compared toconventional drying bed, the thereby resulting advantages are the following.

• Simplicity of operation:


Compared to unplanted beds, far less effort is required for sludge removal inreed beds as planted beds may be loaded over several years beforedesludging becomes necessary.

• Nitrification:

Faecal sludge treatment in facultative ponds is often difficult as high ammoniaconcentrations may prevent the growth of algae. Nitrification in reed bedsmay therefore improve treatability of the drained effluent in facultative ponds.

• Limited clogging

Clogging of the filter layer is likely to be minimal due to the continuous growthof rhizomes (rootstock).

Similar to sludge drying beds, the main disadvantage of reed beds is their largeland requirement. This will limit the use of this treatment option to areas wheresufficient land is available or where the treatment strategy consists in opting fordecentralized systems.Beside the operational advantages, the application of constructed wetlands, as thereed beds are also called, leads to beneficial effects such as wetland conservationand restoration of wildlife habitat.

Pilot Reed Bed Design 5

4. Recommended Design for a Pilot Reed BedBased on the data in Table 1 for temperate climates, experimental or pilot reedbeds treating faecal sludges in tropical zones could possibly be designed asfollows:

- Size: 20-40 m2, multiple units; 1 - 1.5 m freeboard- Bottom ventilation to allow passive aeration- Interval of faecal sludge application: weekly- Loading rate: 100 kg TS/m2y, initially; provision may be made to allow

a stepwise increase of the loading rate to 150 kg TS/m2.yr or above ifthe reed growth and the drying process are not negatively influenced.

Since reeds do not appear to grow well under highly anaerobic conditions, aventilation system allowing for natural bottom aeration is, therefore, necessary,particularly when drying highly anaerobic sludges (Fig. 1). Passive aeration isachieved with the use of hollow blocks at the filter bottom and a vent pipe of a largediameter ( 20 cm). The pipe should extend at least 1 m above the reeds at theirhighest stand; i.e. prior to bed emptying.

It should be noted that uncertainties still exist regarding long-term performance andoptimum operational patterns. Extended monitoring of septage-loaded constructedwetlands shall answer essential questions: Will percolation rate in the soil filterremain constant over several years of sludge loading? How will the plants react tohigh organic loading and a changing water regime induced by alternating septageloading and drying?

AirDrainage

Reeds

Compost*SandFilter bottom

Faecal sludge

*for initial planting

Vent pipe

Wind action

Freeboard

Fig. 1: Functional sketch of a reed bed with natural bottom ventilation

Results of Pilot Cattail Bed Operations 6

Part B

5. Interim Results of Treating Septage in Pilot Cattail Beds(Constructed Wetlands) at AIT, Bangkok

5.1 Introduction

Experience to date in using constructed wetlands or planted soil filters for sludgedewatering and stabilisation is limited almost exclusively to treating excessactivated sludge. The majority of these sludges are either aerobically stabilised oranaerobically digested. Performance data shown in Table 1 above weredetermined in systems situated in temperate climates. Therefore, the three pilotsludge drying beds installed at the AIT campus and treating faecal sludge(septage1) hauled from Bangkok city represent a new approach in using wetlands.

5.2 Operations

The three pilot reed beds have got a size of 5 x 5 m each. Fig. 2 showsschematically the structure of the beds installed at AIT. The support and filteringmedia installed in the concrete embankment lined units are composed as follows(from bottom to top):

- Hollow blocks underdrain each 20x40x20 cm- 40 cm of large gravel ∅ 25-50 mm- 15 cm of small gravel ∅ 10-25 mm- 10 cm fine sand ∅ eff. 0.3-0.75 mm

Ventilation pipes (∅ 20 cm) which are connected to the underdrain system secure rootzone aeration. Fig. 3 shows schematically how the reed beds are operated,including feeding arrangements and post treatment in attached-growth wastestabilisation ponds.

The wetlands have been loaded with septage for 9 months. 1,650 m3 of septagewith an average TS content of 1-2 %, TCOD 14,000 mg/l, and TKN of 1,240 mg/l)have been treated and dewatered to a TS level of around 45 % during this period.Fig. 4 shows the water balance in the constructed wetlands as calculated fromcumulative septage loading, water stored in the dewatered septage and percolateflow measurements.

The pilot reed beds were operated at the following regime:

- Septage loading at once-per-week and twice-per-week intervals

1 Faecal sludge is a general expression for sludges of variable consistency collected from so called

on-site sanitation systems; viz. latrines, non-sewered public toilets, septic tanks, and aqua privies.Septage as one kind of faecal sludge, consists of the contents of septic tanks and usuallycomprises settled and floating solids as well as the interstitial liquid.

- Septage loading rates:Equivalent to 80 – 160 kg TS/m2year, initiallyMore recently set at 250 kg TS/m2year


- TS concentrations of more than 50 % were obtained in the dried septagelayer. It was however observed that at this TS concentration cattailswilting occurred presumably because of insufficient soil moisture.Sustainable plant growth is ensured at TS concentrations of 25-35%. Thiscorresponds to a septage loading rate of 250 kg TS/m2year a. Percolateponding for 2-6 days is being tested to support conditions for healthycattail growth.

Fig. 2: Pilot Reed Bed Installed at AIT (schematic)

Fig. 3: Water Balance in the Pilot Constructed Wetlands Used for thetreatment of Septage in Bangkok, Thailand (Initial phase)

Dried Sludge1%Percolate

77%

Evapotrans-piration 22 %

2-m wood pile

7-cm thickferro-cement

0.25-cmplastic sheet

10-cm reinforcedconcrete slab

20-cm concreteblocks

1.2-cm mesh

20-cm stainlesssteel ventilation

pipe

20-cm PVCdrainage pipe

3-m3 effluentreceiving tank

Outlet pipe


Fig. 4 Functional sketch for unit operations of theconstructed wetlands and AGWSP systems

Percolate feeding tank

AGWSP-1AGWSP-2

Polishing pond

* ERT = Effluent receiving tank** HRF = Horizontal-flow rock filter

AGWSP-3

Mixer-equippedfeeding tankScreening

tank

Storage tank

BMA

CW-1

CW-2

CW-3

ERT*-1

ERT*-2

ERT*-3

To constructedwetland units

From screening & storage units

To AGWSP units& polishing ponds

AGWSP-4

Percolate feeding tank

HRF**

From constructedwetland units

To canal


5.3 Evaluation

Results generated during the first nine months of operations (1997-98), tend toindicate that the process is feasible in principle, for treating septage. However,long-term operation and monitoring over 2-4 years are required to determinedesign and operating criteria, which will allow for a stable process. Moreover,faecal sludges other than septage would have to be tested too, to determine thefeasibility of the process for varying types of FS. It is expected that sludges, whichexhibit a fair degree of biochemical stabilisation, such as pond sludges, may lendthemselves well for reed bed dewatering. Treatment of fresh, public toilet typesludges may constitute a greater challenge, though.

The important question is whether it will be possible to operate the beds over yearswithout removing the sludge and without clogging of the filter layer.

Encouraging results with respect to removal efficiencies in the percolating liquidand with respect to sludge dewatering have been obtained to date. Periodic reedwilting has occurred at the same time. Further investigations are required tounderstand the reasons for it and to develop sustainable measures to achievestable plant growth. One measure, which has been tried to date, and whichappears to improve plant growth is the effluent ponding to a level just below thestored sludge layer. At the current regime, the effluent is then allowed to flow offevery 2-6 days, the main criterion being to avoid anaerobicity in the root zone.

Table 1 shows the average values of percolate quality achieved to date. Post-treatment of the percolate will be required for most discharge situations in spite ofthe fact that high removal efficiencies are attained in the reed beds.

Table 1 Reed Bed Performance With Respect to Percolate Quality

Raw septagemg/l

Percolatemg/l % Removal

SS mg/l 10, - 20,000 700 > 90

CODtot mg/l 14,000 1,500 95CODfilt. mg/l 470 200 57

TKN mg/l 1,200 150 90

Tabl

e 2

Revi

ewed

Pub

licat

ions

Ref.

Title

Ref

eren

ce

1K

lärs

chla

mm

vere

rdun

g m

it H

ilfe

von

Hel

ophy

ten

(in G

erm

an) (

Slu

dge

Hum

ifica

tion

Usi

ng H

elop

hyte

s)R

einh

ofer

M./B

ergh

old

H. (

1994

).K

orre

spon

denz

Abw

asse

r, 8/

94, p

p.13

02-1

305.

2K

lärs

chla

mm

vere

rdun

g in

bep

flanz

ten

Sch

lam

mtro

cken

beet

en (i

n G

erm

an)

(Slu

dge

Hum

ifica

tion

in p

lant

ed d

ryin

g be

ds)

Mor

i K. (

1996

).M

OR

ITE

C In

tern

al d

ocum

ent.

3S

ludg

e D

ewat

erin

g an

d M

iner

alis

atio

n in

Ree

d B

ed S

yste

ms

Nie

lsen

S. M

. (19

90).

In P

roce

edin

gs -

Con

stru

cted

Wet

land

s in

Wat

er P

ollu

tion,

Per

gam

on P

ress

.

4U

se o

f Phr

agm

ites

in S

ewag

e S

ludg

e Tr

eatm

ent

Hof

man

n K

. (19

90).

In P

roce

edin

gs -

Con

stru

cted

Wet

land

s in

Wat

er P

ollu

tion,

Per

gam

on P

ress

.

5U

se o

f Ree

d B

eds

for D

ewat

erin

g S

ludg

e in

the

US

AK

im B

.J./

Car

dena

s R

. (19

90).

In P

roce

edin

gs -

Con

stru

cted

Wet

land

s in

Wat

er P

ollu

tion,

Per

gam

on P

ress

.

6K

lärs

chla

mm

vere

rdun

g au

f zw

ei o

stfri

esis

chen

Inse

ln(in

Ger

man

) (S

ludg

e hu

mifi

catio

n on

two

Eas

t Fris

ian

Isla

nds)

Inge

nieu

rges

ells

chaf

t für

Um

wel

tpla

nung

(IN

FU) (

1995

).In

tern

al d

ocum

ent.

7A

Stu

dy o

f Act

ivat

ed S

ludg

e D

ewat

erin

g in

Exp

erim

enta

lR

eed-

Pla

nted

or U

npla

nted

Slu

dge

Dry

ing

Bed

sLi

énar

d A

. / D

uchè

ne P

h./ G

orin

i D. (

1994

). In

: Pro

ceed

ings

,4th

IAW

Q In

t. S

peci

alis

t Con

fere

nce

on W

etla

nd S

yste

ms

for

Wat

er P

ollu

tion

Con

trol,

Gua

ngzh

ou, P

.R. C

hina

, 6-1

0 N

ov..

8D

er E

insa

tz v

on P

flanz

en z

ur K

lärs

chla

mm

-Ent

wäs

seru

ng(in

Ger

man

) (U

sing

pla

nts

for s

ludg

e de

wat

erin

g)Za

cher

B. /

Stra

uch

D. (

1987

).K

orre

spon

denz

Abw

asse

r 9/8

7, p

p. 9

22-9

30.

9K

lärs

chla

mm

vere

rdun

g in

Sch

ilfbe

cken

Erg

ebn.

und

Erk

ennt

n. e

ines

pra

xisb

ez. P

ilotp

roje

ktes

(in

Ger

man

)(S

ludg

e hu

mifi

catio

n us

ing

reed

bed

s: re

sults

of a

pilo

tpr

ojec

t)

Sch

oll W

. /W

urst

er H

. /Th

alm

ann

A. (

1985

).K

orre

spon

denz

Abw

asse

r 5/8

5, p

p. 3

86-3

95.

Reviewed Publications 10

Tabl

e 1

Sum

mar

y of

Ree

d Be

d Pe

rfor

man

ce D

ata

for S

ludg

e De

wat

erin

g/Dr

ying

Ref.

no.

Size

of

No. o

fPo

p’n

Com

paris

onKi

nd o

fTS

inSl

udge

Appl

ic.

TS lo

adin

gTS

(see

Tabl

e 2)

one

bed

(m^2

)dr

ying

beds

Equi

v.w

. unp

lant

edbe

d ?

Botto

mve

ntila

tion

?tr

eate

dsl

udge

Load

edSl

udge

, g/l

vol.

Appl

ied

m3/

m2·

year

inte

rval

Rate

Kg T

S/m

2,yr

Atta

ined

%

180

210

,000

nono

aero

bica

lly2.

84.

4w

eekl

y12

033

.5st

abilis

ed4-

7cm

2-

--

nono

not s

peci

fied

-5.

2-

7545

310

04

-no

yes

aero

b st

ab.

0.7

1.9

--

20an

aero

b di

g.3.

5-

-4

604

-ye

sno

aero

b. s

tab.

--

fort-

20-3

040

nigh

tlySS

537

-279

-no

noan

aero

bica

lly1

to 1

00.

41-0

.82

-13

-74

(sur

vey

1 to

10

dige

sted

40-5

0re

sults

)-

nono

aero

b. s

tab.

0.5

to 5

0.73

-3.3

8-

29-1

06

6-

50,0

00no

no?

-8-

--

40-5

0

720

3ex

p.be

dsye

sye

sae

rob.

sta

b.0.

313

-15

daily

5515

846

4ye

sno

aero

b st

ab.

1.5

1.5

wee

kly

25-

966

2no

yes

exce

ss8

0.45

wee

kly

100

40ac

tivat

ed s

ludg

e

Rem

arks

:1

Wat

er b

alan

ce e

vapo

ratio

n/dr

aina

ge 5

0:50

; ave

rage

evap

otra

nspi

ratio

n: 1

1mm

/d

Ref

. No

240

% o

rg. N

elim

inat

ion

in th

e dr

aina

ge; a

vera

geev

apot

rans

pira

tion:

12-

20 m

m/d

ay5

Surv

ey o

f 28

beds

in th

eU

S

TS -

Tota

l Sol

ids

6Av

erag

e ev

apot

rans

pira

tion:

5 m

m/d

SS

-Su

spen

ded

solid

s

Summary of Reed Bed Performance Data 11



Lesson 16: More SludgeTreatment Technologies

Here, more sludge treatment technologies are described with design andeconomics as well as O&M considerations and their advantages anddisadvantages. Because they all are suited for Jordanianconditions as well, it is important to know how they work.

The following lesson describes the following technologies:

Sedimentation/Thickening Ponds

Sedimentation or thickening ponds are settling ponds that allow sludge tothicken and dewater. The effluent is removed and treated, while thethickened sludge can be further treated in a subsequent technology.

Co-Composting

Co-composting is the controlled aerobic degradation of organics, usingmore than one feedstock: faecal sludge and organic solid waste. Bycombining the two, the benefits of each can be used to optimize the processand the product.

Biogas Reactor






A biogas reactor is an anaerobic treatment technology that produces adigested slurry and biogas that can be used for energy.

Mechanical Dewatering

Mechanical dewatering is used to separate sludge into a liquid and a solidpart. The process does not treat the sludge, it only separates solid fromliquid parts.


29.10.18, 13*45How Treatment Technologies Impact the Climate: Sedimentation Pond


Sedimentation / ThickeningPond

Sedimentation or thickening ponds are settling ponds that allow sludge tothicken and dewater. The effluent is removed and treated, while thethickened sludge can be further treated in a subsequent technology.

Faecal sludge is not a uniform product and, therefore, its treatment must bespecific to the characteristics of the specific sludge. Sludge, which is stillrich in organics and has not undergone significant degradation, is difficultto dewater. Conversely, sludge that has undergone significant anaerobicdegradation, is more easily dewatered.

In order to be properly dried, fresh sludge rich in organic matter (e.g.,latrine or public toilet sludge) must first be stabilized. Allowing the sludgeto degrade anaerobically in sedimentation/thickening ponds can do this.The same type of pond can be used to thicken sludge which is alreadypartially stabilized (e.g., originating from Septic Tanks), although itundergoes less degradation and requires more time to settle. Thedegradation process may actually hinder the settling of sludge because thegases produced bubble up and re-suspend the solids.

As the sludge settles and digests, the supernatant must be decanted andtreated separately. The thickened sludge can then be dried or furthercomposted.


Two tanks operating in parallel are required; one can be operated, whilethe other is emptied. To achieve maximum efficiency, loading and restingperiods should not exceed 4 to 5 weeks, although much longer cycles arecommon.

When a 4-week loading and 4-week resting cycle is used, total solids (TS)

29.10.18, 13*45How Treatment Technologies Impact the Climate: Sedimentation Pond


can be increased to 14% (depending on the initial concentration).

Appropriateness

Sedimentation/thickening ponds are appropriate where there isinexpensive, available space located far from homes and businesses; itshould be established at the border of the community. The thickened sludgeis still infectious, although it is easier to handle and less prone to splashingand spraying. Trained staff for operation and maintenance is required toensure proper functioning.

This is a low-cost option that can be installed in most hot and temperateclimates. Excessive rain may prevent the sludge from properly settling andthickening.


Both the incoming and thickened sludge are pathogenic; therefore,workers should be equipped with proper protection (boots, gloves, andclothing).

The thickened sludge is not sanitized and requires further treatment (atleast in a drying process) before disposal or end-use.

The ponds may cause a nuisance for nearby residents due to bad odours andthe presence of flies. Thus, they should be located sufficiently away fromresidential areas.


Maintenance is an important aspect of well-functioning ponds, but it is notintensive. The discharging area must be maintained and kept clean toreduce the potential of disease transmission and nuisance (flies and odors).

Solid waste that is discharged along with the sludge must be removed. Thethickened sludge must be mechanically removed (with a front end loader orother specialized equipment) after it has sufficiently thickened.

29.10.18, 13*48How Treatment Technologies Impact the Climate: Co-Composting


Co-Composting

Co-composting is the controlled aerobic degradation of organics,using more than one feedstock (faecal sludge and organic solid waste).Faecal sludge has a high moisture and nitrogen content, whilebiodegradable solid waste is high in organic carbon and has good bulkingproperties (i.e., it allows air to flow and circulate). By combining the two,the benefits of each can be used to optimize the process and the product.

There are two types of co-composting designs: open and in-vessel:

In open composting, the mixed material (sludge and solid waste) ispiled into long heaps called windrows and left to decompose. Windrowpiles are periodically turned to provide oxygen and ensure that all partsof the pile are subjected to the same heat treatment.In-vessel composting requires controlled moisture and air supply,as well as mechanical mixing. Therefore, it is not generally appropriatefor decentralized facilities.

Although the composting process seems like a simple, passive technology, awell-working facility requires careful planning and design to avoid failure.

As the sludge settles and digests, the supernatant must be decanted andtreated separately. The thickened sludge can then be dried or furthercomposted.


The facility should be located close to the sources of organic waste andfaecal sludge to minimize transport costs, but still at a distance away fromhomes and businesses to minimize nuisances. Depending on the climateand available space, the facility may be covered to prevent excessevaporation and/or provide protection from rain and wind.



For dewatered sludge, a ratio of 1:2 to 1:3 of sludge to solid waste should beused. Liquid sludge should be used at a ratio of 1:5 to 1:10 of sludge to solidwaste.

Windrow piles should be at least 1 m high and insulated with compost orsoil to promote an even distribution of heat inside the pile.

Appropriateness

A co-composting facility is only appropriate when there is an availablesource of well-sorted biodegradable solid waste. Solid wastecontaining plastics and garbage must first be sorted. When carefully done,co-composting can produce a clean, pleasant, beneficial soil conditioner.

Since moisture plays an important role in the composting process, coveredfacilities are especially recommended where there is heavy rainfall.

Apart from technical considerations, composting only makes sense if thereis a demand for the product (from paying customers). In order to findbuyers, a consistent and good quality compost has to be produced; thisdepends on good initial sorting and a well-controlled thermophilic process.


Maintaining the temperature in the pile between 55 and 60 °C can reducethe pathogen load in sludge to a level safe to touch and work with.

Although the finished compost can be safely handled, care should be takenwhen dealing with the sludge, regardless of the previous treatment. If thematerial is found to be dusty, workers should wear protective clothing anduse appropriate respiratory equipment.

Proper ventilation and dust control are important.


The mixture must be carefully designed so that it has the proper C:N ratio,


Seite 3

moisture and oxygen content. If facilities exist, it would be useful to monitorhelminth egg inactivation as a proxy measure of sterilization.

A well-trained staff is necessary for the operation and maintenance of thefacility. Maintenance staff must carefully monitor the quality of the inputmaterial, and keep track of the inflows, outflows, turning schedules, andmaturing times to ensure a high quality product. Forced aeration systemsmust be carefully controlled and monitored.

Turning must be periodically done with either a front-end loader or byhand. Robust grinders for shredding large pieces of solid waste (i.e., smallbranches and coconut shells) and pile turners help to optimize the process,reduce manual labour, and ensure a more homogenous end product.

29.10.18, 13*50How Treatment Technologies Impact the Climate: Bio Reactor


Bio Reactor

A biogas reactor or anaerobic digester is an anaerobic treatment technologythat produces a digested slurry (digestate) that can be used as a fertilizerand biogas that can be used for energy. Biogas is a mix of methane, carbondioxide and other trace gases which can be converted to heat, electricity orlight.

A biogas reactor is an airtight chamber that facilitates the anaerobicdegradation of blackwater, sludge, and/or biodegradable waste. It alsofacilitates the collection of the biogas produced in the fermentationprocesses in the reactor.

The gas forms in the slurry and collects at the top of the chamber, mixingthe slurry as it rises. The digestate is rich in organics and nutrients, almostodourless and pathogens are partly inactivated.


Biogas reactors can be brick-constructed domes or prefabricated tanks,installed above or below ground, depending on space, soil characteristics,available resources and the volume of waste generated. They can be built as



fixed dome or floating dome digesters. In the fixed dome, the volume of thereactor is constant. As gas is generated it exerts a pressure and displaces theslurry upward into an expansion chamber. When the gas is removed, theslurry flows back into the reactor. The pressure can be used to transport thebiogas through pipes. In a floating dome reactor, the dome rises and fallswith the production and withdrawal of gas. Alternatively, it can expand (likea balloon). To minimize distribution losses, the reactors should be installedclose to where the gas can be used.

The hydraulic retention time (HRT) in the reactor should be at least 15 daysin hot climates and 25 days in temperate climates. For highly pathogenicinputs, a HRT of 60 days should be considered. Normally, biogas reactorsare operated in the mesophilic temperature range of 30 to 38°C. Athermophilic temperature of 50 to 57°C would ensure the pathogensdestruction, but can only be achieved by heating the reactor (although inpractice, this is only found in industrialized countries).

Often, biogas reactors are directly connected to private or public toilets withan additional access point for organic materials. At the household level,reactors can be made out of plastic containers or bricks. Sizes can vary from1,000 L for a single family up to 100,000 L for institutional or public toiletapplications.

Because the digestate production is continuous, there must be provisionsmade for its storage, use and/or transport away from the site.

Appropriateness

This technology can be applied at the household level, in smallneighbourhoods or for the stabilization of sludge at large wastewatertreatment plants. It is best used where regular feeding is possible.

Often, a biogas reactor is used as an alternative to a septic tank, since itoffers a similar level of treatment, but with the added benefit of biogas.However, significant gas production cannot be achieved if blackwater is the



only input. The highest levels of biogas production are obtained withconcentrated substrates, which are rich in organic material, such as animalmanure and organic market or household waste.

It can be efficient to co-digest blackwater from a single household withmanure if the latter is the main source of feedstock. Greywater should notbe added as it substantially reduces the HRT. Wood material and straw aredifficult to degrade and should be avoided in the substrate.

Biogas reactors are less appropriate for colder climates as the rate oforganic matter conversion into biogas is very low below 15°C. Consequently,the HRT needs to be longer and the design volume substantially increased.


The digestate is partially sanitized but still carries a risk of infection.Depending on its end-use, further treatment might be required. There arealso dangers associated with the flammable gases that, if mismanaged,could be harmful to human health.


If the reactor is properly designed and built, repairs should be minimal. Tostart the reactor, it should be inoculated with anaerobic bacteria, e.g., byadding cow dung or septic tank sludge. Organic waste used as substrateshould be shredded and mixed with water or digestate prior to feeding.

Gas equipment should be carefully and regularly cleaned so that corrosionand leaks are prevented. Grit and sand that have settled to the bottomshould be removed. Depending on the design and the inputs, the reactorshould be emptied once every 5 to 10 years.

29.10.18, 13*54How Treatment Technologies Impact the Climate: Mechanical Dewatering


Mechanical De-Watering

Mechanical dewatering is normally associated with large wastewatertreatment plants and is used to separate sludge into a liquid and a solidpart. The process does not treat the sludge, it only separates solid fromliquid parts.

The techniques are usually sophisticated and rarely cost-efficient forsmaller systems to be implemented on community level.


Mechanical dewatering is done either with the help of presses orcentrifuges. It often requires the use of chemicals (coagulants andflocculants) to enhance the process.

Modern belt presses (see image above) are based on a combinationof chemical conditioning, gravity drainage and mechanical pressure ina continuous feed system to dewater sludge. The sludge is squeezedbetween tensioned serpentine belts and a series of decreasing diameterrollers (to increase the pressure) to remove moisture and create adewatered sludge cake.Centrifuges operate as continuous feed units, which remove solids bya scroll conveyor and discharge liquid over the weir. The bowl isconical-shaped which helps lift solids out of the liquid allowing them todry on an inclined surface before being discharged. The picture at thebottom shows a typical centrifuge thickening and dewatering system.

Appropriateness

Mechanical dewatering is mostly applied for the treatment of residualsludge in large-scale centralised wastewater treatment plants. Dewateringof sludge reduces transport loads and sludge with low moisture content iseasier to handle. It is also required prior to landfilling to reduce leachate

29.10.18, 13*54How Treatment Technologies Impact the Climate: Mechanical Dewatering


production, before composting or incineration of dewatered sludge.


This process does not serve the treatment of wastewater; it only separatessolids from liquids. Both solid and liquid parts still contain pathogens andpollutants (HEEB et al. 2008) and have to be treated.


These technical systems require a high degree of operator supervision, andoperator training. The mechanical systems such as filters, belts, tensioningsystems or bearings have to be maintained correctly to guarantee properfunctioning.

The liquid part needs to be treated: it is either circulated back into thewastewater treatment plant from where the sludge comes from (e.g.activated sludge or treated in vertical flow or horizontal flow constructedwetlands). The solid part has to be burnt in a small or large scaleincineration plant or discharged in a landfill; it may also be a composted.



Lesson 17: Planning a SludgeManagement System

The lesson describes how to plan a feacal sludge managementsystem on city or town level, including a framework of the necessaryactivities. The planning is based on the planning processes describedearlier in the previous e-Larning (Module 2, Lesson 8)

An integrated planning approach is proposed in order to facilitate the workof a planner or engineer in a city. Different activities and ideas can thus bebound together in a logical and structured way. The planning frameworkhighlights the essential tasks and activities and can be used as a template oran aid when getting started.

The lesson describes the factors which are crucial for a successful planningand shows an approach how to plan considering the logical framework.

Enabling Environment

An enabling environment is critical for the success of any type ofinvestment, whether this is for the improvement of a single public latrine orfor a city-wide fecal sludge management system. Without it, the resourcescommitted to bring about change run the risk of not being effective.Understanding the conditions necessary in a particular context for theenvironment to be enabling is part of an integrated approach.





Planning Approach

This page describes the logical framework together with «traditional»phases. Faecal Sludge Management planning links the levels (communityand city) together as the management needs to be organised city-wide, butin close relationship with the users.

Feasibility Study

The main result of the feasibility study is the identification of viable systemsoptions. This phase starts with the quantification and characterisation ofsludge as a prerequisite for the selection and design of technical options.

Implementation

This phase is mainly about translating the Action Plan into work packagesthat will ultimately become contracts for implementing the Faecal SludgeManagement System. In a following stage, the system should be monitoredand evaluated.




29.10.18, 14*01How Treatment Technologies Impact the Climate: Enabling Environment


The Enabling Environment

An enabling environment is critical for the success of any type ofinvestment, whether this is for the improvement of a single public latrine orfor a city-wide fecal sludge management system.

Without it, the resources committed to bring about change run the risk ofnot being effective. Understanding the conditions necessary in a particularcontext for the environment to be enabling is part of an integratedapproach.

In order to understand the large variety of influences, the enablingconditions are classified into six categories (as shown in the figure above):

Government Support

Conflicting political priorities and therefore, a lack of explicit politicalsupport, is often the initial cause for project failure.

Enabling government support includes not only relevant national policyframeworks and sector strategies, but also receptive local authorities anddecision-makers.



Legal and Regulatory Framework

The technical norms and standards that influence the types and levels ofservice that are put in place are clearly important. Typical problems includeregulatory inconsistencies, lack of regulations or unrealistic standards.

A further issue in many countries is the poor enforcement of existingregulations. For the legal framework to contribute to the enablingenvironment, it must be transparent, realistic and enforced.

Institutional Arrangements

Public institutions and private actors are integral to an enablingenvironment and getting the institutional environment right is a keyingredient for the sustainable delivery of sanitation services.

This encompasses the correct understanding of roles and responsibilitiesand capacities of each stakeholder, as well as their influence and interest inimproving service provision. A potential obstacle may be overlappingmandates between different institutions and ministries.

Skills and Capacities

Developing the required skills and capacities at all levels is a keyrequirement and an issue that can take considerable time to develop.Identifying capacity gaps, particularly at district and municipal level, andthen filling the gaps with tailored training courses, on-the-job training etc.is a pre-requisite.

Financial Arrangements

Implementing and maintaining an environmental sanitation services iscostly and requires an enabling financial environment. Financialcontributions and investments are required from users, from governmentagencies and from the private sector.

Socio-cultural Acceptance



Achieving socio-cultural acceptance depends on matching each aspect of theproposed sanitation system as closely as possible to the users’ preferences.Failure to ensure the implemented solution is socio-culturally embedded isone of the most common reasons for past project failure.

(taken from: L. Strande: Fecal sludge management: Systems Approach forImplementation and Operation, p. 369ff)

29.10.18, 14*04How Treatment Technologies Impact the Climate: Feasibility Study


Exploratory & Feasibility StudyExploratory and Preliminary Studies

The exploratory study is usually short (e.g. two weeks) and should focus onestablishing lines of communication with potential partners (includingauthorities), a first inventory of the stakeholders and a preliminaryassessment of the current situation.

Feasibility Study

The main result of the feasibility study is the identification of viable systemsoptions. This phase starts with the quantification and characterisation ofsludge as a prerequisite for the selection and design of technical options.

Detailed Project Development (Action Plan)

Based on the options validated in the previous phase, a detailed projectdocument or Action Plan can be developed. This document should includethe following items:

Detailed design of treatment plant;Detailed definition of roles and responsibilities in the new system andterms of references;O&M management plan with a clear allocation of costs, responsibilitiesand training needs;Agreements between stakeholders, securing financial and institutionalmechanisms;Strategy for control and enforcement: including the frequency ofcontrol, means needed and sanctions;Definition of needs for capacity building and job creation;Definition of contracts and biding processes;Monitoring and evaluation strategy for the implementation phase; andTimeline for implementation with distinct phases and itemisedimplementation budget.

29.10.18, 14*04How Treatment Technologies Impact the Climate: Feasibility Study


29.10.18, 14*04How Treatment Technologies Impact the Climate: Implementation


Implementation & Follow-upImplementation

This phase is mainly about translating the Action Plan into work packagesthat will ultimately become contracts for implementing the Faecal SludgeManagement System.

Several arrangements are applicable for the implementation of the plans,the most common being through private sector contractors based oncompetitive tendering and bidding procedures. In parallel to the process,stakeholders should be organised according to the Action Plan.

If needed, the legal and regulatory framework should be adapted. Accordingto the identified needs, capacity building should be provided for a smoothtransfer of roles and responsibilities. The public should also be properlyinformed about the new Faecal Sludge system and the improvementscarried out in their municipality.

Monitoring & Evaluation (M&E)

Any Faecal Sludge Management system should be monitored and evaluated.Many development projects have failed because there was no follow-upafter commissioning the Faecal Sludge Treatment Plant.

The stability of the plant treatment units, the satisfaction of thestakeholders, the functioning of the organisational scheme, the costrecovery level and the sustainability of financial mechanisms should bemonitored.

Adjustments will probably still have to be made after commissioning.

29.10.18, 14*08How Treatment Technologies Impact the Climate: Questions?


Self-Test Module 5This page gives the opportunity to check yourself whether all of contentoffered in this module has been understood correctly. Perhaps you shouldre-read some pages? The decision about this and the identification ofcontent which has not been digested correctly is totally up to you!

Your answers in the «Self-test» section are not controlled. However, if youare able to give correct answers in these self-tests, you are also wellprepared for the obligatory online test at the end of the whole e-Learningcourse!

Following are some multiple choice (several answers per questions may becorrect in this case!) or «free text» questions. Please click on «± Proposedanswers» to learn if you can give a correct answer!

Question 1.: Unplanted drying beds have many advantages.Among these are the following:

[ ] Odors and flies are not noticeable

[ ] Relatively low capital cost

[ ] No electrical energy is required

[ ] Good stabilisation and pathogen removal

Question 2.: Planted drying beds have further advantages overunplanted drying beds...

[ ] They require no expert design

[ ] Filters do not need to be desludged after each feeding/drying cycle

[ ] Leachate requires no further treatment



[ ] Minimal labour needs

Question 3.: Where can Biogas Reactors be applied?

[ ] On household level

[ ] In small neighborhoods

[ ] At large water treatment plants

[ ] In drinking water treatment plants

Question 4.: What does Co-composting combine?

[ ] Faecal sludge and organic solid waste

[ ] Wastewater and compost

[ ] Aerobic and anaerobic digestion

Question 5.: Mechanical dewatering is...

[ ] associated with single household wastewater processes

[ ] used to separate sludge in a liquid and a solid part

[ ] done with the help of presses or centrifuges

[ ] not serving to treat wastewater

[ ] requiring a high degree of operator supervision

Question 6.: When designing a sludge management system, afeasibility study will precede a detailed project developmentplan. The results of the feasibility study will be...



[ ] Quantification and characterization of the sludge

[ ] Detailed timeline for implementation

[ ] Identification of viable options

[ ] O&M management plan with allocation of costs

lesson 15: sludge treatment in jordan · planted drying bed this page considers the general generic...

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