effectiveness of an innovative technology for treating raw municipal

8/18/2019 Effectiveness of an Innovative Technology for Treating Raw Municipal

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Component 5: Pilot Projects

Phase 5.2: QUALITY STRESS

Deliverable: 5.2.4

Effectiveness of an innovative technology for treating raw municipal

wastewater in tourist areas

Responsible partner: IRSA

Deliverable Author/s: Claudio Di Iaconi

Contact for queries: [email protected]


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MEDIWAT - 2G-MED09 - 262

Project Details

Programme MED (2007-2013)

Priority Objective 2-1

Axe 2 – Protection of the environment and promotion of a

sustainable territorial development

Objective 2.1 – Protection and enhancement of natural resources and

heritage

Project Title Sustainable management of environmental issues related to

water stress in Mediterranean islands

Project Acronym MEDIWAT

Project Code No 1G-MED09-262

Lead Partner Regional Department o f Water and Wastes – Water

Observatory

Total Budget 1.480.000,00 Euro (€)

Time FrameStart Date – End Date

010/06/2010 – 31/05/2013

Deliverable Details

Component C.5 – Pilot Project

Phase 5.2 – Quality stress

Title of Deliverable D.5.2.4 - Effectiveness of an innovative technology for treating

raw municipal wastewater in tourist areas

Partner Responsible IRSA

Partners Involved IRSA

Due Date of Deliverable December 2012


3/35MEDIWAT - 2G-MED09 - 262

EXECUTIVE SUMMARY………………………………………………………….. 4

1. INTRODUCTION …………………………………………………………………... 5

2. PILOT DESCRIPTION…………………………………..………………………… 8

3. RESULTS………………………..………………………………………………....... 15

4. CONCLUSIONS ………………………………………………………………….... 33

REFERENCES ……………………………………………………………………….. 34


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EXECUTIVE SUMMARY

MEDIWAT project is aimed at identifying and/or developing innovative and integrated

solutions (technical, operational and administrative) for managing environmental

issues related to the quality and quantity stress presently afflicting Med islands.

One of the specific objectives of the project is carrying out pilot projects for

evaluating specific tools for mitigating water quantity and quality stress as well as

managing water demand. In particular, several pilot projects are foreseen in the three

phases of the component 5, i.e.: phase 5.1: pilot projects on quantity stress; phase 5.2:

pilot projects on quality stress; phase 5.3: pilot projects on demand management.

This deliverable reports the results obtained in the pilot project titled “testing a single

step innovative process for treating raw municipal wastewater in tourist areas”, carried

out in Apulia (Italy) by the partner IRSA, within phase 5.2 of the component 5.

This report is structures as follows. Chapter 1 briefly summarized the background of

the pilot project (i.e., state of art of wastewater treatment in tourist areas) whereas

Chapter 2 describes the methodology used (i.e., the innovative SBBGR technology)

and the operating programme. Chapter 3 shows and discusses the results obtained

during the pilot experimental campaign. The main relevant results (i.e., those

exploitable and feasible in all the Mediterranean islands) are summarized in Chapter 4.


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1. INTRODUCTION

Tourist areas are usually featured by a strong population variation during the holiday

season which determines an intense seasonal water demand. For example, the

Mediterranean region with about 46,000 km of coastline is the world’s favourite

holiday destination area, attracting more than one third of global tourist arrivals every

year. About 40% of all arrives are concentrated during the summer period; moreover,

the increase in population within this period doesn’t follow a gradual trend but surges

on certain dates.

Population fluctuation in tourist areas affects not only water demand but also

wastewater quality and quantity. In fact, in comparison with a typical municipal

sewage the wastewater coming from heavily tourist areas is more concentrated in terms

of typical pollutant parameters, more variable in terms both of flow and contaminant

variation, and less disintegrated in terms of particulate matter because of the shorter

sewerage system (Odegaard, 1989).

A reliable wastewater collection, treatment and disposal system should be implemented

in tourist areas since in these areas, especially in coastal ones, the receiving water is the

main value but also the main concern for its possible pollution.In tourist areas wastewater treatment is usually carried out decentrally by small plants

each serving single or group of homes, hotels and other tourist establishments (Figure

1). In fact, wastewater collection based on a branched sewer network, which cost may

contribute up to 60% of the total budget for wastewater management in large systems,

should be too expensive for coastal recreational areas (such as resorts, hotel restaurants

and bars) often located along coastline at considerable distance from each other.

Wastewater treatment systems in use in tourist areas, mainly based on extended

aeration activated sludge process, suffer problems of shock loads, sludge bulking,

absence of regular supervision and maintenance, and flow fluctuations which may lead

to a low effluent quality (Christoulas and Andreadakis, 1989). The situation is

particularly critical at the beginning of holiday season when a sharp increase in

wastewater flow takes place as these systems require a certain period for the

development of the biomass necessary for the treatment. Therefore, during this period,


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which often lasts several weeks, a low quality effluent is produced.

Fig.1 - Decentralized wastewater treatment in tourist areas.

Furthermore, the sludge produced represents one of the most concern issues in the

small treatment plants (Kuai et al., 2000). In fact, sludge treatment methods usually

applied in large-scale wastewater treatment plants (i.e., aerobic or anaerobic sludge

stabilization and dewatering) are basically not suitable for small wastewater treatment

plants since they should be too expensive. The sludge produced in these plants is

usually transported to a nearby larger treatment plant (that in costal areas may be a

long distance) where these facilities are available. The reduction of excess sludge

production is then highly desirable in small wastewater treatment plants.

Therefore, more reliable and robust wastewater treatment technologies with lower

sludge production and better operational flexibility are required in tourist areas.

Among the new systems recently proposed that can comply with this request, one of

the most promising is the system developed by the Water Research Institute (IRSA) of

the National Research Council of Italy (CNR) whose acronym is SBBGR (Sequencing

Batch Biofilter Granular Reactor).

SBBGR system combines the advantages of attached biomass systems (i.e., greater

robustness and compactness) with those of periodic systems (i.e., greater flexibility and

treatment plant

source

treatment plant

source

treatment plant

source

treatment plant

source

treatment plant

source

treatment plant

source


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stability). SBBGR is however a unique system for the particular type of biomass

growing in it. In fact, the biomass present in this system consists of two different

fractions: the biofilm attached to the carrier material and the granules entrapped in the

pores produced by packing the reactor with a filling material. Therefore, the whole

biomass (i.e., biofilm and granules) is completely confined in a dedicated zone of the

reactor (a secondary settler is therefore no longer necessary). This feature allows

greater biomass retention in the reactor to be obtained (up to one magnitude order

higher than that recorded in conventional biological systems). As a result, a notable

increase in sludge age is achieved with consequent reduction in sludge production. In

fact, the microorganisms spend much time in the endogenous metabolism phase where

the biomass decay rate is high, and thus the biomass production rate is low (Di Iaconi

et al., 2005; Di Iaconi et al., 2010a).

SBBGR technology has been already applied for treating different wastewater types

such as municipal primary effluents, tannery wastewater, municipal landfill leachates

and textile wastewater with a low excess sludge production (Di Iaconi et al., 2010a, Di

Iaconi et al., 2010b, Di Iaconi et al., 2011a, Di Iaconi et al., 2011b; Lotito et al., 2011).

In particular, when the system was applied for treating municipal primary effluent a

80% reduction of sludge production was obtained (Di Iaconi et al., 2010a).The benefits of SBBGR technology can be summarized as follows: a) interesting

conversion capacities; b) the absence of a secondary settling tank; c) a low footprint

due to the possibility of carrying out in a single operative unit all the steps of a

biological treatment; d) great flexibility - a particularly attractive feature for the

treatment of wastewater characterized by great variability in volumetric flow rate and

composition such as sewage coming from tourist areas; e) a very low sludge

production.


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2. PILOT DESCRIPTION

A pilot plant, based on SBBGR technology, with a treatment capability up to 1 m3/d,

was purposely designed and constructed with the aim of evaluating its effectiveness in

treating municipal wastewater of tourist areas. Figures 2 and 3 show a sketch and

photograph of the plant, respectively.

SBBGR pilot plant is basically made of 2 units: biofilter and aerator. The biofilter is

the reactive zone of the plant as it contains the biomass; it consists of a steel cylindrical

reactor (diameter: 220 mm; height: 3200 mm) filled with the wheel shaped plastic

elements shown in Figure 4 (features: 7 mm high, 11 mm diameter, specific area 650

m2/m

3, 0.95 g/cm

3 density, 0.7 bed porosity and 50-80 mm

3voids dimension). These

elements are packed (fixed) between two holed plates (see Figure 5). The whole

Fig.2 - Pilot plant sketch. Fig.3 - Pilot plant photograph.

a e r a t o r

b i o f i l t e r

r e c p u m p

fill. pump

blower

AeratorBiofilter

blower

rec. pump

inf.

fill. pump

eff.

EV


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biomass of the plant is completely confined in the biofilter (entrapped in the filling

material) and then a secondary settler is no longer required.

Fig.4 - A photograph of

plastic elements.

Fig.5 - Plastic elements packed in the

biofilter.

The aerator, consisting of a steel cylindrical reactor (diameter: 273 mm; height: 3200

mm), is the zone of the liquid phase (i.e., wastewater); its role is to supply air for the

process by means of a blower connected with a diffuser plate located at the bottom ofthe unit. The air supply in a dedicated reactor separate from the biomass gives the

advantage of avoiding the installation of complex devices as in the conventional

systems where clogging problems are encountered (due to the biomass that clogs the

holes of the devices used for air supply). The biofilter and aerator are hydraulically

connected by means of a pump (rec. pump in Figures 2 and 3) which continuously

recycles the liquid in the aerator through the biomass supporting material of the

biofilter. Furthermore, this recycle assures a homogeneous distribution of the biomass

along all the height of the biofilter.The operation of the pilot plant is based on a succession of treatment cycles, each

consisting of three consecutive phases (see Figure 6): the filling, reaction and drawing

phases. During the filling phase, a fixed volume of wastewater to be treated is added

(by means of the filling pump) to the liquid volume retained by the aerator from the

previous treatment cycle. During reaction phase, the liquid in the aerator is


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continuously aerated and recycled through the biomass supporting material of the

biofilter. Finally, the treated wastewater is discharged exploiting the gravity by

opening a motorized valve (EV in Figures 2 and 7) connected to different heights of the

aerator (see Figure 7). The plant is then ready to start a new treatment cycle. The

operative schedule (filling, recirculation, aeration, drawing) is completely automated,

using a programmable logic controller (PLC) equipped with a touch screen monitor

(see Figure 8) for changing the working conditions (i.e., the duration of the working

period) of the components (i.e., filling pump, recirculation pump, blower and drawing

valve).

Fig.6 - Pilot plant operation. Fig.7 - A photograph of drawing system.

effluent

EV


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Fig.8 - Photos of PLC with touch screen monitor

Pressure probes, set at different heights of the biofilter unit (see Figure 9), measure on-

line head losses due to the biomass growth and captured suspended solids present in

the wastewater. When a fixed set value of head loss is reached at the lowest probe, a

washing step is carried out by compressed air injected into the bottom of the biofilter

unit (see Figure 10) until the headloss is decreased down to a definite value. Washing

water is collected and measured (as TSS and VSS) for calculating the specific sludge

production. Furthermore, nitrogen and phosphorous content of expelled sludge was

also measured. Washing operations are an important operating parameter of the

SBBGR system as they determine the quantity of sludge produced. In fact, sludge can

leave the SBBGR system either with the effluent (i.e., as suspended solids) or as a

result of a washing operation (i.e.,“forced exit”). Unlike first way, the amount of

sludge expelled by washing operation can be controlled by changing the operative

parameters of the operation (i.e., by increasing/decreasing the set point value for

carrying out the washing). In particular, by increasing the set point value for carrying

out the washing operation it is possible to reduce the frequency of the operation and


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then the sludge production. Nevertheless, high headloss values increase the risk of

clogging of the bed with consequent reduction of treatment capability. Therefore, the

headloss set-point value should be as high as possible consistently with a satisfactory

(requested) removal level.

Fig.9 - Photos of pressure probes

along biofilter height (the probes are

highlighted by red arrows)

Fig.10 - A photograph of compressed

air injection system.

The pilot plant was installed at the experimental site of IRSA located in Bari, a

southern Italy town, and fed with the raw wastewater (i.e., without any pre-treatment)

coming from a residence located on the Adriatic Sea coast near Bari. The wastewater

was transported to the experimental site by means of pump truck.

The experimental activities of the pilot plant were arranged in two main periods(periods A and B). Period A referred to the generation of the typical biomass of

SBBGR technology (i.e., biomass made of biofilm and granules) by gradual shift of

attached biomass fraction from biofilm to granules (De Sanctis et al., 2010), whereas

period B was addressed to the evaluation of the effectiveness of the pilot plant in

coping with organic load variation.


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In particular, during period A (200 d), taking into account the know how about SBBGR

gained in previous studies (De Sanctis et al., 2010; Di Iaconi et al., 2005; Di Iaconi et

al., 2009), the hydraulic loading to the plant was adjusted in order to have an applied

organic loading rate (OLR) in the range of 0.2-0.4 kgCOD/m3d. Once typical biomass

had been achieved, the experimental activity was focussed on the evaluation of the

effectiveness of the pilot plant in coping with organic load variations typical of tourist

areas. In particular, the impact of a wide range of organic loading rates (0.2 to 5

kgCOD/m3d) on plant performance was evaluated, operating at hydraulic residence

times (HRT) of 2.2 to 1.0 d.

HRT and OLR values adopted throughout period B of pilot campaign are shown in

Figure 11.

Fig.11 - HRT and OLR applied during period B

The plant operated with 8 h treatment cycles during period A and 6-8 h treatment

cycles in period B. The filling phase lasted for a few minutes (up to a maximum of 20

min, depending on the volume of influent loaded) whereas the drawing phase lasted 30

min. During reaction phase no air was provided during the first hour for supporting

0

1

2

3

4

5

6

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

0.5

1

1.5

2

2.5

3

OLR

HRT

Time (d)

H R

T

( d )

O L R ( k g C O D / m 3 d )


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denitrification process.

Treatment performance was evaluated by measuring several parameters of influent and

effluent, usually two times per week. The removal efficiencies of all parameters were

calculated as percentage reduction in value between influent and effluent sample.

Chemical oxygen demand (COD), total (TN), nitric (N-NO2) and nitrous (N-NO3)

nitrogen, and total phosphorous (P) were determined by Dr Lange test kits (COD:

LCK314; TN: LCK238; N-NO2: LCK341; N-NO3: LCK339; P: LCK350).

Ammoniacal nitrogen (NH3-N) and total and volatile suspended solids (TSS and VSS)

were determined using standard methods (APHA 2005). Soluble COD (CODsol) was

measured after sample filtration through a 0.45 µm filter. Oxidised nitrogen (N-NOx)

was calculated as the sum of nitric (N-NO2) and nitrous (N-NO3) nitrogen. Kjeldahl

nitrogen (TKN) was calculated as difference between total (TN) and oxidised (N-NOx)

nitrogen.

The specific sludge production was calculated assuming that SBBGR operating

conditions, in particular the very high sludge age, guaranteed the complete

metabolization of all particulate organic matter occurring in the wastewater.

Accordingly, the specific sludge production (kgTSS/kgCODremoved ) was calculated

dividing TSS leaving the system (i.e., TSS discharged with the effluent + TSS removedduring the washing operations) by the amount of COD removed during the time period

after the first washing operation.


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3. RESULTS

As reported in previous chapter, Period A was addressed to the generation of the

typical biomass of SBBGR technology consisting of granules embedded in biofilm. In

previous studies (Di Iaconi et al., 2005) it was found that the generation process,

depicted in Figure 12, involves four steps: (1) formation of a thin biofilm that fully

covers the carrier surface, (2) increase in biofilm thickness, (3) detachment of a biofilm

portion that covers the carriers with release of biofilm particles, and (4) rearrangement

of biofilm particles in smooth granules.

Fig.12 - Sketch of the generation process of SBBGR biomass.

Fundamental studies have shown that three factors play a decisive role in the

generation of SBBGR biomass: the trend of the hydrodynamic shear forces, the start-

up operative conditions (i.e., the organic loading rate applied during the first period),

and bed material features (Di Iaconi et al., 2009). In particular, it was found that during

the first two steps of the generation process depicted in Figure 12, the reactor is

characterised by rather weak shear force values. Under these weak forces, the biofilm,

which is regulated primarily by the organic substrate loading rate, continuously

increases in thickness. This produces a corresponding increase in the shear forces with

negative effects on biomass stability, causing the detachment of biofilm particles (step

3). This, in turn, triggers a further sharp increase in the shear forces, promoting the

rearrangement of the detached biofilm particles into smooth granules by continuous

removal of protuberances (step 4). When biofilm detachment takes place, however, the

filling material characteristics are crucial in granule generation since they must

carriergranules biofilms

(1) (4)(2) (3)


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guarantee the retention of the detached biofilm particles. In particular, if a filling

material which generates beds characterised by large pore volumes is used, biomass

granulation cannot be achieved because of the expulsion of biofilm particles from the

bed. Therefore, on the basis of the process described above, it is clear that the SBBGR

system differs from conventional biofilter in its final step (i.e., step 4) and that to

obtain the desired granule formation, the biofilm particles detached from the carrier

material have to remain in the bed. In fact, if the biofilm particles were expelled from

the bed, the bed porosity would increase with a consequent reduction in the shear force

value and thus a return to the previous step.

Therefore, as reported in the previous chapter, during period A the hydraulic loading to

the plant was adjusted in order to have and applied organic loading in the range 0.2-0.4

kgCOD/m3d.

The typical biomass of SBBGR was obtained towards the end the seventh month. The

performances of the plant (in terms of average values standard deviation) recorded

during period A are summarized in Table 1.

Tab.1- Plant performance recorded during period A.Parameter Mean value standard deviation

TSS [mg/L] Influent [mg/l] 467 414

Effluent [mg/l] 13 9

Removal [%] 96.2 2.7

VSS [mg/L] Influent [mg/l] 363 318

Effluent [mg/l] 8 6

Removal [%] 97.1 2.5

COD [mg/L] Influent [mg/l] 847 652


Removal [%] 91.5 7.0

CODsol [mg/L] Influent [mg/l] 202 201


Removal [%] 74.9 17.7


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TKN [mg/L] Influent [mg/l] 93.8 37.4

Effluent [mg/l] 9.1 10.6

Removal [%] 91.3 7.3

NH4+[mgN/L] Influent [mg/l] 72.9 31.3


Removal [%] 93.1 9.9

TN [mg/L] Influent [mg/l] 93.9 37.4


Removal [%] 47.5 24.4

P-tot [mgP-PO4/L] Influent [mg/l] 6.8 4.1


Removal [%] 25.1 21.8

The data reported in Table 1 show removal efficiencies higher than 90% for COD,

TSS, TKN and NH4+ with residual concentrations in the effluent much lower than the

discharge limits independently of the influent concentration values. TN removal

efficiency was somewhat low as no final anoxic phase was inserted in the treatmentcycle for denitrification process.

After biomass generation, the effectiveness of the pilot plant in coping with organic

load variation was evaluated (period B). Moreover, in order to enhance such a

variation, hydraulic residence time of the plant was stepwise reduced from 2.2 down to

1.0d by increasing the hydraulic loading . Referring to this period, Figures 13 and 14

show the concentration-time profiles of total and soluble COD measured in the influent

and effluent of the plant, respectively, throughout period B whereas Figure 15 reports

COD removal efficiency and OLR applied to the plant during the same period.

Figure 13 shows that COD concentration in the influent of the plant mainly consisted

of particulate organic material (an influent COD/CODsol ratio usually higher than 2

was measured). This was due to the shortness of the sewerage system in tourist areas

which leads to less extension of disintegration process of particulate matter.


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Fig.13 - Total and soluble COD concentrations measured in the influent of the plant during period B.

Fig.14 - Total and soluble COD concentrations measured in the effluent of the plant during period B.

0

300

600

900

1200

1500

1800

2100

2400

2700

3000

200 220 240 260 280 300 320 340 360 380 400 420 440 460

tot

sol

Time (d)

C O D i n f ( m g / L )

0

10

20

30

40

50

60

70

80

90

100

200 220 240 260 280 300 320 340 360 380 400 420 440 460

tot

sol

Time (d)

C O D e f f ( m g / L )


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Looking at data in Figures 13, 14 and 15, it is possible to observe that the COD

concentration in the effluent of the plant was always lower than 80 mg/L (most of the

time lower than 50 mg/L) with average removal efficiencies of 91% (however, always

higher than 80%) independently of influent COD concentration, that ranged from 200

up to 2,700 mg/L and organic loading rate applied to the plant that was even as high as

5 kg COD/m3d. It is worthy to remind that mean effluent concentrations between 30

and 150 mg/L (in terms of BOD5) are usually reported in the literature for small onsite

extended aeration package systems in use in tourist areas (Christoulas and

Andreadakis, 1989).

Fig.15 - COD removal efficiency and OLR applied to the plant throughout period B.

Contrarily to the conventional sewage treatment plants operating in tourist areas which

are sensitive to the fluctuations in organic loading (Christoulas and Andreadakis, 1989;

Katsiris and Kouzeli-Katsiri, 1989), data in Figures 13, 14 and 15 show an high

robustness of SBBGR system in coping with short-term loading variations. In

particular, it is interesting to observe how there was no deterioration in effluent quality

of the plant during the sudden ten-fold increase of organic loading rate occurred around

0

12

3

4

5

6

7

8

9

10

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

1020

30

40

50

60

70

80

90

100

OLR

%COD

Time (d)

C O D

r e m o v a l e f f i c i e n c y ( % )

O L R ( k g C O D / m 3 d )


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day 400, although the plant operated at hydraulic residence time as low as 1d. In fact, it

should be noted that the extended aeration plants, widely used in tourist areas, are

designed with a much higher hydraulic residence time (Boller, 1997).

Regarding total suspended solids, Figure 16 shows the concentration-time profiles of

total and volatile suspended solids in the influent of the plant during period B, whereas,

in Figure 17 are reported the profiles of effluent suspended solids concentration and

removal efficiency for the same period.

Fig.16 -Total (TSS) and volatile (VSS) suspended solids concentrations measured in the influent of the

plant throughout period B.

The data reported in Figures 16 and 17 highlight excellent filtration performances

although a raw sewage (i.e., without any preliminary treatment) was used. In fact, an

effluent with a suspended solids content always below the discharge limit of 35 mg/Lwas recorded (most of the time lower than 20 mg/L) with removal efficiencies always

higher than 80% (most often above 90%) independently of the influent value that was

even as high as 1,200 mg/L. Furthermore, the profiles reported in Figure 16 show that

the total suspended solids consist primarily of organic material.

0

150

300

450

600

750

900

1050

1200

1350

1500

200 220 240 260 280 300 320 340 360 380 400 420 440 460

VSS

TSS

Time (d)

T S S i n f ; V S S i n f

( m g / L )


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The excellent filtration performance can be appreciate also visually in Figure 18

showing a picture of influent and effluent sample from the plant .

Fig.17 - Total suspended solids concentrations measured in the effluent of the plant and removal

efficiency throughout period B.

Fig.18 - Photograph of the influent (on the right) and effluent (on the left) sample.

The high effectiveness and flexibility of the plant for handling the variation in the

0

8

16

24

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40

48

56

64

72

80

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

10

20

30

40

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60

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80

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100

TSS

%

Time (d)

T S S r e m o v a

l e f f i c i e n c y

( % )

T S S e f f ( m g / L )


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wastewater flow and composition was also confirmed by profiles recorded within

treatment cycles and reported in Figures 19 and 20.

Fig.19 - COD and TSS concentration, and removal efficiency profiles in a typical treatment cycle

recorded at day 203 (HRT: 2.2 d; OLR: 1.1 kgCOD/m3d).

Fig.20 - COD and TSS concentration, and removal efficiency profiles in a typical treatment cyclerecorded at day 433 (HRT: 1.2 d; OLR: 0.5 kgCOD/m

3d).

0

80

160

240

320

400

480

560

640

720

800

0 2 4 6 8

0

10

20

30

40

50

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70

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COD

TSS

%COD

%TSS

C O D

a n d T S S r e m o v a l e f f . ( % )

C O D a n d T S S ( m g / L )

Cycle time (h)

0

35

70

105

140

175

210

245

280

315

350

0 1.5 3 4.5 6

0

10

20

30

40

50

60

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80

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100

CODTSS

%COD

%TSS

C O D a n d T S S r e m o v a l e f f . ( % )

C O D a n d T S S ( m g / L )

Cycle time (h)


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In fact, they show that the removal of COD and TSS is almost complete during the first

hours of the treatment cycle regardless both initial concentrations, applied hydraulic

residence time and organic loading leaving, so, always a somewhat large residual

treatment capability of the plant. It can be ascribed to the particular type of biomass

growing in SBBGR system (consisting of biofilm and granules mixture packed into a

filling material of biofilter compartment) which acts as a filtering media for removing

suspended particulate matter (and then COD associated) from the wastewater. This

high filtering capability of SBBGR biomass is clearly shown in Figures 19 and 20

where it is possible to observe that almost the whole content of suspended solids is

rapidly removed from the wastewater independently of its value. Furthermore, the high

age of SBBGR biomass allows the hydrolysis of the solids captured so as to produce

soluble organic compounds which are removed by the same biomass.

As far as nitrogen is concerned, Figures 21 and 22 show the profiles of TKN, NH 3 and

NOx concentrations measured in the influent and effluent of the plant, respectively,

throughout period B.

Fig.21 - Total Kjeldahl (TKN), ammoniacal (NH3) and oxidised (NOx) nitrogen concentrations

measured in the influent of the plant throughout period B.

Looking at these profiles it is possible to observe that the effluent concentration of both

0

15

30

45

60

75

90

105

120

135

150

165

180

200 220 240 260 280 300 320 340 360 380 400 420 440 460

NH3TKN

NOx

Time (d)

T K N i n f , N H 3 i n f , N O x

+ i n f ( m g N / L )


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parameters was always (except at day 363 and 400) lower than 15 mg/L (often lower

than 5 mg/L) independently of influent value that was even as high as 150 mg/L,

indicating so the establishment of a stable nitrification process with oxidised nitrogen

concentrations in the effluent usually in the range 10-20 mg/L. Furthermore, contrarily

to what reported for the conventional biological treatment systems, the data in Figure

23 show that removal efficiency of these two parameters was not greatly affected by

organic loading rate applied. In fact, removal efficiencies higher than 80% were

recorded even for temporary organic loading rates as high as 4-5 kgCOD/m3d in spite of

the strong competition existing between autotrophic and heterotrophic bacteria for

dissolved oxygen. Once again, this surprising result can be ascribed to the high

operating flexibility of the system. Nevertheless, as expected, data in Figure 24 clearly

show that nitrification process becomes more unstable as HRT decreases.

Fig.22 - Total Kjeldahl (TKN) and ammoniacal (NH3) nitrogen concentrations measured in the effluent

of the plant throughout period B.

In fact, the lowest TKN and ammonia removal efficiencies (i.e., around 70%) were

recorded at lowest hydraulic residence times applied (i.e., 1.0 d) whereas a HRT of 1.2

d assures removal efficiencies above 80%. Therefore, from the data reported in Figure

0

5

10

15

20

25

30

35

40

45

50

200 220 240 260 280 300 320 340 360 380 400 420 440 460

NH3

TKN

Time (d)

E f f l u e n t T K N a n d N H 3

( m g N / L )


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25


23 and 24 it seems that nitrification process is more affected by hydraulic residence

time than organic loading applied to the plant.

TN profiles shown in Figure 25 also highlights the existence of denitrification process

somewhat extended although no planned final anoxic phase was included in the

treatment cycle of the plant.

Fig.23 - TKN and ammonia removal efficiency, and OLR applied to the plant throughout period B.

In fact, average removal efficiencies of 72% were achieved with residual effluent

concentration around 20 mg/L (on average). Furthermore, Figure 25 shows that the

values of TN removal efficiencies were somewhat sparse, however, ranging from 25 to

90%, because of the influent COD/N ratio which sometime was low (i.e., lower than 6)

and then did not allow a satisfactory denitrification efficiency (in such an instance,

however, an external carbon source could be used for improving the nitrogen removal).TKN and oxidized nitrogen profiles within a typical treatment cycle reported in Figure

26 clearly show the existence of a such simultaneous nitrification-denitrification

process. In fact, looking at these profiles it is possible to observe that during the first 4

hours of the cycle time the concentration of oxidised nitrogen is low (i.e., below 5

mg/L) while most of TKN is removed.

0

1

2

3

4

5

6

7

8

9

10

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

10

20

30

40

50

60

70

80

90

100

OLR

TKN

NH3

Time (d)

T K N

a n d N H 3 r e m o v a

l e f f i c . ( % )

O L R ( k g C O D / m

3 d )


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26


Fig.24 - TKN and ammonia removal efficiency, and HRT applied to the plant throughout period B.

Fig.25 - TN influent and effluent concentrations and removal efficiency profiles throughout period B.

0

0.5

1

1.5

2

2.5

3

200 220 240 260 280 300 320 340 360 380 400 420 440 460

40

50

60

70

80

90

100

HRT

TKN

NH3

Time (d)

T K N

a n d N H

3 r e m o v a l e f f . ( % )

H

R T ( d )

0

25

50

75

100

125

150

175

200

225

250

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

10

20

30

40

50

60

70

80

90

100inf eff

%

Time (d)

T N

( m g / L )

T N r e m o v a l e f f i c i e n c y

( % )


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27


The simultaneous nitrification-denitrification process can be ascribed to the high

biomass concentration usually measured in SBBGR (higher than 40 kgTSS/m3 bed ) and

to the transient conditions (typical of sequential reactors) which generate contiguous

anoxic and aerobic biomass layers. It has been reported in previous studies performed

by SBBGR technology that the ammonium oxidizers situated in the biomass outer

layers carry out the oxidation of ammonium to nitrite/nitrate while denitrifying bacteria

located in deeper layers, where oxygen cannot penetrate, reduce these compounds tonitrogen gas by using carbon sources coming from storage or hydrolysis products of

particulate organic matter present in the feed (De Sanctis et al., 2010).

Fig.26 - TKN and NOx concentration profiles in a typical treatment cycle recorded at day 299 (HRT: 1.4

d; OLR: 0.78 kgCOD/m3d)

Finally, the existence of simultaneous nitrification-denitrification process is also

confirmed by nitrogen balance carried out from day 371 to day 463. In fact, Figure 27

reports the values of nitrogen request for biomass growth, calculated by multiplying

sludge production (i.e., 0.15 kgTSS/kgCODremoved ; see below) and measured N biomass

0

10

20

30

40

50

60

70

80

0 2 4 6 8

TKN

NOx

T K N , N

O x ( m g N / L )

Cycle time (h)


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content (i.e., 0.03 gN/gTSS), and nitrogen removed recorded in the period 371 to 463.

Looking at this figure it leaps out as the nitrogen request for biomass growth (usually

lower than 10 mg/L) is negligible in comparison with measured nitrogen removed.

Fig.27 - Measured TN removed and calculated nitrogen request for biomass growth in the period 371 to463 d.

As reported in previous chapter, during period B, particular attention was paid for

evaluating and setting the headloss set-point for carrying out the washing operations. In

fact, by increasing the set point value for carrying out the washing operation it is

possible to reduce the frequency of the operation and then the sludge production.

Nevertheless, high headloss values increase the risk of clogging of the bed with

consequent reduction of treatment capability. In particular, nitrification process (and

then TKN removal) could be particularly affected by high headloss values because of

strong competition between autotrophic and heterotrophic bacteria for dissolved

oxygen. Therefore, the headloss set-point value should be as high as possible

consistently with a satisfactory (requested) removal level.

0

10

20

30

40

50

60

70

80

90

100

3 7 1

3 7 7

3 8 1

3 9 0

3 9 6

4 0 4

4 0 9

4 1 7

4 2 4

4 3 3

4 3 8

4 4 1

4 4 9

4 5 5

4 6 3

N removed

N for growth

Time (d)

N ( m g /

L )


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Profiles shown in Figure 28 confirm that TKN removal efficiency is more affected by

headloss increase compared to COD and total suspended solids removal efficiency. In

particular, data from day 370 to day 395 seem to indicate that TKN removal

efficiency is reduced below 90% when headloss value exceeds 16 m. Therefore 16 m

seem to be the threshold value of headloss for carrying out the washing operations.

The first washing operation was then carried out at day 390, and an increase of TKN

removal efficiency occurred after the washing operation so confirming what reported

above. Nevertheless, data from day 395 to day 463 show TKN removal efficiencies

higher than 90% even at headloss values greater than 20 m. Therefore, the threshold

value of headloss for carrying out the washing operations was progressively

increased, and definitely set at 24 m (due to operating constraints on plant

components, headloss cannot overcame 3 bar).

Fig.28 - COD, TSS and TKN removal efficiency, and headloss profiles in the period 370 to 463 d.

As far as sludge production is concerned, according to what reported in previous

chapter, it should be calculated by the balance of COD removed and the solids leaving

0

4

8

12

16

20

24

28

32

36

40

370 380 390 400 410 420 430 440 450 460

0

10

20

30

40

50

60

70

80

90

100

dP

%TSS

%COD

%TKN

Time (d)

H e a d l o s s ( m )

C O D , T S S , T K N r e m o v a l e f f . ( % )


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the reactor (by washing and effluent) carried out during the time after the first washing

operation. In fact, washing operations regulate the sludge age in SBBGR system (they

play the same role as the sludge wasting flow rate in conventional activated sludge

systems) which is the main cause of reducing excess sludge production in this system.

It must be pointed out, however, that SBBGR operates in a range of sludge ages having

maximum and minimum value just before and after washing operation, respectively

(i.e., a drop of sludge age takes place during washing operation). As reported above,

the first washing operation was carried out at day 391; after this 4 more washings were

carried out as shown in Figure 29.

Figure 29. Headloss profile recorded from day 370 to day 463. Red arrows indicate washing operations

carried out.

The balance of sludge produced and COD removed during this interval of time gives a

sludge production value of about 0.15 kgTSS/kgCODremoved (or 0.09 in terms of

gVSS/gCODremoved ). This value is much lower (i.e., about 80% lower) than that

reported in the literature for extended aeration systems (widely used in tourist areas)

operating without primary clarifier (Schultz et al., 1982). An acceptable level of

0

4

812

16

20

24

28

32

36

40

370 380 390 400 410 420 430 440 450 460

Time (d)

H e a d l o s s ( m )


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stabilization of excess sludge was also obtained (a VSS/TSS ratio of about 0.57 was

measured) so that a further stabilization process could be not longer required. This

result can be ascribed to the high sludge age (i.e., higher than 200 d) so that the

microorganisms spend much time in the endogenous metabolism phase where the

biomass decay rate is high, and thus the biomass production rate is low (Di Iaconi et

al., 2010a).

It should be born in mind, however, that the above balance is very conservative. In

fact, it basically considers that the inorganic total suspended solids leaving the plant do

not come from the influent (as it is well known, basically, inorganic suspended solids

cannot be really removed in a biological system). On the contrary, if the inorganic

(fixed) suspended solids entering the plant are taken into account in the balance, the

following equation (i.e., sludge production really associated to COD removal) can be

written:

EFF IN

IN WASHING EFF

CODCOD

FTSS TSS TSS removalCODtoassociated productionsludge

where:

TSSEFF = total suspended solids content leaving the plant with the effluent;

TSSWASHING = total suspended solids content leaving the plant with the washing

operations;

FTSSIN = fixed (or inorganic) total suspended solids content entering the plant with the

influent;

CODIN = COD content entering the plant with the influent;

CODEFF = COD content leaving the plant with the effluent;

Using the above equation for the same time period a sludge production value of just

0.04 kgTSS/kgCODremoved is obtained. This result clearly indicates that the sludge


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produced by the plant is mostly (i.e., for 70%) due to inorganic suspended solids

entering the plant, and then not associated to COD removal.

Finally, according to the low sludge production value the plant showed low phosphorus

removal efficiencies as well. The high values of the removal efficiency shown in

Figure 30 recorded during some days must be ascribed to the filtering capability of

SBBGR system against suspended solid particles containing phosphorus.

Fig.30 - Total phosphorus concentrations measured in the influent and effluent of the plant, and removal

efficiency throughout period B.

0

2

4

6

8

10

12

1416

18

20

200 220 240 260 280 300 320 340 360 380 400 420 440 460

0

10

20

30

40

50

60

7080

90

100inf

eff

%

Time (d)

P t o t (

m g P / L )

P r e m o v a l e f f i c i e n c y ( %

)


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33


4. CONCLUSIONS

The main results obtained during a pilot project aimed at evaluating the performance of

an innovative biological system (SBBGR) for treating municipal wastewater of tourist

areas are as the follows:

- the plant showed a great operation flexibility and stability in response to organic loadvariations typical of tourist areas. Average removal efficiencies higher than 90% were

obtained for COD, total suspended solids and TKN independently of the influent

concentration values and applied organic loading which ranged from 0.2 to 5

kgCOD/m3d. No deterioration in effluent quality of the plant was observed even when

a sudden ten-fold increase of organic loading rate occurred.

- high nitrogen removal efficiencies (80%, on average) were also obtained due to

simultaneous nitrification-denitrification process.

- the plant was characterized by an excess sludge production 80% lower than that of

extended aeration systems in use in tourist areas. Furthermore, an acceptable level of

stabilization of excess sludge was also obtained indicating that a further stabilization

process could be not longer required.


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Kuai L., Doulami F., Verstraete W. (2000). Sludge treatment and reuse as soil

conditioner for small rural communities. Bioresource Technology 73, 213-219

Lotito A.M., Di Iaconi C., Fratino U., Mancini A., Bergna G. (2011). Sequencing batch

biofilter granular reactor for textile wastewater treatment. New Biotechnology 29, 9-

16.

Odegaard H. (1989). Appropriate technology for wastewater treatment in coastal tourist

areas. Water Science and Technology, 21 (1), 1-17.

Scultz J.R., Hegg B.A., Rakness K.L. (1982). Realistic sludge production for activated

sludge plants without primary clarifiers. Journal Water Pollution Control Federation 54

(10), 1355-1360.

Standard Methods for the Examination of Water and Wastewater 21th edn, American

Public Health Association, 2005, Washington DC, USA.

effectiveness of an innovative technology for treating raw municipal

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