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Artificial Wetlandsfor WASTEWATER TREAMENTAn economical and a sustainable solutionBy: Miaaza HussainRoll No: 10/CE/611

INTRODUCTIONWhat is a wetland?artificial wastewater treatment systems consisting of shallow (usually less than 1 m deep) ponds or channels which have been planted with aquatic plants and mimic a natural wetland.Wetlands are defined as land where the water surface is near the ground surface long enough each year to maintain saturated soil conditions, along with related vegetation. eg : swamps and marshesProvide ambient environment for biological and microbial activity for treatment and removal of pollutantsWhat is an artificial wetland?2

HISTORYThousand years ago natural wetlands are used by Chinese and Egyptians to clarify liquid effluent Over the past 50 to 60 years these processes have been analyzed and evaluatedFirst artificial wetland was used in Australia in 1904. Indias first constructed wetland was installed at Sainik School, Bhubaneswar, Orissa over 5,000 constructed wetlands have been built in Europe and about 1,000 are currently in operation in the United States

3Constructed wetlands are generally built on uplands and outside floodplains or floodways in order to avoid damage to natural wetlands and other aquatic resources.

Wetlands are frequently constructed by excavating, backfilling, leveling, compaction, diking and installing water control structures to establish desired hydraulic flow patterns.

If the site has highly permeable soils, an impervious, compacted clay liner is usually installed and the original soil placed over the liner. Wetland vegetation is then planted or allowed to establish naturally.

How are they built?4COMPONENTSof an artificial wetland

VegetationSubstrate (rock, gravel, sand and soil used )LinerBasinOutletInletIn some cases brick masonry used in construct the basin along with liner5

Bulrush (Scirpus spp.)

Giant reed (Phragmites australis )

Cattail (Typha spp.) VEGETATION: primary role of vegetation is providing structure for enhancing flocculation, sedimentation, and filtration of suspended solids

rooted emergent plant species interact with the wastewater at the root zone/ Microbial attached growth

Duckweed(Lemna spp.) Giant duckweed(Spirodela polyrhiza )6CLASSIFICATIONof artificial wetland based on flow patternARTIFICIAL WERLANDSURFACE FLOW orFREE WATER SURFACE FLOW (FWS)SUB-SURFACE FLOW (SSF)VERTICAL FLOW (VF)HORIZONTAL FLOWHYBRID/COMBINED SYSTEM FLOWBy the location of water surface7

FREE WATER SURFACE (FWS) WETLANDS Surface-flow wetlands move effluent above the soil in a planted marsh or swamp, and thus can be supported by a wider variety of soil types includingbay mudand othersiltyclays.Fig: A free surface flow wetlandShallow water (depth of 0.1-0.6 m)Emergent vegetationThis system is also called rootzone or vegetated submerged bed or rock-reed filters8SUB-SURFACE FLOW WETLANDS In Subsurface-flow wetlands waste water moves through aporous media/ gravel (generally limestone or volcanic rocklava stone) orsand medium on which plants are rooted.Water level stays below the ground surface

Fig: A sub-surface flow wetlandHORIZONTAL FLOW

wastewater flows more or less horizontally through the substrateEfficient in BOD5 , COD and TSS removalLess nitrification

wastewater is dosed intermittently onto the surface of sand and gravel filters and gradually moves vertically through the filter media downwards and collected in slotted drainage pipes Nitrification process is prominentVERTICAL FLOWTREATMENT MECHANISMS in WETLANDSThe pollution through such a system is removed by a combination of physical, chemical and biological processesOxygen supplied by diffusion or by oxygen leakage from rootsThese processes includes:: sedimentation/ filtrationMicrobial degradation (aerobic and anaerobicAdsorption on root surface oxidation/reductionPrecipitationUV treatment in open water area provides some disinfection

12WW ConstituentRemoval MechanismSuspended Solids Sedimentation FiltrationSoluble organics Aerobic and anaerobic microbial degradationPhosphorous Matrix sorption Plant uptakeBiotic assimilationNitrogen

Ammonifi cation followed by microbial nitrifi cation Denitrifi cation Plant uptake Matrix adsorption Ammonia volatilization (mostly in SF system)Metals

Adsorption and cation exchange Complexation Precipitation Plant uptake Microbial Oxidation /reduction

Pathogens

Sedimentation Filtration Natural die off Predation UV irradiation (SF system) Excretion of antibiotics from roots of macrophytes

Pollutant Removal Mechanisms in Constructed WetlandsDESIGN ASPECTSDetermine design requirements ( design flow rates/ effluent discharge location/ type of wetland and location)Determine water balance limitation ( evaporation/ precipitation)Preliminary and primary treatment: (size and layout/ retention time) Wetland design ( size / configuration/water depth/ aspect ratio/ hydraulic retention time/ density of vegetation/ media depth and gradation/ Bed cross section area ( for HF wetland))Inlet and outlet structure design

14PRELIMINARY TREATMENTSSF constructed wetlands are extremely susceptible to plugging. Not much effect on surface flow though surface flow wetlands affected by algal growth

Minimum preliminary/ primary treatment should be provided to remove the settleable solids

preliminary treatment of wastewater comprises of mainly screen and grit chamber.

Coarsely dispersed solid/ debris are removes

PRIMARY TREATMENT

When solids are overloaded the porosity of drainage beds are impactedSeptic tanks have been evaluated for SSF wetland pretreatment regime.

Need for de-suludging

In septic tanks solids are allowed to settle and the liquid component is discharged onto the wetlands

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Fig: Schematic cross- section of a two-compartment septic tank

Fig: Schematic cross- section of an up flow anaerobic baffle reactor (improved septic tank)Baffles increases contact with biomass in accumulated sludgeThe wetland might be sized based on the equation proposed by Kickuth:

Ah = Qd (ln Ci ln Ce)/ KBOD

Ah = Surface area of bed (m2) Qd = average daily flow rate of sewage (m3/d) Ci = influent BOD5 concentration (mg/l) Ce = effluent BOD5 concentration (mg/l) KBOD = rate constant (m/d) : dependent on temperatureKBOD is determined from the expression KTdn, where, KT = K20 1.06(T-20)

K20 = rate constant at 20 oC (d-1) T = operational temperature of system (oC) d = depth of water column (m)1-2m2 per PE in HF and 0.8-1.5 m2 per PE in VF

SIZING OF WETLANDDepth of substrate For horizontal flow wetlands, its is recommended to provide a depth of 40 cm taking into considerations of the precipitation

VF systems are built with larger depth ( 50 to 100 cm in usage)

It is recommended to use substrate depth of 70 cm, which can provide adequate nitrification in addition to the organic pollutants removal.

Bed cross sectional area is calculated by the equation: Ac = Qs / Kf (dH/ds)

Ac = Cross sectional area of the bed (m2) Qs = average flow (m3/s) Kf = hydraulic conductivity of the fully developed bed (m/s) dH/ds = slope of bottom of the bed (m/m)

For graded gravels a value of Kf of 1 x 10-3 to 3 x 10-3 m/s is normally chosen. In most cases, dH/ds of 1% is usedBED CROSS SECTIONAL AREAThe media perform several functions. They: are rooting material for vegetation, help to evenly distribute/collect flow at inlet/outlet, provide surface area for microbial growth, and filter and trap particles.

small particles have low hydraulic conductivity and large particles have less SA per unit volume of microbial habitat. Hence medium sized media particles used

It is recommended that the media in the inlet and outlet zones should be between 40 and 80 mm in diameter to minimize clogging and should extend from the top to the bottom of the system

INLET/OUTLETInlet and outlet structures distribute the flow into the wetland, control the flow path through the wetland, and control the water depth. Multiple inlets and outlets spaced across either end of the wetland are essential to ensure uniform influent distribution into and flow through the wetland.

Inlets: perforated pipe, open trenches extending along the widthFactors effecting performance Water Balance ( precipitation, evapotranspiration): too little water stresses vegetation and too much water causes over flow and hinders settling. This factor needed to be taken into account for HRT calculation. Small impact in SSFHRT: must be able to take all possible water flowsAspect ratio: increase in L/W ratio; concern for head loss though it increases treatment performance.Media gradation: Soils with high humic and sand components are easier for aquatic macrophytes to migrate through. The soil substrate for SF type constructed wetlands should be loam, well loosened and at least 6 inches deep. Temperature(FSF wetlands mostly effected):Ice formation may also alter wetland hydraulics and limit oxygen transfer. Decreased temperatures have been show to reduce rates of biological reactions.

Reliability of CWConstructed wetlands are an effective and reliable water reclamation technology if they are properly designed, constructed, operated and MaintainedDesigned usually to remove BOD and suspended solidsLoading rate is designed for effluent concentration of: BOD: 30 mg/l TSS: 30 mg/l TKN: 10 mg/lAlso used to remove metals, including cadmium, chromium, iron, lead, manganese, selenium, zinc, and toxic organics from wastewaterDifferent case studies shows about 80-95% COD, BOD5 and TSS removal and about 20% nitrogen removalMethodEase of OperationPower Req.Skill for O & MReliabilityLand req.Detention TimeApplicabilityWSPSimpleNILlowVery goodVery large15-20 daysBest method provided the area is largeASPDiff.HighMed.LeastSmall4-8 hrsBest method if land available is lessRODiff.LowHighMed.Small3- 5 daysEffluent can be used for cooling purpose in industriesUASBSimpleLowHighMed.low1.5-2 daysBest method when combined with maturation pond if the land available is very lessFABSimpleLowHighMed.low16-24 hrsBest method if land available is lessCWVery SimpleLowVery lowVery GoodVery Large6-8 daysBest method for small communitiesComparison of Existing Methods of Secondary Treatment for WastewaterWaste Stabilization Pond (WSP), Activated Sludge Process (ASP),Reverse Osmosis Process (RO), Up flow Anaerobic Sludge Blanket (UASB),Reactor, Fluidized Anaerobic Bio (FAB) Reactor and Constructed Wetland(CW)25Advantages ADVANTAGES AND DISADVANTAGES of ARTIFICAL WETLANDSRelatively inexpensive to construct and operateEasy to maintainProvide effective and reliable wastewater treatmentRelatively tolerant of fluctuating hydrologic and contaminant loading ratesProvide indirect benefits such as green space, wildlife habitats, and recreational and educational areasDisadvantagesRelatively large area required for advance treatment than conventional mechanical treatment systemsPossible problems with pests and Potential for odor problemsReduced performance during the vegetation establishment periodFor surface flow systems, mosquito control may be necessaryPossible groundwater contaminationStandard design criteria not readily available to engineers and regulators/ less adoption of the method

Application of Constructed Wetlands in IndiaThe discharge of untreated wastewater is a major contribution to deteriorating health conditions and pollution of nearby water bodies

Concerns for contamination of available water with the rapid pace of urban growth

Best option for developing countries and in small villages with less people

Also suitable for single households

Less expensive, natural and a sustainable solution.CONSTRUCTED WETLANDS TECHNOLOGY ASSESSMENT AND DESIGN GUIDANCE : Iowa Department of Natural ResourcesCONSTRUCTED WETLANDS MANUAL United Nations Human Settlements ProgrammeCONSTRUCTED WETLANDS: A Techno Economic and Echo Friendly Approach for waste water treatment technology by Dr. Sunil Sharma and Er. Mahendra Pratap ChoudharyCONSTRUCTED TREATMENT WETLAND : United States Environmental Protection Agency

REFERENCESThank you