DECENTRALIZED WASTEWATER MANAGEMENT

CURRENT STATUS IN INDIAThe wastewater generation increased from 7,000 mld in 1978-79 to 17,000 mld in 1994-95 in Class I cities. 39% of wastewater was treated in the year 1978-79. But, in the year 2003, only 26% of wastewater generated in cities was treated27 cities have only primary treatment facilities

The mode of disposal is:

indirectly into the rivers/ lakes/ ponds/ creeks in 118 cities; on to the agriculture land in 63cities directly into rivers in 41 cities. in 44 cities, it is discharged both into rivers and on agriculture land.

In many of the coastal cities, the wastewater finds its way into estuaries, creeks, bays etc. (Around 25% of total wastewater)

PARADIGM SHIFT IN RECENT PASTIn the past, wastewater was a problemNow, it is considered as a resource

Example:Newater scheme in Singapore

Treated domestic wastewater for Industrial use

Zero Discharge norm for major industries

Recycled water for domestic use

Treated wastewater for groundwater recharge & irrigation Zero Discharge

ISSUES TO BE ADDRESSEDTo develop tailor made treatment processes for various situationsWastewater treatment, reuse and recycleLife cycle analysis of wastewater treatment systems.

How can we solve the problem..Develop Tailor Made wastewater treatment processes for various situationsDecentralized, economically viable and environmental friendly technologiesPond systemsConstructed wet landsPhyto-remdiation systemsBiofiltration and sand filtersSeptic Tanks Biomembrane processesBiotowersSelection of the systems depends on soil and groundwater conditions and availability of land

Phyto-remdiation systemsPond systemsConstructed wet lands

Biofiltration and sand filtersSeptic TanksBiomembrane processes

Aerobic processes

TypeCommon NameUseSuspended GrowthActivated-Sludge process (es)Aerated LagoonsAerobic digestionMembrane bioreactorsCarbonaceous BOD removal, nitrificationCarbonaceous BOD removal, nitrificationStabilization, carbonaceous BOD removal Attached growthTrickling FiltersRotating biological contactorsPacked bed reactorsCarbonaceous BOD removal, nitrification-do--do-Hybrid (Combined) suspended and attached Growth processesTrickling filters/ activated sludgeCarbonaceous BOD removal, nitrification

Anoxic processes

TypeCommon NameUseSuspended GrowthSuspended-growth denitrificationDenitrification

Attached growthAttached-growth denitrificationDenitrification

Anaerobic processes

TypeCommon NameUseSuspended GrowthAnaerobic contact processes Anaerobic digestion Carbonaceous BOD removalStabilization, solids destruction, pathogen killAttached growthAnaerobic packed and fluidized bedCarbonaceous BOD removal, waste stabilization denitrification Sludge blanketUpflow anaerobic sludge blanket Carbonaceous BOD removal, especially High-strengthWasteHybridUpflow sludge blanket/attached growthCarbonaceous BOD removal

Combined aerobic, anoxic, and anaerobic processes

TypeCommon NameUseSuspended GrowthSingle- or multistage processes,Various proprietary processesCarbonaceous BOD removal, nitrification, denitrification, and phosphorus removalHybridSingle- or multistage processes with packing for attached growthCarbonaceous BOD removal, nitrification, denitrification, and phosphorus removal

Ponds and Lagoons

Sewage ContainsPathogens or disease-causing organismsWater, with only 0.06 percent of the dissolved and suspended solid material.Suspended particles present in untreated sewage ranges from 100 to 350 mg/l. Pathogens or disease ranges from 100 to 350 mg/l. Sewage also contains nutrients (such as ammonia and phosphorus), contains nutrients (such as ammonia and phosphorus),Ammonia can range from 12 to 50 mg/l and phosphorus can range from 6 to 20 mg/l in untreated sewage.

Lagoon processes

TypeCommon NameUseAerobic lagoonsAerobic lagoonsCarbonaceous BOD removalMaturation (tertiary) lagoonsMaturation (tertiary) lagoonsCarbonaceous BOD removal, nitrification Facultative lagoonsFacultative lagoonsCarbonaceous BOD removalAnaerobic lagoonsAnaerobic lagoonsCarbonaceous BOD removal, waste stabilization.

LagoonsLike most natural environments, conditions inside facultative lagoons are always changing.Lagoons experience cycles due to variations in the weather, the composition of the wastewater, and other factors. In general, the wastewater in facultative lagoons naturally settles into three fairly distinct layers or zones. Different conditions exists in each zone, and wastewater treatment takes place in all three

LagoonsThe top layer in a facultative lagoon is called the aerobic zone, because the majority of oxygen is present there.How deep the aerobic How deep the aerobic zone is depends on loading, climate, amount of sunlight and wind, and how much algae is in the water. The wastewater in this part of the lagoon receives oxygen from air, from algae, and from the agitation of the water surface (from wind and rain, for example). This zone also serves as a barrier for example). This zone also serves as a barrier for the odors from gases produced by the treatment processes occurring in the lower layers.

Preliminary treatmentThings like rags, sand, gravel and larger pieces of organic matter must be removed before it enters the Treatment System.

Aerial View of a Lagoon System

Advantages and DisadvantagesAdvantagesInexpensive and Reliable system in tropical countriesMin operation and maintenanceNo energy requirementDisadvantagesRequirement of large areaOdor and rodent problemEffluent with high total BOD

Constructed Wetlands

Removal MechanismsWetland treatment: Organic matter, TSS, N, P, pathogensRemoval mechanism: Biological:microbial degradationplant uptake Physico- chemical:adsorptionsedimentation precipitation

Organic Matters Sugars, Proteins, lipids;Toilet wastes, cleaning, food wastes

PollutionBiomass + breakdown products (Sludge)Aerobic (with oxygen)Anaerobic (without oxygen)Microorganisms

Phosphorous removalPhosphorous adsorption: clay-humus complexPhosphorous precipitation: iron, aluminum, calciumProblems: saturation and clogging Plant uptake

PathogensSedimentation / filtrationNatural die-offExcretion of antibiotics from roots of macrophytes

PlantsThe role of the plants:The root system increases the surface available to bacterial colonisation;Transfer oxygen to provide an aerobic/oxidized environment, oxygen leakage from the roots( limited);Nutrient assimilation (N and P) (limited);Maintain hydraulic pathways in the substrate;Plant litter provides substrate to the microorganisms;Accumulated liter serves as thermal insulation;Aesthetics of the wastewater treatment plant.

Plants A wide variety of aquatic plants can be used.Selecting plants:Native plants;Active vegetative colonizers;Considerable biomass, stem densities;Sometimes a combination of species.

Wastewater treatment Primary treatment :Septic tank : lower the total organic loading, and separate the solids from the liquid

Secondary treatment:Constructed wetland: convert the dissolved or suspended material into a useful form separated from the water

Constructed wetlands: Different types

Aerobic Suspended Growth Systems(s32)

Process Description The aerobic conversion of the organic matter occurs in three steps:

Oxidation

COHNS + O2 + BACTERIA CO2 + NH3 + END PRODUCTS+ ENERGY (Organic matter) Synthesis of new cellsCOHNS + O2+ BACTERIA + ENERGY C5H7NO2 (new cells )Endogenous respirationC5H7NO2 + 5O2 5 CO2+ NH3+ 2H2O + ENERGY

Pathways for the breakdown of organic matter

Extended Aeration SystemExternal substrate is completely removed.Auto oxidation (internal substrate is used)Net growth = 0

AdvantagesSludge production minimalStabilized sludge No digesters are requiredNutrient requirement minimal

Disadvantages High power requirementLarge volume of aeration tankSuitable for small communities

Oxidation ditch Pasveer Ditch

Attached Growth systemsAerobicTrickling filtersRotating biological contactors

AnaerobicAnaerobic filtersDenitrification systems

System biology - Heterogeneous microbes

Rate of organic matter removalWastewater flow rateOrganic loading rateRate of diffusivity of food and oxygen into the biofilm.Temperature

Trickling FiltersT.F Reactor in which randomly packed solids forms provide surface for microbial growth. - system for wastewater distributionSpecific surface area and porositySpecific surface area: The amount of surface area of the media that is available for bio film growth

RBCs

Membrane BioreactorsEmploy biological reactor and membrane filtration as a unified system for the secondary treatment of wastewaterMembranes perform the separation of the final effluent from the biomass through filtration Filtration takes place by the application of a pressure gradient

Process BasicsSS

Process Basics

Submerged MBR SystemRe-circulationFeedSS

Assessment of MBR TechnologyAdvantagesHigh effluent quality No sludge settling problems Reduced volume requirements DisadvantagesMembrane fouling Increased operational costs

Space RequirementMany Compact Units are available

For Sustainability1. Promote Anaerobic treatment technologies for energy generationLess energy intensiveCan generate alternate energySo far not very successful due to the lack of information about the processDemonstration plantsOperational guidelinesTraining in design, maintenance and operation

2. Develop Wastewater reuse and recycle systems after adequate treatmentWastewater is not a problem, but a resourceTreat the waste according to the beneficial use

Agricultural - Preserve as much nutrients as possible, kill the pathogens (low cost technologies)

Industrial Higher degree of treatment- (bio membrane processes)

Domestic Flushing toilets, gardening etc

Groundwater Recharge- needs high end treatment if the GW table is high, otherwise the soil will act as a treatment unit..

Base flows in Rivers Needs treatment based on the carrying capacity of the existing river, water body

Wastewater reuse applications

Wastewater reuse categories Issues/ constraintsAgricultural irrigation crop irrigationCommercial nurseriesSurface and groundwater contaminationMarketability of crops and public acceptanceLandscape irrigation Parks, School yards, Freeway medians, Golf courses, Cemeteries Green belts, ResidentialEffect of water quality, particularly salts, on soils and cropsPublic health concerns related to pathogensUse area control including buffer zone may result in high user costsIndustrial recycling and reuseCooling waterBoiler feedProcesses waterHeavy constructionConstituents in reclaimed water related to scaling, corrosion, biological growth, and fouling Public health concerns, particularly aerosol transmission of pathogens in cooling waterCross connection of potable and reclaimed water

Groundwater recharge Groundwater replenishment Saltwater intrusion controlSubsidence controlPossible Contamination of groundwater aquifer used as a source of potable waterOrganic chemicals in reclaimed water and their toxicological effects Total dissolved solids, nitrates, and pathogens in reclaimed water

Wastewater reuse applications

Wastewater reuse categories Issues/ constraintsRecreational/environmental usesLakes and pondsMarsh enhancementStream-flow augmentationFisheries, SnowmakingHealth concerns related to presence of bacteria and virusesEutrophication due to nitrogen and phosphorus in receiving waterToxicity to aquatic life

Nonpotable urban usesFire protectionAir conditioningToilet flushingPublic health concerns about pathogens transmitted by aerosolsEffect of water quality on scaling, corrosion, biological growth, and foulingCross connection of potable and reclaimed water linesPotable reuseBlending in water supply reservoirsPipe-to-pipe water supplyConstituents in reclaimed water, especially trace organic chemicals and their toxicological effectsAesthetics and public acceptanceHealth concerns about pathogens transmission, particularly enteric viruses

Selection of Treatment Technologies

Life cycle analysis of wastewater treatment systemsThe treatment system should beEconomically viable, Environmentally Friendly, and Sustainable. Many times these factors are not being considered. Develop guidelines for life cycle analyses of wastewater treatment systems.Pros and cons of the systemsEg: Energy consumption, Residual pollution left over, Environmental degradation, contribution to global warming etc..