DECENTRALIZED WASTEWATER MANAGEMENT

CURRENT STATUS IN INDIA The 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 treated

27 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 PAST

In the past, wastewater was a “problem” Now, 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 ADDRESSED

To develop tailor made treatment processes for various situations

Wastewater treatment, reuse and recycle Life cycle analysis of wastewater treatment

systems.

How can we solve the problem..• Develop “Tailor Made” wastewater treatment processes

for various situations– Decentralized, economically viable and environmental

friendly technologies• Pond systems• Constructed wet lands• Phyto-remdiation systems• Biofiltration and sand filters• Septic Tanks • Biomembrane processes• Biotowers

– Selection of the systems depends on soil and groundwater conditions and availability of land

Phyto-remdiation systems

Pond systems

Constructed wet lands

Biofiltration and sand filters

Septic Tanks

Biomembrane processes

Aerobic processes

Type Common Name Use

Suspended Growth

Activated-Sludge process (es)

Aerated Lagoons

Aerobic digestion

Membrane bioreactors

Carbonaceous BOD removal, nitrification

Carbonaceous BOD removal, nitrification

Stabilization, carbonaceous BOD removal

Attached growth Trickling Filters

Rotating biological contactors

Packed bed reactors

Carbonaceous BOD removal, nitrification

-do-

-do-

Hybrid (Combined) suspended and attached Growth processes

Trickling filters/ activated sludge

Carbonaceous BOD removal, nitrification

Anoxic processes

Type Common Name Use

Suspended Growth

Suspended-growth denitrification

Denitrification

Attached growth

Attached-growth denitrification

Denitrification

Anaerobic processes

Type Common Name Use

Suspended Growth

Anaerobic contact processes

Anaerobic digestion

Carbonaceous BOD removal

Stabilization, solids destruction, pathogen kill

Attached growth

Anaerobic packed and fluidized bed

Carbonaceous BOD removal, waste stabilization denitrification

Sludge blanket

Upflow anaerobic sludge blanket

Carbonaceous BOD removal, especially High-strength

Waste

Hybrid Upflow sludge blanket/attached growth

Carbonaceous BOD removal

Combined aerobic, anoxic, and anaerobic

processes

Type Common Name Use

Suspended Growth

Single- or multistage processes,

Various proprietary processes

Carbonaceous BOD removal, nitrification, denitrification, and phosphorus removal

Hybrid Single- or multistage processes with packing for attached growth

Carbonaceous BOD removal, nitrification, denitrification, and phosphorus removal

Ponds and Lagoons

Sewage Contains• Pathogens or disease-causing organisms• Water, 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

Type Common Name Use

Aerobic lagoons

Aerobic lagoons Carbonaceous BOD removal

Maturation (tertiary) lagoons

Maturation (tertiary) lagoons

Carbonaceous BOD removal, nitrification

Facultative lagoons

Facultative lagoons

Carbonaceous BOD removal

Anaerobic lagoons

Anaerobic lagoons

Carbonaceous BOD removal, waste stabilization.

Lagoons

• Like 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

Lagoons…

• The 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 treatment

• Things 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 Disadvantages

Advantages• Inexpensive and Reliable system in tropical

countries• Min operation and maintenance• No energy requirement

Disadvantages• Requirement of large area• Odor and rodent problem• Effluent with high total BOD

Constructed Wetlands

Removal Mechanisms

Wetland treatment:

Organic matter, TSS, N, P, pathogens• Removal mechanism:

– Biological:• microbial degradation• plant uptake

– Physico- chemical:• adsorption• sedimentation• precipitation

Organic Matters •Sugars, Proteins, lipids;

•Toilet wastes, cleaning, food wastes

Pollution Biomass + breakdown products

(Sludge)

Aerobic (with oxygen) Anaerobic (without oxygen)

Microorganisms

Proteins

nitrate- N

ammonia-N

N2 gas

autotrophic- aerobic

heterotrophic- anaerobic

nitrification

denitrification

Nitrogen removal

Plant uptake

Ammonia volatilization

Storage in detritus and sediment

Phosphorous removal

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

Pathogens

• Sedimentation / filtration• Natural die-off• Excretion of antibiotics from roots of macrophytes

Plants

The 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

Vertical subsurface flow

Floating Macrophytes system

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 cells • COHNS + O2+ BACTERIA + ENERGY C5H7NO2 (new cells )

• Endogenous respiration • C5H7NO2 + 5O2 5 CO2+ NH3+ 2H2O + ENERGY

 

Pathways for the breakdown of organic matter

 

Extended Aeration System

External substrate is completely removed.

Auto oxidation (internal substrate is used)

Net growth = 0

Advantages

•Sludge production minimal

•Stabilized sludge No digesters are required

•Nutrient requirement minimal

Disadvantages

•High power requirement

•Large volume of aeration tank

•Suitable for small communities

Oxidation ditch – Pasveer Ditch

Attached Growth systems

Aerobic

Trickling filters

Rotating biological contactors

Anaerobic

Anaerobic filters

Denitrification systems

System biology - Heterogeneous microbes

Rate of organic matter removal

1.Wastewater flow rate

2.Organic loading rate

3.Rate of diffusivity of food and oxygen into the biofilm.

4.Temperature

Trickling Filters

T.F Reactor in which randomly packed solids forms provide surface for microbial growth.

- system for wastewater distribution

Specific surface area and porosity

Specific surface area: The amount of surface area of the media that is available for bio film growth

RBCs

Membrane Bioreactors

• Employ biological reactor and membrane filtration as a unified system for the secondary treatment of wastewater

• Membranes perform the separation of the final effluent from the biomass through filtration

• Filtration takes place by the application of a pressure gradient

Process Basics

SS

Deni NitriSS

SCT

discharge

conventional technologymembrane technology

NDN

effluentUF notSec. Clarif.

Process Basics

membranewater

suction

dis. solids

sludge floc

viruses

bacteriakinet. energy

Re-circulation

Feed

SS

Submerged MBR System

Cleaningchemicals

Module Back pulse

BP Tank

effluent

Permeate

ZeeWeedAeration

aeration

Assessment of MBR Technology

• Advantages– High effluent quality – No sludge settling problems – Reduced volume requirements

• Disadvantages– Membrane fouling – Increased operational costs

Space Requirement

• Many 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 process• Demonstration plants• Operational guidelines• Training in design, maintenance and operation

2. Develop Wastewater reuse and recycle systems after adequate treatment

Wastewater 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 applicationsWastewater reuse categories Issues/ constraints

Agricultural irrigation crop irrigation

Commercial nurseries

Surface and groundwater contamination

Marketability of crops and public acceptance

Landscape irrigation

Parks, School yards, Freeway medians, Golf courses, Cemeteries

Green belts, Residential

Effect of water quality, particularly salts, on soils and crops

Public health concerns related to pathogens

Use area control including buffer zone may result in high user costs

Industrial recycling and reuse

Cooling water

Boiler feed

Processes water

Heavy construction

Constituents in reclaimed water related to scaling, corrosion, biological growth, and fouling

Public health concerns, particularly aerosol transmission of pathogens in cooling water

Cross connection of potable and reclaimed water

Groundwater recharge

Groundwater replenishment

Saltwater intrusion control

Subsidence control

Possible Contamination of groundwater aquifer used as a source of potable water

Organic chemicals in reclaimed water and their toxicological effects

Total dissolved solids, nitrates, and pathogens in reclaimed water

Wastewater reuse applications

Wastewater reuse categories Issues/ constraints

Recreational/environmental uses

Lakes and ponds

Marsh enhancement

Stream-flow augmentation

Fisheries, Snowmaking

Health concerns related to presence of bacteria and viruses

Eutrophication due to nitrogen and phosphorus in receiving water

Toxicity to aquatic life

Nonpotable urban uses

Fire protection

Air conditioning

Toilet flushing

Public health concerns about pathogens transmitted by aerosols

Effect of water quality on scaling, corrosion, biological growth, and fouling

Cross connection of potable and reclaimed water lines

Potable reuse

Blending in water supply reservoirs

Pipe-to-pipe water supply

Constituents in reclaimed water, especially trace organic chemicals and their toxicological effects

Aesthetics and public acceptance

Health concerns about pathogens transmission, particularly enteric viruses

Selection of Treatment Technologies

Life cycle analysis of wastewater treatment systems• The treatment system should be• Economically 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 systems• Eg: Energy consumption, Residual pollution left over,

Environmental degradation, contribution to global

warming etc..