Environmental Effects of Wastewater use in Agriculture

4th Regional SUWA , Peru

A combination of one or more of: -domestic effluent consisting of blackwater (excreta, urine and faecal sludge) and greywater (kitchen and bathing wastewater); -water from commercial establishments and institutions, including hospitals; -industrial effluent, stormwater and other urban run-off; -agricultural, horticultural and aquaculture effluent, either dissolved or as suspended matter

(definition adapted from Raschid-Sally and Jayakody, 2008)

“Sick Water” Definition of Wastewater

UNEP wastewater management program – delivered through the GPA (Global Program of Action for the Protection of the Marine Environment from Land-based Activities);

Oceans, seas, islands and coastal areas form an integrated whole that is essential component of the Earth’s ecosystem and is critical for global food security and for sustaining economic prosperity and the well-being of many national economies

Other Pragmatic Considerations:• 70% mega-cities are coastal 38% global population live on the coast Many more come to the coast as visitors , or economic opportunities ……

UNEP/GPA- Area of focus:• Nutrients• Marine Litter• Wastewater  

Open ocean25%

Terrestrial38%

Estuaries12%

Coastal38%

Seagrass/ algae beds

11%

Coral reefs 1%

Shelf13%

Contribution of Coast and OceanContribution of Coast and Ocean in Global GDPin Global GDP

• Wastewater (raw, diluted or treated) is a resource of increasing global importance, particularly in urban and peri-urban areas due to growing wastewater volume,

• 10% percent of the world’s population would starve if they didn’t have access to food grown that way

• 20 million hectares in 50 countries are irrigated with raw or partially treated wastewater.

• The use of greywater is growing in both developed and less-developed countries – it is culturally more acceptable in some societies

• Without proper management, wastewater use poses serious risks to human health and environment

• With proper management, wastewater use can contribute significantly to sustaining livelihoods, foods security and the quality of the environment

Why bother about wastewater?

Sewage systems are lacking, under-dimensioned or decayed

Wastewater management….a big challenge

UNEP/GEF WIO-LaB Project 6

Wastewater………a global issue?

Simplified scheme of agricultural wastewater use & effects on environment (adapted from WHO Guidelines)

WW treatment plan(in developing countries)

Evaporation

Aquifer

ConsumerCropsCattleWater

Sewage Industrial discharge

Sewage system

Aquaculture

Aquatic plants

Storage dam

Infiltration

Aquatic plants

Irrigation channels

Infiltration

Water + salts

Soils(retains metals, organic matter &

phosphorus)Compounds & water absorption by plants

Sprinklers

Cattle consuming irrigated crops

Irrigation drainage

Lake

UNEP/GEF WIO-LaB Project 8

Dead zones are spreading………

• Dead zones are now thought to affect more than 245 000km2 of marine ecosystems, predominantly in the northern hemisphere (Diaz and Rosenberg, 2008)

- Water security- Ecology- Ecosystem Services- Biodiversity

Impacts of wastewater on……

• Loss of food security• Loss of fisheries, livelihoods• Loss of blue carbon sinks• Economic loss :

• Healthy reefs can produce up to 35 tons of fish/km2/year

Impacts on climate Change

• Wastewater generates methane (21 times more powerful than CO2) and nitrous oxide (310 time more powerful than CO2).

• CH4 & NO2 will rise 25% and 50% respectively in just a decade

• Nutrients increase acidification of freshwater

But, wastewater is a resource… Already 10% of the world Population supplied with food

grown using WW (Mexico, California, Cambodia),

Water scarcity

Water pollution

Source of nutrients

Available all year round

Where is it most needed?

a) Innovative water technology

• Reduce the discharge of WW r, treat & re-use

b)Inventive governance & management

• Intelligence water use: Different water uses need different water Quality

Trends in industrialized countries reversed but are on the increase in developing countries

Shortcutting the trends…..a must

A need for decentralised Technologies ....

• Septic Tanks, Constructed Wetlands, Composting Toilets, Biodigestor, Anaerobic Filter, Duckweed Lagoons

• Collection, treatment, and final disposition of the WW on/or close to the location;

• Useful in treating wastes from residences, households, small villages, isolated communities, etc.

Advantages for decentralized systems: Economy of structural arrangements such as transportation,

reservation and elevation; Possibility for reuse of the effluent and potentiality for aquifer

recharging; A problem in a unit doesn’t collapse the whole system; Development of the local potentialities: small systems can be

designed, built and managed by local professional, improving the local economy.

TypeKind of treatment Kind of WW treated Advantages Disadvantages Nutrients removal

Septic Tank sedimentation, flotation and digestion

Domestic wastewater (communities until 100 inhabitants)

Simple, durable, easy maintenance, small area required

Low treatment efficiency, necessity of a secondary treatment, effluent not odorless

COD, BOD, TSS; grease.

Subsurface Flow Constructed Wetlands

biological and physical processes

Domestic and agricultural wastewaters; small communities; tertiary treatment for industries.

Low or no energy requirements; Provide aesthetic, commercial and habitat value.

system clogging; recommended as a secondary treatment, large areas required;

TSS; COD; TN; TP.

Composting Toilets

unsaturated and aerobic conditions provide biological and physical decomposition

human excreta, toilet paper, carbon additive, food waste

Resulting "humus" used as a resource; conservation of water resources; recycling of nutrients.

If not well sized and maintained can be a environmental problem and a threat for human being, due to its contaminant potential

Volume reduced from 10 to 30%; pathogens.

Biogas Digestor Sedimentation, flotation and digestion

human excreta, animal and agricultural wastes

Recycling of resource; gas produced is used for cooking and lighting

Biogas plants can be expensive to build and difficult to operate. Poor maintenance leads to loss of gas production and blockage of the digester tank with solids.

Similar to septic tanks systems; The long period of storage can also remove some pathogens.

Anaerobic Filter anaerobicdegradation ofsuspended anddissolvedsolids

pre-settleddomestic andindustrialwastewater ofnarrowCOD/BOD ratio

simple and fairly durable if well constructed and wastewater has been properly pre-treated, hightreatment efficiency, little permanent space required

costly in construction because of special filter material, blockage of filterpossible, effluent smells slightly despite high treatment efficiency

BOD, TDS, TSS

Duckweed Based WW Stabilizations Ponds

sedimentation, anaerobic degradation and sludge stabilization

Domestic and agricultural wastewater;

No clogging risk; High nutrient removal rates

Necessity of large areas; necessity of constant harvesting; unsuitable in very windy regions.

BOD, SS, TN, TP, metals

Septic Tank

• The aim of primary treatment is to separate out heavy constituents and particularly light constituents from the sewage.

• Due to its low treatment efficiency in terms of nutrient removal, a secondary treatment is recommended to polish the final effluent.

• This system consists of a closed, often prefabricated tank and is usually applied for primary sewage treatment. The treatment consists of sedimentation, flotation and digestion procedures.

• Septic tank is designed to receive all kinds of domestic wastes (kitchen, domiciliar laundries, washrooms, latrines, bathrooms, showers, etc) and it is economically viable to attend to 100 inhabitants.

Constructed Wetland• Constructed Wetlands are man-made systems which aims to simulate

the treatment processes in natural wetlands by cultivating emergent plants e.g. reeds (Phragmites), bulrushes (Scirpus), and cattails (Typha) on sand, gravel, or soil media.

• Constructed wetlands can serve the same small communities as natural wetlands and can be incorporated into the treatment systems for larger communities as well;

• They are subdivided, basically, into two wide groups:

(i) Surface Flow (the water or sewage flows through the soil surface); and

(ii) Subsurface Flow. (Vertical and Horizontal Flow)

Subsurface Vertical Flow Constructed Wetland (SVFW)

• In SVFW the wastewater is loaded onto the planted filter bed’s surface. The pollutants are removed or transformed by microorganisms that are attached to the filtersand and the plants’ root system.

• Due to the biofilm presents in the filter material, and high Oxygen concentration in the system, vertical flow systems have been applied for both BOD5 and SS removal and nitrification promotion;

• However, it is important ensure that the filter is not saturated or covered with water in order to secure a high oxygen level in the filter.

Subsurface Horizontal Flow Constructed Wetland (SHFW)

• In SHFW the sewage is uniformly fed in the inlet work and due to a longitudinal slight slope (~1%) the liquid flows through the pores of the filter bed until it reaches the outlet work.

• SHFW usually provide high treatment effect in terms of removal of organics (BOD5, COD) and suspended solids (SS). The removal of nitrogen and phosphorus is lower but comparable with conventional treatment technologies which do not include special nutrient removal step.

Composting Toilets• A composting toilet system contains and processes excrement, toilet

paper, carbon additive, and sometimes, food waste. • As a nonwater-carriage system, a composting toilet relies on

unsaturated conditions where aerobic bacteria break down waste.

• When exposed to an unfavorable environment for an extended period of time, most pathogenic microorganisms will not survive. However, caution is essential when using the compost end-product and liquid residual in case some pathogens survive.

• The composting unit must be constructed to separate the solid fraction from the liquid fraction and produce a stable, humus material with less than 200 MPN per gram of fecal coliform.

• If sized and maintained properly, a composting toilet breaks down waste 10 to 30% of its original volume.

Biogas Digestor• Biogas latrines and communal biogas plants are, in principle, a

more advanced form of the septic tank system. • When human excreta is combined with animal and agricultural

wastes and water, it will give off gas as it decomposes. • The mix of gases produced is called ‘biogas’ which can be used for

cooking and lighting.

• Biogas plants typically store the wastes for about 30 days which can remove some of the pathogenic organisms but by no means all.

Anaerobic Filter• Anaerobic filters are used for wastewater with a low content of

suspended solids (e.g. after primary treatment in septic tanks) and narrow COD/BOD ratio. Biogas utilisation may be considered in case of BOD > 1.000 mg/l.

• The anaerobic filter, also known as fixed bed or fixed film reactor, includes the treatment of non-settleable and dissolved solids by bringing them in close contact with a surplus of active bacterial mass.

• The larger the surface for bacterial growth, the quicker is the digestion.

Duckweed-Based Wastewater Stabilizations Ponds

• In general, duckweed ponds are used to treat domestic or agricultural wastewaters.

• Lemnaceae have the greatest capacity in absorbing macro-elements (e.g. nitrogen, phosphorus, potassium, calcium, sodium and magnesium among others);

• Effluents with both a high BOD and nutrient load may require adequate primary treatment to reduce the organic load.

• Plants must be harvested regularly in order to prevent dead plants forming bottom sludge.

Ecological Sanitation (EcoSan)

• Ecological Sanitation is a decentrilised sanitation system that understands human excreta, organic wastes and wastewater as a resource (not as a waste) with high potential for reuse and recycling.

• EcoSan systems enable a complete recovery of nutrients in household wastewater and their reuse in agriculture. They also help preserve soil fertility and safeguard long-term food security. Moreover, they minimise the consumption and pollution of water resources.

Ecological Sanitation (EcoSan) Stages (or Phases)

Waste segregation and possible utilization options. (UNESCO/IHP & GTZ, 2006)

CH4

CO2

Electricity generator by Biogas

Food Methane Combustion= CO2

Swine waste

Duckweeds Lagoon

Targeted and sustained investments are necessary to:

-Reduce volume and extent of water pollution-Capture water once polluted

-Treat polluted water for return to environment-Safely reuse and recycle ww conserving water & nutrients

-Provide a platform for the development of new and innovative technologies & management practices social, economic and environmental dividends

exceeding original investments

Conditions for success:Conditions for success:

A. Tackle immediate consequences• Adopt a multi-sectoral approach

• Use a cocktail of innovative approaches• Innovative financing

B. Thinking must be long-term:• plan wastewater management against

future scenarios.• Solutions must be socially and culturally

appropriate, as well as economically and environmentally viable into the future.

• Education must play a central role

Conditions for success:Conditions for success:

From the Sick Water reportFrom the Sick Water report

THANK YOUTHANK YOU