Environmental Effects of Wastewater use in Agriculture
4th Regional SUWA , Peru
“Sick Water” Definition of Wastewater
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)
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
Estuaries
12%
Terrestrial
38%
Coastal
38%
Seagrass/
algae beds
11%
Coral reefs 1%
Open ocean
25%
Shelf
13%
Contribution of Coast and Ocean
in Global GDP
Why bother about wastewater?
• 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
Wastewater management….a big challenge
Sewage systems
are lacking, underdimensioned or
decayed
Wastewater………a global issue?
UNEP/GEF WIO-LaB Project
6
Simplified scheme of agricultural wastewater use &
effects on environment (adapted from WHO Guidelines)
Evaporation
Aquatic
plants
Sewage
Industri
al
discharg
e
Aquaculture
Storage
dam
WW treatment plan
(in developing countries)
Aquatic
plants
Sewage system
Infiltration
Sprinkler
s
Irrigation
channels
Lake
Irrigation
drainage
Soils
(retains metals, organic matter &
phosphorus)
Compounds &
water absorption
by plants
Cattle
consuming
irrigated crops
Infiltration
Water + salts
Aquifer
Consumer
Crops
Cattle
Water
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)
UNEP/GEF WIO-LaB Project
8
Impacts of wastewater on……
- Water security
- Ecology
- Ecosystem Services
- Biodiversity
•
•
•
•
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?
Shortcutting the trends…..a must
Trends in industrialized countries reversed but are on the increase in
developing countries
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
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.
Kind of treatment
Type
Septic Tank
Subsurface Flow
Constructed
Wetlands
Kind of WW treated
Advantages
Disadvantages
Nutrients removal
sedimentation, flotation Domestic wastewater
and digestion
(communities until 100
inhabitants)
Simple, durable, easy
maintenance, small
area required
COD, BOD, TSS;
grease.
biological and physical Domestic and agricultural
processes
wastewaters; small
communities; tertiary
treatment for industries.
Low or no energy
requirements; Provide
aesthetic, commercial
and habitat value.
Low treatment
efficiency, necessity of a
secondary treatment,
effluent not odorless
system clogging;
recommended as a
secondary treatment,
large areas required;
Composting Toilets unsaturated and aerobic human excreta, toilet
conditions provide
paper, carbon additive,
biological and physical food waste
decomposition
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
Biogas Digestor
Sedimentation,
human excreta, animal and Recycling of resource; Biogas plants can be
flotation and digestion agricultural wastes
gas produced is used
expensive to build and
for cooking and
difficult to operate. Poor
lighting
maintenance leads to loss
of gas production and
blockage of the digester
tank with solids.
Anaerobic Filter
anaerobic
pre-settled
simple and fairly
costly in construction
degradation of
domestic and
durable if well
because of special filter
suspended and
industrial
constructed and
material, blockage of
dissolved
wastewater of
wastewater has been
filter
solids
narrow
properly pre-treated,
possible, effluent smells
COD/BOD ratio
high
slightly despite high
treatment efficiency,
treatment efficiency
little permanent space
required
Duckweed Based sedimentation,
Domestic and agricultural No clogging risk; High Necessity of large areas;
WW Stabilizations anaerobic degradation wastewater;
nutrient removal rates necessity of constant
Ponds
and sludge stabilization
harvesting; unsuitable in
very windy regions.
TSS; COD; TN;
TP.
Volume reduced
from 10 to 30%;
pathogens.
Similar to septic
tanks systems; The
long period of
storage can also
remove some
pathogens.
BOD, TDS, TSS
BOD, SS, TN, TP,
metals
Septic Tank
•
•
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.
•
•
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.
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 nonsettleable 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)
Electricity generator by Biogas
CH4
Methane Combustion= CO2
Swine waste
Food
CO2
Duckweeds Lagoon
Conditions for success:
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:
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
From the Sick Water report
THANK YOU