Vol. 23 No. 1 Quarterly, July 2004
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... in this issue
Editor Clare Tawney
Technical Editors Maryla and Richard Carter
Managing Director Toby Milner
Editorial Advisory Board
Aquamore, Zimbabwe
Peter Morgan
CARE, Sri Lanka
Lahiru Perera
Christian Engineers in Development, UK
Peter Stern
Department for International Development, UK
Ian Curtis
Development and Project Planning Centre,
University of Bradford, UK
Frances Cleaver
Environmental Health Project, USA
Dan Campbell
Global Water Policy Project, USA
Sandra Postel
Visiting Researcher, University of Goiás, Brazil
Jonathan Parkinson
International Rainwater Catchment
Systems Association
John Gould
International Water and Sanitation Centre,
Netherlands
Dick de Jong
Oxfam UK
Paul Sherlock
Tufts University
Astier Almedom
Swiss Centre for Development Co-operation in
Technology and Management, Switzerland
Karl Wehrle
WaterAid, UK
Simon Trace
Arsenic Policy Support Unit, Dhaka, Bangladesh
Guy Howard
Water, Engineering and Development Centre, UK
John Pickford
Water, Engineering and Development Centre, UK
Julie Fisher
Water Resources Management Ltd, UK
Charles Batchelor
Water Supply and Sanitation Collaborative Council,
Switzerland
Darren Saywell
World Bank, USA
Pete Kolsky
Waterlines is available online at
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Wastewater reuse in agriculture and aquaculture
As cities grow rapidly all over the developing world, the problem of how to dispose of the
wastewater they produce is escalating. For many centuries wastewater has been used in agriculture and aquaculture, with the result that nutrients are recycled productively, livelihoods and
food production are supported on the fringes of the city, and the uncontrolled discharge of raw
sewage into the rivers is prevented. Dealing with raw or partially treated sewage is not, of
course, without its hazards, and much of this issue of Waterlines is concerned with adapting
these practices to reduce risk. Small-scale, decentralized wastewater treatment plants will
reduce much of the risk from pathogens and Jonathan Parkinson and Liqa Raschid-Sally outline
how these may operate as part of an integrated approach to wastewater reuse. Richard Carr
describes WHO guidelines designed to suit the level of treatment to the type of crop grown; for
example, untreated sewage can be used on tree plantations with few precautions, but for salad
crops the level of wastewater treatment needs to be high in order to remove pathogens.
Wastewater reuse in agriculture is especially relevant in hot, arid climates, and it is in these
regions that we can learn about current practice. Peter McCornick surveys how wastewater is
used in the Middle East and North Africa; and David Meerbach describes a demonstration project in the West Bank. Finally, Stuart Bunting outlines the problems affecting fish farmers from
Kolkata, India, who for many years have been making use of the city’s wastewater to produce
affordable, fresh fish for poor communities. My thanks go to Jonathan Parkinson of the Federal
University of Goiás, Brazil, and Liqa Raschid-Sally of the International Water Management
Institute, Sri Lanka, for all their work in helping to assemble this edition.
Clare Tawney
Editor
Contents
2
5
9
Wastewater reuse for agriculture
and aquaculture – current and
future perspectives for low-income
countries
Liqa Raschid-Sally and Jonathan Parkinson
Regular features
11 Webwatch
15 Technical Brief: Waste
Stabilization Ponds
24 Conference call
The safe use of urban wastewater in
agriculture
Richard M. Carr
25 Resources guide
Wastewater reuse in the Middle
East and North Africa
Peter McCornick
27 Crossfire
12 The Al-Bireh demonstration project
on agricultural reuse of wastewater
in the West Bank
David Meerbach
19 Wastewater aquaculture and
livelihoods in peri-urban Kolkata
Stuart W. Bunting
26 Waterpoints
30 Books
32 Diary
Cover: Agriculture, Thailand. Farmer
watering crops using watering-cans
Photo credit: JINDA
UTHAIPANUMAS/UNEP/Still Pictures
Readers’ articles
22 Realizing the right to water
Melvin Woodhouse
Vol. 23 No. 1 July 2004
Typeset by The Studio Publishing
Services Ltd, Exeter EX4 8JN
Printed by: Russell Press Ltd,
Nottingham NG6 0BT
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Page 2
Wastewater reuse for
agriculture and
aquaculture – current and
future perspectives for
low-income countries
Liqa Raschid-Sally and
Jonathan Parkinson
Exploiting the nutrient and water value in wastewater
through agriculture and aquaculture may also help limit
uncontained pollution that results from unregulated
disposal of wastewater in surface water bodies. Treatment
processes form an important part of wastewater reuse
strategies, alongside other measures to protect health,
but a concerted effort to promote capacity at all levels
is required to enable the benefits of wastewater reuse
to be realized.
B
y 2015, cities will be home to
half of the world’s population.
Every day, city dwellers consume substantial amounts of water for
a wide variety of domestic, commercial
and industrial activities, and each of
these produces wastewater. On average,
a city with a population of 10 million
generates 0.7M m3 of water per day
(at a lower end consumption of
100 litres/capita/day). The total urban
population in Africa, Asia and Latin
America produces 204M m3 of wastewater every day.
Even in the best-case scenario, it is
estimated that only 35 per cent of this
wastewater will be treated prior to disposal or reuse.1 The cost of improvement is enormous – for example, even
if New Delhi triples its present capacity
for wastewater treatment, at an estimated cost of US$7.5 billion, this will
be insufficient to meet the required
capacity for safe disposal and reuse of
wastewater.2
We can safely assume that for the
foreseeable future, most wastewater
will be discharged without treatment,
causing widespread degradation of
the quality of natural water resources.
Making productive use of wastewater
through planned management and disposal on agricultural land is one way of
exploiting its water and nutrient values
2
as well as regulating wastewater
disposal and preventing uncontrolled
pollution. In countries facing the limits
of their natural water resources there
are increasing demands from agriculture and industry to reuse wastewater.
While industrial wastewater recycling
requires effluents to be treated to a high
degree before reuse, currently agricultural reuse utilizes waters of varying
quality, from highly treated wastewater
to partially treated and untreated wastewater.
Farmers in Faisalabad, Pakistan, block sewers
to divert wastewater onto adjacent fields for
irrigation
The treatments and precautions suggested here for agriculture, which is the
main subject of this article, also apply
in general terms to aquaculture.
Existing practices and
guidelines
The productive use of wastewater in
agriculture and aquaculture is a
centuries-old practice, and it can be
particularly beneficial to poor farming
communities around cities. In countries
where wastewater reuse is recognized,
it is associated with formal schemes;
but in the majority of countries it is
associated with informal reuse. In cases
of formal use, which is usually accompanied by treatment, the demand can be
directly attributed to water scarcity. In
Israel, treated wastewater currently supplies 10 per cent of the national
demand for water and there are plans to
capture and treat all of its wastewater
by 2015. Australia aims to treat and
reuse 3 per cent of its wastewater for
agriculture and irrigation by 2020. In
some of the water-scarce Mediterranean
cities of Europe and in California USA,
wastewater reuse after treatment is
common. In the Middle East, most
countries treat wastewater before use
but, despite strict compliance
requirements, some informal use does
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Box 1. Treatment systems for
municipal sewage effluents
●
●
●
●
Preliminary – simple physical
processes such as screening
and grit removal to remove
large particles and gross solids.
Primary – sedimentation of
settleable solid material in
storage tanks.
Secondary – aerobic or anaerobic biological processes to
break down organic matter.
Tertiary – processes for the
removal of pathogens, nitrogen
and phosphorus, or specific
industrial pollutants.
occur because it is a viable alternative
for the farmers (see McCornick’s article in this issue).
The extent to which wastewater is
treated before application in compliance
with existing regulations varies with the
income level of the country. In Pakistan,
only 2 per cent of cities have any form
of treatment facilities, and even in these
cities less than 30 per cent of wastewater is treated. Local farmers block
sewers so that the wastewater level rises
to the surface and overflows onto the
fields. Sometimes local authorities auction wastewater to farmers as a means
of disposal. Stormwater retention ponds
in Vietnam, designed for flood control,
receive wastewater which is then
pumped onto nearby fields. These ponds
are often used for aquaculture as well.
In poor countries, wastewater is
applied untreated and there is a
burgeoning business of high-value
vegetable production downstream of
cities in urban and peri-urban locations.
In Pakistan, it is estimated that 26 per
cent of all vegetable production is
grown using highly polluted water.3
In Hanoi, Vietnam, up to 80 per cent
of vegetable production is irrigated
with wastewater.4 In Hyderabad, India,
up to 40 000 direct and indirect beneficiaries depend on wastewater as a
source of livelihood. The African
situation is no different, with Senegal,
Kenya, Ghana and Mauritania producing high-value vegetables for urban
consumption using wastewater.
The potentially serious health consequences for both those who work in
agriculture and aquaculture and those
who consume their produce are overlooked under the conditions of market
Vol. 23 No. 1 July 2004
demand for fresh produce grown in
proximity to the cities. To date, guidelines have been developed to be universally appropriate – one size fits all –
but there are considerable problems in
implementing these same standards in
poor countries. The success of these
guidelines is relative to the conditions
in a country. In rich countries, wastewater is treated to safe levels for the
use intended, and WHO5 and US-EPA
guidelines6 are two examples used to
set standards in such instances. In poor
countries, the application of standards
has to fit into a holistic approach that
integrates wastewater management with
productive use.
Strategies for mitigating the
health risks
It is evident that the answer to these
complex problems does not lie in the
centralized government agencies that
set official standards for wastewater
reuse – not unless the realities of the
existing situation are taken into consideration in the formulation of
national guidelines. It is also clear
that conventional treatment processes
are generally unaffordable and inappropriate for use in the locations where
the demand for wastewater reuse is
greatest – peri-urban areas and small
towns where agriculture is near to a
sufficiently large source of wastewater.7
Experience suggests that some form
of treatment prior to reuse is necessary,
but the most appropriate form of treatment will depend on the characteristics of
the wastewater itself, local site conditions
and desired performance requirements,
which will be dictated by the reuse application. Industrial wastewater mixed with
wastes from domestic sources can create
a potential additional problem from the
perspective of treatment and reuse for
agriculture and aquaculture.
Because wastewater usually contains
large amounts of dissolved and suspended organic matter that has the
potential to clog soil pores and irrigation equipment, pre-treatment is a
necessity for all forms of wastewater
reuse. Preliminary treatment is a simple
process involving screening and grit
removal to remove the gross solid
pollution and larger settleable solids.
It is generally advisable to include
primary treatment, involving sedimen-
A small-scale wastewater treatment plant in
Colombia. Credit: WHO photo library
tation of settleable particulate material
in storage tanks. Typical removal efficiencies of suspended solids will be
between 55–60 per cent after two hours
detention in sedimentation tanks, and
this will also result in a 35 per cent
reduction in organic pollutant load
(measured as biochemical oxygen
demand). Sometimes wastewater will
require treatment to remove oil and
grease, and wastewater effluent that is
applied through drip irrigation systems
will typically require sand filtration to
avoid problems with clogging.
Treatment systems may be effective
at reducing pollutant concentrations in
wastewater, but this is only part of the
solution,8 because they are generally
not effective at removing pathogens.
Wastewater is pumped onto farmers’ fields
from a drainage channel in Than Tri, peri-urban
Hanoi, Vietnam
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In this wastewater reuse facility run by PRISM
in Mirzapur, Bangladesh, duckweed is grown
in wastewater stabilization ponds and is then
harvested to feed to fish
The other primary problem associated
with using treated wastewater for agriculture and aquaculture is the inherent
health risk from a wide range of pathogenic organisms – such as bacteria,
viruses and helminths. Various treatment technologies such as waste
stabilization ponds (see the Technical
Brief in this issue) and reedbeds can
be used for treating wastewater to
reduce pathogen concentrations, but
even these relatively simple technologies need to be managed properly for
optimum benefit.
Perhaps a more pragmatic approach
is to consider a combination of partial
wastewater treatment in combination
with one or more of the other measures
to reduce the health risks of wastewater
reuse (as described by Richard Carr in
this issue of Waterlines). In the case
of agriculture there are various strategies to reduce health risks to farm
workers and consumers which include:
restricting the range of crops grown,
choosing appropriate methods to apply
wastes, post-harvest handling of crops,
human exposure control, and consumer
awareness and protection measures. In
particular, cooking vegetables and fish
can go a long way towards protecting
consumers’ health.
How should the situation be
improved?
The productive use of wastewater in
developing countries has to be linked to
flexibility in applying treatment guidelines. Applying current guidelines
strictly would immediately limit reuse,
4
resulting in either uncontrolled use or
the pollution of water bodies, leading to
unmitigated health risks. It is clear that
an incremental approach to applying
guidelines is required (see Carr’s article
in this issue). To enable this to be
achieved effectively, a decentralized
approach towards wastewater management is advocated that promotes decision making for sanitation and
wastewater management down to the
most appropriate level.
It is important that those who make
the decisions are adequately equipped
with the knowledge and skills to make
the best decision. It is also necessary to
consider the various constraints, other
than cost, to the application of treatment
and other forms of protection in developing countries, which may explain
why these strategies are not widely
applied in practice. These include:
●
●
●
●
●
●
a lack of awareness of the dangers by
producers, consumers and politicians
unwillingness to comply with existing regulations
an awareness of dangers, but lack of
demand for improvements
few alternatives for the poor farmer –
linked to a lack of knowledge of
cost-effective ways of reducing the
risks
a lack of financial incentives to
implement solutions
weak regulatory bodies – an ineffectiveness of institutions to regulate,
monitor and enforce existing regulations.
To overcome these constraints, capacity building is required at the both the
local level and higher levels in order to
promote collaboration between sectors
using a multi-stakeholder, multidimensional integrated approach. Wastewater
reuse needs to be planned in conjunction with water resource management,
water supply, wastewater production,
management and disposal; and technical solutions have to be combined with
a range of preventive measures to mitigate health risks.
Based upon international experience,
it is clear that improvements in wastewater management practices are only
feasible where there is political will.
Advocacy at all levels is possibly the
most important requirement – to get
politicians and decision makers to
understand the issues and to promote a
pragmatic wastewater reuse strategy to
their constituencies.
About the authors
Liqa Raschid-Sally (l.raschid@cgiar.org) is a Senior
Researcher at the International Water Management
Institute, Colombo, Sri Lanka; and Jonathan Parkinson
is a Visiting Researcher in the School of Civil
Engineering at the Federal University of Goiás, Brazil.
References
1
2
3
4
5
6
7
8
As quoted in Scott, Christopher, Naser
Faruqui and Liqa Raschid-Sally (eds)
(forthcoming) Wastewater use in
irrigated agriculture: confronting the
livelihood and environmental realities,
Commonwealth Agricultural Bureau
International (CABI), Orient-Longman,
and International Development Research
Centre (IDRC), Ottawa, Canada.
Agarwal, A., and S. Narain (2002)
‘Private sector cannot solve India’s water
and sanitation problems’, Water and
Wastewater International Vol. 17 No. 2.
Ensink, J.H J., T. Mahmood, W.Van der
Hoek, L. Raschid-Sally, F.P.
Amerasinghe (2004) ‘A nation-wide
assessment of wastewater use in
Pakistan: an obscure activity or a vitally
important one?’
Lai, Tran Van (2000) ‘Perspectives of
peri-urban vegetable production in
Hanoi’, background paper prepared for
the Action Planning Workshop of the
CGIAR Strategic Initiative for Urban
and Peri-Urban Agriculture (SIUPA),
Hanoi, Vietnam, 6–9 June, convened by
the International Potato Center (CIP),
Lima, Peru.
World Health Organization (WHO)
(1989) ‘Health guidelines for the use
of wastewater in agriculture and aquaculture’ World Health Organ Tech Rep
Ser. 1989, 778: 1–74.
US Environmental Protection Agency
(2004) EPA Guideline for Water Reuse,
U.S. Environmental Protection Agency,
Health Effects Research Laboratory.
Cincinnati, Ohio.
Parkinson, Jonathan and Kevin Tayler
(2003) ‘Decentralized wastewater management in peri-urban areas in lowincome countries’ Environment and
Urbanization, Vol. 15 No.1.
International Institute for Environment
and Development, (IIED), London.
Blumenthal, Ursula, Anne Peasey,
Guillermo Ruiz-Palacio, and Duncan
Mara (2000) ‘Guidelines for wastewater
reuse in agriculture and aquaculture: recommended revisions based on new
research evidence’, Report summary of
WELL Task No. 68 (Part 1).
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