1
General Scope
Substrates from
decentralised water management may supply nutrients to
agroecosystems. But to apply these substrates they have to be
hygienically safe and match site specific demands depending on soil
and plant production. A new interdisciplinary approach is described
how water management may be linked with agriculture.
The general aim of the
project is the use of substrates from rural (decentralised) waste
water treatment in agriculture in an economical and ecological
sensible
way and to implement decentralised waste water treatment as an
essential part of rural water management systems. The experimental
region will be the Mekong Delta.
In a first step the
ecological demands of characteristic and representative
agroecosystems in the Mekong Delta will be analysed. Based on
these
information suitable fertilisers for the agricultural production are
defined, i.e. fast/slow release fertilizer, consistence (e.g.
liquid, sludge, solid). Depending from the kind of fertilizer
identified, decentralised WWTS are recommended. Besides the analysis
of nutrient fluxes and agroecological studies this systemtic
approach includes also hygienical and socio-economic project groups.
In Part 1 of the
project this approach will result in a Handbook that can be used as
a basis for future planning of
waste water and
drinking water facilities.
In Part 2 of the
project, systems for water management will be implemented and
tested. These
technologies should help to perform sustainable food production in
terms of nutrient cycling, hygienic considerations and pollution.
The proposal is based on
the announcement of the BMBF „Dezentrale Wasserver- und
Entsorgungssysteme“ (Decentralised systems for drinking water supply
and waste water treatment)
The project wants to
develop a general applicable decision tool for engineers to design
an appropriate decentralised WWTS, that
(i)
Treat the WW reliably in terms of hygienic aspects
(ii)
provide adequate fertiliser for agriculture
(iii)
minimise the loss of nutrients
The studies will be
performed at two sites in the Mekong Delta in Vietnam which is a
highly populated and agricultural intense used / exploited area. In
an interdisciplinary “bottom up” approach we will analyse the
present water management situation:
-
technology of drinking
water supply and waste water treatment
-
drinking
water quality
-
tradition of
inhabitants (how and how much water is used, is there an acceptance
for new technologies?)
-
costs of
drinking water supply
-
fluxes of
nutrients through the sites (imports and exports of nutrients and
pollutants)
-
cropping
system and fertilizer demand
-
geoecological conditions
(e.g. soil quality)
Figure 1 shows the nutrient fluxes that have to be
analysed and the involved disciplines. In
Part 3 the working programs are described
in detail.
Figure 1: Fluxes
and planned processes to be optimised; the diciplines refer to the
detailed workplan (see Part 3: Hy: Hygiene (HyÖG), Ae: Agriculture (IPE),
I: Industry (ith), S: Sociology (Soz.), Wb: Water engineering (LWK),
Geo: Hydrogeology (U+Oe).
The
Mekong-Delta (MD) in Vietnam is populated by about 17 millions of
inhabitants on about 4 million hectar land. In this area the main
part of the vietnamese production of rice, vegetable and fish takes
place.
About
40-50% of the inhabitants have access to fresh water and only about
30-35% access to treated water (Lam Minh Triet and Nguyen Thanh Hung
2001). Most of the drinking water plants are situated in bigger
cities. If you look at the remote areas, only about 9% of the
population can get safe drinking water (Research Institute on
Strategy and Policy for Science and Technology Development. 2000.
Challenges in rural development in Vietnam). The reasons are low
nfrastructure and relatively high costs for water supply systems
(Pollard & Hoang Thi Hoa, 2000).
Sustainable
water supply and water treatment does not only mean providing
hygienically safe drinking water and cleaned waste water. It also
means recycling of nutrients (N, P, K) and organic substance.
In developed
countries water treatment eliminates nitrogen, carbon and
phosphorus. Here there are mainly central plants in combination with
a costly infrastructure. In areas where there is not yet water
supply and water treatment, decentralised concepts are more
advisable. It is sensible to implement water supply and waste water
treatment at the same time.
In
developing countries production of plants resp. food is the basis
for living and income for the majority in rural areas. To get a
reliable and high agricultural production it is necessary to use
fertiliser and return organic carbon to the soils especially for
intense cultures like vegetable but also for rice. For low input
agriculture inorganic fertiliser is hardly affordable.
On the other
hand the use of black water as a fertiliser in tropical and
subtropical agriculture is hygienically unsafe especially when it is
applied directly in the garden or when irrigation water passes the
rice field and runs directly into the river. If this water is used
for drinking water supply, there is a severe health risk for humans.
Substrates
of waste water treatment are potential resources in developing
countries that should be used in agriculture (Sanchez et al., 1989).
A treatment that provides -dependent on the agricultural demands-
the nutrients for agricultural will help farmers to reduce their
health risk (clean surface water for drinking water) and the use of
inorganic fertiliser (nutrients of the waste substitute inorganic
fertilizer) (UNDP, 1996; Richter et al., 1995).
This is not
only true for low-input agriculture where appropriate
substrates from waste water treatment are a substitute for mineral
fertiliser (Becker et al., 1995), but also in high-input
agriculture on minor places (e.g. areas of the Mekong Delta).
Organic substance can meliorate the soil by buffering acids,
increase the binding capacity for nutrients and improve the water
retention potential (Mabeye, 1994).
The Mekong
Delta, like many developing countries faces big problems in waste
water treatment and drinking water supply. Waste water and organic
waste seep into surface water or fields without any pre-treatment.
This means that
-
Organic fertiliser is lost.
-
Soil and surface water are
contaminated with pathogens.
-
Only part of the population
have access to drinking water which quite often is hygienically
unsafe.
-
As a result this causes
economic problems like loss of income during illness and expensive
cost for water and fertiliser.
-
Additionally this causes
ecological problems: contamination of surface and ground water,
use of precious ground water, infiltration of uncontaminated
ground water by connection between different groundwater layers as
a result of uncontrolled building wells, soil degradation.
For drinking
water, different sources are used.
Rain
water is used as drinking water.
Problems can occur when collection or storage lead to any
inoculation with pathogens. Also the availability of rain water may
be too low during the “sunny season”.
Ground
water out of uncontrolled wells in the
Mekong Delta is frequently used as drinking water. Usually there is
no examination whether these wells provide suitable dinking water.
Neither there is a periodic control of the water. Aquifers close to
the surface are contaminated with agrochemicals like fertiliser and
pesticides (Le Quy An 2000, Tran Duc Kham 1988, Minh et al. 1997a).
For deeper layers uncontrolled wells represent a big risk of
contaminating ground water by connecting non-contaminated with
contaminated groundwater layers.
The increase
of saline ground water also shortens the amount of available
drinking water (SIWRMP 1995).
Furthermore
the flooding of big areas in the Mekong Delta ( about 1,2-1,9 Mio.
ha) which occurs every year can also lead to a contamination of
ground water wells by polluted surface water.
Surface
water is used for irrigation,
aquaculture and drinking. The multiuse of surface water may lead to
user conflicts i.e. aquaculture may pollute surface water and lead
to restriction in its use as drinking water. On the other hand
aquaculture which provides most of the proteins for the population
is very sensible when to faecal contamination
There are a
lot of negative effects caused by the yearly flood like destruction
of houses and pollution of groundwater wells. Some positive effects
result out of sedimentation (input of nutrients) and the washing out
of acids of acid sulfate soils which reduces their toxiticity (Minh
et al. 1997 b).
In rural and
poor areas decentralised systems may improve the health situation,
soil fertlility and agricultural production. Additionally they may
be implemented much faster compared to centralised systems that need
high investments.
2.4
Summary
Drinking
water supply
So far water
is treated with aluminiumsulfate for flocculation and heat. However
boiling cannot remove all pathogens reliably. Thus, other systems
may be introduced, i.e. a combination of different filtring systems
or UV-desinfection.
Waste
water treatment
For Black
Water there are several applicable technologies: anaerobic
digestion, composting, urine separation, vermiculture. These
technologies have been used for animal excrements first.
Additionally (i.e. anaerobic digestion) some of them have been
extended to treat human excrements. However there is no knowledge
about nutrient fluxes and the use of the substrates as fertilisers.
Especially
the existing methods neglect the specific demands of the soils for
agricultural production.
§
So far there is no integrated
concept regarding decentralised waste water and waste in the
Mekong Delta
§
There are existing methods for
decentralized water management. These methods should be optimized in
a way that drinking water should be hygienically safe and substrates
from waste water should contain as much nutrients as possible for
agricultural production. The WWTS have to match the agroecological
demands.
Project website:
http://www.sansed.uni-bonn.de/
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