Alternate strategy for municipal waste water management
R.C. Srivastava
India supports 17 per cent of the human and 15 per cent of
the livestock population of the world with only 2.4 per cent of the land and 4
per cent of the water resources. Out of the total annual precipitation of 4000
billion cubic meters (BCM), the utilizable water resources of the country have
been assessed as 1123 BCM, of which 690 BCM is from surface water and 433 BCM
from groundwater sources. It has been projected that population and income
growth will boost the water demand in future to meet food production, domestic
and industrial requirements. The projected total water demand of 1447 BCM in
2050 will outstrip the present level of utilizable water resources (1123 BCM)
out of which 1074 BCM will be for agriculture alone. Since the total projected
demand will be 324 BCM more than the present level of utilizable water
resources, the challenge will be to: (i) produce more from less water by
efficient use of utilizable water resources in irrigated areas, (ii) enhance
productivity of challenged ecosystems, i.e., rainfed and water logged areas,
and (iii) utilize a part of grey water for agriculture production in a
sustainable manner.
Let us discuss the third challenge here. Presently about 350
Class I and Class II urban centres having >50,000 population generate around
38,254 million litres per day (mld) of waste water out of which only 11,787
mld, (31 per cent) get treated. It has been projected that wastewater
generation will cross 170,000 mld (62 BCM) by 2051 in addition to 30 BCM
wastewater generated per year from various industries (CSE 2010). Recycling and
reuse of this huge wastewater resource is a challenge for maintaining food
security and restore health of the natural resources vis-à-vis the environment.
How to deal with this challenge is a very controversial
subject? One group argue to treat every drop of municipal waste water and then
discharge it in rivers. Most of the Ganga plan Namami Gange is based on this
concept with treatment being in public, PPP and private mode. However I have a
different view of tackling this problem. Why not use this water for greening
our vast waste lands spread all over the country. We have denuded forest lands
as well as other lands which are crying for afforestation. The afforestation drive
taken up every year is not successful to desired level because of very high
mortality due to water scarcity. Because of this factor only, Supreme Court
directed that for every diversion of 1 ha land from forest to non-forest use,
there should be 10 time area afforestation. If we use this municipal waste
water for an irrigated aforestation, it will green a huge denuded area. Besides
greening it will also conserve soil, enhance employment opportunities in
hinterland both in plantation and processing the product in addition to
reducing pressure on forest for wood. However whenever I have raised this
option, it has been turned down on only one point that the actual wastelands
are far away from municipal waste water generation place. In my view the
problem can be tackled in three stages. Firstly by removing large suspended
material from waste water and using suspended material for composting or
filling up at construction site where we are using our valuable soil. This can be done by filering in the channel itself
by constructing filters in the nala
itself. A proper design will do this. At IIWM, Bhubaneswar, we are in process
of designing such systems which can filter the municipal waste in nala itself.
The suspended material will have to be removed periodically and sent to compost
pits or fills or for use as filling material on construction sites.
Once the waste water has been filtered of suspended material,
we can divide it in three qualities depending upon heavy metal content, and
bacterial population present. At IIWM,
Bhubaneswar, we have almost developed design of an on line filter which reduces
turbidity of water by 60%, Cd by 83%, 90% of total coliforms, E coli with
a discharge of 0.5 lps while pumping with a 1 hp pump. If the waste water
treated with this filter has qualities within desired parameters, this can be
used for peri-urban horticulture. It is expected that about 5-10% of municipal
waste water especially from those urban areas which donot have waste water from
small and micro industries, when filtered and treated with this on line filter
will be suitable for use in peri-urban horticulture. In case it is not within desired limits, this
water can be used for urban landscaping, which can utilize another 5% of water.
Here a major concern will be to manage the irrigation in urban landscaping in
such a way that there is no percolation to contaminate ground water. This can
be achieved by using modern irrigation techniques which donot allow percolation
as well as creating barrier between root zone of plants and sub soil. Further
care will have to be taken to control
runoff from such areas for its asffe delievery to waste water drains
without getting mixed with fresh water supplies.
The remaining water can be pumped away from urban centre for
irrigating denuded lands. For example, if filtered municipal waste water of
Kanpur is pumped 50-150 km away in denuded areas of Bundelkhand, it can provide
water to re-green small hillocks of this region. It has been estimated that for
pumping 50 Mlpd discharge from an urban centre like Kanpur to a head of about
250 metre (elevation difference as well as friction losses), it will be
requiring about 4000 kWh of energy per hour. Assuming it runs for 275 days in a
year (during monsoon, we can discharge
this in river) the total electric consumption will be about 26.4 million
units., which will cost around Rs 80 million if we take energy rate @ Rs 3 per
kWh. Keeping another 80 million for maintenance, and another 80 million on
fixed cost of pipeline etc. , the total cost will be about 250 million per
year. This amount of water i.e., 13.75 million
cubic meter (MCM) can provide about 30 cm of water annually (enough for timber
plantation if applied through drip) to about 4500 ha area. The total cost of
irrigation will be Rs 55000 p.a., but the returns from a poplar plantation will
be about 3-5 lakhs per ha from 5th year onward. Other economic value
plants can also be identified to be irrigated by this nutrient rich water. The
benefit in terms of carbon sequestration will be additional. All these economic
analysis has been made with assumption that denuded land will be available at a
distance of 150 km, although the distance between Kanpur and Banda of Bundelkhand
is just little more than 100 km and one
finds a number of denuded areas on the way. This distance will be much less
with many cities. For example, if you travel at Nagpur –Mumbai highway NH 6,
you will find denuded hillocks just 20 km away from Nagpur dotting the
landscape on both side of highway. In such cases, the cost will be much less.
Such system
will not only provide ecological and economic benefits, but will also generate
huge employment both operation of system as well as plantation and further
downstream processing of timber products.
During
discussion with my peer group, a concern was raised whether withdrawing such
huge amount of water from river system will not create water shortage? The
total amount of water flowing in our river system presently is about 1100 BCM. If we treat all municipal waste water
and divert it to convert our degraded/denuded lands in forest plantations, we
will be diverting about 13 BCM of water which is little more than 1 percent. By
2050, it can maximum increase to 10% when our municipal discharge is expected
to be 62 BCM and by utilizing our surface water the total flow will decrease to
700 BCM.
This
alternative need to be discussed and evaluated by a team of engineers, foresters,
and microbiologists and evaluated at pilot scale before we embark upon taking
care of our wate water on a very large scale.
