Alternate strategy for municipal waste water management
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.