Dirty deal

The sewerage network, over 1,400 km, comprises 41 satellite pumping stations and seven major pumping stations -- one for each zone, each with their own sewage collection and treatment system. Sewage is collected in sewer lines through gravity and conveyed to satellite pumping stations. From here it is pumped to the main sewage pumping station (sps). The sps sends untreated sewage to a sewage treatment plant (stp) of a zone, for treatment and final disposal into the sea. mcgm, with financial support from the World Bank, is implementing an integrated water supply and sewerage project and has prepared a sewerage master plan till 2025. According to a recent paper, Sewerage operations of mcbm, by P R Sanglikar, deputy municipal commissioner, mcgm, the master plan is a five-phase programme (2005-2025) with a total cost of Rs 55,70.4 crore -- Rs 39,45.15 crore for sewerage work and Rs 16,25.25 crore for slum sanitation. The plan is under implementation. Still, untreated sewage continues to flow into the sea. Why?

Marine outfall
Marine outfall is basically a conduit to dispose sewage into the sea after partial treatment. A typical marine outfall has an influent pumping station (ips) and an effluent pumping station (eps). The former discharges sewage in normal conditions; eps comes into play during high tide.

Down To Earth visited Bandra ips and eps sewage facility. The facility is on reclaimed land near the Mahim creek. Stiff local opposition delayed the plant's completion by over two decades. But since May 27, 2003, it has been functioning.

The inflow of sewage here is about 600 million litres daily (mld); this increases during the monsoon. According to the sewerage operations department of mcgm the increase is due to rainwater inflow in sewer lines. But the municipality's stormwater division claims it is the raw sewage that mostly flows in the stormwater nullahs throughout the year and needs to be diverted to the sps for proper treatment. "Before this facility began, untreated sewage was emptied out in the sea through various nullah s and Mithi river. But things have changed now and fish can be seen near the coast, proving the facility's success... . Although the normal flow of sewage is up to 600 mld, the total capacity of this facility is over 2,100 mld. This will take care of additional load for the coming 15 years in Bandra zone," says V P Pandey, assistant engineer, Bandra ips facility. But things are not as rosy as mcgm would want us to believe.

The method
The treatment method followed in marine outfall facilities is rather incomplete. Firstly the floating matter (chiefly plastics) is removed using screen bars at ips . Sewage is then pumped up to the eps facility, where the floating materials are once more. "Plastics are a major problem as they form a wall against the screen bars and restrict sewage flow. This leads to grit settling in the first chamber itself, whereas it should settle in the next chamber. Grit up to 6 feet height has deposited in some chambers and we are physically removing it," says an engineer at Bandra eps facility.

After screening chamber, the sewage enters the aerated grit chamber, where compressed air helps settle grit. mcgm engineers claim such aeration is tantamount to 'treatment'. The sewage is finally disposed off in the sea through a 3 km pipeline. The whole process, according to Pandey, takes eight hours. Both the floating matter and the grit is transported to Deonar dumping ground for disposal.

But is the present eight-hours-aerated-grit-chamber-treatment method effective for sewage treatment? Not so, if one goes by the data of mcgm's laboratory at Dadar. According to lab reports Down To Earth (dte) chanced upon, the so-called treated effluent fails to meet prescribed mpcb standards (see table:Treated sewage?). This data is collected during the monsoon, when rainwater dilutes sewage. So what must the situation be in other months?

Lagoons any better?
The second method of sewage treatment mcgm uses is aerated lagoons. These lagoons are operational in Versova, Ghatkopar and Bhandup and follow a more elaborate treatment process. dte visited Versova Waste Water Treatment Facility and Lagoons (vwwtfl), at Versova near Andheri. This facility, running since 1998 and built at a cost of Rs 34 crore, has a total capacity of 180 mld of wastewater and 90 mld for lagoons. This means: the facility can receive up to 180 mld of sewage, but the lagoons can treat only 90 mld. So where does the rest go? "We have no option but to bypass excess untreated sewage straight into the [Malad] creek," admits a mcgm official.

vwwtfl follows an exhaustive treatment process -- physical treatment that removes floating materials and grit, and biological treatment in lagoons that removes organic matter. Lagoons consist of six ponds. The first two ponds are aerobic lagoons whereas the rest four follow both aerobic and anaerobic processes. These ponds consist of aerators, which help microorganisms present in the sewage digest the organic pollutants. The whole process takes about four-and-a-half days to complete," says Sagar Kharde, sub engineer, vwwtfl. The results indeed are encouraging, with bod reduced to as low as 30 mg/l, tss at less than 50 mg/l, and cod as low as 80 mg/l. Treatment cost is also low, at Rs 340 per million litres.

But this is true only of 90 mld. What of the untreated 60 mld to 110 mld sewage? " mcgm has two options. Either to reduce the retention time for sewage treatment or to set up more lagoons. For the latter we need more land and there is hardly any free land in Mumbai. An entrepreneur has approached mcgm with a chemical whose addition, he claims, will reduce retention time from over four days to less than a day. mcgm is testing the chemical's efficacy," says a mcgm official on condition of anonymity.

The Versova facility faces other problems as well. The lagoon capacity is decreasing; one and half metre thick sludge has accumulated in the ponds that has not been removed since the facility started functioning.

Unofficial sewage
"The present sewerage covers only 60 per cent of Mumbai, leaving out slums and maybe some upcoming residential/commercial complexes. Efforts are on to provide sewerage facilities to these areas," says Dange.

Experts claim this is a typical development syndrome most urban cities across the world are facing. "Cities are growing at such a rapid pace that basic infrastructure has failed to keep pace with it. Hence in Mumbai, more and more multi-storey buildings are coming up, whereas the municipality is not able to provide these basic services. More and more of drinking water is being sourced for Mumbai from many kilometres away, and more water supply means more wastewater. Also, many localities that do not have adequate municipal water supply depend on water tankers, so their wastewater does not count as official sewage. Again, to cut costs, many housing colonies prefer throwing their sewage into a nearby nullah rather than pay for an official connection," says Kapil Gupta, professor at civil engineering department of Indian Institute of Technology Bombay, Mumbai.

Where does the sewage from 40 per cent of Mumbai go? "Where else other than nullahs, rivulets and rivers such as Mithi, all of which empty into the sea. And it is wrong to only attack slums for polluting waterbodies. How much wastewater can a slum household generate, that hardly receives any drinking water supply? It is these housing societies/commercial complexes that are playing havoc with Mithi and government has turned a blind eye towards them," says Girish Raut, a Mumbai-based activist.

It stinks
"In Greater Bombay, dumping sites ... are located along creeks... waste is deposited below high tide level without any soil cover. The creek water gets polluted on account of direct contact with refuse and on account of leachate. The refuse...does not get decomposed even after 3 years."

-- Draft Regional Plan for Bombay Metropolitan Region ( drpbmr ) 1996-2011, October 1995

Mumbai generates between 7,000 and 7,800 tonnes per day (tpd) of waste. And, as a recent paper Waste management scenario in Mumbai: things can improve , by Rakesh Kumar, director of the Mumbai office of National Environmental Engineering Research Institute (neeri ) puts it: "Mumbai's waste management problems are unique... It has least available space, hence landfilling is not sustainable... Residential colonies are in close proximity to dumping grounds... And due to high commercial activity, volume of waste generated is also high.