Sewage recycle in housing colonies by Aquachem

January 13, 2015 12:15 pm

 In India water is a highly subsidised commodity leading to market inefficiencies and hence inefficient use of the already scarce resource. Recycling and reuse of domestic sewage is occurring since historical times in India, especially for plantation. But treatment and reuse of sewage emanating from large housing complex has remained very limited in the country, but picking up now.
Benefits of promoting sewage recycling/reuse as a means of supplementing water resources and avoidance of environmental degradation needs to be recognised and publicised such that it becomes motivational and voluntary action rather than a compulsion from the statutory bodies.
Key drivers • Limited and decreasing freshwater sources • Environmental concerns: Sewage recycling supports the environmental cause by: • Minimising the potentially negative impact of nutrients released into the other water bodies • Conservation of fresh water for other uses; • Satisfying the demand from the general community to have greener water strategies and water conservation • Economic reasons
Case study of housing complex in Mumbai A large housing complex in Mumbai decided to undertake recycling of treated sewage for toilet flushing and gardening, landscaping etc. This case study indicates that logical decision of spending enough capital and operating expenses for treatment, a little addition could enable the users to recycle the treated sewage for various purposes such as flushing, gardening etc. thus reducing the fresh water intake as well as result in less treated sewage discharge to the environment.
Key points:• Plant commissioned and in operation since November 2010 • Present case study is of a Mumbai-based housing complex in suburbs • Housing colonies with 17 towers, 73 flats/tower and over 6,200 people• Water supply rate: 140 lpcd • Total water supply: 870 cu.m/day • Wastewater/sewage generation: 750-800 cu.m/day • Effluent conveyance system: sewage carrying pipes
Treatment options and its selection Based on various technology options available and deliberations, finally selected treatment option was Membrane Bioreactor (MBR) based on the factors: quality requirements, financial issues, low space requirements/availability and relative ease of operation.
Treatment scheme involved screening, collection, degritting, anoxic/MBR, disinfection and sludge handling by filter press. Entire plant is located in the basement due to space constraint. MBR is the heart of the system and technical details of MBR is as under:
• Type: Flat sheet submerged • Material: Chlorinated polyethylene • Small and uniform pore size: Mean pore diameter: 0.4 micron • No. of membranes/tank: 800/tank (two such tanks) • Membrane area/membrane module: 640 sq.m (approximately) • Flux rate: 0.7 cu.m/sq.m/hour• Pressure: 0.3 – 3.0 psig• Membrane life time: 5 – 7 years
MBR system offers various advantages like simple process set-up, easy cleaning, easy maintenance, good effluent quality, low sludge production, small footprint, low operational cost and no smell nuisance
Cost benefit • Capital investment for the system: Rs. 2 crore• Quantity of recovered water: 750-800 cu.m/day • Annual savings on water charges: 40 lakh/annum @ Rs. 40 / cu.m (Commercial water rates in Mumbai) • Annual savings on sewerage charges: 7.2 lakh/annum • Plant annual O&M cost including power: 32 lakh/annum
ConclusionSewage recycling will reduce the cost of living for the housing colonies at the same time they will be doing service for the community by making that much water available for others.
Authored by- M. A. Naik Managing Director Aquachem Enviro Engineers Pvt. Ltd.