P. S. Kelkar

Hydrodynamic assessment of sewage impact on water quality of Malad Creek, Mumbai, India

The rapid population growth and uncontrolled development in the coastal zone have led to major pollution impacts on creeks, estuarine, and coastal environment. Water quality models are valuable tools to understand the environmental processes for prediction of pollution impacts and evaluate future trends for management. Presently, the Malad creek in west coast of Mumbai receives wastewater and sewage from open drains and partially treated sewage from Malad and Versova treatment plants. The objective of the paper is to assess the environmental quality and estimate the extent of improvement in different parts of the creek by enhancing the collection efficiency and adequate treatment of sewage as well as disposal through ocean outfall. A hydrodynamic and water quality simulation has been carried out for the present condition in the creek and calibrated and validated with two different season data for better representation of the system. Calibrated model has been used to generate future scenarios based on various options. Among scenarios, option of treated effluent diverted to propose outfall and improvement in collection of unorganized flow through sewerage up to 40% and 60% are found most significant for biochemical oxygen demand reduction and increase in dissolved oxygen. Fecal coliform reduction is also found drastically but still very high against standard. To improve the environmental quality of the creek, still upper stretch requires more dilution and flushing due to narrow width and contribution of heavy pollution from open drains.

Performance evaluation of reverse osmosis desalination plants for rural water supply in a developing country--a case study.

Performance evaluation of two reverse osmosis (RO) desalination plants (DSP) at villages: Melasirupodhu (30 m3 day-1) and Sikkal (50 m3 day-1) in Ramanathpuram district,Tamil Nadu (India) were studied so as to bring out the state-of-art of their operation and maintenance (O&M). Detailedinformation on plant design and engineering, water quality,plant personnel, and cost of O&M was collected for a period ofthree years after commissioning of the two plants. Feed waterwas brackish, the TDS varied in the range of 6500–8500 mg L-1 at Melasirupodhu and 5300–7100 mg L-1 atSikkal villages. The product water quality was observed to begradually deteriorating as the salt rejection by the membranesdecreased with time. The salt rejection was 97–99% atthe time of commissioning of the plants, and came down to89–90% at the end of 3 years of operation. Product water TDS soonafter installation of the plants was excellent and within desirable limits of BIS. After three years of operation, few parameters exceeded the desirable limits, however, they were found to be within permissible limits of BIS. The analyses of thedata showed that both plants were operated only at 30–36% of the design capacity. Plant shut-down due to inadequate and erratic power supply, and plant break-down and inherent delay in repairs due to lack of adequate infrastructure were found tobe the major causes for the low utilization of the plants. Consequently the recurring cost of product water production enhanced to Rs. 25.0/m3 at Melasirupodhu and Rs. 17.5 m-3 at Sikkal, as against the estimated cost of Rs. 15.0/m3 and Rs. 11.0/m3, respectively, as per the design. Over the years, the energy consumption for the product water output increased reflecting higher operational pressures needed with the aging of the membranes.