MATERIALS AND METHODS

The wastewater generated in the city flows across three main storm water channels in the three catchments. These wastewater samples were periodically assessed for algal growth, nutrient content (HACH, Protocols) and the physico-chemical parameters following Standard Methods (APHA, 1995). Treatment plants from each catchment were investigated on the effluent discharges and their quality. For finding out the algal potentials, two lakes situated on the South of Bangalore were studied for algal growth and biomass estimations. The field level algal productivity or algal biomass production is based on the data collected from the algal growth in lakes that were tested in the laboratories. The field studies show an areal productivity of 10g/m2/d and a nominal lipid content of (14%) the highest being 24 %. The studies in the lab showed an average ~24g/m2/d and lipid content closest to 30%.  The total amount of oil that could be produced annually under each productivity scenario was calculated based on the land or wastewater available in the Bangalore city (land especially near the existing wastewater treatment plants) in order to determine the limiting factor of production and to assess the potential of either resource in producing algal biodiesel. A 60% overall processing efficiency was assumed for the conversion of algal lipids to biodiesel. A lipid density of 918 kg/m3 was assumed.

The potential algal biofuel production under wastewater conditions was determined using wastewater effluent concentrations of nitrogen and phosphorus investigated earlier 2010-2011. (Unpublished data). The average total nitrogen (TN) and total phosphorus (TP) concentrations, in units of mg/l, during the study were determined for each representative treatment plant from the three catchments in Bangalore city. Average seasonal nutrient concentrations of wastewaters collected from drains, lakes etc. were investigated and the molar N/P ratio was determined during the study (Dec-May-Oct, 2010-11). The molar N/P ratio was used to determine whether the WWTP’s effluents were overall nitrogen-limited (N/P<16) or phosphorus limited (N/P>16). The studies showed TN concentrations varying from 35 to 80 mg/l and TP concentration varying from 8 to 31 mg/l.

The algal nutrient uptake studies were performed in the laboratory in ambient conditions in batch cultures with a culture time of 8-10 days. Lipids were extracted by Bligh and Dyers method, and were then processed for FAME analysis by GC-MS. The potential algal biodiesel production was calculated on the basis of field level observations and laboratory studies with average N and P concentrations of the effluent, in relation to the N nad P content of algae and available wastewater loads in the three different catchments V Valley (400 MLD), Koramangla and Challaghata Valley(500 MLD) and Hebbal valley (300 MLD). The GHG emissions were calculated according to the IPCC 1996 and 2006 guidelines, taking into considerations the regional TOC, TN values and the corresponding emission factors.