Conclusion

The present study reveals that manmade lake systems as Bellandur and Varthur, lake in Bangalore appreciably treated the influent wastewater havinghigher organic load. The treatment resulted in 70 %, 73 % and 22 % removal of COD, TN and TP respectively. . However the facultative pond based systems in, Mysore were very effective in removal of suspended solid (SS) (93%) and BOD (82%). The mechanically aerated (Extended aeration) STP, Bangalore is were superior in removal of SS removal (88%), COD (74%) and BOD (63%), but were highly ineffective in nutrient removal.

The wastewater algal biomass present in ponds and lakes showed promising lipid contents and the FAME analysis revealed high C16:0 (>40 %) followed by C18 fatty acids that further provides scope for algal biofuel generation to meet the regional energy demand. Such biofuel generation requires efficient methods of harvesting algae periodically. This necessitates an efficient algal capture mechanism to capture algal biomass from the final treatment plant effluent that helps in removing algal BOD and solids.

The economic evaluation of treatment processes assessed through the capital investment, annual OM costs, COD removal cost and land needs reveals that the mechanical systems require 5 times more capital and OM costs than Facultative ponds. Evaluation of treatment systems in terms of capital investment, human resources, chemical usage, wear and tear repair, electricity needs and land requirement)showed lake based systems followed by facultative pond based system are economically a better alternative than mechanically aerated technologies. Finally, it was found that large algal pond based systems could economically be potential option for the country considering all factors that include expenses and treatment efficiency.

The existing large lake systems and the facultative pond systems can be innovated for a better photosynthetic yield resulting in higher algal biomass which would not only polish the wastewater but at the same time will acts as substrate for lipid/biofuel generation by specific algal trap mechanism.

The treatment efficiency analysis for the period of study showed facultative pond based systems to be the most effective options for the urban wastewater systems compared to the lake based systems as well the energy intensive mechanical systems with a nutrient integrated treatment efficiency (NITE) of > 68% with the treated water that can be reused for irrigation and domestic purposes.