Water treatment potential in relation to phytoplankton dynamics in tropical sewage-fed urban water bodies
Durga Madhab Mahapatra1, Chanakya H. N1,2,3* and Ramachandra T. V 1,2,4
1 Centre for Sustainable Technologies, 2 Centre for infrastructure, Sustainable Transportation and Urban Planning, 3 Centre for Contemporary Studies,
4 Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560 012, India


Urban water bodies frequently receive untreated sewage and water levels in such water bodies are maintained by daily inputs of sewage. They function as “variable-zone” anaerobic-aerobic lagoons suffering several macrophyte, biotic and abiotic stresses. We have studied two such lakes in Bangalore (Bellandur-360 ha and Varthur-220 ha) to understand whether such an occurrence could be made beneficial (maintaining water levels as well as treatment). Such hypertrophic water body receives sewage at 180-250mg/L and is discharged at 25-80mg/L COD/BOD in different seasons. In an earlier study we reported macrophyte altering the purification function of the water body. In this paper we studied the impact of phytoplankton dynamics and macrophyte cover on the functions such as organic load removal. Algal community analysis, algal biomass, macrophyte cover, water quality, nutrient status was studied seasonally during 2009-2010. Oxygen deficiency and sometimes anoxia, recorded from surface samples resulted in high quantities of NH4+-N (30-40mg/L) and phosphate (0.5-4mg/L)-characteristics of anoxic hypertrophic urban lakes. The productiveness favoured high phytoplanktonic community characterized by small cells (<10μm; Chlorella sp. - highest numbers). The lake could be clearly demarcated into an initial anaerobic zone (40% area), a facultative zone (20%) and an aerobic zone (40%) based on redox values and GIS/bathymetry. During summer the lake is covered by floating macrophytes converting the lake into an anoxic/anaerobic water pool subduing the water purification function as well as aesthetics. When macrophytes are controlled such sewage fed water bodies can be used for treating urban wastewater while also maintaining water sustainability in these semi-arid ecosystems. This paper reports the community dynamics of phytoplankton, their function and competition with macrophytes.

Keywords: Phytoplankton, sewage, urban lakes, treatment, nutrients.

Citation: Durga Madhab Mahapatra, Chanakya H. N and T. V. Ramachandra, 2011, Water treatment potential in relation to phytoplankton dynamics in tropical sewage-fed urban water bodies. Proceedings of the Conference on Microbes in Wastewater and Waste Treatment, Bioremediation and Energy Production, January 24-27, 2011, Goa, India.
   *Corresponding Author :
  Dr. H N Chanakya,
Centre for Sustainable Technologies, Indian Institute of Science, Bangalore, India.
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