ENVIS Technical Report: 76,  April 2014
http://www.iisc.ernet.in/

Integrated Wetlands Ecosystem: Sustainable Model to Mitigate Water Crisis in Bangalore

 http://wgbis.ces.iisc.ernet.in/energy/
    T.V. Ramachandra*         Durga Madhab Mahapatra         Sudarshan P. Bhat         Asulabha K S         Sincy Varghese         Bharath H. Aithal    
Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560012, India.
*Corresponding author: cestvr@ces.iisc.ernet.in

INTEGRATED WETLANDS ECOSYSTEM: SUSTAINABLE MODEL TO MITIGATE WATER SHORTAGE IN BANGALORE



Performance assessment of an integrated wetland ecosystem at Jakkur provides vital insights towards mitigating water crisis in Bangalore. An integrated system as outlined in Figure 10. The integration of sewage treatment plant with wetlands (consisting of reed bed and algal pond) has helped in sustained treatment of water for reuse.



Figure 10: Integrated wetlands system for managing water and wastewater

8.1 Functional aspects of the integrated wetlands systems are:

  • Sewage Treatment Plant (STP): The purpose of sewage treatment is to remove contaminants (Carbon and solids) from sewage to produce an environmentally safe water. The treatment based on physical, chemical, and biological processes include three stages – primary, secondary and tertiary. Primary treatment  entails holding the sewage temporarily in a settling basin to separate solids and floatables. The settled and floating materials are filtered before discharging the remaining liquid for secondary treatment to remove dissolved and suspended biological matter. STP’s effluents were still nutrient rich requiring further treatment (for nutrient removal) and stabilization for further water utilities in the vicinity.  
  • Integration with wetlands [consisting of reed (typha etc.) beds and algal pond] would help in the complete removal of nutrients in the cost effective way. A nominal residence time (~5 days) would help in the removal of pathogen apart from nutrients. However, this requires regular maintenance of harvesting macrophytes and algae (from algal ponds). Harvested algae would have energy value, which could be used for biofuel production. The wetland systems helps in the removal of ~77 % COD, ~90% BOD, ~33% NO3-N and ~75% PO43-P (Figure 11).


Figure 11: Level of treatment at various stages of integrated wetlands system


Pilot scale experiment in the laboratory has revealed nutrient removal of algae are 86%, 90%, 89%, 70% and 76% for TOC, TN, Amm.-N, TP and OP respectively (Figure 11) and lipid content varied from 18-28.5 % of dry algal biomass. Biomass productivity is of ~122 mg/l/d and lipid productivity of ~32 mg/l/d. Gas chromatography and mass spectrometry (GC-MS) analysis of the fatty acid methyl esters (FAME) showed a higher content of desirable fatty acids (biofuel properties) with major contributions from saturates such as palmitic acid [C16:0; ~40%], stearic acid [C18:0; ~34%] followed by unsaturates as oleic acid [C18:1(9); ~10%] and linoleic acid [C18:2(9,12); ~5%]. The decomposition of algal biomass and reactor residues with calorific exothermic heat content of 123.4 J/g provides the scope for further energy derivation (Mahapatra et al., 2014). Water that comes out of the wetlands is portable with minimal efforts for pathogen removal via solar disinfection.
Our earlier experiments have shown the vital role of wetlands in recharging the groundwater resources, evident from the decline of groundwater table to 200-300 m from 30 to 50 m with the removal of wetlands. This means, Jakkur lake system is helping in recharging the groundwater sources. There need to be regulation on the exploitation of groundwater in Bangalore. Over exploitation of groundwater through borewells by commercial private agencies would harm the sustainability, depriving the local residents in the vicinity who are dependent on borewells in the absence of piped water supply from the government agency.
Measures required to mitigate water crisis in burgeoning Bangalore are:

  1. Rainwater harvesting at decentralized levels through wetlands (lakes) is the most efficient and cost effective mechanism to address the water crisis in the region than technically infeasible, ecologically unsound and economically unviable river diversion or inter linking of river schemes being proposed by vested interests in various parts of the country.
  2. Rejuvenation, restoration of existing lakes. This is necessary to decontaminate water bodies due to the unabated inflow of effluents and sewage.
  3. Removal of deposited silt would enhance the storage capacity as well as bioremediation capability of lakes.
  4. Integrated wetlands ecosystem (consisting of reed bed (typha, etc.), algal pond) with lake helps in the treatment of water entering the lake through bioremediation. Replicating Jakkur wetland ecosystem would help in the treatment of water and reuse. This also has an added advantage of maintaining groundwater quality in the vicinity. Studies have shown that groundwater sources in the vicinity of sewage fed lakes are contaminated, evident from the nutrient enrichment, presence of coliform, etc.
  5. Sustainable management of integrated wetlands ecosystem includes
  • Letting only treated sewage to wetlands.
  • Maintaining at-least 33% vegetation cover in the lake catchment. This is necessary to ensure sufficient infiltration of rainwater to ensure water in the lake throughout the year.
  • Ban on number of borewells (or extraction of groundwater) in the lake catchment and command area
  • Restriction on overexploitation of groundwater in the lake catchment to ensure sustained water availability to the local residents
  • Regular harvesting of macrophytes
  • Mechanism to harvest algae at regular interval and manufacture of biofuel and other beneficial biochemical products. These would enhance the employment opportunity in the region.
  • Provision of appropriate infrastructure for washer men who depend on the lake for livelihood through washing clothes.
  • Restriction on the introduction of exotic species of fish by commercial vendors
  • Permission to scientific fish culturing through strict regulations (on fish species introduction, type of nets, frequency of harvesting, restrictions during breeding season and locations)