ENVIS Technical Report: 114,  July 2016
   T.V. Ramachandra*       Vinay S      Durga Madhab Mahapatra      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
Constructed Wetlands

The loss of ecologically sensitive wetlands is due to the uncoordinated pattern of urban growth happening in Bangalore. This is due to a lack of good governance and decentralized administration evident from a lack of coordination among many para-state agencies, which has led to unsustainable use of the land and other resources. Failure to deal with water as a finite resource is leading to the unnecessary destruction of lakes and marshes that provide us with water. This failure in turn is threatening all options for the survival and security of plants, animals, humans, etc. There is an urgent need for:

  • Restoring and conserving the actual source of water—the water cycle and the natural ecosystems that support it—are the basis for sustainable water management.
  • Reducing the environmental degradation that is preventing in attaining the goals of good public health, food security, and better livelihoods.
  • Improving the human quality of life that can be achieved in ways while maintaining and enhancing environmental quality.
  • Reducing greenhouse gases to avoid the dangerous effects of climate change is an integral part of protecting freshwater resources and ecosystems.

A comprehensive approach to water resource management is needed to address the myriad water quality problems that exist today from nonpoint and point sources as well as from catchment degradation. Watershed-based planning and resource management is a strategy for more-effective rejuvenation, protection and restoration of aquatic ecosystems and for protection of human health. In this regard, recommendations to improve the situation of the lakes are:

  • The need for good integrated governance systems in place with a single agency with statutory and financial autonomy to act as the custodian of lakes for maintenance and action against polluters.
  • Effective judicial systems for speedy disposal of conflicts related to encroachment
  • Access to information for the public through digitisation of land records and availability of this geo-referenced data with query based information systems
  • Measures to clean and protect lakes
    • Removal of encroachments from lakes, lake water beds and storm water drains, regular cleaning of lakes.
    • Proper measures such as fencing to protect lakes and prevent solid waste from going into lakes
    • Install water fountains (music fountains) which enhances the aesthetic value of the lake and also aid as recreation facility to IT professionals (working in IT sector in this locality) and elderly people. This also helps in enhancing oxygen levels through aeration.
    • Introduce ducks (which helps in aeration)
    • Introduces fish (surface, column and benthic dwellers) which helps in maintaining food chain in the aquatic ecosystem. This has to be done in consultation with fish experts.
    • No exotic fish species introduction avoid commercial fish culturing (commercial fishery)
  • Decentralised treatment of sewage and solid waste (preferably at ward levels). Sewage generated in a locality /ward is treated locally and letting only treated sewage into the lake (Integrated wetlands ecosystem as in Jakkur lake). Integrated wetlands system consists of sewage treatment plant, constructed wetlands (with location specific macrophytes) and algal pond integrated with a lake. Constructed wetland aid in water purification (nutrient, heavy metal and xenobiotics removal) and flood control through physical, chemical, and biological processes. When sewage is released into an environment containing macrophytes and algae a series of actions takes place. Through contact with biofilms, plant roots and rhizomes processes like nitrification, ammonification and plant uptake will decrease the nutrient level (nitrate and phosphates) in wastewater.  Algae based lagoons treat wastewater by natural oxidative processes. Various zones in lagoons function equivalent to cascaded anaerobic lagoon, facultative aerated lagoons followed by maturation ponds. Microbes aid in the removal of nutrients and are influenced by wind, sunlight and other factors (Ramachandra et al., 2014). This model is working satisfactorily at Jakkur. The sewage treatment plant removes contaminants  (evident from lower COD  and BOD) and mineralises organic nutrients (NO3-N,  PO43- P  to inorganic constituents. Integration of the conventional treatment system with wetlands [consisting of reed bed (with typha etc.) and algal pond] would help in the complete removal of nutrients in the cost effective way. Four to five days of residence time in the lake helps in the removal of pathogen apart from nutrients. However, this requires regular maintenance through harvesting macrophytes and algae (from algal ponds). Harvested algae would have energy value, which could be used for biofuel production. The combined activity of algae and macrophytes helps in the removal of  ~45% COD, ~66 % BOD, ~33 % NO3-N and ~40 % PO43- P.  Jakkur lake acts as the final level of treatment that removes ~32 % COD, ~23% BOD, ~ 0.3 %  NO3-N and ~34 % PO43- P.  The lake water with a nominal effort of sunlight exposure and filtration would provide potable water. Replication of this model in rapidly urbanizing landscapes (such as Bangalore, Delhi, etc.) would help in meeting the water demand and also mitigating water scarcity through recharging of groundwater sources with remediation.
  • Better regulatory mechanisms such as
    • To make land grabbing a cognizable, non bailable offence
    • Implementation of the polluter pay principle
    • Ban on construction activities in the valley zones
    • Restriction of diversion of the lakes for any other purposes
    • Decentralised treatment of sewage and solid waste and restriction for entry of untreated sewage into the lakes
  • Encouraging involvement of local communities: Decentralised management of lakes through involvement of local communities in the formation of local lake committees involving all stakeholders.

Area required for Constructed Wetlands: Taking advantage of remediation capability of aquatic plants (emergent macrophytes, free floating macrophytes) and algae, constructed wetlands have been designed and implemented successfully for efficient removal of nutrients (N, P, heavy metals, etc.). Different types of constructed wetlands (sub surface  0.6 m depth, surface: 0.4 m, could be either horizontal or vertical) are given in Figure 10.1. Area required for constructed wetlands depends on the influent sewage quality and expected treatment (BOD removal, etc) is given in equation 1 (Vymazal et.al, 1998). Estimates show that to treat 1 MLD influent, area required is about 1.7 hectares. Figure 10.2 gives the design of wetlands to treat 1 MLD.
A = Qd(lnCo – lnCt) / KBOD
where  A = area; Qd= ave flow (m3/day); Co & Ct = influent & effluent BOD (mg/L);   KBOD = 0.10
For example to treat influent (raw sewage: BOD: 60-80) and anticipated effluent (with BOD 10), area required is about 1.7 to 2 hectares.





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