Waste Feeds a City

Systems in Kolkata Wetlands

Preparation for Research Project

As addressed in an earlier post, I intended to investigate some aspect of vertical farming for my research project for the course, and have since narrowed this topic down to aquaculture.  A former employer of mine plans to begin an indoor fish farm in Minneapolis, for which he is experimenting and in need of further research.  To this end, I have decided to analyze three existing case studies of fish farms, from which I will adapt a system for a currently vacant industrial building in Minneapolis.  Two of the case studies are indoor fish farms, located in Baltimore and Milwaukee.  To first understand the essential needs of aquaculture before mechanical systems become involved, however, I have located a series of wetlands in India that clearly demonstrate the synergistic relationships embodied in aquaculture and are worth an in-depth overview here.

Located to the east of Kolkata and comprising over 12,000 hectares, the East Kolkata Wetlands consist of over 250 sewage fed fisheries, small-scale agricultural areas, solid waste farms, and some urban development placed interstitially among the wetlands.[1] Credited as being the largest wastewater-fed aquaculture system in the world and considered to be wetlands of international importance by the Ramsar Bureau, the EKW are fed by some 600 million liters of sewage and upwards of 2500 metric tons of solid waste daily.[2] Through various processes that will be addressed below, fishermen, farmers, and garbage collectors and sorters, in addition numerous species of flora and fauna, are able to treat sewage, filter water, and return to the city 150 tons of vegetables per day and fully one-third of its yearly fish consumption (13,000 tons).[3] The area, further, is even developing aspects of an eco-tourism economy as a result of the diverse flora and fauna found at the wetlands.

As with many cities, before Kolkata utilized the synergistic system evident at the EKW to address wastewater, it discharged sewage into a nearby river, which in this case was unable to effectively drain the sewage or annual rainfalls.  As a result, the health of the city was linked to the ineffective system, and the city turned to other options, which at one point included releasing sewage at low tide to a different river at a greater distance than before that eventually led to the Bay of Bengal.  This, however, caused heavy siltation of the river due to the use of locks and dams to distribute the sewage, and the river was declared “undrainable and dead.”[4]

According to Nitai Kundu, one of the reservoirs or retention areas for sewage in this system was the Salt Lake, which later became a part of what is now known as the East Kolkata Wetlands.  In the 1860s, while the city was shifting to the use of the second river to discharge sewage, the Salt Lake became an informal experimentation area for sewage-fed fisheries.[5] By the early twentieth century, formal aquaculture efforts began and a new sewage canal was constructed that led directly into the lake, reducing the salinity of the water.  Carp culture reportedly began in 1929 with the introduction of regular sewage inputs, and this led, over time, to increased freshwater fishing in the lake.  As fishing became more profitable, more residents began to utilize the sewage-fed system, which eventually resulted in the abundance of fisheries present today and what is regarded as the key to resolving wastewater treatment needs.[6]

As indicated in the diagram at the top of the post, these fisheries form an essential part of the overall EKW system.  Sewage is currently distributed into the fisheries, which, instead of sending wastewater downstream as was enacted earlier, utilize the sewage in an anaerobic system that contributes to fish maturation.  As sewage is sent into fish ponds and is detained for a matter of days, biodegradation of the organic matter in the sewage occurs, which is then capable of being taken up by local plants, bacteria, and plankton in the lagoons – which, in turn, feed the fish that are then sold at markets nearby.  The wetlands therefore act as waste stabilization ponds, and as the sewage becomes treated through pisciculture and local plants, filtered water is sent to other bodies of water and farms downstream instead of the heavy, untreated sewage that clogged rivers in the past.[7]

Kolkata Wetland System, Part 1 - The City (via Google Earth)

Kolkata Wetland System, Part 2 - Garbage Agriculture (via Google Earth)

Kolkata Wetland System, Part 3 - Sewage-Fed Fish Farms (via Google Earth)

Kolkata Wetland System, Part 4 - Conventional Farms with Filtered Water (via Google Earth)

Further, according to Peter Newman, sewage is also fed to agricultural plots in the wetlands area, which in addition to the fisheries take advantage of the nutrients available in the wastewater and return vegetables to the city.[8] This is largely enacted by farmers who live in the area, who also sort through solid waste to reuse organic waste on the gardens.  Trash that can be recycled or resold serves as an additional profit-generating aspect of the EKW, which also helps address accumulation of garbage from the city.[9]

According to Tony Juniper, the EKW thus contributes to the livelihoods of approximately 50,000 Kolkatans.  Approximately 8,000 are employed in the fisheries, with others making crafts, raising livestock, and maintaining the canals that direct sewage into the agricultural plots and fisheries.[10] Kundu indicates, further, that the local fishermen have developed the utilization of sewage in fisheries to such an accurate extent that the yield-cost ratio is far greater than that demonstrated in any other fish farm in India.  As such, organic pollution in the wetland system is reduced by over 80 percent, and plankton and algae overpopulation and overgrowth is stemmed by the fish.[11]

Aerial of Kolkata Wetlands (via Flickr user paddy)

As a result, the East Kolkata Wetlands demonstrate numerous advantages to be gained through sewage-fed aquaculture, especially when it serves as a part of a larger system that also addresses garbage and water filtration for nearby farms. Although it is unlikely that all of these systems can be incorporated in indoor fish farming in Minneapolis, certain lessons to be gained are that it may be advantageous to find a source of sewage to be used in the aquaculture system, as well as organic trash. Because both plants and fish can utilize this waste, both produce and fish can be sold partly as a result of “waste” inputs. A fishery that incorporates these lessons thereby helps to close a loop between the energy inputs to and outputs from a population, and is certainly worth addressing for the design in Minneapolis.

 


 

[1] Nitai Kundu et al., “East Kolkata Wetlands: A Resource Recovery System Through Productive Activities,” in Proceedings of Taal2007: The 12th World Lake Conference, edited by M. Sengupta and R. Dalwani (2008): 868.

[2] Tarasankar Bandyopadhaya et al., Preliminary Study on Biodiversity of Sewage EFD Fisheries of East Kolkata Wetland Ecosystem (Kolkata: Institute of Wetland Management and Ecological Design, 2004), 5; and Kundu, 876-77.

[3] Kundu, 868-77.

[4] Kundu, 874-5.

[5] Ibid., 875.

[6] Ibid., 868, 875.

[7] Ibid., 876.

[8] Peter Newman, “The Distributed City,” Blog Post, Island Press, February 9, 2009 (http://blog.islandpress.org/300/peter-newman-the-distributed-city) (accessed September 18, 2010).

[9] Tony Juniper, “Kolkata: Wonders of the Waste Land,” Guardian Weekly (UK), August 6, 2004 (http://www.mindfully.org/Water/2004/Kolkata-Wetlands6aug04.htm) (accessed September 19, 2010).

[10] Ibid.

[11] Kundu, 877.

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One thought on “Waste Feeds a City

  1. Hi John,

    We have developed a system for small-scale indoor fish farm that only require 40 sq.meter of land footprint with the ability to produce up to 3 tons of fish a year (depending on species).

    The waste from our indoor fish farm system can be used for aquaponics to grow vegetable.

    Let me know your email and I will send you the details you may require.

    Cheers,
    Mukhriz

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