The Dal cleaning project
Aswin Dinakar, Shantanoo Bhattacharyya and Mritunjay Kachru on Dal Lake, its problems clean-up and sustainable management.
Constructed Wetlands & Artificial Floating Islands
Certain nutrients such as nitrate and phosphate when present in excess amounts cause eutrophication in water bodies. Constructed wetlands act as storage sinks of these nutrients and microorganisms present in wetlands breakdown these nutrients to allow for aquatic plant uptake. Not all of the nutrients are however broken down as some are retained in the root zone while others are adsorbed onto the sediments. Generally speaking efficiency of nutrient removal by constructed wetlands can be increased by providing a greater surface area for microbial activity.
While we still strongly recommend constructed wetlands for natural wastewater treatment practical considerations may not always permit the construction of wetlands. The acquisition of land near public lakes in a densely populated country like India can cause project delays. This would mean that the wetlands would have to be constructed outside the city and pipes would have to be laid to transport the wastewater from the source to the wetlands. In order to overcome these challenges we recommend in situ treatment of water through the usage of artificial floating islands. Artificial floating islands come in several flavours. The simplest ones can be constructed using a combination of plastic and bamboo with coir fibres used to fasten the aquatic plants to the raft. Classified in the phytoremediation world as hydroponic treatment these floating rafts in conjunction with certain “miracle” aquatic plants can provide the same level of efficiency as constructed wetlands.
While floating rafts may serve as a first generation phytoremediation treatment advances in ecological engineering have provided second and third generation treatment methodologies. The key as always is to note that greater the surface area provided for microorganisms to grow a greater percentage of nutrients will be broken down and made available for plants. Material science and surface chemistry have enabled a combination of synthetic and biodegradable materials that can act as a constructed wetland on the artificial floating island and provide enormous surface area for bacterial colonies and roots to grow. The very same idea is used in adsorption and usage of activated carbon and illustrated by a simple example. Mathematically 50 square foot of surface area is about a thousandth of an acre. However within our “constructed wetland” 50 square foot will provide the equivalent of approximately one fifth of an acre of surface area . This is then combined with a bio-fertilizer that promotes root growth. These floating water bodies can be chained to one another leading to an archipelago providing a very large surface area. Over a period of time these artificial floating islands can grow into full fledged ecosystems supporting aquatic organisms of various kinds.
Importance Of Native Aquatic Microorganisms
We emphasize again that the success of an efficient phyto-remediation site depends greatly on the microorganisms as many biochemical reactions in the root zone of plants are catalyzed by microorganisms. In this regard we have noted that eminent scientists from Kashmir have documented the biodiversity of aquatic plants of Kashmir found in wetlands & lakes. This we believe needs to be supplemented by studies on the wetland aquatic microorganisms of Kashmir. We believe that native microorganisms are better suited to local conditions and will perform as good as commercial microorganisms. Studies to monitor their growth in those conditions will need to be performed to determine what growth parameters are required to establish thriving colonies of beneficial microorganisms. The enumeration of beneficial microorganisms does not begin and end with bacteria alone as fungi, yeast and protozoans can be potential decomposers as well.
Choice Of Aquatic Plants
Based upon the available information on the wetland flora of Jammu and Kashmir a small set of macrophytes that are recommended are Nelumbo Nucifera, Euryale Ferox , Acorus Calamus and Blyxa Oryzetorum. Local botanists and ecologists should be able to provide a more exhaustive list. In addition certain aquatic plants can also be brought from neighbouring states and adapted to grow in Kashmir's conditions if they are found to have economic potential.
The approaches that we have outlined over the past week have utility beyond in situ purification of lakes. They can be used to treat agricultural wastewater, aquifer & groundwater cleanup, removal of pollutants from natural wetlands and enhance efficiency of aerated lagoons.
Our approach has outlined benefits in all the three areas – science, technology and social engineering. Farmers have supplemental income through production of eco friendly coagulants. Industrial strength activated carbon manufacturing units can provide jobs for local people and its usage can lead to cost savings for sewage treatment plants. Beneficial biological cultures have broader applications beyond wastewater treatment as they can be used for increasing yields in agriculture. Artificial floating islands permit for in situ purification of lakes and construction of floating walkways/docks can provide revenue for governments as tourists would be attracted by the natural beauty of these floating bodies.
Lastupdate on : Wed, 7 Oct 2009 21:30:00 Makkah time
Lastupdate on : Wed, 7 Oct 2009 18:30:00 GMT
Lastupdate on : Thu, 8 Oct 2009 00:00:00 IST
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