Bio-drains to reduce pollutants
DRAINS ARE usually designed to carry different type of wastewater — from rainfall runoff to spent water generated from residential and commercial centres.
At times sewage too finds their way into these water carriage units through unauthorised openings made. An appropriate method to keep the drains less loaded with decaying matter has become inevitable.
An attempt have been made by our team to develop a `bio-drain' which consist of a conduit embedded with fibrous materials capable of retaining microbial population needed to undertake the removal of organics and nutrients from flowing water has been developed.
Bio-drain technology
The fibrous materials have been identified as better media for supporting the microbial population in wastewater treatment operations due to their higher specific area.
Hence, coir geotextiles in the non-woven form is used as the media for attachment in these systems.
The basic principle involved is to allow the wastewater to flow through the coir geotextile bed placed in a specific configuration by eliminating the problems of stagnation.
Fibre filters
The microbes in the fibre filters acts on the organics and nutrients for their sustenance and helps the water to be cleared of its waste load. The samples of treated effluent were tested to assess the capability of these systems to remove BOD5, COD and other parameters used to represent the pollution index.
Rate of flow
The rate of flow of effluent was established by repeated trials on different packing density of geotextiles for various configurations in order to arrive at optimal design.
A rich sludge of wastewater from any biological treatment unit can be used as the initial bacterial load.
The process could be either under aerobic or anaerobic conditions with necessary provisions to eliminate any gas build up in the reactor units.
Two types
Biodrains are configured into two different types mainly Annular flow systems and baffled flow systems.
In the baffled flow systems 5 cm thick fibrous packing of coir geotextiles is placed as baffles with maximum possible packing density so that the wastewater is able to move in upward/downward manner in addition to a portion percolating through the filter pads.
One metre length of bio-drain having a square cross section of 1 sq ft is able to reduce the organic load by 70-75 per cent. In the case of annular flow systems similar fibrous pads kept as concentric rings and wastewater flows through them with out any significant obstruction to flow.
The purification is dependent on the contact established between the flowing water and the microbes present in the filter.
Even though the annular flow systems causes less reduction to flow in comparison with the baffled type, they require at least 50 percent more length to attain an identical level of treatment.
Future potential
The bio-drain configuration could be easily fabricated and installed in the existing residential units and commercial establishments to reduce the decaying matter being taken directly to drains.
These products could also be incorporated in a municipal sewage system where the bio-drains installed before the inlet to the main sewer can reduce the organic loading rate on the sewage treatment unit significantly.
A. PRAVEEN
Assistant Professor In Civil Engineering
Rajiv Gandhi Institute of Technology, Kottyam,
Kerala
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