Taking the stink out of urinals

A TECHNOLOGY to treat domestic sewage, in existence since the '60s, has been put to new use: treating and recycling wastewater from public urinals. Mukesh Khare of the Indian Institute of Technology in Delhi claims the rotating biological contactor (RBC) process can eliminate foul odour from the urinals, especially in the summers when there is a perpetual water shortage.

Wastewater from urinals contains both organic matter - dead cells, proteins, urea and sugars - and inorganic substances such as phosphorus and nitrates. To make the wastewater reusable, the urea content, which is responsible for the odour, had to be reduced and the suspended and dissolved solids had to be removed. Khare and two of his students decided to use the RBC after reviewing various options for treating the wastewater.

The RBC consists of a series of plastic discs fixed to a rotatable horizontal shaft and placed in a tank in which the wastewater is collected. The discs are partially submerged in the wastewater and rotated. Microorganisms present in the wastewater bind to the revolving discs, forming a layer of slime or biofilm. The rotation of the discs serves two purposes: it exposes the biofilm alternately to the wastewater and air, facilitating processes that eliminate the odour and also enables the thick layers of slime to be slo'ughed off and deposited at the bottom of the tank, from where it can be removed.

Khare and his team have fabricated a simple prototype consisting of a tank and RBC discs made of asbestos to keep costs low. Urinal wastewater is collected in a tank and then fed at a steady rate into the RBC system.

Khare says the results of this experiment were "very encouraging". He now plans to submit a project to the department of science and technology for carrying out further studies. Khare intends to construct a pilot recycling plant for IIT's academic complex.

An innovative aspect of Khare's system is the use of solar energy to drive the RBC discs and pump wastewater and the treated effluents. He is of the opinion that once the design and other parameters of the plant are worked out, the system could offer an efficient and inexpensive treatment and recycling system for urinal wastewater. He feels that such systems would be ideal in shopping complexes, cinema halls and other non-domestic complexes.