The Hindu Business Line : RRL-T develops tech for houseboat sewage disposal

The prototype marine sanitation device is designed to treat 1,000 litres per day of `black' water (from toilets), `grey' water (from showers and washing) and macerated kitchen waste and food waste from the pantry.

Thiruvananthapuram , April 29

`KETTUVALLOMS' or houseboats, the showpieces of Kerala's backwater tourism, can now hope to deal effectively with the problem of disposal of sewage.

The Regional Research Laboratory, Thiruvananthapuram (RRL-T) has developed a modular marine sanitation device (MSD) for deployment on board.

According to RRL-T sources, a prototype has already been installed on board a kettuvallom, which is undergoing extensive testing. The prototype has been found to achieve complete treatment of houseboat sewage and sullage (biochemical oxygen demand or BOD and coliforms) using a combination of biological processes.

The kettuvallom was traditionally used for cargo transport along the State's extensive waterways. Modified to meet a novel concept of holidaying, these houseboats now feature open lounge(s), one or two bath-attached bedrooms and a kitchenette. Every kettuvallom is manned by a crew - usually a cook, a guide and an oarsman.

Discharging of waste into the water body used variously for swimming and fishing had not jelled with the overall scheme of backwater tourism.

Concerns of threat to public health on this count had challenged the sustainability of this unique tourism model. It was in this context that the Department of Tourism contracted RRL-T to design an MSD suitable for houseboats. The MSD was supposed to provide complete treatment of sewage and sullage including COD (chemical oxygen demand) removal and disinfection. It had to align to other unique specifications, too.

The kettuvallom, or `boat with knots', is so called because the entire boat is held together with coir knots only; not a single nail is used during the construction. It is made of planks of jack-wood joined together with coir. This is then coated with a caustic black resin made from boiled cashew kernels.

With careful maintenance, a kettuvallom could last for generations. Given this, the MSD had to be compact for under-deck fitting and its power consumption had to be as low as possible since solar power could prove extremely expensive.

Being handcrafted with hardly any design drawings, each kettuvallom has unique dimensions and arrangement of its structural members. Thus, while the MSD had to be suitable for mass manufacture in order to be of affordable costs, the design itself had to be flexible and modular for being fitted with boats of varied dimensions.

RRL-T's prototype MSD is designed to treat 1,000 litres per day of `black' water (from toilets), `grey' water (from showers and washing) and macerated kitchen waste and food waste from the pantry.

The quantity of wastewater is taken as 200 litres per day per guest (often four in number) and 66 litres per day per staff (three).

The treatment system employed is the biological treatment system - anaerobic primary treatment with aerobic secondary treatment. It is also equipped with strainer to remove large material to avoid blockage.

It provides for anaerobic treatment of black water, and will have a separate anaerobic tank for grey water. The treated discharge will meet water body (inland surface water) discharge standards.

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