Odour control project at Thames Water

London – Thames Water has installed odour scrubbing and activated carbon deodoriser technology from air pollution control company ACWA Air, at its Little Marlow wastewater treatment works. The project is part of extensive improvements to the WTW, under the utility’s AMP5 programme.

The UK water company opted to construct a new ventilation plant, which would incorporate best available technology (BAT) for delivery in the early part of the new AMP5 period.

Thames Water’s requirements were for a ventilation system that could increase the rate of ventilation within the composting building and reduce atmospheric odour emissions from the air-stream to less than 1000ouE/m3.

According to ACWA, the increased rate of extraction from its system has resulted in low levels of odour within the building and a consequent improvement in working conditions for plant operatives.

In operation, odour-laden air-stream is carried inside and outside the building through more than 50 metres of ductwork, ranging from 500mm to 2000mm in diameter – effectively extracting contaminated air from the composting building to a new odour control system.

The odour control system treats 135,000m3/h of contaminated air, extracted from the Thames Water composting process which is passed through a 4.2m diameter, 13m high scrubber, using sulphuric acid to neutralise ammonia in the air stream.

The ammonia sulphate produced in this process is then returned to the inlet of the sewage works for biological treatment before being removed as part of the works discharge of high quality clean water into the River Thames.

The relative humidity of the airstream, after the scrubbing process, had to be in the order of 70%, to ensure that the extremely large activated carbon deodorisers perform at their highest level of efficiency.

To achieve this, an in-line electric heating system was selected as being the most reliable means of conditioning the treated air from the scrubber before it passes to the three activated carbon deodorisers.

Each of the three activated carbon deodorisers contains 20 tonnes of reagent which effectively remove hydrocarbons from the air-stream, using a system design which reduces both process down-time and operating costs for Thames Water and its customers. From the deodorisers, air is discharged to atmosphere through a 15m stack.

Following commissioning, independent consultants were appointed to monitor and measure plant performance over a defined period of operation - a procedure which established that the plant was not only achieving expected performance targets, but comfortably exceeding them.

Environmental consultancy ADAS UK, was contracted to take samples of air discharged from the emissions stack over a period of 30 days. These were then measured in the Silso laboratories, where the odour concentration was found to be less than 500ouE/m3.

The new plant, said ACWA, is now fully operational and proving to be extremely efficient and operationally reliable - improving working conditions for Thames Water operators and securing a cleaner environment in the surrounding area.

“As part of AMP5, [Thames Water] is currently driving forward to install more advanced odour control at a number of its key treatment plants,” noted David Harrison, ACWA’s executive director.