Steady progress on lagoon

WORK is progressing steadily on the construction of an anaerobic lagoon at the Feilding Wastewater Treatment Plant as a major improvement programme at the Kawakawa Road location gathers momentum.

The $2.5 million lagoon contract is part of the Manawatu District Council’s on-going programme of upgrades aimed at improving the quality of the plant discharge in line with the requirements of the Horizons Regional Council’s proposed “One Plan”.

Contractors began work on the new lagoon, which is about 120m long, 60m wide and just under 4m deep, in April and expect to have it completed by September.

MDC’s Professional Services Manager Andrew Higgs said the lagoon, which has a capacity in excess of 25,000 cubic metres, uses an innovative cover system that retains the effluent temperature at an optimum for the bacterial treatment process to take place.

“The cover is made from recycled plastics and has to be specially imported from the United States,” he said.

Mr Higgs said advantages of the new lagoon included a better standard of treatment, a balanced flow of effluent through the plant to optimise the efficiency of the treatment process, a lower energy requirement and less cost to operate.

“The existing aerobic lagoons require the effluent to be constantly agitated by mechanical equipment to mix oxygen into the liquid and encourage the bacteria that breaks down the ‘nasties’ in the sewage,” he said. “It’s a process that requires a lot of energy.”

The new anaerobic process relies on bacteria that does not need oxygen to survive and means the lagoon does not require any energy input to work.

“The cover retains heat in the lagoon at an optimum temperature for the anaerobic bacteria to live,” said Mr Higgs.