Bio filter may reduce smell

Press, 30 August 1984, Page 9

Bio filter may reduce smell

The Christchurch Drainage Board' will investigate bio filter processes as a means of abolishing the smell from its treatment works.

The odour, described by one board member as diabolical, has increased since the board removed a temporary dome cover from one of its filters.

It was necessary to remove the cover because it had caused problems in actually hindering the working of the filter, Mr C. H. Russell said. “We had to ensure that one filter would work unimpeded because we were about to begin experiments with the other filter on treatment processes. One filter had to handle all the work and we had to be sure the cover was not in the way,” he said. The cover had been sold, and it would be nine to 12 months before a permanent cover could be built over

the dome, said the engineer, Mr H. P. Hunt. Tenders for the cover would be called as soon as the board heard from the Health Department about a subsidy for deodorising process work.

The board had been investigating the wet oxidation process with a pilot plant this year. The process was capable of destroying the odours from fixed growth reactors at the treatment works. A preliminary design for a full-scale wet oxidation process plant had been prepared, Mr Hunt said. The Health Department had advised that an alternative means of deodorising using bio filters could be used. The department had indicated that a subsidy could be tied to the investigation of this process. The engineer reported to the board’s meeting yesterday that a partial plant to carry out trials on the bio

filter methods would cost $lOO,OOO. It could be built in a third of the time it would take to build a dome for the wet oxidation process. There would be a large saving in capital and running costs on the bio filter method and it should therefore be investigated. The board decided to set aside temporarily the wet oxidation process and investigate the bio filter method. It would construct a trial plant to allow full-scale trials to be carried out. The board would also request urgency on the subsidy from the Health Department and amend its subsidy application to cover the alternative method. The board also approved in principle sending a staff member overseas to investigate the bio filter method. Waltham Road Parts of Waltham Road will be dug up to renew a stormwater drain between

the Heathcote River and Austin Street.

The board last evening adopted a four-part scheme to renew the drain. The $l.O million scheme will stretch over 12 years with each stage to be carried out at three-year intervals. The first stage to be done immediately, will cost $77,000. It will cover the drain from Hargest Crescent to Hastings Street. Mr Hunt said the drain had been inspected three years ago when Waltham Road had been freshly sealed but it was not known then that it would need replacing. He acknowledged the “detriment to public relations” caused by digging up a relatively new road. The board adopted the scheme, making provision for funding for the .first stage from the renewals fund. Further provision of funds will be made for later stages.

Tuam St depot The board will investigate moving its Tuam Street depot to the treatment works site. The depot would soon need improvement but the buildings were not worth improving, Mr Hunt said. Already some activities unrelated to the treatment works had been sited at the works rather than at Tuam Street. To replace the depot elsewhere would cost $1.2 million. The Tuam Street site and buildings would realise $200,000, he said. Sea wall The Christchurch Yacht Club’s sea wall at Moncks Bay collapsed recently and the club believes it was because of a Drainage Board outfall drain along the wall. It wrote to the board asking for the drain to be extended and a headwall built to support it. Mr Hunt reported that the wall collapsed because of its poor design and construction and not because of the drain. The extension of the drain would be costly and was not needed for drainage. The board decided to

advise the club that it did not consider the drain was the cause of the collapse and would not modify it. It would also suggest the club seek engineering advice on rebuilding the sea wall. Woolston Cut The board will finance its Woolston Cut project from its special fund rather than raise money by loans, because of increased interest rates. The new rates for local body stock are: for one or two years, 15 per cent (previously 8.5 per cent); three, four, and five years, 15.5 per cent (9 per cent); and six or more years, 16 per cent (9.5 per cent). Capital works between now and March, 1985, will be $BOO,OOO for the Woolston Cut and $500,000 for the east and north-east sewer relief scheme. Further funds will not be needed for the sewer but money will be necessary for the Woolston Cut. The special Woolston Cut fund stands at $900,000. Using this money will be cheaper than raising loans. The board will review the project’s funding before next year’s estimates.