Fine weather boosts progress on wastewater site

Gisborne District Council is going to great lengths to ensure no odour arises from the new Banks Street wastewater treatment plant once it is commissioned by year’s end.

The latest are lengths of fibreglass pipe – about 60 metres in total – placed at the base of three “odour beds”, each of which is dug out to a depth of 1.8 metres.

The 20m by 8m beds are lined with geotextile cloth and 1mm thick polyethylene, the joins of which are double welded, to prevent leakage. The 20m pipes sit on and are surrounded by a layer of gravel and then covered with just under a metre of bark mixed with five percent shell. Each pipe has a series of diffusers – short pipes with perforations through which odour is released and contained within the gravel and bark.

The pipes are connected to another network of about 300 metres of odour control pipes within the biological trickling filter tank which itself is covered by an aluminium geodesic dome roof, a key part of controlling odour and aerosols from the trickling filter process.

Colin Newbold, project manager for main contractor HEB Structures, says an air extractor system draws out odour from the bottom of the tank, recycles three quarters and pushes the remaining quarter out into the three odour beds.

“This involves five large fans placed outside at the base of the trickling filter tank, and another two fans within the control building. The last three fans for the tank will be installed early next week.”

He says the project is progressing well, thanks in no small part to the recent fine weather but also to the 60 people – half of them Gisborne people – working on site from 7am until 6.30pm and Saturday mornings.

Work is virtually complete on the outfall pump station, where treated wastewater is contained until being pumped out through the outfall and 1.8km to sea. The trickling filter pump station is expected to be finished next week and the influent pump station, where the wastewater arrives on site before being treated, by the end of the month.

The pre-treatment building, where wastewater is screened and large solids removed, is close to being weathertight with the roof completed this week and windows and doors installed.

“The roof is aluminium Kingspan, an insulated composite panel made in Ireland. The travelling crane inside the building will be operating once electricity is connected to the site next week, and lastly the concrete floor needs to be painted to provide a non-slip surface. Then we can wire up the machinery and get it commissioned.”

Hastings firm Kinetic is responsible for the electrical installation and Gisborne’s Electrinet for providing the high voltage supply and transformers on site.

“Once we have electricity to the site early next week, we can hook up to the main panel and start testing.”

Banks Street businesses will be pleased to see their road sealed again from next week after several months of roadworks required for installing new pipes and other services.

Mr Newbold said the whole project was coming together with the tie-in of the western interceptor this week, which brings industrial wastewater from the industrial area including Cedenco across the Waikanae Stream pipe bridge at the bottom of Banks Street, and the eastern interceptor by the existing Stanley Road facility next week. In the western industrial area that includes Ovation (formerly Bernard Matthews) and Juken NZ, new pipework and pump stations will soon be tested, commissioned and linked in.

ENDS

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