No smell at Greenlea Hamilton

Dissolved air filtration (DAF) plant at Greenlea HamiltonNo smell, full automation and environmentally-friendly. Those were the design brief demands from a North Island meat processor for a new wastewater treatment plant that not only met the company’s needs, but also went beyond Council standards and – possibly most importantly – kept the neighbours happy.

In late 2013, a brand new state-of-the-art $1.3 million wastewater treatment plant was commissioned at Greenlea Premier Meat’s Hamilton meat processing plant to handle all of the plant’s trade waste processing water.

Designed and built by Rendertech Ltd, the new plant uses dissolved air filtration (DAF) technology, which has been around for a while, Greenlea’s chief engineer Neville Thompson explains, but “we’ve taken it forward a couple of steps.”

Absolutely no smells at all was possibly the most important consideration for the company, which has been at the same site for the past 20 years and prides itself on good neighbourly relations.

To achieve this, the treatment plant was installed into a purpose-built building with a mechanical ventilation system to maintain negative pressure inside and ensure there is no escape of odours. The ventilation air is then de-odourised in a biofilter before discharge to the atmosphere, says Thompson.

Full automation was another requirement. The treatment plant, which basically runs itself with minimal human intervention, starts up automatically one hour after production starts and closes down again one hour after production finishes. In addition, the system is linked in to a supervisory control and data acquisition (SCADA) control, which alerts the engineers immediately if there is a problem. It is monitored 24 hours a day by a security company.

The ‘chemical flotation’ treatment process takes place in a large stainless steel rectangular tank. Acid and polymer are dosed into the wastewater, prior to entering the tank, to precipitate all the fat and protein contaminants. These are then floated to the surface of the tank using dissolved air and removed by a slow moving scraper as wet sludge.

The wet sludge is further processed using a Belt Filter Press. In the press, the sludge is squeezed between two permeable belts to remove the free water to produce a solid cake. The cake, following further processing off-site at the renderers to extract proteins and other nutrients, is then incorporated into stock food.

The treated water is then discharged to the Hamilton City Council sewer system – the company is one of Hamilton City Council’s Big Five users. “As the Council constantly raises the bar for water standards, we wanted to make sure we got it 100 percent right and also future-proofed,” he says.

Good relations with the neighbours and the Council, plus attention to detail meant that the resource consent process went smoothly and trials are currently ongoing to work out daily flow rates, purification levels and that chemical balances are correct.

Thompson is very pleased, to date, with the treatment plant performance. “It’s doing what it’s supposed to – and more.”

This article has appeared in Food NZ magazine (February/March 2014) and is reproduced here with permission.

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