In good odour

An Australian chemical engineering company claims to have developed a technological process that can remove the stench from sewage. Virotec said its new technology, called Virosewage, leaves solid effluent smelling no more objectionable than freshly dug soil.

According to Virotec, Virosewage, a combination of chemical reagents and a controlled application process, removes all the active sulphides that make sewage smell. The two-stage process uses ferric chloride to reduce the soluble inorganic phosphorus content to virtually nil. Most of this is then transferred to solid waste matter, rendering it odour free.

The Australians claimed that when applied early in the treatment cycle it can render sewage sludge, the worst culprit, inoffensive.

The company has completed tests in conjunction with two municipal authorities in its native Queensland. Virosewage was used at a conventional ‘trickle-filter’ sewage works – the most common form of treatment plant – and a more advanced biological nutrient-removal facility. Virotec said foul smells were all but eliminated.

Odour pollution from treatment works is a major problem for the water industry. This year has seen high-profile campaigns, and even legal action, by residents and local authorities against the stink from sewage plants in Edinburgh, Liverpool, Plymouth and Anglesey.

Some residents complain that it is impossible to leave the house or open the windows if the wind is blowing in the wrong direction.

However, the industry has struggled to contain the impact despite using a variety of odour-control methods. These include the addition of lime or clean water to sewage, introducing odour-eating bacteria and even spraying the sludge with perfume.

Daniel Drew, Virotec’s chief scientist, claimed the Australian company’s approach is wholly new. ‘We’ve done a very extensive patent search and found no other technology like it,’ said Drew. ‘We don’t know of anyone else claiming the same level of odour control that we have been able to achieve.’

Alongside smell reduction, Virotec is claiming other significant benefits for the Virosewage process. These include the almost complete removal of phosphorus from liquid effluent and the creation of high-quality ‘biosolid cake’ that can be reused as fertiliser.

‘At no stage does the matter treated become a waste material. The result is a product that you can spread on your lawn,’ said Drew.

Virosewage is the result of several years’ R&D by Virotec. The company, which originally developed chemical processes for the mining industry, began research in the area in response to the increasing burden on Australia’s sewage treatment utilities.

With population increasingly concentrated in the nation’s urban coastal areas, utilities need to deal with rising amounts of waste each year while treating it as close to the source of supply as possible.

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