Microbes to munch Sasol sludge

Cape Town - Oil and chemical giant Sasol is looking to use microbes to turn thousands of tonnes of waste sludge into compost.

The company said it had developed a novel method to transform the potentially harmful trace elements found in industrial waste sludges into an environmentally friendly form, it said in a statement on Wednesday.

"While composting of domestic sludges is practised worldwide, composting of industrial waste sludges is a unique concept," it said.

The process involved using specialised "microbial populations" of heavy-metal composting bacteria to "target, assimilate and bio-chemically transform the potentially harmful trace elements" found in the sludges.

A so-called bulking agent - Sasol is using a type of grassy fodder crop called sugargraze - is then mixed with the treated sludge, transforming it into a compost, which can be used to grow more of the fodder crop.

"The compost produced as a result of the process is then used to grow more bulking agent to be used in subsequent batches, making the process a closed loop."

Contacted for further details, Sasol environmental technology manager Sarushen Pillay said the company had been conducting trials using sludge-transforming microbes since 2012.

"We are looking at five waste sludge streams from processes at our Secunda coal-to-oil plant... involving 200 000 tons of sludge a year, 40 000 tons of which is oily waste."

Pillay said the waste sludge and bulking agent was mixed in a 1:1 ratio, producing about 400kg of compost for each two tonnes of mix.

Currently the company was using four incinerators and a hazardous waste site to dispose of its sludge waste.

He said Sasol was in the process of applying for an environmental impact assessment (EIA) so it could go ahead and use the compost on a 2000 hectare farm, located on its own land.

"Our results show us that we have succeeded in producing compost that meets the stringent specifications of the Fertilisers, Farm Feeds, Agricultural Remedies and Stock Remedies Act," said Pillay.

This is the legislation that regulates compost and fertiliser use in South Africa.

Pillay said if all went as planned with the EIA process, and permission was obtained, the company hoped to have the project up and running by "the second half of next year [2015]".