Converting human sewage into quality fertiliser

Adapted from Institute research; and from Business Week and RCRA Review (USA), monitored for the Institute by Roger Knights.

As fertiliser, human sewage has grave deficiencies. Even after treatment, the sludge that comes out of sewage plants is loaded with hazardous micro-organisms and laced with heavy metals, That rules out using it on soil intended for cultivation or even pasturage. In addition, the human waste lacks potassium, an essential element in fertiliser.

But disposing of sludge has become a serious environmental problem for many communities, so the incentive to find new uses for it is growing. N-Viro Energy Systems Ltd, a private Toledo company, has found a way to convert the waste into fertiliser - by mixing three parts sludge with one part cement-kiln dust, another waste product. The highly alkaline dust kills off lingering micro-organisms, binds up the heavy metal, and is loaded with potassium, says N-Viro Chief Executive J. Patrick Nicholson. The result is an odourless, granular powder. At $100 per dry ton of sludge processed, N-Viro says its method costs about half as much as incineration and about 60% as much as composting.

'A way to convert the human sewage into fertiliser - by mixing three parts sludge with one part cement-kiln dust, another waste product'

The City of Toledo, Ohio, produces approximately 160 tons of sewage sludge daily. In the past, Toledo had trucked its sludge to landfill at a cost of approximately $8,000 a day. This was high cost and the problem of the smell induced Toledo to look for a better solution.

Now its Bayview Reclamation Plant recycles sludge into a fertiliser supplement to be used in agriculture, forestry and land reclamation. The Bayview Reclamation Plant was built in six months and can handle 15,000 dry tons of sludge annually. The facility cost less than $3 million to construct, and operation and maintenance cost will run at approximately $100 per dry tonne. The Toledo facility is built adjacent to a public golf course and two private marinas so it had to be smell-free. 'Neighbourhood support was critical in the development of this project,' says Pat Nicholson, president of N-Viro Energy Systems.

'The processing time for this technique is only three to seven days, compared to seven to 90 days for composting'

The process utilises kiln dust to pasteurise, stabilise, disinfect, deodorise, dry and granulate municipal waste water sludge. The processing time for this technique is only three to seven days, compared to seven to 90 days for composting.

By combining two waste products, the result is a product which will be a benefit to society.

Earth Day Certificate of Merit

From an Earth Day report.

A Certificate of Special Merit was awarded to N-Viro Energy Systems for 'outstanding achievement in the area of solid waste reduction and recycling.' N-Viro was selected from more than 1,000 entries nationally in a 'Searching for Success' Programme sponsored by Renew America.

The first UK plant

The first UK soil from a sewage sludge plant is being provided for Southern Water by Simon-N-Viro, who are the UK agents for N-Viro Energy Systems Ltd. The plant at the Horsham Sewage Treatment Works in West Sussex is operating on a trial basis. 750 dry tonnes of sewage sludge cake will be processed into the pasteurised final product, N-Viro Soil. Their technical release concludes that 'using the proper dosage and mixture of alkaline admixtures is the key to the process. There are a combination of factors which produce the pasteurisation and drying of the product such as: high pH for 72 hours creates an anti-microbial environment; the correct volume of admixture for absorption of moisture will accelerate drying; at 52 degrees C pathogens, including parasites and ascaris, will not survive; ammonia released in the pile is also a disinfectant and the sludge product will have soil type organisms, but will resist microbial recontamination.'

N-Viro Energy Systems Ltd (Sally Robinson), 3450 West Central Avenue, Suite 250, Toledo, Ohio 43606, USA (tel 419 535 6374; fax 419 535 7008). Their agent in the UK is Dr Neville Hampton, Simon-Hartley Ltd, Stoke-on-Trent, Staffordshire ST4 7BH (tel 0782 202300; fax 0782 261494).

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