City turns pit latrine sewage into fertiliser
July 13th, 2011
Ethekwini metro (Durban) is the first city in Africa to test pit latrine faecal sludge disposal by sanitising and pelletising as soil fertiliser.
A similar sewage pellet technology was tested in Cape Town. Ethekwini municipal water and sanitation education and capacity manager, Teddy Gounden, said they are developing a faecal sludge sanitation machine in partnership with the Pollution Research Group at the chemical engineering department of the University of KwaZulu Natal (UKZN).
“There is no other device like it in the world,” said Chris Buckley, research group head. The machine separates organic manner from pit latrine sludge, then sanitises and pelletises dry material. A number of sewage and sludge pelletising mills, patents and processes are used around the world, however.
Gounden and Buckley shared their waste management innovation at the African Conference on Sanitation and Hygiene in July 2011 in Kigali, Rwanda.
Two million pit latrines in SA
South Africa had dug two million Ventilated Improved Pit (VIP) latrines and similar on-site sanitation systems since the early 1990s, and many are becoming full and unusable, posing public health and groundwater crises.
Ethekwini Metro had recently emptied 30 000 pit latrines as deep as two metres in a bid to extend the useful life of these toilets, mostly in informal settlements,
Pit toilet health and groundwater risks
A pit latrine and sewage waste seminar in Durban in March 2011, found that water service authorities, including municipalities, need affordable solutions to several emerging sewage challenges;
• At what rate does sewage waste accumulate in on-site sanitation systems?
• How to manage sewage waste from ventilated pit latrines?
• What technologies are available for emptying VIPs?
• What waste disposal options are available for faecal sludges?
• What is the cost of sewage waste management?
• Are pit additives effective?
Some pits and linings are poorly constructed, undersized, filled by dumping of solid wastes, requiring smell retardants and disinfectants.
Research by the Water Research Commission (WRC) confirms that pits are filling up faster than their expected design life.
Pit latrines remains part of an ongoing drive to provide basic sanitation in informal and basic unit settlements. Many sewage pits are yet to be dug.
The WRC had commissioned a number of research studies on pit latrines, in collaboration with University KZN, Partners in Development, and EThekwini metro (Durban) municipality.
One of the potential solutions is lightweight superstructures, sewage treatment, and beneficial sewage waste disposal, without burdening generally ageing and poorly maintained waste water treatment works.
Jay Bhagwan, WRC Director for Water Use and Waste Management, said “municipalities face challenges with planning and budgeting for emptying pit latrines.”
“Emptying of a pit toilet could cost from R700 to R5 000, says David Still, a WRC project leader spearheading development of technology options for pit emptying.
“EThekwini Water and Sanitation had emptied 45 000 ventilated pit latrines in the metro in 2008 and 2010, and plans to empty them again every five years. Ethekwini contracted local entrepreneurs for emptying and disposal processes. The average cost per pit was R2 100, or R420 per pit per year”, said Still.
Faecal sludge sanitised by 500 degrees C
The University of KwaZulu Natal Pollution Research Group is involved in the Ethekwini trial. The conventional way of dealing with the contents of a full pit latrine has been to put the sludge through treatment works, already overloaded.
Sludge is sanitized by heating to 500 degrees Celsuis, killing pathogens by pasteurization. Dry sewage pellet solids are packed into 20kg bags and used as crop fertiliser.
Sanitised sewage pellets do not smell and is safe for workers or gardeners to handle. The Durban sewage sludge pelletising trial unit is housed in two shipping containers that could be moved to municipal areas where many pit latrines occur.
The metro aims to set up a job creation scheme involving buying of sewage fertiliser pellets from investors.
Foreign objects thrown into pit latrines hamper sewage extraction and treatment. The metro plans to tech the public to separate waste.
PHOTO; Sanitised human faecal fertiliser is undergoing crop and plant growth tests in Durban.
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