Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 26 April 2010
Researchers at the University of Pretoria and other academic institutions in the developing world say single-cell proteins extracted from sewage sludge are rich in amino acids, minerals and vitamins and hold “enormous potential” to alleviate severe human malnutrition by lowering the rising cost of animal meat.
Several experiments have already been done in South Africa and Nigeria to fatten up chickens, goats and pigs on food supplemented with extracts from urban sewerage works or dried chicken manure.
This was one of the more bizarre proposals presented to delegates at the Water Institute of South Africa conference in Durban last week by researchers from the University of Pretoria’s chemical engineering department.
A research paper by associate professor Evans Chirwa and masters student Moses Lebitso reports on experiments at the university to feed more than 40 chickens on a variety of diets – including treated extracts from 100 percent sewage sludge collected from the Zeekoeigat sewage works in Gauteng.
According to Chirwa and Lebitso, the chickens raised on 100 percent sludge gained weight faster than a control group of chickens raised on conventional feeds such as fishmeal. They also calculated that it was far cheaper to feed chickens on sewage sludge than fish meal, soya oilcake or lucerne.
It cost the researchers R7,63 to fatten up broiler chicks to a weight of 1,88kg using conventional fishmeal, but only R6,65 to fatten broilers to 1,97kg using extracts from sludge.
One potential problem, they note, is that sludge from city sewage works often contains toxic heavy metals from industrial wastewater, including lead, manganese, copper, cadmium and zinc.
It was therefore important to “remove or reduce” the heavy metal content to levels which complied with allowable or tolerable levels before feeding the sludge to animals.
To extract protein-rich cells, they heated the sludge at high temperature and the resulting material was dipped in nitric acid, perchloric acid, citric acid or hydrochloric acid. Although some of the nutritional value of the sludge proteins was destroyed during the process to remove heavy metals, the resultant extracts still contained high levels of amino acids.
Thereafter the broiler chicks were fed on five different diets, varying between no sludge and 100 percent sludge extracts.
Lebitso noted that providing good air quality for the chicks was critical to ensure they had sufficient oxygen and that they were “gently placed” into the brooding area as soon as possible after arrival.
“The birds also had unrestricted access to a supply of fresh, good quality clean water at all times.”
The researchers note that almost 8 million metric tons of animal feedstock is needed every year in South Africa, Lesotho and Botswana, and that as a fast-growing developing nation, the rising cost of importing animal feeds could be reduced by harvesting proteins from local sewage works and using them as supplementary feed.
While some meat-eaters may cringe at the thought, the concept is not unique. Several similar experiments have been done at the University of Ibadan in Nigeria since 1986.
Some of these experiments involved feeding chickens with dried chicken excreta, while goats and pigs were fed dried, activated sewage sludge.
According to a paper published by Ibadan University animal sciences researcher Anthony Ologhobo in 1989, there were noticeable taste differences among broiler chicks fed on both dried chicken droppings and sewage sludge.
While there were “no significant differences in cooked meat texture, tenderness or juiciness” between the control animals and manure-fed animals, the taste-scores were much higher for chickens fed on a conventional diet compared to chickens raised on a 10 percent mixture of chicken droppings and urban sewage sludge.