Properties of animal manures and sewage sludges and their utilisation for algal growth

Agricultural waste is the most important cause of water pollution in Hong Kong, especially in the New Territories. Sewage sludge removed from wastewater after treatment also introduces problems of disposal. Animal manure has been used for biogas production, nutrient enrichment for a freshwater culturing system, refeeding to livestock and land application. Sewage sludge has been applied on agricultural land and used for the cultivation of green algae. Aqueous extracts of activated sludge, digested sludge, chicken manure and pig manure were used to cultivate Chlorella pyrenoidosa in the laboratory. Cell number, oven-dried weight, chlorophyll and heavy metal contents were measured. Activated sludge extracts produced and algal product with the lowest oven-dried weight and highest content of copper and zinc. Chicken manure and pig manure were more suitable for algal growth, as indicated by the higher yield, protein content and a lower level of various metals in the algae. Recycling of nutrients in animal manure not only introduces a new protein source but also helps to solve the problem of water pollution by these wastes. Cultivation of algae in sewage should only be carried out for the purpose of removing the excessive nutrients and heavy metals before final disposal of the sewage. © 1981.