ECOTOXICITY ASSESSMENT OF BIOGAS DIGESTATE TO Clarias gariepinus

ABSTRACT

Anaerobic digestion is a solution for energy generation and global warming control. Production of biogas and utilization of the resulting digestates as potential fertilizers for agricultural land application has become as important as producing the maximum yield of biogas.The application of biogas digestates and its environment and human health impacts are still unexplored.Ecotoxicity analyses of digestates before their exploitation in agriculture can predict environmental impact and the necessity for additional treatments. In the present study, Clarias gariepinus catfish was exposed to varying concentration of cattle slurry digestate to determine behavioural response, mortality and histopathological alteration. Results of chemical analyses showed that heavy metal concentrations were above permissible limits set for wastewater by World Health Organization with the exception of Zn and Cu. Histopathological changes of the gills, and liver of fish exposed to 0%, 20%, 40% and 60% concentration of digestate for four days (24, 48, 72 and 96 hours) showed gill distortion and fusion of adjacent lamella, the liver showed swelling of hepatocytes with mild, prominent steatosis and fatty changes. The result showed that the digestate was very toxic and present extremely high environmental risk. It is therefore recommended that a pre-treatment is needed to reduce its toxicity and environmental impact before deployment to agricultural use.