Impacts of different treatment methods on spread of pathogens from organic wastes to vegetable crops in Nigeria

Organic wastes, such as cattle manure, are widely used as organic amendments but may constitute a potential risk to human and animal health if they are not properly treated before application to agricultural soil. This study investigated the impact of different common household treatment methods on the reduction of pathogens in organic wastes and the spread of pathogens to food crops. Fresh cattle manure was subjected to three different treatments available to households; anaerobic digestion, burning and composting. Sub-samples were screened for E. coli contents using standard plating and IDEXX Colilert Quanti-Tray 2000 system. The numbers of organisms were used to assess the effectiveness of the treatment methods in the reduction of pathogens in the organic wastes. The E. coli count of the cattle manure was 391.42 CFU/g before treatment. After treatment, there was significant reduction in the E. coli in all treatments. Burning was most effective at reducing pathogens in the cattle manure (95%) followed by anaerobic digestion (50%) and composting (40%). Ash, bioslurry, compost and untreated manure were all significantly different in the ratio of pathogens to nitrogen. Bioslurry contained more nitrogen than ash, compost and untreated manure. Application of the recommended nitrogen dose of 120 kg/ha as bioslurry resulted in significantly lower contamination of soil (4.19 most probable number (MPN) per g) than ash (9.73 MPN/g), compost (6.89 MPN/g) or untreated manure (13.77 MPN/g). The E. coli content of lettuce grown on soil amended with ash, bioslurry or compost at recommended rates was significantly lower than lettuce crop grown on soil amended with untreated cattle manure. The results from this study provide information on the transmission of the pathogens remaining in the treated and untreated wastes when applied as organic fertilizer to food crops. This information will help to reduce the potential risks associated with the use of organic manures in growing food crops, as well as determining the optimum rate of application of organic waste after treatment.