Assessment of the quality of sludge from small-scale anaerobic bio-digesters as potential organic fertilizers.

Abstract

Many biogas plants are now being set up in the various areas across the country. With this comes in the challenge of disposal of the sludge (residue) as waste from the bio-digesters. During biogas digestion, about 25-30% of the total dry matter (total solids content of fresh dung) of animal/human wastes will be converted into a combustible gas, methane and a residue of 70-75% of the total solids content of the fresh dung comes out as sludge which was known as bio-digester effluent or biogas slurry or sludge.

The availability of bio-digester sludge as a waste from biogas digestion has a great role to play in sustainable development by use as a bio-fertilizer, which can be a very good approach to pollution control, and reduction in the cost of the necessary waste and sewage treatment.

The quality of residual sludge from biogas production process is better than the manure obtained directly from the cattle cage. It is because anaerobic digestion of organic material occurs in the fermentation process in the digester. It results in the more readily available increasing concentration of Nitrogen, Phosphorus and Potassium which are the vital elements needed by plants.

The purpose of this study was to assess the quality of sludge from selected small scale anaerobic digesters for potential use as organic fertilizers, and by doing so checking on the above mentioned challenges.

The study set out to determine the general pH, Total-Nitrogen, Total Phosphorus and Potassium present in a sludge sample and the results showed that this specific sludge sample had a pH of 6.34, 3.8% N, 0.17% P and 0.32 % K. These results, alongside other results from literature review gave a basis that bio-digester sludge could actually be used conveniently as an organic fertilizer in place of inorganic fertilizers such as NPK.