Chelating ligands: enhancers of quality and purity of biogas
The quality of biogas depends largely on the percentage of methane and hydrogen sulphide gas present. High concentration of hydrogen sulphide results in low quality biogas. This work employed the use of chelating ligands in scrubbing hydrogen sulphide gas while improving the yield of methane gas. Experimental analyses were carried out using Biogas 5000 analyser, Atomic Absorption Spectrophotometer and other classical analytical tools. Results from the analyses showed a 12 to 15 % improvement in the methane gas yield and reduction in the concentration of hydrogen sulphide gas from 80 to 30%. All digesters recorded pH within the optimum values. The cow dung (CD) digester shows significantly low volatile fatty acids concentrations which contributed to the increased methane gas yield. Trace metals like Iron, Cobalt and Nickel, found to be present within the digesters; reacted with the chelating ligands to form metal chelates which increased the bioavailability of essential nutrients; promoting the growth and stability of methanogens thus, improving methane production. The metal chelates equally undergoing a redox reaction with the hydrogen sulphide gas, produced elemental sulphur with the release of H+ ions; thereby reducing the concentration of hydrogen sulphide. Generally, addition of ligands to substrate digesters increased methane production and significantly decreased hydrogen sulphide concentration.
Keywords: Biogas, Volatile fatty acids, Methane, Hydrogen sulphide and Ligands