Isolation and characterization of methanogenic bacteria from brewery wastewater in Kenya

Abstract

The production of biogas from renewable resources is becoming a prominent feature of most developed and developing countries of the world. A study was undertaken to characterize methanogenic microbial community found in brewery waste water. Their performance with regards to methane production was also studied. Thirty-two isolates were obtained using brewer thyglycollate agar medium. Characterization of the isolates was done by culture and biochemical methods. 65% of the isolates were found to be positive with Gram staining reaction, while 35% were negative. The isolates were identified by method of polymerase chain reaction (PCR). From the phylogenetic analysis, thirteen isolates were clustered into genus Bacillus sp., isolate 9^3b was closely related to Bacillus subtilis strain, while isolates 20^a1, 17¹ and 7 closely related to Bacillus methylotrophicus isolate 10 was grouped together with Bacillus tequilensis, isolate 31 was clustered together with Bacillus licheniformis, while isolates 13², 25², 15, 26² and 18² were closely related to Lysinibacillus sp. and isolate 191 was clustered together with Lactobacillus casei. The study also shows that three isolates 3², 18¹ and 4 were closely related to Ralstonia pickettii, Providencia rettgeri and Myroides odoratimimus, respectively. The presence of isolates 20^1a, 17¹ and 7 with abilities to ferment different sugars, hydrolysis starch, liquefy gelatin, split amino acid tryptophan, produce catalase enzyme and hydrogen sulphide gas suggests their involvement in biogas production. The percentage methane content in the total gas produced at pH 8 varied significantly (p<0.001) for all the temperature ranges. The highest concentration of methane for most isolates was recorded at temperatures of 35 and 37°C for all the pH ranges.

Key words: Biogas, characterization, methanogenic bacteria, pH, temperature, wastewater.