Molecular characterization of micro-organism with Industrial potential for Methane production in sludge from Kangemi sewage treatment plant, Nyeri County- Kenya

Abstract

Sewage sludge (biosolids) is a by-product of the waste water treatment plants (WWTPs). Microbial consortia under anaerobic conditions are involved in the reduction of organic matter in the wastewater of such sludge to produce methane gas. However, in developing countries like Kenya, these microbes have not been fully identified in order to target them for the efficient harnessing of biofuel. In this study, wet sludge samples were collected using strerile containers from the two anaerobic digestion lagoons at Kangemi sewage treatment plant, Nyeri County Kenya, between September to December, 2022. This treatment plant is one of the best managed and accessible treatment plants in Kenya. RNA/DNA shield were then added to the samples and transported to the laboratory at 4°C and stored at -20°C. Total community DNA was extracted from samples using available ZymoBlOMlCSTM DNA Miniprep Kit and sequenced using Shotgun metagenomics. Samples were analyzed using MG-RAST software which allowed for comparison of taxonomic and fiinctional diversity as well as identification of microorganisms directly involved in various stages of methanogenesis pathways. In addition, physico-chemical parameters were measured in-situ from the sludge tank, the two sludge digestion lagoons, and the dry beds. Results showed that parameters such as bulk density (0.14 :1: 0.03 and 0.24 :1: 0.02 g/cn13), pH (5.53 to 6.52), EC (3.77 i 0.05 and 4.03 zt 0.05 mS/cm) and TS (12.66 zt 0.48% and 53.40 i 8.82%) recorded significant differences between raw and dry sludge respectively. The sludge temperature (249101 0.910 °C) and TS (17.20 i 0.089%) in lagoon 2 were significantly higher than in lagoon l with temperature (24.36:l: 0.85 °C) and TS (ll.60 :1: 0.036%). Microorganisms identified from the sequences were directly involved in different stages of methane production with hydrogenotrophic methanogens, such as Methanospirillum (32%) or Methanobacterium (27%), being predominant in the lagoon communities, whereas acetoclastic Methanoregula (22%) and the acetate oxidating bacteria such as Clostridia (68%) were the key microbes for that pathway in the sewage sludge. Furthermore, the methylotrophic pathway was carried out by Methanothermobacter (18%), Methanosarcina (21%), Methanosaeta (15%) and Methanospirillum (13%), which appearing to play an important role in methane production. In contrast, Methanosarcina (23%), Methanoregula (14%), methanosaeta (13%) and methnanoprevibacter (13%) seemed to play an important role in the final step of methane release. This study concluded that the sludge produced from this WWTP harbours microbes with significant potential for biogas production besides being an abode for many other unique microbes. The study further recommends investigations into