A high concentration of hydrogen sulfide (H2S) released from pig farming is one of the major environmental problems affecting surrounding communities. In modern pig farms, the bioscrubber is used to eliminate H2S, which is found to be driven mainly by the sulfur-oxidizing bacteria (SOB) community. Therefore, in this study, molecular biology techniques such as next-generation sequencing (NGS) and DNA microarray are proposed to study the linkage between enzyme activity and the abundance of the SOB community. The starting sludge (SFP1) and recirculating sludge (SFP2) samples were collected from the bioscrubber reactor in the pig farm. The abundance of microbial populations between the two sampling sites was considered together with the gene expression results of both soxABXYZ and fccAB. Based on the NGS analysis, the members of phylum Proteobacteria such as Halothiobacillus, Acidithiobacillus, Thiothrix, Novosphingobium, Sulfuricurvum, Sulfurovum, Sulfurimonas, Acinetobacter, Thiobacillus, Magnetospirillum, Arcobacter, and Paracoccus were predominantly found in SFP2. The presence of Cyanobacteria in SFP pig farms is associated with increased biogas yields. The microarray results showed that the expression of soxAXBYZ and fccAB genes involved in the oxidation of sulfide to sulfate was increased in Halothiobacillus, Paracoccus, Acidithiobacillus, Magnetospirillum, Sphingobium, Thiobacillus, Sulfuricurvum, Sulfuricurvum, Arcobacter, and Thiothrix. Both NGS and DNA microarray data supported the functional roles of SOB in odor elimination and the oxidation of H2S through the function of soxABXYZ and fccAB. The results also identified the key microbes for H2S odor treatment, which can be utilized to monitor the stability of biological treatment systems and the toxicity of sulfide minerals by oxidation.

The coir industry in India’s southern coastal regions, especially in the state of Kerala, is becoming increasingly concerned about the environmental impact of the accumulation and incremental increase of coir pith each year. The objective of this study was to assess the effect of pretreatment on the anaerobic digestion of coir pith. The characterization study of coir pith shows high organic content, which can be anaerobically digested to produce biogas. But, the high lignin content (30.91%) makes the process slow. To overcome this, a biological pretreatment method was tried using two microbial cultures belonging to fungal genera known to be lignin decomposers, viz., Trichoderma and Pleurotus. By using Trichoderma, lignin content was reduced by 3.7%, and the maximum gas production was obtained in a shorter time (19 days) in comparison with the sample without any pretreatment (24 days). When Pleurotus was used for lignin degradation, the lignin content was reduced by 6.78%, and the maximum gas production was obtained in a much shorter time period (14 days) in comparison with the former two methods. The gas produced comprises 74 ppm of methane, which has fuel value. The sludge after digestion was tested, which indicated a marginal increase in NPK value and hence can be used as fertilizer. The results of the study appear to be quite promising in the transition towards green energy by providing scope for the process of biomethanation, with the conclusion that further research can transform coir pith into a good renewable energy resource.