Vipin Chandra Kalia

Anaerobic digestion of banana stem waste

Abstract Waste banana stem has a high organic content (83%); with 15–20% (w/w) lignin and cellulose which gives it a sheath-like texture. Banana stem slurries (BSS) at 2–16% total solids (TS) concentration were anaerobically digested under mesophilic (37–40°C) as well as thermophilic conditions (50–55°C) in batch culture. The final biogas yields, 267–271 l/kg TS fed, were observed with 2–4% TS slurries, under mesophilic conditions. In the thermophilic range, the biogas yields, 212–229 l/kg TS fed, were found with 2–8% TS slurries. However, thermophilic digestion rates were 2.4 times faster than mesophilic. Methane accounted for 59–79% of the total biogas. Methane yield was maximum at 2% TS BSS in both the temperature ranges. The process led to 45–50% reduction in organic solids and 40–55% reduction in COD. With 16% TS BSS inhibition resulted in 50–60% loss in biomethanation process efficiency.

Identification of genes conferring arsenic resistance to Escherichia coli from an effluent treatment plant sludge metagenomic library

The majority of bacteria elude culture in the laboratory. A metagenomic approach provides culture-independent access to the gene pool of the whole bacterial community. A metagenomic library was constructed from an industrial effluent treatment plant sludge containing about 1.25 Gb of microbial community DNA. Two arsenic-resistant clones were selected from the metagenomic library. Clones MT3 and MT6 had eight- and 18-fold higher resistance to sodium arsenate in comparison with the parent strain, respectively. The clones also showed increased resistance to arsenite but not to antimony. Sequence analysis of the clones revealed genes encoding for putative arsenate reductases and arsenite efflux pumps. A novel arsenate resistance gene (arsN) encoding a protein with similarity to acetyltransferases was identified from clone MT6. ArsN homologues were found to be closely associated with arsenic resistance genes in many bacterial genomes. ArsN homologues were found fused to putative arsenate reductases in Methylibium petroleiphilum PM1 and Anaeromyxobacter dehalogenans 2CP-C and with a putative arsenite chaperone in Burkholderia vietnamiensis G4. ArsN alone resulted in an approximately sixfold higher resistance to sodium arsenate in wild-type Escherichia coli W3110.

Biomethanation of plant materials

Apple pomace and vegetable waste (radish leaves, cauliflower leaves and stalk and rotten cabbage) were subjected independently and also in succession to anaerobic digestion inoculated with cattle dung, on a laboratory scale. Each kilogram (dry weight) of apple pomace fed could generate 275 l of biogas (57% CH4), fresh vegetable waste generated 210 l of biogas (72% CH4) and rotten cabbage led to the generation of 320 l of biogas (68% CH4). Adaptation of methanogens to changing feed material was also observed.

Conversion of waste biomass (pea-shells) into hydrogen and methane through anaerobic digestion

Abstract Waste pea-shells were digested under batch anaerobic conditions. Digestion of pea-shell slurries (PSS) at 1–5% total solids (TS) concentration, with H 2 -producting organisms yielded 99–362l biogas-H/kg organic solids reduced (biogas-H: mixture of H 2 , CO 2 and H 2 S). Hydrogen constituted 33–46% of the total biogas-H. Methanogenesis of PSS (1–5% TS) was most effective at 1% TS level. During 25 days of incubation, 507 l biogas/kg was generated (biogas: mixture of CH 4 , CO 2 and H 2 S). Methane accounted for 43% of the total biogas yield. Biogas yield of 1% TS PSS without the fibrous sheath was only 16·5% of that of 1% TS PSS with the fibrous sheath. However, 3% TS PSS without the fibrous sheath showed improved results, which could be employed for continuous-culture digestions.

Effect of some physiological factors on nitrogenase activity and nitrogenase mediated hydrogen evolution by mixed microbial culture

Fermentative H2 evolution, nitrogenase activity (acetylene reduction) and nitrogenase mediated H2 evolution was studied in free cells of mixed microbial population of H2 producers. At 3% glucose level, the cells produced 8.35 1 H2/mol glucose utilized. The role of nitrogenase system in H2 generation was evident by derepressed nitrogenase activity (0.46 nmoles C2H4 produced/mg protein/h) under defined in vitro conditions. For maximum expression of the activity, the cells required preactivation under anaerobic conditions by incubating at 40 °C for 20‐24h with 0.2% glucose in the culture medium. At an O2 level of more than 0.25%, the acetylene reduction activity decreased significantly and could not be detected at a level of 20%. Nitrogenase activity development was higher at acetylene: inoculum ratio between 4.2‐6.25. H2 evolution was lower when the mixed cells were incubated under an atmosphere of 10% C2H2 and 5%CO gas. This decrease in H2 evolution was also evident at 2.5‐6.5 mM NaNO3 and KNO3 concentrations in the liquid culture medium thus establishing more than 50% H2 evolution through nitrogenase.

Mining of Microbial Wealth and MetaGenomics

The existence of living organisms in diverse ecosystems has been the focus of interest to human beings, primarily to obtain insights into the diversity and dynamics of the communities. This book discusses how the advent of novel molecular biology techniques, the latest being the next-generation sequencing technologies, helps to elucidate the identity of novel organisms, including those that are rare. The book highlights the fact that oceans, marine environments, rivers, mountains and the gut are ecosystems with great potential for obtaining bioactive molecules, which can be used in areas such as agriculture, food, medicine, water supplies and bioremediation. It then describes the latest research in metagenomics, a field that allows elucidation of the maximum biodiversity within an ecosystem, without the need to actually grow and culture the organisms. Further, it describes how human-associated microbes are directly responsible for our health and overall wellbeing.<

Optimization and Applicability of Bioprocesses

In the scenario of increasing population and concomitant pressure on the depleting fossil fuel resources, the focus of current research is on the development of innovative options for achieving sustainability and eco-efficiency in industrial and environmental bioprocesses. Further, there is a need for managing the everincreasing waste generated as a result of human and industrial activities in an efficient manner. Of the currently available tools, environmental processes based on biomass utilization hold the highest potential owing to the abundance and renewable nature of such biomass. For achieving the highest efficiencies, these processes need to be optimized. In the current chapter, the underlying functioning of the various bioprocesses active in the environment has been discussed with particular reference to their optimization in bioremediation of solid and liquid waste. The chapter further discusses the tools for achieving higher efficiencies in such bioprocesses in addition to the value addition through energy generation in order to achieve the twin objectives of profitability and sustainability.