Raghuram Chetty

Water utilization is in a steep hike due to urbanization and population increase. On the other hand, pollution of fresh water due to human activities is increasingly a major concern as it affects economy and growth of a nation. Among various water pollutants, nitrogen compounds form a significant role in wastewater contamination due to increase in anthropogenic sources like agriculture. Release of nitrate into fresh water poses severe problems including eutrophication, methemoglobinemia, and other health issues. Thus, nitrate contamination in water and soil has become a growing environmental concern. According to USEPA standards, the maximum contamination level for nitrate is 45 mg L−1, and the same standard is adopted by the Bureau of Indian Standards (BIS). Among various technologies employed for treating nitrate-contaminated water, biological denitrification is one of the more versatile and promising methods widely being employed. The treatment of NO3− using bacteria referred as denitrification or bioremediation of nitrate has high separation efficiency. This chapter focuses on various biodenitrification processes, immobilization of microorganism, and different reactors employed for removing the nitrate from water. Different reactor designs ranging from fixed-bed reactors to biological aerated filters have been demonstrated for effective denitrification.

In this chapter, preliminary discussion on the need for mitigation of greenhouse gas emissions in today’s scenario is emphasized, followed by the foundation to the conversion of CO2 into useful chemicals. Various techniques employed for CO2 sequestration are introduced, and in the midst of these approaches, electrochemical reduction of CO2 is emphasized, owing to its advantages in product selectivity, operation at ambient conditions without supplementary chemical requirements, environmental compatibility, relatively simple modularity and quick scalability. Different types of catalysts reported in the literature for activating and reducing CO2 are critically analysed. To start with, metallic electrodes in aqueous solutions and nanoporous materials are discussed. The reaction mechanism and effect of supporting electrolytes, pressure, and temperature are summarized. Combination of various techniques such as bio-electrochemical reduction and photocatalytic technologies have been accentuated. Furthermore, limitations and outlook of electrochemical reduction of CO2 are presented, in which development of modules similar to that of commercially available H2O electrolysers could pave the way for commercialization of electrocatalytic reduction of CO2.

Chemical modification of different morphologies of ZnO nanoparticles (spherical, flowers). Modification of thin-film composite (TFC) using ZnO nanoparticles by surface coating. Measured flux, NaCl rejection and hydrophilicity. Fouling resistance studies on unmodified and modified membrane. Best membrane performance was observed with 0.02 wt% ZnO-S-modified membrane.