Contamination of arsenic (As) in water, especially groundwater, has been recognized as a major problem across the world. The presence of arsenic in groundwater has become a global problem in the past decades. Health risks have also been reported for many years. Different areas of the world are affected by arsenic contamination of groundwater, the largest population at risk in Bangladesh, followed by West Bengal in India. Arsenic concentrations in drinking water cause severe health effects on human, more than 150 million people worldwide. The current drinking water standard regulation has become strict and requires a reduction in arsenic content. Therefore, the treatment of arsenic contaminants can be the only effective option to reduce health risks. This review paper briefly describes arsenic sources, arsenic chemistry, arsenic contamination in groundwater, its impact on human health and many conventional as well as advanced techniques that are used to remove arsenic from water.

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Biohydrogen is regarded as an attractive future clean energy carrier due to its high energy content and environmentally friendly conversion. Biohydrogen reactor is widely used in studies concerning the anaerobic co-digestion of food waste, sewage sludge, wastewater and other organic solids. Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material (biomass or waste feedstock) in the absence of oxygen to produce biogas, which may generate electricity and heat, or can be processed into renewable natural gas and transportation fuels. This review article explains the scientific processes of anaerobic digestion process such as hydrolysis, acidogenesis, acetogenesis and hydrogenesis as well as methods to produce biohydrogen gas such as fermentation and biophotolysis for the waste management technology and sources of renewable energy and concludes with solutions that may allow anaerobic digestion to become more widely adopted throughout the developing countries to control the waste management system.