4. Environmental Health Hazards of Post-Methanated Distillery Effluent and Its Biodegradation and Decolorization

Anaerobically digested distillery effluent is a mixture of complex organic and inorganic pollutants which is composed of several plant sterols which do not only affect the water quality but also aquatic flora and fauna. Research has revealed the adverse effects of post-methanated distillery effluent (PMDE) on the seed germination and plant growth of Phaseolus mungo even at lower concentrations. Studies have also showed the adverse effect on soil fertility by inhibiting the nitrogen-fixing bacteria and root nodulation. The major colorant of distillery effluent is melanoidin, reaction product of amino-carbonyl compounds at elevated temperature in the sugar industries and distilleries due to condensation reaction. Due to its high solubility in aquatic ecosystem and negative charge, it makes complexation with all the humic substances and heavy metals in the environment. Therefore, the decolorization and degradation of PMDE is still a global challenge due to its complexity. The physical, chemical, and biological techniques have been attempted for its detoxification and color removal but still warranted for its feasible application. Manganese peroxidase (MnP) and laccase have been reported as key enzymes from fungi and bacteria. During the degradation process of PMDE, different metabolic products through GC-MS/MS analysis have also been characterized. The integration of bacterial treatment with constructed wetland plant treatment (Phragmites communis, Typha angustifolia, and Cyperus esculentus) technique has been reported recently as an effective approach for decolorization and degradation of PMDE. The major challenge of PMDE biodegradation and decolorization is its high total dissolved solids (TDS) containing complex organic pollutants including heavy metals. The high TDS is a result of precipitation of metal sulfides during anaerobic digestion of distillery spentwash due to complexation of heavy metals and sulfates which impose inhibitory effects on the microorganisms, consequently inhibiting the biodegradation process. Several complex organic pollutants present in PMDE have been also reported as endocrine-disrupting chemicals (EDCs) which directly affect the aquatic and terrestrial ecosystems.