Sequential valorization strategies for dairy wastewater and water hyacinth to produce fuel and fertilizer

Abstract

AbstractTo overcome the obstacles of treatment of dairy wastewater (DW) under anaerobic mono‐digestion and sustainable disposal of harvested water hyacinth (WH) a novel sequential valorization strategy was adopted to obtain fuel and fertilizer. Initially, DW and WH were subjected for anaerobic co‐digestion to elucidate the synergistic effect of the substrates to improve the process efficiency and increased biomethane production. The results indicated that the co‐digestion mixture (DW: WH‐1:1) has resulted in biomethane yield of 504.38 L/Kg VSfed which is 1.28‐fold and 3.14‐fold higher as compared to the mono‐digestion of WH (431.71 L/Kg VSfed) and DW (160.59 L/Kg VSfed), respectively. Further, the residual digestate was subjected for slow pyrolysis (320 ± 15°C) to obtain bio‐oil and biochar. The obtained bio‐oil shown superior fuel characteristics as compared to direct WH bio‐oil resulting in density, viscosity, and calorific value of 1.21 ± 0.04 g/ml, 1.8 ± 0.05 cSt and 1766.82 ± 11.53 KJ/Kg, respectively. The biochar residue from pyrolysis was amended to the soil to determine its bio‐fertilizing property. The soil properties in terms of bulk density, porosity, organic carbon, and pH were enhanced. Tomato cultivation in biochar amended soil shown comparable vegetative growth to that of digestate and urea thereby advocating the replacement of chemical fertilizers.Practical ApplicationWith recent increase in environmental concerns and requirement to meet the prescribed limits for effluent discharge from the industries, especially from food processing for the protection of aquatic bodies, there is a requirement of adoption of cost effective technology that could provide both economic and ecological sustainability. In this study, a sequential valorization strategy was adopted for efficient management of dairy wastewater and harvested water hyacinth from the water resources. The resultant products biogas, bio‐oil and biochar could be potentially used as fuel and fertilizer. Circular bio‐economy is in need of time which could be attainable by the implementation of such strategies in large scale industries for efficient waste management and resource recovery. This will not only benefit the environment but also to the society by galvanizing the sustainable development technology.