Wastewater treatment and resource recovery: an essential component for biorefineries

Abstract A biorefinery involves sustainable processing of biomass into a wide variety of bio-based products and bioenergy. During biomass processing for biofuels, many chemicals and enzymes are likely to be used in multi-step processes involving various unit operations and unit processes such as milling, pretreatment, enzymatic hydrolysis, fermentation, and purification. A biorefinery is expected to generate multiple complex wastewater streams characterized by higher chemical oxygen demand along with color, poor biodegradability, inorganic salts, which can pose various challenges during treatment by conventional primary, secondary, and tertiary methods. Further, unlike other industries, the wastewater from biorefineries warrants sustainable energy-efficient treatment processes, preferably with the recovery of the biodegradable portion of chemical oxygen demand (COD) as biogas in order to improve the net energy ratio of the biorefinery. However, the production of biofuels such as biogas and biohydrogen using wastewater from biorefineries is prone to inhibition due to the presence of a number of chemicals that are most likely used in upstream biorefinery operations. This chapter discusses wastewater treatment as an integral part of 1G (molasses-based) and 2G (lignocellulosic residues-based) ethanol biorefineries, with respect to characteristics, conventional treatment options, advanced treatment strategies, and future research needs in view of the emerging stringent regulatory requirements of zero liquid discharge.