Bioremediation of ethanol wash by microalgae and generation of bioenergy feedstock

The disposal of waste from industrial sources is becoming a serious problem throughout the world. To produce one liter (L) of ethanol, about 15-L Ethanol Spent Water (ESW) is discharged from the ethanol industry adversely impacting aquatic and terrestrial ecosystems. This study investigated the bioremediation of ESW in two stages, first filtration through biochar (byproduct after HTL processing of algal biomass) followed by bioremediation using algae. In the first step up to 99.4% toxic melanoidin pigment and suspended pollutants from ESW were removed. The colorless ESW was then tested for the growth of marine Parachlorella kessleri-I (PK-I), and freshwater Chlorella vulgaris (CV) and Chlorella sorokiniana-I (CS-I). Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis was conducted before and after bioremediation of ESW using algae. The chemical oxygen demand (COD) 28,900 mg L-1 was reduced to 55-118 mg L-1, biological oxygen demand (BOD) 7200 mg L-1 was reduced to 28-55 mg L-1, total organic carbon (98.7%), phenol (64%), sugar (99.5%), nutrients and toxic metal concentrations were also reduced significantly after 12 days of algae-cultivation in ESW. The highest biomass (115.4 mg L-1 day(-1)) and lipid (9.1 mg L-1 day(-1)) productivity were observed in PK-1 using biochar-filtered ESW. The biodiesel properties and cetane number 48.1-63.9 in FAME studied by GC-MS were observed as per the international standard of fuels. The ESW cultivated algal biomass contained a significant amount of lipids, proteins, and carbohydrates compared to the control medium grown biomass. Thus algae-derived biochar has the potential to effectively remediate the hazardous ESW thereby facilitating the efficient growth of different algal species to generate the feedstock for biofuel applications.

Automated summary

The study successfully removed toxic substances from ethanol spent water (ESW) using biochar and algae, and reduced the chemical oxygen demand (COD) and biological oxygen demand (BOD) in the wastewater. Furthermore, the cultivation of algae in ESW also produced high-quality biofuel.