Anaerobically Digested Distillery Wastewater Treatment Using Coagulation-Flocculation Followed by Microalgal Treatment: Optimization of Coagulant Dosage, Dilution Ratio, and Photoperiod

The treatment of anaerobically digested distillery wastewater (ADWW) was investigated via coagulation-flocculation (C-F), followed by a microalgal system. As a first step, C-F was carried out using FeCl3 and polyaluminum chloride (PAC). Around 99.3%, 73.6%, and 58.3% of turbidity, color, and chemical oxygen demand (COD) removals, respectively, were observed under optimized C-F conditions (FeCl3 approximately 3 g/L, PAC approximately 6 mg/L, pH approximately 5, and dilution ratio approximately 4D). Subsequently, C-F-treated ADWW (CADWW) was subjected to microalgal treatment under various dilutions (1D-30D, with and without PO43- addition) and photoperiods. CADWW treatment was found to be higher at 10D in the microalgal system. However, PO43- - addition has not shown any significant improvement in treatment efficiency. A photoperiod of a 16 h:8 h light:dark cycle was optimal for CADWW treatment, which had shown 85% melanoidin, 22.9% total organic carbon (TOC), and 75% total nitrogen (TN) removal rates. However, phenolics removal was found to be the highest (75.7%) under a 12 h:12 h light:dark cycle, and a phenolic content of 1.74 mg of GAE/g dry weight of algae was observed. The overall removal rates of COD, TOC, TN, melanoidin, and phenolics by this sequential process (C-F followed by algal treatment) under optimum conditions were 68%, 51%, 78%, 93%, and 90%, respectively. The algae harvested in the microalgal system was found to have a higher heating value of 28.66 MJ/kg and a lipid content of 24.2%. Overall, sequential C-F and microalgal treatment could be an effective strategy for internal energy recovery during ADWW treatment.