Physical–chemical and biomethanization treatments of wastewater from biodiesel manufacturing

The mesophilic anaerobic digestion of wastewater derived from biodiesel manufacturing, in which total chemical oxygen demand (COD total) was found to be 428 g/L, was studied at laboratory scale. Firstly, wastewater was acidified to recover its free fatty acid content. The resulting aqueous phase was then neutralized and subjected to coagulation–flocculation and electrocoagulation to demulsify the remnant organic matter. A 45% and 63% reduction in overall COD total was observed with the acidification–electrocoagulation and acidification–coagulation–flocculation pre-treatments, respectively. However, the anaerobic biodegradability of acidified-electrocoagulated wastewater was found to be the highest (98% COD), while the methane yield coefficient reached a mean value of 297 mL CH4/g COD removed (1 atm, 0 °C). Moreover, the allowed organic loading rate and the mean methane production rate were considerably higher for acidified-electrocoagulated wastewater. Consequently, the combination of acidification–electrocoagulation with anaerobic digestion might be a good alternative to efficiently purify wastewater derived from biodiesel manufacturing.