Foaming Tendency in Anaerobic Digestion of Wastewater Inoculated with Anaerobic Sludge and Cow Manure: Effect of Protein Concentration

Abstract

Foaming has impacted the digestion process causing severe process failures. The basis of foaming is often unclear due to multiple foaming compounds in a single system. This study aims to elucidate the effect of protein concentration on foaming in anaerobic sludge and cow manure (CM) digesters inoculated with synthetic wastewater as a substrate. Gelatine was used to alter the protein concentration in the digesters. The foaming tendency, biogas production, protein, and chemical oxygen demand (COD) removal were measured to comprehend the findings. The results show that the foaming tendency increased with protein concentration in anaerobic sludge digesters. It also had the highest biogas production. There was no evident process inhibition observed in the anaerobic sludge digester, even at higher protein and COD concentrations. For CM digester, the foaming tendency and biogas production increased to 9 g/L; however, the biogas production decreased with increased substrate protein concentration, indicating process inhibition. The results indicate that the biogas production, foaming tendency, COD and protein removal increased steadily for both digesters. However, the trend decreased for CM digester at increased protein concentrations. This study also concluded that protein creates foaming when inoculated with anaerobic sludge and CM even at low substrate protein concentration.