High-carbohydrate wastewater treatment by IAL-CHS with immobilized Candida tropicalis

Abstract

A novel immobilized-cell bioreactor was developed and utilized for treatment of high-carbohydrate wastewater and production of single-cell protein (SCP) simultaneously. The system is the internal airlift loop reactor with ceramic honeycomb support for biofilm (IAL-CHS), and the microorganisms tested was Candida tropicalis, which has a high protein yield. The optimum temperature for C. tropicalis was 35–40 °C, and bioreactor experiments were performed at 35 °C. The internal airlift loop reactor with ceramic honeycomb supports allowed a large and dense accumulation of biomass, but also generated significant SCP. Mass-transport resistance did not limit the overall COD-removal kinetics and oxygen mass transfer may have been accelerated to the biofilm. Fermentation of carbohydrates to organic acids lowered the pH below the optimum range of 4.5–6.5, and pH below 4.5 retarded or stopped the oxidation reactions for the organic acids. Since organic-acid oxidation is necessary for attaining COD removal from the wastewater, pH control may be essential for effective treatment in some cases with high-carbohydrate wastewaters. The addition of 0.35 g/L urea could increase the COD removal rate. Continuous wastewater was carried out and the organic loading reached 15 kg COD/(m3 day).