Growth of Aspergillus oryzae during treatment of cassava starch processing wastewater with high content of suspended solids

Abstract

Aspergillus oryzae IFO 30113 was used for the treatment of the cassava starch processing (CSP) wastewater. The observations on the fungal morphology showed that, in the shake flasks containing the CSP wastewater with the high concentration of suspended solids, the formation of pellets originated from the adherence of germinated spores to solid particles in medium. The attached solid particles were also digested during the fungal fermentation and resulted in the formation of the smooth and hollow pellets. The changes of the culture conditions such as inoculum size, initial pH of wastewater, inoculum type and nutrient elements affected on the fungal morphology, biomass accumulation and treatment efficiencies of A. oryzae IFO 30113. In the typical pH range (pH 4–5) of the CSP wastewater, the formation of smooth pellets was predominant and A. oryzae IFO 30113 was satisfiable for the production of fungal biomass and treatment efficiencies. The supplementation of nitrogen sources has shown an improvement in the fungal biomass accumulation and the treatment efficiency of A. oryzae IFO 30113 growing in the CSP wastewater. Especially, high biomass yields (up to 0.8 g/g-COD) were achieved in flasks supplied with peptone. With ammonium sulfate as nitrogen source, 87% total organic carbon (TOC), 91% COD and 94% starch were removed after 96-h incubation. The possibility of the pellet formation despite the presence of the high content of suspended solids would be of great advantage to perform the treatment process and the fungal biomass production on the airlift-type bioreactors by lowering medium viscosity and better mass exchange of oxygen and nutrients.