Abstract
The treatment of cassava starch processing wastewater was carried out in the airlift reactor (ALR) with an internal-loop by using Aspergillus oryzae pellets. This study demonstrated that the effective organic matter removal and biomass production were similar to those obtained in the shake flask culture. In ALR, the spore inoculation produced small and fluffy pellets because of the influence of the high concentration of suspended solids in the wastewater. The use of the precultured hyphae inoculation resulted in the compact and lager pellets in ALR, which were convenient for the mass transfer in ALR and the biomass separation. The ageing, aeration rate and nutrient composition strongly affected the fragmentation of mycelia. The supplementation of ammonium sulfate as nitrogen source improved the treatment efficiencies, biomass yield and protein content significantly. With the concentrations of (NH4)2SO4 in the range of 0.50-0.75 g l-1, TOC, COD and starch removal, biomass yield and crude biomass protein content were 76%, 84%, 93%, 0.57 g (g-COD)-1, and 34%, respectively, after 4 days at the initial COD loading of 8,700-8,900 mg l-1. In particular, the fragmentation was strongly diminished during the cultivation in the medium with plentiful nitrogen source. In addition, evaluating the volumetric oxygen transfer coefficient was considered to provide effectively the determination of the initial COD loading limitation suitable for batch process in ALR. The operation of ALR was highly efficient at the initial COD concentrations less than 10,000 mg l-1, corresponding to the initial starch concentrations less than 12,000 mg l-1 when the wastewater was supplemented with the reasonable amount of ammonium nitrogen.
