Exploring the Effects of Fillers and Cultivation Conditions on Microbial-Algal Biofilm Formation and Cattle Wastewater Treatment Efficiency

With the rapid development of the livestock farming industry, the treatment of livestock farming wastewater has become increasingly important. The microbial-algal biofilm method has gained widespread attention for cattle wastewater treatment owing to its non-toxic nature, resistance to shock loading, and high treatment efficiency. In this study, three types of substrates—polyurethane sponge, ceramic material, and moving bed biofilm reactor media—were evaluated. The formation of biofilms was assessed through variations in chlorophyll content, microscopic observations, and measurements of biofilm dry weight and attachment rate. Biofilm characterization on the different substrates was conducted via Fourier transform infrared spectroscopy, confocal laser scanning microscopy, and scanning electron microscopy. The results demonstrated that polyurethane sponge was the most effective substrate. Furthermore, a single-factor experiment was conducted to optimize the cultivation conditions for the microbial-algal biofilms and identify the optimal parameters based on the ability of the biofilm to remove COD, TN, TP, and NH4+-N. The optimal conditions were as follows: an illumination intensity of 8000 lux, red light, a temperature of 20 °C, a pH of 7, and an aeration intensity of 8 L/min. Under these conditions, the pollutant removal rates were exceptionally high: ~73.4% for COD, 51.8% for TP, 57.0% for TN, and 75.1% for NH4+-N.