The sustainable utilization of anaerobic digestion effluents treating in suspended filler algae assisted systems

Abstract

Significant amounts of anaerobic digestion effluents (ADE) containing high concentration of inorganic salts (source of nitrogen and phosphorus) and hardly degradable organic matter are produced during the generation of biogas using livestock manure. Without appropriate treatment, the imbalanced carbon to nitrogen ratio may lead to severe pollution of the environment. Considering different environmentally friendly processes such as recycling, energy regeneration, and sustainable development, suspended fillers were added to traditional algal-bacterial symbiosis (ABS) systems. In the present research, three systems including suspended filler algae assisted bio-reactor (SFA-PBR), no filler algae assisted bio-reactor (NFA-PBR), and single activated sludge system (ABS) were examined. Changes in bacterial communities were analyzed using high throughput sequencing. In addition, the mechanisms of ADE degradation in the presence and absence of suspended algae fillers were studied by comparing their effect on the degradation of COD (chemical oxygen demand), TN (total nitrogen), AN (ammonia nitrogen), and TP (total phosphorus). Systems where the ratio of active microalgae to bacteria was higher promoted the interaction between the two types of microorganisms, accelerating the stability of the ABS. Thus, the daily COD degradation rate in the stage was still high. Flora such as microalgae and bacteria were embedded in the filler spheres, which increased the microorganisms resistance to the poor environment induced by high concentrations of inorganic nutrients and organic matter present in the ADE. This favored the sustainable water utilization of ADE. After the treatment in the SFA-PBR system, the COD degradation rate was 75.32 %. The effluent COD concentration was 334.21 ± 39.18 mg/L. TN and AN degradation rates were 89.34 and 91.32%, respectively. The TN and AN concentrations in the effluent were 35.42 ± 2.65 and 29.97 ± 2.65 mg/L, respectively. The degradation rate of TP was 95.39 %. The effluent TP concentration was 0.86 ± 0.18 mg/L. The Chao diversity and ACE index values in the SFA-PBR system were higher than those of other groups. This result further supports the conclusion formulated with the Shannon diversity index result. Specifically, the effective sequence in the SFA-PBR system group presented a higher degree of homogeneity and abundance.