Nitrogen and phosphorus removal of sequencing batch reactor with algae treating piggery wastewater and microbial community structure

Abstract:

[Background] As high concentration organic wastewater, piggery wastewater was one of the main factors that lead to area-source pollution of agriculture in China. At present, an increasing number of researchers focused on piggery wastewater treatment with bacteria-algae symbiotic system. Compared with the traditional sequencing batch reactor (SBR), the algal-assisted SBR showed better performance in nitrogen and phosphorus removal, sludge activity improvement and energy consumption reduction. [Objective] Aiming at the influence of algal-bacterial symbiosis system on the nitrogen and phosphorus removal, the distinction on sludge characteristics and microbial community structure were anlyzed between the algal-bacterial symbiosis system and the conventional SBR. [Methods] The algal-assisted SBR (R1) and the conventional SBR (R2) were operated in parallel at room temperature to study the performance of piggery wastewater treatment. The sludge characteristics were also observed, such as sludge particle size, sludge settleability and microbial metabolites. Denaturing gradient gel electrophoresis (DGGE) was used to analyze the microbial community structure in R1 and R2 systems. [Results] compared to the R2, chemical oxygen demand (COD), NH₄⁺-N, total nitrogen (TN) and total phosphorus (TP) were increased by 5.1%, 20.3%, 19.4% and 23.9%. The average values of extracellular polymeric substances (EPS) and soluble microbial product (SMP) in the R1 were 3.7% and 38.5% higher than that in the R2, respectively. Compared to that of R2, the sludge particle size of R1 was increased by14.8%, due to the adhesion of algal to the sludge. In addition, the SVI value of R1 was 11.7% less than that of R2, indicating a poor settleability of sludge in the R1. The sludge specific oxygen uptake rate (SOUR) of R1 was 64.8% higher than that of R2. The formation of stable bacteria algae symbiosis system further reduced the concentration of suspended solids in the effluent of the R1, which further indicated that the addition of algae could improve the characteristics of R1 sludge. [Conclusion] Actinobacteria, Alphaproteobacteria and Gammaproteobacteria as the dominant species in the R1 played an important role in the piggery wastewater treatment. The major Chlorophyta were Desmodesmus and Acutodesmus which had a significant effect on nitrogen and phosphorus removal.