Wenai Liu’s research while affiliated with Changchun University of Science and Technology and other places

To address the problems of low efficacy and low microbial activity in low-temperature municipal wastewater treatment, this study utilized an air-lift micro-pressure internal circulation integrated reactor (AMICIR). Through controlling the amount of aeration and dissolved oxygen (DO) in the reactor, AMICIR creates alternating aerobic and anaerobic environments, explores the enrichment conditions of aerobic denitrifying bacteria, examines the changes in pollutant removal efficiency and the characteristics of bacterial colony structure during the process of enrichment of aerobic denitrifying bacteria in the system, and reveals the mechanism of nitrogen removal by aerobic denitrifying bacteria cooperating with anaerobic denitrifying bacteria in the low-temperature municipal wastewater treatment system. Experimental results showed average removal rates of NH 4 ⁺ -N, chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) reaching 93.85%, 89.30%, 92.75%, and 75.4%, respectively. The microorganisms secreted large amounts of proteins and polysaccharides, forming zoogloea and anaerobic microenvironments conducive to traditional denitrification reactions. IlluminaMiSeq sequencing analysis revealed the presence of anaerobic phyla. The system was enriched with a large number of microorganisms, and aerobic denitrifying bacteria ( Flavobacterium , Rhodoferax , and Pseudomonas ) were successfully cultured. Flavobacterium emerged as the dominant species, with relative abundance ranging from 18.56% to 22.60%. Functional gene prediction indicated high abundance of aerobic denitrification genes, such as napA . Aerobic denitrifying bacteria were successfully enriched in the system to improve nitrogen removal from municipal wastewater at low temperatures.

In this study, a coupling anaerobic anoxic oxic (AAO) activated sludge-biofilm process with segmental influent was constructed to increase the concentration of functional microorganisms in the reactor and improve the efficiency of municipal wastewater treatment at low temperature, and investigated the pollutant removal pattern and microbial characteristics at low temperature. Conventional pollutants and sludge characteristics indicator were tested at the segmental influent flow distribution ratio of A1:O1 = 2:1. The study showed that the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4⁺-N), total nitrogen (TN), and total phosphorus (TP) were 89 %, 90.74 %, 76.60 %, and 96.60 %, in contrast to the conventional AAO process, at low temperature, COD degradation was concentrated in A1 and O1, simultaneous nitrification and denitrification (SND) occurred in O1 to achieve effective N removal, the phosphorus (P) significant removal in O1. The extracellular polymeric substances (EPS) content of activated sludge in the compartment was negatively correlated with the incoming COD content. And the distribution of carbon and nitrogen sources in the segmental influent contributed to the higher active activity of microorganisms and higher removal efficiency. The analysis of microbial communities in activated sludge and filler samples by Illumina high-throughput sequencing showed that the abundance and diversity of microbial communities in the biofilm were more significant than the activated sludge, and Proteobacteria were the most abundant phylum in the community. The presence of many denitrifying phylum such as Firmicutes and Nitrospira ensured the stability of the modified AAO system at low temperature. Dokdonella, Denitratisoma, Rhodoferax, and other genera ensured efficient phosphorus removal.

This study aimed to propose a novel air-lift multi-stage circulating integrated bioreactor (AMCIB) to treat urban sewage. The AMCIB combined the reaction zone and sedimentation zone, the alternating circulation of activated sludge in separate aerobic and anaerobic environments facilitates the enrichment of HN-AD bacteria. The preliminary study showed that AMCIB had high removal efficiencies for COD, NH4⁺-N, TN and TP under high dissolved oxygen (DO) concentration conditions, with average removal rates of 93.21 %, 96.04 %, 75.06 % and 94.30 %, respectively. IlluminaMiSeq sequencing results showed that the system successfully cultured heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria (Pseudomonas, Acinetobacter, Aeromonas) that played a crucial role in sewage treatment, and Tetrasphaera was the central phosphorus removing bacteria in the system. Functional gene predictions showed that the HN-AD played a dominant role in the system.

To explore the reasons for the excellent denitrification performance of the Micro-pressure double-cycle reactor (MPDR), the nitrogen removal mechanism of the reactor in the treatment of municipal wastewater was studied. Through analysis of flow simulation and dissolved oxygen (DO) distribution, it was determined that the reactor had a macroscopic biochemical reaction environment for simultaneous nitrification and denitrification (SND) because of the special structure of reactor. The result of sewage treatment showed that the average removal rates of COD, NH4⁺-N, TN, TP were 92.29%, 96.64%, 73.6% and 91.66% respectively, and the SND rate was 60.9%. Dechloromonas, Thermomonas, Micropruina, Tetrasphaera, etc. for nitrogen and phosphorus removal existed in the reactor at the same time to explain the excellent performance of the system. PICRUSt2 showed that the metabolic pathways related to nutrient degradation in the reactor were highly active and the abundance of denitrification functional genes was higher in the central zone and lower in the peripheral zone. The research results not only perfected the basic theory of the reactor, but more importantly, provided theoretical and technical support for the further application of the reactor.