Performance and microbial community of a novel combined anaerobic bioreactor integrating anaerobic baffling and anaerobic filtration process for low-strength rural wastewater treatment

Carbon Reduction and Pollutant Abatement by a Bio-Ecological Combined Process for Rural Sewage

In order to explore the treatment effect of a bio-ecological combined process on pollution reduction and carbon abatement of rural domestic wastewater under seasonal changes, the rural area of Lingui District, Guilin City, Guangxi Province, China was selected to construct a combined process of regulating a pond, biological filter, subsurface flow constructed wetland, and ecological purification pond. The influent water, effluent water, and the characteristics of pollutant treatment in each unit were investigated. The results showed that the average removal rates of COD, TN, and NH3-N in summer were 87.57, 72.18, and 80.98%, respectively, while they were 77.46, 57.52, and 64.48% in winter. There were significant seasonal differences in wastewater treatment results in Guilin. Meanwhile, in view of the low carbon:nitrogen ratio in the influent and the poor decontamination effect, the method of adding additional carbon sources such as sludge fermentation and rice straw is proposed to strengthen resource utilization and achieve carbon reduction and emission reduction. The treatment effect of ecological units, especially constructed wetland units, had a high contribution rate of TN treatment, but it was greatly impacted by seasons. The analysis of the relative abundance of the microbial community at the phylum level in constructed wetlands revealed that Proteobacteria, Acidobacteria, Chloroflexi, Firmicutes, Bacteroidetes, Planctomycetota, and Actinobacteria were the dominant phyla. The relative abundance of microbial communities of Proteobacteria, Chloroflexi, and Acidobacteria decreased to a large extent from summer to winter, while Firmicutes, Bacteroidetes, and Planctomycetota increased to varying degrees. These dominant bacteria played an important role in the degradation of pollutants such as COD, NH3-N, and TN in wetland systems.

Nitrogen Removal from the Simulated Wastewater of Ionic Rare Earth Mining Using a Biological Aerated Filter: Influence of Medium and Carbon Source

In engineering application, a two-stage biological aerated filter (BAF) has been deployed to achieve the steady nitrogen removal of the wastewater from the mining area of ionic rare earth with a low carbon to nitrogen (C/N) ratio. However, the cost-efficiency of the medium and carbon source casts a shadow over further development. In this study, the influences of four media (i.e., volcanic, zeolite, quartz, and ceramisite) and three soluble carbon sources (i.e., acetate, glucose, and methanol) on the N removal were systematically compared. Applying volcanic and quartz showed a favorable start-up performance due to the biophilic surface and dense packing, respectively. However, regardless of medium type, with [NH4+-N]0 = 50 and [NO3−-N]0 = 30 mg/L, the C/N ratio of 3 was required to meet the discharge standards of NH4+-N, TN, and COD, and acetate was confirmed applicable for all the selected medium-packed BAFs. Introduction of sweet potato residues as the solid carbon source decreased the amount of added acetate by more than 13%. The 16S rRNA high-throughput gene sequencing revealed that Sphingomonas and Nitrospira were abundant in the aerobic stages of the volcanic and zeolite-packed BAFs, respectively. Such a community integrated with the extensively distributed Thauera, Clostridium_sensu_stricto, and Proteiniclasticum in the anoxic stage accounted for the efficient N removal. Thus, deploying volcanic as the medium and acetate as the soluble carbon source was proposed. These findings will provide valuable references for the selection of medium and carbon source and, consequently, further optimize the operational performance.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45-10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68-95% of the total organics), particularly the fraction of 1-5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

Distribution of antibiotic resistance genes and their association with bacteria and viruses in decentralized sewage treatment facilities

The distribution of antibiotic resistance genes (ARGs) has been intensively studied in large-scale wastewater treatment plants and livestock sources. However, small-scale decentralized sewage treatment facilities must also be explored due to their possible direct exposure to residents. In this study, six wastewater treatment facilities in developed rural areas in eastern China were investigated to understand their risks of spreading ARGs. Using metagenomics and network analysis tools, ARGs and bacterial and viral communities were identified in the influent (INF) and effluent (EFF) samples. The dominant ARGs belonged to the bacitracin class, which are different from most of municipal wastewater treatment plants (WWTPs). The dominant hosts of ARGs are Acidovorax in bacterial communities and Prymnesiovirus in viral communities. Furthermore, a positive relationship was found between ARGs and phages. The ARGs significantly correlated with phages were all hosted by specific genera of bacteria, indicating that phages had contributed to the ARG's proliferation in sewage treatment facilities. Paying significant concern on the possible enhanced risks caused by bacteria, viruses and their related ARGs in decentralized sewage treatment facilities is necessary.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s11783-021-1469-4 and is accessible for authorized users.

Anaerobic treatment of slaughterhouse wastewater: a review

This article presents a review of anaerobic treatment technologies to treat slaughterhouse wastewater including its advantages and disadvantages. Physico-chemical characteristics and biochemical methane potential (BMP) of slaughterhouse wastewater are addressed. Various anaerobic treatment technologies are presented with the related operating parameters, viz., hydraulic retention time (HRT), organic loading rate (OLR), upflow velocity (V_up), and biogas yield vis-a-vis treatment efficiency in terms of chemical oxygen demand (COD). In addition, various factors that affect the anaerobic treatment of slaughterhouse wastewater such as high oil & grease (O & G) concentration in influent, inhibitors, volatile fatty acids (VFAs), and the loading rate are also addressed. The literature review indicated that the slaughterhouse wastewater can be treated effectively by employing any anaerobic treatment technologies at OLRs up to 5 kg COD/m³.d with more than 80% COD removal efficiency without experiencing operational problems. Anaerobic hybrid reactors (AHRs) were found the most effective among various reviewed technologies because of their ability to operate at higher OLRs (8 to 20 kg COD/m³.d) and lower HRTs (8 to 12 hrs).