Enhanced denitrification of the AO-MBBR system used for expressway service area sewage treatment: A new perspective on decentralized wastewater treatment

Impact of polyethylene microplastics on the nitrogen removal and bacterial community in sequencing batch reactor at different hydraulic retention times

Both hydraulic retention time (HRT) and microplastics (MPs) are factors affecting the performance of biological wastewater treatment processes, but how MPs affect the role of HRT in biological wastewater treatment performance has not been investigated. In this study, the effects of polyethylene MPs (PE-MPs) on the nitrogen removal performance in a sequencing batch reactor (SBR) at different HRTs were investigated by analyzing the changes in the content and composition of extracellular polymer substances (EPS) and in the bacterial communities and metabolic pathways. In the PE-MPs absence, the HRT was shortened from 1440 to 720 min, resulting in a decrease in the average elimination of chemical oxygen demand and ammonia nitrogen by 13.21 % and 3.78 %, respectively. Whereas the presence of 0.5 mg/L PE-MPs enhanced the reduction by 73.36 % and 93.85 %, respectively. PE-MPs did not change the promotional impacts of HRT shortening on the levels of protein (PN) and polysaccharide (PS) within EPS, while amplified this effect. Aromatic PN of EPS was more sensitive to PE-MPs and HRT than tryptophan-like PN. PE-MPs resulted in a lower enzyme level in nitrification and denitrification metabolism pathways at different HRTs compared to no PE-MPs. This research offers novel perspectives for understanding how PE-MPs intervene in the influence of HRT on biological wastewater treatment performance.

Comparison of the start-up of rotating biofilm contactor reactor with HN-AD bacteria inoculation under high and low influent ammonia conditions

Biofilm formation is critical for the engineering application of pure biofilm RBC processes inoculated with HN-AD bacteria. This study focused on comparing the startup of pure biofilm RBC systems inoculated with HN-AD bacteria under high ammonia nitrogen (NH4+-N = 500 mg/L, H-RBC) and low ammonia nitrogen (NH4+-N = 120 mg/L, L-RBC) influent conditions. The results showed that H-RBC shortened the biofilm formation time by 6 days. Additionally, the average removal efficiencies of ammonia nitrogen and TN were 30.70 % and 38.98 % higher than those of L-RBC, respectively. High-throughput sequencing indicated that compared with L-RBC, H-RBC did not significantly change the types of HN-AD bacteria but significantly increased the abundance of the key HN-AD bacterial genera Planktosalinus and Corynebacterium. Functional gene prediction analysis showed that the abundance of key functional genes affecting the nitrogen removal process, nirS and nosZ, in H-RBC was significantly higher than in L-RBC. Phenotypic prediction analysis revealed that H-RBC could better resist changes in the external environment and had stronger nitrogen removal capacity. These findings provide a theoretical basis and effective approach for the start-up of pure biofilm RBC system.

Genome-resolved metagenomic analysis reveals a novel denitrifier with truncated nitrite reduction pathway from the genus SC-I-84

Understanding the genomic and ecological traits of partial denitrification (PD) bacteria is of high importance for developing wastewater treatment technologies. In this study, a PD-based bioreactor was operated, resulting in a mixed culture dominated by a potentially novel PD functional bacterium (SC-I-84). Progressively increased activity in both nitrate reduction and nitrite production were observed in the SC-I-84 enrichment system, whereas the nitrite reduction activity was always negligible. The phylogenetic analysis indicated that SC-I-84 was closely related to an uncultured beta-proteobacterium (99 %), whereas its denitrification functional genes (napA, napB, narV, and narY) exhibited evidence of co-evolution with chromosomal genes from the genus Cupriavidus, order Burkholderiales. In the genetic sketch of SC-I-84, only nitrate-reduction genes (nar and nap) were identified, whereas nitrite-reduction genes (nir) were absent. Notably, nitrate reduction genes were adjacent to carbon metabolism genes (sucB/C, mdh, idh) and a high abundance of tricarboxylic acid (TCA) cycling genes were found. This can promote the utilization efficiency of electron donors by nitrate reduction genes in SC-I-84, thus enhancing the denitrification activity. Furthermore, SC-I-84 positively cooperated with some bacteria that participate in nitrogen and carbon metabolism and other PD bacteria, but negatively interacted with full-denitrification bacteria. These results indicate that the enrichment of SC-I-84 restricted the growth of full-denitrification bacteria, aiding in the maintenance of a stable PD process. Taken together, the meta-genomic analysis of the novel PD functional bacterium is expected to enhance our understanding of PD processes and aid in the development of PD-based wastewater treatment processes.

Evaluation of vanadium effect on methane oxidation and the microbiome composition in soil

Carbon transformations in the environment are extremely important due to observed climate changes. Various types of pollution resulting from human activity are a factor that modifies the occurrence of these natural processes in the environment. One of these pollutants is vanadium, the presence of which is constantly increasing in the environment. For this reason, the aim of the study was to investigate the influence of vanadium (the most toxic form, pentavalent) on the efficiency of methane oxidation in Leptosol soil. Our research allowed us to identify methanotrophs of the genera Methylobacter and Methylomicrobium in the soil. The presence of these methanotrophs was negatively correlated with the doses of vanadium tested. A decrease in Methylobacter abundance was observed with increased vanadium doses of 188 and 500 mg kg-1, which was reflected in the methanotrophic activity. A decrease in Methylomicrobium abundance was observed starting from the lower vanadium dose (18.39 mg kg-1). The presence of both genera was positively correlated with methanotrophic activity, suggesting that both genera may be involved in methane oxidation in this soil. Our research also indicated the genera of microorganisms whose presence was stimulated by the addition of vanadium, including: Nocardioides, Rubrobacter, Bacillus, Paenibacillus, Streptomyces, which indicates that they have defense mechanisms against vanadium and may participate in lowering its concentration in the environment. There were also those whose presence was clearly reduced, such as Acidobacter, Pseudomonas, Hassallia, Gemmatimonas, Methylotenera. This research provides new insight into how vanadium contamination regulates the methanotrophy process in the soil environment.

Improving organic and nutrient removal efficiencies in seafood processing wastewater using anaerobic membrane bioreactor (AnMBR) integrates with anoxic/oxic (AO) processes

Wastewater from seafood processing is a significant source of pollution, containing many harmful organic and inorganic compounds such as proteins, lipids, carbohydrates, nitrogen and phosphorus. This study investigated the enhancement of organic and nutrient removal efficiencies in seafood processing wastewater by integrating an Anaerobic Membrane Bioreactor (AnMBR) with an anoxic/oxic (AO) processes. A pilot-scale system was constructed with a capacity of 0.5 m3/day directly at the factory operated continuously, featuring an AnMBR process with a 24-hour hydraulic retention time (HRT) and an AO process with HRT values and internal recycle changes. The AnMBR system exhibited consistent and high-performance biochemical oxygen demand (COD) elimination, approximately 80 ± 5 %. However, this system demonstrated low-efficiency removal of total nitrogen (TN) at about 20 ± 5 %, and total phosphorus (TP) 15 ± 5 %, under organic loading rates (OLR) of 0.6 to 1.3 kg-COD/(L·d). The AO process was then continually employed to improve the treatment efficacy (at HRT, 5 h in the anoxic phase, and 8.3 h in the oxic phase, at a recycling rate of 300 %) resulting in the final post-treatment concentrations of COD 27-41 mg/L (removal 98.3 ± 0.3 %), TN 12-25 mg/L (90 ± 2 %), and TP 18 ± 2 mg/L (35 ± 5 %). The performance of the integrated AnMBR-AO system met the established Vietnamese discharge standards for seafood processing wastewater, as outlined in QCVN 11-MT: 2015/BTNMT.

Nutrient removal and microbial community succession in moving bed biofilm reactor: Effects of influent carbon to nitrogen ratio fluctuation

This study investigated the nutrient removal and microbial community succession in moving bed biofilm reactor under stable and three levels of influent carbon/nitrogen (C/N) ratio fluctuation (± 10%, ± 20%, and ± 30%). Under the conditions of influent C/N ratio fluctuation, the removal efficiency of COD and PO43--P decreased 4.7-6.4% and 3.7-12.9%, respectively, while the nitrogen removal was almost unaffected. A sharp decrease in the content of culturable functional bacteria related to nitrogen and phosphorus removal including nitrite-oxidizing bacteria (NOB), aerobic denitrifying bacteria (DNB), and polyphosphate-accumulating organisms (PAOs) from the carrier biofilm was observed. Sequencing analysis revealed that the abundance of Candidatus Competibacter increased 10.3-25.9% and became the dominant genus responsible for denitrification, potentially indicating that nitrate was removed via endogenous denitrification under the influent C/N ratio fluctuation. The above results will provide basic data for the nutrient removal in decentralized wastewater treatment under highly variable influent conditions.

Food wastewater treatment using a hybrid biofilm reactor: nutrient removal performance and functional microorganisms on filler biofilm and suspended sludge

In this study, a laboratory-scale hybrid biofilm reactor (HBR) was constructed to treat food wastewater (FWW) before it is discharged into the sewer. The chemical oxygen demand (COD) of 29 860 mg L-1 in FWW was degraded to 200-350 mg L-1 using the HBR under the operating parameters of COD load 1.68 kg m-3 d-1, hydraulic retention time (HRT) of 426.63 h, dissolved oxygen (DO) of 8-9 mg L-1, and temperature of 22-23 °C. The biomass of biofilm on the surface of filler was 2.64 g L-1 for column A and 0.91 g L-1 for column O. Microbial analysis revealed richer and more diverse microorganisms in filler biofilms compared to those in suspended sludge. The hybrid filler was conducive to the development of functional microbial species, including phyla Firmicutes, Actinobacteriota, and Chloroflexi, and genus level norank_f_JG30-KF-CM45, which will improve FWW treatment efficiency. Moreover, the microorganisms on the filler biofilm had more connections and relationships than those in the suspended sludge. The combination of an up-flow anaerobic sludge bed (UASB) and HBR was demonstrated to be an economical strategy for practical applications as a shorter HRT of 118.34 h could be obtained. Overall, this study provides reliable data and a theoretical basis for the application of HBR and FWW treatments.

Optimizing carbon sources regulation in the biochemical treatment systems for coal chemical wastewater: Aromatic compounds biodegradation and microbial response strategies

The complex composition of coal chemical wastewater (CCW), marked by numerous highly toxic aromatic compounds, induces the destabilization of the biochemical treatment system, leading to suboptimal treatment efficacy. In this study, a biochemical treatment system was established to efficiently degrade aromatic compounds by quantitatively regulating the dosage of co-metabolized substrates (specifically, the chemical oxygen demand (COD) Glucose: COD Sodium acetate = 3:1, 1:3, and 1:1). The findings demonstrated that the system achieved optimal performance under the condition that the ratio of COD Glucose to COD Sodium acetate was 3:1. When the co-metabolized substrate was added to the system at an optimal ratio, examination of pollutant removal and cumulative effects revealed that the removal efficiencies for COD and total organic carbon (TOC) reached 94.61 % and 86.40 %, respectively. The removal rates of benzene series, nitrogen heterocyclic compounds, polycyclic aromatic hydrocarbons, and phenols were 100 %, 100 %, 63.58 %, and 94.12 %, respectively. Research on the physiological response of microbial cells showed that, under optimal ratio regulation, co-metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, the contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) for proteins in the optimal group were 7.12 mg/g-SS and 152.28 mg/g-SS, respectively. Meanwhile, the ratio of α-Helix / (β-Sheet + Random coil) and the proportion of intermolecular interaction forces were also increased in the optimal group. At system completion, the ratio of α-Helix / (β-Sheet + Random coil) reached 0.717 (LB-EPS) and 0.618 (TB-EPS), respectively. Additionally, the proportion of intermolecular interaction forces reached 74.83 % (LB-EPS) and 55.03 % (TB-EPS). An in-depth analysis of the metabolic regulation of microorganisms indicated that the introduction of optimal ratios of co-metabolic substrates contributed to a noteworthy upregulation in the expression of Catechol 2,3-dioxygenase (C23O) and Dehydrogenase (DHA). The expression levels of C23O and DHA were measured at 0.029 U/mg Pro·g MLSS and 75.25 mg TF·(g MLSS·h)-1 (peak value), respectively. Correspondingly, enrichment of aromatic compound-degrading bacteria, including Thauera, Saccharimonadales, and Candidatus_Competibacter, occurred, along with the upregulation of associated functional genes such as Catechol 1,2-dioxygenase, Catechol 2,3-dioxygenase, Protocatechuate 3,4-dioxygenase, and Protocatechuate 4,5-dioxygenase. Considering the intricate system of multiple coexisting aromatic compounds in real CCW, this study not only obtained an optimal ratio for carbon source addition but also enhanced the efficient utilization of carbon sources and improved the capability of the system to effectively degrade aromatic compounds. Additionally, this paper established a theoretical foundation for metabolic regulation and harmless treatment within the biochemical treatment of intricate systems, exemplified by real CCW.

New insights into nitrogen removal by divalent iron-enhanced moving bed biofilm reactor: Performance, interfacial interaction and co-occurrence network

A divalent iron-mediated moving bed biofilm reactor with intermittent aeration was developed to enhance the nitrogen removal at low carbon-to-nitrogen ratios. The study demonstrated thatammonia removal increased from 51 ± 4 % to 79 ± 4 % and nitrate removal increased from 72 ± 5 % to 98 ± 4 % in phases I-IV, and 2-5 mg·L-1 of divalent iron significantly increased the anoxic denitrification process. Divalent iron stimulated the secretion of extracellular polymeric substances, which facilitated the formation of cross-linked network between microbial cells. Furthermore, the cycle between divalent and trivalent iron decreased the energy barrier between the biofilm and the pollutant. The microbial community further revealed that Proteobacteria (relative abundance: 40-48 %) andBacteroidota(relative abundance: 31-37 %) were the dominant phyla, supporting the synchronous nitrification and denitrification processes as well as the lower accumulation of nitrite. In conclusion, iron redox cycling significantly enhanced the nitrogen removal. This study proposes a viable strategy for the efficient treatment of nutrient wastewater.