Environmental factors and microbial communities jointly regulate biological dephosphorization process in pond-ditch circulation systems (PDCSs) for rural wastewater treatment

How do glyphosate and AMPA alter the microbial community structure and phosphorus cycle in rice-crayfish systems?

Glyphosate, a commonly used organophosphorus herbicide in rice-crayfish cropping regions, may alter regional phosphorus cycle processes while affecting the structure of microbial communities. However, the effects of glyphosate residues on rice-crayfish systems remain unclear. In this study, we assessed the spatial and temporal distribution characteristics of glyphosate and its primary degradation products, as well as the impact mechanisms of glyphosate on microbial communities and the phosphorus cycle in rice-crayfish systems such as paddy fields, breeding ditches and recharge rivers. The detection rates of glyphosate and aminomethylphosphonic acid (AMPA) were 100% in rice-crayfish systems. Concentrations of glyphosate in the water phase and soil/sediment were as high as 0.012 μg/L and 7.480 μg/kg, respectively, and concentrations of AMPA were as high as 17.435 μg/L and 13.200 μg/kg, respectively. Glyphosate concentrations were not affected by rainfall or sampling site, but concentrations of AMPA in the water phase of recharge rivers were affected by rainfall. The glyphosate concentration was significantly and positively correlated with RBG-16-58-14 abundance, and the AMPA concentration was significantly and positively correlated with Actinobacteria and Lysobacter abundance, and negatively correlated with Cyanobacteria abundance (P < 0.05). The highest abundances of phoD, phnK, and ppx genes were found in all soils/sediments. Glyphosate concentration in soil/sediment was significantly and positively correlated with the abundance of phoD gene encoding an organophosphorus-degrading enzyme and ppx gene encoding poly inorganic phosphate (Pi) hydrolase (P < 0.05). In addition, the glyphosate concentration was significantly and positively correlated with the Ca-bonded Pi content (P < 0.05). This implies that glyphosate may promote the production of stable Pi in rice-crayfish systems by increasing the abundance of phoD and ppx genes. The results of this study reveal the impact mechanism of glyphosate on the phosphorus cycle in rice-crayfish systems and provide a basis for the risk assessment of glyphosate.

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.

Different microbial functional traits drive bulk and rhizosphere soil phosphorus mobilization in an alpine meadow after nitrogen input

Enhanced nitrogen (N) input is expected to influence the soil phosphorus (P) cycling through biotic and abiotic factors. Among these factors, soil microorganisms play a vital role in regulating soil P availability. However, the divergent contribution of functional microorganisms to soil P availability in the rhizosphere and bulk soil under N addition remains unclear. We conducted an N addition experiment with four N input rates (0, 5, 10, and 15 g N m-2 year-1) in an alpine meadow over three years. Metagenomics was employed to investigate the functional microbial traits in the rhizosphere and bulk soil. We showed that N addition had positive effects on microbial functional traits related to P-cycling in the bulk and rhizosphere soil. Specifically, high N addition significantly increased the abundance of most microbial genes in the bulk soil but only enhanced the abundance of five genes in the rhizosphere soil. The soil compartment, rather than the N addition treatment, was the dominant factor explaining the changes in the diversity and network of functional microorganisms. Furthermore, the abundance of functional microbial genes had a profound effect on soil available P, particularly in bulk soil P availability driven by the ppa and ppx genes, as well as rhizosphere soil P availability driven by the ugpE gene. Our results highlight that N addition stimulates the microbial potential for soil P mobilization in alpine meadows. Distinct microbial genes play vital roles in soil P availability in bulk and rhizosphere soil respectively. This indicates the necessity for models to further our knowledge of P mobilization processes from the bulk soil to the rhizosphere soil, allowing for more precise predictions of the effects of N enrichment on soil P cycling.

Metagenomics, metatranscriptomics, and proteomics reveal the metabolic mechanism of biofilm sequencing batch reactor with higher phosphate enrichment capacity under low phosphorus load

The biofilm sequencing batch reactor (BSBR) process has higher phosphate recovery efficiency and enrichment multiple when the phosphorus load is lower, but the mechanism of phosphate enrichment at low phosphorus load remains unclear. In this study, we operated two BSBR operating under low and high phosphorus load (0.012 and 0.032 kg/(m3·d)) respectively, and used metagenomic, metatranscriptomic, and proteomics methods to analyze the community structure of the phosphorus accumulating organisms (PAOs) in the biofilm, the transcription and protein expression of key functional genes and enzymes, and the metabolism of intracellular polymers. Compared with at high phosphorus load, the BSBR at low phosphorus load have different PAOs and fewer types of PAOs, but in both cases the PAOs must have the PHA, PPX, Pst, and acs genes to become dominant. Some key differences in the metabolism of PAOs from the BSBR with different phosphorus load can be identified as follows. When the phosphorus load is low, the adenosine triphosphoric acid (ATP) and NAD(P)H in the anaerobic stage come from the TCA cycle and the second half of the EMP pathway. The key genes that are upregulated include GAPDH, PGK, ENO, ppdk in the EMP pathway, actP in acetate metabolism, phnB in polyhydroxybutyrate (PHB) synthesis, and aceA, mdh, sdhA, and IDH1 in the TCA cycle. In the meantime, the ccr gene in the PHV pathway is inhibited. As a result, the metabolism of the PAOs features low glycogen with high PHB, Pupt, Prel, and low PHV. That is, more ATP and NAD(P)H flow to phosphorus enrichment metabolism, thus allowing the highly efficient enrichment of phosphorus from low concentration phosphate thanks to the higher abundance of PAOs. The current results provide theoretical support and a new technical option for the enrichment and recovery of low concentrations of phosphate from wastewater by the BSBR process.

Response of microbial community to different media in start-up period of Annan constructed wetland in Beijing of China

Microbial community, as the decomposers of constructed wetland (CW), plays crucial role in biodegradation and biotransformation of pollutants, nutrient cycling and the maintenance of ecosystem balance. In this study, 9 water samples, 6 sediment samples, and 8 plant samples were collected in Annan CW, which has the functions of water treatment and wetland culture park. The characteristics of microbial community structure in different media were illustrated by using of high-throughput sequencing-based metagenomics approach and statistical analysis. Meanwhile, this study identified and classified human pathogens in CW to avoid potential risks to human health. The results showed that dominant bacteria phyla in CW include Proteobacteria, Bacteroides, Actinobacteria, Firmicutes and Verrucomicrobia. The distribution of microorganisms in three media is different, but not significant. And the pH and DO profoundly affected microbe abundance, followed by water temperature. The microbial diversity in sediments is the highest, which is similar with the detection of human pathogens in sediments. Moreover, compared with Calamus, Lythrum salicaria and Reed, Scirpus tabernaemontani has fewer pathogenic microorganisms. The distribution of microorganisms in the CW is complex, and a variety of human pathogens are detected, which is more prone to create potential risks to human health and should receive additional attention.

Effect of anaerobic duration on biological phosphorus removal in reversed AAO process (anoxic-anaerobic-oxic)

In this study, the effect of anaerobic duration on phosphorus (P) removal in reversed AAO (anoxic-anaerobic-oxic) process was investigated using synthetic wastewater (with different volatile fatty acid (VFA) ratios) and real wastewater. The P, poly-hydroxyalkanoates (PHAs), dehydrogenase activity (DHA), polyphosphate kinases (PPK), electron transfer system (ETS), and adenosine 5'-triphosphate (ATP) were determined as indicators. The highest P removal efficiencies were achieved at an anaerobic duration of 3, 4, and 6 h for 15, 30, and 60% VFA ratio in synthetic wastewater. The amount of the released P and stored PHAs can be manipulated by different anaerobic durations, but the P removal efficiency cannot be guaranteed with higher stored PHAs. Additionally, the energy metabolism confirmed the significance of anaerobic duration extension on microbial activity. The highest values of four indicators were all achieved at anaerobic duration of 4 h with 30% VFAs ratio which achieved the highest P removal efficiency. Real wastewater experiments also proved the reproductivity of these results. We defined this phenomenon as the "hunger response" where microorganisms responded to suppression (anaerobic duration extension) with higher activity after the end of the anaerobic condition. These results can provide references for better design and operation of biological phosphorus removal in RAAO process.

Simultaneous nitrification and denitrification in a novel rotating self-aerated biofilm reactor for decentralized wastewater treatment

Decentralized wastewater pollution in rural areas has become a serious problem for the rural environment. In this study, a novel rotating self-aerated biofilm reactor was developed for decentralized wastewater treatment without any aeration equipment. After the long-term operation of 110 days, the removal efficiency reached to 96.06 % (COD), 98.06 % (NH₄⁺-N), and 62.58 % (TN) in the last phase. Under high dissolved oxygen level, the simultaneous nitrification-denitrification (SND) maintained at a stable ratio of 62.53 % and the denitrification rates reached over 28.37 mg/L/h. With the organic loading rate increased, key nitrogen functional bacterial communities such as anoxic denitrifiers (Thiothrix, Flavobacterium, Pseudoxanthomonas, Aquimonas and Azoarcus) and aerobic denitrifiers (Hydrogenophaga, Zoogloea and Terrimonas) increased obviously. Overall, microbial analysis and nitrogen metabolism pathway indicated that an integration of SND process was achieved in this single reactor by the combined action of nitrification, denitrification and comammox without any aeration equipment.

The Existing Recovery Approaches of the Huangjiu Lees and the Future Prospects: A Mini Review

Huangjiu lees (HL) is a byproduct in Chinese Huangjiu production with various nutrient and biological functional components. Without efficient treatment, it could cause environmental issues and bioresource wasting. Existing dominant recovery approaches focus on large-scale disposal, but they ignore the application of high-value components. This study discusses the advantages and limitations of existing resourcing approaches, such as feed, food and biogas biological production, considering the efficiency and value of HL resourcing. The extraction of functional components as a suggestion for HL cascade utilization is pointed out. This study is expected to promote the application of HL resourcing.

Microbial response to biogeochemical profile in a perpendicular riverbank filtration site

Due to extensive water exchanges and abundant active biochemical compositions, active and complex hydrogeochemical processes often exist in riverbank filtration (RBF). The distribution of microbes is considered to be profoundly affected by these processes and is considered to impact the hydrogeochemical processes and the migration and transformation of water pollutants in turn and then impact the water quality. The distribution of microbes and their response to the physiochemical properties along a vertical RBF profile perpendicular to the Songhua River in Northeast China was explored by using 16 S rRNA and redundancy analysis (RDA). The results showed that various microbes were found in the vertical riparian filter (RBF) curve, including Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, and Firmicutes. With increasing depth (vertical) and distance from the river (lateral), the microbial community and diversity in the RBF sediment profile decreased. Nitrospirota, Pseudomonas, Gammaproteobacteria, Ochrobactrum, Acinetobacter and Desulfobacterota of the RBF core taxa were also significantly correlated with the biotransformation behavior of typical groundwater pollutants (ammonia, Fe, Mn and S). The amount of As in the RBF is too low to sustain microbial survival. Some microbes in RBF can also degrade natural organic pollutants. This study not only revealed the spatial distribution of geological microbes under the impact of hydrological processes but also lays a foundation for the further study of the hydrobiogeochemical processes of active biochemical compositions in groundwater and water quality evolution, which is of positive significance to ensure the quality safety of the drinking water supplied by RBFs.

Effects of root exudates on rhizosphere bacteria and nutrient removal in pond-ditch circulation systems (PDCSs) for rural wastewater treatment

Pond-ditch circulation system (PDCS) is a promising remediation strategy for rural wastewater treatment. Aquatic plants play nonnegligible roles in the nutrient removal of the PDCS. However, mechanisms of root exudates regulating nutrient removal in PDCSs remained unclear. In our study, the PDCS achieved higher total nitrogen (TN) and phosphorus (TP) removal rates (72.7-97.4%) compared to the static system. Protein contents in root exudates of the PDCS ranged from 0.041 to 1.332 mg L^-1, showing negative associations with Simpson index. Lactic acid and tartaric acid in the PDCS varied from 0.045 to 0.380 mg L^-1 and 0.024 to 5.446 mg L^-1, which were tightly linked with TN, TP, and TP removal rates and most sediment properties, especially sediment total nitrogen (STN) and total organic carbon (TOC), and sediment inorganic phosphorus (SIP). Moreover, the top 3 relative dominant genus were Bacillus (0.11%-17.90%), Geobacter (0.35%-12.04%), and Clostridium sensu stricto 1 (0.14%-12.05%), which might be the predominant groups in nutrient removal of PDCSs. RDA results indicated that lactic acid, protein, and amino acids were positively correlated with Geobacter; while Bacillus was significantly affected by water content. Path analysis further demonstrated that the indirect effect of secretion from plant roots on nutrient removal rates was mainly through modulating bacteria diversity and relative abundance. Taken together, root exudates, especially protein, amino acids, and lactic acid, altered rhizosphere microbial relative abundance and diversity, where the impacts were bacterial species-dependent.