Effect of asparagine, corncob biochar and Fe(II) on anaerobic biological treatment under low temperature: Enhanced performance and microbial community dynamic

Effects of microplastics accumulation and antibiotics contamination in anaerobic membrane bioreactors for municipal wastewater treatment

Municipal wastewater treatment plants are the main collection points for plastics and antibiotics. Anaerobic membrane bioreactor (AnMBR) is one the most potential municipal wastewater treatment technologies. This study evaluated the impact of microplastic (aged polyvinyl chloride, aged PVC, 1.5 g/L), antibiotics (ciprofloxacin, CIP, 100 μg/L) and their interaction effect on AnMBR treatment performance and membrane fouling. Results showed that the inhibition of CIP on AnMBR organic removal and methane production was intensified, owing to the CIP adsorption on aged PVC. The enzyme activities of electron transport (ETS), adenosine triphosphate (ATP) and F420 were also significantly restrained by 47-52 % with combined exposure. The combined effects also significantly aggravated the membrane fouling of AnMBR, which shorted the membrane operational period by half due to more soluble microbial products (SMP) secretion. The microbial diversity analyses indicated that aged PVC and CIP addition can accumulate some main anaerobic fermentation bacteria but inhibit the archaea. The abundance of related enzyme in the acetoclastic and hydrogenotrophic methanogenesis decreased with the sole aged PVC and CIP addition and severely inhibited with their combine effect. The absolute abundance mcrA significantly reduced by 92 % with combined exposure, validating the negative impact on methanogenic activity. These findings provide valuable insight into the AnMBR implementation in complex wastewater treatment.

The mechanism and prospect of exogenous promoters enhancement Anammox at low temperatures: a review

The anaerobic ammonium oxidation (Anammox) process has revolutionized nitrogen removal in wastewater treatment with its exceptional cost-effectiveness and carbon-neutral characteristics. Nevertheless, the intrinsic psychrophilic sensitivity of anaerobic ammonium-oxidizing bacteria (AnAOB), particularly their rapid metabolic suppression below 15 °C, poses a critical bottleneck for sustainable implementation in cold-climate regions. Recent advancements in exogenous stimulation strategies offer promising solutions to this challenge, with particular emphasis on iron supplementation and cryogenic activity regulators (CARs) due to their non-invasive operational compatibility and mechanistic versatility. This review provides a comprehensive analysis of the operational performance, functional enzyme activity, and microbial abundance associated with the use of iron and CARs as exogenous promoters in low-temperature Anammox system. Building upon current limitations in single-factor approaches, the dual-modulation strategy integrating iron-chelated CARs complexes are proposed, which leverages the complementary benefits of iron-mediated metabolic activation and CARs-induced cryoprotection, potentially enabling year-round Anammox operation under low temperatures. This mechanistic-to-applied review provides critical insights for advancing Anammox implementation in circular economy-driven wastewater infrastructures under climate change scenarios.

Improved anaerobic digestion of food waste under ammonia stress by side-stream hydrogen domestication

High ammonia concentration inhibits archaea's activity, causing the accumulation of H2 and acetate, which suppresses methane production in anaerobic digestion (AD). The study aimed to enhance microbial hydrogen metabolism through a side-stream hydrogen domestication (SHD) strategy, which involves applying hydrogen stimulation to a portion of the sludge separately. SHD maintained a stable methane yield of 407.5 mL/g VS at a high total ammonia nitrogen (TAN) concentration of 3.1 g/L. In contrast, the control group gradually decreased and stopped methane production at a TAN concentration of 2.3 g/L. Further analysis using enzyme activity assays, flow cytometry, and metagenomics explored the mechanisms underlying ammonia tolerance of SHD-treated group. SHD reshaped the microbial community, enriching homoacetogens and Methanosaeta-dominated methanogenic archaea. Key metabolic pathways including homoacetogenesis, butyrate degradation, propionate degradation, and methane production were enhanced. The activity of related enzymes also increased. Gene abundance in energy-generating pathways, such as glycolysis, was enhanced, ensuring adequate ATP production. Additionally, the high gene abundance of ion transport systems contributed to regulating proton imbalance and supplementing intracellular K+. This study provides important insights and practical guidance for developing novel techniques in the field of anaerobic digestion.

Enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation with addition of red mud: Performance and mechanisms

Red mud (RM) as hazardous waste produced from aluminum refining industry has threatened the environment and human health. In this study, RM was added into the fermenter to promote short chain fatty acids (SCFAs) production from waste activated sludge (WAS) anaerobic fermentation. Results showed that the addition of RM could effectively improve the SCFAs production, especially, acetic acid. In particular, the production of total SCFAs and acetic acid in 20 g/L RM added fermenter were 1108.1 mg COD/L and 415.5 mg COD/L, which were 116.0% and 1308.0% higher than that in control fermenter. Batch experiment revealed that RM could enhance the hydrolysis and acidification process. Further study indicated that the activity of enzyme related to hydrolysis-acidification, abundance of fermentative bacteria for SCFAs production and functional metabolism genome were all improved with the addition of RM. The potential mechanism maybe that the RM promoted the hydrolysis-acidification process with the contained varies Fe(Ⅲ) oxides as electron acceptor, and the produced Fe2+ could serve as necessary trace elements to synthesize enzyme and then stimulate the expression of enzyme genes.

Removal of organic matter from food wastewater using anaerobic digestion at low temperatures enhanced by exogenous signaling molecule N-hexanoyl-homoserine lactone enhancement: Insight to extracellular polymeric substances and key functional genes

This experiment aimed to study the effects of adding the exogenous signaling molecule N-hexanoyl-homoserine lactone (C6-HSL) on the anaerobic digestion of food wastewater at low temperature (15 °C). Daily addition of 0.4 μmol C6-HSL increased the average chemical oxygen demand removal from 45.98% to 94.92%, while intermittent addition (adding 2 μmol C6-HSL every five days) increased it from 45.98% to 72.44%. These two modes of C6-HSL addition increased protease and acetate kinase activity by 47.99%/8.04% and 123.26%/127.91% respectively, and increased coenzyme F420 concentrations by 15.79% and 63.16%, respectively. The regulation of loosely bound extracellular polymeric substances synthesis was influenced by C6-HSL, which increased protein and polysaccharide content in sludge. The relative abundance of Firmicutes and Bacteroidetes increased following addition of C6-HSL. After continuous addition of C6-HSL, the relative abundance of related functional genes such as amy, apgM, aceE, and accC increased, indicating that methanogens obtained sufficient substrate. The abundance of glycolysis-related functional genes such as glk, pfk, pgi, tpiA, gap, pgk, gpmA, eno, and pyk increased after the addition of C6-HSL, ensuring the efficient transformation and absorption of organic matter by anaerobic sludge at low temperatures. This study provides new comprehensive insights into the mechanism behind the enhancement of food wastewater anaerobic digestion by C6-HSL at low temperature.

Evaluation of ecological impacts with ferrous iron addition in constructed wetland under perfluorooctanoic acid stress

In this study, ferrous ion (Fe(II)) had the potential to promote ecological functions in constructed wetlands (CWs) under perfluorooctanoic acid (PFOA) stress. Concretely, Fe(II) at 30 mg/L and 20-30 mg/L even led to 11.37% increase of urease and 93.15-243.61% increase of nitrite oxidoreductase respectively compared to the control. Fe(II) promotion was also observed on Nitrosomonas, Nitrospira, Azospira, and Zoogloea by 1.00-6.50 folds, which might result from higher expression of nitrogen fixation and nitrite redox genes. These findings could be explanation for increase of ammonium removal by 7.47-8.75% with Fe(II) addition, and reduction of nitrate accumulation with 30 mg/L Fe(II). Meanwhile, both Fe(II) stimulation on PAOs like Dechloromonas, Rhodococcus, Mesorhizobium, and Methylobacterium by 1.58-2.00 folds, and improvement on chemical phosphorus removal contributed to higher total phosphorus removal efficiency under high-level PFOA exposure. Moreover, Fe(II) raised chlorophyll content and reduced the oxidative damage brought by PFOA, especially at lower dosage. Nevertheless, combination of Fe(II) and high-level PFOA caused inhibition on microbial alpha diversity, which could result in decline of PFOA removal (by 4.29-12.83%). Besides, decrease of genes related to nitrate reduction demonstrated that enhancement on denitrification was due to nitrite reduction to N2 pathways rather than the first step of denitrifying process.

Enhancement of methane production from anaerobic digestion of Erigeron canadensis via O2-nanobubble water supplementation

Malignant invasive Erigeron canadensis, as a typical lignocellulosic biomass, is a formidable challenge for sustainable and efficient resource utilization, however nanobubble water (NBW) coupled with anaerobic digestion furnishes a prospective strategy with superior environmental and economic effectiveness. In this study, influence mechanism of various O2-NBW addition times on methanogenic performance of E. canadensis during anaerobic digestion were performed to achieve the optimal pollution-free energy conversion. Results showed that supplementation of O2-NBW in digestion system could significantly enhance the methane production by 10.70-16.17%, while the maximum cumulative methane production reached 343.18 mL g-1 VS in the case of one-time O2-NBW addition on day 0. Furthermore, addition of O2-NBW was conducive to an increase of 2-90% in the activities of dehydrogenase, α-glucosidase and coenzyme F420. Simultaneously, both facultative bacteria and methanogenic archaea were enriched as well, further indicating that O2-NBW might be responsible for facilitating hydrolytic acidification and methanogenesis. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) cluster analysis, provision of O2-NBW enhanced the metabolism of carbohydrate and amino acid, translation as well as membrane transport of bacteria and archaea. This study might offer the theoretical guidance and novel insights for efficient recovery of energy from lignocellulosic biomass on account of O2-NBW adhibition in anaerobic digestion system, progressing tenor of carbon-neutral vision.

Modified basalt fibers boost performance of constructed wetlands: Comparison between surface coating and chemical grafting

Modified basalt fiber (MBF) is a potential material that has been applied in wastewater treatment fields. In this study, superior performances of MBFs by calcium (Ca-MBF) and polyethyleneimine modification (PEI-MBF) were compared in constructed wetlands (CWs). Via chemical grafting, higher biofilm contents were observed on the surface of PEI-MBF, compared to Ca-MBF. Moreover, MBF increased key enzyme activities particularly in lower substrate layer, contributing to positive responses of microbial community in CWs. For instance, PEI-MBF boosted microbial richness and diversity and improved the abundances of denitrifying functional bacteria and biomarkers like Thauera, Vulcanibacillus, and Maritimimonas, probably promoting nitrate removal compared with Ca-MBF group. By contrast, Ca-MBF enriched more functional genera involved in nutrients removal, with the highest removal of ammonium (43.9 %), total nitrogen (66.2 %), and total phosphorus (37.1 %). Overall, this work provided new findings on improved performance of CWs with MBF.

Performance and microbial metabolic mechanism of imidacloprid removal in a microbial electrolysis cell-integrated adsorption biological coupling system

Coke used as a filler to treat imidacloprid (IMI) wastewater by both adsorption biological coupling and microbial electrolysis cells (MEC)-adsorption biological coupling technologies, the removal efficiencies on pollutions in wastewater containing IMI were investigated, and the key functional genes related to IMI degradation pathways were also revealed. Results showed that the removal rates of COD, ammonia nitrogen, TP, and IMI under the adsorption biological coupling treatment and MEC-adsorption biological coupling treatment were 94.61-95.54%, 93.37-95.79%, 73.69-83.80%, and 100%, respectively. MEC increased the relative abundance of Proteobacteria by 9.01% and transformed the dominant bacteria from Lysobacter and Reyranella to Brevundimonas and Aquincola. Moreover, MEC up-regulated the abundance of the coding genes PK (9.30%), narG (2.26%), pstS (3.63%), and phnD (1.32%), and converted the IMI degradation products to smaller molecular weight C6H8N2 and C6H6ClNO. This study provided an important reference information for efficient treatment of IMI wastewater using the MEC-adsorption biological coupling technology.

A review of application of combined biochar and iron-based materials in anaerobic digestion for enhancing biogas productivity: Mechanisms, approaches and performance

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application.

Ultrasonic-assisted hypochlorite activation accelerated volatile fatty acids production during sewage sludge fermentation: Critical insights on solubilization/hydrolysis stages and microbial traits

The effective disruption of extracellular polymeric substances using appropriate pretreatment is critical to achieving resource recovery from sewage sludge (SS) by anaerobic fermentation. This work proposed an ultrasonic-assisted hypochlorite activation strategy for enhanced production of volatile fatty acids (VFAs) during SS fermentation. The results demonstrated that after individual ultrasonic and hypochlorite pretreatment, the maximum VFAs yield improved by 8 and 107% with that in control, respectively, while a combination of both techniques led to an improvement of 119%, indicating their synergistic effects on SS fermentation. This method enhanced the solubilization and hydrolysis efficiencies and contributed to the increased biodegradable substrates, which would be beneficial in enhancing microbial activity for VFAs production. The functional anaerobes, metabolic pathways, and gene expressions involved in VFAs biosynthesis were effectively improved. This work would bring a novel insight into the disposal of municipal solid waste for resource recovery.

Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response

Polycyclic aromatic hydrocarbons (PAHs) pose a high risk to ecosystems owing to their adverse environmental effects. The use of biochar in constructed wetlands (CWs) to remove PAH has received increased interest, but is frequently challenging because of saturation adsorption. To enhance the microbial degradation, electron acceptors are provided. This study aimed to remove a representative PAH, benzofluoranthrene (BbF), using iron-modified biochar as a supplement to the CW substrate. Results revealed that iron-mediated biochar based CWs increased the removal of BbF by 20.4 % and ammonium by 25.6 %. The BbF retained in substrate with biochar (36.6 % higher content) and further removed with iron modification (40.6 % lower content). Iron-modified biochar increased dissolved organic carbon content, particularly low-aromaticity, and low-molecular-weight organic matters (25.7 % higher tryptophan-like material), which contributed to PAH degradation by microorganisms. Microbial analysis confirmed that iron-mediated biochar enriched the abundance of microbes (e.g., Cellulomonas, Actinotalea, and Sphingomonas) and key enzymes (e.g., catA, lipV, and sdhA) that are involved in PAH degradation. Higher proportion of iron-reducing bacteria (e. g., Thiobacillus, Rhodobacter) played a significant role in driving microbial iron cycle, which was beneficial for PAHs removal. Based on the results, we confirmed that the use of iron-modified biochar in CWs enhance PAH removal.