Search Results (101)

Constructed wetlands operated in plateau habitats may experience constrained biological treatment because low temperature, low atmospheric pressure, and low-carbon wastewater can jointly limit microbial metabolism. This 80-day pilot screening study evaluated three nonreplicated modular constructed wetland configurations (MCW1-MCW3) containing different sequences of zeolite, ceramsite, and quartz sand and planted with Veronica anagallis-aquatica. Each configuration consisted of one independent treatment train; therefore, the comparisons were interpreted as configuration-specific and exploratory rather than as statistically generalizable treatment effects. Pollutant-removal performance and microbial community succession were evaluated through repeated water-quality monitoring and 16S rRNA gene sequencing. MCW1 showed the highest observed mean NH₄⁺-N removal efficiency (88.6%), whereas MCW3 showed the highest observed mean TP and COD removal efficiencies (79.56% and 47.40%, respectively) and an NH₄⁺-N removal efficiency of 85.51%. TN removal by MCW3 remained limited at 20.49%, consistent with carbon limitation of denitrification. Under the naturally low-temperature plateau laboratory conditions, the observed COD reduction indicated partial mineralization or retention of organic pollution loads, potentially supported by substrate biofilms and cold-adapted microbial assemblages. Apparent module-contribution analysis suggested that zeolite contributed substantially to NH₄⁺-N reduction, whereas ceramsite contributed to TP and COD removal under the tested sequences. Because plant biomass and tissue nutrient contents were not measured, nitrogen and phosphorus removal could not be attributed quantitatively to hydrophyte uptake. Overall, substrate sequence influenced pollutant-removal patterns and microbial community assembly, providing preliminary evidence for habitat-adapted optimization of modular constructed wetlands for plateau domestic wastewater. Full article

Biological nitrogen removal is often inhibited under low-temperature conditions due to reduced microbial activity and impaired metabolic processes. A novel cold-resistant bacterium, Acinetobacter pragensis FX1, was isolated and exhibited efficient nitrogen removal capacity across a broad temperature range of 5–30 °C. Notably, strain FX1 remained metabolically active at 5 °C, with a specific growth rate of 0.04 h⁻¹ and a generation time of 18.09 h, demonstrating excellent cold-resistant capability. Under ideal operating conditions (sodium citrate as carbon source, C/N ratio of 10, pH 7, and a shaking speed of 150 rpm) at 10 °C, removal efficiencies of NH₄⁺-N, NO₃⁻-N, and NO₂⁻-N reached 99.39%, 81.30%, and 99.78%, respectively. Nitrogen balance analysis, combined with genome annotation, revealed that nitrogen assimilation was the predominant pathway, thereby avoiding the potential for greenhouse gas (N₂O) generation. Genes associated with cold shock response and fatty acid biosynthesis supported the maintenance of membrane stability and the sustainability of metabolic activity under cold stress. Furthermore, bioaugmentation with strain FX1 successfully improved nutrient removal performance at 10 °C, driven by synergistic interactions with indigenous microbial communities. Overall, these results demonstrate the potential of strain FX1 as a promising candidate for enhancing biological nitrogen removal performance in cold-region wastewater treatment. Full article

To explore a new approach to reducing the use of external carbon sources and phosphorus removal chemicals in conventional wastewater treatment, this study developed an anaerobic–oxic–anoxic sequencing batch reactor (AOA-SBR) system (Rf) with iron shavings addition (180 g, 60 g/L), using a blank reactor (R0) as the control. Synthetic wastewater with a C/N ratio of 7.5 was used as the influent. The operating cycle of the AOA-SBR reactor consisted of a 120 min anaerobic phase, a 120 min aerobic phase, and a 60 min anoxic phase, with a hydraulic retention time (HRT) of 12 h. Results showed that the SVI₃₀ of Rf remained at approximately 35 mL/g. The average removal efficiencies of TN and TP in Rf reached 70% and 96%, respectively, which were higher than those of the control. The addition of waste iron shavings improved sludge settleability and nitrogen and phosphorus removal performance of the biochemical system. Fe-C microelectrolysis significantly enriched Candidatus_Competibacter and Candidatus_Nitrocosmicus while inhibiting nitrite-oxidizing bacteria (NOB). This triggered persistent low-level nitrite accumulation within the system, diversified nitrogen-removal pathways, and ultimately improved the total nitrogen-removal efficiency. The extended anaerobic period in the anaerobic–oxic–anoxic (AOA) mode enriched phosphate-accumulating organisms, achieving synergistic chemical and biological phosphorus removal. This study provides a novel strategy for advanced wastewater treatment without external carbon sources or phosphorus additives. Full article

A pilot-scale moving-bed biofilm reactor (MBBR), operated under alternating intermittent aeration (IA) and non-aeration phases, was used for single-stage carbon (C) and nitrogen (N) removal from high-fluctuating municipal wastewater via simultaneous nitrification–denitrification. The reactor was operated under highly variable chemical oxygen demand to total nitrogen (COD/TN) ratios, low dissolved oxygen (DO) conditions, and progressively extended non-aerated periods to evaluate process robustness under real operational conditions. An active denitrifying biofilm developed on the carriers after 23 days of the anoxic start-up, as confirmed by batch activity tests. Under the most carbon-limited condition tested (COD/TN = 5.5), the application of 16 h·d⁻¹ of non-aerated phases at DO levels of 0–1.0 mg·L⁻¹ enabled simultaneous COD, N–NH₄⁺ and TN removal efficiencies of 70, 95 and 84%, respectively. These results confirm that transient IA is an effective strategy for simultaneous C and N removal at very low COD/TN ratios and real fluctuating influent concentrations. Energy assessment showed that extended non-aeration phases reduced blower energy demand by 67% and total plant energy consumption by 34%, improving the environmental sustainability of the single-stage process. The main novelty of this study lies in the pilot-scale validation of an IA-MBBR for SND using real municipal wastewater under naturally fluctuating C and N loadings, thereby bridging previous laboratory-scale evidence with realistic operating conditions. Full article

Ammonium nitrogen pollution presents a significant challenge in wastewater treatment. Traditional activated sludge processes often suffer from limitations such as low efficiency and high energy consumption when treating high-ammonium nitrogen wastewater. This study utilized previously screened high-efficiency heterotrophic nitrification aerobic denitrification (HN-AD) bacterial strains (Pseudomonas alcaliphila and Paracoccus versutus) synergistically with microalgae to construct an immobilized bacteria algae symbiotic system (IBAS). The nitrogen removal performance and microbial community response of the system were investigated under different nitrogen sources, carbon to nitrogen (C/N) ratios, and light intensities. Results demonstrated that the system achieved a removal rate of over 95% for nitrite and nitrate. Under conditions of C/N = 15 and high light intensity (335.36 μmol/(m² · s)), the removal rates of NH₄⁺-N, TN, and COD exceeded 90% without nitrite accumulation. Microbial community analysis revealed that high C/N conditions significantly enriched HN-AD functional bacteria (such as Acinetobacter) in the Pseudomonadota phylum and Gammaproteobacteria class. High light intensity promoted the proliferation of microalgae (Chlorella and Halochlorella), enhanced algal bacterial interaction, and improved system stability. This study elucidated the nitrogen removal mechanism of the IBAS under multi-factor regulation, providing a theoretical foundation and demonstrating application potential for low-carbon and high-efficiency wastewater treatment technologies. Full article

The challenge of attaining energy–efficient nitrogen removal at low carbon–to–nitrogen (C/N) ratios is a fundamental issue in the sustainable management of municipal wastewater treatment plants (WWTPs). This study investigates a pilot–scale Anaerobic–Swing–Anoxic–Oxic (ASAO) system coupled with an AvN (Ammonia versus NOx⁻–N)–based aeration control strategy. A systematic evaluation of the system’s performance, nitrogen removal mechanisms, and microbial communities under a 350–day long–term pilot–scale operation using real municipal sewage is presented. The results reveal that the AvN control strategy can optimize aeration intensity and enhance nitrogen removal efficiency. Even under low influent C/N conditions, the ASAO system maintained stable operation with low dissolved oxygen levels (0.5–1.5 mg L⁻¹), and the AvN control strategy effectively optimized aeration intensity and stabilized nitrogen conversion, achieving a total nitrogen (TN) removal rate of 83% and an average effluent TN concentration of 4.9 ± 2.6 mg L⁻¹. Mechanistic analysis indicated that AvN regulation could alleviate over–nitrification and enhance intracellular carbon storage, thereby creating conditions that support the coordinated operation of multiple nitrogen removal routes, such as simultaneous nitrification–denitrification (SND), endogenous denitrification (EnD), and potentially anaerobic ammonium oxidation (anammox). These findings suggest that the AvN–controlled ASAO process offers a robust and scalable strategy for achieving high–efficiency nitrogen removal with reduced aeration demand, providing a promising technological pathway toward energy–neutral and sustainable municipal wastewater treatment. Full article

To address the bottleneck of poor biological nitrogen removal efficiency caused by the extremely low carbon-to-nitrogen (C/N) ratio of domestic sewage in alpine plateau regions, this study used Hordeum vulgare var. coeleste L., a characteristic crop endemic to the Qinghai–Tibet Plateau, as raw material and adopted pretreated highland barley straw as an external carbon source. Three parallel experiments were carried out using the anaerobic–aerobic–anoxic sequencing batch reactor (AOA-SBR) process to investigate the nitrogen removal performance and functional succession of the microbial community in the AOA-SBR system under three C/N ratio ranges: 5~7, 7~9, and 9~11. The results showed that the addition of an external carbon source significantly improved nitrogen removal efficiency. The optimal C/N ratio range for nitrogen removal in this study was determined to be 7~9. A weakly alkaline environment was conducive to denitrification. The fermentation broth prepared by alkali pretreatment contained a large amount of readily biodegradable organic matter with low toxicity, and achieved excellent nitrogen removal performance, helping to realize cost reduction and efficiency improvement in wastewater treatment. At the optimal C/N ratio of 7~9, the average removal efficiencies of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) reached 94.46% and 61.32%, respectively, which were significantly improved compared with the blank control group without external carbon addition. During the experimental period, no obvious changes were observed in microbial abundance at the phylum level, whereas the community structure at the genus level responded significantly to the addition of a straw carbon source. Among them, genera with specific degradation capabilities for straw hydrolysates, such as norank_f__Chitinophagaceae and unclassified_f__Comamonadaceae, were highly sensitive to variations in the C/N ratio. These genera could partially replace the nitrification and denitrification functions of other microorganisms and played a key role in the nitrogen removal process. In contrast, Thauera, a typical conventional heterotrophic denitrifier, showed no significant response to changes in the C/N ratio, indicating that the straw-based external carbon source mainly affected microbial genera with specific hydrolysate-degrading functions. Full article

Although numerous studies have focused on the potential application of heterotrophic nitrification–aerobic denitrification (HNAD) bacteria in wastewater treatment, research exploring their potential in aquaculture biofloc systems remains limited. In this study, a promising HNAD strain, identified as Stutzerimonas stutzeri MJ20, was isolated from mature biofloc. This strain efficiently utilized low-cost carbon sources (e.g., glucose) and small-molecule carbon sources (e.g., sodium acetate and sodium succinate). Under conditions with glucose as the carbon source, a carbon-to-nitrogen (C/N) ratio of 15, pH 6–9, temperature 25–35 °C, salinity 0–35‰, and shaker speed of 0–150 rpm, it achieved removal rates of 95–100% for NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N at initial concentrations of 100 mg/L each. Even at higher concentrations (up to 200 mg/L NH₄⁺-N and 500 mg/L for both NO₂⁻-N and NO₃⁻-N), removal rates exceeded 99%. Under mixed nitrogen sources, strain MJ20 demonstrated efficient nitrogen removal, preferentially utilizing NH₄⁺-N, with only minimal and transient accumulation of nitrite and nitrate. Genomic analysis revealed that MJ20 carries key denitrification genes, including napA, nirS, norB and nosZ, and possesses complete pathways for nitrate reduction to nitrogen gas and ammonia assimilation, although typical autotrophic nitrification genes were not detected. Combined genomic data and autotrophic culture experiments indicated that, in addition to utilizing various organic carbon sources, the strain also exhibited certain autotrophic growth capabilities. Furthermore, MJ20 showed strong flocculation ability (flocculation rate > 96% within 16 h), sensitivity to multiple common antibiotics, and no toxicity to zebrafish, demonstrating favorable biosafety. In simulated seawater aquaculture wastewater with a C/N ratio of 5, it achieved a total nitrogen removal rate exceeding 94% within 72 h. These results indicate that strain MJ20 possesses comprehensive advantages, including efficient nitrogen removal, broad carbon source adaptability, strong environmental resilience, minimal accumulation of intermediate nitrogen products, excellent flocculation ability, and high biosafety. These traits highlight its potential for application in biofloc systems and in treating aquaculture tail water with a low C/N ratio. This study provides theoretical insights and practical guidance for screening HNAD bacteria suitable for biofloc systems. Full article

The widespread presence of ciprofloxacin (CIP) in aquatic environments threatens ecological and public health, yet conventional treatment processes fail to remove such persistent contaminants. Conventional solvothermal synthesis of Bi-doped g-C₃N₄ photocatalysts involves complicated procedures and low productivity. Herein, we employ a single-step, template-free and solvent-free green calcination method to construct Bi³⁺-modified g-C₃N₄ with strong Bi-N coordination interactions. A series of Bi/g-C₃N₄ photocatalysts with Bi-doping mass ratios of 0.09–0.34 wt% was prepared, and the structure–performance relationship as well as the surface–interface reaction mechanism for ciprofloxacin (CIP) degradation were systematically elucidated. Experimental results confirm that Bi³⁺ incorporates into the lattice via Bi-N coordination bonds with nitrogen in the g-C₃N₄ framework, which narrows the band gap, suppresses photogenerated carrier recombination, and constructs a loose porous morphology beneficial for increasing specific surface area and active sites. Under optimal conditions, 15Bi/g-C₃N₄ achieves 97.6% degradation of 15 mg L⁻¹ CIP within 90 min, which is 13.7% higher than that of pristine g-C₃N₄. The effects of catalyst dosage, initial pH, CIP concentration, common coexisting ions, and different real water matrices on the degradation performance were systematically investigated. Radical quenching experiments combined with ESR characterization confirm that h⁺ is the dominant reactive species responsible for CIP degradation. This green, simple and scalable method yields uniform products, and the resulting materials exhibit high efficiency, economic feasibility and environmental safety, demonstrating promising potential for antibiotic wastewater treatment. Full article

Landfill leachate membrane concentrate (LLMC) is a high-salinity and high-organic wastewater stream that poses significant treatment challenges to conventional evaporation technologies. This study investigated the treatment performance and operating costs of a low-temperature atmospheric evaporation (LTAE) system for LLMC treatment under mild operating conditions. The effects of key operational parameters—including evaporation temperature (60–95 °C), pH (5–11), air–liquid mass ratio (A/L = 0.5–10), and concentration factor (CF = 5–20)—were systematically evaluated based on condensate quality parameters (UV₂₅₄, COD_Cr, and NH₃–N). Results demonstrated that the LTAE system achieved a higher concentration ratio (CF = 20) compared to the on-site mechanical vapor compression (MVC) system (CF ≈ 10). The optimal operating conditions for meeting effluent discharge standards were determined to be 70 °C, pH: 5, A/L = 5 and CF = 20. Under these conditions, the condensate contained ~5.6 mg/L NH₃–N and ~91.6 mg/L COD_Cr, while the concentrate reached ~4200 mg/L NH₃–N and ~38,000 mg/L COD_Cr, indicating that some organic matter and ammonia nitrogen escaped from the system and a gas scrubbing unit is recommended to minimize secondary pollution. Within the experimental range, the system achieved the highest K_cA = 22,871.25 kW/(m³·°C) and the highest K_dA reached 6.52 kg/m³·s. Economic analysis revealed a specific energy consumption of 110.5 kWh/t of freshwater produced. Despite the relatively high energy consumption, the LTAE system demonstrates considerable potential for the advanced treatment of high-organic wastewater, offering enhanced freshwater recovery under mild thermal conditions. This study provides theoretical and data support for the application of LTAE technology in LLMC treatment and similar challenging organic wastewater. Full article

Swine wastewater is a high-strength agricultural effluent characterized by high organic loading, elevated ammonium nitrogen and phosphorus concentrations, and frequently low C/N ratios, which make simultaneous pollutant removal and resource recovery challenging. Conventional physicochemical, anaerobic, and aerobic treatment technologies are widely used, but they are often constrained by high energy demand, ammonia inhibition, insufficient nitrogen recovery under low C/N conditions, and limited resource valorization. This review comparatively evaluates these conventional technologies alongside microalgal and algal–bacterial symbiotic (ABS) systems for swine wastewater treatment and resource recovery. Particular attention is given to algal–bacterial interactions, oxygen and carbon exchange, nitrogen and phosphorus removal pathways, reactor configurations, key operational parameters, and biomass valorization routes. The reviewed evidence shows that conventional anaerobic–aerobic systems generally achieve stable COD removal (>80%) but often provide limited nitrogen recovery, whereas microalgal systems can remove 80–90% of nitrogen and phosphorus but remain restricted by ammonia toxicity, light attenuation, and biomass harvesting costs. Under optimized conditions, ABS granular systems have achieved >90% COD removal, >80% total nitrogen removal, and 70–95% total phosphorus removal, while also improving biomass settleability and process stability. Overall, ABS systems offer a promising route to shift swine wastewater treatment from discharge-oriented pollution control toward resource-oriented management. Future research should prioritize reactor scale-up, long-term operational stability, biological monitoring, and economically viable biomass valorization. Full article

The removal of nitrogen and phosphorus from wastewater with low organic carbon content requires the addition of an external carbon source. The objective of this study was to assess the influence of hydraulic retention time (HRT) on the efficiency of external carbon source utilization and on nitrogen and phosphorus removal in a Rotating Electro-Biological Disc Contactor (REBDC). The energy demand was evaluated based on energy consumption (E) and current efficiency (CE). Hydroponic tomato wastewater was treated in the REBDC at a constant current density of 2.5 A/m². Sodium acetate was used as the carbon source. Two C/N ratios were tested, 2.0 and 3.0, under HRT conditions of 24 h and 48 h. For both C/N ratios, extending the HRT resulted in decreased nitrogen removal efficiency. At HRT = 48 h and C/N = 3.0, the nitrogen concentration in the effluent was more than three times lower compared with C/N = 2.0. The highest phosphorus removal efficiency was achieved at C/N = 3.0 and HRT = 48 h (98.8%). Increasing the HRT led to reduced TOC utilization for both C/N ratios. As a consequence of extended HRT, lower CE values and higher E values were observed, indicating increased energy demand for nutrient removal. Full article

Developed by Marais and Rabinowitz, the A²/O process is a pivotal biotechnology for biological nitrogen and phosphorus removal, developed by optimizing the five-stage Phoredox protocol. Renowned for its efficient configuration and straightforward operation, it has been extensively adopted in municipal and industrial wastewater treatment projects globally, including numerous facilities in China. However, the conventional A²/O process faces inherent operational challenges: the conflicting SRT requirements between autotrophic nitrifying bacteria (needing long SRT for stable nitrification) and PAOs, intense competition for carbon sources among PAOs and denitrifying bacteria, and the inhibitory effects of residual nitrate and DO on phosphorus release and denitrification. To address these issues, a range of optimization strategies has been developed, including SRT adjustment, carbon source distribution optimization, the integration of biofilm carriers, the addition of external carbon sources, and innovative modified configurations such as the Reversed A²/O, JHB, UCT, and MUCT. These approaches synergistically mitigate nitrate interference and enhance nutrient removal efficiency by decoupling microbial SRT demands, supplementing readily biodegradable carbon sources, and optimizing hydraulic flow paths. Future research should focus on deepening the understanding of the metabolic mechanisms underlying nitrogen and phosphorus removal, developing sustainable and efficient external carbon source systems, refining multi-mode reactor design for engineering scalability, optimizing combined processes for ultra-low C/N ratio wastewater treatment, and advancing low-temperature adaptation technologies. These efforts aim to further improve the process’s efficacy, stability, and sustainability, enabling it to meet increasingly stringent environmental discharge standards. Full article

Increasing demands for improved energy efficiency and resource recovery in wastewater management have driven intensified research on microalgal–bacterial consortia (M-BC). This technological approach represents one of the most promising and continuously evolving concepts for integrated wastewater treatment and energy recovery. M-BC systems exploit complementary processes, including photosynthesis, oxygen production, nutrient uptake by microalgae, as well as heterotrophic degradation of organic contaminants and CO₂ generation by bacteria. Laboratory- and pilot-scale studies demonstrate that such integration can substantially reduce energy demand while significantly improving technological performance. Metabolic synergy, metabolite exchange, intercellular communication, and the specific aggregate architecture collectively determine the stability and high productivity of these consortia. Depending on operational conditions, M-BC may occur as suspended cultures, biofilm-based systems, or granules, which differ in process characteristics and biomass recovery potential. Available evidence indicates that M-BC biomass can serve as a highly efficient substrate for anaerobic digestion (AD). The methane production potential of M-BC reaches 350–365 mL CH₄/gVS, and following pretreatment may increase to 530–560 mL CH₄/gVS, exceeding typical ranges reported for conventional sewage sludge. These values were obtained under specific process conditions and depend on biomass characteristics, consortium structure, inoculum type, and operational parameters; therefore, their generalisation should be interpreted with caution. However, practical implementation remains constrained by process-related barriers directly affecting AD performance, including extracellular polymeric substance (EPS)-mediated hydrolysis limitation and nitrogen-associated inhibition linked to low C/N ratios and ammonia accumulation. Additional challenges include seasonal variability in biomass composition and incomplete understanding of M-BC behaviour under anaerobic conditions, particularly at scale. This paper provides a comprehensive and integrative analysis of the structure and biochemistry of M-BC biomass, their ecological mechanisms, technological configurations, and current knowledge regarding their susceptibility to anaerobic digestion. The review identifies the key biological, chemical, and process-related barriers and highlights research directions required for future integration of M-BC into circular wastewater treatment systems and energy-oriented biomass valorisation. Full article

Phosphorus is a key nutrient regulating algal growth and eutrophication in aquatic systems, yet its isolated effect on microalgae-based wastewater treatment remains underexplored. This study evaluated how varying phosphorus loads drive microalgal community structure and purification performance in controlled photobioreactors fed synthetic wastewater. The synthetic wastewater was formulated with constant carbon and nitrogen but graded phosphorus at C/N/P ratios of 100/5/1, 100/5/10, and 100/5/20 under 6000 lux, a 14 h photoperiod, and 24 ± 2 °C with a 15-day hydraulic retention time. Monitoring of chlorophyll a, pH, total and volatile suspended solids, and algal composition showed that phosphorus enrichment significantly increased chlorophyll a (up to 43.9 µg/L at 20 mg P/L) and particulate biomass (TSS and VSS), while pH remained near neutral to slightly alkaline, with no significant differences among the three bioreactors. Although the same core taxa—Chlorella spp., Scenedesmus spp., Navicula spp., and filamentous algae were present across all bioreactors, their relative abundances shifted significantly with phosphorus concentration. A two-way ANOVA confirmed a highly significant interaction between bioreactor (P level) and genus (p < 0.001), demonstrating phosphorus-driven changes in the microalgal community. Notably, filamentous cyanobacteria (Anabaena spp.) were undetectable in the low- and medium-phosphorus treatments but emerged prominently only at the highest phosphorus level (20 mg/L). Nutrient removal efficiencies peaked in this high-phosphorus bioreactor (C), achieving 85% for bCOD, 78% for nitrogen, and >70% for phosphorus. These results show that phosphorus loading drives predictable shifts in microalgal community composition toward fast-growing algae and cyanobacteria and that these shifts likely contribute to enhanced nutrient removal. The findings support optimization of phosphorus supply and hydraulic residence time in low-cost, sunlight-driven systems to improve polishing performance for small settlements in arid regions. Full article