The expansion of global wastewater treatment capacity has led to increased production of residual sludge from activated sludge processes, posing significant environmental challenges while highlighting the need for resource recovery strategies. In this study, a microbial fuel cell-anaerobic digestion (MFC-AD) coupled system was developed, employing o-chlorophenol (oCP) as an uncoupling agent to enhance sludge reduction and energy recovery. The dual regulatory role of oCP was systematically evaluated, focusing on anaerobic digestion performance and bioelectrochemical behaviour. Results indicated that optimal sludge reduction occurred at 100 μg/L oCP, accompanied by maximum acetic acid accumulation and methane yield. In contrast, electrochemical performance exhibited a biphasic response, peaking at 50 μg/L. Intermediate oCP concentrations achieved overall system optimization, associated with higher microbial diversity and metabolic flexibility. Microbial community analysis suggested that oCP altered the composition of the anode biofilm community and was associated with shifts in energy recovery pathways. Comparative operation showed similar total energy recovery in U3 and U4, but with distinct pathways: U4 favoured volatile fatty acid (VFA) and methane production, whereas U3 enhanced electrochemical energy output.

The multistage anammox biofilm system constructed on anaerobic baffled biofilm reactor was enhanced by ultrasound irradiation. The optimal ranges of ultrasonic working parameters for enhancing the specific anammox activity (SAA) were explored. When the ultrasonic frequency, power and irradiation duration were in the range of 35∼55 kHz, 60∼100 W and 1.0∼3.5 min, SAA increased by 35.57%∼43.96%. Then, the long-term effect of ultrasound on the multistage anammox biofilm system was further studied. The optimal ultrasonic parameters with 40 kHz, 90 W and 3 min per week were adopted and the remarkable enhancing effect was attained. Furthermore, the ultrasonic enhancing mechanism was uncovered. The EPS analysis indicated that the introduction of ultrasound increased EPS and its PN/PS to promote the formation and renewal of anammox biofilms. The bacterial community analysis revealed that Candidatus Kuenenia emerged as the predominant bacteria in the mature biofilms of the control group while Candidatus Brocadia predominated in the mature biofilms of the ultrasonic group. The microbial community succession was redirected under the function of ultrasonic irradiation, which was helpful to improve the anammox performance. Moreover, the ultrasonic irradiation increased the abundance and biodiversity of AnAOB. This study offers the significant theoretical basis for construction of the ultrasound-strengthened multistage anammox system.

Food waste and residual sludge co-digestion suffers from poor biodegradability and frequent acid inhibition, due to abundant refractory organics and dense extracellular polymers. Batch anaerobic digestion experiments were performed to explore the combined promotion effect of alkaline pretreatment combined with zero-valent iron (ZVI) on the co-digestion of food waste and residual sludge. Preliminary trials confirmed that 3% NaOH was optimal for substrate disintegration. Under the tested conditions, the numerically highest cumulative methane yield was achieved at the F4 group (5 g/L ZVI), which was 62.72% and 19.61% higher than the untreated KB and alkali-only F0 groups, respectively. Moderate ZVI improved system pH buffering, lowered oxidation-reduction potential (ORP), accelerated the conversion of acetic and propionic acids, and reduced acidification risk. Fe2+ presented a three-stage variation governed by ZVI corrosion, chemical precipitation and microbial assimilation. High-throughput sequencing revealed ZVI enriched hydrolytic Bacteroidetes and mixotrophic Methanosarcina while decreasing the proportion of hydrogenotrophic Methanobacterium. Redundancy analysis (RDA) supported indirectly Fe2+, ORP and pH correlated with microbial succession and methanogenic performance. Excessive ZVI triggered performance decline, which may arise from potential salting-out effects, further experimental validation is required. This study clarifies the coupling mechanism of alkali-ZVI and provides technical guidance for organic solid waste resource recovery.

This study explores the influence of experimental variables on the electrodialytic (ED) treatment of freshwater sediment for extraction and separation of phosphorus (P) and heavy metals (Cd, Cu, Pb, Zn). The overall idea is to extract an uncontaminated P product and an unpolluted sediment fit for recycling. The influence of the experimental variables, current, liquid-to-solid ratio (L/S), duration, stirring rate, suspension liquid (distilled/tap water), was studied in 11 ED experiments with the help of a multivariate analysis tool, projection to latent structures (PLS). In the experimental domain studied, current and L/S had the most influence on P extraction (50%), and the extracted P was uncontaminated with heavy metals. The stirring rate and current had the most influence on the extraction of Zn (90%) > Cd (87%) > Cu (60%) > Pb (48%). The concentration of heavy metals was compared with the limits for soil improvers because that is one of the options for sediment recycling. Cd and Zn in the treated sediment met the standards for soil improvers, whereas optimization is necessary for Cu and Pb. The multivariate analysis revealed that the extracted Cd and Zn were mostly associated with the exchangeable and reducible fractions of the sediment. It was also revealed that the extracted Cu was mostly associated with the oxidizable fraction, whereas for Pb, no clear relationship could be established. The optimization for improving the extraction of Cu and Pb associated with the oxidizable fraction could be done by treating the sediment at a high stirring rate, high current, and long duration.

The removal of aromatic organophosphate flame retardants (OPFRs) from water remains a significant challenge due to their persistence, hydrophobicity, and resistance to conventional treatment processes. In this study, a combined adsorption-electrochemical oxidation system using graphite intercalation compound (GIC) was evaluated for the removal of five representative aromatic OPFRs: triphenyl phosphate (TPP), 2-ethylhexyl diphenyl phosphate (EHDPP), cresyl diphenyl phosphate (CDPP), tricresyl phosphate (TCP), and tris(4-tert-butylphenyl) phosphate (TTBP). Batch adsorption experiments showed rapid initial removal governed by pseudo-second-order kinetics, indicating that surface interactions dominate the adsorption process. Adsorption capacity and rate varied among compounds, with more hydrophobic OPFRs exhibiting faster removal and lower residual concentrations. Cyclic adsorption-regeneration experiments demonstrated that overall performance is strongly dependent on electrochemical conditions. At low current (0.5 A), regeneration was incomplete and partially governed by desorption, whereas increasing the current to 3 A resulted in higher Apparent Oxidative Removal (AOR) values, lower residual concentrations and more stable treatment performance over successive cycles. Under optimal conditions (3 A, 20 min regeneration), several OPFRs were reduced to concentrations below the GC-MS detection limits, and all compounds were reduced to concentrations below 5 µg L[-1]. Mechanistic analysis revealed that adsorption dominates initial removal, while electrochemical oxidation is essential for regenerating adsorption sites and preventing contaminant release. The combined GIC-electrochemical system offers a synergistic and effective approach for the treatment of aromatic OPFRs, with performance governed by compound structure, hydrophobicity, and operating conditions. These findings provide new insights into adsorption-electrochemical processes for the removal of persistent organic contaminants.

Digestate reuse has been proposed as a strategy for enhancing anaerobic digestion (AD) performance; however, full-scale validation remains limited. This study evaluated digestate reuse for municipal sludge treatment through full-scale monitoring, biochemical methane potential (BMP) assays, semi-continuous continuous stirred-tank reactor (CSTR) experiments, and economic assessment. Operational data from two wastewater treatment plants revealed substantial differences in baseline digestion performance. BMP results showed that digestate reuse increased methane production by up to 28% and improved solids degradation in underperforming sludge, whereas limited benefits were observed in a well-performing system. Semi-continuous CSTR experiments demonstrated that intermittent digestate dosing at approximately 10% (v/v) improved total solids (TS) and volatile solids (VS) removal without compromising process stability. The enhancement effect persisted for 10-20 days following a single addition, suggesting that digestate acted primarily as a transient bio-stimulant rather than a conventional carbon source. Full-scale evaluation indicated that digestate reuse could reduce sludge disposal demand and generate net cost savings of approximately NT$100,000 (∼US$3,125) per month. These findings demonstrate that intermittent digestate reuse is a practical strategy for improving AD performance while supporting resource recovery and circular economy implementation.

This study evaluates distillation as an integrated treatment and resource recovery approach for wastewater generated from unsaturated polyester resin (UPR) production. An integrated experimental and modelling approach was developed to evaluate separation performance and support industrial process design. Laboratory experiments were conducted using a packed distillation column under different operating conditions, and a thermodynamic model based on vapour-liquid equilibrium data was developed and validated against experimental results. A continuous two-column distillation process was subsequently simulated and optimized using actual industrial UPR wastewater, with the total annualized cost as the optimization criterion. The system recovered water at 99.7% purity with a yield of 95%, while PG was obtained at 99.1% purity and 83.5% recovery efficiency at the lab scale. Recommended conditions for water separation were atmospheric pressure, 0.20 kW heat duty, and a reflux ratio of 0.25, whereas PG recovery achieved the highest performance under reduced pressure (<0.1 bar) with a reflux ratio of 1.8-2.0. The optimized industrial process achieved 86.63% overall valuable-chemical recovery using 9 and 22 theoretical stages for the water and phenol separation columns, respectively. The results demonstrate the feasibility of integrating validated process simulation with laboratory experiments for industrial wastewater treatment and resource recovery.

Microbial competition that is driven by substrates plays an essential role in the stable denitrifying phosphorus removal (DPR) of low carbon wastewater treatment. This paper used a dual-sludge membrane bioreactor (A2N-MBR) to evaluate C/N ratios of 3-6 using acetate, followed by a comparison of acetate, propionate and their mixture at C/N = 5. Stoichiometric analysis estimated substrate allocations among denitrifying polyphosphate-accumulating organisms (DPAOs), denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying ordinary heterotrophic organisms (DOHOs), while 16S rRNA gene sequencing and Pearson correlation analysis characterised community composition and its associations with nutrient removal. At C/N = 5, stoichiometric estimates assigned 53% of anaerobic COD consumption and 82% of anoxic nitrate reduction to DPAOs, with nitrate and phosphate removal efficiencies of 76.93% and 77.00%, respectively. At C/N = 6, the estimated substrate allocations shifted towards DGAOs and DOHOs pathways. Phosphorus removal was not as consistent as nitrate removal. In the subsequent carbon source comparison at C/N = 5, the acetate propionate mixture improved reactor performance. As a result, the maximum nitrate and phosphate removal efficiencies were 91.72% and 88.50%, respectively. Correlation analysis indicated that Thauera and Zoogloea were associated with NO3[-]-N and PO4[3-]-P removal. Conversely, Nitrospira relative abundance was negatively associated with nitrate removal. All in all, these findings link substrate conditions with community composition and DPR performance within the respective C/N and carbon source comparisons.HighlightsEmployed a novel A2N-MBR system to investigate anoxic nitrate reduction and phosphate uptake.C/N ratios altered estimated substrate allocations among microbial pathways.Acetate-propionate (1:1) improved nitrate and phosphate removal.

This study systematically evaluated the nitrogen removal performance and microbial community characteristics of the sulfur-based autotrophic denitrification (SAD) process under various influent loads (15-140 mg N/L). After 22 days acclimation at 15 mg N/L, the system achieved >90% stable NO3[-]-N removal. Notably, the system demonstrated exceptional stability at a high load of 140 mg N/L, with an average total nitrogen removal rate of 98% (peaking at 99%). This performance indicates a successful adaptation to elevated loading conditions. The high removal efficiency is attributed to the coordinated metabolic processes within the system. As the nitrate load increased, sulfur oxidation accelerated, releasing protons and causing a decline in pH. The ratio of sulfate production to nitrate removal (6.8-10 mg/mg) remained consistent with the theoretical value of 7.54 mg/mg, confirming the integrity of the sulfur metabolic pathway across various loading conditions. Furthermore, the nitrate load acted as a selective pressure, promoting the dominance of Pseudomonadota and Thiobacillus to establish a robust functional microbial ecosystem. In conclusion, this study confirms the viability of the SAD process for treating wastewater with medium to high nitrate concentrations. It also reveals the metabolic and community mechanisms that support performance stability under various load conditions.

This study investigated the acute inhibitory impacts of two widely used antibiotics, erythromycin (ERY) and tetracycline (TET), on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) within an enriched nitrifying culture. For this purpose, a lab-scale wastewater treatment system sustaining enriched nitrifiers was exposed to antibiotic concentrations ranging from 25 to 100 mg L[-1]. Model evaluations of oxygen uptake rate (OUR) evolution, together with ammonia and nitrite oxidation profiles, revealed distinct metabolic disruptions. ERY severely impaired the system, dropping overall nitrification efficiency to as low as 25% and halving the growth rates for both AOB and NOB. In contrast, TET exposure largely maintained overall nitrification performance with slightly reduced NOB activity. Under TET stress, the half-saturation constants for ammonia (KNH) and nitrite (KNO) increased to 32 and 2 mg N L[-][1], respectively, indicating competitive inhibition and decreased substrate affinity. Both antibiotics reduced heterotrophic activity - more severely with ERY-triggering the release and utilisation of hydrolyzable biomass fractions. The results demonstrate that acute antibiotic toxicity and inhibitory impacts are markedly less pronounced in enriched nitrifying systems compared to conventional mixed activated sludge systems.

Dairy wastewater air flotation sludge (DWAFS) is resistant to conventional mechanical dewatering due to its high fat content and protein-stabilized emulsion structure. To address this challenge, this study employed electron beam (EB) irradiation as a pretreatment method. The effects of irradiation dose on sludge dewaterability were systematically investigated, and the multi-dimensional underlying mechanisms were elucidated through integrated multi-scale characterization. The results showed that EB irradiation significantly enhanced dewaterability, with 5 kGy identified as the optimal dose based on a combined evaluation of dewatering performance and specific energy consumption. EB irradiation was shown to efficiently disrupt the protein-stabilized emulsion, likely via water radiolysis-derived free radicals. This process is proposed to drive organic component transformation, surface charge neutralization, protein-lipid co-aggregation and floc reconstruction, ultimately contributing to the conversion of bound water to free water and enhanced dewaterability. These findings clarify the demulsification-dewatering coupling mechanism of EB irradiation on DWAFS and provide a theoretical basis for engineering application in high-fat oily sludge treatment.

This study characterizes the dynamic development process of photogranules, explores the role of related substances in their formation, and verifies the resource recovery potential in nitrogen and phosphorus removal from wastewater. The characteristics of photogranules were observed, and the nitrogen and phosphorus removal efficiency of the system was measured. The content of protein and polysaccharide in extracellular polymeric substances was determined over time. Excitation-emission matrix fluorescence was used to analyse the types and changes of substances in the system. Resource recovery assessments were conducted by adopting the method of freeze-thaw combined with trituration to extract phycocyanin and determine the content of phycobiliprotein. Photogranule development went through three sequential phases: initially, photogranules were under 1 mm in diameter, with peripheral filaments proliferating to create an irregular, meteorite-like surface; densification: loosely woven filaments contracted, increasing density and reducing surface pits, forming more compact structures; at maturation, granules reached approximately 1.3 mm and became spherical. The system achieved approximately 98% nitrogen and 56% phosphorus removal. Protein and polysaccharide content in extracellular polymeric substances increased slightly over time. Excitation-emission matrix fluorescence showed abundant humic-like substances in the early phase, while microbial byproducts and aromatic proteins remained stable later. The freeze-thaw combined with trituration yielded the highest concentration of phycocyanin (0.31 mg L[-1]), with phycobiliprotein content stable at about 50 mg L[-1]. This study describes photogranule growth characteristics, confirms the structural role of EPS, and demonstrates the dual functionality of photogranules in nutrient removal and resource recovery.

Aquaculture wastewater commonly contains excess nutrients and residual antibiotics, whereas conventional plant-only ecological ponds may provide insufficient removal of these coexisting contaminants. To enhance system performance through substrate engineering, iron-modified oyster shell biochar (IOBC) was developed as a functional medium and coupled with Myriophyllum in an ecological purification system. Response surface methodology identified optimal IOBC preparation conditions of 700 °C, a modification ratio of 1:1, and 3.5% iron addition, under which oxytetracycline (OTC) removal reached 89.37%. The optimized IOBC was subsequently incorporated into a continuous-flow system treating simulated aquaculture wastewater. In the continuous-flow system treating simulated aquaculture wastewater, pollutant removal increased with hydraulic retention time, and the coupled IOBC-Myriophyllum treatment consistently outperformed the filler-only and plant-only systems. At 72 h, the coupled system achieved removal efficiencies of 38.89% for NH4[+]-N, 38.79% for TN, 72.81% for TP, 67.67% for CODMn, and 59.46% for OTC. Sequencing and mechanistic analyses indicated that the enhanced performance resulted from coordinated adsorption, plant uptake, microbial nitrification and denitrification, Ca- and Fe-mediated phosphorus precipitation, and oxidative and biological transformation of OTC. These findings demonstrate that functional substrate modification can strengthen ecological treatment of nutrient- and antibiotic-containing aquaculture wastewater.

The increase in sheep populations to meet the demand for meat generates large volumes of sheep wool, most of which is considered agro-industrial waste and poses a potential risk of contamination due to improper handling. Protein recovery is an attractive strategy for generating agricultural inputs, such as protein hydrolysates (PHs). This study aimed to evaluate the agrobiotechnological potential of sheep wool-derived PHs as (i) an alternative peptone source for Trichoderma harzianum and (ii) growth-promoting inputs in hydroponic green fodder (HGF) production. To this end, an alkaline-enzymatic hydrolysis process was evaluated, incorporating pretreatment with an anionic surfactant applied to sheep wool. SDBS-pretreated wool underwent alkaline solubilization (2.5% NaOH) followed by enzymatic hydrolysis using Esperase® or papain. The process achieved 90-92% solubilization and 29-39% hydrolysis, producing peptides of 10-2 kDa and increasing soluble nitrogen and primary amino groups. Compounds with reducing capacity were also detected without affecting antioxidant activity (FRAP and DPPH), particularly in the Esperase®. Sheep wool hydrolysates used as a peptone source promoted moderate mycelial growth and sporulation of T. harzianum, while enhancing enzymatic activity associated with biological control potential, as indicated by increased halo diameters. Furthermore, foliar application of hydrolysates at 3 g L[-][1] in HGF promoted greater shoot length (8.2-9.6%) and higher total protein content (27.2%) compared to the control, along with an increase in dry matter content (4.1%). Overall, alkaline-enzymatic hydrolysis of sheep wool represents a promising strategy to produce bio-based inputs for microbial culture and plant growth.