Search Results (96)

Two-stage anaerobic digestion (TSAD) is an alternative to single-stage anaerobic digestion, separating hydrolytic–acidogenic and methanogenic phases to improve stability, organic matter degradation, and methane production. This review examines TSAD for co-digestion of sewage sludge (SS) and the organic fraction of municipal solid waste (OFMSW), emphasizing performance, scale-up challenges, digestate intensification, and nutrient recovery. TSAD can increase methane production by 25–50% compared with single-stage systems, while volatile solids removal can reach 87–93% depending on substrate type, temperature regime, hydraulic retention time, and organic loading rate. However, improvement remains variable and depends on substrate biodegradability, reactor configuration, and process control. Beyond methane recovery, the review highlights valorizing digestate as a secondary resource. Digestate post-treatment technologies, including thermal hydrolysis and steam explosion, report methane improvements from 26% to more than 300%, although energy demand and economic feasibility remain constraints. Nitrogen recovery technologies, including ammonia stripping and membrane contactors, can achieve efficiencies above 80–95% under optimized conditions, while phosphorus may be recovered through struvite precipitation, calcium phosphate recovery, or biochar-based pathways. Future TSAD development should integrate biological conversion, digestate recirculation, nutrient recovery, techno-economic assessment, and life-cycle evaluation to support circular, resource-efficient organic waste treatment systems. Full article

Low organic carbon utilization efficiency is a core bottleneck restricting the application of biofloc technology (BFT) in intensive aquaculture, accompanied by limited total nitrogen removal, excessive biofloc accumulation, and underutilized chemical energy in organic wastes. To address this issue, this study develops a novel biofloc technology–microbial fuel cell (BFT-MFC) coupled system that exploits surplus carbon sources in BFT as electron donors for bioelectricity generation while synergistically enhancing water purification performance. Compared with a conventional standalone BFT system, the coupled system was systematically evaluated in terms of water quality regulation, biofloc control and electricity generation performance. Results showed that the BFT-MFC system maintained relatively stable dissolved oxygen, pH, and temperature throughout the operation period. The ammonia nitrogen concentration remained relatively low in the BFT-MFC system, although a transient increase to approximately 0.35 mg/L occurred around day 20 before subsequently declining, and total nitrogen fluctuated within 4.29–12.87 mg/L, with substantially less accumulation than that observed in the BFT system, in contrast to the control group, where TN continuously rose to a peak of 23.55 mg/L. Total organic carbon was stabilized within a narrower range of 150–245 mg/L, compared with the wide fluctuation of 129.6–360 mg/L in the single BFT system. Additionally, the coupled system exhibited lower net biofloc accumulation based on floc-volume measurements, while maintaining effective water-quality regulation, and the integrated MFC delivered a maximum output voltage of 295.9 mV and a peak power density of 1716.8 mW m⁻². Overall, the BFT-MFC coupled system integrates wastewater purification, biofloc regulation and energy recovery into a single unit, offering a promising sustainable strategy for industrial recirculating aquaculture. Full article

Recovering nitrogen from wastewater is vital for a circular economy, yet conventional air stripping is limited by aerodynamic backpressure and CO₂-induced pH drops. This study evaluates a novel pilot-scale engineering approach for municipal reject water, integrating chemical phosphorus precipitation with a fundamentally redesigned ammonia stripping column. Upstream calcium hydroxide dosing achieved >99.9% phosphorus recovery and spontaneously alkalized the effluent (pH > 12.1), eliminating supplementary caustic addition. The downstream stripping column utilized negative-pressure (vacuum) operation and high-pressure liquid atomization to maximize mass transfer while preventing flooding and alkalinity neutralization. Comprehensive on-site testing established a clear mathematical relationship between aerodynamics and efficiency. Results demonstrate that high-efficiency recovery requires gas-to-liquid (G/L) ratios exceeding 70:1, a threshold uniquely unlocked by this negative-pressure design. Under optimal conditions, the continuous-flow system achieved 87.6% ammonia removal. A low-resistance acid scrubber captured ~100% of the volatilized ammonia (exhaust 0–1 ppm), producing a concentrated ammonium sulfate bio-fertilizer. This integrated technology provides a scalable, applied engineering blueprint for advancing sustainable Water Resource Recovery Facilities. Full article

Undergraduate Water Quality Engineering courses rely on verification experiments lacking real engineering scenarios, limiting undergraduate participants’ comprehensive problem-solving skills. To remedy this issue, this study constructs an inquiry-oriented experiment using carbon-coated nano-calcium carbonate (C@CaCO₃) to enhance biological nitrification for digested wastewater with low alkalinity and high ammonia. It involves wastewater characterization, sequencing batch reactor (SBR) operation, quantification of chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N) removal, mechanism discussion on alkalinity slow release and microbial carrier role of C@CaCO₃, and high-throughput analysis of microbial communities. Experimental results show that C@CaCO₃ increases NH₄⁺-N removal by 94.5 ± 4.8% in low-alkalinity water, while COD removal improves from 5.7 ± 3.0% to 29.5 ± 5.2%. These findings demonstrate that C@CaCO₃ effectively mitigates alkalinity limitation, facilitates microbial attachment, and promotes functional microbe enrichment, offering a practical solution for sustainable nitrogen management in nutrient-rich waste streams. Pedagogically, the case links water-quality monitoring, reactor control, and solid-waste resource recovery, enabling undergraduate participants to trace the full engineering workflow problem identification through quantitative design, operation, and mechanistic interpretation. Post-laboratory surveys and performance assessments indicate significant gains in experimental competence, data-analysis skills, and engineering judgment. By embedding a real-world, low-alkalinity wastewater challenge within the curriculum, the module advances sustainable water-resource management education and provides a replicable model for reforming laboratory teaching in Water Quality Engineering and related environmental-engineering courses. Full article

High-ammonium poultry digestate from thermophilic dry anaerobic digestion is often recycled, but excessive ammonia accumulation may inhibit anaerobic digestion and reduce process stability. This study developed a gas-driven ammonia stripping process coupled with gypsum-mediated absorption for digestate deammonification, nitrogen recovery, and CO₂-assisted carbonate formation. Laboratory stripping experiments were conducted using simulated biogas to evaluate the effects of pH, temperature, and gas–liquid ratio. Under the selected condition of pH 11, 65 °C, and a gas–liquid ratio of 2, NH₄⁺-N in 10 L digestate decreased from approximately 7980 to 1648 mg L⁻¹ within 12 h, corresponding to about 80% removal. In the absorption step, the slightly soluble CaSO₄ solution showed more stable NH₃ capture than the CaSO₄ suspension, and the corrected NH₃-N recovery reached approximately 90–95%. XRD, SEM-EDS, precipitate mass estimation, and gas-phase CO₂ variation supported the formation of CaCO₃-containing precipitates. Pilot-scale operation using real biogas further reduced NH₄⁺-N from approximately 8000 to 700–800 mg L⁻¹ during 36 h of extended pilot-scale operation. Overall, the coupled process provides a preliminary resource-recovery route integrating ammonia burden reduction, nitrogen recovery, sulfate transfer, and CO₂-assisted carbonate precipitation. However, full-scale sustainability still requires further long-term operation, complete nitrogen–carbon–calcium–sulfur mass balances, complete heat and energy-balance assessment, product-quality evaluation, and techno-economic or life-cycle assessment. Full article

Pig farming generates high-strength piggery wastewater (PWW) with extreme organic and nutrient concentrations. This research evaluated an integrated treatment system combining Vertical Flow Constructed Wetlands (VFCW), Microbial Fuel Cells (MFC), and Microalgae Photobioreactors (PBR) to enhance resource recovery, evaluate bio-electrochemical activity, and produce microalgal biomass. Findings showed that hydraulic saturation in the VFCW–MFC stage enhanced the open-circuit voltage response, reaching a maximum of 539 mV, indicative of bio-electrochemical activity. The optimized VFCW–MFC configuration, featuring pulsed feeding, achieved removals of total suspended solids (TSS, 83%) and chemical oxygen demand (COD, 69%). This integrated pretreatment mitigated ammonia toxicity and turbidity, enabling the subsequent cultivation of Tetradesmus obliquus microalga, reaching biomass yields of 1.1–1.3 g L⁻¹ while providing crucial tertiary polishing. Overall, the combined VFCW–MFC–PBR system achieved removal efficiencies exceeding 90% for total Kjeldahl nitrogen (TKN) and approximately 80% for COD. This synergistic approach successfully transforms PWW liabilities into valuable assets, including nutrient-rich biomass and bio-electrochemical activity, underscoring the potential of VFCW–MFC–PBR for sustainable wastewater management. Full article

In the treatment of high-salinity wastewater, the removal of nitrogen and organic pollutants remains a challenge, while the production of value-added compounds, such as ectoine from halophilic bacteria, offers a promising resource recovery pathway. In this study, halophilic activated sludge enriched with Thauera as the dominant strain was cultivated in a sequencing batch reactor (SBR) to treat synthetic high-salinity wastewater (30 g/L NaCl) under different sludge retention times (SRTs). The optimal nitrogen and organic carbon removal performances were achieved at an SRT of 10 days, with an ammonia nitrogen removal rate of 77.67% and a total organic carbon (TOC) removal rate of 72.51%. Ectoine production was strongly SRT dependent, as volumetric ectoine concentration was ~2 mg/L at 5 d SRT, almost undetectable at 10 d SRT, ~10 mg/L at 16 d SRT, and peaked at 21.5 mg/L at 22 d SRT. Short SRTs favored dynamic ectoine utilization for osmoprotection and metabolic stability, whereas long SRTs led to passive ectoine accumulation and deteriorated treatment performance. The system realized stable short-cut heterotrophic nitrification with negligible nitrite and nitrate accumulation, indicating direct conversion of ammonia to gaseous nitrogen. These results demonstrate that SRT regulation effectively balances ectoine synthesis and pollutant removal, providing a feasible strategy for resource-oriented treatment of high salinity wastewater. Full article

Partial nitrification (PN) is a promising strategy for reducing aeration demand and improving the energy efficiency of biological nitrogen removal in wastewater treatment. However, maintaining stable PN in continuous-flow activated sludge reactors remains challenging due to the recovery of nitrite-oxidizing bacteria (NOB) and the absence of cyclic operational phases that naturally promote microbial selectivity in sequencing batch reactors. This study proposes a model-based multi-criteria optimization framework to identify and classify feasible operating conditions for stable PN in continuous-flow activated sludge reactors. A modified Activated Sludge Model No. 1 (ASM1) was used to describe the dynamics of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and heterotrophic biomass, while equilibrium points were determined through steady-state optimization and evaluated using a multi-criteria feasibility analysis based on nitrite accumulation ($\beta$), ammonium oxidation efficiency ($\alpha$), oxygen uptake rate (OUR), hydraulic retention time (HRT), and sludge retention time (SRT). Seasonal variability was incorporated through summer and winter operating scenarios. Results indicate that stable PN can be achieved under operating conditions of pH 7.5–8.5, dissolved oxygen concentrations between 0.3 and 2.5 mg/L, HRT values of approximately 2–3 h, and SRT values between 10 and 20 d. Under these conditions, high nitrite accumulation ($\beta >0.8$) and ammonium oxidation efficiency ($\alpha >0.8$) were maintained with moderate oxygen demand, although seasonal differences revealed greater operational flexibility in summer and tighter constraints in winter. The proposed framework provides a systematic approach for identifying robust and energy-efficient operating regions in continuous-flow PN systems and establishes a foundation for future supervisory control implementation in full-scale wastewater treatment applications. The study also shows that over 40% energy savings could be achieved at optimal equilibrium points for partial nitrification compared to full nitrification. Full article

A binder-free Co₃O₄ nanoneedle electrode grown directly on nickel foam (Co₃O₄@NF) was fabricated by hydrothermal synthesis followed by calcination and evaluated for electrocatalytic nitrate reduction to ammonium. The integrated three-dimensional architecture combines the catalytic activity of Co₃O₄ with the high conductivity and open porosity of nickel foam, thus exposing abundant active sites, shortening electron-transfer pathways, and facilitating mass transport. Among the electrodes prepared at different calcination temperatures, Co₃O₄@NF calcined at 400 °C delivered the best performance. Under the optimal conditions of −1.4 V vs. Ag/AgCl, pH 7, and an initial NO₃⁻-N concentration of 50 mg L⁻¹, the electrode achieved 83.4% nitrate removal within 480 min together with 98.7% ammonium selectivity. Electrochemical measurements revealed a markedly enlarged electrochemically active surface area and reduced charge-transfer resistance after Co₃O₄ loading. Mechanistic analyses via TBA quenching experiments and DFT calculations revealed that both the direct pathway and the hydrogen-assisted indirect pathway were operative, with the indirect pathway being dominant due to its lower free energy barrier while maintaining negligible nitrite accumulation. The electrode also showed good cycling stability and retained high ammonium selectivity in real water matrices. These results demonstrate that binder-free Co₃O₄ nanoneedles supported on nickel foam constitute a promising cathode architecture for coupling nitrate removal with ammonia recovery. Full article

This study evaluated the phytoremediation potential of the halophytic plant Sesuvium portulacastrum (L.) L. for treating industrial wastewater (IWW) in a hydroponic system over a nine-day exposure period. After treatment, the physicochemical analysis of IWW revealed a significant decrease in chemical oxygen demand (COD), biological oxygen demand (BOD), TSs (total solids), total dissolved solids (TDSs), TSSs (total suspended solids), ammonia, phosphate, and nitrate. The COD and BOD were reduced by 90.7% and 82.9%, respectively. The metal analysis indicated a significant decrease in Fe (95%), Mn (87.4%), and Al (93.9%) and complete removal of Ni, Pd, and Zn. The plant stress responses were assessed through the estimation of photosynthetic pigments (Chlorophyll-a, Chlorophyll-b, Total chlorophyll), phenolic and flavonoid contents, and antioxidant activity. Total chlorophyll declined from 1.449 mg/g (control) to 1.20 mg/g on Day 3, followed by partial recovery to 1.25 mg/g by Day 9, indicating physiological acclimatization. Total phenolic content reached 14 mg GAE/g in leaves and 12 mg GAE/g in stems on Day 6, while Total flavonoid content increased from ~70 µg/g (control) to 115 µg/g on in leaves. The metabolic profiling using GC-MS/MS revealed distinct time- and tissue-specific metabolic responses, with 53 metabolites identified in roots and 62 metabolites in leaves. The major differentially accumulated metabolites were sucrose, pinitol, talose and psicose, with peak accumulation at Day 6. A biphasic metabolic response pattern, characterized by early stress perception followed by adaptability, was observed. Phytotoxicity assays using Vigna radiata demonstrated improved germination from 15% (untreated IWW) to 95% after treatment. Overall, the study highlights the strong phytoremediation potential of halophyte S. portulacastrum as an environmentally friendly alternative for industrial wastewater remediation. Full article

Livestock wastewater is an important source of nitrogen pollution, but it also represents a potential feedstock for nitrogen recovery. In this study, longan wood-derived biochar was used as an immobilization carrier in a bio-ammonification system developed with aerobic and facultative ammonifying bacteria isolated from swine wastewater. The system was designed to enhance microbial retention and promote the conversion of organic nitrogen into ammonium concentration (NH₄⁺-N) under oxygenated conditions. Among the tested strains, Lysinibacillus sp. (strain 4-1) showed the highest ammonification activity, reaching an NH₄⁺-N concentration of 340 mg/L in NB medium within 5 days. In sterilized swine wastewater, the biochar-immobilized strain 4-1 achieved 47.17% organic nitrogen removal. The results suggest that coupling microbial ammonification with biochar immobilization may provide a low-carbon approach for nitrogen recovery from livestock wastewater and facilitate decentralized bio-ammonia production. Full article

Efficient recovery of ammonia from sludge hydrolysate (SH) remains a challenging task. This study developed a superhydrophobic capillary ceramic-membrane contactors (MCs), which, by establishing a stable gas-phase mass transfer interface, provides a reliable guarantee for ammonia recovery under high-temperature, high-pH, and high-organic-load conditions. In a controllable simulation system, the system investigated the effects of key operational parameters such as pH, flow rate, and feed ammonia concentration on ammonia mass transfer behavior, and verified the feasibility of this MCs in efficient ammonia removal. Then, this membrane contactor was applied to the actual sludge hydrolysate (SH) system, and its anti-pollution effects, wetting stability, and adaptability to fluctuating conditions under long-term continuous operation were evaluated. The results showed that after operating for 10 h, the ammonia removal in the simulation system and the actual system reached 93.6% and 90.3%, respectively. During long-term operation, the ammonia recovery reached 90.3%. Meanwhile, the organic matter in SH was completely retained, and (NH₄)₂SO₄ was not contaminated by organic matter. Throughout the entire operation process, the contact angle of the membrane remained above 129.6°. This study provides a theoretical basis and practical reference for recovering ammonia using a hydrophobic capillary ceramic-membrane contactor in SH. 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

Global data center electricity demand is projected to double to 945 TWh by 2030, yet no optimization framework jointly sizes renewable generation, battery storage, hydrogen export infrastructure, and flexible computing loads within a single industrial hub. This paper develops a two-layer techno-economic workflow for an integrated renewable–hydrogen–data center hub in Yanbu Industrial City, Saudi Arabia. HOMER Pro provides baseline capacity sizing and dispatch across four scenarios; a Pyomo-based mixed-integer linear program, calibrated to within 2% of the baseline, then extends the system to include a 60 MW data center (30 MW critical, 30 MW flexible), multi-sink hydrogen allocation (domestic, ammonia, methanol), and low-grade waste heat recovery. Battery storage emerges as the dominant cost–carbon lever: its removal raises the levelized cost of electricity (LCOE) from 0.052 to 0.181 USD/kWh (+250%) and increases CO₂ emissions from 1.83 to 2763 kt/yr, a factor of 1510. The Integrated Hub reduces annualized costs by 8.2% (36.9 M USD/yr) and emissions by 28% relative to a separate-build counterfactual, driven by shared PV–battery infrastructure and hydrogen export revenues of 58.5 M USD/yr. Export demand raises the electrolyzer capacity factor from 8.65% to 24.3%, cutting the levelized cost of hydrogen from 10.5 to 6.8 USD/kg. Waste heat recovery reduces the levelized cost of heat by 17%, and co-location lowers the levelized cost of compute by 23% (from 0.055 to 0.042 USD/GPU/hr). These results provide quantitative design principles for industrial hub planners considering data center co-location in high-solar regions with hydrogen export ambitions. Full article

Background: Valproic acid (VPA) poisoning has a dynamic clinical course and may require extracorporeal toxin removal (ECTR) in severe cases. Intermittent hemodialysis is the preferred ECTR technique; however, clinical experience with expanded hemodialysis (HDx) using medium cut-off (MCO) membranes in acute VPA intoxication is scarce. We describe a case of severe VPA poisoning managed with intermittent HDx and outline the clinical rationale and kinetic response. Case Report: A 54-year-old woman presented to the emergency department after accidental presumably ingesting approximately 4 g of VPA, with depressed consciousness (Glasgow Coma Scale 7) and metabolic acidosis (pH 7.10, HCO₃⁻ 13 mmol/L, PCO₂ 50 mmHg, lactate 2.8 mmol/L, ionized calcium 0.8 mmol/L, elevated anion gap). Initial plasma VPA was 262.99 µg/mL, ammonia was 14 µmol/L, and cranial computed tomography showed no acute abnormalities. ECTR was initiated in the intensive care unit as intermittent HDx using an MCO dialyzer for 4 h. Serial VPA concentrations were obtained before treatment, at 2 h, and at the end of the session to guide real-time prescription adjustment, with an increase in blood flow from 200 to 230 mL/min. Results: VPA decreased from 262.99 µg/mL pre-HD to 141.48 µg/mL at 2 h (46.2% reduction) and 97.81 µg/mL at 4 h (62.8% reduction), with clear improvement in the level of consciousness. A mild post-dialysis rebound was observed (100.07 µg/mL at 14 h). The patient recovered without additional ECTR and was discharged with normalized VPA levels on follow-up. Conclusions: In this patient, intermittent HDx with an MCO membrane was feasible, well tolerated, and associated with rapid VPA clearance and neurological recovery. Serial drug monitoring enabled bedside optimization of the dialysis prescription and post-treatment evaluation. A single HDx session was sufficient, and VPA therapy was safely reintroduced under close monitoring. Full article