Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review.

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

Size-Dependent Uptake and Depuration of Nanoplastics in Tilapia (Oreochromis niloticus) and Distinct Intestinal Impacts.

Nanoplastics (NPs, <1 µm) are of great concern worldwide because of their high potential risk toward organisms in aquatic systems, while very little work has been focused on their tissue-specific toxicokinetics due to the limitations of NP quantification for such a purpose. In this study, NPs with two different sizes (86 and 185 nm) were doped with palladium (Pd) to accurately determine the uptake and depuration kinetics in various tissues (intestine, stomach, liver, gill, and muscle) of tilapia (Oreochromis niloticus) in water, and subsequently, the corresponding toxic effects in the intestine were explored. Our results revealed uptake and depuration constants of 2.70-378 L kg-1 day-1 and 0.138-0.407 day-1 for NPs in tilapia for the first time, and the NPs in tissues were found to be highly dependent on the particle size. The intestine exhibited the greatest relative accumulation of both sizes of NPs; the smaller NPs caused more severe damage than the larger NPs to the intestinal mucosal layer, while the larger NPs induced a greater impact on microbiota composition. The findings of this work explicitly indicate the size-dependent toxicokinetics and intestinal toxicity pathways of NPs, providing new insights into the ecological effects of NPs on aquatic organisms.

Anaerobic membrane bioreactor for carbon-neutral treatment of industrial wastewater containing N, N-dimethylformamide: Evaluation of electricity, bio-energy production and carbon emission.

The feasibility of anaerobic membrane bioreactor (AnMBR) for the treatment of N, N-dimethylformamide (DMF)-containing wastewater was theoretically compared with the conventional activated sludge (CAS) process in this study. The electricity consumption and expenditure, bio-energy production and CO2 emission were investigated using the operational results of a lab-scale AnMBR operated in a long-term operation. The AnMBR was capable of producing bio-methane from wastewater and generated 3.45 kWh/m3 of electricity as recovered bio-energy while the CAS just generated 1.17 kWh/m3 of electricity from the post-treatment of excessive sludge disposal. The large quantity of bio-methane recovered by the AnMBR can also be sold as sustainable bioresource for the use of household natural gas with a theoretical profit gain of 29,821 US$/year, while that of the CAS was unprofitable. The AnMBR was also demonstrated to significantly reduce the carbon emission by obtaining a theoretical negative CO2 production of -2.34 kg CO2/m3 with the recycle of bio-energy while that for the CAS was 4.50 kg CO2/m3. The results of this study demonstrate that the AnMBR process has promising potential for the carbon-neutral treatment of high-strength DMF-containing wastewater in the future.

Microbial behaviours inside alternating anaerobic-anoxic environment of a sulfur cycle-driven EBPR system: A metagenomic investigation.

Denitrifying sulfur conversion-assisted enhanced biological phosphorus removal (DS-EBPR) was recently developed for saline wastewater treatment. However, the main functional bacteria and the interrelationship of functional bacteria of the DS-EBPR have not been defined and identified so far. This study used metagenomics and multivariate statistics to deduce the functional microbial community and distribution of functional genes associated with the critical metabolic pathways of carbon (C), nitrogen (N), phosphorus (P) and sulfur (S), particularly regarding how they would behave under the alternating anaerobic-anoxic conditions inside a long-term DS-EBPR system. An analysis of the metagenomics and metabolic functions identified 11 major microbial species which were classifiable into four groups: sulfate reducing bacteria (SRB, 0.8-2.2%), sulfur oxidizing bacteria (SOB, 31.9-37.7%), denitrifying phosphate accumulating organisms (DPAOs, 10.0-15.8%) and glycogen accumulating organisms (GAOs, 3.7-7.7%). The four groups of microorganisms performed their respective metabolisms synergistically. In terms of distribution of functional genes, SRB (Desulfococcus and Desulfobacter) and SOB (Chromatiaceae and Thiobacillus) are not only encoded by the related sulfur conversion genes (sqr, dsrAB, aprAB and sat), but also encoded by the necessary ppx and ppk1 gene for P removal that they can be considered as the potential S-related PAOs. Between the anaerobic and anoxic conditions, the metagenome-based microbial community remained structurally similar, but the functional genes, which encode various key enzymes for the P, N, and S pathways, changed in abundance. This study contributes to our understanding on the interactions and competition between the SRB, SOB, DPAOs, and GAOs in a DS-EBPR system.

Comparative metabolic modeling of multiple sulfate-reducing prokaryotes reveals versatile energy conservation mechanisms.

Sulfate-reducing prokaryotes (SRPs) are crucial participants in the cycling of sulfur, carbon, and various metals in the natural environment and in engineered systems. Despite recent advances in genetics and molecular biology bringing a huge amount of information about the energy metabolism of SRPs, little effort has been made to link this important information with their biotechnological studies. This study aims to construct multiple metabolic models of SRPs that systematically compile genomic, genetic, biochemical, and molecular information about SRPs to study their energy metabolism. Pan-genome analysis was conducted to compare the genomes of SRPs, from which a list of orthologous genes related to central and energy metabolism was obtained. Twenty-four SRP metabolic models via the inference of pan-genome analysis were efficiently constructed. The metabolic model of the well-studied model SRP Desulfovibrio vulgaris Hildenborough (DvH) was validated via flux balance analysis (FBA). The DvH model predictions matched reported experimental growth and energy yields, which demonstrated that the core metabolic model worked successfully. Further, steady-state simulation of SRP metabolic models under different growth conditions showed how the use of different electron transfer pathways leads to energy generation. Three energy conservation mechanisms were identified, including menaquinone-based redox loop, hydrogen cycling, and proton pumping. Flavin-based electron bifurcation (FBEB) was also demonstrated to be an essential mechanism for supporting energy conservation. The developed models can be easily extended to other species of SRPs not examined in this study. More importantly, the present work develops an accurate and efficient approach for constructing metabolic models of multiple organisms, which can be applied to other critical microbes in environmental and industrial systems, thereby enabling the quantitative prediction of their metabolic behaviors to benefit relevant applications.

Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics.

A prominent source of hydroxyl radicals (•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol, n-butanol, or formate as •OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO2-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO2-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2 for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.

Electrochemical Pretreatment for Sludge Sulfide Control without Chemical Dosing: A Mechanistic Study.

Sulfide is a toxic and corrosive odorant generated in various sludge treatment and disposal systems. We developed an electrochemical pretreatment (EPT) approach to eliminate sludge sulfide production without adding chemicals. Biochemical sulfide potential (BSP) test was used to evaluate the effectiveness of EPT on sludge sulfide production. The sulfide control was effective with EPT, and we determined the underlying mechanism of EPT. EPT which was operated at 12 V for 720 s eliminated 99% of dissolved sulfide and 100% of gaseous H2S(g). In comparison, the dissolved sulfide reached 104 ± 1 mg S/L in the control BSP test. A sulfur mass balance analysis in the BSP test showed that 90% of the produced sulfide was removed via metal precipitation. Metal distribution results confirmed that metals (i.e., Fe, Mn, and Ni) in the sludge became soluble after EPT and were released from their residual and organically bound fractions. EPT which was operated at 15 V solubilized around 73, 92, and 72% of Fe, Mn, and Ni, and these metals precipitated the sulfide that was produced from biological sulfate reduction. Sludge analysis revealed that EPT disintegrated sludge flocs and disrupted metal-binding functional groups. Specifically, reduction of 17% C═O functional groups in the sludge was found, which could be associated with metal release. The impact of oxidants (e.g., chlorine) generated from EPT on sulfide oxidation was minimal. The findings of this study broadened up our understanding of the electrochemical process for sulfide control during saline sludge digestion.

A novel approach to quantifying elemental sulfur (S0) in environmental samples.

The quantification of elemental sulfur (S0) is an important part of monitoring and controlling sulfur-involving processes. Existing methods of S0 detection either require significant time or involve the use of toxic chemicals. We have developed and validated a new method to determine S0 in environmental samples using calorimeter-ion chromatography (IC), in which S0 is fully oxidized to sulfur trioxide (SO3) with pure oxygen at 20 atm in a calorimeter. The resulting SO3 is then absorbed by a sodium bicarbonate (NaHCO3) solution and analyzed using IC. To verify this method, standard samples with various sulfur contents (5-200 mg S), possible interfering substances (SO42-, SO32-, S2O32- and S2-), and mixed environmental samples were tested and compared. The high correlation of R2 = 0.999 between the examined and theoretical values was obtained with a high recovery rate of ≥95% and a low relative standard deviation (RSD) of ≤1%. Samples containing at least 25 mg of S0 were accurately measured (recovery error < 5%). Thiosulfate was identified as the main interfering substance, and pretreatment was needed to eliminate it. This new method is more efficient, cost-effective, easier to operate, and more secure and accurate than existing methods.

Resilience of sulfate-reducing granular sludge against temperature, pH, oxygen, nitrite, and free nitrous acid.

Sulfate-reducing granular sludge has recently been developed and characterized in detail as part of the development of the sulfate reduction, autotrophic denitrification, nitrification integrated (SANI) process. However, information regarding temperature of granules to environmental fluctuation is lacking, an aspect that is important in dealing with real wastewater. A comprehensive assessment of sulfate-reducing granular sludge performance under various environmental conditions was thus conducted in this study, including temperature, pH, oxygen, nitrite, and free nitrous acid (FNA) as possible encountering conditions in the removal of organics and/or nitrate. Specific chemical oxygen demand removal rate of the granules was determined to be reduced by 65 % when the temperature varied between 10-15 °C, reduced by 70 % when dissolved oxygen (DO) was 0.5 mg/L or greater, and at least, reduced by 75 % when nitrite was 30 mg N/L or above. Nevertheless, the sludge activity recovered by 82, 100, and 86 % from exposure to high oxygen and nitrite and low temperature levels, respectively. Combined inhibition of nitrite and FNA on the sludge is strong and complex, while FNA alone reduced cell viability from 60 to 40 % when its concentration increased to 2.3 mg N/L. The present study demonstrates that sulfate-reducing bacteria (SRB) granules possess high resilience against varying environmental conditions, showing the high application potential of sulfate-reducing granular sludge in dealing with brackish and saline industrial or domestic wastewaters.

New insights on ecological roles of waste activated sludge in nutrient-stressed co-digestion.

There have been extensive applications of waste activated sludge (WAS) in anaerobic co-digestion (AcoD). Nonetheless, mechanisms through which AcoD systems maintain stability, particularly under nutrient-stressed conditions, are under-appreciated. In this study, the role of WAS in a nutrient-stressed WAS-food waste AcoD system was re-evaluated. Our findings demonstrated that WAS-based co-digestion increased methane production (by 20-60%) as WAS bolsters such systems' resilience via establishing a core niche-based microbial balance. The carbon utilization investigation suggested a microbial niche balance is attainable if two conditions are satisfied: 1) hydrolysis efficiency is greater than 50%; and 2) both the acidogenesis-to-hydrolysis and acetogenesis-to-hydrolysis efficiencies surpass 0.5. Metagenomic assembly genome (MAG) analysis indicated that the versatile metabolic characteristics strengthened the microbial niche balance, rendering the system resilient and efficient through a syntrophic mode, contributing to both acidogenesis and acetogenesis. The findings of this study provide new insights into the ecological effects of WAS on AcoD.

Carbon fixation via volatile fatty acids recovery from sewage sludge through electrochemical-pretreatment-based anaerobic digestion.

Capturing the carbon in volatile fatty acids (VFA) produced from the anaerobic digestion (AD) of sewage sludge has the potential to not only provide economic benefits but also reduce greenhouse gas production. This study demonstrates a chemical-free method to collect VFA from an AD instead of methane that involves electrochemical pretreatment (EPT) of sludge. Experimental results show that applying 15 V EPT for 45 min enhances acidogenesis and selectively inhibits methanogenesis, leading to a substantial VFA accumulation (2563.1 ± 307.9 mg COD/L) and achieving 2.5 times more carbon fixation than via methane production. Interfacial thermodynamic analysis shows that EPT induces a decrease in both the repulsive electrostatic energy (from 152.9 kT to 12.2 kT) and the energy barrier (from 57.0 kT to 2.6 kT) in the sludge, leading to increased sludge aggregation and entrapment of microorganisms. Molecular docking sheds lights on how the methanogens interacts with the organic matter released from EPT (e.g., alanine-tRNA ligase), showing that these interactions potentially interfere with the proteins that are associated with the activities of the methanogens and the electron transfer pathways, thereby impeding methanogenesis. Integrating EPT into AD therefore facilitates the recovery of valuable VFA and the capture of carbon from freshwater sludge, providing notable economic and environmental benefits in sewage sludge treatment.

Disentangling microbial niche balance and intermediates' trade-offs for anaerobic digestion stability and regulation.

Anaerobic digestion (AD) is a key technology for converting organic matters to methane-rich biogas. However, nutrient imbalance can destabilize the whole digestion. To realize stable operation of AD and improve its efficiency, this work considers a new strategy to control the intermediate concentrations of poor AD under nutrient stress. For this purpose, long-term digestion under different nutrient conditions was investigated. Results showed that the feedstock with a low C/N ratio (= 6) caused VFA accumulation (2072 ± 632 mg/L), leading to the inhibition of methane production. Employing a substrate with a higher C/N ratio (= 11) and/or adding NH4HCO3 (200 mg NH4+-N/Ladd) could alleviate the VFA inhibition, but excessive dosage of NH4HCO3 would induce ammonia inhibition. Through the established digestion balance between free ammonia nitrogen (FAN) between 0 and 25 mg/L, volatile fatty acid (VFA) 510-2100 mg/L, and alkalinity (ALK) 3300-7800 mg/L, an efficient methane yield of 150-250 mL/g VS was achieved and stable operation of AD under nutrient stress (low C/N ratio) was realized. Metabolic reconstruction between Euryarchaeota sp. MAG162, Methanosarcina mazei MAG53 and Mesotoga infera MAG119 highlighted that microbial niche balance was developed as a result of digestion balance, which is beneficial for stable operation of AD. These findings improved our understanding of the interaction mechanism between intermediates and microbial niches for stability control in AD.

Chlorination-improved adsorption capacity of microplastics for antibiotics: A combined experimental and molecular mechanism investigation.

Microplastics and antibiotics not only pollute aquatic environments and threaten human health, but are also tricky to remove. Microplastics adsorb antibiotics, and, before being released into the natural environment, most microplastics pass through some wastewater treatment and/or disinfection (such as chlorination) facilities. It is therefore necessary to understand how these treatment processes may affect or alter microplastics' properties, particularly their ability to adsorb antibiotics, and whether or not the two, when bound together, may present exacerbated harm to the environment. This study used both laboratory tests and molecular dynamics simulation to investigate the mechanism through which chlorinated microplastics (specifically polystyrene) adsorb the antibiotic tetracycline, and showed that chlorination gave the polystyrene a larger interaction area (> 21%) and more free energy (> 14%) to adsorb tetracycline. Van der Waals (vdW) forces played a more dominant role than electrostatics in facilitating tetracycline's adsorption. Moreover, a density functional theory analysis demonstrated that the vdW potentials of the microplastics decreased as more and more hydrogen atoms became replaced by chlorine, suggesting a facilitation of the adsorption of polycyclic antibiotic molecules. The experimental results confirmed the simulation's prediction that a higher degree of chlorination significantly increases the polystyrene's adsorption capacity, whereas pH and salinity had almost no effect on the adsorption. This study demonstrates that disinfection elevates the risk of antibiotics adhering to and accumulating on the surface of microplastics.

Sulfur bacteria-reinforced microbial electrochemical denitrification.

Two limiting factors of microbial electrochemical denitrification (MED) are the abundance and efficiency of the functional microorganisms. To supply these microorganisms, MED systems are inoculated with denitrifying sludge, but such method has much room for improvement. This study compared MED inoculated with autotrophic denitrifying inoculum (ADI) versus with heterotrophic denitrifying inoculum (HDI). ADI exhibited electroactivity for 50% less of timethan HDI. The denitrification efficiency of the ADI biocathode was42% higherthan that of the HDI biocathode. The HDI biocathode had high levels of polysaccharides while the ADI biocathode was rich in proteins, suggesting that two biocathodes may achieveMED but via differentpathways. Microbial communities of two biocathodes indicated MED of HDI biocathode may rely on interspecies electron transfer, whereas sulfur bacteria of ADI biocathode take electrons directly from the cathode to achieve MED. Utilizing autotrophic sulfur-oxidizing denitrifiers, this study offers a strategy for enhancing MED.

Long-term stable and efficient degradation of ornidazole with minimized by-product formation by a biological sulfidogenic process based on elemental sulfur.

Conventional biological treatment processes cannot efficiently and completely degrade nitroimidazole antibiotics, due to the formation of highly antibacterial and carcinogenic nitroreduction by-products. This study investigated the removal of a typical nitroimidazole antibiotic (ornidazole) during wastewater treatment by a biological sulfidogenic process based on elemental sulfur (S0-BSP). Efficient and stable ornidazole degradation and organic carbon mineralization were simultaneously achieved by the S0-BSP in a 798-day bench-scale trial. Over 99.8 % of ornidazole (200‒500 µg/L) was removed with the removal rates of up to 0.59 g/(m3·d). Meanwhile, the efficiencies of organic carbon mineralization and sulfide production were hardly impacted by the dosed ornidazole, and their rates were maintained at 0.15 kg C/(m3·d) and 0.49 kg S/(m3·d), respectively. The genera associated with ornidazole degradation were identified (e.g., Sedimentibacter, Trichococcus, and Longilinea), and their abundances increased significantly. Microbial degradation of ornidazole proceeded by several functional genes, such as dehalogenases, cysteine synthase, and dioxygenases, mainly through dechlorination, denitration, N-heterocyclic ring cleavage, and oxidation. More importantly, the nucleophilic substitution of nitro group mediated by in-situ formed reducing sulfur species (e.g., sulfide, polysulfides, and cysteine hydropolysulfides), instead of nitroreduction, enhanced the complete ornidazole degradation and minimized the formation of carcinogenic and antibacterial nitroreduction by-products. The findings suggest that S0-BSP can be a promising approach to treat wastewater containing multiple contaminants, such as emerging organic pollutants, organic carbon, nitrate, and heavy metals.

From liquid to solid: A novel approach for utilizing sulfate reduction effluent through phase transition - Effluent-induced nanoscale zerovalent iron sulfidation.

This study investigated the use of sulfate reduction effluent (SR-effluent) to induce sulfidation on nanoscale zerovalent iron (nZVI). SR-effluent-modified nZVI achieved a 100% improvement in Cr(VI) removal from simulated groundwater, a result comparable to cases where other, more typical sulfur precursors (Na2S2O4, Na2S2O3, Na2S, K2S6, and S0) were used. Through a structural equation model analysis, amendment of nanoparticles' agglomeration (standardized path coefficient (std. path coeff.) = -0.449, p < 0.05) and hydrophobicity (std. path coeff. = 0.100, p < 0.05) and direct reaction between iron-sulfur compounds and Cr(VI) (std. path coeff. ranged from -0.195 to 0.322, p < 0.05) were primarily contributing to sulfidation-induced Cr(VI) removal enhancement. Regarding the property improvement of nZVI, the SR-effluent's corrosion radius played a crucial role in tuning the content and distribution of the iron-sulfur compounds based on the core-shell structure of the nZVI and the redox processes at the aqueous-solid interface.

Mechanistic study on the ferric chloride-based rapid cultivation and enhancement of aerobic granular sludge.

Aerobic granular sludge (AGS) can achieve simultaneous carbon, nitrogen and phosphorus removal owing to its three-dimensional oxygen gradient structure. However, long start-up period and poor operational stability restrict its application and promotion. A novel rapid granulation strategy, viz., the short-term (7 days) addition of ferric chloride at the commissioning stage, was developed and verified in this study. The granulation period was shortened by 9 days, and the formed granules were compact and dense with an Fe3+ concentration of 250 mg L-1. The addition of flocculant not only maintained a high sludge concentration during the initial stages of granulation (5.3 g L-1), but also stimulated the secretion of TB-EPS and increased protein and polysaccharide contents, thereby expediting granule formation. Additionally, ferric chloride induced a diverse microbial community in granules, resulting in the emergence of new genera, such as Thaurea, Brevundimonas and Kinneretia, which improved pollutant removal performance and flocculent aggregation. The removal efficiencies of COD, PO43--P, and NH4+-N stabilized at 94.2, 62.4, and 71.3%, respectively. Therefore, it has been demonstrated that short-term ferric chloride dosing has a synergistic effect on aerobic granulation.

Achieving tetracycline removal enhancement with granules in marine matrices: Performance, adaptation, and mechanism studies.

Using the aerobic granular sludge (AGS) to improve tetracycline (TET) removal in the treatment of mariculture wastewater was investigated in the present study. The AGS rapidly adapted to and was sustained in seawater matrices with a robust granule strength (k = 0.0014) and a more stable sludge yield than the activated sludge (AS) (0.14 vs 0.11 g-VSS/g-CODrem). The compact structure provided the AGS with an anoxic environment, which favored the growth of N (37.3 %) and P removal bacteria (30.4 %) and the expression of functional genes (nos, nor, and nar), resulting in more than 62 % TN and TP removals, respectively. Similar abundances of aromatic compound-degrading bacteria (∼34 %) in both reactors (AGS and AS) led to comparable TET biodegradation efficiencies (∼0.045 mg/g-VSS). The greater size and surface area of the AGS expanded the boundary layer diffusion region, leading to 16 % increases in the granule's TET adsorption capacity.

In situ coagulation-electrochemical oxidation of leachate concentrate: A key role of cathodes.

To efficiently remove organic and inorganic pollutants from leachate concentrate, an in situ coagulation-electrochemical oxidation (CO-EO) system was proposed using Ti/Ti4O7 anode and Al cathode, coupling the "super-Faradaic" dissolution of Al. The system was evaluated in terms of the removal efficiencies of organics, nutrients, and metals, and the underlying cathodic mechanisms were investigated compared with the Ti/RuO2-IrO2 and graphite cathode systems. After a 3-h treatment, the Al-cathode system removed 89.0% of COD and 36.3% of total nitrogen (TN). The TN removal was primarily ascribed to the oxidation of both ammonia and organic-N to N2. In comparison, the Al-cathode system achieved 3-10-fold total phosphorus (TP) (62.6%) and metal removals (>80%) than Ti/RuO2-IrO2 and graphite systems. The increased removals of TP and metals were ascribed to the in situ coagulation of Al(OH)3, hydroxide precipitation, and electrodeposition. With the reduced scaling on the Al cathode surface, the formation of Al3+ and electrified Al(OH)3 lessened the requirement for cathode cleaning and increased the bulk conductivity, resulting in increased instantaneous current production (38.9%) and operating cost efficiencies (48.3 kWh kgCOD -1). The present study indicated that the in situ CO-EO process could be potentially used for treating persistent wastewater containing high levels of organic and inorganic ions.

From micro to macro: The role of seawater in maintaining structural integrity and bioactivity of granules in treating antibiotic-laden mariculture wastewater.

Granular sludge (GS) has superior antibiotic removal ability to flocs, due to GS's layered structure and rich extracellular polymeric substances. However, prolonged exposure to antibiotics degrades the performance and stability of GS. This study investigated how a seawater matrix might help maintain the structural integrity and bioactivity of granules. The results demonstrated that GS had better sulfadiazine (SDZ) removal efficiency in a seawater matrix (85.6 %) than in a freshwater matrix (57.6 %); the multiple ions in seawater enhanced boundary layer diffusion (kiR1 = 0.0805 mg·g-1·min-1/2 and kiR2 = 0.1112 mg·g-1·min-1/2) and improved adsorption performance by 15 % (0.123 mg/g-SS freshwater vs. 0.141 mg/g-SS seawater). Moreover, multiple hydrogen bonds (1-3) formed between each SDZ and lipid bilayer fortified the adsorption. Beyond S-N and S-C bond hydrolyses that took place in freshwater systems, there was an additional biodegradation pathway for GS to be cultivated in a saltwater system that involved sulfur dioxide extrusion. This additional pathway was attributable to the greater microbial diversity and larger presence of sulfadiazine-degrading bacteria containing SadAC genes, such as Leucobacter and Arthrobacter, in saltwater wastewater. The findings of this study elucidate how seawater influences GS properties and antibiotic removal ability.