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Owing to the development of urbanization, the amount of sewage sludge generated through biological activated sludge process has increased dramatically. Anaerobic fermentation of sludge is recognized as an expedient and efficient treatment process, widely applied for biogas generation, resource recovery, and volatile fatty acid production. Volatile fatty acids are one of the most widely used carbon sources and have great use in biological nutrient removals. Volatile fatty acids production in anaerobic sludge fermentation is affected by sludge properties, metabolic pathways, and operating parameters. This paper aims to present an overview of the recent advancement in volatile fatty acids production from waste activated sludge. Standalone and hybrid pretreatment methods prior to the sludge fermentation were introduced and assessed based on VFAs accumulation rate and system performance. In addition, different metabolic steps involved in anaerobic fermentation (i.e. hydrolysis, acidification, and methanogenesis) were deeply evaluated. More importantly, the effects of humic substances were evaluated, among which, the electron transfer, the enzyme activity of microbial species, and the interaction between exogenous electron transporters and humic substances were illustrated. Furthermore, the influence of nitrogen and phosphorus ingredients in sludge fermentation and volatile fatty acids production was introduced. It was found that the additives and pretreatment of waste activated sludge are energetically preferred for the hydrolysis improvement and accelerating the volatile fatty acids accumulation. It was concluded that different structures of humic substances may have different effect on the fermentation process and volatile fatty acids production. The synergistic addition of hydrolytic enzymes assisted to reverse the negative effect of humic acids in some cases, and mitigated the adverse effect of humic substances on the inhibition of bacterial growth. The composition and properties of waste activated sludge may limit its biodegradability and hamper the volatile fatty acids production.

Hemin has attracted considerable interest as an efficient catalyst recently, however, its direct application is inefficient due to severe molecular aggregation. Immobilizing hemin on various supports is a feasible approach to address this issue. In this work, a CNTs-hemin catalyst was prepared by loading hemin onto multiwalled carbon nanotubes (CNTs) through ball milling. Compared with hemin, CNTs-hemin demonstrates remarkably enhanced performance in the peroxymonosulfate system, with a 650-fold improvement of apparent rate constant, reaching 97.8% degradation of sulfathiazole in 5 min. High-valent iron-oxo porphyrin cation ((Porp)

Arsenic-alkali residue (AAR) from antimony production can pose significant health and environmental hazards due to the risk of arsenic (As) leaching. In this study, geopolymer composite synthesized from fly ash (FA) was investigated for efficient stabilization of high-arsenic-containing AAR (As

Waste activated sludge and food waste are two typical important domestic low-value organic solid wastes (LOSW). LOSW contains significant organic matter and water content resulting in the transboundary transfer of liquid-solid-gas and other multi-mediums, such that the complexity of microplastics (MPs) migration should be of greater concern. This article provides a review of the literature focusing on the separation and extraction methods of MPs from LOSW. The occurrence and source of MPs are discussed, and the output and impact of MPs on LOSW heat and biological treatments are summarized. The fate and co-effects of MPs and other pollutants in landfills and soils are reviewed. This review highlights the migration and transformation of MPs in domestic source LOSW, and future perspectives focused on the development of a unified extraction and analysis protocol. The objective of this review is to promote the technological development of decontamination of MPs in LOSW by sufficient understanding of the fate of MPs, their interaction with coexisting pollutants and the development of targeted preventive research strategies.

Sludge hydrolysis is a vital step in anaerobic digestion of sludge. This study compared the efficacy of free versus immobilized enzymes at different concentrations in promoting sludge disintegration. Pretreatment with 1,000 mg/L immobilized enzymes was more efficient in promoting sludge disintegration than free enzymes at the same concentration. Under the optimized conditions, volatile fatty acids (VFAs) were produced at 10.6 g/L, accounting for 85 % of total soluble chemical oxygen demand. Improved VFA production was attributed to the release of large amounts of polysaccharides and proteins from the enzymatically pretreated sludge. Released organic matter are the substrates for VFAs generated by the determined microbial community of Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi. In this study, anaerobic fermentation was used to successfully convert organic matter in sludge into high-value-added VFAs. Therefore, this process can be selected as a strategy to reduce carbon emissions from wastewater treatment plants (WWTPs).

This study investigated the effects of electrical signaling disruption induced by adding tetraethylammonium (TEA, a potassium channel blocker) on the formation of mixed-cultured electroactive biofilms, especially the relative abundance of Geobacter over time. Results showed that TEA addition decelerated the biofilm formation, but selectively enriched Geobacter over time (45.8% on Day 32, 67.7% on Day 60 and 78.1% on Day 90), thus resulting in higher final extracellular electron transfer (EET) efficiency. Redundancy analysis (RDA) confirmed that TEA and operation time were significant factors for the selective enrichment of Geobacter. Moreover, increase in cellular processes and signal processing by PICRUSt analysis indicated adaptive responses of electrogenic biofilms to electrical signaling disruption. Furthermore, qRT-PCR indicated the compensatory roles of key cytochromes and pilA in electrochemical communication, which induced Geobacter enrichment. This work provided a broader understanding of electroactive biofilm regulation and potential applications for electricity generation and biosensor in the future.

A microbial fuel cell-photocatalysis system with a novel photocatalytic air-cathode (MFC-PhotoCat) was proposed for synergistic degradation of 2,4,6-trichlorophenol (TCP) with simultaneous electricity generation. Stable electricity generation of 350 mV was achieved during 130 days of operation. Besides, 50 mg L−1 TCP was completely degraded within 72 h, and the rate constant of 0.050 h−1 was 1.8-fold higher than MFC with air-cathode without N-TiO2 photocatalyst. Degradation pathway was proposed based on the intermediates detected and density functional theory (DFT) calculation, with two open-chain intermediates (2-chloro-4-keto-2-hexenedioic acid and hexanoic acid) detected. Furthermore, hierarchical cluster and PCoA revealed significant shifts of microbial community structures, with enriched exoelectrogen (55.2% of Geobacter) and TCP-degrading microbe (7.1% of Thauera) on the cathode biofilm as well as 61.8% of Pseudomonas in the culture solution. This study provides a promising strategy for synergic degradation of recalcitrant contaminants by intimate-coupling of MFC and photocatalysis.

Biological wastewater treatment generates a large quantity of sewage sludge that requires proper treatments. In this study, the biochar pyrolyzed by sludge conditioned with Fenton's reagent and lime (referred to as Fenton-lime system) was first used as an efficient silicon fertilizer for rice cultivation. When the pyrolysis temperature was 750 °C, the dissolved silicon and available silicon contents in biochar derived from sludge conditioned with Fenton-lime system were much higher than those in raw sludge derived biochar without conditioning (3.49 vs. 0.72, 77.25 vs. 2.33 mg/g dry solid, respectively). The enhanced available silicon content was attributed to the newly formed calcium aluminosilicate from the reactions between the added lime and silicon-rich phases in sludge. The rice cultivated with biochar derived from Fenton-lime conditioned sludge showed improved biomass of stem and root by 76.85% and 36.11%, respectively, compared to blank group without the addition of Si source. Heavy metals and the reactive oxygen species (ROS) accumulation in rice were not observed after a culture period of 30 days in the application of sludge-derived biochar as silicon fertilizer. This study provides a promising approach for sewage sludge recycling as an efficient silicon fertilizer in silicon-deficiency land.

Groundwater treatment sludge is an industrial waste that is massively produced from groundwater treatment plants. Conventional methods for treatment of this sludge, such as discharge into deep wells or the sea, or disposal at landfills, are not environmentally sustainable. Here, we demonstrate an alternative strategy to recycle the sludge by preparing a magnetic maghemite adsorbent via a one-step hydrothermal method with NaOH solution as the only solvent. With this method, the weakly magnetized sludge, which contained 33.2% iron (Fe) and other impurities (e.g., silicon (Si), aluminum (Al), and manganese (Mn)), was converted to magnetic adsorbent (MA) with the dissolution of Si/Al oxides (e.g., quartz and albite) into the liquid fraction. At a NaOH concentration of 2 mol·L−1, approximately 18.1% of the ferrihydrite in the Fe oxides of the sludge was converted into 11.2% maghemite and 6.9% hematite after the hydrothermal treatment. MA2 (i.e., MA produced by a 2 mol·L−1 NaOH concentration) exhibited a good magnetic response of 8.2 emu·g−1 (1 emu = 10−3 A·m2), and a desirable surface site concentration of 0.75 mmol·g−1. The synthesized MA2 was used to adsorb the cationic pollutant tetracycline (TC). The adsorption kinetics of TC onto MA2 fitted well with a pseudo-second-order model, and the adsorption isotherms complied well with the Langmuir model. The maximum adsorption capacity of MA2 for TC was 362.3 mg·g−1, and the main mechanism for TC adsorption was cationic exchange. This study is the first to demonstrate the preparation of an MA from recycled sludge without a reductant and/or exogenous Fe source. The prepared adsorbent can be used as a low-cost adsorbent with high capacity for TC sorption in the treatment of TC-containing wastewater. Keywords: Groundwater treatment sludge, Maghemite, Cationic exchange, Adsorption, Tetracycline

Wet chemical approach is widely applied for P extraction from incinerated sewage sludge ash (ISSA) due to the relatively simple process and low lost. In this study, H2SO4 and H2C2O4 were compared to recover P from ISSA through three steps of acid leaching, cation exchange resin (CER) purification and precipitation. Transformations of P speciation and mineral phases in ISSA from 600 to 900 °C were studied. The results showed that the ISSA samples were mainly composed of inorganic P (IP), and part of non-apatite IP (NAIP, mainly AlPO4) would transform to apatite P (AP, Ca3(PO4)2) with the increase in temperature. The ratio of NAIP to IP dropped from 71.9% at 600 °C to 53.7% at 900 °C. Effect of acid concentration on the leaching efficiency of P from the ISSA samples incinerated at different temperatures by H2SO4 and H2C2O4 was investigated, and the leaching behaviors of key elements of P, Ca, Al and Fe were compared. H2C2O4 exhibited a better performance than H2SO4 for the leaching efficiency of P. Severe sintering of ash particles occurred at temperature >800 °C inhibited the P leaching by H2SO4. During CER purification, the impurity elements in the H2SO4 leachate were easily removed by CER, whereas the Al and Fe elements in the H2C2O4 leachate were hardly removed due to the formation of anionic complexes between Al3+/Fe3+ and oxalic ions. Finally, high-purity struvite product was synthesized from the purified H2SO4 leachate, which could be directly utilized as a fertilizer with negligible environmental risk. Amorphous aluminum and iron hydroxyphosphates were obtained from the H2C2O4 leachate. This study provides insights for P recovery from ISSA samples by different acid leaching systems.

In this study, a method to reduce the emission of NOx precursors (e.g., hydrogen cyanide (HCN) and ammonia (NH3)) while simultaneously reclaim more plant-available P was proposed through pyrolyzing ferric sludge (sludge conditioned by Fenton's reagents) rather than raw sludge. The nitrogen and phosphorus transformation at different pyrolysis temperatures was investigated. The results indicated that in comparison with the pyrolysis of raw sludge, the remaining iron compounds in ferric sludge can fix char-N in more stable forms (e.g., appearance of pyrrole-N at 900 °C). The secondary cracking of amine-N compounds in tar-N (e.g., 81.67% increase of amine-N at 900 °C) can be inhibited. Hence, more amine-N was remained and less heterocyclic-N and nitrile-N compounds were generated in tar N. Less generation of NH3-N and HCN-N was also observed in NOx precursors (e.g., 5.46% decrease of NH3-N and 6.91% decrease of HCN-N at 900 °C). Moreover, the results of X-ray diffractometry, liquid 31P nuclear magnetic resonance spectroscopic, X-ray photoelectron spectroscopic, and chemical analyses collectively indicated that iron present in ferric sludge also favored reclamation of more plant-available P. In comparison with the pyrolysis of raw sludge, an increase in the total phosphorus pool was noted (18.06–36.26 versus 15.54–30.59 mg g−1 dry solids). A decrease in mobility with the predominant P as sodium hydroxide (NaOH)-P, and an increase in plant-available P can be also obtained. This study indicated that pyrolysis of ferric sludge was a feasible way to simultaneously reduce emission of NOx precursors, reclaim plant-available P, and reuse ferric sludge.

Pre-oxidation is effective in enhancing sludge dewaterability. Different types and doses of oxidants are used to improve sludge dewaterability in pre-oxidation. Rapid evaluation of the sludge dewaterability is vital for optimizing the type and dose of oxidants in pre-oxidation. It normally takes more time to evaluate sludge dewaterability by measuring typical indicators such as specific resistance to filtration (SRF), content of bound water, and composition of EPS. This study presented a rapid parameter, oxidation-reduction potential (ORP), to correlate it with the dewaterability of pre-oxidized sludge samples. An index of ΔORP (ΔORP = ORPt=0.5 min–ORPt=0 min) showed positive correlations with SRF (r = 0.89, p

Mn-containing sludge from groundwater treatment was converted to magnetic particles (MPs) via a one-step hydrothermal method using sodium ascorbate (SA) as the reductant. The MPs were characterized by X-ray diffraction spectroscopy, Mossbauer spectroscopy, X-ray fluorescence spectroscopy, magnetometry and Gran titration and the results showed that magnetic jacobsite was obtained as an intermediate product in transformation of Fe/Mn oxides to siderite and rhodochrosite. When the molar ratio of SA to Mn in the sludge was two, the produced MPs-2 contained a mixture of ferrihdyrite, hematite, jacobsite and Si/Al oxides, and could magnetize at 2.4 emu/g. Ferrihydrite content in MPs decreased with increase of the SA/Mn molar ratio, leading to decrease of the surface sites concentration (Hs). Thus, MPs-2 contained optimized Hs of 6.7 mmoL/g and a desirable adsorption capacity of Cu(II) (73.1 mg/g). The adsorption isotherms of MPs-2 on Cu(II) complied with the Langmuir model and the adsorption kinetics fitted well with the pseudo-second-order model. The major mechanism of adsorption was cationic exchange of the coordinated H and Na ions on MPs-2 surface sites with the Cu(II) ions. This study was the first time to report preparation of MPs by recycling Mn-containing sludge, which could be used as a high-capacity and low-cost adsorbent in treatment of heavy metal-containing wastewater.

Cell lysis in sludge pretreatment by advanced oxidation process (AOP) has a great effect on sludge dewaterability. Cell lysis caused by reactive radicals (e.g. hydroxyl radical) was dependent on the reaction site of AOP. However, little is known about the accurate radical generation site of AOP in sludge pretreatment. In this study, two kinds of oxidation behaviors from different oxidants (HOCl vs. H2O2) catalyzed by ferrous iron were comparatively investigated. Higher amount of living cells (84.3%) and hydroxyl radicals (9.86 × 10−5 M), and more fragmentized sludge flocs (particle sizes of D50 was 50.1 vs. 57.3 μm of RS) were detected in sludge conditioned by Fe2+/H2O2, which implied that Fenton reaction mainly happened at surface and outside of sludge flocs (such as EPS layer and liquid phase). Thus, it could be regarded as “extracellular oxidation”. Fewer living cells (undetectable), fewer amount of hydroxyl radicals (undetectable in sludge), and more integrated sludge flocs (particle size of D50 was 56.1 vs. 57.3 μm of RS) were determined in sludge conditioned by Fe2+/Ca(ClO)2. Hence, it could be regarded as “Intracellular oxidation”. In addition, sludge pretreatment based on Fe2+/Ca(ClO)2 could achieve simultaneous deep-dewatering performance and total coliforms inactivation. Based on response surface methodology, the optimal dosages of Fe2+ and Ca(ClO)2 were proposed as 106.1 and 234.5 mg/g volatile solids respectively, without any acidification of sludge. Under these optimal dosages, the water content of dewatered sludge cake was 51.9 ± 0.1 wt% and the pH of the final filtrate was 5.8 ± 0.2. Total coliforms of sludge could be inactivated in 10 s after Fe2+/Ca(ClO)2 addition.

Bio-electro-Fenton (BEF) system holds great potential for sustainable degradation of refractory organics. Activated carbon (AC) air cathode was modified by co-pyrolyzing of AC with glucose and doping with nano-zero-valent iron (denoted as nZVI@MAC) in order to promote two-electron oxygen reduction reaction (2e- ORR) for enhanced oxidizing performance. Single chamber microbial fuel cells (SCMFCs) with nZVI@MAC cathode was examined to degrade landfill leachate. It was revealed that nZVI@MAC cathode SCMFC showed higher degradation efficiency towards landfill leachate. Six landfill leachate treatment cycles indicated that nZVI@MAC cathode SCMFC exhibited higher COD removal efficiencies over AC and nZVI@AC and greatly enhanced columbic efficiency compared to AC and nZVI@AC cathode. Anti-biofouling effect was found on nZVI@MAC cathode because of the high Fenton oxidation effects at the vicinity of the cathode. Electrochemical characterizations indicated that MAC cathode had superior 2e- ORR capability than AC and nZVI@AC cathode, which was further evidenced by higher H2O2 production from nZVI@MAC cathode in SCMFC. Graphitic structure of MAC was evidenced by High Resolution Transmission Electron Microscopy, and glucose pyrolysis also resulted in nano carbon spheres on the activated carbon skeletons. Raman spectra indicated more defects were generated on MAC during its co-pyrolyzation with glucose.

Electroplating sludge is a hazardous waste produced in large quantities in the electroplating industry during production. It is rich in heavy metal resources and can be recovered as value-added heavy metal products. To recover Zn in electroplating sludge, Fe/Al/Ca impurities were effectively removed as hematite, boehmite, and calcium sulfate, respectively, via a facile hydrothermal method with reduction of nitric acid by addition of glucose. After the sludge was dissolved in nitric acid, the generated solution contained 6.1 g/L of Zn, 2.2 g/L of Fe, 2.5 g/L of Al, and 2.9 g/L of Ca. First, approximately 100% Fe was extracted as hematite nanoparticles containing 94.6 wt% Fe2O3 after the solution was treated at 190 °C for 6 h. Second, when the temperature was elevated to 270 °C, nearly 99% Al was isolated as boehmite particles containing 95.2 wt% Al2O3. Third, more than 98% Ca was removed as anhydrite, which contained 95.9 wt% CaSO4, by adding sulfuric acid. During the steps, the total loss of Zn was less than 3%, and 5.75 g/L of residual Zn was recovered as zincite containing 92.2 wt% ZnO by adjusting the pH to 8. The dissolved Fe, Al, and Ca impurities were successfully removed as purified hematite, boehmite, and anhydrite, respectively, through the stepwise separation method by adjusting reaction temperatures and pH. The high content of Zn in the electroplating sludge was finally purified as zincite.

Microplastic accumulation in agricultural soils can stress plants and affects quality of the products. Current research on the effects of microplastics on plants is not consistent and the underlying mechanisms are yet unknown. Here, the molecular mechanisms of the stress response were investigated via metabolomic and transcriptomic analyses of rice Oryza sativa L. II Y900 and XS123 under the exposure of polystyrene microplastics (PS-MPs) in a field study. Distinct responses were obtained in these two rice subspecies, showing decreased head rice yield by 10.62% in Y900 and increase by 6.35% in XS123. The metabolomics results showed that PS-MPs exposure inhibited 29.63% of the substance accumulation-related metabolic pathways and 43.25% of the energy expenditure-related metabolic pathways in the Y900 grains; however, these related pathways were promoted in the XS123 grains. The transcriptomics results indicated that the expression of genes encoding proteins involved in the tricarboxylic acid cycle in the Y900 grains was inhibited, but it was enhanced in the XS123 grains. The XS123 subspecies could response against microplastic exposure stress through the metabolite accumulation and energy expenditure pathways, while the Y900 could not. The results provide insight into the perturbation of rice grains in farmlands with microplastics contamination.

Microbial fuel cell (MFC) sensor exhibits attractive prospects for online monitoring of water toxicity as an early warning device. However, the accumulation of dead cells in anode biofilm might decrease the sensing sensitivity of MFC during long term operation. In addition, with repeated exposure to toxins, the microbial community of anode biofilm would also adjust to build up higher endurance to environmental toxicity. In this study, the long term sensing sensitivity of MFC sensor and the microbial community changes were characterized with Pb2+ as the target toxin. The results show that newly formed biofilm with higher live/dead cell ratio exhibited higher sensitivity than mature biofilm. Modification of anodic biofilm via high current stimulation was applied to increase the ratio of live cells, which led to enhanced sensing sensitivity of MFC with mature anode biofilm. However, the enhancement was relatively limited for biofilm that was previously exposed to repeated Pb2+ shocks. Microbial community analysis revealed that the proportions of microbial species possessing higher environmental robustness, such as Hyphomicrobiaceae and Cloacibacillus, significantly increased in the anode biofilm after long term repeated Pb2+ shocks.

Oxidation ditches (ODs) are often used for wastewater treatment. However, limitations of ODs like high energy expenditure and increased sludge sedimentation hinder its wide application. In this study, the computational fluid dynamics (CFD) model integrated with Activated Sludge Model No. 2 (ASM2) was proposed and applied in a full-scale OD. The integrated model provided heterogeneous information on the characteristics of hydrodynamics and biokinetics of OD, especially with respect to the simulation of total phosphorus removal by CFD-ASM2 integration model for the first time. The simulated values of flow velocities, suspended solids (SS), dissolved oxygen, chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus concentrations were well validated with the measured results, with the standard deviation errors of less than 5.56%, 0.28%, 0.74%, 7.39%, 3.17%, 5.27%, and 7.40%, respectively. Based on the integrated model, four different operational strategies were simulated. The proposed operational strategy of operating 7 surface aerators and 10 submerged impellers not only met the standard discharge requirements (GB 18918-2002) but also consumed less energy by 22.3%, compared with the original strategy of operating 9 surface aerators and 13 submerged impellers. Meanwhile, this proposed operational strategy also reduced the SS concentrations in the second and fourth channels, which was beneficial to elimination of sludge sedimentation. Moreover, the proposed operational strategy was successfully applied and validated in full-scale OD. The foregoing results collectively suggest that the CFD-AMS2 integration model is numerically capable to optimize the operational strategy of ODs.

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation–reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Over half of century, sanitary landfill was and is still the most economical treatment strategy for solid waste disposal, but the environmental risks associated with the leachate have brought attention of scientists for its proper treatment to avoid surface and ground water deterioration. Most of the treatment technologies are energy-negative and cost intensive processes, which are unable to meet current environmental regulations. There are continuous demands of alternatives concomitant with positive energy and high effluent quality. Microbial fuel cells (MFCs) were launched in the last two decades as a potential treatment technology with bioelectricity generation accompanied with simultaneous carbon and nutrient removal. This study reviews capability and mechanisms of carbon, nitrogen and phosphorous removal from landfill leachate through MFC technology, as well as summarizes and discusses the recent advances of standalone and hybrid MFCs performances in landfill leachate (LFL) treatment. Recent improvements and synergetic effect of hybrid MFC technology upon the increasing of power densities, organic and nutrient removal, and future challenges were discussed in details.

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride.

A hybrid electrochemical conditioning strategy for enhanced sewage sludge dewatering was proposed. A water content of 47.2 wt.% for the dewatered sludge cake was achieved at an applied voltage of 20 V for 30 min, which was significantly lower than previously reported results. The capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 75.6% and 90.9%, respectively. Four simultaneous processes, including electrooxidation, the electro-Fenton process, molecular oxygen activation via zero valent iron (ZVI) and Fe(III) flocculation, had synergetic effects on the degradation of extracellular polymeric substances (EPS) to enhance sludge dewaterability. The in situ generation of ZVI on the cathode electrode facilitated the reduction of Fe(III) to Fe(II) via activation of molecular oxygen. The sludge pH decreased spontaneously and remained acidic due to the competitive reaction of ZVI generation to hydrogen evolution as well as the Fe(III) flocculation process, which further guaranteed the high efficiency of hydroxyl radical generation. Changes in the physiochemical properties of the sludge (particle size distribution, zeta potential, viscosity and EPS characteristics) induced by the hybrid conditioning process were further explored. In addition, the economic potential of the hybrid system was preliminarily assessed (USD$ 127.6/ton dry sludge).

A method to improve bromine fixation by co-pyrolysis of non-metallic fractions (NMFs) of waste printed circuit boards (WPCBs) with Bayer red mud (RM) has been developed. More than 78.59 wt% of bromine was fixed into the solid residues with an addition of 15 wt% RM after co-pyrolysis at 500 °C, comparing with 36.42 wt% without the RM addition. Metal oxides (Fe2O3, Al2O3, TiO2, and Na2O, etc.) in the RM contributed significantly to the bromine fixation. The bromine fixation percentages were 62.94, 65.05, 47.24, and 49.05 wt% with an individual addition of 15 wt% Fe2O3, Na2O, Al2O3, and TiO2, respectively. Metal oxides in the RM showed synergistic effects on the bromine fixation, and this can be attributed to the secondary reaction of Na2O and bromine decomposed from FeBr3. The mechanisms of bromine fixation by RM are formation of Br-M (M: Fe, Al, Ti, and Na) and O H bonds generated from the direct elimination and a two-step of dissociative adsorption and β-H elimination reactions between metal oxides and bromide.

Fe3O4@SiO2-NH2 magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the Fe3O4@SiO2-NH2 magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g-1, surpassing original carboxylated biochar (18.2mg·g-1). VSM and XPS characterizations demonstrated that the attached Fe3O4@SiO2-NH2 magnetic particles not only endowed biochar with perfect magnetic property (23emu·g-1) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L-1. The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater.

Microbial fuel cells (MFCs) are promising biotechnologies tool to harvest electricity by decomposing organic matter in waste water, and the anode material is a critical factor in determining the performance of MFCs. In this study, chestnut shell is proposed as a novel anode material with mesoporous and microporous structure prepared via a simple carbonization procedure followed by an activation process. The chemical activation process successfully modified the macroporous structure, created more mesoporous and microporous structure and decreased the O−content and pyridinic/pyrrolic N groups on the biomass anode, which were beneficial for improving charge transfer efficiency between the anode surface and microbial biofilm. The MFC with activated biomass anode achieved a maximum power density (23.6 W m−3) 2.3 times higher than carbon cloth anode (10.4 W m−3). This study introduces a promising and feasible strategy for the fabrication of high performance anodes for MFCs derived from cost-effective, sustainable natural materials.

In this study, the influence of Na2SO4 on electro-dewatering (EDW) of waste activated sludge (WAS) was investigated. The highest water removal efficiency of 42.5% was achieved at the optimum Na2SO4 dosage of 12.5 g kg−1 DS during EDW process at a constant voltage of 20 V. The migration and distribution of water, organic matters and Na+ at different Na2SO4 dosages were investigated through layered experiments. The results indicated the entire EDW process followed the S curve model, and it can be divided into three stages: (1) initial desalination stage: at the initial few min of EDW process, the rate of electroosmosis was extremely slow while electromigration of ions like Na+ was intense, and the electromigration was more obvious with increased Na2SO4 dosage; (2) dewatering stage: the dewatering efficiency increased dramatically via electroosmosis; (3) the dewaterability limit stage: the maximum value of dewatering efficiency has been achieved, while the water removal efficiency and dry solids content remained constant. During the EDW process, the possible electrolysis resulted in a pH gradient in the sludge cake. With the addition of Na2SO4 in the EDW, the pH gradient was intensified, and the migration rate of organic matters moving from cathode to anode increased while compared with the raw WAS. This study provided insights into the mechanism of EDW process at different dosages of Na2SO4.

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min −1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe 0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe 0 under acidic conditions and single-electron-transfer by Fe II under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound Fe II species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

The electrogeneration of H2O2 and electro-regeneration of ferrous are conflicting matters in electro-Fenton system. In this research, the degradation of Rhodamine B, methyl orange (MO) and 4-chlorophenol (4-CP) was investigated using a novel dual-cathode microbial fuel cell (MFC) electro-Fenton (EF) hybrid system. An air-cathode of an EF system was used for H2O2 electrogeneration and a carbon felt cathode of a MFC was used to accelerate Fe2+ regeneration. Synergistic improvement of MFC power generation and the degradation of the above refractory organics through EF reaction was achieved. The EF air-cathode was fabricated by adopting activated carbon/graphite powder mixture and PVDF binder, which showed higher H2O2 generation but slower Fe3+ reduction rate than MFC carbon felt cathode. The Rhodamine B removal rate constant and mineralization current efficiency of the MFC coupled EF were 64% and 42% higher than that of uncoupled EF, respectively. The MFC-EF coupled system also exhibited significantly higher removal efficiency for MO and 4-CP than that of un-coupled EF system. Moreover, the power density of MFC was greatly enhanced by coupling EF due to higher Fe3+/Fe2+ redox potential than oxygen reduction.

This study investigated the synergistic effect of water content and a composite conditioner of Fenton's reagent combined with red mud (Fenton-RM) on the pyrolytic products (fuel gas, tar, and solid char) of deep-dewatered sludge. The catalytic effect of metal oxides in Fenton-RM could be promoted by the presence of water during sludge pyrolysis, showing higher gas yield with increased water content. Maximum gas outputs of the deep-dewatered sludge conditioned with Fenton-RM (S-Fenton-RM) and the conventional dewatered sludge conditioned with polyacrylamide (S-PAM), both appeared at 900 °C with a water content of 65 wt%, and were 0.257 and 0.189 L/g dry solid (DS), respectively. At the same temperature and with the same water content, the hydrogen (H2) yields of the S-Fenton-RM samples were always higher than those of the S-PAM samples. At 900 °C, the maximum H2 yield of the S-Fenton-RM samples was 0.102 L/g DS, which was 85.5% higher than that of the S-PAM samples. The results indicated that water in the wet sludge provided the steam atmosphere for pyrolysis, and the water vapor then involved in secondary cracking reformation of tar and char gasification reactions, which would be catalyzed by the presence of metal oxides in the Fenton-RM conditioner, thus increasing the yield of fuel gas, especially hydrogen. The H2 production cost from the S-Fenton-RM system is less than that from the S-PAM system. The results suggest that pyrolysis of the wet deep-dewatered sludge conditioned with Fenton-RM is an economical and promising alternative for sewage sludge dewatering and disposal/reuse.

Electro-dewatering (EDW) is an innovative method for volume reduction of sewage sludge before re-utilization and disposal. In this study, dewaterability limit and energy consumption in sludge electro-dewatering process were directly explored using in-situ linear sweep voltammetry (LSV) analysis by a high-voltage electrochemical workstation instead of a traditional DC power source. Dewaterability limits of biosolids EDW were identified under a constant-voltage dewatering mode with different applied voltages at 10, 20, 30, 40, and 50 V, independently. The LSV tests reveal that the dewaterability limit of sludge is attributed to the higher electrical resistance of the sludge layer near the anode. The mass of the filtrate flow was linearly proportional to the total amount of electric charge corresponding to the energy consumption in EDW, which elucidated the principal mechanism of EDW. Under a constant-voltage dewatering mode, the applied voltage is a key factor in controlling the energy consumption. Reducing the applied voltage while extending the dewatering time is proposed to reduce the energy consumption and obtain a good dewatering result. As the applied voltage decreased from 50 to 10 V, the energy consumption could be reduced from 403.6 to 80.3 kWh/m 3 removed water, the dewatering times was increased from 6.4 to 85.4 min, and the dry solids content of dewatered cake increased from 16.1 to 34.4 wt%. Those results indicate that LSV is an effective method to reveal the mechanism of EDW and optimize the operation parameters to reduce energy consumption.

Redox metal ions play the crucial role in versatile advanced oxidation technologies, in which controlling the active species formation through catalyst design is one of the key challenges in oxidant utilization. This work describes an example of different active species formations in CuO-mediated degradation just because of supporting material differences. Although three CuO catalysts were prepared by similar procedures, it was found that CuO-MgO catalyst demonstrated high efficiency in phenol degradation with bicarbonate activated H2O2, in which the superoxide radical is crucial, while hydroxyl radical and singlet oxygen are ignorable. For the CuO-MgO-Al2O3 and CuO-Al2O3 catalysts, the degradation proceeds by popular hydroxyl radical based process, however, the efficiency was poor. The EPR experiments also confirmed the absence of hydroxyl radical in CuO-MgO system but its presence in CuO-MgO-Al2O3 and CuO-Al2O3 system. The high catalytic efficiency with ignorable hydroxyl radical in the CuO-MgO system leads us to propose that an alternative Cu(III) species dominates the degradation. The basic MgO support may facilitate the formation of the Cu(III) species, whereas the neutral MgO-Al2O3 and acidic Al2O3 supports are unable to stabilize the high valent Cu(III) species, leading to the common hydroxyl radical mechanism with low efficiency of H2O2 in alkaline conditions.

For economic reasons and availability, there has been substantial interest in using natural organic polymers in sludge conditioning as alternative substances to replace inorganic conditioners in developing countries. Many investigations have been done on their efficiency regarding the enhancement of sludge dewaterability. Moringa oleifera seeds extract and chitosan, widely investigated, have proved their ability to act as a coagulant and/or flocculant, binding and improving sludge flocs, especially, the sludge flocculation, settling and dewatering. However, with regard to the most used sludge treatment methods in developing countries, extracellular polymeric substances (EPS), compounds that appear to be a key factor in sludge dewaterability are entirely missing in studies discussing the mechanisms of natural organic polymers sludge dewaterability. In advanced sludge treatment, EPS govern all the important mechanisms in sludge dewaterability. The aim of this review is to articulate a comparative st...

In this study, the long-term stability of Cr(VI) in the FeSO4 and H2SO4 (FeSO4-H2SO4) treated chromite ore processing residue (COPR) after 400 curing days and the stabilization mechanisms were investigated. FeSO4-H2SO4 treatment significantly reduced toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) Cr(VI) concentrations to lower than the regulatory limit of 1.5mgL-1 (HJ/T 301-2007, China EPA) even for the samples curing 400days, achieving an outstanding long-term stability. Our independent leaching tests revealed that H+ and SO42- have synergistic effect on promoting the release of Cr(VI), which would make Cr(VI) easier accessed by Fe(II) during stabilization. The contributions of H+ and SO42- to Cr(VI) release ratio were 25%-44% and 19%-38%, respectively, as 5mol H2SO4 per kg COPR was used. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and alkaline digestion analyses were also employed to interpret the possible stabilization mechanism. Cr(VI) released from COPR solid was reduced to Cr(III) by Fe(II), and then formed stable FexCr(1-x)(OH)3 precipitate. This study provides a facile and reliable scheme for COPR stabilization, and verifies the excellent long-term stability of the FeSO4-H2SO4 treated COPR.

During advanced oxidation treatment for enhancing sludge dewaterability, the peptide chains of protein can be decomposed into amino acids. Protein exhibits a great impact on sewage sludge dewaterability. However, the role of amino acids in sludge dewatering remains unclear. In this study, among the 23 types of amino acids investigated, tryptophane (Trp) and lysine (Lys) were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment. The content of lysine showed positive correlations with capillary suction time (CST), specific resistance to filtration (SRF), and bound water content, and the concentrations of total protein, low molecular weight protein, amines and amides, and 3-turn helix of proteinaceous compounds in bound extracellular polymeric substances (EPS), while the content of tryptophane showed negative correlations with the above parameters. The amino acids may be sourced from damage of the membrane and ribosomal proteins by hydroxyl radicals, and the peptide bonds connected with tryptophane were more inclined to be decomposed than other amino acids. Particularly, more amino acids of tryptophane can result in more hydrophobic interaction, and less necessary energy barrier for aggregation of particles. As such, regulating protein degradation towards production of tryptophane may be related with enhanced sludge dewaterability by Fenton oxidation treatment.

Biogas and phosphorus recovery from waste activated sludge (WAS) with sequential homogeneous protocatechuic acid (PCA) enhanced Fenton pretreatment, anaerobic digestion (AD) and microbial electrolysis cell (MEC) were investigated. The cumulation of biogas production of WAS-Fenton-AD was 330.4 mL/g VS, which was 2.05-fold of the control without pretreatment (WAS-AD) during anaerobic digestion. Biogas production of 178 mL/L/d from WAS-Fenton-AD-MEC was achieved, which was 5.23-fold of the WAS-MEC, 2.28-fold of WAS-Fenton-MEC and 1.46-fold of WAS-AD-MEC, respectively. Enhanced phosphorus recovery in form of struvite reached 1.72 g/g TS (18.03% of total P) with a purity of 74.4%. Microbial community richness and diversity analysis revealed that the pretreatment process under circumneutral condition improved the diversity of microbial community, which was consisted of Bacteroidetes (33.90%), Proteobacteria (33.14%), and Chloroflexi (10.14%), compared to a majority of Firmicutes (70.81%) in WAS-AD. This study provides a feasible strategy for the recovery of biogas combined with phosphorus from WAS.

In this study, a green recycling process of discarded lead–acid battery paste, which could avoid both the smelting and electro-winning route has been developed. Leaching reagents containing sodium citrate, acetic acid and hydrogen peroxide were reacted with spent lead paste in aqueous media at the pH of 5–6. Lead paste was leached and formed into lead citrate precursor, which was recrystallized and separated from the solution. The optimal conditions for the leaching process at room temperature were found to be the: concentration of acetic acid solution of 0.92 mol L-1; concentration of sodium citrate solution of 0.478 mol L-1; initial mass ratio of solid spent lead paste to liquid (solid/liquid ratio) of 1/5 g/mL; and reaction time of 2 hours. The results showed that the desulphurization efficiency of lead paste was up to 99.9%. The optimal conditions for lead citrate re-crystallization from the leaching mixed solution were found to be the re-crystallization temperature of 55oC for 5 hours in a water bath. The lead citrate precursor synthesized from discarded lead–acid battery pastes was the chemical formula of Pb3(C6H5O7)2·3H2O with columnar shape in the length of 30–50 μm, which was easily separated from the leaching solution. The results of kilogram-scale experiments made progress easier for obtaining the ultrafine lead oxide product (PbO and Pb) from discarded lead–acid battery paste.

A microbial fuel cell system with intimately coupled photocatalytic-electrogenic anode (photocatalytic-MFC) was proposed for the synergetic degradation of 2,4,6-trichlorophenol (2,4,6-TCP) which has a structure of three chlorine groups connecting to a phenol ring and is well recognized as a recalcitrant pollutant for its high toxicity, bioaccumulation and persistence. The photocatalytic-electrogenic anode was prepared by coating mpg-C3N4 on a carbon felt anode, followed by inoculating with municipal sewage and acclimating with 2,4,6-TCP at gradient concentrations. Improved TCP degradation was achieved, showing 79.3% of TCP removal in 10 h with an original concentration of 200 mg L−1, which was higher than that obtained with the unilluminated MFC (66.0%) and the photocatalytic-only process (56.1%). The coupled photocatalytic-electrogenic process demonstrated different degradation pathways compared with the photocatalytic-only process, with one open-chain compound (2-chloro-4-keto-2-hexenedioic acid, 2-CMA) detected in the photocatalytic-MFC system. Microbial community analysis revealed that Pseudomonas, instead of Geobacter observed in the unilluminated MFC bioanode, dominated in the photocatalytic-electrogenic anode MFC biofilm, which might be responsible for enhanced current generation in the coupled system. In addition, biofilm rich with Rhodococcus on air-cathode was also responsible for the enhanced TCP removal. This research provides an efficient strategy for the treatment of wastewater with recalcitrant contaminants by intimate-coupling of the photocatalytic and the electrogenic processes.

A liquid–gas two-phase computational fluid dynamics (CFD) model was developed to simulate flow field and gas hold-up in a pilot-scale oxidation ditch (OD). The volume of fluid (VOF) model and the mass flow inlet boundary condition for gas injection were introduced in this model. The simulated values of the flow velocities and the gas hold-up were verified by experimental measurements in the pilot-scale OD. The results showed that the gas hold-up at test-site 3, immediately downstream of the surface aerator, was the highest among all three test-sites. Most of the gas existed in the upper portion of the ditch and was close to the inner side of the channel. Based on the liquid–gas two-phase CFD model, three operating conditions with different setting height ratios of the submerged impellers were simulated. The simulated results suggested that the setting heights of the submerged impellers have significant impacts on the flow velocity distribution. Lowering the setting height could increase the flow velocity in the pilot-scale OD. An optimal setting height ratio of 0.273 was proposed, which would be beneficial for minimizing sludge sedimentation, especially near the inner side of the curve bend.

A hybrid electrochemical process with Ca(ClO)2 addition for simultaneous sludge dewaterability, stabilization and phosphorus fixation was proposed. Under optimal conditions (150 mg/g VS Ca(ClO)2, 15 V), the capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 88% and 92%, respectively. Efficient sludge stabilization with E. coli colonies of less than 1000 MPN/g TS was achieved. Phosphorus of 99% was removed from the filtrate and successfully fixed in the sludge cake and on the electrode surface. The integration of electrochemical and hypochlorite oxidation could effectively degrade the tightly bound extracellular polymeric substances (TB-EPS) structure with a total organic carbon (TOC) reduction of 52%. Besides, the disintegration of microbial cell envelopes was also achieved, with a reduction of living cell fraction of 98%. Furthermore, system pH could be maintained at near neutral (7.45) and the conversion of Fe(II) to Fe(III) was also facilitated with the addition of Ca(ClO)2, resulting in improved electrocoagulation process for enhanced sludge dewatering and phosphorus fixation. The multifunctional effects were achieved with the cooperated extracellular electrooxidation for EPS destruction and the active chlorine for intracellular microbial cell disintegration. This research provides a promising strategy for integrated sludge treatment and recycling for possible land utilization.

Although polyhalogenated carbazoles (PHCZs) can be generated and detected in drinking water, their occurrence and potential health risks to humans via drinking water ingestion are not well known. In this study, 11 PHCZs were screened in drinking water samples from Wuhan, the most populous city in central China. The total concentration of PHCZs could be up to 53.48 ng/L with a median level of 8.19 ng/L, which was comparable to polychlorinated biphenyls and poly- and perfluoroalkyl substances reported in the literatures for drinking water. Composition profiles revealed that 3,6-dichlorocarbazole, 3-chlorocarbazole, 3-bromocarbazole and 3,6-dibromocarbazole were the predominant PHCZ congeners in the tested samples. Regional differences in the levels and patterns of PHCZs suggested that anthropogenic releases should be the dominant source compared to natural generation. Boiling of the water samples caused no significant change in PHCZs concentrations after correcting the volume change due to evaporation. Potential health risks associated to the levels of PHCZs in drinking water were assessed using the toxic equivalent (TEQs) method. The estimated daily intake of PHCZs via drinking water ingestion is up to 0.38 pg-TEQ/kg body weight/day for infants, nearly 4.5 times higher than that for adults, and appears to reach the maximum permissible concentration set by certain authority agencies. Overall, drinking water ingestion represents an important exposure pathway for PHCZs. This is the first comprehensive study on the abundance and health risks of PHCZs in drinking water.

Sludge samples taken from different sources and times may have different characteristics that could affect dewatering performance. In this study, 20 sludge samples from five wastewater treatment plants and different seasons in 1 year were characterized. Pearson correlation analysis indicated that solid content (SC), total suspended solid (TSS), polysaccharides and proteins contents had positive correlations with the capillary suction time (CST), whereas volatile suspended–solid/total suspended solid (VSS/TSS) exhibited negative correlations with CST. Moreover, no correlations between CST and specific resistance to filtration were found among these different sludge samples. The principal component analysis confirmed that only two group variables could represent most of the sludge characteristic parameters. The first set of variables represents the particulate nature of the biotic factors (SC, VSS/TSS, SCOD, TSS, polysaccharides and proteins), and the second set is the pH. CST could not be a reasonable indicator of dewaterability in sludge deep dewatering by Fe2+/S2O8 2−-phosphogypsum composite conditioning. Furthermore, the results of diaphragm filter press dewatering showed that initial SC and VSS/TSS were the most dominant sludge characteristics affecting the solid content of dewatered cake (R p = 0.610, p = 0.016; R p = −0.838, p = 0.000, respectively) with Fe2+/S2O8 2−-phosphogypsum composite conditioning. Results from this study suggest that dewatering performance is predictable by sludge characteristics parameters for Fe2+/S2O8 2−-phosphogypsum conditioning.

Aerobic granular sludge (AGS) was successfully cultivated in a double column cyclic aerobic granular reactor (DCCAGR) within 18 days by inoculating with 30% (w/w) mature aerobic granules and 70% activated sludge, while granulation process and reactor performance was investigated in the continuous flow reactor. The AGS cultivated was white or pale yellow, while granule’s SVI, average particle size, granulation rate, extracellular polymeric substances, polysaccharides/proteins ratio and water content were about 46 mL/g, 1.2 mm, 92%, 37 mg/g MLVSS, 1.4 and 98.3% on the 20th day. Observed from the microscopic structure of the cultivated AGS, a large number of microorganisms tightly adhered together inhibited inside the granules, including coccus, bacillus and protozoa. Finally, effluent chemical oxygen demand, total inorganic chemical demand, ammonium nitrogen and total phosphorus of the system were 33 mg/L, 8.46 mg/L, 7.3 mg/L and 1.26 mg/L, and their removal rates were 97%, 88%, 90% and 87% respectively. Effective hydraulic selection pressure can be created in DCCAGR, while inoculated AGS had positive significance to the agglomeration of other flocculent sludge, which greatly reduced the startup time and consumption of mature aerobic granules.

Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H2O2 to enhance sludge dewaterability. The FeAl2O4 phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe2O3 and Al2O3, since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl2O4 phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl2O4 phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl2O4 phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl2O4 contributed to weak the O-O bond in H2O2 and reduce the activation energy of H2O2 decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H2O2 and the amount of ·OH generation were obviously promoted by FeAl2O4 phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability.