Bioenergy recovery and carbon emissions benefits of short-term bio-thermophilic pretreatment on low organic sewage sludge anaerobic digestion: A pilot-scale study.

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria, was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%.

Removal of particulate matter and dissolved organic matter from sedimentation sludge water during pre-sedimentation process: Performances and mechanisms.

Sedimentation sludge water (SSW), a prominent constituent of wastewater from drinking water treatment plants, has received limited attention in terms of its treatment and utilization likely due to the perceived difficulties associated with managing SSW sludge. This study comprehensively evaluated the water quality of SSW by comparing it to a well-documented wastewater (filter backwash water (FBW)). Furthermore, it investigated the pollutant variations in the SSW during pre-sedimentation process, probed the underlying reaction mechanism, and explored the feasibility of employing a pilot-scale coagulation-sedimentation process for SSW treatment. The levels of most water quality parameters were generally comparable between SSW and FBW. During the pre-sedimentation of SSW, significant removal of turbidity, bacterial counts, and dissolved organic matter (DOM) was observed. The characterization of DOM components, molecular weight distributions, and optical properties revealed that the macromolecular proteinaceous biopolymers and humic acids were preferentially removed. The characterization of particulates indicated that high surface energy, zeta potential, and bridging/adsorption/sedimentation/coagulation capacities in aluminum residuals of SSW, underscoring its potential as a coagulant and promoting the generation and sedimentation of inorganic-organic complexes. The coagulation-sedimentation process could effectively remove pollutants from low-turbidity SSW ([turbidity]0 < 15 NTU). These findings provide valuable insights into the water quality dynamics of SSW during the pre-sedimentation process, facilitating the development of SSW quality management and enhancing its reuse rate.

Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method.

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a-b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44-34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Pathways of inhibition of filamentous sludge bulking by slowly biodegradable organic compounds.

The organic compound composition of wastewater, serves as a crucial indicator for the operational performance of activated sludge processes and has a major influence on the development of filamentous bulking in activated sludge. This study focused on the impact of typical soluble and slowly-biodegradable organic compounds, investigating the pathways through which these substrates affect the occurrence of filamentous bulking in systems operated under both high- and low-oxygen conditions. Results showed that slowly-biodegradable organic compounds lead to a concentrated distribution of microorganisms within flocs, with inward growth of filamentous bacteria. Both Tween-80 and granular starch treated systems exhibited a significant increase in protein content. The glucose system, utilizing soluble substrates, exhibited a markedly higher total polysaccharide content. Microbial communities in the Tween-80 and granular starch treated systems were characterized by a higher abundance of bacteria known to enhance sludge flocculation and settling, such as Competibacter, Xanthomonadaceae and Zoogloea. These findings are of high significance for controlling the operational performance and stability of activated sludge systems, deepening our understanding and providing a novel perspective for the improvement of wastewater treatment processes.

Optimization of nitrogen-doped sludge char preparation and mechanism study for catalytic oxidation of NO at room temperature.

Catalytic oxidation of NO at room temperature was carried out over nitrogen (N)-doped sludge char (SC) prepared from pyrolysis of municipal sewage sludge, and urea was adopted as nitrogen source. The effects of different N-doping methods (one-step and two-step method), dried sludge (DS)/urea mass ratios (5:1, 4:1, 3:1, 2:1, and 1:1), SC preparation procedures (pyrolysis only, pyrolysis with acid washing, and pyrolysis with KOH activation and acid washing), and different pyrolysis temperatures (500, 600, 700, and 800°C) on the catalytic oxidation of NO were compared to optimize the procedure for SC preparation. The results indicated that N-doping could obviously promote the catalytic performance of SC. The one-step method with simultaneous sludge pyrolysis (at 700°C), KOH activation, and N-doping (DS/urea of 3:1) was the optimal procedure for preparing the N-doped SC with the NO conversion rate of 54.7%, whereas the optimal NO conversion rate of SC without N-doping was only 47.3%. Urea worked both as carbon and nitrogen source, which could increase about 2.9%-16.5% of carbon and 24.8%-42.7% of nitrogen content in SC pyrolyzed at 700°C. N-doping significantly promoted microporosity of SC. The optimal N-doped SC showed specific surface areas of 571.38 m2/g, much higher than 374.34 m2/g of the optimal SC without N-doping. In addition, N-doping also increased amorphousness and surface basicity of SC through the formation of N-containing groups. Finally, three reaction paths, i.e. microporous reactor, active sites, and basic site control path, were proposed to explain the mechanism of N-doping on promoting the catalytic performance of NO.

Effect of lysozyme combined with hydrothermal pretreatment on excess sludge and anaerobic digestion.

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier.

Effects of salinity and betaine addition on anaerobic granular sludge properties and microbial community succession patterns in organic saline wastewater.

In this study, the effects of different salinity gradients and addition of compatible solutes on anaerobic treated effluent water qualities, sludge characteristics and microbial communities were investigated. The increase in salinity resulted in a decrease in particle size of the granular sludge, which was concentrated in the range of 0.5-1.0 mm. The content of EPS (extracellular polymeric substances) in the granular sludge gradually increased with increasing salinity and the addition of betaine (a typical compatible solute). Meanwhile, the microbial community structure was significantly affected by salinity, with high salinity reducing the diversity of bacteria. At higher salinity, Patescibacteria and Proteobacteria gradually became the dominant phylum, with relative abundance increasing to 13.53% and 12.16% at 20 g/L salinity. Desulfobacterota and its subordinate Desulfovibrio, which secrete EPS in large quantities, dominated significantly after betaine addition.Their relative abundance reached 13.65% and 7.86% at phylum level and genus level. The effect of these changes on the treated effluent was shown as the average chemical oxygen demand (COD) removal rate decreased from 82.10% to 79.71%, 78.01%, 68.51% and 64.55% when the salinity gradually increased from 2 g/L to 6, 10, 16 and 20 g/L. At the salinity of 20 g/L, average COD removal increased to 71.65% by the addition of 2 mmol/L betaine. The gradient elevated salinity and the exogenous addition of betaine played an important role in achieving stability of the anaerobic system in a highly saline environment, which provided a feasible strategy for anaerobic treatment of organic saline wastewater.

Effect of gradual increase of salt on performance and microbial community during granulation process.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.

The effect of fine grits and fine debris concentrations on the MLVSS/MLSS ratio of an activated sludge system.

This study embarks on an explorative investigation into the effects of typical concentrations and varying particle sizes of fine grits (FG, the involatile portion of suspended solids) and fine debris (FD, the volatile yet unbiodegradable fraction of suspended solids) within the influent on the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio of an activated sludge system. Through meticulous experimentation, it was discerned that the addition of FG or FD, the particle size of FG, and the concentration of FD bore no substantial impact on the pollutant removal efficiency (denoted by the removal rate of COD and ammonia nitrogen) under constant operational conditions. However, a notable decrease in the MLVSS/MLSS ratio was observed with a typical FG concentration of 20 mg/L, with smaller FG particle sizes exacerbating this reduction. Additionally, variations in FD concentrations influenced both MLSS and MLVSS/MLSS ratios; a higher FD concentration led to an increased MLSS and a reduced MLVSS/MLSS ratio, indicating FD accumulation in the system. A predictive model for MLVSS/MLSS was constructed based on quality balance calculations, offering a tool for foreseeing the MLVSS/MLSS ratio under stable long-term influent conditions of FG and FD. This model, validated using data from the BXH wastewater treatment plant (WWTP), showcased remarkable accuracy.

Promoting effects of bioplastics and sludge anaerobic co-fermentation for carboxylates production with pH regulation: Insights into the plastic structure, microbial metabolic traits, and adaptive mechanism.

Biodegradable plastics (BPs) are presenting new challenges for their reutilization. This work found that volatile fatty acids (VFAs) production by co-fermentation of BPs with waste activated sludge (WAS) reached 4-37 times of the WAS fermentation alone, which was further amplified by pH regulation (especially alkaline regulation). Moreover, the VFAs composition is highly associated with BPs category. By contrast, the traditional plastic showed a limited effect on the VFAs yield and composition. Alkaline regulation enhanced the breakdown of BPs' ester bonds and boosted WAS disintegration, increasing bioavailable substrates. The hydrolytic-acidogenic anaerobes (i.e., Serpentinicella and Proteiniclasticum) and the major metabolic processes participated in the transformation of BPs and WAS to VFAs were upregulated under alkaline conditions. Further exploration unveiled that quorum sensing and peptidoglycan synthesis played important roles in counteracting alkaline stress and maintaining microbial activity for effective VFAs generation. The works demonstrated the effectiveness of pH-regulated anaerobic co-fermentation for BPs valorization.

Comprehensive evaluation of bioavailable phosphorus in biochar synthesized by co-pyrolysis of sewage sludge and straw ash.

The world's phosphorus (P) resources are gradually depleting. Sewage sludge is an important secondary P resource, and sludge-derived biochar for land use is an effective way to achieve P recovery. However, P in biochar synthesized by direct pyrolysis of sludge usually shows comparatively low bioavailability. In this study, biomass ash from different types of straw was used as an additive for co-pyrolysis with sludge. The distribution of different P fractions in the obtained co-pyrolyzed biochar was investigated. The P bioavailability of the co-pyrolyzed biochar was comprehensively evaluated by three methods, including chemical extraction, diffusive gradients in thin films (DGT) technology and pot experiments. The results indicate that the bioavailable P in co-pyrolyzed biochar is significantly positively correlated with the contents of K, Ca, and Mg elements in straw ash, which facilitate the transformation of P in sludge into forms that are more easily utilized by plants, including monetite (CaHPO4), hydroxyapatite (Ca5(PO4)3OH) and pyrocoproite (K2MgP2O7). Moreover, pot experiments show that the P contents in ryegrass shoots and roots cultivated in co-pyrolyzed biochar-added soils increased by 11.98-114.97 % and 28.90-69.70 %, respectively, compared to the control soil. The DGT technology could better reflect the uptake of P by plants with a Pearson correlation coefficient as high as 0.94. This study provides references for P resource recovery, and the collaborative reutilization of sewage sludge and straw ash.

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor.

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

Treatment of sludge hydrothermal carbonization wastewater by ferrous/sodium percarbonate system: Effect of wastewater composition and role of coagulation and oxidation.

It is crucial to explore the effect of complex wastewater compositions on the ferrous/sodium percarbonate (Fe(Ⅱ)/SPC) system and the role of oxidation-coagulation in designing water treatment processes. This study employed redundancy analysis to investigate the effects of wastewater constituents on oxidation and coagulation. Raman analysis, X-ray Photoelectron Spectroscopy, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry were used to determine the roles of oxidation and coagulation in the system. The results showed that sulfates and phosphates formed amorphous complexes with iron species via coprecipitation, thereby promoting coagulation to remove organics. Some heavy metals can also be removed by coagulation. The co-activation of SPC by pre-existing transition metals and the added Fe(Ⅱ) facilitated the oxidative removal of organics, while chloride and arsenic were the main inhibitory inorganic substances in the system. Aromatic compounds mainly promoted coagulation, polysaccharides promoted oxidation, humic acid promoted oxidation and coagulation, and C=C/C=O inhibited the Fe(Ⅱ)/SPC system. The oxidation process removed graphitic structures and unsaturated organic matter in the region of (O/C, H/C) = (0.2-0.4, 0.9-2.0) through free radicals and generated amorphous carbon structures and saturated organic matter in the region of (O/C, H/C) = (0.3-0.7, 1.2-1.9). The coagulation process removed aromatic organics with 2-5 rings and unsaturated organics in the region of (O/C, H/C) = (0.2-0.6, 0.7-1.6) with oxygen-containing organics. The combined effects of coagulation and oxidation enhanced the removal efficiency of organic carbon by approximately 40%. This study facilitates the optimization of hydrothermal carbonization wastewater treatment and advanced oxidation processes.

Partitioned granular sludge coupling with membrane-aerated biofilm reactor for efficient autotrophic nitrogen removal.

The partial nitritation-anammox process based on a membrane-aerated biofilm reactor (MABR) faces several challenges, such as difficulty in suppressing nitrite-oxidizing bacteria (NOB), excessive effluent nitrate, and ineffective synergy between denitrification and anammox bacteria. Therefore, a novel partitioned granular sludge coupling with MABR (G-MABR) was constructed. The chemical oxygen demand (COD) and nitrogen removal efficiency were 88.8 ±â€¯1.8 %-92.6 ±â€¯1.2 % and 88.8 ±â€¯1.5 %-93.6 ±â€¯0.7 %, respectively. The COD was mainly lowered in the lower granular sludge-zone, while nitrogen was removed in the upper MABR-zone. NOB was significantly suppressed in the MABR-zone due to competition for substrate with denitrifying bacteria and anammox bacteria. This partitioned configuration reduced the C/N ratio in the MABR-zone, thus facilitating autotrophic nitrogen removal. Both partial nitrification and denitrification provided nitrite for anammox bacteria in granular sludge, whereas partial nitrification mainly supplied nitrite to the anammox bacteria in membrane biofilms.

Airborne antibiotic resistome from sludge dewatering systems: Mobility, pathogen accessibility, cross-media migration propensity, impacting factors, and risks.

Bioaerosol contamination was considered as a potential health threat in sludge dewatering systems (SDSs), while emission and risk of airborne antibiotic resistome remain largely unclear. Herein, seasonal investigations of fine particulate matter (PM2.5) were conducted using metagenomics-based methods within and around different SDSs, together with an analysis of sewage sludge. Featured with evident seasonality, antibiotic resistance genes (ARGs) in SDS-PM2.5 also possessed greater accumulation, transfer, and pathogen accessibility than those in ambient air PM2.5. Mobile ARGs in SDS-PM2.5 mainly encoded resistance to tetracycline, and most were flanked by integrase. Some pathogenic antibiotic resistant bacteria (PARB), including Enterobacter asburiae, Escherichia coli, Enterococcus faecium, and Staphylococcus aureus, also carried mobile genetic elements in SDS-PM2.5. Dewatering behavior actuated > 50.56% of ARG subtypes and > 42.86% of PARB in sewage sludge to aerosolize into air. Relative humidity, temperature, and PM2.5 concentration collectively drove the evolution of bacterial community and indirectly promoted the antibiotic resistance of SDS-PM2.5. SDS-PM2.5 posed more serious resistome risks than sewage sludge and ambient air PM2.5, and the highest levels were discovered in winter. These findings underline the role of dewatering behavior in facilitating resistome's aerosolization, and the need to mitigate this potential air pollution.

Enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation with addition of red mud: Performance and mechanisms.

Red mud (RM) as hazardous waste produced from aluminum refining industry has threatened the environment and human health. In this study, RM was added into the fermenter to promote short chain fatty acids (SCFAs) production from waste activated sludge (WAS) anaerobic fermentation. Results showed that the addition of RM could effectively improve the SCFAs production, especially, acetic acid. In particular, the production of total SCFAs and acetic acid in 20 g/L RM added fermenter were 1108.1 mg COD/L and 415.5 mg COD/L, which were 116.0% and 1308.0% higher than that in control fermenter. Batch experiment revealed that RM could enhance the hydrolysis and acidification process. Further study indicated that the activity of enzyme related to hydrolysis-acidification, abundance of fermentative bacteria for SCFAs production and functional metabolism genome were all improved with the addition of RM. The potential mechanism maybe that the RM promoted the hydrolysis-acidification process with the contained varies Fe(Ⅲ) oxides as electron acceptor, and the produced Fe2+ could serve as necessary trace elements to synthesize enzyme and then stimulate the expression of enzyme genes.

A pilot-scale evaluation of residual sludge quality in a worm-sludge treatment reed bed in the Mediterranean region.

A pilot-scale study on sludge treatment reed beds investigated the combined effects of earthworms and Arundo donax on sewage sludge dewatering and residual sludge quality. Four units were tested: one planted with earthworms, one planted without earthworms, one unplanted with earthworms, and one control, each unit replicated. Over a year, 24 cycles of sludge (dry and volatile solid contents of 24.71 g.L-1, and 19.14 g.L-1) were fed onto the units at a sludge loading rate: 43.59 kg.DS.m-2.year-1. Afterward, the units experienced 132 days of resting period, increasing dry solids from 21 to 70 % and decreasing volatile solids from 81 to 69 % on average (40 % sludge volume reduction). The bottom layers of the planted unit with earthworms showed a 30 % reduction in volatile solids, indicating improved sludge stabilization. Macronutrient abundance in the residual sludge followed the sequence N > Ca > P > K > S > Mg. The planted unit with earthworms reduced micronutrient concentrations by 22 % compared to the control unit (Fe > Na > Mn > B > Mo). Earthworms also played a key role in reducing heavy metal concentrations by 11 % compared to the planted unit without earthworms (Zn > Cr > Pb > Ni > Cd). Heavy metal levels in the residual sludge met EU and Portugal standards, with a 99.9 % reduction in Escherichia coli and fecal coliforms. Cost estimation showed centrifugation and W-STRB scenarios cost 167 and 183 €.PE-1 for a ten-year operation, with O&M costs of 7 and 3 €.PE-1.year-1, respectively.

Simulation and optimization of cheese whey additive for value-added compost production: Hyperparameter tuning approach and genetic algorithm.

Cheese whey is a difficult and costly wastewater to treat due to its high organic matter and mineral content. Although many management strategies are conducted for whey removal, its use in composting is limited. In this study, the effect of cheese whey in the composting of sewage sludge and poultry waste on compost quality and process efficiency was investigated. Also, valid and consistent simulations were developed with Gaussian Process Regression (GPR), Support Vector Regression (SVR), and Neural Network Regression (NNR) Machine Learning (ML) algorithms. The results of all physicochemical parameters determined that 3% of cheese whey addition for both feedstocks improved the composting process's efficiency and the final product's quality. The best results obtained through hyperparameter tuning showed that Gaussian Process Regression (GPR) was the most effective modeling tool providing realistic simulations. The reliability of these simulations was verified by running the GPR process 50 times. MdAPE demonstrated the validity and consistency of the created process simulations. Moreover, a genetic algorithm was used to optimize these dependent simulations and achieved almost 100% desirability. Optimization studies showed that the effective cheese whey ratios were 3.2724% and 3.1543% for sewage sludge and poultry waste, respectively. Optimization results were compatible with the results of experimental studies. This study provides a new strategy for the recovery of cheese whey as well as a new perspective on the effect of cheese whey on both physicochemical parameters and composting phases and the modeling and optimization processes of the results.

Recovering chromium from electroplating sludge using an integrated technology of bipolar membrane electrodialysis and H2O2 oxidation.

Chromium electroplating produces Cr(III)-containing electroplating sludge (EPS) in large volumes, which is easily oxidised to Cr(Ⅵ) and is harmful to the environment and human health. This study recovered Cr(III) as Na2CrO4 from EPS using an integrated bipolar membrane electrodialysis (BMED)-H2O2 oxidation technology. During the treatment process, Cr(III) was oxidised to Cr(VI) using H2O2 in an alkaline environment, BMED was used to separate and recover Cr(VI). Experimental results showed that H2O2 dosage and pH affected Cr(III) oxidation-the highest Cr(III) oxidation ratio of 68.4% was observed when H2O2 dosage and pH were 5.5 mL and 12.0, respectively. The current density, solid/liquid ratio and sludge particle size affected Cr(III) recovery, energy consumption and current efficiency. Under a current density of 20.0 mA/cm2, solid/liquid ratio of 1.0:45 and sludge particle size of 100 mesh, 58.2% of Cr(III) was recovered. When the number of the equipped EPS compartments was increased from one to two and three, the specific energy consumption decreased from 1.04 to 0.87 and 0.81 kW·h/g, respectively, but the current efficiency remained almost constant. After EPS treatment, the Cr(III) remaining in the sludge was mainly in the residual state, which is less environmentally harmful. The obtained Na2CrO4 had similar properties according to X-ray diffraction analysis. Thus, the proposed integrated technology effectively recovers Cr(III) from EPS and other chromium-containing solid wastes.

Synchronous and efficient removal of carbon, nitrogen, and phosphorus from actual rural sewage by composite wetlands enhanced with functional fillers.

A composite wetland (CECW) was constructed by introducing P-adsorption filler (EPAF) and activated sludge into traditional wetlands for treating actual sewage. The results showed that EPAF improved P removal through physico-chemical adsorption, and it could be stably regenerated after adsorption saturation without potential risks. Meanwhile, zeolite promoted NH4+-N reduction in sewage by cation exchange. In addition, simultaneous biological removal of carbon, nitrogen, and phosphorus was achieved through nitrification, denitrification, anammox, and aerobic P-accumulation processes induced by Nitrobacter, Proteus Hauser, Candidatus Paracaedibacter, and Brevundimonas. Under the coupling of filler interception/adsorption, microbial assimilation/transformation, flocculation, and plant uptake, CECW obtained the removal rates of 93.22 %, 85.75 %, 91.80 %, 95.38 %, 97.07 %, and 78.05 % for turbidity, TN, NH4+-N, TP, PO43--P, and TCOD, which met the Class 1A standard (GB18918-2002). Therefore, the experiment systematically investigated the effects and mechanism of CECW in treating actual sewage, which could provide reference for rural sewage treatment and sludge utilization.