COD Removal Rate Research Articles

Alkaline electrolyzer-improving electrocatalytic oxidation of landfill leachate coupling with hydrogen production

A hybrid electrolytic water system was constructed including the anodic electro-oxidation treatment of the leachate from a waste incineration plant as well as the coupled cathodic electrolysis for hydrogen production. Four types of electrolyzers were designed with different flow channels and investigated the effect of different electrolysis parameters on the coupled reactions. The results indicate that the pin-type electrolyzer is superior to the other three electrolyzers in term of the degradation performance and energy consumption. At high current density of 4000 A/m2 and the flow rate of 100 ml/min, the pin-type electrolyzer shows the lowest potential of 6.09 V, the COD removal rate of 98.17% for the leachate and the energy consumption of 200.14 W h. The mass transfer mechanism was further explored under different flow channels and current densities, illustrating that the excellent performance of the pin-type electrolyzer is due to its largest mass transfer area and the most uniform inside flow field distribution. The apparent COD degradation kinetic behaviors were studied, indicating that the maximum degradation rate was 0.033 min-1 at the electric density of 4000A/m2. Such electrocatalytic oxidation of waste leachate coupled with hydrogen production would provide a promising route to construct new hybrid electrolytic water systems.

External resistance as a potential tool for bioelectricity and methane emission control from rice plants in hydroponic microbial fuel cell

Recently, hydroponic plant microbial fuel cell (H-PMFC) was incorporated into cultivation medium to decrease methane (CH4) production while generating bioelectricity. However, no information is available about the effect of the external/internal resistance (Rext/Rint) ratio on the performance of H-PMFCs. To study the possibility of controlling biomass production, bioelectricity generation, and CH4 emissions from hydroponic rice plants (Oryza sativa L.) under different Rext/Rint ratios. In this study three H-PMFCs were operated as follows: H-PMFC-A had external resistance (Rext) lower than internal resistance (Rint); H-PMFC-B had Rext equal to Rint, and H-PMFC-C had Rext higher than Rint. Results showed that H-PMFC-B (Rext = Rint) has the highest biomass yield. H-PMFC-C (Rext > Rint) displayed the highest average power density (PDmax), which was 4.77 and 1.23 times higher than H-PMFC-A and H-PMFC-B over 131 days of operation. The PDmax was obtained from H-PMFC-C of 536.79 mW/m3 when Rext/Rint = 150 %. The highest current with the lowest CH4 was produced by H-PMFC-A (0.14 mA and 453.52 ± 0.28 g/m2/h). The CH4 emission exhibits an inverse trend with current production, which decreasing with the Rext/Rint decreased from 50 % to 5 %. The total CH4 emission flux in H-PMFC-A was 1.42 and 2.07 times lower than H-PMFC-B and H-PMFC-C, respectively. Furthermore, the COD removal rate in H-PMFCs negatively correlates with Rext/Rint, and the Rext does not affect the COD removal rate when 50 % ≤ Rext/Rint ≤ 150 %. The above results indicated that the performance of H-PMFCs can be controlled by changing the Rext/Rint ratio of H-PMFC according to actual needs. If the goal is to achieve higher biomass production, then Rext = Rint; to obtain the highest PDmax, then Rext > Rint; to obtain the highest current and lowest CH4 generation, then Rext < Rint.

Treatment of mature landfill leachate using chemical and electrical Fenton with novel Fe-loaded GAC heterogeneous catalysts

In this study, heterogeneous Fenton catalysts were prepared by loading iron oxides on granular activated carbon (GAC), with which as heterogeneous Fenton catalysts, mature landfill leachate (MLL) was treated by chemical and electrical Fenton method. For chemical Fenton treatment of MIL, the optimum conditions were optimised by orthogonal experiments and the removal of COD, NH3-N and colour reached 93.7 %, 65.5 % and 84 % respectively for static experiments, whereas the heterogeneous Fenton fluidized bed reactor removed >90 % of COD in all the 12 h of continuous operation. For electrical Fenton treatment of MIL, the removal rates of COD, colour, NH3-N, and TN were 97.4 %, 99 %, 100 %, and 94.2 %, respectively under the optimum treatment conditions of pH = 5, the GAC/α-FeOOH catalyst dosage of 13.3 g L−1, and the applied voltage of 8 V with the energy consumption of only 0.23 kWh (g COD)−1. Upon characterization, humic acid, fulvic acid and xanthohumic acid in the MLL were completely degraded and the complex macromolecules such as polycyclic aromatic hydrocarbons and heterocyclic rings were reduced and converted to simple small molecules such as alkanes. The quenching experiments verified that the ·OH produced in the heterogeneous electrical Fenton system plays an important role in the degradation of MLL, while the removal of NH3-N also relies on indirect oxidation with the active chlorine produced by the electrochemical system. GAC-based heterogeneous Fenton catalysts with high catalytic capacity and easy recycling have good application prospects in treating MLL.

Integrated system of electro-catalytic oxidation and microbial fuel cells for the treatment of recalcitrant wastewater

The emission of recalcitrant wastewater poses serious threats to the environment. In this study, an integrated approach combining electrocatalytic oxidation (EC) for pretreatment and microbial fuel cells (MFC) for thorough pollutant degradation is proposed to ensure efficient degradation of target substances, with low energy input and enhanced bioavailability of refractory organics. When phenol was used as the pollutant, an initial concentration of 2000 mg/L phenol solution underwent EC treatment under constant current-exponential attenuation power supply mode, resulting in a COD removal rate of 54.53%, and a phenol degradation rate of 99.83%. Intermediate products such as hydroquinone and para-diphenol were detected in the solution. After subsequent MFC treatment, only minor amounts of para-diphenol were left, and the degradation rate of phenol and its intermediate products reached 100%, with an output power density of 110.4 mW m−2. When coal chemical wastewater was used as the pollutant, further examination of the EC-MFC system performance showed a COD removal rate of 49.23% in the EC section, and a 76.21% COD removal rate in the MFC section, with an output power density of 181.5 mW m−2. Microbiological analysis revealed typical electrogenic bacteria (such as Pseudomonas and Geobacter), and specific degrading functional bacteria (such as Stenotrophomonas, Delftia, and Brevundimonas). The dominant microbial communities and their proportions adapted to environmental changes in response to the variation of carbon sources.

Evaluating water quality and fouling propensity in a pilot-scale ceramic membrane bioreactor treating municipal wastewater subjected to increasing salinity levels.

This study aims to optimize the removal of carbon and nitrogen pollutants from saline municipal wastewater using both membrane-based and biological treatment methods. It examines a pilot-scale sequential aerobic ceramic membrane bioreactor (AeCMBR) under various salinity levels (0-20 g NaCl/L) to assess biological processes and fouling behavior. While high COD removal rates of (≈90%) were consistently achieved, ammoniacal nitrogen removal dropped from 82 to 55% at 15 g NaCl/L, despite increased oxygenation flow rates. Notably, the biomass quickly adapted to salinity changes. Indicators such as mixed liquor suspended solids (MLSS), mixed liquor suspended volatiles (MLVSS), MLVSS/MLSS ratio, and sludge volume index (SVI) showed no significant correlation with increasing salt concentrations. Soluble microbial product (SMP) production was also unaffected by rising salinity levels. The transmembrane pressure (TMP) fluctuated, with the most pronounced trend at 15 g NaCl/L, even after reducing the flux from 20 to 15 L/m2/h. The primary fouling mechanism observed was reversible cake deposition. Overall, this research enhances our understanding of short-term operational impacts on AeCMBR performance as a function of different salinity levels.

Treatment of membrane-concentrated landfill leachate by heterogeneous chemical and electrical Fenton processes with Iron-loaded granular activated carbon catalysts

The composition of the membrane-concentrated landfill leachate (MCLL) is complex with a high concentration of organic matter and inorganic ions. In this study, a chemical and an electro-Fenton system were constructed to treat MCLL from a mature landfill using granular activated carbon loaded with iron oxides as heterogeneous Fenton catalysts. In the chemical Fenton treatment optimized by orthogonal experiments, the COD and colour removal rates were 93.9% and 80.2%. For the electro-Fenton system, the best COD, colour, and TN removal rates of MCLL reached 95.7%, 99%, and 94.9% with an energy consumption (EC) of 0.098 kWh·(g COD)−1 under the condition of pH 6, applied voltage 8 V, the reaction time 4 h, and the catalyst dosage 16.67 g L−1. Various spectral analyses confirmed that refractory organic matter and toxic substances in the MCLL were effectively degraded. The synergistic effect study of the factors in chemical Fenton indicated that as far as the effect on COD removal is concerned, heterogeneous Fenton system > catalyst adsorption > activated carbon/H2O2 system > activated carbon adsorption. The results of free radical quenching experiments illustrate that a large amount of ·OH was produced in the chemical heterogeneous Fenton system, while both ·OH and active chlorine play important roles in the removal of pollutants for the electro-Fenton system. MCLL can be disposed of costly and effectively by chemical and electrical Fenton processes with Iron-loaded granular activated carbon catalysts.

Effect of Aeration and External Carbon Source on Nitrogen Removal and Distribution Patterns of Related-Microorganisms in Horizontal Subsurface Flow Constructed Wetlands

Nitrogen pollution of surface water is still a critical issue worldwide. In this study, a total of four treatments were conducted in horizontal subsurface flow constructed wetlands (HSSFCWs) to explore the removal rate of nitrogen in the carbon-deficient wastewater, including combination of aeration and external carbon source (CW_CA), external carbon source (CW_C), aeration (CW_A), and control group without aeration and carbon source (CW_CK). Results showed that the removal rates of total nitrogen (TN) in the enhanced treatments were increased compared with CW_CK. The highest removal rates of COD (66.56%), NH4+-N (73.51%), NO3−-N (79.31%), and TN (76.19%) were observed in the CW_CA treatment. The bacterial community structure at the fore and rear ends of HSSFCWs was simultaneously changed in the CW_CA and CW_C treatments, respectively. The highest richness index at both the fore and rear ends of HSSFCWs was found in the CW_CA treatment. The richness and diversity indices of CW_C declined at the fore ends of HSSFCWs, but increased at the rear ends of HSSFCWs. Furthermore, the functional bacteria and genes significantly changed among different treatments. At the fore ends of HSSFCWs, the highest relative abundance of nitrifiers and absolute abundance of amoA and nxrA were obtained in CW_A, and the highest relative abundance of denitrifying bacteria and absolute abundance of nirS, nirK, nosZ were found in CW_C. However, at the rear ends of HSSFCWs, the highest relative abundance of nitrifiers and denitrifying bacteria as well as the absolute abundance of related genes were also observed in the CW_CA treatment. Overall, CW_CA improved the nitrogen removal rate by increasing the abundance of nitrogen-converting functional microbes and the genes associated with nitrification and denitrification.

Enhanced coking wastewater advanced treatment by using particle electrodes excited persulfate in the three-dimensional electrocatalytic reactors

Problems such as low concentration of organic pollutants in the biochemical effluent of coking wastewater and poor mass transfer efficiency have seriously affected the effectiveness of coking wastewater depth. Three-dimensional electrode oxidation processes (3DEOPs) are a very promising advanced oxidation process for wastewater treatment. Compared with the 3DEOPs, the treatment effect of coking wastewater was greatly improved by adding persulfate (PS) into the 3DEOPs. The experimental results showed that under the condition of adjusting the current density of 32 mA/cm2, adding 35 g of TSC6/BC particle electrodes and 2 mM PS, the COD concentration of the coking wastewater was reduced from 245.40 mg/L to 71.00 mg/L after 40 min of electrolysis, which has already met the discharge requirements. After 120 min of electrolysis, the UV254 of coking wastewater was reduced from 2.46 cm−1 to 0.35 cm−1, and the removal rate of COD and TOC in coking wastewater reached 93.44% and 78.19%, respectively. Compared with the use of BC and TiO2/BC, TS9/BC particle electrodes，the time for coking wastewater to meet the discharge standard was shortened by 20–30 min with TSC6/BC particle electrodes. Furthermore, the TSC6/BC particle electrodes improves the current efficiency and also saves energy of the system. The experimental results showed that both SO4−· and ·OH radicals in the 3DEOPs excited PS system play a very important roles to the degradation of organic pollutants in coking wastewater. This study provides theoretical guidance and technical support for the application of three-dimensional electrocatalytic technology for the treatment of actual coking wastewater.

Conductive adsorbents enhance phenol removal from wastewater by direct interspecies electron transfer "DIET"-based anaerobic biodegradation process

This study examined the hybrid adsorption and anaerobic biodegradation processes of phenol by using activated carbon cloth (CC) to stimulate direct interspecies electron transfer (DIET). Phenol biodegradation was tested over three sequential runs using 100 mL lab-scale bioreactors and compared with two different types of CC and granular activated carbons (GAC). The addition of the carbon adsorbents to the bioreactors significantly accelerated the methane production rate. This high rate of methane production was also accompanied by the complete removal of phenol, and a high COD(s) removal rate of about 95%, compared to 43.68% and 48.65% in the control sets in the first and second runs, respectively. The enhancement of the phenol biodegradation is attributed to the synergy of the adsorption and biodegradation processes. An initial adsorption stage has contributed to a significant and rapid reduction of phenol, leading to a lower inhibition effect of phenol, followed by anaerobic biodegradation of the adsorbed phenol stimulated by the DIET process. Specifically, the optimal concentration for Single Weave carbon cloth (CCSW) of 1.6 g L−1 promoted both the DIET and the adsorption processes. Microbial community composition analysis revealed that CCSW facilitated the growth of syntrophic bacterial groups (Rikenellae, Syntrophorhabdaceae, Gracilibacteraceae, and DTU014), and archaea (Methanosaetaceae and Methanoregulaceae), previously reported as key players in the DIET processes to promote phenol degradation. To the best of our knowledge, this is the first work that demonstrates the contribution of CC to stimulate DIET mechanism of anaerobic biodegradation synergistically combined with adsorption process for enhanced phenol removal.

Efficient nitrogen removal by multi-stage A/O mud membrane composite process with segmented influent: Performance and microbial community structure

In this paper, a multi-stage A/O mud membrane composite process with segmented influent was constructed for the first time and compared with the traditional activated sludge process and the multi-stage A/O pure membrane process with segmented influent. The nitrogen removal efficiency of the process under different influencing factors was studied. Under the optimum conditions, the highest removal rate of ammonia nitrogen can reach 99%, and the average removal rate of total nitrogen was 80%. The removal rate of COD in effluent reached 93%. The relative abundance of Proteobacteria was the highest in the multi-stage A/O mud membrane composite reactor with segmented influent. The community diversity and richness of activated sludge and biofilm in aerobic pool were the highest. Dechloromonas, Flavobacterium and Rhodobacter were dominant bacteria, and they were aerobic denitrifying bacteria that significantly contributed to the removal rate of ammonia nitrogen.

Preparation and application of microfiltration porous coal gangue–loess‐based ceramic membrane

AbstractThe ceramic membrane is widely used in the field of domestic sewage treatment due to its high flexural strength, acid and alkali corrosion resistance, easy cleaning, and other advantages. This article uses coal gangue and loess as the main raw material (coal gangue:loess = 8:2), calcium carbonate as the pore‐forming agent, and carboxymethyl cellulose as the binder. The ceramic membrane was prepared by extrusion molding method and solid particle sintering method. The effects of pore‐forming agent content and sintering temperature on the physical and chemical properties of the ceramic membrane, such as flexural strength, microstructure, pure water flux, and acid‐base corrosion rate, were investigated. The results show that when the sintering temperature is 1000°C and the pore‐forming agent content is 10wt%, the pure water flux exceeds 1434L/h m2 MPa, the flexural strength exceeds 25.4 MPa, the porosity exceeds 46.9%, and the acid‐alkali corrosion rate of the ceramic membrane below 1.6%/0.15%. At this time, the treatment efficiency of domestic sewage is excellent, the removal rate of COD, suspended solids and ammonia nitrogen exceeds 27.66%, 99.9%, and 26.77%, respectively. This work has trend‐setting significance for the fabrication and application of low‐cost ceramic membranes.

Pretreatment of hypersaline and high-organic wastewater with a three-dimensional electrocatalytic system: a pilot-scale study.

The three-dimensional electrocatalytic oxidation (3DEO) is a promising electrochemical system in the treatment of refractory wastewater, but still far from large-scale applications. In this work, we prepared 146.5 Kg Ti-Sn-Sb@γ-Al2O3 particle electrodes to construct a 3DEO system for the pretreatment of hypersaline and high-organic wastewater in an industrial park sewage plant, with activated carbon particle electrodes as a comparison. The average COD removal rates of Ti-Sn-Sb@γ-Al2O3 and activated carbon-based 3DEO systems were 24.43 and 48.73%, respectively, and the energy consumption of the two 3DEO systems were 102.8 and 31.4 kWh/Kg COD, respectively. However, compared to the negligible enhancement of wastewater biodegradability in the activated carbon 3DEO system, the Ti-Sn-Sb@γ-Al2O3 3DEO system greatly improved the biochemical index (B/C) from 0.021 to 0.166 (by 690.5%). Due to its superior catalytic capacity, Ti-Sn-Sb@γ-Al2O3 outperforms activated carbon in improving biodegradability as the latter relies mainly on adsorption. The results of this work provide a 3DEO engineering practice experience on the pretreatment of hypersaline and high-organic wastewater.

Comparative study of Fe2+/H2O2 and Fe2+/persulfate systems on the pre-treatment process of real pharmaceutical wastewater.

Advanced oxidation technologies based on hydroxyl radical (•OH) and sulfate radical (SO4-•) are two common types of advanced oxidation technologies, but there are not many reports on the application of advanced oxidation methods in actual wastewater pretreatment. This article compares the pre-treatment performance of Fe2+/H2O2 and Fe2+/Persulfate systems in actual pharmaceutical wastewater, and combines EEM, GC-MS, and toxicity testing results to explore the differences in TOC, COD, and NH3-N removal rates, optimal catalyst dosage, applicable pH range, toxicity of effluent after reaction, and pollutant structure between the two systems. The results indicate that the Fe2+/H2O2 system has a higher pollutant removal rate (TOC: 71.9%, COD: 66.9%, NH3-N: 34.1%), but also requires a higher catalyst (Fe2+) concentration (6.0 g/L), and its effluent exhibits characteristic peaks of aromatic proteins. The Fe2+/Persulfate system has a wider pH range (pH ≈ 3-7) and is more advantageous in treating wastewater containing more cyclic organic compounds, but the effluent contains some sulfur-containing compounds. In addition, toxicity tests have shown that the toxicity reduction effect of the Fe2+/Persulfate system is stronger than that of the Fe2+/H2O2 system.

Effects of Cu (II) on the Growth of Chlorella vulgaris and Its Removal Efficiency of Pollutants in Synthetic Piggery Digestate.

C. vulgaris has a positive effect on the removal of nutrients from pig farm biogas slurry. However, swine wastewater often contains heavy metal ions, such as Cu (II), which may have impacts on the nutrient removal performance of C. vulgaris. Additionally, the heavy metal ions in wastewater can be adsorbed by microalgae. In this study, the stress effect of Cu (II) on the growth of Chlorella vulgaris, the Cu (II) removal by microalgae, and the effect of different concentrations of Cu (II) on the nutrient removal efficiency of C. vulgaris in biogas slurries were explored. The results showed that the microalgae biomass of microalgae on the sixth day of the experiment was the highest in the treatment with a Cu (II) concentration of 0.5 mg/L, which was 30.1% higher than that of the 2.5 mg/L group. C. vulgaris had higher removal efficiencies of Cu (II) at a Cu (II) concentration of 0.1~1.5 mg/L. The-OH, C=O, -COOH, and C-O groups on the surface of the algal cells play a significant role in the removal of Cu (II). The removal rates of COD, NH3-N, TN, and TP by C. vulgaris at a Cu (II) concentration of 0.5 mg/L were the highest, which were 89.0%, 53.7%, 69.6%, and 47.3%, respectively.

Impact analysis of hydraulic residence time and dissolved oxygen on performance efficiency and microbial community in N, N-dimethylformamide wastewater treated by an AnSBR-ASBR

Suitable operating parameters are one of the key factors to efficient and stable biological wastewater treatment of N, N-dimethylformamide (DMF) wastewater. In this study, an improved AnSBR-ASBR reactor (anaerobic sequencing batch reactor, AnSBR, and aerobic SBR, ASBR, run in series) was used to investigated the effects of operating conditions such as hydraulic residence time (HRT), AnSBR stirring speed and ASBR dissolved oxygen (DO) for DMF wastewater treatment. When HRT decreased from 24 h to 12 h, the average removal rates of COD by the AnSBR were 34.59% and 39.54%, respectively. Meanwhile, the removal rate of NH4+-N by ASBR decreased from 88.38% to 62.81%. The DMF removal rate reached the best at 18 h and the expression of dehydrogenase was the highest in the AnSBR. The abundance of Megasphaera, the dominant sugar-degrading bacteria in the AnSBR, continued to decline due to the decrease of HRT. The relative abundance of Methanobacterium gradually increased to 80.2% with the decrease of HRT and that hydrotrophic methanogenesis dominated the methanogenic process. The HRT decrease promoted butyrate and pyruvate metabolism in anaerobic sludge, but the proportion of glycolysis and methane metabolism decreased. The AnSBR-ASBR reactor had the best operation performance when HRT was 18 h, AnSBR speed was 220 r/min, and ASBR DO content was 3–4 mg/L. This study provided an effective reference for the reasonable selection of operating parameters in the treatment of DMF-containing wastewater by the AnSBR-ASBR.

A modified anaerobic-anoxic-oxic system for optimizing rural sewage treatment with fluctuating influent flows

Due to the challenges presented by rural environments, such as dispersion, fluctuation, and low efficiency, treating domestic sewage in rural areas requires a unique approach compared to urban areas. To address these challenges, this study proposes a modified AAO (anaerobic-anoxic-aerobic) system designed to effectively treat poor water quality caused by varying water quantity in rural sewage. After 127 days of operation with both single and multiple influent flows, the system consistently achieved effluent COD concentrations of 27.38 ± 19.13 mg/L, and TN concentrations below 15 mg/L. The removal rates of COD and TN reached 96 % and 80 %, respectively. Moreover, mass balance analysis showed that the multiple influent flow has higher pollutant removal efficiency than the single influent flow. Long-term operation increased the abundance of Rudaea, Luteococcus, Labrys, and Rhodoblastus in the system to become the dominant bacterial group compared with the inoculated sludge. The AAO-modified system is specifically designed to address the challenge of significant influent fluctuation coefficients by implementing structural modifications. It can systematically redistribute nutrients and enhance microbial activity, effectively adapting to fluctuating influent wastewater flows. Overall, this innovative system offers significant advantages for the treatment of domestic sewage in rural areas.

Association of magnetic-flyash in anaerobic co-digestion for biomethane optimization: Promoting biofilm formation

The application of low-cost magnetic industrial wastes as accelerants can significantly improve the performance of anaerobic co-digestion (AcoD), thereby enhancing the biogas yield. In this work, varying concentrations (1.0–4.0 wt.%) of magnetic flyash (MFA) were applied to the AcoD of cow manure (CM) and aloe peel waste (APW). All AcoD systems were operated under mesophilic condition (37 ᴼC) with a 5 mT magnetic field. The AcoD system with 2.0 wt.% of MFA showed the highest cumulative biogas yield (487 mL/g VS), methane content (65.17%), COD, TS and VS removal rates (36.45, 45.49 and 52.10%, respectively), and fertility (3.4%). However, the 1.0 wt.% of NMFA also showed higher cumulative biogas yield (432 mL/g VS), methane content (60.23%), COD, TS and VS (27.69, 18.24 and 43.64%, respectively), and fertility (3.31%) than other NMFA concentrations (1.5 & 2.0 wt.%). Kinetic models verified that MFA coupled with a magnetic field could increase biogas potential and production rate. A strategy for determining the role of MFA in microbial biofilm formation and improving biodegradation, which increases the biogas yield, is also suggested. This work demonstrates a cost-effective application of MFA in bioenergy production systems by improving the AD process.

Effect of elastic filler on the treatment effect and archaea community structure of ABR

This research endeavored to elucidate the influence of elastic fillers on the performance and archaeal community configuration of the Anaerobic Baffled Reactor (ABR). Utilizing high-throughput sequencing technology, the archaeal community structure was assessed in two distinct ABR sets. The findings revealed that the introduction of elastic fillers led to an enhancement in the average COD removal rate, BOD5 removal rate, effluent biodegradability, and fecal coliform removal rate of the ABR by 3.55%, 3.02%, 7.45%, and 96.85% correspondingly. Concurrently, it facilitated the transformation and degradation of organic matter within the ABR, thus resulting in an increased conversion of organic matter into Volatile Fatty Acids (VFA) within the initial compartment, and enhanced VFA degradation in the subsequent compartments. Indices such as Chao1, Observed species, Simpson, and Shannon concurred that the abundance and heterogeneity of the archaeal community within the ABR were augmented. The average relative abundance of dominant archaea (Methanosaeta and Methanobacterium) in the first compartment of ABR diminished by 3.44%, whereas in the second, third, and fourth compartments, the abundance escalated by 10.50%, 4.18%, and 2.78% respectively. The inclusion of elastic fillers not only amplified the hydrolysis and acid production process in the first compartment of the ABR but also fostered the methane production process in the subsequent compartments.

Potential of ash from agricultural waste as substitute of commercial FeCl3 in primary treatment of landfill leachate

Due to the ever increasing global population, higher volumes of industrial waste discharges to landfill have caused major problems for the environment. This study investigated the performance of rice straw ash (RSA) as a natural coagulant under different conditions for the treatment of landfill leachates by coagulation-flocculation and microfiltration, with and without addition of FeCl3. The highest performing treatment conditions (RSA = 2.48 g/L, FeCl3 = 4.98 g/L, settling time = 54.75min) were achieved with the combined use of RSA and FeCl3 as coagulant and led to a sludge volume index of 41.65 mL/g, 51.27% COD removal and 76.48% total suspended solid removal. In contrast, FeCl3 alone achieved slightly better COD and total suspended solid removal rates, however it resulted in higher sludge volume index and sludge production. The combined use of RSA and FeCl3 reduced the consumption of these two coagulants by 78.76% and 46.69% respectively. Functional groups and thermal stability of the flocs showed that RSA + FeCl3 synergistically enhance the mechanisms of the coagulation-flocculation process, including adsorption by particle's bridging, charge neutralization and size of flocs. Combining the coagulants resulted in increased van der Waals forces and lower attractive forces of the inter-colloidal energy barrier in the leachate. Additionally, the highest and lowest heavy metals removal rates for treatment by microfiltration were found for Fe (92.15%) and Mg (7.63%), with a total heavy metals removal efficiency in the range of 6.08–90.78%. The findings of this study show that RSA can serve as a natural eco-friendly coagulant both alone and in combination with FeCl3 in the leachate treatment.

Efficient electrochemical oxidation of refractory organics in actual petrochemical reverse osmosis concentrates by Ti/SnO2-Sb mesh anode

The efficient treatment of refractory organics in reverse osmosis concentrate (ROC) is a critical issue for achieving emission reduction or even zero emission in the petrochemical industry. A simple and efficient electrocatalytic process was proposed for treating actual petrochemical ROC using a highly active self-assembling Ti/SnO2-Sb anode. The Ti/SnO2-Sb anode was prepared by using citric acid (CA) and ethylene glycol (EG) as precursors, with a mole ratio of Sn:Sb of 5:1 and a metal salts to CA to EG mole ratio of 1:3:16. The resulting electrode surface had a complete mesh pit structure after calcination at 550 ºC. Several key factors were found to affect the degradation of dissolved organic carbon (DOC), including current density, chloride ion concentration, Fe (II) concentration, and acidity. The presence of chloride ions on the anode surface significantly improved the conversion efficiency of hydroxyl radicals, which played a crucial role in the oxidation of the organics. Additionally, near the cathode, oxidative radicals such as H2O2 and O2-∙ were generated, while hydroxyl radicals were produced with the addition of Fe (II) and H+. Under a current density of 20 mA·cm−2, the Ti/SnO2-Sb anode achieved a COD removal rate of 94.5% and a DOC removal rate of 43.4%.