Iron [Fe(0)]-rich substrate based on iron-carbon micro-electrolysis for phosphorus adsorption in aqueous solutions

Removal of phosphate from wastewater by Fe-C micro-electrolysis: application of a novel integrated Fe/C aggregate

To overcome the drawbacks of typical Fe-C micro-electrolysis in wastewater treatment, we developed a new electrolysis material, integrated Fe/C aggregate (FCA) made from Fe0 and carbon powder, and used it for phosphate removal from wastewater. Results show that the free iron ions could quickly react with PO 4 3 - and form an iron phosphate precipitate in phosphate-containing wastewater. The release rate of iron ions was extremely rapid in the first 10 h, indicating that Fe-C microscopic galvanic cells formed on the aggregate surface. Acid conditions are beneficial for accelerating the Fe-C micro-electrolysis reaction and enhancing the iron ion release capacity and phosphate removal capacity. In batch experiments, the maximum phosphate removal capacity of FCA was found to be 10.84 mg P/g. The phosphate removal behaviour of FCA can be well described by the Langmuir isotherm model and the pseudo-second-order kinetic model. SEM and XPS investigations also revealed that phosphates were absorbed by ferrous or ferric hydroxide and generated Fe-P precipitate, which adhered to the surface of FCA throughout the phosphate removal process. Because of its low cost and outstanding performance, the FCA aggregate has a high potential for P removal in wastewater treatment.

Enhanced biological phosphorus removal in low-temperature sewage with iron-carbon SBR system

This study proposed an AO-SBR (Anaerobic Aerobic Sequencing Batch Reactor) combined with iron-carbon micro-electrolysis (ICME) particles system for sewage treatment at low temperature and explored the dephosphorisation mechanism and microbial community structure. The experimental results illustrated that ICME particles contributed to phosphorus removal, metabolic mechanism of poly-phosphorus accumulating organism (PAO) and microbial community structure in the AO-SBR system. The optimal treatment effect was achieved under the conditions of pH 7, DO 3.0 mg/L and particle dosage of 2.6 g Fe-C/g MLSS, and the removal rates of COD, TP, NH4+-N and TN reached 80.56%, 91.46%, 69.42% and 57.57%. The proportion of phosphorus accumulating organisms (PAOs) increased from 4.54% in the SBR system to 10.89% in the ICME-SBR system at 10°C. Additionally, the metabolic rate of PAOs was promoted, and the activities of DHA and ETS both reached the maximum value of 13.34 and 102.88 μg·mg-1VSS·h-1. These results suggest that the ICME particles could improve the performance of activated sludge under low-temperature conditions. This technology provides a new way for upgrading the performance of sewage treatment in the cold area.

A novel constructed wetland based on iron carbon substrates: performance optimization and mechanisms of simultaneous removal of nitrogen and phosphorus

In recent years, the combination of iron carbon micro-electrolysis (ICME) with constructed wetlands (CWs) for removal of nitrogen and phosphorus has attracted more and more attention. However, the removal mechanisms by CWs with iron carbon (Fe-C) substrates are still unclear. In this study, the Fe-C based CW (CW-A) was established to improve the removal efficiencies of nitrogen and phosphorus by optimizing the operating conditions. And the removal mechanisms of nitrogen and phosphorus were explored. The results shown that the removal rates of COD, NH₄⁺-N, NO₃^--N, TN, and TP in CW-A could reach up to 84.4%, 94.0%, 81.1%, 86.6%, and 84.3%, respectively. Wetland plants and intermittent aeration have dominant effects on the removal of NH₄⁺-N, while the removal efficiencies of NO₃^--N, TN, and TP were mainly affected by Fe-C substrates, wetland plants, and HRT. XPS analysis revealed that Fe(0)/Fe²⁺ and their valence transformation played important roles on the pollutants removal. High-throughput sequencing results showed that Fe-C substrates and wetland plants had considerable impacts on the microbial community structures, such as richness and diversity of microorganism. The relative abundance of autotrophic denitrification bacteria (e.g., Denitatsoma, Thauera, and Sulfuritalea) increased in CW-A than CW-C. The electrons and H₂/[H] produced from Fe-C substrates were utilized by autotrophic denitrification bacteria for NO₃^--N reduction. Microbial degradation was the main removal mechanism of nitrogen in CW-A. Removal efficiency of phosphorus was enhanced resulted from the reaction of phosphate with iron ion. The application of CWs with Fe-C substrates and plants presented great potential for simultaneous removal of nitrogen and phosphorus.

Constructed wetland-microbial fuel cells enhanced with iron carbon fillers for ciprofloxacin wastewater treatment and power generation

In this study, the following three experimental devices were operated for 70 days for the treatment of ciprofloxacin pollutants in wastewater: constructed wetlands (CW), constructed wetland-microbial fuel cells (EG), and constructed wetland-microbial fuel cells with new iron-carbon fillers (TPFC). The water quality, power generation capacity, microbial community structure, and changes in the resistance gene qnrs were studied. The efficiency of removal of total phosphate in the TPFC (97.1% ± 2.5%) was significantly higher than that in the EG (51.6% ± 4.8%) and the CW (68.1% ± 2.9%). The efficiency of removal of ciprofloxacin was also significantly higher (TPFC: 91.2% ± 3.4%, EG: 82.1% ± 2.3%, and CW: 75.1% ± 5.6%) (P < 0.05). The voltage of TPFC reached 300.16 ± 12.12 mV, which was apparently greater than that of EG (180.36 ± 16.73 mV) (P < 0.05), possibly because of the higher abundance of microorganisms such as Burkholderiaceae, Hydrogenophaga, and Proteobacteria. There were more copies of the resistance gene qnrs (TPFC: 7.74/μL, EG: 5.52/μL, and CW: 2.65/μL), which may be associated with stronger resistance; therefore, the efficiency of removal of ciprofloxacin was higher in the TPFC. TPFCs are a promising way to remove ciprofloxacin in wastewater.

Pilot study on the treatment of low carbon and nitrogen ratio municipal sewage by A1/O2/A3/A4/O5 sludge-membrane coupling process with multi-point inflow

A new multi-point inflow pre-anoxic/oxic/anaerobic/anoxic/oxic (A1/O2/A3/A4/O5) sludge-membrane coupling process and pilot plant were developed and designed to solve the problem of nitrogen and phosphorus removal of low carbon and nitrogen (C/N) ratio domestic sewage in southern China. The removal effect and transformation rule of organic matter, nitrogen, and phosphorus in the system were studied by changing the distribution ratio of multi-point influent. The average C/N ratio of the influent was 2.09 and the influent distribution ratio was 1:1. When the temperature was 16-25 °C, the average concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺- N), total nitrogen (TN), and total phosphorus (TP) in the effluent were 21.31 (±2.65), 0.60 (±0.24), 12.76 (±1.09), and 0.34 (±0.05) mg/L, respectively, and their average removals are 87.3 (±1.2)%, 98.7 (±0.4)%, 74.1 (±1.3)%, and 88.1 (±0.4)% respectively. When the low temperature was 12-15 °C, the average removals were 78.6 (±1.1)%, 90.5 (±1.3)%, 73.7 (±1.13)%, and 86.6 (±1.7)%, respectively. Compared with the traditional anaerobic/anoxic/aerobic (A2O) process under the same conditions, the TN removal was increased by 15.4%, and the TP removal was increased by 22.2%. This system has obvious advantages in treating wastewater with low C/N ratio, thereby solving the problem wherein the effluent of biological phosphorus removal from low C/N ratio domestic sewage was difficult when it was lower than 0.5 mg/L.

Iron-carbon microelectrolysis for wastewater remediation: Preparation, performance and interaction mechanisms

Rapid industrialization and urbanization have produced a lot of hazardous substances in water and wastewater, which has turned into a crucial issue to the environment and the public health. Recently, iron carbon microelectrolysis (IC-ME) has attracted extensive attention in environmental remediation due to its low costs and excellent performance. Nevertheless, there is still a lack of a more systematic review on IC-ME preparation methods, their performance, and the interaction mechanisms of IC-ME in the remediation of wastewater. Herein, this work summarizes the synthetic methods, application of IC-ME materials, and the mechanism of pollutant removal by IC-ME. A variety approaches have been applied to prepare IC-ME materials, and the preparation methods and conditions have a certain influence on the properties of IC-ME materials, thus affecting the performance of pollutant removal. The mechanisms of IC-ME for contaminants removal are very complex, including adsorption, coprecipitation, reduction, surface complexation, and oxidation. Moreover, research vacant fields and problems that existed in the application of IC-ME are proposed. At last, the problems to be addressed to adapt IC to future applications are introduced. This paper reviews and prospects IC-ME wastewater remediation technology, which provides a reference for further scientific research and engineering applications.

Current intensities altered the performance and microbial community structure of a bio-electrochemical system

A novel integrated bio-electrochemical system with sulfur autotrophic denitrification (SAD) and electrocoagulation (BESAD-EC) system was established to remove nitrate (NO₃^--N) and phosphorus from contaminated groundwater. The impacts of a current intensity gradient on the system's performance and microbial community were investigated. The results showed that NO₃^--N and total phosphorus (TP) could be effectively removed with maximum NO₃^--N reduction and TP removal efficiencies of 94.2% and 75.8% at current intensities of 200 and 400 mA, respectively. Lower current intensities could improve the removal efficiencies of NO₃^--N (≤200 mA) and phosphorus (≤400 mA), while higher current intensity (600 mA) caused the inhibition of nutrients removal in the system. MiSeq sequencing analysis revealed that low electrical stimulation improved the diversity and richness of microbial community, while high electrical stimulation reduced their diversity and richness. The relative abundance of some genus involved in denitrification and phosphorus removal processes such as Rhizobium, Hydrogenophaga, Denitratisoma and Gemmobacter, significantly (P < 0.05) reduced under high current conditions. This could be one of the main reasons for the deterioration of denitrification and phosphorus removal performance. The results of this study could be helpful to enhance the nutrient removal performance of bio-electrochemical systems in groundwater treatment processes.

Treatment of microcystin (MC-LR) and nutrients in eutrophic water by constructed wetlands: Performance and microbial community

Cyanobacterial harmful algal blooms and microcystins (MCs) pollution pose serious threat to aquatic ecosystem and public health. Planted and unplanted constructed wetlands (CWs) filled with four substrates (i.e., gravel (G-CWs), ceramsite (C-CWs), iron-carbon (I-CWs) and slag (S-CWs)) were established to evaluate nutrients and a typical MCs variant (i.e., MC-LR) removal efficiency from eutrophic water affected by the presence of plant and different substrate. The response of the microbial community to the above factors was also analyzed in this study. The results indicate that the presence of plant can generally enhance nutrients and MC-LR removal efficiency in CWs, except for I-CWs. Throughout the experiment, all CWs exhibited good nitrogen removal efficiency with removal percentages exceeding 90%; TP and MC-LR average removal efficiency of C-CWs and I-CWs were greater than G-CWs and S-CWs irrespective of the presence of plant. The best MC-LR removal efficiency under different MC-LR loads was observed in planted C-CWs (ranged from 91.56% to 95.16%). Except for I-CWs, the presence of plant can enhance relative abundances of functional microorganisms involved in nutrients removal (e.g., Comamonadaceae and Planctomycetaceae) and MCs degradation (e.g., Burkholderiaceae). The microbial community diversity of I-CWs was simplified, while the relative abundance of Proteobacteria was highest in this study. The highest relative abundances of Comamonadaceae, Planctomycetaceae and Burkholderiaceae were observed in planted C-CWs. Overall, ceramisite and iron-carbon were more suitable to be applied in CWs for nutrients and MC-LR removal. This study provides a theoretical basis for practical application of CWs in eutrophication and MCs pollution control.

Application of iron [Fe(0)]-rich substrate as a novel capping material for efficient simultaneous remediation of contaminated sediments and the overlying water body

Release of contaminants from sediments has been one of the main pollution sources causing eutrophication and malodorous black of ponds. In this study, an iron-rich substrate (IRS) was developed based on iron‑carbon micro-electrolysis and applied for simultaneous sediments and overlying water remediation. IRS obtained high ammonia and phosphate adsorption capacities (Langmuir isotherm) of 13.02 and 18.12 mg·kg^-1, respectively. In the 90-day long-term remediation, IRS reduced NH₄⁺-N, PO₄^3--P, organic-N, organic-P, TN and TP in overlying water by 48.6%, 97.9%, 34.2%, 67.1%, 53.2% and 90.4%, respectively. In sediments, IRS reduced NO₃^--N, NH₄⁺-N and organic-N by 98.5%, 26.5% and 6.3%, respectively. The unstable P-compounds (i.e., organic-P, Ca-bounded-P and labile-P) were effectively transferred (20.1%, 54.3% and 98.2%, respectively) into inert P-compounds (i.e., Fe-bounded-P and residual-P). Meanwhile, flux rates of nitrogen and phosphorus from sediments to overlying water were reduced from 7.02 to 4.92 mg·m^-2·d^-1 (by 29.9%) and from 7.42 to 2.21 mg·m^-2·d^-1 (by 70.2%), respectively. Due to micro-electrolysis, Fe²⁺/Fe³⁺/[H] were in-situ generated from IRS and NO₃^--N was effectively reduced. Additionally, the generation of O₂^· was promoted by Fe²⁺/[H] and strengthened the NH₄⁺-N, organic-N/P oxidation. Fe³⁺ enhanced the immobilization of PO₄^3- (e.g., as FePO₄·H₂O and Fe_nPO₄(OH)_3n-3). The released Fe²⁺/Fe³⁺ from IRS were finally stabilized as poorly reactive sheet silicate (PRS)-Fe and magnetite-Fe in the sediments and hardly showed side effect to sediments and water body. The developed IRS obtained advantages of high efficiency, ecologically safe and cost-effective in contaminated sediments and overlying water remediation.

An oxic/anoxic-integrated and Fe/C micro-electrolysis-mediated vertical constructed wetland for decentralized low-carbon greywater treatment

The treatment of decentralized low-carbon greywater in rural area, particularly in cold weather, remains a challenge. Oxic/anoxic process and Fe/C micro-electrolysis were incorporated into vertical constructed wetland to develop ME-(O/A)CW for practical decentralized low-carbon greywater treatment. ME-(O/A)CW provided NH₄⁺-N, TN, TP and COD removal of 94.3%, 86.2%, 98.0% and 92.7%, respectively, at hydraulic loading rate of 0.9 m³/(m²·d) under low ambient temperature of -11.5 to 8.0 °C. Effective nitrification, phosphorus-accumulating and organic-degradation were proceeded in the aerobic layers and efficient H₂-/Fe²⁺-mediated autotrophic denitrification and Fe³⁺-based phosphorus immobilization were developed in the anaerobic layers through in-situ H₂-/Fe²⁺-supply by Fe/C micro-electrolysis. AOB (e.g. Nitrosomonadales), NOB/PAOs (e.g. Nitrospira), autotrophic denitrificans (e.g. Thiobacillus, Hydrogenophaga and Sulfurimonas), heterotrophic denitrificans (e.g. Denitratisoma) and Fe(II)-oxidizing bacteria (e.g. Ferritrophicum) dominated ME-(O/A)CW and confirmed the reaction mechanisms. The developed ME-(O/A)CW presented significant potential in the practical application for decentralized low-carbon greywater treatment under low ambient temperature.

Preparation of a New Iron-Carbon-Loaded Constructed Wetland Substrate and Enhanced Phosphorus Removal Performance

Iron-carbon substrates have attracted extensive attention in water treatment due to their excellent processing ability. The traditional iron-carbon substrate suffers from poor removal effects, separation of the cathode and anode, hardening, secondary pollution, etc. In this study, a new type of iron-carbon-loaded substrate (NICLS) was developed to solve the problems of traditional micro-electrolytic substrates. Through experimental research, a preparation method for the NICLS with Fe and C as the core, zeolite as the skeleton, and water-based polyurethane as the binder was proposed. The performance of the NICLS in phosphorus-containing wastewater was analyzed. The results are as follows: The optimal synthesis conditions of the NICLS are 1 g hydroxycellulose, wood activated carbon as the cathode, an activated carbon particle size of 200-60 mesh, and an Fe/C ratio of 1:1. Acidic conditions can promote the degradation of phosphorus by the NICLS. Through the characterization of the NICLS (scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy-dispersive spectrometer (EDS), etc.), it is concluded that the mechanism of the NICLS phosphorus removal is a chemical reaction produced by micro-electrolysis. Using the NICLS to treat phosphorus-containing wastewater has the advantages of high efficiency and durability. Therefore, it can be considered that the NICLS is a promising material to remove phosphorus.

Microbial network succession along a current gradient in a bio-electrochemical system

A lab-scale three dimensional biofilm-electrode reactor (3DBER) coupled with sulfur/iron (3DBER-Fe/S) system was established to examine the impacts of current gradient on the performances and microbial network dynamics. Results showed that generally low current could promote nitrogen and phosphorus removal, while high current caused the inhibition of nutrients removal. Molecular ecological network (MEN) analysis showed that the current altered the overall architecture of the networks, and low currents could improve the scale and complexity of networks (<100 mA), while high current (≥100 mA) likely decrease the networks scale and complexity. Stronger competition was observed among Proteobacteria and Chloroflexi at high current conditions, which may be relevant to the deterioration of nutrients removal. In addition, the current dramatically altered the network interactions among denitrifiers, and the keystone species were intensively dynamic among various networks under the current gradient.

Review: recent developments of substrates for nitrogen and phosphorus removal in CWs treating municipal wastewater

Substrates are the main factor influencing the performance of constructed wetlands (CWs), and especially play an important role in enhancing the removal of nitrogen and phosphorus from CWs. In the recent 10 years, based on the investigation of emerged substrates used in CWs, this paper summarizes the removal efficiency and mechanism of nitrogen and phosphorus by a single substrate in detail. The simultaneous removal efficiency of nitrogen and phosphorus by different combined substrates is emphatically analyzed. Among them, the reuse of industrial and agricultural wastes as water treatment substrates is recommended due to the efficient pollutant removal efficiency and the principle of waste minimization, also more studies on the environmental impact and risk assessment of the application, and the subsequent disposal of saturated substrates are needed. This work serves as a basis for future screening and development of substrates utilized in CWs, which is helpful to enhance the synchronous removal of nitrogen and phosphorus, as well as improve the sustainability of substrates and CWs. Moreover, further studies on the interaction between different types of substrates in the wetland system are desperately needed.

Iron-carbon galvanic cells strengthened anaerobic/anoxic/oxic process (Fe/C-A2O) for high-nitrogen/phosphorus and low-carbon sewage treatment

The treatment of sewage with high-nitrogen/-phosphorus and low-carbon remains a challenge. A novel iron-carbon galvanic cells strengthened anaerobic/anoxic/oxic process (Fe/C-A2O) was developed for high-nitrogen/-phosphorus and low-carbon sewage treatment. The cost-effective iron-scraps (ISs) was recycled as Fe(0)-source under the mediation of Fe/C galvanic cell reaction to develop effective Fe(0)-oxidizing autotrophic-denitrification and -dephosphorization. Utilizing practical high-nitrogen/-phosphorus and low-carbon sewage as target wastewater, the performance, impact factors, contribution of Fe/C galvanic cell reactions, microbial characteristics, strengthening mechanisms, and application potential of Fe/C-A2O process were investigated. The Fe/C-A2O process achieved high TN and TP removal efficiencies of 92.0 ± 1.3% and 97.2 ± 0.9% with removal loads of 0.176 ± 0.002 kg TN/(m³·d) and 0.017 ± 0.002 kg TP/(m³·d), respectively. Optimal HRT of 12 h, DO of 4.0-4.5 mg/L, and reflux-ratio of 4:1 were obtained, and no sludge-reflux was required. Autotrophic-denitrification and -dephosphorization supported by the Fe/C galvanic cell reactions contributed 63.1% and 75.3% of TN and TP removal, respectively. Microbial characterization revealed the dominance of autotrophic denitrifiers (e.g., Thiobacillus), AOB (e.g., Nitrosomonas), NOB (e.g., Nitrospira), and heterotrophic denitrifiers (e.g., Zoogloea). The mechanism analysis demonstrated that Fe/C galvanic cells strengthened nitrogen removal by raising Fe²⁺/H₂-supported autotrophic denitrification; and strengthened dephosphorization by introducing Fe³⁺-based PO₄^3--precipitation and enhancing the denitrifying phosphate-accumulation by denitrifying phosphate-accumulating organisms (DPAOs). Based on the efficiency and cost evaluation, the ISs-based Fe/C-A2O process showed significant application potential as an upgrade strategy for traditional A2O process in advanced high-nitrogen/phosphorus and low-carbon sewage treatment.

Water quality retrieval and algae inhibition from eutrophic freshwaters with iron-rich substrate based ecological floating beds treatment

Ecological floating rafts in restoration of eutrophic freshwaters were deemed to a frequently used method. In this study, a manipulative experiment using ecological floating rafts based on iron-rich substrate (IRS) was conducted. The approach was attempted to study the nutrient removal efficiency and algae inhibition effect of IRS. The results showed that 98.2% chlorophyll-a (chl-a) removal rate was achieved in 7-day restoration by IRS accompanied with high nutrient removal efficiency. In addition, iron-rich substrate based ecological floating beds could reached 82.1% chl-a removal rate and 98.5% total phosphorus (TP) removal rate with the increasing activity of aquatic organisms through a 50-day pilot scale experiment. The findings imply that iron-rich substrate-based ecological floating beds are an alternative method for ecological restoration of eutrophic freshwaters.

Application potential of simultaneous nitrification/Fe0-supported autotrophic denitrification (SNAD) based on iron-scraps and micro-electrolysis

Oxygen has not been purposely introduced to the autotrophic denitrification systems and simultaneous nitrification/autotrophic denitrification (SNAD) has not been proposed. In this study, oxygen was introduced into a micro-electrolysis-enhanced Fe⁰-supported autotrophic denitrification (mFe⁰AD) system. The nitrogen removal performance was investigated and the application potential of iron-scraps-supported simultaneous nitrification/mFe⁰AD was evaluated. The results showed that Fe⁰AD was surprisingly enhanced by oxygen together with nitrification at average dissolved oxygen (DO) of 0.08-1.56 mg/L. The ammonia oxidizing bacterial, nitrite oxidizing bacteria, facultative autotrophic denitrificans, and iron compounds transformation bacteria were markedly enriched. Average denitrification rate shifted from 0.116 to 0.340 kg N/(m³·d) with increase of average total nitrogen removal efficiency from 31.4% to 90.5%. Oxygen could enhance the biological conversion and storage of iron compounds, which was capable of reducing the coating of Fe⁰ surface.The accelerating of oxygen on  Fe0 passivation appeared when increasing the average DO from 1.56 to 2.17 mg/L. Therefore, the SNAD was recommended to be operated at the DO range of 0.08-1.56 mg/L. ME significantly enhanced Fe⁰AD, and the utilization of iron-scraps reduced its cost. The denitrification rate is comparable with methanol supported heterotrophic denitrification with 58.9% reduction on the cost. The iron-scraps supported SNAD is competitive in both denitrification rate and costs in the ammonia contaminated low-carbon water treatment.

Enhanced Simultaneous Nitrogen and Phosphorus Removal in A Denitrifying Biological Filter Using Waterworks Sludge Ceramsite Coupled with Iron-Carbon

In this study, waterworks sludge ceramsite (WSC) was combined with 3% iron-carbon matrix in a denitrifying biological filter (ICWSC-DNBF) to enhance the simultaneous removal of carbon, nitrogen and phosphorus in secondary effluent of wastewater treatment plant (SE-WTP). The chemical oxygen demand (COD) and nitrogen removal, as well as phosphorus removal and the adsorbed forms of phosphorus were measured and the removal mechanism of these pollutants by the ICWSC-DNBF system for treating SE-WTP were investigated. The results showed that the ICWSC-DNBF achieved good removals of COD, NH₄⁺-N, NO₃^--N, total N and total P; effluent concentrations were 17.23 mg/L, 3.72 mg/L, 14.32 mg/L, 17.38 mg/L and 0.82 mg/L, respectively. WSC enhanced the P removal due to its high specific surface area and the high number of adsorption sites. Fe-P and Al-P were the main forms of P adsorbed by WSC, accounting for 78.53% of the total adsorbed P. WSC coupled with Fe and C improved the biodegradability of SE-WTP and promoted the removal of organic matter. The removal of N was attributed to the abundant denitrifying microorganisms in the system and the electrochemical effect produced by the internal electrolysis of Fe and C.

Combination with catalyzed Fe(0)-carbon microelectrolysis and activated carbon adsorption for advanced reclaimed water treatment: simultaneous nitrate and biorefractory organics removal

A process combining catalyzed Fe(0)-carbon microelectrolysis (IC-ME) with activated carbon (AC) adsorption was developed for advanced reclaimed water treatment. Simultaneous nitrate reduction and chemical oxygen demand (COD) removal were achieved, and the effects of composite catalyst (CC) addition, AC addition, and initial pH were investigated. The reaction kinetics and reaction mechanisms were calculated and analyzed. The results showed that CC addition could enhance the reduction rate of nitrate and effectively inhibit the production of ammonia. Moreover, AC addition increased the adsorption capacity of biorefractory organic compounds (BROs) and enhanced the degradation of BRO. The reduction of NO₃^--N at different pH values was consistently greater than 96.9%, and NH₄⁺-N was suppressed by high pH. The presence of CC ensured the reaction rate of IC-ME at high pH. The reaction kinetics orders and constants were calculated. Catalyzed iron scrap (IS)-AC showed much better nitrate reduction and BRO degradation performances than IS-AC and AC. The IC-ME showed great potential for application to nitrate and BRO reduction in reclaimed water.

Enhanced removal mechanism of iron carbon micro-electrolysis constructed wetland on C, N, and P in salty permitted effluent of wastewater treatment plant

In this study, the combination of a constructed wetland (CW) with iron-carbon (Fe-C) system was used to enhance the simultaneous removal of carbon, nitrogen and phosphorus in salty permitted effluent of wastewater treatment plant (SPE-WTP). The removal mechanism of Fe-C micro-electrolysis CWs with different salinity (0.027, 0.308, and 0.511%) for treating SPE-WTP was investigated, including chemical oxygen demand (COD), phosphorus and nitrogen removal, the mass balance, as well as the changes in the microbial community structure. The results showed the salinity has a certain influence on the contaminant removals, and can enhance nitrogen removal under certain conditions. When the salinity increased from 0.308% to 0.511%, the removal of COD decreased from 68.20% to 62.69%, whereas the removal of total nitrogen (TN) increased from 72.02% to 81.21% in the ICCW-p system (including P. australis as the plant and gravel doped with 3% iron-carbon as the matrix). Microbial degradation, including the electrochemical effect (the degradation by iron-carbon micro-electrolysis) was the main N removal pathway in the ICCW-p system. The ICCW-p system always achieved higher removal rates (such as 81.21% TN and 62.69% COD removals at 0.511% salinity) than that in ICCW-n system (without plants and gravel doped with 3% iron-carbon as the matrix, 63.76% TN and 56.31% COD removals, respectively) and CW-n (without plants and gravel as the matrix, 14.90% TN and 22.39% COD removals, respectively). In addition, high-throughput sequencing analysis revealed that high salinity increased the abundance of N-removing bacteria in the ICCW-p system. Furthermore, with the introduction of iron-carbon in CWs, the removal methods in ICCW-p were diverse, which has enough ability to resist the impact of salinity. Fe electrolysis produced different valence states that acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions, which enhanced the simultaneous removal of carbon, nitrogen and phosphorus.

Global development of various emerged substrates utilized in constructed wetlands

Substrate selection is one of the key technical issues for constructed wetlands (CWs), which works for wastewater treatment based mainly on the biofilm principle. In recent years, many alternative substrates have been studied and applied in CWs, and a review is conducive to providing updated information on CW R&D. Based on the intensive research work especially over the last 10 years on the development of emerged substrates (except for the three conventional substrates of soil, sand, and gravel) in CWs, this review was made. The substrates are categorized depending on their main roles in pollutant removal as ion-exchange substrates, P-sorption substrates, and electron donor substrates. Among these, reuse of various waste products as substrates was suggested due to their competitive pollutant removal efficiency and minimized waste disposal. Regarding substrate development, future research on avoiding substrate clogging to extend their lifetime in CWs is needed.

A Review of Research on Substrate Materials for Constructed Wetlands

Based on the improvements in the decontamination ability and decontamination range of constructed wetlands, this study of constructed wetland substrates was carried out using literature research and comparative meta-analysis. The results show that, for static adsorption, the absorption levels of nitrogen and phosphorus in a given constructed wetland are different. As for hydraulic load, the average removal rate of total nitrogen in wastewater is less than 50%. Compared with single substrates, a combination of substrates is typically superior in terms of the removal rate of sewage pollutants. Adsorption is the key in removing pollutants in constructed wetlands, and modification of the wetland materials is an effective way to improve the decontamination ability of the substrate material. At present, there are areas of potential improvement in the research on the development of new wetland materials for the study of pollutant characteristics, as well as a dearth of modification methods for single and reclaimable wetland substrates in constructed wetlands. These issues should be taken into account in the future studies on constructed wetland materials.

A novel bio-electrochemical system with sand/activated carbon separator, Al anode and bio-anode integrated micro-electrolysis/electro-flocculation cost effectively treated high load wastewater with energy recovery

A novel bio-electrochemical system (BES) was developed by integrating micro-electrolysis/electro-flocculation from attaching a sacrificing Al anode to the bio-anode, it effectively treated high load wastewater with energy recovery (maximum power density of 365.1 mW/m³ and a maximum cell voltage of 0.97 V), and achieving high removals of COD (>99.4%), NH₄⁺-N (>98.7%) and TP (>98.6%). The anode chamber contains microbes, activated carbon (AC)/graphite granules and Al anode. It was separated from the cathode chamber containing bifunctional catalytic and filtration membrane cathode (loaded with Fe/Mn/C/F/O catalyst) by a multi-medium chamber (MMC) filled with manganese sand and activated carbon granules, which replaced expensive PEM and reduced cost. An air contact oxidation bed for aeration was still adopted before liquid entering the cathode chamber. micro-electrolysis/electro-flocculation helps in achieving high removal efficiencies and contributes to membrane fouling migration. The increase of activated carbon in the separator MMC increased power generation and reduced system electric resistance.

Phosphorus sorption-desorption and effects of temperature, pH and salinity on phosphorus sorption in marsh soils from coastal wetlands with different flooding conditions

Wetland soils act as a sink or source of phosphorus (P) to the overlaying water due to phosphorus sorption-desorption processes. Litter information is available on sorption and desorption behaviors of phosphorus in coastal wetlands with different flooding conditions. Laboratory experiments were conducted to investigate phosphorus sorption-desorption processes, fractions of adsorbed phosphorus, and the effects of salinity, pH and temperature on phosphorus sorption on soils in tidal-flooding wetlands (TW), freshwater-flooding wetlands (FW) and seasonal-flooding wetlands (SW) in the Yellow River Delta. Our results showed that the freshly adsorbed phosphorus dominantly exists in Occluded-P and Fe/AlP and their percentages increased with increasing phosphorus adsorbed. Phosphorus sorption isotherms could be better described by the modified Langmuir model than by the modified Freundlich model. A binomial equation could be properly used to describe the effects of salinity, pH, and temperature on phosphorus sorption. Phosphorus sorption generally increased with increasing salinity, pH, and temperature at lower ranges, while decreased in excess of some threshold values. The maximum phosphorus sorption capacity (Q_max) was larger for FW soils (256 mg/kg) compared with TW (218 mg/kg) and SW soils (235 mg/kg) (p < 0.05). The percentage of phosphorus desorption (P_des) in the FW soils (7.5-63.5%) was much lower than those in TW (27.7-124.9%) and SW soils (19.2-108.5%). The initial soil organic matter, pH and the exchangeable Al, Fe and Cd contents were important factors influencing P sorption and desorption. The findings of this study indicate that freshwater restoration can contribute to controlling the eutrophication status of water bodies through increasing P sorption.

Enhanced decolorization of methyl orange in aqueous solution using iron-carbon micro-electrolysis activation of sodium persulfate

Reactivity of sodium persulfate (PS) in the decolorization of methyl orange (MO) in aqueous solution using an iron-carbon micro-electrolysis (ICE) method was investigated. The effects of sodium persulfate doses, pH, Fe-to-C mass ratios, initial MO concentration as well as the reaction temperature were comprehensively studied in batch experiments. The ICE-PS coupled process was more suitable for wide ranges of pH, initial MO concentration and reaction temperature, accompanied by the reduction of Fe compared ICE. The MO removal efficiency improved substantially by ICE-PS technique, 76.03% for ICE and 91.27% for ICE-PS at experimental conditions of pH 3.0, Fe-to-C mass ratio 3:1, PS addition 10 mM and initial MO concentration 0.61 mM. Furthermore, the biodegradability index (BI) dramatically increased from 0.26 to 0.65. The binary hydroxyl and sulfate radicals that non-selectively degrade MO to the derivatives with small molecules are ascribed to ICE-PS method as detected by the UV-vis spectra. The PS activation resource was Fe²⁺ through the hydroxyl radical quenching reaction by the additive tert-butanol (TBA). This study provides an in-depth theoretical understanding of the development and wide commercial application of the ICE technology to refractory industrial dye wastewater treatment.