Treatment of nanofiltration concentrates of mature landfill leachate by a coupled process of coagulation and internal micro-electrolysis adding hydrogen peroxide

Natural and anthropogenic dissolved organic matter in landfill leachate: Composition, transformation, and their coexistence characteristics

A large number of natural and anthropogenic wastes were landfilled, and dissolved organic matter (DOM) were formed during landfill. However, the composition, transformation, and coexistence characteristics of natural and anthropogenic DOM in leachate remain unclear. Fourier transform ion cyclotron resonance mass spectrometry, size exclusion chromatography, gas chromatography coupled with mass spectrometry, and three-dimensional excitation-emission matrix spectrum were employed to clarify comprehensively the abovementioned question. The results showed that natural DOM in young leachate constituted mainly straight-chain organic acids, protein substances, and building blocks of humic substances (BB). Straight-chain organic acids vanished in old leachates, and the concentration of protein substances and BB decreased from 44% to 26% and from 47% to 12%, respectively, while CHON and CHONS were degraded to CHO and CHOS during the process. As to anthropogenic DOM, its types and relative content in leachate increased during landfill, and aromatic acids, terpenes, halogenated organics, indoles, and phenols became the main organic components in old leachate. Compared to natural DOM, anthropogenic DOM was degraded slowly and accumulated in leachate, and some of the natural DOM facilitated the dechlorination of dichlorinated organic compounds. This study demonstrates that landfill led to an increase in humic substances and halogenated organic compounds in old leachate, which was intensified with concentrated leachate recirculation.

Effective treatment of leachate concentrate from waste incineration plant by combination of coagulation and direct contact evaporation

In order to verify that coagulation as pre-treatment can reduce the temperature of the hot air used for direct contact evaporating the leachate concentrate (LC) and low-grade waste heat such as exhaust steam in the waste incineration plant can be used to evaporate the LC. The supernatants after coagulation using polymerized ferrous sulfate (PFS), polymeric-aluminum (PAC), polymeric silicate aluminum ferric (PSAF) and poly-aluminum ferric chloride (PAFC) as coagulants were further treated in a lab-scale direct contact evaporation system. The results showed that the best performance with removal efficiencies of COD and NH3-N of 58.70% and 29.09% was achieved after coagulation when PAFC dosage = 15 g/L, PAM dosage = 30 mg/L and initial pH of supernatant = 6. After coagulation, a large amount of the fulvic-like acid and aromatic heterocyclic compounds were removed and the degree of complexity and aromaticity of organics decreased. After direct contact evaporation, using PAFC as coagulant still was the best selection due to its lowest concentrations of COD and NH3-N (22 mg/L and 1.02 mg/L) in the condensate produced by this two-stage treatment when initial pH of supernatant was 6 during evaporation and the condensate produced by this two-stage treatment met the water quality standard for using as supplying water for circulating cooling water system when temperature of hot air used for heating LC was at low temperature (250 °C). The fulvic-like acid and aromatic heterocyclic compounds in the condensate continuously reduced. Phenol, adamantane, 1-isocyanato, phthalic anhydrid, tri(2-chloroethyl) phosphat, Heptadecane, 2-methyl, ginsenol and Octadecane, 2-methyl- in the condensate obviously decreased. The effect of four coagulants as pretreatment on reducing the temperature of hot air used for evaporating LC was ranked as PAFC > PFS > PAC > PSAF. PSAF was not recommended due to the large amount of NH3-N produced when using PSAF to treat the LC.

Challenges and engineering application of landfill leachate concentrate treatment

Landfill leachate concentrate (LLC) is a concentrated waste stream from landfill leachate treatment systems and has been recognized as a key challenge due to its high concentration of salts, heavy metals, organic matters, etc. Improper management of LLC (e.g. reinjection) would exacerbate the performance of upstream treatment processes and pose risks to the surrounding environments near landfill sites. Addressing the challenge and recovering resources from LLC have thus been attracting considerable attention. Although many LLC treatment technologies have been developed, a comprehensive discussion about the challenges still lacks. This review critically evaluates mainstream LLC treatment technologies, namely incineration, coagulation, advanced oxidation, evaporation and solidification/stabilization. We then introduce a geopolymer-based solidification (GS) process as a promising technology owning to its simple casting process and reusable final product and summarizes engineering applications in China. Finally, we suggest investigating hybrid systems to minimize LLC production and achieve the on-site reuse of LLC. Collectively, this review provides useful information to guide the selection of LLC treatment technologies and suggests a sustainable alternative for large-scale application, while also highlighting the need of joint efforts in the industry to achieve efficient, ecofriendly and economical on-site management of landfill waste streams.

Treatment of nanofiltration membrane concentrates integrated magnetic biochar pretreatment with anaerobic digestion

nanofiltration membrane concentrate (NMC) is an emerging type of wastewater with significant environmental concerns. which can be treated efficiently by an integrated method. In this study, magnetic biochar (MBC) pretreatment integrated with anaerobic digestion (AD) (MBC + AD) was used to treat NMC. Results showed that under the optimal MBC + AD conditions, 79%, 69.4%, 52.9%, and 86.5% of COD, total nitrogen (TN), chromaticity, and light absorbing substances were reduced. For heavy metals removal, 18.3%, 70.0%, 96.4%, 43.8% and 97.5% of Cr (VI), Cd, Pb, Cu and Zn were removed, respectively. LC-MS analysis indicated that p-nitrophenol (4-NP) diethyl and phthalate (DEP) were the main organic pollutants in NMC with a removal rate of 60% and 90%. Compared with single AD, in MBC + AD samples, bacterial activity was improved, and genus DMER64 (23.2%) was dominant. The predominant archaea were Methanocorpusculum (53.3%) and Methanosarcina (25.3%), with microbial restructuring and slight methane generation. Additionally, metabolic pathway prediction revealed that both bacterial and archaeal metabolism were significantly enhanced, contributing to the central functional pathways, namely microbial activity metabolism and biodegradation metabolism. In addition, the significantly increased genera Syner-01, Vulcanibacillus, Methanocorpusculum, and Norank_c_Bathyarchaeia were significantly positively related to metabolic function. This finding demonstrated that MBC + AD enhanced contaminant removal, mainly by regulating bacterial diversity and activity. Moreover, the toxicity of NMC decreased after MBC + AD treatment. This study provides a potential biological strategy for the treatment of membrane concentrates and water recovery.

A review on membrane concentrate management from landfill leachate treatment plants: The relevance of resource recovery to close the leachate treatment loop

Membrane filtration processes have been used to treat landfill leachate. On the other hand, closing the leachate treatment loop and finding a final destination for landfill leachate membrane concentrate (LLMC) - residual stream of membrane systems - is challenging for landfill operators. The re-introduction of LLMC into the landfill is typical; however, this approach is critical as concentrate pollutants may accumulate in the leachate treatment facility. From that, leachate concentrate management based on resource recovery rather than conventional treatment and disposal is recommended. This work comprehensively reviews the state-of-the-art of current research on LLMC management from leachate treatment plants towards a resource recovery approach. A general recovery train based on the main LLMC characteristics for implementing the best recovery scheme is presented in this context. LLMCs could be handled by producing clean water and add-value materials. This paper offers critical insights into LLMC management and highlights future research trends.

A techno-economical assessment of treatment by coagulation-flocculation with aluminum and iron-bases coagulants of landfill leachate membrane concentrates

Landfill leachate treatment involved with the membrane bioreactor (MBR) combined with membrane treatment via nanofiltration (NF) and/or reverse osmosis (RO) is widely used in Turkey. This treatment produces landfill leachate membrane concentrates (LLMCs) with an undesirably high concentration of contaminants. In the study, two different nanofiltration concentrates of leachate were coagulated. Coagulant dosages from 0.10 to 5.0 g of Me³⁺/L (Me³⁺: Al³⁺ or Fe³⁺), and the pH values ranged from 4.0 to 8.0 and 3.0-9.0 for Al-based and Fe-based coagulants, respectively. The most efficient pH values were 5.0 and 4.0 for Al³⁺ and Fe³⁺, respectively. These pH values are lower than those known to be effective in coagulants. The reason for this is the presence of humic substances in the wastewater. The cost of Fe₂(SO₄)_3.xH₂O was the lowest than other coagulants at the end of the cost analyses obtained from İstanbul region landfill leachate NF concentrate (NFCL-1) and Kocaeli region landfill leachate NF concentrate (NFCL-2). Under optimum conditions, the costs for NFCL-1 and NFCL-2 were calculated as 0.55 and 0.46 $/removed kg COD, respectively.

Persulfate-enhanced continuous flow three-dimensional electrode dynamic reactor for treatment of landfill leachate

Compared with sequencing batch reactor, continuous flow dynamic reactors are more conducive to promotion and application. In this study, the ability of a three-dimensional (3D) electrode dynamic reactor to remove pollutants in the landfill leachate was investigated, in which landfill leachate entered through continuous flow. Either increased of current density or the decreased of flow rate was conducive to the removal of pollutants. The optimal process parameters for current density and flow rate were 16 mA cm^-2 and 0.75 L h^-1, respectively. When the current density was constant at 16 mA cm^-2 and the flow rate was kept at 0.75 L h^-1, 60.02% of total organic carbon (TOC), 96.50% of chroma, 64.98% of chemical oxygen demand (COD) and 99.46% of ammonia nitrogen (NH₃-N) were removed. The characteristic peaks of refractory organic pollutants were reduced by 97.95%. After the reaction, the biological oxygen demand (BOD)/COD was increased from 0.24 to 0.32. As one of the emerging trace organics in landfill leachate, 85.90% of ibuprofen (IBU) was removed. The results showed that the 3D electrode dynamic reactor constructed in this study could reduce the TOC, refractory trace organic pollutant, NH₃-N and chroma in the landfill leachate. The 3D electrode dynamic reactor constructed in this research has application potential in the field of landfill leachate treatment.

A review on the landfill leachate treatment technologies and application prospects of three-dimensional electrode technology

With the expansion of urbanisation, the total amount of solid waste produced by urban residents has been increasing, and the problem of municipal solid waste disposal has also been aggravated. Landfill leachate treatment technologies could be divided into three categories: biological, physical and advanced oxidation treatment technology. Among them, advanced oxidation treatment technology has a good effect on the treatment of landfill leachate with little secondary pollution and has excellent application potential. Three-dimensional (3D) electrode technology, as a new type of advanced oxidation technology, could remove refractory pollutants in water and has attracted considerable attention. This article aims to (1) compare existing landfill leachate treatment technologies, (2) summarise 3D electrode technology application scenarios, (3) discuss the advantages of 3D electrode technology in landfill leachate treatment and (4) look ahead the future directions of 3D electrode technology in landfill leachate treatment. We hope that this article will be helpful to researchers who are interested in the field of landfill leachate treatment.

Combining chemical coagulation with activated coke adsorption to remove organic matters and retain nitrogen compounds in mature landfill leachate

Mature landfill leachate usually contains high levels of both recalcitrant organic matters and nitrogen compounds, which are hard to be removed simultaneously. In view of the difficulty, this study explored an innovative alternative that treated organic matters and nitrogen compounds separately by combining ferric trichloride (FTC) and polyacrylamide (PAM) coagulation with activated coke adsorption. Our study results have shown that the combination of chemical coagulation (750 mg/L of ferric trichloride and 2.0 mg/L of anionic polyacrylamide at pH = 5) with activated coke adsorption (5 g per 100 mL) was able to remove total organic carbon (TOC), chemical oxygen demand (COD), and colority by 91%, 57%, 100%, respectively. The removal efficiency (R.E.) of humic- and protein-like matters both exceeded 95%. Meanwhile, nitrogen compounds, such as nitrite and ammonia nitrogen, were mostly retained in the effluent. They could either be recovered as value-added products through technologies such as negative pressure steam-stripping or removed through methods such as air stripping and ion exchange. Overall, the proposed coagulation-adsorption process may provide a feasible alternative for tackling the worldwide concern over the secondary pollution caused by mature landfill leachate and its effective disposal.

Removal of ibuprofen by sodium alginate-coated iron-carbon granules combined with the ultrasound and Fenton technologies: influencing factors and degradation intermediates

This study focuses on the preparation of sodium alginate-coated iron-carbon granules (FeCGs) and their capacity to remove ibuprofen (IBU) by combining Fenton and ultrasound technologies. The preferred preparation conditions are as follows: 2% (w/v) sodium alginate, 10% (w/v) iron fillings and biochar, and used CaCl2 as the cross-linking agent. 74.72% of IBU was removed by ultrasound/FeCG under 10 g/L FeCG and 250 W ultrasound power. Fenton/FeCG could remove 92.41% of IBU under 10 g/L FeCG and 2 mM H2O2. Under the above experimental conditions, ultrasound/FeCG has higher reaction speed (9.44 × 10-3 min-1) than Fenton/FeCG (4.95 × 10-3 min-1). However, Fenton/FeCG could remove more TOC than ultrasound/FeCG. During the reaction using the Fenton/FeCG system, 11 degradation intermediates were detected, but only 7 intermediates were produced by the ultrasound/FeCG system. A common single-chain product C5H10O3 formed by IBU degradation was detected in the reaction products during Fenton/FeCG reaction, which benzene ring structure was destroyed; however, the minimum molecular weight of the product detected using the ultrasound/FeCG system was that of C8H10O; the benzene ring structure of IBU is not destroyed. This study provides guidance in the preparation of sodium alginate-coated FeCGs, evaluating the applicability of Fenton/FeCG and ultrasound/FeCG, which was meaningful for organic pollution wastewater treatment.

Interactions among low-molecular-weight organics, heavy metals, and Fe(III) during coagulation of landfill leachate nanofiltration concentrate

The generation of landfill leachate nanofiltration concentrate (LLNC) has been a dilemma for leachate treatment plants because it contains large amounts of refractory organics with low molecular weight (LMWO), as well as heavy metals (HMs), and is difficult to handle. The coagulation removal of LMWOs is a significant challenge, as is the removal of HMs bonded to LMWOs. In this study, coagulation through the dosing of FeCl₃ was used to remove LMWOs and HMs from LLNC. The results interestingly demonstrated that the removal rates of dissolved organic carbon (DOC), Cr, Ni, and As reached up to 84.1% ± 3.9%, 91.0 ± 1.1%, 73.1 ± 2.2%, and 96.9 ± 1.5%, respectively. The partition of LMWO components, as well as the interactions among the LMWOs, HMs, and Fe(III) were investigated to determine the mechanism behind the LMWO and HM removal. LMWOs with a high degree of humification, including humic and fulvic acid-like components, were preferentially removed through aggregation and electrostatic attraction originating from the specialistic adsorption of Fe₂(OH)₂⁴⁺ and Fe₃(OH)₄⁵⁺. In addition to being removed, a portion of these two components was dissociated into aromatic protein I, aromatic protein II, and soluble microbial by-product-like materials due to an acid effect and the formation of inner-sphere complexes. A redundancy analysis revealed that As, Cr, and Ni are mainly removed through the electrostatic attraction of Fe(III), bonding to humic substances and hydrophilic organics, respectively. The outcomes provide a new understanding on the coagulation removal of LMWOs and HMs.

Treatment of landfill leachate with combined biological and chemical processes: changes in the dissolved organic matter and functional groups

Leachates contain complicated and hazardous substances that need multiple treatment processes to meet the discharge standards. Few studies have considered the changes in different fractions, based on their molecular weight (MW), of dissolved organic matter, during the different treatment processes. In this study, we investigated the application of a biological method, using sequencing batch reactors, and a chemical method, using the electro-Fenton oxidation process, in combination. The combined treatment, and the electro-Fenton process alone, was applied to a landfill leachate. Samples taken at various points during the treatment processes were fractionated according to their MW using ultra-membranes; this divided the samples into their less biodegradable constituents (0.45 μm: >10 kDa MW), their bio-refractory constituents (10-1 kDa MW) and their biodegradable constituents (<1 kDa MW). The dominant contributors to the chemical oxygen demand (COD) in the raw leachate comprised the biodegradable constituents (79% of total COD). The COD was reduced to 33.6% and 18.5% of its original levels, by the electro-Fenton process alone and the combined treatment, respectively. Based on the absorption intensities in the Fourier transform infrared (FTIR) spectra, the functional groups in the raw leachate were reduced by the biological treatment, but changed by the electro-Fenton process.

Pilot-scale in situ treatment of landfill leachate using combined coagulation-flocculation, hydrolysis acidification, SBR and electro-Fenton oxidation

The treatment of a landfill leachate was developed at the pilot scale using a combination of processes, including coagulation, hydrolysis acidification (HA)-sequence batch reactors (SBR) and electro-Fenton oxidation in series. The aim was to enhance the removal of pollutants in the landfill leachate, which contained high organic and NH₃-N loadings. During the 156-day in situ operation, the average removal efficiency of the chemical oxygen demand (COD) was 97.8% and the lowest effluent COD was 78 mg/L. The removal efficiencies of colour, turbidity and total phosphorus were all higher than 97%. The overall operating cost was US$ 4.84/m³. This combined process showed a high potential to efficiently remediate landfill leachate at an acceptable expense.

Efficiency of Combined Processes Coagulation/Solar Photo Fenton in the Treatment of Landfill Leachate

The combined coagulation-solar photo Fenton treatment of leachate from the sanitary landfill located in Atlantico-Colombia was investigated. Firstly, the efficiency of two alternative combined treatments for the reduction of chemical oxygen demand in leachate was assessed, coagulation with poly-aluminum chloride followed by solar photo-Fenton process (Treatment 1) and coagulation with FeCl3·6H2O followed by ferrioxalate-induced solar photo-Fenton process (Treatment 2). Afterwards, treatments 1 and 2 were compared with the treatment currently used in the sanitary landfill (only coagulation with poly-aluminum chloride), in terms of efficiency and costs. An optimization study of alternative treatments was performed combining central-composite experimental design and response surface methodology. The optimum conditions resulted in a chemical oxygen demand reduction of 73 % and 80 % for Treatment 1 and 2, respectively. Both alternative treatments for the leachate are more efficient than the treatment currently used in the sanitary landfill (chemical oxygen demand reduction of 20 %). In terms of costs, treatment 1 would be the most competitive to implement in the sanitary landfill, since this would have an increase of 13.3 % in the total unitary cost compared to an increase of 39.5 % of treatment 2.

Combination of self-organizing map and parallel factor analysis to characterize the evolution of fluorescent dissolved organic matter in a full-scale landfill leachate treatment plant

The dissolved organic matter (DOM) characterization in a full-scale landfill leachate treatment plant is of great importance for the design and operation of treatment processes. In this study, the long-term removal behaviors of DOM during landfill leachate treatment were explored using excitation emission matrix fluorescence spectroscopy (EEMs) coupled with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicated that the application of combining PARAFAC and SOM on EEMs analysis effectively characterized long-term removal behaviors of DOM during leachate treatment. The DOM in raw leachate was dominated by humic substances, while its composition exhibited significant seasonal differences. A large proportion of protein-like fluorescent dissolved organic matter (FDOM) and bulk DOM were removed within membrane bioreactor (MBR) system. Meanwhile the humic-like FDOM removal capacity in nanofiltration (NF) process was well comparable with those in the MBR system owing to the bio-recalcitrant nature of humic substances. The protein-like FDOM and bulk DOM were removed synchronously in both the process of MBR and NF. Moreover, samples distribution exhibited obvious differences among NF concentrate samples. In general, the performance of MBR-NF treatment for landfill leachate displayed reasonable stability in DOM removal irrespective of seasonal variations. This study enhanced our understanding of EEMs application in characterizing leachate-derived DOM composition and has potential implications for the associated monitoring investigations in engineered systems.

Effect of the structure of stacked electro-Fenton reactor on treating nanofiltration concentrate of landfill leachate

The membrane concentrate from landfill leachate has great potential risks of the environmental pollution. The aim of this study was to investigate the structure effect of stacked electro-Fenton (EF) reactor on the nanofiltration (NF) concentrate treatment from landfill leachate. The stacked EF reactor was constructed with a carbon-PTFE gas diffusion cathode and an IrO₂-Ta₂O₅ anode with different electrode spacings (i.e., 2, 5, 10, and 40 mm) and electrode pairs (i.e., 1, 3, 6, and 9). Results showed that smaller electrode spacing and more electrode pairs in the stacked EF reactor improved the COD removal in the NF concentrate treatment. The specific energy consumption decreased with smaller electrode spacing but increased with more electrode pairs. Under the current density of 15 mA cm^-2, Fe²⁺ dosage of 560 mg L^-1, the stacked EF reactor with 9 electrode pairs and the electrode spacing of 2 mm removed 71 ± 6% of the total COD in the NF concentrate within 6 h and the specific energy consumption was 207 ± 20 kWh∙kg COD^-1. The COD removal was kept stable in the stacked EF reactor within 3 cycles of operation. Three-dimensional fluorescence spectroscopic and gas chromatographic mass spectrometric analysis showed that humic acids and aromatic proteins were efficiently degraded in the EF process and large amount of aromatic hydrocarbons was detected in the treated NF concentrate. Our stacked EF reactor could be used to treat leachate concentrates with effectively degradation of the refractory organic pollutants.

Degradation of recalcitrant organics in landfill concentrated leachate by a microwave-activated peroxydisulfate process

A microwave-activated peroxydisulfate process was used to the pre-treatment for recalcitrant organics in concentrated leachate.

Molecular Insights into the Transformation of Dissolved Organic Matter in Landfill Leachate Concentrate during Biodegradation and Coagulation Processes Using ESI FT-ICR MS

Landfill leachate concentrate is a type of refractory organic wastewater with high environmental risk. Identification of refractory components and insights into the molecular transformations of the organics are essential for the development of efficient treatment process. In this report, molecular compositions of dissolved organic matter (DOM) in leachate concentrate, as well as changes after anaerobic/aerobic biodegradation and coagulation with salts, were characterized using electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM in leachate concentrate were more saturated and less oxidized with more nitrogen and sulfur-containing substances (accounting for 50.0%), comparing with natural organic matter in Suwannee River. Selectivity for different classes of organics during biodegradation and coagulation processes was observed. Substances with low oxidation degree (O/C < 0.3) were more reactive during biodegradation process, leading to the formation of highly oxidized molecules (O/C > 0.5). Unsaturated (H/C < 1.0) and oxidized (O/C > 0.4) substances containing carboxyl groups were preferentially removed after coagulation with Al or Fe sulfate. The complementary functions of biodegradation and coagulation in the treatment of DOM in leachate concentrate were verified at the molecular level. Lignin-derived compounds and sulfur-containing substances in leachate concentrate were resistant to biodegradation and coagulation treatments. To treat leachate concentrate more effectively, processes aimed at removal of such DOM should be developed.

Ferrous ion-activated persulphate process for landfill leachate treatment: removal of organic load, phenolic micropollutants and nitrogen

The innovative [Formula: see text] treatment technology based on sulphate radicals induced oxidation was applied for the treatment of landfill leachate. The performance of chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal in the Fe²⁺-activated persulphate system was moderate; however, the results of dissolved nitrogen (DN) and total phenols removal showed significant efficacy (≤39% and ≥87%, respectively). [Formula: see text] addition to the [Formula: see text] system enhanced the treatment efficacy and resulted in supplementary 15% of COD and 5% of DN removal. Hydroxyl radical-based H₂O₂/Fe²⁺ treatment of the landfill leachate was performed as well; the results indicated higher removal efficacy of COD and DOC compared to the [Formula: see text] system. However, practical application of the H₂O₂/Fe²⁺ system is considerably influenced by temperature rise and excessive foam formation. Generally, the ferrous ion-activated persulphate treatment could be a promising technology for ex situ as well as in situ landfill leachate treatment applications.

Effective removal of contaminants in landfill leachate membrane concentrates by coagulation

Leachate membrane concentrates containing high concentrations of organics and trace toxic compounds pose a major threat to the environment, and their treatment is an urgent issue. In this work, various coagulants were used to treat leachate membrane concentrates. Appropriate pH values for treatments with FeCl₂, FeSO₄, polyaluminum chloride, and FeCl₃ were 3, 5, 5, and 4, respectively. FeCl₃ achieved the highest total organic carbon (TOC) removal efficiency. The effect of the various anions in ferric coagulants [FeCl₃, Fe₂(SO₄)₃, and Fe(NO₃)₃] on the TOC removal efficiency was negligible. The main organics remaining in the leachate membrane concentrates after coagulation were humic and fulvic acids. The conditions for coagulation with FeCl₃ were optimized using the response surface method (RSM). The highest TOC, chemical oxygen demand (COD), and chromaticity reduction efficiencies, 81%, 82%, and 97%, respectively, were achieved at pH 4 using FeCl₃ (5 g L^-1) and polyacrylamide (PAM; 0.07 g L^-1). The COD of leachate membrane concentrates was reduced from 4000 to 718 mg L^-1. The mole ratio of removed COD and Fe(III) (2.4 mol) at 5 g L^-1 FeCl₃ (pH 4, PAM 0.07 g L^-1) was lower than that (3.8 mol) at 3 g L^-1 FeCl₃ (pH 4, PAM 0.07 g L^-1); based on the cost and COD removal efficiency, the latter conditions were the best choice. Our work provides guidelines for the treatment of leachate membrane concentrates in engineering.

Effects of returning NF concentrate on the MBR-NF process treating antibiotic production wastewater

The optimization of the nanofiltration (NF) concentrate backflow ratio (R cb) and the influence of the NF concentrate on the performance of membrane bioreactor-nanofiltration (MBR-NF) process treating antibiotic production wastewater were investigated on a laboratory scale. The R cb was optimized at 60 % based on the removal rates of chemical oxygen demand (COD) and NH4 (+)-N by MBR. Data analyses indicated that salinity brought by NF concentrate is the major driver leading to the decrease of sludge activity, especially at a high R cb. EPS analysis showed that electric conductivity (EC), proteins in soluble microbial products (SMP), and SMP brought by NF concentrate are the dominant factors causing the severe membrane fouling in MBR. Furthermore, undegradable substances including fulvic acid-like and humic acid-like compounds accumulated in NF concentrate showed significant influence on fouling of NF. MBR could well degrade small MW compounds in NF concentrate, which confirmed the enhancement of organic removal efficiency by recycling the NF concentrate to MBR. The MBR-NF process showed a relatively stable performance at the R cb of 60 % (volume reduction factor (VRF) = 5), and the NF permeate could satisfy the water quality standard for fermentation process with a water recovery rate of 90.9 %.

Enhancing zero valent iron based natural organic matter removal by mixing with dispersed carbon cathodes

Former studies have shown that adding granular activated carbon (GAC) cathodes could enhance the overall performance of the zero valent iron (ZVI) process for organics removal. The present study evaluates for the first time the performance of such an enhanced ZVI process to remove natural organic matter (NOM), an important water quality parameter in drinking water. Lab-scale batch tests were conducted with surface reservoir feed water from a drinking water plant. In the GAC enhanced ZVI process dissolved organic carbon (DOC) and UV254 were reduced by 61±3% and 70±2%, respectively, during 24h treatment corresponding to 1.8min empty bed contact time. The process was superior to ZVI alone, particularly during the earlier stages of the process due to the synergistically increased iron dissolution rate. Besides GAC, graphite and anthracite also prove to be suitable and potentially more cost-effective options as cathode materials for the enhanced ZVI process, whereby electrically conductive graphite clearly outperformed anthracite. The dominant mechanisms in terms of NOM removal from surface water were found to be coagulation following iron dissolution and adsorption in the case of employing GAC. Oxidation was also occurring to a lesser degree, converting some non-biodegradable into biodegradable DOC.

Effects of concentrated leachate injection modes on stabilization of landfilled waste

Injection of concentrated leachate to landfills is a simple and cost-effective technology for concentrated leachate treatment. In this study, the effects of injection mode of concentrated leachate and its hydraulic loading rate on the stabilization of landfilled waste were investigated. Compared with the injection of concentrated leachate, the joint injection of leachate and concentrated leachate (1:1, v/v) was more beneficial to the degradation of landfilled waste and mitigated the discharge amount of pollutants at the hydraulic loading rate of 5.9 L m(-2) day(-1). As the hydraulic loading rate of the joint injection of leachate and concentrated leachate was increased from 5.9 to 17.6 L m(-2) day(-1), the organic matter, biologically degradable matter, and total nitrogen of landfilled waste were degraded more rapidly, with the degradation constant of the first-order kinetics of 0.005, 0.004, and 0.003, respectively. Additionally, NO2(-)-N and NO3(-)-N in the concentrated leachate could be well removed in the landfill bioreactors. These results showed that a joint injection of concentrated leachate and raw leachate might be a good way to relieve the inhibitory effect of high concentrations of toxic pollutants in the concentrated leachate and accelerate the stabilization of landfilled waste.