Characterization and detoxification of a mature landfill leachate using a combined coagulation-flocculation/photo Fenton treatment

Treatment of landfill leachate by coagulation: A review

Landfill leachate is a seriously polluted and hazardous liquid, which contains a high concentration of refractory organics, ammonia nitrogen, heavy metals, inorganic salts, and various suspended solids. The favorable disposal of landfill leachate has always been a hot and challenging issue in wastewater treatment. As one of the best available technologies for landfill leachate disposal, coagulation has been studied extensively. However, there is an absence of a systematic review regarding coagulation in landfill leachate treatment. In this paper, a review focusing on the characteristics, mechanisms, and application of coagulation in landfill leachate treatment was provided. Different coagulants and factors influencing the coagulation effect were synthetically summarized. The performance of coagulation coupled with other processes and their complementary advantages were elucidated. Additionally, the economic analysis conducted in this study suggests the cost-effectiveness of the coagulation process. Based on previous studies, challenges and perspectives met by landfill leachate coagulation treatment were also put forward. Overall, this review will provide a reference for the coagulation treatment of landfill leachate and promote the development of efficient and eco-friendly leachate treatment technology.

A Bipolar Membrane-Integrated Electrochlorination Process for Highly Efficient Ammonium Removal in Mature Landfill Leachate: The Importance of ClO• Generation

Electrochemical oxidation has been demonstrated to be a useful method for removing biorefractory organic pollutants in mature landfill leachate but suffers from low efficiency in eliminating ammonium because of its resistance to being oxidized by HO• or free chlorine (FC) at decreased pH. Here, we propose a new bipolar membrane-electrochlorination (BPM-EC) process to address this issue. We found that the BPM-EC system was significantly superior to both the undivided and divided reactors with monopolar membranes in terms of elevated rate of ammonium removal, attenuated generation of byproducts (e.g., nitrate and chloramines), increased Faradaic efficiency, and decreased energy consumption. Mechanistic studies revealed that the integration of BPM was helpful in creating alkaline environments in the vicinity of the anode, which facilitated production of surface-bound HO• and FC and eventually promoted in situ generation of ClO•, a crucial reactive species mainly responsible for accelerating ammonium oxidation and selective transformation to nitrogen. The efficacy of BPM-EC in treating landfill leachates with different ammonium concentrations was verified under batch and continuous-flow conditions. A kinetic model that incorporates the key parameters was developed, which can successfully predict the optimal number of BPM-EC reactors (e.g., 2 and 5 for leachates containing 589.4 ± 5.5 and 1258.1 ± 9.6 mg L-1 NH4+-N, respectively) necessary for complete removal of ammonium. These findings reveal that the BPM-EC process shows promise in treating ammonium-containing wastewater, with advantages that include effectiveness, adaptability, and flexibility.

A sequential aerated electrocoagulation and peroxicoagulation process for the treatment of municipal stabilized landfill leachate by iron and graphite electrodes

Electrochemical treatment has emerged as a viable technology for the treatment of leachate due to its efficient removal of ammonaical nitrogen and other recalcitrant organics. The main technical issues that prevent its practical deployment are restricted performance of a single electrochemical process and the lengthy tertiary treatment time required to achieve the disposal quality standards. This study demonstrates the performance of electrochemical treatments such as peroxicoagulation (PC) and aerated electrocoagulation (A-EC) separately and also sequentially for the treatment of stabilized leachate. In aerated electro coagulation iron is used as both anode and cathode, whereas in peroxicoagulation, iron is used as anode and graphite as cathode. The area of electrode used for treatments was fixed as 12.5 cm2. The initial concentration of NH4-N, TN, COD, and TOC of the leachate was found to be 480 mg/L, 997 mg/L, 40,200 mg/L, and 9850 mg/L respectively. Removal efficiency of aerated electrocoagulation for NH4-N, TN, COD and TOC were 25.6%, 23.67%, 25.6% and 28.7% respectively, current density of 30 mAcm-2, electrolysis time of 60 min and pH 7.3. Meanwhile for peroxicoagulation, the removal efficiency was found to be 37.2%, 43%, 37.3%, and 45.6% for NH4-N, TN, COD, and TOC respectively, at an current density of 30 mAcm-2, electrolysis time of 120 min and a pH of 3. The sequential aerated electrocoagulation - peroxicoagulation process achieves a maximum removal efficiency of 63%, 68%, 78%, and 75% for NH4-N, total nitrogen, COD, and TOC respectively for a reaction time of 180 min. Removal of NH4-N, total nitrogen, COD and TOC from stabilized landfill leachate with a BOD/COD ratio less than 0.1 was very much effective with the sequential aerated electrocoagulation - peroxicoagulaton treatment. The results also indicate that for the treatment of leachate, a significant synergistic index of 1.22 exists between aerated electrocoagulation and peroxicoagulation.

Combination of electrochemically activated persulfate process and electro-coagulation for the treatment of municipal landfill leachate with low biodegradability

To handle complex wastewater with limited biodegradability, hybrid treatment systems are necessary. The current study represents the combined effectiveness of sulfate-radical associated electro-chemical advanced oxidation process (SR-EAOP) and electro-coagulation (EC) for the treatment of stabilized landfill leachate. For SR-EAOP, Pt/Ti was employed as the anode and an iron plate as the cathode; while EC treatment was performed by switching the polarity. Hence, both electrochemical treatment was carried out in single reactor. Initially, the effects of pH, applied voltage, persulfate and Fe2+ dosage, on the performance of SR-EAOP was examined. Sulfate radical was generated in the electrolytic system via cathodic reduction of persulfate (PS) and ferrous (Fe2+) ion activation. Auxiliary processes such as anodic oxidation via Pt/Ti anode and indirect electro-chemical oxidation were also contributed for pollutant degradation. Combined process SR-EAOP followed by EC (SR-EAOP + EC) has better leachate treatment efficacy in comparison with EC + SR-EAOPs. The SR-EAOP + EC based combined treatment mechanism achieved an efficient COD reduction of 88.67% than that of EC + SR - EAOP process (74.51% COD reduction). Characterization studies have been carried out for post-treated dried-sludge using Field Emission scanning electron microscope (FE-SEM) and X-ray powder diffraction (XRD) techniques. The combined process treatment (SR-EAOP + EC) can be applied as pre-treatment for leachate decontamination.

Optimal pre-treatment of moderately old landfill leachate at the pilot-scale treatment plant using the combined aerobic biochemical and reagent method

Landfill leachates contain highly concentrated pollutants, and their uncontrolled discharge poses significant risks to the public health and environment. This study validated a pilot-scale two-stage aerobic biochemical and reagent method for the pre-treatment of moderately old landfill leachate at a pilot-scale treatment plant with a capacity of 400 L per day. The kinetic curves of key pollutants were described using two-factor dimensionless exponential equations, allowing for predicting maximally achievable treatment effects during the first aerobic biochemical stage. The optimal duration of aerobic biochemical pre-treatment was determined based on the concept of limiting pollutant content and minimizing operating costs for the two-stage process. Reagent-based leachate pre-treatment using the modified Fenton method was verified in a batch reactor. Optimal concentrations and dosages of reagent solutions, including polyacrylamide, aluminium sulphate, ferrous sulphate, and hydrogen peroxide, were found to comply with Ukrainian regulations for wastewater discharge into sewerage networks. Key pollution indicators of pre-treated leachate, such as NH₄⁺-N (13.4-15.5 mg × L^-1), TKN (25.7-30.2 mg × L^-1), BOD_tot (71.8-76.9 mg × L^-1), and COD (390-459 mg × L^-1), meet the required standards.

Treatment of raw sanitary landfill leachate using a hybrid pilot-scale system comprising adsorption, electrocoagulation and biological process

The effectiveness of a three-stage pilot approach using adsorption (AD), electrocoagulation (EC) and biological (BIO) processes for the treatment of raw sanitary landfill leachate (SLL) was investigated. SLL is loaded with hazardous substances such as organic load and heavy metals with high ammonium nitrogen (NH₄⁺-N) concentrations and is also produced in large quantities, causing serious risks to both living organisms and the environment. In this study, column adsorption experiments were initially performed to examine the removal of toxic NH₄⁺-N using different initial NH₄⁺-N concentrations and recirculation flow rates. The adsorption process was then examined as a pre-treatment step in two sequential treatment scenarios, i.e., AD-EC-BIO and AD-BIO-EC, to determine which achieved the highest removal of pollutants and leachate toxic potential, thus ensuring the biosafety of these processes during the release of the respective effluents into surface waters. The overall removal efficiencies of NH₄⁺-N, color, dissolved chemical oxygen demand (d-COD), manganese (Mn), nickel (Ni), zinc (Zn) and iron (Fe) achieved after the application of the AD-EC-BIO system were 95.5 ± 0.1%, 98.8 ± 0.1%, 85.7 ± 0.8%, 100 ± 0.1%, 71.4 ± 1.7%, 63.8 ± 1.9% and 94.2 ± 0.2%, respectively, while the values for the AD-BIO-EC system were 98.5 ± 0.2%, 98.7 ± 0.1%, 85.7 ± 0.4%, 98.9 ± 1.2%, 67.7 ± 1.7%, 76.1 ± 1.6% and 94.8 ± 0.1%, respectively. In accordance with the latter, the assessment of leachate toxic potential using a Thamnocephalus platyurus bioassay revealed that the AD-EC-BIO system could be considered a promising treatment strategy for the purification of raw SLL.

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 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.

Fenton Reaction–Unique but Still Mysterious

This study is devoted to the Fenton reaction, which, despite hundreds of reports in a number of scientific journals, provides opportunities for further investigation of its use as a method of advanced oxidation of organic macro- and micropollutants in its diverse variations and hybrid systems. It transpires that, for example, the choice of the concentrations and ratios of basic chemical substances, i.e., hydrogen peroxide and catalysts based on the Fe2+ ion or other transition metals in homogeneous and heterogeneous arrangements for reactions with various pollutants, is for now the result of the experimental determination of rather randomly selected quantities, requiring further optimizations. The research to date also shows the indispensability of the Fenton reaction related to environmental issues, as it represents the pillar of all advanced oxidation processes, regarding the idea of oxidative hydroxide radicals. This study tries to summarize not only the current knowledge of the Fenton process and identify its advantages, but also the problems that need to be solved. Based on these findings, we identified the necessary steps affecting its further development that need to be resolved and should be the focus of further research related to the Fenton process.

Retrofitting a full-scale multistage landfill leachate treatment plant by introducing coagulation/flocculation/sedimentation and ultrafiltration process steps

Considering that landfilling still remains among the most commonly used methods for the confrontation of solid wastes, effective methods should be applied to treat the leachate generated, due to its recalcitrant nature. In this work, a full-scale system consisting of two SBRs operating in parallel (350 m³ each) and two activated carbon (AC) columns operating in series (3 m³ each) was retrofitted by introducing a coagulation/flocculation/sedimentation (C/F/S) unit of 7.8 m³ and an ultrafiltration (UF) membrane of 100 m² to effectively treat landfill leachate. The raw leachate was characterized by high COD and NH₄⁺-N concentration, i.e., 3095 ± 706 mg/L and 1054 ± 141 mg/L respectively, a BOD/COD ratio of 0.22, and high concentrations of certain heavy metals. Leachate processing in this retrofitted multistage treatment system resulted in total COD removal efficiency of 89.84%, with biological treatment, C/F, UF, and AC contributing 46.31%, 4.68%, 15.98%, and 22.87% to the overall organic content removal. The retrofitted scheme achieved an overall NH₄⁺-N and TKN removal of 92.03% and 91.75% respectively, attributed mostly to the activity of an effective nitrifying community. Color number (CN) was reduced by 26.96%, 10.29%, 15.94%, and 5.39% after the activated sludge, the C/F, the UF, and the AC adsorption process respectively, corresponding to a 58.91% overall decrease. Regarding heavy metal removal, all elements examined, apart from Ni, i.e., effluent As, Cd, Co, Cr, Cu, Hg, Mg, Mn, and Pb, were below the legislative limits set by the national authorities for restricted or unrestricted irrigation. Lastly, total operating expenses (OPEX) were estimated as equal to 72,687 €/year or 6.64 €/m³.

Evaluation of aqueous Cd2+ and Pb2+ removal by natural loess using spectral induced polarization and microscopic characterization

Mining and landfill activities can cause serious soil and groundwater contamination with lead (Pb) and cadmium (Cd). Loess soils are common and have been reported as effective for the removal of heavy metals. The spectral induced polarization (SIP) technique has been approved for its nondestructive ability to characterize the contaminant transport process and surface geochemical properties in porous media. In the present study, SIP was applied to monitor Pb²⁺ and Cd²⁺ removal processes using loess through column flow-through experiments. The outflow aqueous geochemical analyses indicated a better retention capability of loess for Pb²⁺, which was through precipitation induced by calcite dissolution and aqueous pH increment, as confirmed by SEM-EDS and XRD results. Cd retention took place mainly through ion exchange with Ca²⁺ and Mg²⁺ on the loess surface. The SIP signals showed a continuous decrement on the magnitude of imaginary conductivity during both Pb²⁺ and Cd²⁺ flow-through, which was attributed to the total surface area and decrement of polarizable surface charges. The SIP signals differentiated the interactions between loess and Pb²⁺/Cd²⁺ by displaying a peak shift to a higher frequency on the imaginary conductivity spectra during Pb²⁺ flow-through, which was attributed to calcite dissolution and proved by the high correlation (R² = 0.9366) between the estimated dissolved calcite mass and the peak of imaginary conductivity. The above results suggest that loess has a great potential for field heavy metal remediation applications, and the SIP technique displays a promising capability of monitoring the remediation performance.

Synergistic effects of oxidation, coagulation and adsorption in the integrated fenton-based process for wastewater treatment: A review

Fenton process is the most popular for wastewater treatment among all available advanced oxidation processes (AOPs). Numerous endeavors have been devoted to improving the oxidation efficiency of Fenton reaction in terms of promoting ·OH generation, accelerating iron redox cycle and extending applicable pH range. However, in addition to oxidation, coagulation and adsorption also simultaneously occur in the Fenton process, which play important role in the removal of pollutants. Rapid progress has revealed the synergistic effects of oxidation, coagulation and adsorption in the Fenton process, providing new ideas for the treatment of complex and refractory wastewater. Based on available studies, this review is the first to systematically summarize the research progress regarding the synergistic effects of oxidation, coagulation and adsorption in the integrated Fenton-based processes for wastewater treatment. The involved mechanism of the synergistic effects in different Fenton processes (homogeneous Fenton, heterogeneous Fenton and physical field-assistant Fenton coupling process) are critically reviewed. Furthermore, special attention has been paid to the representative applications of the synergistic effects in wastewater treatment (such as industrial organic wastewater, landfill leachate and heavy metal-organic complexes, etc.), particularly focusing on the operation parameters and removal performance. Finally, a conclusion of the review and subsequently, perspectives are given for possible research directions. We believe this review can provide useful information for researchers and end-users involved in the development and application of the Fenton process in wastewater treatment.

Assessment of Pretreatments for Highly Concentrated Leachate Waters to Enhance the Performance of Catalytic Wet Peroxide Oxidation with Sustainable Low-Cost Catalysts

Matured compost, derived from a mechanical and biological treatment (MBT) plant, was used as a precursor to produce catalysts through hydrothermal and thermal carbonization, HC and PC, respectively. HC and PC displayed suitable properties to act as catalysts in the catalytic wet peroxide oxidation (CWPO) treatment of the highly polluted leachate waters generated in the same MBT plant (TOC0 = 27 g L−1; COD0 = 60 g L−1; BOD5,0 = 23 g L−1). The influence of catalyst loading and pH were studied, considering multiple additions of H2O2. The best experimental conditions found were T = 80 °C, pH0 = 3.0, 7.2 g L−1 of HC catalyst, 85.7 g L−1 of H2O2, added in five batches in one-hour intervals between each addition. Under these experimental conditions, removals of 43%, 52%, 93%, 82%, 35%, 95% and 93% for the COD, TOC, BOD5, aromaticity, chlorides, turbidity and color number (CN) were, respectively, observed. Ion exchange resins and coagulation–flocculation were studied as pretreatment options to reduce the complexity of the leachate waters and enhance the CWPO results. Both strategies resulted in higher mineralization and enhanced the consumption efficiency of H2O2 (ηH2O2). The sequential treatment using coagulation–flocculation and CWPO with PC catalyst showed the best results, achieving abatement of 94%, 70%, 98%, 93%, 31%, 96% and 95% for COD, TOC, BOD5, aromaticity, chlorides, turbidity and CN, respectively.

Occurrence of organic micropollutants in municipal landfill leachate and its effective treatment by advanced oxidation processes

Landfilling is the most prominently adopted disposal technique for managing municipal solid waste across the globe. However, the main drawback associated with this method is the generation of leachate from the landfill site. Leachate, a highly concentrated liquid consisting of both organic and inorganic components arises environmental issues as it contaminates the nearby aquifers. Landfill leachate treatment by conventional methods is not preferred as the treatment methods are not much effective to remove these pollutants. Advanced oxidation processes (AOPs) based on both hydroxyl and sulfate radicals could be a promising method to remove the micropollutants completely or convert them to non-toxic compounds. The current review focuses on the occurrence of micropollutants in landfill leachate, their detection methods and removal from landfill leachate using AOPs. Pharmaceuticals and personal care products occur in the range of 10^-1 to more than 100 μg L^-1 whereas phthalates were found below the detectable limit to 384 μg L^-1, pesticides in the order of 10^-1 μg L^-1 and polyaromatic hydrocarbons occur in concentration from 10^-2 to 114.7 μg L^-1. Solid-phase extraction is the most preferred method for extracting micropollutants from leachate and liquid chromatography (LC) - mass spectrophotometer (MS) for detecting the micropollutants. Limited studies have been focused on AOPs as a potential method for the degradation of micropollutants in landfill leachate. The potential of Fenton based techniques, electrochemical AOPs and ozonation are investigated for the removal of micropollutants from leachate whereas the applicability of photocatalysis for the removal of a wide variety of micropollutants from leachate needs in-depth studies.

How does the pre-treatment of landfill leachate impact the performance of O3 and O3/UVC processes?

In this study, O₃ and O₃/UVC processes were evaluated for the treatment of landfill leachate after biological nitrification/denitrification, coagulation, or their combinations. The O₃-driven stage efficiency was assessed by the removal of color, organic matter (dissolved organic carbon (DOC) and chemical oxygen demand (COD)), and biodegradability increase (Zahn-Wellens test). Also, fluorescence excitation-emission matrix (EEM) and size exclusion chromatography coupled with OC detector (SEC-OCD) analysis were carried out for each strategy. The bio-nitrified-leachate (L_N) was not efficiently mineralized during the O₃-driven processes since the high nitrites content consumed ozone rapidly. In turn, carbonate/bicarbonate ions impaired the oxidation of the bio-denitrified-leachate (L_D), scavenging hydroxyl radicals (HO^•) and inhibiting the O₃ decomposition. For both bio-leachates, only O₃/UVC significantly enhanced the effluent biodegradability (>70%), but COD legal compliance was not reached. EEM and SEC-OCD results revealed differences in the organic matter composition between the nitrified-coagulated-leachate (L_NC) and denitrified-coagulated-leachate (L_DC). Nonetheless, the amount of DOC and COD removed per gram of ozone was similar for both. Cost estimation indicates the O₃-driven stage as the costliest among the treatment processes, while coagulation substantially reduced the cost of the following ozonation. Thus, the best treatment train strategy comprised L_DC (with methanol addition for denitrification and coagulated with 300 mg Al³⁺/L, without pH adjustment), followed by O₃/UVC (transferred ozone dose of 2.1 g O₃/L and 12.2 kJ_UVC/L) and final biological oxidation, allowed legal compliance for direct discharge (for organic and nitrogen parameters) with an estimated cost of 8.9 €/m³ (O₃/UVC stage counting for 6.9 €/m³).

Potential toxicity of leachate from the municipal landfill in view of the possibility of their migration to the environment through infiltration into groundwater

Leachate from landfills is a product of complex biological and physicochemical processes occurring during waste storage. In the present study, the toxicity of landfill leachate (LL) to human and bacterial cells was investigated for better understanding of LL environmental toxicity. Studies regarding LL physicochemical properties and cytotoxicity analysis were conducted. In Escherichia coli, Pseudomonas fluorescens, Bacillus subtilis, fibroblasts and melanoma A-375 cells, cell viability assays were applied. For the determination of LL antibacterial activity, twofold dilution series of LL were prepared in the range from 50% to 0.1% (50%, 25%, 12.5%, 6.25%, 3.13%, 1.56%, 0.78%, 0.39%, 0.2%, 0.1%). Human cells viability was examined at LL concentrations of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 5%, 10%, 15%, 20% and 30%. ROS (reactive oxygen species) content and apoptosis level were also measured in bacterial and human cells under the influence of LL. Unexpectedly obtained results indicate stimulation of bacterial viability by LL. Fibroblasts under the influence of LL showed decrease in their viability and increase in apoptosis level and A-375 melanoma cells showed an increase in relative viability and decrease in apoptosis. ROS level in bacterial cells was elevated in higher LL concentrations and decreased in lower LL concentrations. In human cells, ROS content was rather high in both tested cell lines. Presented results indicate cytotoxic potential of analyzed LL and the necessity of LL monitoring because it may pose a health hazard for exposed human populations and the whole human environment.

Recovery of efficient treatment performance in a semi-aerobic aged refuse biofilter when treating landfill leachate: Washing action using domestic sewage

Semi-aerobic aged refuse biofilters (SAARB) are known to efficiently remove organic matter, nitrogenous substances, and anions from landfill leachate. However, long-term recirculation of mature landfill leachate inevitably leads to accumulation of pollutants and decreases treatment capacity. In this study, the washing action provided by domestic sewage was used to recover and even enhance the treatment performance of SAARBs treating mature landfill leachate. Three SAARB columns were operated for 300 d after which a "Recirculation-Washing-Recirculation" sequence was followed. In the first recirculation period (22 d), removal of chemical oxygen demand (COD) and total nitrogen (TN) decreased from ca. 90% and 60%, respectively, initially to about 75% and less than 20%, respectively. Thereafter, washing (20 d) of the SAARBs was accomplished by applying domestic sewage. In the subsequent second recirculation period (30 d), the SAARBs were operated at the same hydraulic loading as used initially, but achieved high (ca. 90%) COD and relatively high (ca. 59%-76%) TN removal, including degradation of refractory organic matter such as humic- and fulvic-like substances. Overall, the mechanisms of the treatment performance recovery (including organics degradation and nitrification-denitrification) using domestic sewage can be attributed to three main effects: (1) some accumulated pollutants were washed out, thereby leading to recovery of the adsorption ability of aged refuse; (2) the inhibition of bio-refractory organics stress on microbial activities was mitigated by domestic sewage washing; and (3) the wash out of some accumulated salts (e.g., chloride and sulfate ions) probably helped the microbial activity recover.

Transformation of hazardous lead into aluminosilicate ceramics: structure evolution and lead leaching

This study investigated crystallization mechanisms for the formation of lead aluminosilicate by sintering lead stabilization with kaolin-based precursors. PbAl₂Si₂O₈ was found to be the only stable lead aluminosilicate in low-PbO system and demonstrates its highly intrinsic resistance to acid attack in leaching test. A three-stage PbAl₂Si₂O₈ formation mechanism was supported by the results of the changing temperature in the system. Amorphization of sintered products was observed in both PbO/kaolinite and PbO/mullite systems at 600-700°C. When the temperature was increased to 750-900°C, the crystallochemical formation of lead aluminosilicates (i.e., Pb₄Al₄Si₃O₁₆, Pb₆Al₆Si₂O₂₁, and PbAl₂Si₂O₈) was observed. Pb₄Al₄Si₃O₁₆ and Pb₆Al₆Si₂O₂₁ were found to be the intermediate phases at 700-900°C. Finally, PbAl₂Si₂O₈ was found to be the only crystallite phase to host Pb at above 950°C. A maximum of 80% and 96.7% Pb can be incorporated into PbAl₂Si₂O₈ in PbO/kaolinite and PbO/mullite systems, respectively, but the final products exhibited different microstructures. To reduce environmental hazard of lead, this strategy demonstrated a preferred mechanism of immobilizing lead into PbAl₂Si₂O₈ structure via kaolin-based precursors.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Improved oxidation of refractory organics in concentrated leachate by a Fe2+-enhanced O3/H2O2 process

Concentrated leachate from membrane processes, which contains a mass of refractory organics and salt, has become a new problem for wastewater engineers. In this study, removal of organic contaminants in concentrated landfill leachate was investigated by applying the ferrous ion (Fe²⁺) catalyzed O₃/H₂O₂ process. The maximum chemical oxygen demand (COD) and absorbance at 254 nm (UV₂₅₄) removal efficiencies under the optimal conditions (initial pH = 3.0, Fe²⁺ dosage = 6.500 mM, H₂O₂ dosage = 18.8 mM and O₃ dosage = 52.65 mg min^-1) were 48.82% and 63.59%, respectively. These were higher than those achieved using the Fe²⁺/O₃, O₃/H₂O₂, and O₃ processes, and biodegradability of the leachate was improved significantly. Moreover, compared with other processes, the Fe²⁺ had a stronger catalytic effect. Molecular distribution analysis and three-dimensional excitation and emission matrix analysis both indicated that the fulvic acid and humic acid in the concentrated leachate were greatly degraded. Ultraviolet-visible spectra showed that the Fe²⁺/O₃/H₂O₂ process mainly destroyed unsaturated bonds and decreased the aromatic degree of the leachate. The reaction mechanism of the Fe²⁺/O₃/H₂O₂ process mainly was attributed to three factors: (1) O₃ and H₂O₂ reacting to produce ^•OH; (2) H₂O₂ and O₃ decomposing into ^•OH through the oxidation of Fe²⁺ to Fe³⁺; and (3) coagulation by Fe (OH)₃. The ^•OH can rapidly degrade recalcitrant organics, and coagulation also increases the removal of organic matter. Therefore, the Fe²⁺/O₃/H₂O₂ process was an effective method for treating concentrated landfill leachate.

Effective removal by coagulation of contaminants in concentrated leachate from municipal solid waste incineration power plants

Municipal solid waste (MSW) incineration is widely used in China. Concentrated leachate, containing high concentrations of pollutants, is an important type of secondary pollution produced in MSW incineration power plants and requires proper treatment. In this study, various coagulants were used to treat concentrated leachate from a nanofiltration (NF) membrane that treated leachate from an MSW incineration plant. The optimal coagulation condition was determined in this study. Under the optimal condition, removals of chemical oxygen demand, light absorbing substances (at 254 nm), total nitrogen, color and turbidity were 68.42%, 69.01%, 44.14%, 92.31% and 87.44%, respectively. Much of the refractory organic matter with relatively high molecular weight, aromaticity and humification degree was removed, and effluent had a lower molecular weight than raw NF concentrated leachate. Study also found that some parts of high molecular weight compounds from NF CL were removed by coagulation process, but the change of distribution of molecular weight was not outstanding. The NF concentrated leachate, both before and after coagulation, contained a large amount of chloride. Hence, a follow-up study should be conducted to find an effective additional processing that can remove organic matter using the high concentration of chloride in the NF concentrated leachate coagulation effluent. This study provides a theoretical basis for the treatment of concentrated leachate from MSW incineration power plants.

Treatment train for mature landfill leachates: Optimization studies

In the current study, a treatment train strategy for urban mature leachates, comprising biological and physicochemical processes, was tested for full legal compliance. The leachate presents a high organic and nitrogen content (1.1g C/L; 3.6g O₂/L; 2.0gN/L) and low biodegradability (BOD₅/COD=0.05). In the first stage, a sequential batch reactor (SBR), operated in a 24h-cycle mode (15h aeration +8.5h anoxic, with methanol as external carbon source +0.5h settling), was tested for total nitrogen (TN) removal. The maximum daily TN load that could be treated, reaching the legal limit (< 15mgN/L), increased by 50% with the rise in temperature from 20 to 30°C. For the following coagulation stage, the highest dissolved organic carbon (DOC) removal (64%) and lower final turbidity (33 NTU) were obtained with 240mg Fe³⁺/L, at pH3.0. The jar-tests, comparing nitrified (L_NIT.) and nitrified/denitrified (L_N/D.) leachate, stressed the effect of the leachate alkalinity, generated during the denitrification reaction, on process efficiency. For the coagulated L_N/D., with alkalinity of 1.1g CaCO₃/L, the final concentration of sulfate was only slightly below the legal limit (< 2g/L). A photo-Fenton (PF) oxidation process (pH range of 2.8-3.0, 60mg Fe²⁺/L), as third treatment step, promoted a significant enhancement on leachate biodegradability, consuming 75mM of H₂O₂ and 8.9 kJ/L of accumulated UV energy, to achieve an effluent that can be further biologically treated in compliance with the COD discharge limit (150mg O₂/L) into water bodies. Biological continuous mode tests using a conventional activated sludge process, with an hydraulic retention time (HRT) of 12h, allowed to obtain COD and TSS values (107±3 and 50±2mg/L, respectively) below the legal limit.

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.

Landfill leachate treatment by coagulation/flocculation combined with microelectrolysis-Fenton processes

Landfill leachate was pretreated by chemical flocculation with polyaluminum chloride (PAC) as a flocculant, and subsequently purified by the microelectrolysis-Fenton (MEF) process. Response surface methodology was employed to optimize the MEF process, and the optimal conditions were initial pH 3.20, H₂O₂ concentration 3.57 g/L, and Fe-C dosage 104.52 g/L. The PAC coagulation combined with MEF processes obtained a superior decontamination performance, and the predicted chemical oxygen demand (COD) and humic acids (HA) removal were respectively 90.27% and 93.79%. The strong fluorescence peak at 425 nm and the trapping experiment showed that ⋅OH was generated during MEF, which had a strong oxidation ability to degrade organic recalcitrant pollutants. The ultraviolet-visible spectra and three-dimensional excitation-emission matrices spectra (3D-EEMs) indicated that PAC coagulation could preferentially remove protein-like substances, while the MEF process was effective in destructing organic recalcitrant pollutants, especially humic-like and fulvic-like substances.

Sustainable treatment of municipal landfill leachate by combined association of air stripping, Fenton oxidation, and enhanced coagulation

The present world has been facing the problem of municipal solid waste disposal with the generation of highly complex and toxic landfill leachate. Thus, in this research work, treatability of landfill leachate had been investigated by the combined approach of air stripping, Fenton oxidation, and enhanced coagulation to comply with discharge standard. At the initial stage of treatment, air stripping of raw leachate was implemented which removes around 51.50% of COD, 74.60% of BOD₅, and 97.60% of NH₃-N within 36 h of optimum retention time. Following air stripping, Fenton oxidation was applied with an optimum molar ratio of 1.9 of H₂O₂/Fe⁺² which register a maximal removal of 67.70% of COD, 92.30% of BOD₅, and 14.90% of Hg. Finally, enhanced coagulation (EC) with in situ formed Mn-Fe hydr(oxides) was employed and optimized by central composite design (CCD) of response surface methodology (RSM). Response surface plots denote an optimum condition of 0.13 M ratio of Mn/Fe, 22.67 mM of coagulant dose, and 7.78 of pH which corresponds to a maximum removal of 55.98% of COD and 77.68% of Hg. FTIR analysis of the precipitates of EC explained that the hydroxyl groups are primarily involved in the process of Hg removal. Moreover, EDAX spectrum also assured the removal of Hg by its existence with Mn-Fe complexes. Thus, the present line of treatment record an overall removal of 90.80% of COD, 98.0% of BOD₅, 97.60% of NH₃-N, and 82.68% of Hg which proves to be effective for the removal of leachate pollutants.

Bioremediation of Landfill Leachate with Fungi: Autochthonous vs. Allochthonous Strains

Autochthonous fungi from contaminated wastewater are potential successful agents bioremediation thanks to their adaptation to pollutant toxicity and to competition with other microorganisms present in wastewater treatment plant. Biological treatment by means of selected fungal strains could be a potential tool to integrate the leachate depuration process, thanks to their fungal extracellular enzymes with non-selective catalytical activity. In the present work, the treatability of two real samples (a crude landfill leachate and the effluent coming from a traditional wastewater treatment plant) was investigated in decolorization experiments with fungal biomasses. Five autochthonous fungi, Penicillium brevicompactum MUT 793, Pseudallescheria boydii MUT 721, P. boydii MUT 1269, Phanerochaete sanguinea MUT 1284, and Flammulina velutipes MUT 1275, were selected in a previous miniaturized decolorization screening. Their effectiveness in terms of decolorization, enzymatic activity (laccases and peroxidases), biomass growth and ecotoxicity removal was compared with that of five allochthonous fungal strains, Pleurotus ostreatus MUT 2976, Porostereum spadiceum MUT 1585, Trametespubescens MUT 2400, Bjerkanderaadusta MUT 3060 and B. adusta MUT 2295, selected for their well known capability to degrade recalcitrant pollutants. Moreover, the effect of biomass immobilization on polyurethane foam (PUF) cube was assessed. The best decolorization (60%) was achieved by P. spadiceum MUT 1585, P. boydii MUT 721 and MUT 1269. In the first case, the DP was achieved gradually, suggesting a biodegradation process with the involvement of peroxidases. On the contrary, the two autochthonous fungi seem to bioremediate the effluent mainly by biosorption, with the abatement of the toxicity (up to 100%). The biomass immobilization enhanced enzymatic activity, but not the DP. Moreover, it limited the biomass growth for the fast growing fungi, MUT 721 and MUT 1269. In conclusion, robust and versatile strains coming from well-characterized collections of microorganisms can obtain excellent results comparing and even exceeding the bioremediation yields of strains already adapted to pollutants.

Antioxidant biomarkers in Gammarus pulex to evaluate the efficiency of electrocoagulation process in landfill leachate treatment

The discharge of landfill leachate into the environment without effective treatment poses a serious threat for the aquatic ecosystems. This present study was undertaken to evaluate whether electrocoagulation process is efficient for treatment landfill leachate (LL) or not by using antioxidant biomarkers in Gammarus pulex. Glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT) activities and malondialdehyde (MDA) and glutathione (GSH) levels in G. pulex exposed to untreated, treated, and diluted rates 1/10 and 1/20 in both LL during 24 and 96 h were tested. Physiochemical characteristics of leachate (chemical oxygen demand, electrical conductivity, pH, phosphate, turbidity, NH₃, Cl^-, and color) were determined pre and post treatment. All physiochemical characteristics of LL decreased after treatment process. GSH-Px and CAT activities and GSH and MDA levels were increased in untreated groups when compared to control (p < 0.05). After treatment by electrocoagulation, MDA and GSH levels and CAT activities were returned to control values. In conclusion, the abilities of LL to stimulate oxidative stress in G. pulex have been proven. The results revealed that antioxidant parameters are useful biomarkers for determining the treatment efficiency of the electrocoagulation process.

Floc behavior and removal mechanisms of cross-linked Durio zibethinus seed starch as a natural flocculant for landfill leachate coagulation-flocculation treatment

This study investigated the behavior and mechanisms of cross-linked Durio zibethinus seed starch (CDSS) flocculants for landfill leachate treatment. A physical-chemical treatment method of coagulation-flocculation process and starch modification were implemented in treating stabilized leachate from Matang Landfill, Perak, Malaysia. In practical, the removal performance of color, COD, suspended solid and turbidity for CDSS flocculants were evaluated by combining with primary coagulant of polyaluminium chloride (PAC). In this study, the application of crosslinking modification for Durio zibethinus seed waste starch flocculants showed good improvement. The impurities removal for colour, COD, suspended solid and turbidity were increased by the addition of CDSS flocculants. Furthermore, the average size of the floc was also increased from 60.24 µm to 89.5 µm. Despite, the addition of CDSS flocculants produced a reduction of PAC coagulant from 2700 mg/L to 2200 mg/L, with 500 mg/L reduction on the PAC dosage dependency. Therefore, these results affirmed the potentials of crosslinked modification for Durio zibethinus seed waste starch flocculants in landfill leachate treatment.

Process design of high-concentration benzimidazole wastewater treatment based on the molecular structure of contaminants

Benzimidazole is an important intermediate in industry and it is usually difficult to be degraded by many treatment technologies. Looking for a highly effective, environment-friendly degradation process for benzimidazole wastewater is of great significance to reduce pollution. Based on the structure of contaminants, the micro-electrolysis (ME) coupled with the Fenton technique was chosen to degrade the industrial benzimidazole wastewater. Special feeding was applied to maintain the suitable hydrogen peroxide (H₂O₂) concentration to produce the hydroxyl radicals (•OH) as much as possible and protect •OH from being quenched by excess H₂O₂ according to the reaction mechanism. The results showed that this combined technique was highly efficient to decompose benzimidazole compounds. More chemical oxygen demand (COD) could be reduced when flow control was used, compared to the flow not being controlled. The COD removal rate could reach 85.2% at optimal parameters. Then the effluent of this process was combined with the existing biochemical system for further degradation. The studies of Ultraviolet Spectrophotometry, Fourier Transform Infrared Spectroscopy and Liquid Chromatography Mass Spectrometry showed that both 2-(a-Hydroxyethyl) benzimidazole and 2-Acetylbenzimidazole were decomposed to the isopropanolamine and aniline after the ME treatment; then the intermediates were oxidized into oxalic acid after the Fenton reaction.

Environmental monitoring of water resources around a municipal landfill of the Rio Grande do Sul state, Brazil

In Brazil, landfills are commonly used as a method for the final disposal of waste that is compliant with the legislation. This technique, however, presents a risk to surface water and groundwater resources, owing to the leakage of metals, anions, and organic compounds. The geochemical monitoring of water resources is therefore extremely important, since the leachate can compromise the quality and use of surface water and groundwater close to landfills. In this paper, the results of analyses of metals, anions, ammonia, and physicochemical parameters were used to identify possible contamination of surface water and groundwater in a landfill area. A statistical multivariate approach was used. The values found for alkali metals, nitrate, and chloride indicate contamination in the regional groundwater and, moreover, surface waters also show variation when compared to the other background points, mainly for ammonia. Thus, the results of this study evidence the landfill leachate influence on the quality of groundwater and surface water in the study area.

Removal of organic matter from stabilized landfill leachate using Coagulation-Flocculation-Fenton coupled with activated charcoal adsorption

The treatment of stabilized landfill leachate (SLL) by conventional biological treatment is often inefficient due to the presence of bio-recalcitrant substances. In this study, the feasibility of coagulation-flocculation coupled with the Fenton reaction in the treatment of SLL was evaluated. The efficiency of the selected treatment methods was evaluated through total organic carbon (TOC) removal from SLL. With ferric chloride as the coagulant, coagulation-flocculation was found to achieve the highest TOC removal of 71% at pH 6. Then, the pretreated SLL was subjected to the Fenton reaction. Nearly 50% of TOC removal was achieved when the reaction was carried out at pH 3, H₂O₂:Fe²⁺ ratio of 20:1, H₂O₂ dosage of 240 mM and 1 h of reaction time. By coupling the coagulation-flocculation with the Fenton reaction, the removal of TOC, COD (chemical oxygen demand) and turbidity of SLL were 85%, 84% and 100%, respectively. The ecotoxicity study performed using zebrafish revealed that 96 h LC₅₀ for raw SLL was 1.40% (v/v). After coagulation-flocculation, the LC₅₀ of the pretreated SLL was increased to 25.44%. However, after the Fenton reaction, the LC₅₀ of the treated SLL was found to decrease to 10.96% due to the presence of H₂O₂ residue. In this study, H₂O₂ residue was removed using powdered activated charcoal. This method increased the LC₅₀ of treated effluent to 34.48% and the removal of TOC and COD was further increased to 90%. This finding demonstrated that the combination of the selected treatment methods can be an efficient treatment method for SLL.

Bioassays for toxicological risk assessment of landfill leachate: A review

Landfilling is the most common solid waste management practice. However, there exist a potential environmental risk to the surface and ground waters due to the possible leaching of contaminants from the landfill leachates. Current municipal solid waste landfill regulatory approaches consider physicochemical characterization of the leachate and do not assess their potential toxicity. However, assessment of toxic effects of the leachates using rapid, sensitive and cost-effective biological assays is more useful in assessing the risks as they measure the overall toxicity of the chemicals in the leachate. Nevertheless, more research is needed to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants in order to evaluate leachate toxicity. There is a need for a multispecies approach using organisms representing different trophic levels so as to understand the potential impacts of leachate on different trophic organisms. The article reviews different bioassays available for assessing the hazard posed by landfill leachates. From the review it appears that there is a need for a multispecies approach to evaluate leachate toxicity.

Coagulation-flocculation sequential with Fenton or Photo-Fenton processes as an alternative for the industrial textile wastewater treatment

In this study, the industrial textile wastewater was treated using a chemical-based technique (coagulation-flocculation, C-F) sequential with an advanced oxidation process (AOP: Fenton or Photo-Fenton). During the C-F, Al₂(SO₄)₃ was used as coagulant and its optimal dose was determined using the jar test. The following operational conditions of C-F, maximizing the organic matter removal, were determined: 700 mg/L of Al₂(SO₄)₃ at pH = 9.96. Thus, the C-F allowed to remove 98% of turbidity, 48% of Chemical Oxygen Demand (COD), and let to increase in the BOD₅/COD ratio from 0.137 to 0.212. Subsequently, the C-F effluent was treated using each of AOPs. Their performances were optimized by the Response Surface Methodology (RSM) coupled with a Box-Behnken experimental design (BBD). The following optimal conditions of both Fenton (Fe²⁺/H₂O₂) and Photo-Fenton (Fe²⁺/H₂O₂/UV) processes were found: Fe²⁺ concentration = 1 mM, H₂O₂ dose = 2 mL/L (19.6 mM), and pH = 3. The combination of C-F pre-treatment with the Fenton reagent, at optimized conditions, let to remove 74% of COD during 90 min of the process. The C-F sequential with Photo-Fenton process let to reach 87% of COD removal, in the same time. Moreover, the BOD₅/COD ratio increased from 0.212 to 0.68 and from 0.212 to 0.74 using Fenton and Photo-Fenton processes, respectively. Thus, the enhancement of biodegradability with the physico-chemical treatment was proved. The depletion of H₂O₂ was monitored during kinetic study. Strategies for improving the reaction efficiency, based on the H₂O₂ evolution, were also tested.

Hybrid zero valent iron (ZVI)/H2O2 oxidation process for landfill leachate treatment with novel nanosize metallic calcium/iron composite

A novel nanosize metallic calcium/iron dispersed reagent was synthesized and tested as coagulant/catalyst in a hybrid zero valent iron (ZVI)/H₂O₂ oxidation process to treat leachate. Two different types of leachates, one from municipal solid waste (MSW) tipping hall (MSWIL) and second from an MSW landfill site (MSWLL), were collected and characterized. The morphology, elemental composition, and mineral phases of the nano-Ca/CaO and nano-Fe/Ca/CaO were characterized by scanning electron microscopy-electron dispersive spectroscopy (SEM-EDS) and x-ray powder diffraction (XRD) analysis. The coagulation process with 2.5 g L^-1 nano-Ca/CaO attained 64.0, 56.0, and 20.7% removal of color, chemical oxygen demand (COD), and total suspended solids (TSS) in MSWLL. With only 1.0 g L^-1 of nano-Fe/Ca/CaO, relatively high color, COD and TSS removal was achieved in MSWLL at 67.5, 60.2, and 37.7%, respectively. The heavy metal removal efficiency reached 91-99% after treatment with nano-Fe/Ca/CaO in both leachate samples. The coupling process, using 1.0 g L^-1 of nano-Fe/Ca/CaO and 20 mM H₂O₂ doses, achieved enhancement removal of color, COD, and TSS, up to 95%, 96%, and 66%, respectively, without initial pH control. After this treatment, the color, COD, TSS, and heavy metals were significantly decreased, fitting the Korean discharge regulation limit. A hybrid coupled zero valent iron (ZVI)/H₂O₂ oxidation process with novel nanosized metallic calcium/iron dispersed reagent proved to be a suitable treatment for dealing with leachate samples.

IMPLICATIONS

Conventional treatments (biological or physicochemical) are not sufficient anymore to reach the level of purification needed to fully reduce the negative impact of landfill leachates on the environment. This implies that new treatment alternatives species must be proposed. A coupled zero valent iron (ZVI)/H₂O₂ oxidation process proved to be a suitable treatment for dealing with leachate samples. Coagulation with nFe/Ca/CaO allows 91-99% of heavy metals removal. The coupled coagulation-oxidation process by nFe/Ca/CaO reveals excellent ability to treat leachate. After coupled treatment the color, COD, and TSS were also much lower than the discharge regulation limit.

Sorptive removal of HgII by red mud (bauxite residue) in contaminated landfill leachate

The ability of red mud (RM) (bauxite residue) to remove Hg^II from landfill leachate (LL) was assessed. The studied aspects comprised the effects of time, pH, Hg^II concentration and the sorption isotherm, besides the influence of chloride and representative organic ligands. Hg^II removal by RM exhibited a complex kinetics where initial rapid sorption was followed by desorption at longer times. The sorption of Hg^II on RM was strongly pH-dependent. Outstanding maximum sorption was observed at pH∼4-5 (≥99.6%), while it abruptly dropped at higher pH values down to a minimum ∼28% at pH∼10.5. Chloride decreased Hg^II sorption at acid pH and shifted the pH_max towards higher pH∼9.4, which opposes to sorption in LL and suggests Cl^- did not primarily control the process in LL. Amongst the organic ligands, acetate and salicylate slightly affected Hg^II sorption. Conversely, glycine affected sorption in a pH-dependent manner resembling that in LL, which suggests the relevant role of the organic nitrogenated compounds of LL. EDTA suppressed Hg^II sorption at any pH. Hg^II speciation modelling and dissolved organic matter (DOM) sorption support complexation of Hg^II by DOM as the primary factor governing the removal of Hg^II in LL. The sorption isotherm was better described by the Freundlich equation, which agrees with the heterogeneous composition of RM. The results indicate that Hg^II sorption on RM is favorable, but reveal differences in sorption and reduced efficiency, in LL media. Notwithstanding, RM possesses a notable capacity to remove Hg^II, even under the unhelpful complexing and competing conditions of LL.

Treatment of dye wastewater nanofiltration concentrates containing high anion levels by a pH-sensitive nano-sized Fe(iii)@silica microgel

The pH-sensitive dual effects of Fe(iii) in heterogeneous Fenton-like degradation and enhanced coagulation with silica microgel for the treatment of refractory nanofiltration concentrates.

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.

Evaluation of the Treatment Process of Landfill Leachate Using the Toxicity Assessment Method

Landfill leachate is composed of a complex composition with strong biological toxicity. The combined treatment process of coagulation and sedimentation, anaerobics, electrolysis, and aerobics was set up to treat landfill leachate. This paper explores the effect of different operational parameters of coagulation and sedimentation tanks and electrolytic cells, while investigating the combined process for the removal efficiency of physicochemical indices after processing the landfill leachate. Meanwhile, a battery of toxicity tests with Vibrio fischeri, zebrafish larvae, and embryos were conducted to evaluate acute toxicity and calculated the toxicity reduction efficiency after each treatment process. The combined treatment process resulted in a 100% removal efficiency of Cu, Cd and Zn, and a 93.50% and an 87.44% removal efficiency of Ni and Cr, respectively. The overall removal efficiency of chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N), and total nitrogen (TN) were 93.57%, 97.46% and 73.60%, respectively. In addition, toxicity test results showed that the acute toxicity of landfill leachate had also been reduced significantly: toxicity units (TU) decreased from 84.75 to 12.00 for zebrafish larvae, from 82.64 to 10.55 for zebrafish embryos, and from 3.41 to 0.63 for Vibrio fischeri. The combined treatment process was proved to be an efficient treatment method to remove heavy metals, COD, NH₄⁺-N, and acute bio-toxicity of landfill leachate.

Treatment of hazardous landfill leachate using Fenton process followed by a combined (UASB/DHS) system

Fenton process for pre-treatment of hazardous landfill leachate (HLL) was investigated. Total, particulate and soluble chemical oxygen demand (CODt, CODp and CODs) removal efficiency amounted to 67%, 47% and 64%, respectively, at pH value of 3.5, molar ratio (H2O2/Fe(2+)) of 5, H2O2 dosage of 25 ml/L and contact time of 15 min. Various treatment scenarios were attempted and focused on studying the effect of pre-catalytic oxidation process on the performance of up-flow anaerobic sludge blanket (UASB), UASB/down-flow hanging sponge (DHS) and DHS system. The results obtained indicated that pre-catalytic oxidation process improved the CODt removal efficiency in the UASB reactor by a value of 51.4%. Overall removal efficiencies of CODt, CODs and CODp were 80 ± 6%, 80 ± 7% and 78 ± 16% for UASB/DHS treating pre-catalytic oxidation effluent, respectively. The removal efficiencies of CODt, CODs and CODp were, respectively, decreased to 54 ± 2%, 49 ± 2% and 71 ± 16% for UASB/DHS system without pre-treatment. However, the results for the combined process (UASB/DHS) system is almost similar to those obtained for UASB reactor treating pre-catalytic oxidation effluent. The DHS system achieved average removal efficiencies of 52 ± 4% for CODt, 51 ± 4% for CODs and 52 ± 15% for CODp. A higher COD fractions removal was obtained when HLL was pre-treated by Fenton reagent. The combined processes provided a removal efficiency of 85 ± 1% for CODt, 85 ± 1% for CODs and 83 ± 8% for CODp. The DHS system is not only effective for organics degradation but also for ammonia oxidation. Almost complete ammonia (NH4-N) removal (92 ± 3.6%) was occurred and the nitrate production amounted to 37 ± 6 mg/L in the treated effluent. This study strongly recommends applying Fenton process followed by DHS system for treatment of HLL.

Decomposition characteristics of humic-like matters with the hollow ellipsoid structure sludge inoculated from decayed soil in mature landfill leachate

The organics in mature leachate are mainly humic-like matters, which account for over 80% weight of the total organics. In this work, the microorganisms in decayed soil were found to be capable of decomposing the humic-like matters evidently using an anaerobic-aerobic/anoxic bioprocess in two sequencing bio-reactors. The 3D excitation-emission matrix and Fourier transform infrared (FT-IR) were applied to characterize the variation of dissolved organic matters in mature leachate while sludge morphology was characterized by scanning electron microscopy. The intensities of fluorescence peaks A and C of leachate effluents were 71.66% and 48.75% lower than those of influents, respectively, which indicated the extraordinary degradation ability of microorganisms inoculated from the decayed soil. Meanwhile a kind of distinctive hollow ellipsoid structure sludge organized by tiny soil particles was observed, which might favour the humic-like matters' decomposition and has never been reported before as we know. The formation mechanisms of hollow ellipsoid structure sludge will need further study.

Optimization of COD and Color Removal for Matang’s Landfill Leachate Treatment by Using Polyaluminum Chloride

In this research, a physico-chemical treatment method of coagulation-flocculation process is implemented in treating partially stabilized leachate from Matang Landfill, Perak, Malaysia. Central composite design has been used to optimize the independent variables namely polyaluminum chloride (PAC) coagulant dosage (A), rapid mixing speed (B) and rapid mixing time (C). The experimental results were analyzed by using analysis of variance (ANOVA). The results revealed that the percentage of color and COD removal was found increased by increasing rapid mixing speed with optimum removal of 95 % and 56 % respectively. Besides, the R-squared values implied that 86.22 % and 97.34% of the total variation explained by the model equation. Furthermore, the model analysis revealed that rapid mixing speed were significant for removal of color and COD through single parameter (B) and interaction between parameter (AB) respectively. This finding proves the influence of mixing parameter in coagulation-flocculation process for leachate treatment.

A comparative study on the efficiency of ozonation and coagulation-flocculation as pretreatment to activated carbon adsorption of biologically stabilized landfill leachate

The present work investigates the potential of coagulation-flocculation and ozonation to pretreat biologically stabilized landfill leachate before granular activated carbon (GAC) adsorption. Both iron (III) chloride (FeCl3) and polyaluminium chloride (PACl) are investigated as coagulants. Better organic matter removal is observed when leachate was treated with FeCl3. At a dose of 1mg FeCl3/mg CODo (CODo: initial COD content), the COD and α254 removal was 66% and 88%, respectively. Dosing 1mg PACl/mg CODo resulted in 44% COD and 72% α254 removal. The settle-ability of sludge generated by PACl leveled off at 252mL/g, while a better settle-ability of 154mL/g was obtained for FeCl3 after dosing 1mg coagulant/mg CODo. For ozonation, the percentage of COD and α254 removal increased as the initial COD concentration decreased. Respectively 44% COD and 77% α254 removal was observed at 112mg COD/L compared to 5% COD and 26% α254 removal at 1846mg COD/L. Subsequent activated carbon adsorption of ozonated, coagulated and untreated leachate resulted in 77%, 53% and 8% total COD removal after treatment of 6 bed volumes. Clearly showing the benefit of treating the leachate before GAC adsorption. Mathematical modeling of the experimental GAC adsorption data with Thomas and Yoon-Nelson models show that ozonation increases the adsorption capacity and breakthrough time of GAC by a factor of 2.5 compared to coagulation-flocculation.

Removal of arsenic from simulation wastewater using nano-iron/oyster shell composites

In this paper, a nano-iron/oyster shell composite (NI/OS) was firstly prepared by an in-situ synthesis method to explore an efficient treatment technology for arsenic (As) contaminated wastewater. The micromorphologies and composition of the composite were characterized using field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The effects of the preparation parameters, as well as the treatment conditions, on the removal of As(Ⅲ) were also investigated. The characterization results showed that iron nanoparticles with a diameter of 60 nm were introduced into the composite by an in-situ reduction method. The physicochemical properties of the iron nanoparticles, such as diameter and aggregation, were influenced by the iron source more than the choice of reductant and temperature in the synthesis process, and these properties were closely related to the treatment performance of the composite. Under the suitable reaction conditions of a pH value of 6.8, a temperature of 20 °C, and an initial concentration of As(Ⅲ) of 1.8 mg/L, As(Ⅲ) was almost completely removed from the simulation wastewater.

Optimization of electrocoagulation (EC) process for the purification of a real industrial wastewater from toxic metals

In the present work, the efficiency evaluation of electrocoagulation (EC) in removing toxic metals from a real industrial wastewater, collected from Aspropyrgos, Athens, Greece was investigated. Manganese (Mn), copper (Cu) and zinc (Zn) at respective concentrations of 5 mg/L, 5 mg/L and 10 mg/L were present in the wastewater (pH=6), originated from the wastes produced by EBO-PYRKAL munitions industry and Hellenic Petroleum Elefsis Refineries. The effect of operational parameters such as electrode combination and distance, applied current, initial pH and initial metal concentration, was studied. The results indicated that Cu and Zn were totally removed in all experiments, while Mn exhibited equally high removal percentages (approximately 90%). Decreasing the initial pH and increasing the distance between electrodes, resulted in a negative effect on the efficiency and energy consumption of the process. On the other hand, increasing the applied current, favored metal removal but resulted in a power consumption increase. Different initial concentrations did not affect metal removal efficiency. The optimal results, regarding both cost and EC efficiency, were obtained with a combination of iron electrodes, at 2 cm distance, at initial current of 0.1 A and pH=6. After 90 min of treatment, maximum removal percentages obtained were 89% for Mn, 100% for Cu and 100% for Zn, at an energy consumption of 2.55 kWh/m(3).

Mature landfill leachate treatment by coagulation/flocculation combined with Fenton and solar photo-Fenton processes

This work reports the treatment of a mature landfill leachate through the application of chemical-based treatment processes in order to achieve the discharge legal limits into natural water courses. Firstly, the effect of coagulation/flocculation with different chemicals was studied, evaluating the role of different initial pH and chemicals concentration. Afterwards, the efficiency of two different advanced oxidation processes for leachate remediation was assessed. Fenton and solar photo-Fenton processes were applied alone and in combination with a coagulation/flocculation pre-treatment. This physicochemical conditioning step, with 2 g L(-1) of FeCl3 · 6H2O at pH 5, allowed removing 63% of COD, 80% of turbidity and 74% of total polyphenols. Combining the coagulation/flocculation pre-treatment with Fenton reagent, it was possible to reach 89% of COD removal in 96 h. Moreover, coagulation/flocculation combined with solar photo-Fenton revealed higher DOC (75%) reductions than single solar photo-Fenton (54%). In the combined treatment (coagulation/flocculation and solar photo-Fenton), it was reached a DOC reduction of 50% after the chemical oxidation, with 110 kJ L(-1) of accumulated UV energy and a H2O2 consumption of 116 mM. Toxicity and biodegradability assays were performed to evaluate possible variations along the oxidation processes. After the combined treatment, the leachate under study presented non-toxicity but biodegradability increased.