Pilot study on the advanced treatment of landfill leachate using a combined coagulation,fenton oxidation and biological aerated filter process

Mature landfill leachate is typically non-biodegradable. A combination process was developed that includes coagulation, Fenton oxidation, and biological aerated filtering to treat biologically-produced effluent. In this process, coagulation and Fenton oxidation were applied in order to reduce chemical oxygen demand (COD) organic load, and enhance biodegradability. Poly-ferric sulfate (PFS) at 600 mg l^?1 was found to be a suitable dosage for coagulation. For Fenton oxidation, an initial pH of 5, a total reaction time of 3 h, and an H₂O₂ dosage of 5.4 mmol l^?1, with a (H₂O₂)/n(Fe²⁺) ratio of 1.2 and two-step dosing were selected to achieve optimal oxidation. Under these optimal coagulation and Fenton oxidation conditions, the COD removal ratios were found to be 66.67% and 56%, respectively. Following pretreatment with coagulation and Fenton oxidation, the landfill leachate was further treated using a biological aerated filter (BAF). Our results show that COD was reduced to 75 mg l^?1, and the color was less than 10 degrees.     

Application of response surface methodology to the advanced treatment of biologically stabilized landfill leachate using Fenton’s reagent

A Fenton process that uses FeCl₂ as the alternative catalyst was employed to deal with the biologically treated landfill leachate. Data obtained revealed that this Fenton process can provide an equivalent pollutant removal as the Fenton process that uses FeSO₄ as catalyst. Central composite design (CCD) and response surface methodology (RSM) were applied to evaluate and optimize the four key factors, namely initial pH, Fe(II) dosage ([Fe²⁺]), H₂O₂/Fe(II) mole ratio ([H₂O₂]/[Fe²⁺] ratio) and reaction time, which affect the performance of the Fenton treatment. Chemical oxygen demand (COD) and color were selected as response variables. This approach provided statistically significant quadratic models, which were adequate to predict responses and to carry out optimization under the conditions studied. It was demonstrated that the interaction between initial pH and [H₂O₂]/[Fe²⁺] ratio has a significant effect on the COD removal, while the interaction between [H₂O₂]/[Fe²⁺] ratio and reaction time shows a large impact on color removal. The optimal conditions were found to be initial pH 5.9, [Fe²⁺] = 9.60 mmol/L, [H₂O₂]/[Fe²⁺] ratio = 2.38, reaction time = 5.52 h. Under this optimal scheme, the COD and color in the effluent were reduced to 159 mg/L and 25°, respectively, with an increase of BOD₅/COD ratio from 0.05 to 0.21.     

Multi-response optimization of Fenton process for applicability assessment in landfill leachate treatment

Fenton process, as a pretreatment method, was found to be effective in the primary treatment of mature/medium landfill leachate. However, the main problem of the process is the large amount of produced sludge that requires an accurate feasibility evaluation for operational applications. In this study, the response surface methodology was applied for the modeling and optimization of Fenton process in three target responses, (1) overall COD removal, (2) sludge to iron ratio (SIR) and (3) organics removal to sludge ratio (ORSR), where the latter two were new self-defined responses for prediction of sludge generation and applicability assessment of the process, respectively. The effective variables included the initial pH, [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage. According to the statistical analysis, all the proposed models were adequate (with adjusted R² of 0.9116–0.9512) and had considerable predictive capability (with prediction R² up to 0.9092 and appropriate adequate precision). It was found that all the variables had significant effects on the responses, specifically by their observed role in dominant oxidation mechanism. The optimum operational conditions obtained by overlay plot, were found to be initial pH of 5.7, [H₂O₂]/[Fe²⁺] ratio of 17.72 and [Fe²⁺] of 195 mM, which led to 69% COD removal, 2.4 (l sludge/consumed mole Fe²⁺) of SIR and 16.5 (gCOD removed/l produced sludge) for ORSR in verification test, in accordance with models-predicted values. Finally, it was observed that [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage had significant influence on COD removal, while Fe²⁺ dosage and [H₂O₂]/[Fe²⁺] ratio had remarkable effects on SIR and ORSR responses, respectively.     

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30 min), temperature (160-200 °C), Cu²⁺ concentration (250-750 mg L⁻¹) and H₂O₂ concentration (0-1500 mg L⁻¹) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920 mg L⁻¹, was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45 min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H₂O₂ to reactive hydroxyl radicals. WAO at 2.5 MPa oxygen partial pressure advanced treatment further; for example, 22 min of oxidation at 200 °C, 250 mg L⁻¹ Cu²⁺ and 0-1500 mg L⁻¹ H₂O₂ resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H₂O₂ concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H₂O₂ concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.     

Photocatalytic Degradation of Poly(Vinyl Alcohol) on Pt/TiO<Subscript>2</Subscript> with Fenton Reagent

In this research Fenton reagent (Fe²⁺/H₂O₂) was investigated as oxidants to degrade poly (vinyl alcohol) (PVA). The role of nano-TiO₂ photocatalyst was discussed as an additive in Fenton reagent (Fe²⁺/H₂O₂). Pt/TiO₂ composites were also synthesized by photo-reaction to be used as additive in Fenton reagent. The rapid degradation of PVA was obtained when Pt/TiO₂ composites served as photocatalyst. The different photocatalytic efficiency of Pt/TiO₂- Fenton reagent (Fe²⁺/H₂O₂) was studied compared with TiO₂- Fenton reagent (Fe²⁺/H₂O₂) during the degradation of PVA.     

Treatment of mature landfill leachate by biofilters and Fenton oxidation

A series of processes by biofilter and Fenton oxidation to treat mature landfill leachate has been devised. At a hydraulic loading rate of 20 l m^?3 d^?1, a biofilter packed with aged refuse is found to remove 80% of chemical oxygen demand (COD), 89% of ammonia nitrogen and 96% of total phosphorus (TP). Particularly, TP levels dropped below 1 mg l^?1. The optimal condition for Fenton oxidation was selected to be an initial pH of 5, a dosage of 0.01 and 0.02 mol l^?1 of FeSO₄ and H₂O₂, respectively, and a duration of 3 h, where COD removal efficiency reaches 58.6%, and BOD₅/COD ratio is raised from 0.05 to 0.20. Subsequent treatment by a biofilter packed with slag reduces COD, ammonia nitrogen levels to less than 100, 25 mg l^?1, respectively. A pilot scale experiment conducted in situ demonstrates that this series of processes exhibits a high efficiency in removing pollutants from mature landfill leachate and it is viable for application.     

Evaluation of landfill leachate treatment by advanced oxidative process by Fenton’s reagent combined with membrane separation system

A high content of refractory organic matter, ammonia and toxic compounds is characteristic of landfill leachate. Advanced oxidative processes (AOPs) are an attractive alternative for landfill leachate treatment. However, when applied as a unique process treatment, they do not provide a complete solution for the effluent treatment. Combining AOP with a membrane separation process (MSP) presents a number of benefits and provides an adequate solution for this problem. With this in mind, the present work aims to evaluate, using a bench scale, leachate treatability through AOP by Fenton’s reagent (AOP/Fenton) combined with microfiltration (MF) and nanofiltration (NF). A high efficient removal of COD (63%), true color (76%) and humic substances (50%) was observed during AOP/Fenton under optimized conditions (1.7 g H₂O₂/g COD_{raw leachate}; FeSO₄·7H₂O:H₂O₂ = 1:5.3; pH = 3.8; reaction conditions = 115 rpm/28 min). According to the evaluated parameters, MSP presented an efficient complementary treatment, in which the integrity of the stages was sufficient for reaching regulatory levels in the effluent (Deliberação Normativa Conjunta COPAM/CERH-MG N^o. 1, May 5, 2008).     

The use of waste basic oxygen furnace slag and hydrogen peroxide to degrade 4-chlorophenol

A new treatment method is developed to degrade 4-chlorophenol (4-cp) and its oxidation intermediates. The experimental results of this research demonstrate that 4-cp and its oxidation intermediates can be decomposed completely by basic oxygen furnace slag (BOF slag) with hydrogen peroxide (H₂O₂) in an acid solution. The factors that effect the treatment efficiency were studied including initial concentration of 4-cp, pH of the solution, concentration of H₂O₂ and amount of BOF slag. The BOF slags are final waste materials in the steel making process. The major components of BOF slag are CaO, SiO₂, Fe₂O₃, FeO, MgO and MnO. As the BOF slag in an acid solution, FeO and Fe₂O₃ can be dissociated to produce ferrous ion and ferric ion. Ferrous ion reacts with hydrogen peroxide to form “Fenton's reagent” which can produce hydroxyl radicals (OH^.). Hydroxyl radical possession of high oxidation ability can oxidize organic chemicals effectively. Results show that 100 mg/l of 4-cp is decomposed completely within 30 min by 438.7 g/l BOF slag with 8.2 mM hydrogen peroxide in pH=2.8±0.2 solution. The COD value of the solution is reduced from 290 to 90 mg/l. The factors studied which affect the 4-cp decomposition efficiency were the hydrogen peroxide concentration, BOF slag concentration, pH of the solution and initial concentration of 4-cp. Because large amounts of Fe₂O₃ and FeO are present in the BOF slag, the BOF slag not only has a high treatment efficiency, but also can be used repeatedly.     

Trends in the use of Fenton,electro-Fenton and photo-Fenton for the treatment of landfill leachate

Advanced oxidation processes (AOPs) such as Fenton, electro-Fenton and photo-Fenton have been applied effectively to remove refractory organics from landfill leachate. The Fenton reaction is based on the addition of hydrogen peroxide to the wastewater or leachate in the presence of ferrous salt as a catalyst. The use of this technique has proved to be one of the best compromises for landfill leachate treatment because of its environmental and economical advantages. Fenton process has been used successfully to mineralize wide range of organic constituents present in landfill leachate particularly those recalcitrant to biological degradation. The present study reviews the use of Fenton and related processes in terms of their increased application to landfill leachate. The effects of various operating parameters and their optimum ranges for maximum COD and color removal are reviewed with the conclusion that the Fenton and related processes are effective and competitive with other technologies for degradation of both raw and pre-treated landfill leachate.     

Fenton氧化法处理石化含油废水生化出水

采用Fenton氧化法处理石化含油废水生化出水,通过正交实验和单因素实验优化了反应工艺条件。正交实验得到各因素对COD去除率的影响大小顺序为:溶液初始pHH_2O_2投加量n(H_2O_2)∶n(Fe~(2+))反应温度。实验最佳工艺条件为:初始溶液pH 4.0,H_2O_2投加量3.00 mL/L,n(H_2O_2)∶n(Fe~(2+))=10,反应温度35℃,反应时间60 min。在此最佳工艺条件下COD可降至60.33 mg/L,COD去除率达61.33%。在最佳工艺条件下,分别采用超声(US)-Fenton氧化和紫外光(UV)-Fenton氧化技术处理含油废水生化出水,COD去除率分别达76.77%和80.23%。但单一Fenton氧化、US-Fenton氧化和UV-Fenton氧化工艺对NH_3-N的去除效果均并不明显。     

Landfill leachate treatment by electrochemical oxidation

This study investigated the electrochemical oxidation of stabilized leachate from Pulau Burung semi-aerobic sanitary landfill by conducting laboratory experiments with sodium sulfate Na₂SO₄ (as electrolyte) and graphite carbon electrodes. The control parameters were influent COD, current density and reaction time, while the responses were BOD removal, COD removal, BOD:COD ratio, color and pH. Na₂SO₄ concentration was 1 g/L. Experiments were conducted based on a three-level factorial design and response surface methodology (RSM) was used to analyze the results. The optimum conditions were obtained as 1414 mg/L influent COD concentration, 79.9 mA/cm² current density and 4 h reaction time. This resulted in 70% BOD removal, 68% COD removal, 84% color removal, 0.04 BOD/COD ratio and 9.1 pH. Electrochemical treatment using graphite carbon electrode was found to be effective in BOD, COD and color removal but was not effective in increasing the BOD/COD ratio or enhancing biodegradability of the leachate. The color intensity of the treated samples increased at low influent COD and high current density due to corrosion of electrode material.     

Fenton氧化-生物接触氧化工艺处理甲醛和乌洛托品废水

采用Fenton氧化一生物接触氧化工艺处理含甲醛和乌洛托品的模拟废水（简称废水），在H2O2（体积分数30％）加入量2．5g／L、H2O2与Fe^2＋质量浓度比3．75、反应时间3h、不调节废水初始pH的Fenton氧化预处理最佳操作条件下，废水COD从1000mg／L左右降至300mg／L，COD去除率达72％。原废水完全无法直接进行生化处理，经Fenton氧化预处理后其BOD，／COD约为0．5，易于生化处理。Fenton氧化一生物接触氧化工艺处理废水，生物接触氧化停留时间为12h时，废水COD去除率高达94％，处理后出水COD小于70mg／L，处理效果很好。     

Application of quadratic regression model for Fenton treatment of municipal landfill leachate

The effectiveness of Fenton process in municipal landfill leachate treatment, as a pre- or post-treatment approach, has been demonstrated. However, no general recommendations of universal validity could be made in the term of optimized conditions affecting Fenton process. At the first stage of this study, collected leachate samples from Aradkooh site, Tehran, Iran, were investigated using one-factor-at-a-time method to find out optimum coagulation pH and flocculation time values. Subsequently, the obtained results in addition to data issued previously by the authors were employed to develop a predictive model of the true response surface, namely chemical oxygen demand (COD) removal efficiency. Finally, the main parameters of Fenton procedure, i.e. initial pH, [H(2)O(2)]/[Fe(2+)] molar ratio, Fe(2+) dosage, and coagulation pH were optimized taking advantage of the above-mentioned quadratic model. The derived second-order model included both significant linear and quadratic terms and seemed to be adequate in predicting responses (R(2)=0.9896 and prediction R(2)=0.6954). It was found that the interaction between initial pH and Fe(2+) dosage has a significant effect on COD removal. While, the optimal [H(2)O(2)]/[Fe(2+)] molar ratio was independent of ferrous ion dosage. The optimum conditions for the maximum COD removal of 50.76% for the parameters of initial pH, [H(2)O(2)]/[Fe(2+)] molar ratio, Fe(2+) dosage, and coagulation pH were found to be 5.8, 8.0, 22,500mg/L, and 8.7 respectively.     

高级氧化法预处理毛皮加工工业园区集中废水

分别采用臭氧氧化和Fenton氧化两种高级氧化法对毛皮加工工业园区集中废水处理厂的进水进行了预处理,考察了各工艺条件对废水COD去除效果的影响,并比较了两种方法对废水可生化性的改善情况。实验结果表明:在初始废水pH为8、臭氧投加速率为1.2 g/h的最适宜条件下,臭氧氧化法的COD去除率最高达72.7%,废水的可生化性显著提高,废水BOD5/COD由初始的0.06提高至0.12;在,n(Fe~(2+)):月(H_2O_2)=1:10、H_2O_2投加量为1.5 mL/L,、初始废水pH为2.5的最适宜条件下,Fenton氧化的COD去除率最高达33.4%,但废水可生化性不大;经臭氧氧化和Fenton氧化处理后,废水中的不饱和结构物质均得到了有效降解。     

Degradation of petroleum hydrocarbons from bottom sludge of crude oil storage tanks using in-vessel composting followed by oxidation with hydrogen peroxide and Fenton

In this research the feasibility of aerated in-vessel composting process followed by chemical oxidation with H₂O₂ and Fenton for removal of petroleum hydrocarbons from oily sludge of crude oil storage tanks was investigated. The ratios of the sludge to immature compost were 1:0 (as abiotic control), 1:2, 1:4, 1:6, 1:8 and 1:10 (as dry basis) at a C:N:P ratio of 100:5:1 and 55 % moisture content for a period of 10 weeks. Six concentrations of H₂O₂ and Fenton were added to the compost mixture for a period of 24- and 48-h reaction times. Results showed that petroleum hydrocarbons removal in ratios of 1:2, 1:4, 1:6, 1:8 and 1:10 were 66.6, 73.2, 74.8, 80.2 and 79.9 %, respectively. The results of the abiotic experiments indicated that the main mechanism of hydrocarbon removal in the composting reactors was biological. The application of combined composting and chemical oxidation demonstrated a remarkable (about 88 %) overall removal. The study showed that in-vessel composting combined with chemical oxidation is a viable choice for the remediation of the sludge.     

Leachate treatment before injection into a bioreactor landfill: Clogging potential reduction and benefits of using methanogenesis

In this study, an anaerobic sequencing batch reactor (ASBR) was operated with leachate from Brady Road Municipal Landfill in Winnipeg, Manitoba, Canada. Leachate was collected twice from the same cell at the landfill, during the first and 70th day of the study, and then fed into the ASBR. The ASBR was seeded at the start-up with biosolids from the anaerobic digester from Winnipeg’s North End Water Pollution Control Center (NEWPCC). Due to the higher COD and VFA removal rates measured with the second batch of leachate, an increase of approximately 0.3 pH units was observed during each cycle (from pH 7.2 to 7.5). In addition, CO₂ was produced between cycles at constant temperature where a fraction of the CO₂ became dissolved, shifting the CO₂/bicarbonate/carbonate equilibrium. Concurrent with the increase in pH and carbonate, an accumulation of fixed suspend solids (FSS) was observed within the ASBR, indicating a buildup of inorganic material over time. From it, Ca²⁺ and Mg²⁺ were measured within the reactor on day 140, indicating that most of the dissolved Ca²⁺ was removed within cycles. There is precedence from past researches of clogging in leachate-collection systems (Rowe et al., 2004) that changes in pH and carbonate content combined with high concentrations of metals such as Ca²⁺ and Mg²⁺ result in carbonate mineral precipitants. A parallel study investigated this observation, indicating that leachate with high concentration of Ca²⁺ under CO₂ saturation conditions can precipitate out CaCO₃ at the pH values obtained between digestion cycles. These studies presented show that methanogenesis of leachate impacts the removal of organic (COD, VFA) as well as inorganic (FSS, Ca²⁺) clog constituents from the leachate, that otherwise will accumulate inside of the recirculation pipe in bioreactor landfills. In addition, a robust methanogenesis of leachate was achieved, averaging rates of 0.35 L CH₄ produced/g COD removed which is similar to the theoretical removal of 0.4 L CH₄/g COD. Therefore, using methanogenesis of leachate prior to recirculation in bioreactor landfills will help to (1) control clog formation within leachate pipes and (2) produce an important additional source of energy on-site.     

Ammonium removal from landfill leachate by chemical precipitation

The landfill leachate in Hong Kong usually contains quite high NH₄⁺–N concentration, which is well known to inhibit nitrification in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH₄⁺–N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH₄⁺–N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH₄⁺–N in the leachate collected from a local landfill in Hong Kong as magnesium ammonium phosphate (MAP). In the experiment, three combinations of chemicals, MgCl₂·6H₂O+Na₂HPO₄·12H₂O, MgO+85% H₃PO₄, and Ca(H₂PO₄)₂·H₂O+MgSO₄·7H₂O, were used with the different stoichiometric ratios to generate the MAP precipitate effectively. The results indicated that NH₄⁺–N contained in the leachate could be quickly reduced from 5618 to 112 mg/l within 15 min, when MgCl₂·6H₂O and Na₂HPO₄·12H₂O were applied with a Mg²⁺:NH₄⁺:PO₄³⁻ mol ratio of 1:1:1. The pH range of the minimum MAP solubility was discovered to be between 8.5 and 9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl₂·6H₂O and Na₂HPO₄·12H₂O, which may affect microbial activity in the following biological treatment processes. The other two combinations of chemicals [MgO+85% H₃PO₄ and Ca(H₂PO₄)2·H₂O+MgSO₄·7H₂O] could minimise salinity after precipitation, but they were less efficient for NH₄⁺–N removal, compared with MgCl₂·6H₂O and Na₂HPO₄·12H₂O. COD had no significant reduction during this precipitation. It was found that the sludge of MAP generated was easily settled within 10 min to reach its solids content up to 27%. The other characteristics including capillary suction time (CST) and dry density (DD) of the MAP sludge were also tested. The experimental results indicate that the settled sludge is quite solid and can be directly dumped at a landfill site even without any further dewatering treatment.     

Fenton试剂—好氧活性污泥法处理邻苯二甲酸二丁酯废水

采用Fenton氧化—好氧活性污泥法处理邻苯二甲酸二丁酯（DBP）废水,优化了Fenton氧化反应的工艺条件。实验结果表明：在H₂O₂加入量4 g/L、Fe²⁺加入量200 mg/L、反应温度60 ℃、废水pH 4、反应时间60 min的最佳工艺条件下,Fenton氧化出水COD为200~250 mg/L,DBP质量浓度约为0.10 mg/L;在污泥质量浓度2 000 mg/L、DO 2~3 mg/L、水力停留时间8 h的条件下,好氧活性污泥法处理出水的COD基本低于50 mg/L,DBP质量浓度约为0.05 mg/L,均满足GB 8978—1996《污水综合排放标准》,可达标排放。     

Determination of organic compounds in landfill leachates treated by Fenton–Adsorption

The objective of this study was to identify the organic compounds removed from the leachate when treated with Fenton–Adsorption by gas chromatography coupled to mass spectrometry (GC–MS) in order to identify toxic compounds that could be harmful for the environment or human health.The physicochemical characterization of the raw leachate was carried out before and after the Fenton–Adsorption process. The effluent from each stage of this process was characterized: pH, Biological Oxygen Demand (BOD₅), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), Total Carbon (TC), Inorganic Carbon (IC), Total Solids (TS), Total Suspended Solids (TSS) and Color. The organic compounds were determined by GC–MS.The removal of COD and color reached over 99% in compliance with the Mexican Standard NOM-001-SEMARNAT-1996, which establishes the maximum permissible limits for contaminants present in wastewater discharges to water and national goods. The chromatographic analysis from the Fenton–Adsorption effluent proved that this treatment removed more than 98% of the organic compounds present in the initial sample. The mono (2-ethylhexyl) ester 1,2-benzenedicarboxylic acid persisted, although it is not considered as toxic compound by the NOM-052-SEMARNAT-2005. Therefore, the treated effluent can be safely disposed of into the environment.