Optimizing the treatment of landfill leachate by conventional Fenton and photo-Fenton processes

Landfill, a matured and economically appealing technology, is the ultimate approach for the management of municipal solid wastes. However, the inevitable generation of leachate from landfill requires further treatment. Among the various leachate treatment technologies available, advanced oxidation processes (AOPs) are among powerful methods to deal with the refractory organic constituents, and the Fenton reagent has evolved as one promising AOPs for the treatment of leachates. Particularly, the combination of UV-radiation with Fenton's reagent has been reported to be a method that allows both the photo-regeneration of Fe²⁺ and photo-decarboxylation of ferric carboxylates. In this study, Fenton and photo-Fenton processes were fine tuned for the treatment of leachates from the Colmenar Viejo (Madrid, Spain) Landfill. Results showed that it is possible to define a set of conditions under which the same COD and TOC removals (≈ 70%) could be achieved with both the conventional and photo-Fenton processes. But Fenton process generated an important quantity of iron sludge, which will require further disposal, when performed under optimal COD removal conditions. Furthermore conventional Fenton process was able to achieve slightly over an 80% COD removal from a “young” leachate, while for “old” and ”mixed” leachates was close to a 70%. The main advantage showed by the photo-assisted Fenton treatment of landfill leachate was that it consumed 32 times less iron and produced 25 times less sludge volume yielding the same COD removal results than a conventional Fenton treatment.     

响应面法优化电解芬顿协同法深度处理老龄垃圾渗滤液

采用电解芬顿法深度处理老龄垃圾渗滤液,选取电量、进水 pH 值、进水氨氮浓度3个因素为变量,CODCr 去除率为响应值进行 Box-Behnken 中心组合设计。利用响应面法对试验结果进行分析,建立了 CODCr 去除率为响应值的二阶多项式模型并进行了方差分析和显著性检验,通过解模型逆矩阵得到最佳条件：单位面积电量为23．26 Ah／dm2、pH 值为3．58、进水氨氮浓度56．78 mg／L。在最佳条件下,CODCr 去除率为96．5％,与模型预测值偏差为4．45％,吻合度较高。对电解芬顿深度处理前后的渗滤液进行 GC-MS 分析,表明电解芬顿协同处理技术能有效降解垃圾渗滤液中难生化降解的有机物,将有机物种类从42种降低至21种,是较有效的深度处理技术。     

PAEs and BPA removal in landfill leachate with Fenton process and its relationship with leachate DOM composition

An increasing attention has been paid to the trace endocrine disrupting compounds (EDCs) in landfill leachate. In this paper, the removal of EDCs including phthalic acid esters (PAEs) and bisphenol A (BPA) from the fresh and mature landfill leachate by Fenton treatment was studied. More than 40% of PAEs and about 62% of BPA were removed from the raw mature leachate while only 20% of PAEs and 37% of BPA in the raw fresh leachate were reduced, respectively. After the fresh and mature leachates were spiked with PAEs to 1.5 mg L^− 1 and BPA to 0.08 mg L^− 1, the removal efficiencies of BPA and PAEs increased to more than 88%. The results indicated that the removing efficiencies of the EDCs in the leachate had a relationship with their concentrations, and that the trace levels of EDCs in leachate challenged the treatment capacity of the Fenton process. Most of the EDCs in the enriched leachate were removed by oxidation, which had no clear correlation with the hydrophobicity of the EDCs. The flocculation played an important role in the removal of di-(2-ethylhexyl) phthalate that could not be completely oxidized in the Fenton process, in that the EDCs with high n-octanol/water partition coefficient inclined to precipitate after the Fenton process. The dissolved organic matter (DOM) in the fresh leachate inhibited the EDCs removal more than the DOM in the mature leachate did. Both the composition of the leachate DOM and the characteristics of the EDCs determined the removing efficiencies of the EDCs in the Fenton process.     

Stabilized landfill leachate treatment by combined physicochemical-nanofiltration processes

Landfill leachate is a complex wastewater which the composition and concentration of contaminants are influenced by the type of waste deposited and the age of landfill. In the last years, several processes or process combinations were developed and tested to reach requirements for the discharge of leachate. Among the new processes, membrane processes are considered as promising: reverse osmosis is one of the most widely used treatment in the Northwestern European countries and nanofiltration is gained in popularity during the last 5 years. Successful application of membrane technology for the treatment of landfill leachates, requires efficient control of membrane fouling. Two organic membranes of nanofiltration were used for pilot-scale testing. Leachates were subject to several pretreatments (pH modification, prefiltration and coagulation with FeCl3) to remove potential foulants including dissolved organic and inorganic substances, colloidal and suspended particles. These pretreatments do not enhance the performances (retention and permeation flux) of membranes because the pH range and the presence of Fe3+ ions contribute greatly to change the characteristics of organic matter and the surface charges of membranes. However, the results show that nanofiltration is sufficient to eliminate refractory COD, the permeates have a COD lower than the requirements for discharge.     

Fenton试剂对垃圾渗滤液中有机物的去除特性研究

采用Fenton试剂处理垃圾渗滤液,在最佳试验条件下,考察了Fenton试剂对渗滤液中不同表观分子质量和不同种类有机物的去除效果。结果表明,Fenton试剂对表观分子质量〉2ku的COD和表观分子质量〉4ku的UV254的去除效果较好,去除率分别大于60％和80％。Fenton试剂对富里酸（FA）的去除率为85％,对腐殖酸（HA）的去除率为68．4％,对亲水性有机物（HyI）的去除率为36．5％。     

Removal of non-biodegradable organic matter from landfill leachates by adsorption

Leachates produced at the La Zoreda landfill in Asturias, Spain, were recirculated through a simulated landfill pilot plant. Prior to recirculation, three loads of different amounts of Municipal Solid Waste (MSW) were added to the plant, forming in this way consecutive layers. When anaerobic digestion was almost completed, the leachates from the landfill were recirculated. After recirculation, a new load of MSW was added and two new recirculations were carried out. The organic load of the three landfill leachates recirculated through the anaerobic pilot plant decreased from initial values of 5108, 3782 and 2560 mg/l to values of between 1500 and 1600 mg/l. Despite achieving reductions in the organic load of the leachate, a residual organic load still remained that was composed of non-biodegradable organic constituents such as humic substances. Similar values of the chemical oxygen demand (COD) were obtained when the landfill leachate was treated by a pressurised anoxic-aerobic process followed by ultrafiltration. After recirculation through the pilot plant, physico-chemical treatment was carried out to reduce the COD of the leachate. The pH of the leachate was decreased to a value of 1.5 to precipitate the humic fraction, obtaining a reduction in COD of about 13.5%. The supernatant liquid was treated with activated carbon and different resins, XAD-8, XAD-4 and IR-120. Activated carbon presented the highest adsorption capacities, obtaining COD values for the treated leachate in the order of 200mg/l. Similar results were obtained when treating with activated carbon, the leachate from the biological treatment plant at the La Zoreda landfill; in this case without decreasing the pH.     

高级氧化技术对垃圾渗滤液的处理研究

介绍了高级氧化技术中的臭氧氧化法、Fenton法、湿式催化氧化法、超声波氧化法以及组合工艺处理垃圾渗滤液的研究进展,阐述了这些高级氧化技术的反应机理以及特点,并对高级氧化技术处理垃圾渗滤液研究方向进行了分析,对垃圾渗滤液的有效处理具有积极指导意义。     

MBR在蓬莱市生活垃圾渗滤液处理工程中的应用

结合蓬莱市生活垃圾处理场工程实例,介绍了MBR工艺处理垃圾渗滤液的工艺流程、原理等,分析了MBR工艺处理垃圾渗滤液的特点和优势。垃圾渗滤液经过MBR工艺处理,生化部分采用硝化/反硝化工艺,再经超滤/纳滤工艺等膜分离技术和其他方法处理,最终流出液水质可以达到《生活垃圾填埋场污染控制标准》(GB 16889—2008)。     

Oxone/Co oxidation as an advanced oxidation process: Comparison with traditional Fenton oxidation for treatment of landfill leachate

In this paper, the application of Fenton and Oxone/Co²⁺ oxidation processes for landfill leachate treatment was investigated. The removal of the chemical oxygen demand (COD), suspended substances (SS) and the color of the landfill leachate by Fenton oxidation to that by Oxone/Co²⁺ oxidation were compared under optimal operational conditions. For Fenton oxidation process, the optimal conditions were determined as: [H₂O₂] = 80 mmol L⁻¹, [H₂O₂]/[Fe²⁺] = 2.0, initial pH = 2.5, reaction temperature = 37.5 ± 1 °C, reaction time = 160 min, number of stepwise addition = 3. Under the given conditions, 56.9% of the COD removal efficiency was achieved, but the SS and the color of the treated landfill leachate increased due to the generation of a large quantity of ferric hydroxide sludge. In reference to Oxone/Co²⁺ oxidation process, the optimal conditions were determined as: [Oxone] = 4.5 mmol L⁻¹, [Oxone]/[Co²⁺] = 10⁴, pH = 6.5, reaction temperature = 30 ± 1 °C, reaction time = 300 min, number of stepwise addition = 7, the COD, SS and the color removal efficiencies were 57.5, 53.3 and 83.3%, respectively. From this work, it can be concluded that Oxone/Co²⁺ oxidation process demonstrated higher degradation efficiencies of the COD, SS and color for landfill leachate treatment than that by Fenton oxidation process. It also suggested that Oxone/Co²⁺ oxidation process could be considered as one of the most promising technologies for practical applicability to treat landfill leachate in large scale. For further improving the efficiency of Oxone/Co²⁺ oxidation process, we proposed that combination of it with other technologies in future such as ultraviolet, ultrasound and biological methods.     

Abiotic properties of landfill leachate controlling arsenic release from drinking water adsorbents

In this study, As leaching from five arsenic bearing solid residuals (ABSRs) comprised of the iron hydroxide adsorbent Bayoxide E33 used in long-term operations was evaluated in leaching trials using California Waste Extraction Test (CalWET) and Toxicity Characteristic Leaching Protocol (TCLP) leachate solutions, a landfill leachate (LL), and synthetic leachate (SL). The initial As loading of the media, which reflects the influence of source water chemistry and varying treatment conditions at the point of removal, strongly influenced the magnitude of As release. The chemical composition of the leachate also influenced As release and demonstrated the relative importance of different release mechanisms, namely media dissolution, pH-dependent sorption/desorption, and ion exchange. The CalWET solution, which partially dissolved the iron-based media, resulted in 100 times more As release than did the TCLP solution, which did not dissolve the media. The LL had a higher pH than the TCLP solution, and even though its organic carbon content was lower it tended to release more As. Tests with the SL were conducted to determine the influence of variations in leachate pH, phosphate, bicarbonate, sulfate, silicate, and natural organic matter (NOM). Release increased at high pH, in the presence of high concentrations of phosphate and bicarbonate, and in the presence of high NOM concentrations. For pH, this reflects the pH-dependence of sorption reactions, whereas for the anions and NOM, direct competition appeared important. Similar to the CalWET solution, excess NOM dissolved portions of the media thereby facilitating As release. In general, our results suggest that estimating As release into landfills will remain a challenge as it depends upon As loading, which reflects site-specific properties, and the composition of the leachate, which varies from landfill to landfill.     

Monitoring of bacterial community changes in leachate and wetland soil using T‐RFLP analysis

The removal of toxic materials in municipal solid waste (MSW) can be carried out within both bioreactors and constructed wetlands. In this study, the microbial community was analysed to monitor populations related to leachate. Wetland soil samples of two landfill sites were analysed and the microbial communities were compared during organic matter removal processes. The extracted DNA was amplified using FAM63F and HEX518R primers and T‐RFLP analysis was carried on with AluI digested terminal fragments. The bacterial populations of the wetland soil from Bury and Beccles landfill sites were absolutely dissimilar in the beginning of the treatment processes. But after four weeks of treatment the similarity was 45%. These community shifts can explain the effect of leachate on bacterial population. The T‐RFLP electropherograms indicated that the bacterial population of the bioreactor was very similar to the constructed wetland’s population in recent samples. The similarity within both sites might increase as the treatment process continues.     

Landfill evolution and treatability assessment of high‐strength leachate from msw with high organic and moisture content

The generation of contaminated leachate remains an inevitable consequence of the practice of solid waste disposal in landfills. The collection and treatment of leachate have become common practice in order to prevent environmental pollution. Leachate treatment is highly dependent on the quality of leachate, which in turn is influenced by various factors including waste composition and operational procedures. This paper investigates the treatability of high‐strength leachate from pre‐sorted and baled municipal solid waste characterized by high organic and moisture content. For this purpose, waste disposal and leachate generation rates were monitored. Leachate samples were collected and analysed for selected indicators including BOD, COD, pH, and NH₄‐N and a pilot scale treatment plant with coagulation, precipitation and sequential batch biological reactors was constructed to evaluate the feasibility of leachate treatment. Concentration levels were related to biological activity within the landfill and the results indicated that (1) pre‐sorting and baling of the waste did not hinder waste stabilization; and (2) the high organic and moisture contents resulted in an extremely strong leachate, particularly at the onset of biodegradation processes, which can affect the leachate treatment facility. The effectiveness of the pilot plant in treating the leachate exceeded 90% using COD and NH₄‐N as indicators.     

Evaluation of on-site biological treatment for landfill leachates and its impact: A size distribution study

A cost effective and widely applied approach for landfill leachate disposal is to discharge it to a municipal wastewater treatment plant (WWTP). The recalcitrant nature of leachate organics and the impact on the downstream WWTPs were comprehensively investigated in this study. Size fractionation by ultrafiltration (UF) and microfiltration (MF) was employed in conjunction with various analyses (TOC, COD, nitrogen species and UV₂₅₄ absorbance) on raw and biologically treated landfill leachates to provide insight into biological treatability. Overall, landfill leachate organics showed bio-refractory properties. Less than half of the organic matter, measured as total organic carbon (TOC), could be removed in the biological processes examined. Size distribution data showed that the <1 thousand Daltons (kDa) fraction is dominant in most untreated and treated landfill leachates, indicating difficulties for membrane treatment. Also, most removal occurred for the <1 kDa fraction in the biological processes, while the intermediate size fractions increased slightly. This may be caused by bio-flocculation and/or partial degradation of larger molecular weight fractions. Organic nitrogen was investigated in this study as one of the first explorations for landfill leachates. Organic nitrogen in landfill leachates was more bio-refractory than other organic matter. UV quenching by landfill leachates was also investigated since it interferes with the UV disinfection at WWTPs. The combination of activated carbon and activated sludge (PACT) showed some effectiveness for reducing UV quenching, indicating that carbon adsorption is a potential method for removal of UV quenching substances. Fourier transform Infrared (FT/IR) data showed that aromatic groups are responsible for the UV quenching phenomenon.     

Fenton法处理垃圾渗滤液

介绍了Fenton法处理垃圾渗滤液的中型试验,其中Fenton氧化在连续搅拌反应器（CSTR）中进行。试验表明,当双氧水与亚铁盐的总投加比一定（H2O2／Fe^2 =3.0)时,COD的去除率随双氧水投加量的增加而增加,但与双氧水在两个氧化槽的投加比例无关。当双氧水的总投加量为0.1mol/L时,COD的去除率可达67．5％,这一结果同样适用于其他垃圾填埋场的晚期渗滤液处理。     

Treatment of landfill leachate by combined aged-refuse bioreactor and electro-oxidation

Two-stage aged-refuse bioreactor (ARB) was applied to treat landfill leachate in Shanghai Waste Laogang Disposal Plant. The removal efficiencies of chemical oxygen demand (COD), biological oxygen demand (BOD), total organic carbon (TOC), total nitrogen (TN) and ammonia nitrogen (NH(3)-N) of landfill leachate treated by the two-stage bioreactor system were 98.5%, 99.9%, 98.0%, 64.2% and 99.9%, respectively. The COD and BOD in the second stage effluent were 239 and 7 mg l(-1), respectively. Thus three types of electrolysis were employed to further treat the second effluent, undivided electrolysis (UDE), divided electrolysis (DE) with Ti/PbO(2) cathode and DE with gas diffusion cathode. All electrolysis processes possessed good color removal effect, while the DE with gas diffusion cathode had the best TOC removal effect. The optimum electrolysis time of leachate was 30 min. The TOC removal efficiencies were 51.4% and 39.7% in anolyte and catholyte, respectively, after 30 min electrolysis at 5 V. In addition, the DE with gas diffusion cathode showed the least energy consumption of 9.8 k Whm(-3) at 30 min. The organic pollutants in the leachate were analyzed through a gas chromatography coupled with mass spectrometry (GC-MS) system. Through the two-stage ARB, the species and concentrations of organic pollutants in landfill leachate reduced greatly. Several chlorinated organic compounds were detected in the effluent after the UDE and the anolyte of the DE. In addition, the concentration of absorbable organic halogens (AOX) increased greatly during the electrolysis. Hence, careful consideration should be given in the application of electro-oxidation into the treatment of chloride-containing wastewater.     

微波强化Fenton氧化处理垃圾渗滤液的研究

以负载铁(Ⅱ)的颗粒活性炭(GAC)为催化剂,采用微波强化Fenton氧化处理老龄垃圾渗滤液,考察了对垃圾渗滤液的处理效果及微波的作用机理。结果表明,微波对Fenton氧化反应有催化作用,且可促进渗滤液中胶体的絮凝,微波作用时间是影响处理效果的主要因素;当GAC的铁负载量为33.32mg/g、微波功率为720W、微波时间为30min时,对COD和NH3-N的去除率最高,分别达到了95.64%和88.63%;COD主要通过催化氧化作用被去除,而NH3-N主要通过絮凝、吸附作用被去除;另外,微波可使GAC再生,提高了GAC的利用率。     

Fenton氧化/混凝法后续处理垃圾渗滤液研究

六里屯垃圾填埋场的垃圾渗滤液经UASB＋A／O系统处理后,COD和氨氮含量分别在1350～1500和280～420mg／L,还需要进一步处理。因此采用Fenton氧化／混凝法作为后续处理工艺,考察了不同条件下对污染物的去除效果。结果表明,当pH=7、[Fe^2＋]=0．0167mol／L、[H2O2]=0．05mol／L、[FeCl3]=600mg／L、[AP410C]=4mg／L时,该工艺对浊度、COD和氨氮的去除率分别为82％、80．7％、55．9％,去除效果较好。     

Biological degradation of leachate from household and similar waste pre-treated by electro-Fenton process

This study's purpose is to confirm the feasibility and performance of the combination between ‘electro-Fenton’ process and the ‘activated sludge’ biological process, in order to remove the organic matter contained in ‘intermediate’ leachates from technical landfill centre of Hamici (Algiers). This leachate was initially electrochemically pre-treated until the ratio of BOD₅/chemical oxygen deman (COD) = 0.41, then an optimization of the parameters significantly influencing the biological degradation was carried. The results obtained after 13 h of biological treatment show the removal of 97% of the initial COD, with a mixed liquor composed of 700 mL of pre-treated leachate and 300 mL of activated sludge, a dissolved oxygen concentration of 3.5 mg O₂/L and a pH of 7, which allows the effluent to discharge directly into the environment. The conclusions of this work are promising because it was demonstrated that if the operating parameters are well controlled concerning these treatments, its sequence and the referred pre-treatment, the treatment efficiency is very high to the point of direct discharge of the leachate. However, in future studies, the combination of the both processes should be more explored in order to reduce the treatment time and to scale-up the process.     

Dissolved organic matter (DOM) in recycled leachate of bioreactor landfill

Landfill leachate needs sufficient treatment before safe disposal. Bioreactor landfill technology could effectively degrade the organic matters in recirculated leachate, hence leaving a leachate stream of low biodegradability. This study characterized the dissolved organic matter (DOM) in the leachate from simulated bioreactor landfill columns with or without presence of trace oxygen. The removal efficiencies of this DOM using coagulation-sedimentation or electrolysis processes were demonstrated. Recirculated leachates were sampled from the simulated landfill columns applying conventional mode, intermittent-aeration mode, and natural aeration mode, whose DOM was fractionated into humic acids (HA), fulvic acids (FA) and hydrophilic fractions (HyI) by the XAD-8 resin combined with the cation exchange resin method. The recirculated leachate had low BOD/COD ratio, high humic substances contents, and high aromatic content. Their HA fraction comprised mainly large molecules (>10 k Da), while the FA and HyI were composed of smaller molecules (<50 k and <4 k Da, respectively). With the presence of oxygen, the TOC contents and the contents of HA, FA and HyI in leachate reduced, with FA and HyI fractions of molecular weight (MW) lower than 4 k Da more readily degraded. The organic matters left in leachates from intermittent-aeration mode and natural aeration mode were of low biodegradability. It was tested in the following sections the effects of coagulation-sedimentation process and of electrolysis process on the removal of residual DOM in recirculated leachate. Coagulation-sedimentation tests revealed that poly ferric sulphate (PFS) could remove more COD (58.1%) from leachate than polyaluminum chloride (PACl) (22.9%), particularly on the HA fraction with MW>10 k Da. Coagulation-sedimentation could not remove most of HyI in leachate. Furthermore, the corresponding BOD/COD ratio was not improved through coagulation. Electrolysis test could also effectively removed HA of MW>10 k Da. However, the biodegradability of treated effluent considerably was improved. The electrolysis could decompose high MW substances and increase biodegradability of recirculated leachate from bioreactor landfill.     

改性硅藻土处理垃圾渗滤液的中试研究

利用改性硅藻土对老龄垃圾填埋场渗滤液进行了处理,中试结果表明改性硅藻土的后处理效果比预处理效果好。若提高pH值、增加改性硅藻土投量还可提高COD去除率。采用两级硅藻土反应器串联处理老龄填埋场渗滤液生物处理出水,COD去除率可达到57%。