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.     

Characterization and treatment of recirculation-stabilized leachate

This work investigated the characterization and treatment of recirculation-stabilized sanitary landfill leachate. Leachate from recently deposited solid wastes was treated by recirculation through areas of the landfill with old wastes. The stabilized effluent forms a pond at the lowest point of the landfill. This stabilized leachate was characterized by an average COD value of 1141 mg/l, an average BOD value of 85 mg/l and a BOD:N:P ratio equal to 100:312:0.30. Heavy metals concentrations were lower than those of fresh leachate. The BOD/COD ratio of this leachate was below 0.1, which excluded the possibility of biological treatment. Physico-chemical methods of treatment employed were coagulation, powdered activated carbon adsorption and air stripping of ammonia. The results showed that even after the combined treatment the COD remaining in water hardly dropped below 300 mg/l. Ammonia stripping was efficient at pH 11.5, yet the kinetics were slow.     

Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification

The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates.     

投加高效菌处理回灌型垃圾填埋场渗滤液的研究

从垃圾转运站被污染的土壤中筛选出1株高效菌，向垃圾渗滤液中投加该菌株进行厌氧摇瓶试验，结果表明该菌株具有较好的厌氧去除氨氮的性能。将该菌株投加于模拟填埋场生物反应器中，进行了为期282d的试验，结果表明，渗滤液中的氨氮与COD被同时去除，第282天时渗滤液中的COD为770mg／L、NH4^＋ -N为90．1mg／L，大大降低了渗滤液后续处理的难度。     

考虑垃圾体沉降的生物反应器填埋场 渗滤液回灌运移规律

生物反应器填埋场在渗滤液的回灌过程中,垃圾体会产生较大的沉降变形,这主要是由于填埋体的自重和生物降解所致。由于沉降变形会导致生物反应器填埋场中垃圾体的孔隙比减小,孔隙比的减小会影响垃圾体的渗透系数和填埋场所能容纳的渗滤液量。为了研究考虑垃圾体沉降的生物反应器填埋场渗滤液回灌运移规律,根据质量守恒原理,以修正的Darcy定理为基础,结合Elagroudy等人提出的沉降模型,建立了考虑垃圾体沉降的生物反应器填埋场渗滤液回灌的计算模型,应用该模型研究了非饱和条件下渗滤液在生物反应器填埋场中的运移规律,分析了回灌强度、垃圾体初始孔隙比、初始含水率和组成成份等参数变化对垃圾体含水率和填埋场单位表面积回灌量的影响规律。     

Removal of organics from leachates by anaerobic filter

A laboratory-scale study was conducted on two anaerobic filters at several loading rates and four hydraulic detention times. Feed substrates were landfill leachates taken from a recently opened landfill (Keele Valley) and from an older site (Brock North) which had been closed for about 8 years. The strong raw leachate from the new landfill had a COD of 14,000 mg l⁻¹, a BOD/COD ratio of 0.7 and a COD/P value of 17,900. The partially stabilized leachate from the older landfill had a COD of only 3750 mg l⁻¹, a BOD/COD ratio of 0.3 and a COD/P value of 30,640.Results from the treatment of the two leachates were compared with those from a previous study of a “mature” landfill (Beare Road). It was demonstrated that the anaerobic filter could reduce the COD of leachate from landfills of different ages by 90%, at loading rates of 1.26–1.45 kg COD m⁻³ d⁻¹. Total biogas production ranged between 400 and 500 l gas kg⁻¹ COD destroyed and methane content between 75 and 85%. No phosphorus addition was required over the loading range studied.     

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.     

考虑垃圾体成层性的渗滤液回灌运移规律

渗滤液回灌不仅能处理渗滤液、节约费用和保护环境,而且加速了填埋场稳定化,增加了产气率。以上海某填埋场四期工程为计算模型,本文考虑垃圾土沉降导致的成层性,运用SEEP/W有限元软件模拟渗滤液喷洒回灌。垃圾土在自重作用下会产生较大的沉降变形,导致垃圾土的孔隙率随深度变化,残余含水量、饱和含水量及饱和渗透系数也随之变化。在数值模拟中,以VGM(van-Genuchten-Mualem)函数描述垃圾土渗透系数与基质吸力关系,以流量边界模拟填埋场顶部、底部的渗滤液回灌和导排,分析了回灌过程中渗滤液的饱和-非饱和渗流情况,进而探讨了垃圾土成层性、回灌强度和排水流量对渗滤液运移规律的影响。     

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％。     

厌氧垃圾填埋系统渗滤液的生物毒性研究

以嗜热四膜虫作为毒性试验生物，对厌氧生物反应器垃圾填埋系统渗滤液的生物毒性变化进行了研究。结果表明，通过将渗滤液回灌使其在厌氧生物反应器填埋系统中得到处理，可使渗滤液的生物毒性随填埋时间的延长而逐渐降低；渗滤液的半致死浓度（LC50）与COD呈负相关，其常规理化指标并不能完全反映渗滤液在环境中的生物毒性；较高浓度的渗滤液对四膜虫的呼吸量有抑制作用。     

TiO2、Cu2O和氧化石墨烯复合氧化垃圾渗滤液效能

针对垃圾渗滤液中成分复杂的污染物,在自然光照条件下,使用TiO₂/氧化石墨烯、Cu₂O/氧化石墨烯和TiO₂/Cu₂O三种复合催化剂分别对垃圾渗滤液原液进行催化氧化。结果表明,3种复合催化剂中,TiO₂/氧化石墨烯复合催化剂对有机物的去除效果最好,当催化剂与渗滤液COD的质量比为0.7时为该催化剂的最佳投加量,最佳反应时间为2 h。在最佳试验条件下,对垃圾渗滤液原液进行催化氧化后,对COD的去除率达到92.57%,此时渗滤液出水COD为964.79mg/L,出水NH4⁺-N为2015.84 mg/L,BOD₅/COD值达到0.83。     

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.     

采用垃圾准好氧填埋消除酸积累现象的试验研究

针对垃圾厌氧填埋渗滤液在直接回灌初期会出现严重的酸积累现象,分析研究了垃圾准好氧填埋与厌氧填埋的渗滤液直接回灌后的出水水质,发现采用准好氧垃圾填埋的体系内所含挥发性脂肪酸量和COD量比厌氧填埋柱低得多,不存在酸积累现象;从整个降解过程看,准好氧填埋加快了COD的降解速率,加速了垃圾体的稳定化进程;另外,环境温度对垃圾体的降解速率影响很大,较高的温度能够加速垃圾体的降解速度.     

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。     

Aged raw landfill leachate: membrane fractionation, O3 only and O3/H2O2 oxidation, and molecular size distribution analysis

Large molecular refractory organic compounds (i.e., humic substances) were the major chemical oxygen demand (COD) components of aged raw landfill leachate. To investigate the behaviours of the large molecular refractory organic compounds when they were subjected to oxidation with ozone only (O3 only) and ozone combined with hydrogen peroxide (O3/H2O2), the aged raw landfill leachate first was filtered with 0.8 and 0.45 microm pore size filters in series, then was sequentially fractionated with 10,000 MWCO; 5000 MWCO; and 1000 MWCO membranes, and four samples were formed: 0.45 microm-10,000 Da; 10,000-5000 Da; 5000-1000 Da; and < 1000 Da. Mass distribution profiles of COD, 5-day biochemical oxygen demand (BOD5), colour and metals in the aged raw leachate were developed through mass balance. After membrane fractionation of the aged raw leachate, the metals were fractionated with the humic substances. Each fractionated sample as well as the aged raw leachate was oxidised with O3 only and O3/H2O2. The H2O2 enhanced the reduction of COD and colour; while, the BOD5 after O3 only was always higher than that of O3/H2O2. The addition of H2O2 improved the peak reduction of large molecules, but the effects of H2O2 on the fractions of 10,000-5000 Da and 5000-1000 Da were likely insignificant, which is in accordance with the COD results. No correlation was found between the BOD5 increase and the area of new peak formed after oxidation. However, the BOD5 of each sample after oxidation with O3 only was the logarithmic function of its total peak area.     

An index for quantifying the aerobic reactivity of municipal solid wastes and derived waste products

The organic matter contained in municipal solid waste (MSW) and in the MSW fractions obtained by mechanical separation has strong environmental impact when the waste is used as landfill. This is partly due to the biological activity that occurs under anaerobic conditions. Negative effects on the environment include unpleasant odors, biogas, leachate and biomass self-heating. Measuring the biological reactivity of waste with the help of indicators is an important tool to prevent waste impact. The aim of this study was to develop an index capable of describing the aerobic reactivity of waste, using both biological and chemical indicators. To develop this index, 71 MSW and MSW-product samples, including biologically treated MSW and mechanically separated MSW fractions, were analyzed. Fifty of the 71 samples analyzed represented MSWs and their derived products collected from a number of Italian waste plants and sites. The remaining 21 were MSW samples collected at different times during 8 different full-scale aerobic biological processes in four treatment plants used to reduce the biological reactivity of wastes. Five of these processes used the entire (unsorted) MSW, while the remaining three used the organic fraction of the MSW obtained by mechanical pre-treatment (waste sieving). Respirometric activity (Dynamic Respiration Index, DRI) and eluates characterization (chemical oxygen demand--COD, and 5 days biological oxygen demand--BOD5) were used as indicators of waste strength, as they had previously been reported to be indirect measures of waste impact on landfill. Summarizing all studied indicators, Principal Component Analysis (PCA) was used to develop the Putrescibility Index (Ip). The results revealed Ip index of 204+/-33 (mean+/-standard deviation) and 159+/-14 for the organic fraction of MSW and MSW untreated waste respectively, and of 106+/-16 and 101+/-22 for the corresponding biologically treated waste.     

投粉末活性炭SBR处理垃圾渗滤液

结合小型垃圾填埋场渗滤液中有机物浓度较低的特点及简化工艺的要求,以南京市某垃圾填埋场渗滤液为试验对象,经氨吹脱后采用投粉末活性炭SBR/混凝沉淀工艺进行处理,探讨了粉末活性炭投量、泥龄等参数对处理效果的影响.结果表明,对COD、BOD5、NH3-N的总去除率分别为88.4%、93.4%、76.9%,出水水质达到了<生活垃圾填埋场污染控制标准>(GB16889-1997)的Ⅱ级标准.     

MBR对焚烧厂渗滤液中有机污染物的降解特性

采用膜生物反应器(MBR)处理垃圾焚烧厂渗滤液,并采用GC/MS技术考察了MBR处理渗滤液过程中有机污染物的降解特性.结果表明,生化段对C4～C8的有机物有较好的降解能力,而无机膜对C16～C19的有机物的去除效果较好;生化段对渗滤液中酸类有机物的降解效果明显,而无机膜对酮、醇、酸类有机物的去除效果明显;当进水COD为57 000 mg/L、NH3-N为665mg/L时,MBR出水的COD和NH3-N分别可降至457、8.54 mg/L.     

Combined γ-ray irradiation-activated sludge treatment of humic acid solution from landfill leachate

Humic acid, which is a typical microbially refractory organic substance, was extracted from a landfill leachate. The humic acid solution (COD = 367 mg 1⁻¹; TOC = 293 mg 1⁻¹; BOD = 27 mg 1⁻¹) was applied to a batch scale activated sludge treatment after the modification of its biodegradability by γ-ray irradiation. The BOD increased to 64 mg 1⁻¹ by irradiation of 15 kGy (1.5 Mrad), while the COD and TOC decreased to 231 and 230 mg 1⁻¹, respectively. When the irradiated sample was treated with an activated sludge, the BOD decreased rapidly in 2–3 h to about 15 mg 1⁻¹ which was a similar value as the unirradiated sample was treated. The elimination efficiency of TOC by the sludge treatment was approximately equal to that obtained by irradiation of 15 kGy. These facts suggest a utility of applying microbial processes after radiation treatment of microbially refractory wastewaters.