DEVELOPMENT OF AN ELECTROCHEMICAL OXIDATION PROCESS FOR THE TREATMENT OF LANDFILL LEACHATES

Some landfill site operators use wastewater treatment plants for the discharge of complex leachate waste. However, for the water company involved in managing the wastewater plant, leachates can pose a problem to the quality of the effluent, due to the high levels of Chemical Oxygen Demand (COD), ammonia and inorganic metal constituents. Electrochemical oxidation of landfill leachate has been successfully used by researchers^(1,2,3,4) with current densities of 5 to 100 mA/cm². A new laboratory system has been developed which utilises a low current density of 2.42 mA/cm² and the performance has been evaluated with synthetic and 'real' landfill leachates from 2 wastewater sites.
This system reduces COD of synthetic mixtures by 58%, with complete removal of ammonia. For real leachates, 5 out of 8 samples resulted in ammonia reduction, with 2 samples experiencing approximately. 60% COD reduction. Power costs for treatment have been determined and the potential for a full-scale installation considered.     

Water quality and pollution loading of a river segment affected by landfill leachate and domestic waste

The Marikina River in the Philippines has been polluted by Payatas landfill leachate, and domestic and agricultural waste. This study monitored the water quality at five stations on the river and two stations on two creeks that discharge to the river to determine the effects of Payatas landfill and to estimate pollution loading. The dissolved oxygen (DO), chemical oxygen demand (COD) and other water quality parameters were compared with the Philippines Standards for river water classification. It was found that Payatas leachate has a significant influence on the DO and COD levels as well as other water quality parameters. Per capita pollution loading for Quezon City was found to be lower than for Europe and Japan. The effect of leachate is more significant during the dry season. It is recommended that a leachate collection system be established to prevent leachate form entering Payatas creek, and that the Patayas landfill be replaced with a modern landfill site, conforming to current best practice at another location.

List of Abbreviation: BOD= Biological Oxygen Demand COD = Chemical Oxygen Demand DO = Dissolved Oxygen EC = Electrical Conductivity M1, M2, M3, M4, M5 = monitoring stations TDS = Total Dissolved Solids TSS = Total Suspended Solids     

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.     

Characterization and Treatment of Leachates from Hong Kong Landfill Sites

Development of a large landfill site in the North-Eastern New Territories of Hong Kong, which will receive 25 million m³ of wastes during a life of about 13 years, must include the provision of a scheme to manage leachates which will arise in the tropical climate of the region.
The paper presents detailed results from a study commissioned by the Environmental Protection Department of the Hong Kong Government, to characterize and treat leachates generated by landfills in Hong Kong, in order to design a suitable management scheme. Field and laboratory trials which were carried out during 1989 showed that, although leachates from Hong Kong landfills have some specific characteristics (e.g. concentrations of amm.N to 5000 mg/l), they can be treated to high standards by aerobic biological processes.
As a result of these studies, a scheme has been designed which will provide a high degree of environmental protection in respect of leachate, as the landfill is developed.     

垃圾渗滤液处理工艺的试验研究

针对现有垃圾渗滤液处理工艺存在的问题,结合我国北方城市垃圾渗滤液的特征,试验采用混凝气浮、生化、吸附处理工艺处理垃圾渗滤液,结果表明,这套工艺是合理可行的.文中确定的试验参数的运行条件下,CODcr去除率达到99.1%,氨氮去除率达到96.6%,出水达到《生活垃圾填埋场污染控制标准》中的一级排放标准.     

Natural attenuation and characterization of contaminants composition in landfill leachate under different disposing ages

Chemical Oxygen Demand (COD) composition in landfill leachate would vary as the disposal time extended. Leachates with different ages were collected from Laogang Refuse Landfill of Shanghai, the largest landfill in China with a placement scale of 7600 t refuse per day. To characterize COD composition in leachate, samples were size-fractioned into suspended fractions (> 0.45 μm), colloid fraction (0.45 μm < fraction < 1 K Da MW) and dissolved fractions (< 1 KDa MW) based on the molecular weight distribution. The fractions < 0.45 μm (including colloid fraction and dissolved fractions) in leachate were further divided into 6 fractions, i.e. hydrophobic bases (Ho-base), hydrophobic acids (Ho-acid), hydrophobic neutral (Ho-neutral), hydrophilic bases (Hi-base), hydrophilic acids (Hi-acid) and hydrophilic neutral (Hi-neutral). It was found that the ratio of TOC/TC in leachate decreased over time, indicating that the percentage of organic matters in leachate decreased as the disposal time extended. It was also observed that the hydrophobic fraction accounted to about 50% of the total matters presented in the fraction < 0.45 μm of all leachate samples. The main components in < 0.45  μm fraction were the Ho-acid, Hi-acid and Hi-base fractions. The percentage of Ho-acid in leachate decreased from 60.8% (2 a) to 43.2% (12 a). In addition, leachate with different ages was categorized into 3 phases according to the results of Principle component analysis (PCA). TOC/COD ranges of leachate in periods I, II and III were 40-54.6%, 16.9-41.3% and 10-38.9%, respectively, indicating that the COD contribution of non-carbon reduction substances increased over time in leachate. Hence, the corresponding landfill leachate treatment process should be modified according to the leachate characterization. The results obtained in this study might provide the important information for modeling, design, and operation of landfill leachate treatment systems.     

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.     

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.     

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.     

多级生化/物化工艺处理垃圾渗滤液

天津滨海新区汉沽垃圾处理场采用多级生化／物化工艺处理垃圾渗滤液,实际运行结果表明,处理效果良好而稳定,出水可直接用作厂内绿化和生活用水,剩余污泥则回喷垃圾堆体,基本实现了“零排放”。     

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%。     

蒸发浓缩—UASB—A/O工艺处理垃圾渗滤液

根据浙江某生活垃圾焚烧厂的实际情况,采用蒸发浓缩——UASB——A／O主体工艺处理垃圾渗滤液。详细介绍了处理工艺流程、各处理单元的设计参数、运行操作方式以及工艺特点。运行结果表明,该工艺处理效果良好,出水水质达到了《污水综合排放标准》（GB 8978--1996）的一级标准。     

百色市生活垃圾卫生填埋场渗滤液处理工程设计

百色市生活垃圾卫生填埋场渗滤液处理采用了UASB/MBR/活性炭过滤组合工艺。介绍了工艺的设计参数、特点、运行情况和技术经济参数,结果表明,该工艺出水水质达到了《生活垃圾填埋污染控制标准》(GB16889—1997)的二级标准。     

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.     

MBR/DTRO/沸石生物滤池用于垃圾渗滤液处理工程

青岛市小涧西垃圾综合处理厂渗滤液处理扩容改造工程的设计规模为900 m3/d,渗滤液处理采用MBR/DTRO/曝气沸石生物滤池工艺。介绍了工程的设计情况,着重阐述了MBR系统、DTRO系统和曝气沸石生物滤池系统的设计参数、工艺流程及设计特点,为该工艺在垃圾渗滤液处理工程的应用提供参考。     

AF-MBBR技术处理高盐垃圾渗滤液的试验研究

采用厌氧生物滤池一好氧移动床工艺（AF—MBBR）处理垃圾卫生填埋场高盐渗滤液。结果表明：好氧移动床生物反应器对渗滤液中的氨氮具有非常高的去除率；但高盐量对AF—MBBR去除COD产生了明显的抑制作用，致使对COD的平均去除率仅为22％。经研究发现从垃圾渗滤液中分离、筛选出的专性耐盐菌，对高盐渗滤液生物处理系统具有显著的强化作用。     

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。     

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.     

我国城市垃圾渗滤液处理的技术及现状

在简要介绍我国城市垃圾处理的发展历史与现状后，针对国内应用最为广泛的城市垃圾卫生填埋场所产生的垃圾渗滤液处理技术进行了大量的调查、类比工作，并结合国内的多个工程实例总结出我国目前垃圾渗滤液处理的现状．     

混凝/化学氧化/曝气生物滤池深度处理垃圾渗滤液

随着垃圾渗滤液的老龄化,常规的生化处理已经不能使出水达标排放,需要进行深度处理。采用混凝／化学氧化／曝气生物滤池联合工艺深度处理垃圾渗滤液,进水COD为700mg／L左右,出水COD〈100mg／L,去除率〉85％,排放口水质达到《生活垃圾填埋污染控制标准》（GB16889--1997）一级标准。