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.     

Removal and transformation of recalcitrant organic matter from stabilized saline landfill leachates by coagulation-ozonation coupling processes

The Bordo Poniente sanitary landfill in Mexico City currently receives 11,500 ton/day of solid wastes. The landfill has been in operation since 1985, in what was formerly Texcoco Lake, now a dried-up lakebed. The physico-chemical characteristics of the leachate generated by this particular landfill are altered by the incorporation of freatic saline water present in the area. This paper reports the results from a study evaluating coagulation and ozonation as alternative processes for removing and transforming recalcitrant organic matter from stabilized saline landfill leachate. Coagulation with ferric sulfate was found to remove up to 67% of COD and 96% of leachate color. The remaining 33% COD was removed with ozone. Recalcitrant organic matter removal by ozonation is limited by the reaction kinetic due mainly to ozone's low reactivity with the organic compounds present in the leachates (amines, amides, alcohols, aliphatic compounds, and carboxylic acids). However, ozone contributes greatly to changing the recalcitrant characteristics of organic matter. Leachate biodegradability was found to be significantly enhanced through ozonation: BOD(5) values reach 265%, and the BOD(5)/COD ratio increases from 0.003 to 0.015. Infrared analysis of ozonated leachates shows that the main by-products of recalcitrant organic matter ozonation are an increase in the hydroxyl and carboxylic groups, and the presence of aldehydes groups.     

Degradation of industrial waste waters on Fe/C-fabrics. Optimization of the solution parameters during reactor operation

This study addresses the pre-treatment of toxic and recalcitrant compounds found in the waste waters arriving at a treating station for industrial effluents containing chlorinated aromatics and non-aromatic compounds, anilines, phenols, methyl-tert-butyl-ether (MTBE). By reducing the total organic carbon (TOC) of these waste waters the hydraulic load for the further bacterial processing in the secondary biological treatment is decreased. The TOC decrease and discoloration of the waste waters was observed only under light irradiation in the reactor by immobilized Fenton processes on Fe/C-fabrics but not in the dark. The energy of activation for the degradation of the waste waters was of 4.2 kcal/mol. The degradation of the waste waters was studied in the reactor as a function of (a) the amount of oxidant used (H2O2), (b) the recirculation rate, (c) the solution pH and (d) the applied temperature. With these parameters taken as input factors, statistical modeling allows one to estimate the most economic use of the oxidant and electrical energy to degrade these waste waters. The concentration of the most abundant organic pollutants during waste waters degradation was followed by gas chromatography/mass spectrometry (GC-MS). The ratio of the biological oxygen demand to the total organic carbon BOD5/TOC increased significantly due to the Fe/C-fabric catalyzed treatment from an initial value of 2.03 to 2.71 (2 h). The reactor results show that the recirculation rate has no influence on the TOC decrease of the treated waters but affects the BOD increase of these solutions.     

Evaluation of the treatment performance of a multistage ozone/hydrogen peroxide process by decomposition by-products

The performance of a multistage ozone/hydrogen peroxide (O3/H2O2) process was evaluated with respect to total organic carbon (TOC) removal of waste waters. An aqueous humic acid solution (5.2 mgC l(-1) as TOC) and a sand filtered secondary sewerage effluent (5.6mgC l(-1) as TOC) were used as model waste waters. Appropriate range of hydrogen peroxide (H2O2) dose at each stage depended upon the components of the tested solutions that changed as the process proceeded. Higher hydrogen peroxide dose was required at later stages in which low reactivity compounds with hydroxyl radical (HO*), low molecular fatty acids, were predominant. And, oxalic acid concentration related to H2O2 demand at later stages. This was assumed that the slow decomposition of oxalic acid was rate-determining step for TOC removal after its accumulation. Also, it is important to maintain dissolved ozone at low concentration for efficient TOC removal because rapid ozone consumption is required for the rapid formation of hydroxyl radical (HO*).     

Treatability evaluation of general organic matter. Matrix conception and its application for a regional water and waste water system

For the evaluation of the behaviors of general organic compounds in a regional water and waste water system and individual or combined water treatment processes, the authors have proposed to use some water quality indices in connection with scale grouping of organic compounds.The treatability of various types of treatment processes such as biological treatment, chemical coagulation and carbon adsorption were well evaluated with three comprehensive water quality indices such as TOC. TOC/E260 (absorbance at 260 nm) and E220 (absorbance at 220 nm) connected with the gel-chromatographic grouping after a water quality matrix conception.     

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.     

Organic indicators of groundwater pollution by a sanitary landfill

The organic composition of leachate from the Barcelona sanitary landfill is described. According to the low degree of stabilization of the disposed garbage the acid fraction accounts for 80–90% of the total organic extract. More than 50 individual organic components have been identified, indicating catabolic degradation of lipids (e.g. C₄–C₁₁ carboxylic acids), proteins (e.g. indole derivatives) and lignins (e.g. p-hydroxyphenyl derivatives) or simply compounds originally present in the refuse that have been washed out by percolating waters (nicotine, caffeine, phthalates).To obtain a monitoring system for the groundwater pollution originated by this landfill leachate, an analytical method is proposed based on the GC-ECD fingerprinting of groundwater acidic extracts after derivatization with PFB bromide. The chromatogram contains carboxylic and phenolic components and the profiles exhibited by waters from several test wells in the downstream edge of the landfill were indicative of the suspected leachate pollution.     

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.     

垃圾渗滤液及处理出水的有机物MW分布

以西安市江村沟生活垃圾卫生填埋场（15年填埋期）的渗滤液为研究对象，采用分子质量切割法测定了渗滤液原水及厌氧-好氧（AO）工艺出水有机物的分子质量分布及变化。结果表明：垃圾渗滤液原水中，78．8％以上的有机污染物分布在分子质量（MW）〈10ku的范围内；厌氧生物处理单元对有机物的去除率达63％，COD的降低主要发生在MW〈10ku的范围内，而后续的好氧工艺对有机物去除率的贡献仅为0．82％。所以在试验水质条件下，垃圾渗滤液经厌氧工艺处理后尚需进行后续处理，但不宜选用好氧生物处理工艺，考虑到有机物分子质量的分布特点，建议采用物理化学法作为后续处理工艺。     

Stability of organic matter in landfill leachates

Samples of grossly polluted groundwater and of leachate collected from wells or underdrains near solid waste disposal sites were subjected to extensive organic analyses. The soluble organics were concentrated, separated and characterized by membrane ultrafiltration, gelpermeation chromatography and analysis for functional groups and specific organics. Free volatile fatty acids represented the largest group of organics, and this fraction showed a rapid decrease with increasing age of the fill. The most stable group of organics with increasing age was a fulvic-like material with a relatively high carboxyl and aromatic hydroxyl group density. Increasing stability was further noted for carbohydrates, hydrolyzable amino acids and aromatic hydroxyl compounds in that order. Only leachate from a recently generating fill can be treated successfully by microbial processes because of its large biodegradable organic content; leachate from stabilized landfills is best treated by physical-chemical processes.     

Study of catalyzed ozonation for advanced treatment of pulp and paper mill effluents

Ozonation and catalytic ozonation (TOCCATA process) were used as tertiary treatments of wastewaters from three different pulp and paper mills. Laboratory batch experiments were conducted to assess the efficiency of each oxidation system for removal of organic matter. The investigations measured ozone consumption rate, variations in chemical oxygen demand (COD), total organic carbon (TOC), suspended solids (SS) and molecular weight distribution with contact time. For conventional ozonation, ozone consumption rate was dependent on the nature of the effluent. Organic matter elimination occurred both by oxidation and precipitation. Precipitation played a major role on TOC removal varying with the effluent, and was responsible for production of high final SS concentrations. However, the effluent type did not affect the ozone consumption rate for TOCCATA-catalyzed reactions. Using TOCCATA, it was shown that organic matter was removed through steady conversion of organic carbon to carbon dioxide. Finally the two oxidation systems were compared with respect to their impact on molecular weight distribution. A total removal of the two initial fractions of compounds (high and low molecular weights) was observed with two effluents. With the third effluent, only the initial fraction of low molecular weight compounds was removed by the two oxidizing systems. The results showed that ozonation and TOCCATA-catalyzed ozonation could achieve removals of COD of 36-76%. Depending on the effluent type, the amount of ozone consumed per gram of COD removed was lower for conventional or for catalytic ozonation.     

Assessment of water quality using principal component analysis: A case study of the river Ganges

In present study multivariate statistical approaches are used; interpretation of large and complex data matrix obtained during a monitoring of the river Ganges in Varanasi. 16 physicochemical and bacteriological variables have been analyzed in water samples collected every three months for two years from six sampling sites where river affected by man made and seasonal influences. The dataset was treated using Principal Component Analysis (PCA) to extract the parameters that are most important in assessing variation in water quality. Four Principal Factor were identified as responsible for the data structure explaining 90% of the total variance of the dataset, in which nutrient factor (39.2%), sewage and feacal contamination (29.3%), physicochemical sources of variability (6.2%) and waste water pollution from industrial and organic load (5.8%) that represents total variance of water quality in the Ganges River. The present study suggests that PCA techniques are useful tools for identification of important surface water quality parameters.     

Complexation characteristics of sanitary landfill leachates

The complexation of cadmium by organic components of sanitary landfill leachates was investigated using ion-exchange and specific ion electrode methods. Four Southern Ontario leachates were all found to be capable of complexing cadmium, to varying degrees. The complexing ability associated with certain molecular weight fractions was studied. In one leachate, complexation was mainly attributed to low (<500) molecular weight compounds. Their behaviour was consistent with that of simple carboxylic acids. In another leachate, high (> 10,000) molecular weight compounds contributed significantly to complexation. Their behaviour suggested that they might contain phenolic hydroxyl groups having a stability constant towards cadmium of the order of 10⁵. It was concluded that the role of complexation in determining the fate of metals in sanitary landfill leachates depended upon several factors whose importance had not yet been adequately investigated or reported in the literature.     

Integrated ozone and biotreatment of pulp mill effluent and changes in biodegradability and molecular weight distribution of organic compounds

The overall effectiveness of integrating ozonation with biological treatment on the biodegradability enhancement and recalcitrant organic matter (ROM) removal from pulp mill alkaline bleach plant effluent was investigated. Ozonation was performed in a semi-batch bubble column reactor at pH of 11 and 4.5. Batch biological treatment was conducted in shake flasks. Samples obtained during the treatments were monitored for BOD₅, COD, TOC, and molecular weight distribution. At an ozone dosage of 0.7-0.8 mg O₃/mL wastewater, integrated treatment showed about 30% higher TOC mineralization compared to individual ozonation or biotreatment. Ozone treatment enhanced the biodegradability of the effluent (monitored as 21% COD reduction and 13% BOD₅ enhancement), allowing for a higher removal of pollutants. The conversion of high molecular weight (HMW) to low molecular weight (LMW) compounds was an important factor in the overall biodegradability enhancement of the alkaline effluent. The overall biodegradability of the LMW compounds did not change over the course of ozonation, but it increased from 5% to 50% (measured as COD removal) for the HMW portion. Ozonation at pH of 11 was more effective than that at pH of 4.5 in terms of generating more biodegradable compounds.     

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.     

UASB+A/O+MBR+两级RO处理垃圾焚烧发电厂渗滤液

垃圾焚烧发电厂产生的渗滤液具有污染物成分复杂、水质水量波动大、有机物和氨氮浓度高、处理难度大的特点,以国内某垃圾焚烧发电厂450 m³/d的渗滤液处理项目为例,针对垃圾焚烧发电厂渗滤液的特点,采用UASB+A/O+MBR+两级RO组合处理工艺,确保处理后出水稳定达到《生活垃圾填埋场污染控制标准》(GB 16889—2008)。RO浓缩液采用高压管网式反渗透(STRO)减量化处理后回喷焚烧炉。近两年的工程运行结果表明,该组合工艺具有耐冲击负荷能力强、处理出水稳定达标、占地省等优点,对COD、BOD5、NH3-N、TN的平均去除率分别为99.8%、99.9%、99.0%、98.7%,渗滤液处理系统运行成本为47.05元/m³。     

Phthalic acid esters in dissolved fractions of landfill leachates

The distribution of phthalic acid esters (PAEs) (including diisobutylphthalate (DIBP), di-n-butylphthalate (DnBP) and bis(2-ethyl)hexylphthalate (DEHP)) in dissolved organic matter (DOM) fractions of leachates from sanitary or bioreactor landfills was evaluated. The leachate DOM was fractionated into humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fractions. Measurements showed that the PAEs were bound mostly to the HA fraction in leachate, regardless of their landfill age or the presence of leachate recirculation. The PAEs affinity for HA and FA differed considerably relative to the sorption coefficients reported for model compounds. Molecular weight of DOM correlated with PAEs partition in collected leachate samples fractions while aromaticity was a poor predictor. Based on the presence of phenolic, carboxyl or amide groups in DOM fractions, hydrogen bonding is likely to be involved in interactions between PAEs and leachate DOM. The peptide groups, particularly presented in HA fracion, might explain the strong affinity of PAEs for HA. The fluorescence excitation emission matrix contour plots showed that the HyI fractions shared certain similarities with humic substances in terms of molecular structure, which may be one reason why PAEs exhibited a clear sorption to the HyI fractions.     

Comparing microfiltration-reverse osmosis and soil-aquifer treatment for indirect potable reuse of water

Microfiltration (MF) followed by reverse osmosis (RO) and soil-aquifer treatment (SAT) are the two principal technologies considered for indirect potable reuse of wastewater. This study, conducted at the Northwest Water Reclamation Plant, Mesa (Arizona), evaluated MF/RO and SAT (>6 months residence time) treated tertiary effluent with respect to organics removal. Effluent organic matter was characterized as total organic carbon (TOC), by UV absorbance (UVA), solid-state carbon-13 nuclear magnetic resonance spectroscopy, and size exclusion chromatography. Several trace organic micropollutants, including EDTA, NTA, and alkylphenolethoxylate residues, were analyzed by GC/MS. The study revealed that final TOC concentrations of MF/RO and SAT are 0.3 and 1.0 mgl(-1), respectively. Based on the characterization techniques used, the character of bulk organics present in final SAT water resembles the character of natural organic matter present in drinking water. Depending on the molecular weight cut-off, RO membranes can efficiently reject high molecular weight organic matter (characterized as humic and fulvic acids). However, approximately 40-50 percent of the remaining TOC in permeates consists of low molecular weight acids and neutrals representing a molecular weight range of approximately 500Da and less. In the SAT treated effluent, EDTA and APECs were removed to approximately 4.3 and 0.54 microg/l, respectively, but were below the detection limit in the MF/RO treated effluent.     

Equilibrium and intra-particle diffusion of stabilized landfill leachate onto micro- and meso-porous activated carbon

Stabilized landfill leachate has previously been treated with activated carbon (AC); however, information on the selectivity of AC depending upon the pore size is minimal. Isotherm and kinetic experiments were conducted using three commercially available AC products, one micro-porous and two meso-porous. Equilibrium adsorption and intra-particle diffusion of organic matter from stabilized leachate was studied. Isotherm experimental data were fitted to Langmuir, Freundlich, and Redlich-Peterson isotherm models in non-linear forms. Of the three isotherm models, the Redlich-Peterson model provided the best fit to the experimental data and showed a similar organic matter adsorption capacity (approximately 0.2 g total organic carbon (TOC) g⁻¹ AC) for both micro-porous and meso-porous AC. The organic matter effective intra-particle diffusion coefficients (D_e) in both AC types were on the order of 10⁻¹⁰ m² s⁻¹ for AC particle sizes greater than 0.5 mm. Meso-porous ACs showed slightly higher D_e compared to micro-porous AC. Rapid small-scale tests showed a maximum of 80% TOC removal from leachate by each AC investigated. Fluorescence spectroscopy showed a preferential adsorption of fulvic-type organic matter with an increase in empty bed contact time by each AC.     

Assessment of organic chlorinated compound removal from aqueous matrices by adsorption on activated carbon

Adsorption on activated carbon is currently the most frequently used technology to remove organic chlorinated pollutants from wastewaters. The present study examines the ability of five commercially available types of activated carbon to remove organic chlorinated compounds from the effluent of a chemical plant. The various types were tested on the basis of Freundlich adsorption isotherms for 14 pure organic chlorinated compounds, of molecular weight ranging from that of dichloromethane (MW=84.93 gmol(-1)) to hexachlorobenzene (MW=284.78 gmol(-1)). The best was selected and used in a laboratory fixed-bed column to assess its removal efficiency with respect to the tested organic chlorinated compounds. Removal efficiency was always higher than 90%. These results provide information necessary to optimize scale-up from the pilot plant to the real one.