Influence of organic matter on municipal solid waste incinerator bottom ash carbonation

The biodegradation of organic matter in municipal solid waste incinerator (MSWI) bottom ash was studied in order to investigate the interaction between the CO(2) produced by microbial respiration and bottom ash. Respiration tests were performed on bottom ash at different moisture contents in an incubator at 30 degrees C. O(2) consumption and CO(2) production were monitored and quantified. Leaching tests were carried out at the end of the experiments. Total organic carbon (TOC) leaching had decreased. Over a period of three weeks, pH decreased from 10.7 to 8.2 and bottom ash was considered to be fully carbonated. This showed that the organic matter found in bottom ash can provide a substrate for microbial activity. The CO(2) produced by microbial respiration was directly dissolved in bottom ash pore water in order to be mineralized in carbonate form. The origin of the carbon dioxide which induces maturation of bottom ash on weathering areas has never been really discussed and is often presumed to be atmospheric CO(2). However, biodegradation of organic matter could contribute for a large part to this phenomenon, depending on field-scale physico-chemical weathering conditions.     

Size and XAD fractionations of trihalomethane precursors from soils

Soil organic matter is an important source of allochthonous dissolved organic matter inputs to the Sacramento-San Joaquin Delta waterways, which is a drinking water source for 22 million people in California, USA. Knowledge of trihalomethane (THM) formation potential of soil-derived organic carbon is important for developing effective strategies for organic carbon removal in drinking water treatment. In this study, soil organic carbon was extracted with electrolytes (deionized H2O and Na- or Ca-based electrolytes) of electrical conductivity bracketing those found in Delta leaching and runoff conditions. The extracts were physically and chemically separated into different fractions: colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (<0.025 microm); hydrophobic acid (HPOA), transphilic acid, and hydrophilic acid. Two representative Delta soils, Rindge Muck (a peat soil) and Scribner Clay Loam (a mineral soil) were examined. Results showed that less than 2% of soil organic carbon was electrolyte-extractable and heterogeneous organic fractions with distinct THM reactivity existed. Regardless of soil and electrolytes, DOC and HPOA fractions were dominant in terms of total concentration and THMFP. The amounts of extractable organic carbon and THMFP were dependent on the cation and to a lesser extent on electrical conductivity of electrolytes. Along with our previous study on temperature and moisture effects on DOC production, we propose a conceptual model to describe the impacts of agricultural practices on DOC production in the Delta. DOC is mainly produced in the surface peat soils during the summer and is immobilized by accumulated salt in the soils. DOC is leached from soils to drainage ditches and finally to the Delta channels during winter salt leaching practices.     

Biodegradability of algal-derived organic matter in a large artificial lake by using stable isotope tracers

In order to understand the biodegradability of algal-derived organic matter, biodegradation experiments were conducted with ¹³C and ¹⁵N-labeled natural phytoplankton and periphytic algal populations in experimental conditions for 60 days. Qualitative changes in the dissolved organic matter were also determined using parallel factor analysis and the stable carbon isotopic composition of the hydrophobic dissolved organic matter through the experimental period. Although algal-derived organic matter is considered to be easily biodegradable, the initial amounts of total organic carbon newly produced by phytoplankton and periphytic algae remained approximately 16 and 44 % after 60 days, respectively, and about 22 and 43 % of newly produced particulate nitrogen remained. Further, the dissolved organic carbon derived from both algal populations increased significantly after 60 days. Although the dissolved organic matter gradually became refractory, the contributions of the algal-derived organic matter to the dissolved organic matter and hydrophobic dissolved organic matter increased. Our laboratory experimental results suggest that algal-derived organic matter produced by phytoplankton and periphytic algae could contribute significantly to the non-biodegradable organic matter through microbial transformations.     

pH对污水污泥中污染物浸出的影响

研究pH对污泥中污染物浸出的影响可以为投海过程中海洋水体酸碱性变化对污泥中污染物浸出的影响及其变化规律提供理论依据。为了得出不同pH值对污泥中污染物浸出的影响，采用CEN/TS 14429：2005浸出实验对上海5个污水处理厂脱水污泥中重金属、溶解性有机碳、溶解性硫化物和主要离子的浸出情况进行了研究，同时分别以超纯水和海水为浸提剂研究在相应pH范围内盐度对上述指标浸出的影响。结果表明，Zn、Cd、Pb和As在酸性和碱性条件下浸出量较高，在中性或接近中性条件下浸出量则最低，且海水中Zn和Cd的浸出量比超纯水中高；Cu在碱性条件下的浸出量明显比酸性条件高；在所研究的pH范围内，5个污泥样品中溶解性有机碳的浸出量均随pH的升高而增高；仅酸挥发性硫含量最高的S5在海水中有较明显的溶解性硫化物浸出；部分污泥样品中的氮在酸性纯水中有较高的浸出量，海水中浸出量较少；而无论海水或纯水中，磷在强酸和强碱条件下均有明显浸出。     

Intrinsic degradation of volatile fatty acids in laboratory-compacted clayey soil

Volatile fatty acids (VFAs) represent the major organic constituent of landfill leachate and provide the greatest potential for leachate induced organic contamination of groundwater (e.g. as represented by an increase in the concentration of dissolved organic carbon and chemical oxygen demand). Long-term diffusion tests were performed for laboratory-compacted clayey soil plugs exposed to continuous supply of synthetic leachate containing VFAs. Significant microbial activity developed upon exposure of the soil's indigenous microorganisms to these degradable contaminants. The growth of heterotrophic aerobic bacteria (HAB, which include facultative anaerobes), sulfate reducing bacteria (SRB) and methanogenic bacteria carrying out fermentation and mineralization of the VFAs became evident after 30-50 days of testing. The maximum microbial counts of (2-8) x 10(8) and (0.1-1) x 10(8) cfu/g for HAB and SRB were localized in the soil layer at the interface with the source of organic and inorganic nutrients. Regardless of this rapid growth in microbial population, the VFA consumption was small and measurable only after a lag of 140-180 days. It is considered that this lag of otherwise readily degradable organic compounds (such as VFAs) persisted due to a combination of the effects of a high initial concentration of these acids (2.4 g/l as dissolved organic carbon, DOC) applied to carbon starved soil microorganisms and the small pore size of the compacted clay. Once the significant amounts of gas were generated from fermentation, conditions developed for improved mass transport and exchange of the nutrients and bacteria and the outcome of the intrinsic degradation was more apparent. The breakdown of VFAs that followed after the lag was localized near the top of the soil and was characterized by a short half-life of 0.75-5 days for DOC (total VFAs as dissolved organic carbon).     

Influence of soil conditions on dissolved organic matter leached from forest and wetland soils: a controlled growth chamber study

This study investigated the effects of various soil conditions, including drying-rewetting, nitrogen deposition, and temperature rise, on the quantities and the composition of dissolved organic matter leached from forest and wetland soils. A set of forest and wetland soils with and without the nitrogen deposition were incubated in the growth chambers under three different temperatures. The moisture contents were kept constant, except for two-week drying intervals. Comparisons between the original and the treated samples revealed that drying-rewetting was a crucial environmental factor driving changes in the amount of dissolved organic carbon (DOC). The DOC was also notably increased by the nitrogen deposition to the dry forest soil and was affected by the temperature of the dry wetland soil. A parallel factor (PARAFAC) analysis identified three sub-fractions of the fluorescent dissolved organic matter (FDOM) from the fluorescence excitation–emission matrices (EEMs), and their compositions depended on drying-rewetting. The data as a whole, including the DOC and PARAFAC components and other optical indices, were possibly explained by the two main variables, which were closely related with the PARAFAC components and DOC based on principal component analysis (PCA). Our results suggested that the DOC and PARAFAC component information could provide a comprehensive interpretation of the changes in the soil-leached DOM in response to the different environmental conditions.     

Water extractable organic carbon in untreated and chemical treated biochars

Biochar, as a soil amendment, can increase concentrations of soil organic matter, especially water-extractable organic carbon (WEOC). This can affect the adsorption-desorption equilibrium between the dissolved solid phases in soil organic matter. Dissolved organic carbon (DOC) represents a small proportion of soil organic matter, but is of significant importance in the soil ecosystem due to its mobility and reactivity. Here, water extracts obtained from twelve non-herbaceous biochars (before, and after, chemical treatment with either H(3)PO(4) or KOH), were tested by Liquid Chromatography - Organic Carbon Detection (LC-OCD) to identify the effects of both pyrolysis conditions and chemical treatments on WEOC content. LC-OCD has the capacity to provide a fingerprint of WEOC, which allows analysis of the various fractions present. WEOC content was affected by both the pyrolysis temperature and the feedstock used. High mineral ash contents deriving from the feedstock can prompt thermochemical reactions of lignocelluloses to produce a relatively high WEOC content, which includes low molecular weight neutrals and humic acids as dominant components. A significant change in WEOC occurred during pyrolysis due to secondary reactions which resulted in a much lower WEOC in the high temperature biochars where fractions of low molecular weight acids and neutrals are dominant. Chemical treatments with H(3)PO(4) or KOH increased WEOC concentration, possibly by promoting hydrolysis reactions on biochar surfaces. These observations assist in assessing the contribution of biochar additions to the soil ecosystem and demonstrate the utility of LC-OCD in providing an understanding of how biochar additions to soil can alter DOC.     

Transformation of dissolved organic matter in a novel groundwater recharge system with reclaimed water

A novel process, enhanced direct injection-well recharge system (EnDir), can overcome the technical difficulties during the application of conventional surface spreading and has been developed to recharge groundwater with reclaimed water. In this study, removal and transformation of dissolved organic matter (DOM) in the system were investigated in laboratory-scale experiments. Results demonstrated that dissolved organic carbon and trihalomethane formation potential values could be reduced from 6.54 +/- 1.30 mg/L and 267.9 +/- 24.3 microg/L to 1.59 +/- 0.64 mg/L and 104.5 +/- 10.2 microg/L, respectively, as a result of DOM biodegradation in the aerobic short-term vadose soil treatment. Fluorescence spectra showed that aromatic protein-like substances and soluble microbial byproducts could be removed, to a great extent, in the soil system. Despite different removal efficiencies of DOM in different molecular weight fractions, the residual DOM was composed mainly of fulvic acid-like and humic acid-like substances, with molecular weights of 500 Da to 1 kDa.     

Transformation of effluent organic matter during subsurface wetland treatment in the Sonoran Desert

The fate of dissolved organic matter (DOM) during subsurface wetland treatment of wastewater effluent in a hot, semi-arid environment was examined. The study objectives were to (1) discern changes in the character of dissolved organics as consequence of wetland treatment (2) establish the nature of wetland-derived organic matter, and (3) investigate the impact of wetland treatment on the formation potential of trihalomethanes (THMs). Subsurface wetland treatment produced little change in DOM polarity (hydrophobic-hydrophilic) distribution. Biodegradation of labile effluent organic matter (EfOM) and internal loading of wetland-derived natural organic matter (NOM) together produced only minor changes in the distribution of carbon moieties in hydrophobic acid (HPO-A) and transphilic acid (TPI-A) isolates of wetland effluent. Aliphatic carbon decreased as a percentage of total carbon during wetland treatment. The ratio of atomic C:N in wetland-derived NOM suggests that its character is determined by microbial activity. Formation of THMs upon chlorination of HPO-A and TPI-A isolates increased as a consequence of wetland treatment. Wetland-derived NOM was more reactive in forming THMs and less biodegradable than EfOM. For both HPO-A and TPI-A fractions, relationships between biodegradability and THM formation potential were similar among EfOM and NOM isolates; the less biodegradable isolates exhibited greater THM formation potential.     

Carbon deposition in soil rhizosphere following amendments with compost and its soluble fractions, as evaluated by combined soil-plant rhizobox and reporter gene systems

We determined the organic carbon released by roots of maize plants (Zea mays L.) when grown in soils amended with compost and its soluble fractions. In rhizobox systems, soil and roots are separated from the soil of a lower compartment by a nylon membrane. Treatments are applied to the upper compartment, while in the lower compartment luminescent biosensors measure the bioavailable organic carbon released by roots (rhizodeposition). The rhizobox-plants systems were amended with a compost (COM), its water extract (TEA), the hydrophobic (HoDOM) and hydrophilic (HiDOM) fractions of the dissolved organic matter (DOM) extracted from the compost. After root development, the lower untreated compartments were sampled and sliced into thin layers. The bioavailable organic carbon in each layer was assessed with the lux-marked biosensor Pseudomonas fluorescens 10586 pUCD607, and compared with total organic carbon (TOC) analyses. The TOC values ranged between 8.4 and 9.6 g kg(-1) and did not show any significant differences between bulk and rhizosphere soil samples in any treatment. Conversely, the biosensor detected significant differences in available C compounds for rhizosphere soils amended with various organic materials. Concentrations of available organic compounds in the first 2 mm of soil rhizosphere were 1.69 (control), 1.09 (COM), 2.87 (HiDOM), 4.73 (HoDOM) and 2.14 (TEA)micromol Cg(-1) soil g(-1) roots. The applied rhizobox-biosensor integrated method was successful in detecting and quantifying effects of organic amendments on organic carbon released by maize plant roots. This approach may become important in assessing the carbon cycle in agricultural soils and soil-atmosphere compartments.     

A pilot and field investigation on mobility of PCDDs/PCDFs in landfill site with municipal solid waste incineration residue

A field investigation by boring was carried out in a landfill site primarily with municipal solid waste incineration residue. From the collected core samples, vertical profiles of homologous content of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs) in the landfill layer were traced and the behavior of PCDDs/PCDFs was examined. In addition, a pilot-scale study was conducted on the PCDDs/PCDFs leached from incineration fly ash and the treated one using large landfill simulation columns (lysimeters) and the leaching behavior of PCDDs/PCDFs was examined. As a result, it was found that the coexistence of dissolved coloring constituents (DCCs), which might be composed of constituents like dissolved humic matters having strong affinity for hydrophobic organic pollutants, could enhance the leachability of PCDDs/PCDFs, thus contributing to the vertical movement and leaching behavior of PCDDs/PCDFs in the landfill layers of the incineration residue. Moreover, it is highly probable that DCCs derive from the unburned carbon in the bottom ash mixed and buried with the fly ash containing a high content of PCDDs/PCDFs.     

Effects of water washing on removing organic residues in bottom ashes of municipal solid waste incinerators

Due to their potential toxicity and odourous nature, the residual organics in municipal solid waste incinerators are recently gaining attention as an important issue of resources recovery apart from their complex mixture of organic counterpart. Studies of the organic fractions in municipal solid waste incinerator residues have been limited. In this study, extended solid-phase extraction of the water-washed bottom ash and liquid-phase extraction of the washing water were carried out with regard to bottom ash samples from three mass-burning incinerators in Taipei County (Taiwan) during four consecutive seasons of year 2008-2009. Supercritical fluid extraction and Soxtec extraction techniques along with GC-MS were successfully used to characterize the residual organics in weathered and washed bottom ashes. Supercritical fluid extraction provided the quantification of aliphatics and aromatic compounds such as hexanoic acid and benzaldehyde, respectively. Soxtec extraction was useful for qualitative analysis of aromatic and aliphatic groups in the ashes and many of which were odourous and toxic compounds. By mixing one unit weight (g) bottom ash with two unit volume (mL) water for 15 min, total organic carbon in the bottom ash was greatly reduced (e.g., from 4.1 to 1.8 wt.%). Among the removed were foul odour-causing compounds such as pyridine and quinoline derivatives, while some aromatic compounds such as 4-hydroxybenzaldehyde and low-molecular-weight aliphatics such as hexanoic acid remained. The results here suggest that washing with water can be an effective pre-treatment step for removing odour-causing and environmental concerned organics.     

INFLUENCE OF SOIL ORGANIC MATTER ON THE LEACHING OF POLYCYCLIC AROMATIC HYDROCARBONS IN SOIL

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Aside from total organic carbon, the ratio among the different organic matter fractions [dissolved organic matter, fulvic acid (FA), humic acid (HA) and humin] can also affect the mobility of these hydrocarbons in soils. In this study the effect of the whole organic carbon pool has been compared with that of HA and FA on the translocation of four PAHs (biphenyl, fluorene, phenanthrene and pyrene) in soil columns. Oxidized and untreated soil columns with and without HA or FA, were prepared, spilled with hydrocarbons and leached with a 0.01 M CaCl₂ solution. The influence of HA and FA on PAH translocation was investigated through determinations of the PAH contents and total organic carbon (TOC) in the layers of the columns. All molecules were moved vertically by the percolating solutions, their concentrations decreasing with depths. The non-oxidized soil tended to retain more PAHs (96%) than the oxidized one (60%), confirming that organic matter plays an important role in controlling PAH leaching. The whole organic matter pool reduced the translocation of pollutants downward the profile. The addition of HA enhanced this behaviour, by increasing the PAH retention in the top layers (7.55 mg and 4.00 mg in the top two layers, respectively) while FA increased their mobility (only 2.30 and 2.90 mg of PAHs were found in the top layers) and favoured leaching. In fact, in the presence of HA alone, the higher amounts of PAHs retained at the surface and the good correlation (r²=0.936) between TOC and hydrocarbon distribution can be attributed to a parallel distribution of PAHs and HA, while in the presence of FA, the higher mobility of PAHs can be attributed to the high mobility of the humic material, as expected by its extensive hydrophilic characteristics.     

Influence of soil organic matter on the leaching of polycyclic aromatic hydrocarbons in soil

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Aside from total organic carbon, the ratio among the different organic matter fractions [dissolved organic matter, fulvic acid (FA), humic acid (HA) and humin] can also affect the mobility of these hydrocarbons in soils. In this study the effect of the whole organic carbon pool has been compared with that of HA and FA on the translocation of four PAHs (biphenyl, fluorene, phenanthrene and pyrene) in soil columns. Oxidized and untreated soil columns with and without HA or FA, were prepared, spilled with hydrocarbons and leached with a 0.01 M CaCl2 solution. The influence of HA and FA on PAH translocation was investigated through determinations of the PAH contents and total organic carbon (TOC) in the layers of the columns. All molecules were moved vertically by the percolating solutions, their concentrations decreasing with depths. The nonoxidized soil tended to retain more PAHs (96%) than the oxidized one (60%), confirming that organic matter plays an important role in controlling PAH leaching. The whole organic matter pool reduced the translocation of pollutants downward the profile. The addition of HA enhanced this behaviour by increasing the PAH retention in the top layers (7.55 mg and 4.00 mg in the top two layers, respectively) while FA increased their mobility (only 2.30 and 2.90 mg of PAHs were found in the top layers) and favoured leaching. In fact, in the presence of HA alone, the higher amounts of PAHs retained at the surface and the good correlation (r2=0.936) between TOC and hydrocarbon distribution can be attributed to a parallel distribution of PAHs and HA, while in the presence of FA, the higher mobility of PAHs can be attributed to the high mobility of the humic material, as expected by its extensive hydrophilic characteristics.     

Influence of dissolved humic substances on the leaching of MCPA in a soil column experiment

The influence of dissolved humic substances on the transport of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in a sandy soil with a low organic carbon content was studied in a column experiment. Soil columns were eluted with aqueous solutions containing different fractions of humic substances. More than 70% of the applied compound was found in the leachate in all sandy soil experiments, but distinct differences were obtained depending on the composition of the eluent. The addition of both humic and fulvic acids to the eluent affected the leaching behaviour of MCPA. While the presence of humic acids increased and accelerated the movement of MCPA in the investigated sandy soil, fulvic acids caused the opposite effect: increased retention was observed relative to the control. We concluded that a possible carrier transport or retention strongly depends on the composition of the dissolved organic matter. Thus, changes in the composition of dissolved organic matter may affect MCPA movement into deeper soil layers.     

Fate of nitrogen during composting of chicken litter

Chicken litter (a mixture of chicken manure, wood shavings, waste feed, and feathers) was composted in forced-aeration piles to understand the changes and losses of nitrogen (N) during composting. During the composting process, the chemical [different N fractions, organic matter (OM), organic carbon (C), and C:N ratio], physical, and microbial properties of the chicken litter were examined. Cumulative losses and mass balances of N and organic matter were also quantified to determine actual losses during composting. The changes in total N concentration of the chicken litter piles were essentially equal to those of the organic N. The inorganic N concentrations were low, and that organic N was the major nitrogenous constituent. The ammonium (NH(4)(+))-N concentration decreased dramatically during first 35 days of composting. However, the rapid decrease in NH(4)(+)-N during composting did not coincide with a rapid increase in (NO(3)(-)+NO(2)(-))-N concentration. The concentration of (NO(3)(-)+NO(2)(-))-N was very low (<0.5 g kg(-1)) at day 0, and this level remained unchanged during the first 35 days of composting suggesting that N was lost during composting. Losses of N in this composting process were governed mainly by volatilization of ammonia (NH(3)) as the pile temperatures were high and the pH values were above 7. The narrow C:N ratio (<20:1) have also contributed to losses of N in the chicken litter. The OM and total organic C mass decreased with composting time. About 42 kg of the organic C was converted to CO(2). On the other hand, 18 kg was lost during composting. This loss was more than half (59%) of the initial N mass of the piles. Such a finding demonstrates that composting reduced the value of the chicken litter as N fertilizer. However, the composted chicken contained a more humified (stabilized) OM compared with the uncomposted chicken litter, which would enhance its value as a soil conditioner.     

Relation between PAH and black carbon contents in size fractions of Norwegian harbor sediments

Distributions of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAH) were investigated in different particle size fractions for four Norwegian harbor sediments. The total PAH (16-EPA) concentrations ranged from 2 to 113 mg/kg dry weight with the greatest fraction of PAH mass in the sand fraction for three of the four sediments. TOC contents ranged from 0.84% to 14.2% and BC contents from 0.085% to 1.7%. This corresponds to organic carbon (OC = TOC - BC) contents in the range of 0.81-14% and BC:TOC ratios of 1.3-18.1%. PAH isomer ratios suggested that the PAH in all four sediments were of pyrogenic origin. Furthermore, stronger correlations between PAH versus BC (r2 = 0.85) than versus OC (r2 = 0.15) were found. For all size fractions and bulk sediments, the PAH-to-BC ratios for the total PAHs were on average 6+/-3 mg PAH/g BC. These results suggest that PAH distributions were dominated by the presence of BC, rather than OC. As sorption to BC is much stronger than sorption to OC, this may result in significantly lower dissolved concentrations of PAH than expected on the basis of organic carbon partitioning alone.     

铁盐和铝盐混凝对印染废水生化出水中溶解性有机污染物的去除特性

以三氯化铁和硫酸铝为混凝剂,印染废水二级生化出水为研究对象,并利用XAD-8/XAD-4吸附树脂联用技术将印染废水生化出水中溶解性有机物分为疏水酸、非酸疏水物质、弱疏水物质及亲水物质4类有机物,通过小试实验探讨了2种混凝剂对生化出水中各类溶解性有机物的去除效果及特点。实验结果表明,对于该印染废水的生化出水,溶解性有机物的主要成分是疏水性物质,以DOC表征时占总DOC的75%,其中疏水酸约占41%,疏水性物质也是引起色度的主要物质,所占比例以ADMI7.6表征时为89%,其中以非酸疏水物质的贡献最大,达到52%,并且非酸疏水物质中不饱和双键或芳香环有机物的含量较高。在三氯化铁和硫酸铝各自最佳的混凝条件下,均能够有效去除由疏水性物质（疏水酸和非酸疏水物质）引起的色度,但三氯化铁对弱疏水性物质以及亲水物质的去除率高于硫酸铝,这使得三氯化铁对印染废水生化出水中的溶解性有机物的去除效果优于硫酸铝。并且三氯化铁和硫酸铝混凝工艺均能明显降低生化出水的毒性。     

Batch test assessment of waste-to-energy combustion residues impacts on precipitate formation in landfill leachate collection systems

Disposal practices for bottom ash and fly ash from waste-to-energy (WTE) facilities include emplacement in ash monofills or co-disposal with municipal solid waste (MSW) and residues from water and wastewater treatment facilities. In some cases, WTE residues are used as daily cover in landfills that receive MSW. A recurring problem in many landfills is the development of calcium-based precipitates in leachate collection systems. Although MSW contains varying levels of calcium, WTE residues and treatment plant sludges have the potential to contribute concentrated sources of leachable minerals into landfill leachates. This study was conducted to evaluate the leachability of calcium and other minerals from residues generated by WTE combustion using residues obtained from three WTE facilities in Florida (two mass-burn and one refuse-derived fuel). Leaching potential was quantified as a function of contact time and liquid-to-solid ratios with batch tests and longer-term leaching tests using laboratory lysimeters to simulate an ash monofill containing fly ash and bottom ash. The leachate generated as a result of these tests had total dissolved solid (TDS) levels ranging from 5 to 320 mg TDS/g ash. Calcium was a major contributor to the TDS values, contributing from 20 to 105 g calcium/kg ash. Fly ash was a major contributor of leachable calcium. Precipitate formation in leachates from WTE combustion residues could be induced by adding mineral acids or through gas dissolution (carbon dioxide or air). Stabilization of residual calcium in fly ashes that are landfilled and/or the use of less leachable neutralization reagents during processing of acidic gases from WTE facilities could help to decrease the calcium levels in leachates and help to prevent precipitate formation in leachate collection systems.     

Comparison of sludge characteristics and PCR-DGGE based microbial diversity of nanofiltration and microfiltration membrane bioreactors

The objective of this study was to compare the sludge characteristics and microbial community diversity between the submerged nanofiltration membrane bioreactor (NF MBR) and microfiltration membrane bioreactor (MF MBR) treating the same municipal wastewater. The influence of a higher concentration of organic matter and salt was investigated. The results of water qualities showed that the dissolved organic carbon (DOC), total phosphorus (T-P) and salt concentrations of the supernatant in the NF MBR were three, four and two times as high as those in the MF MBR, respectively. The specific oxygen uptake rate of the NF MBR (2.9+/-0.4 mg O(2)g(-1)MLSSh(-1)) was lower than that of the MF MBR (4.3+/-1.1 mg O(2)g(-1)MLSS h(-1)). Result of extractable extracellular polymeric substances showed that the NF MBR sludge had more protein and less polysaccharide compared to the MF MBR sludge, whereas specific amount of total organic carbon were the same in both MBRs. The median floc diameters of the NF MBR and the MF MBR were 72+/-12 microm and 59+/-12 microm, respectively, which could be attributable to the different polysaccharide concentrations between both MBR mixed liquor. A higher concentration of materials (DOC, T-P and salt) in the bioreactor, determined by the high rejection rate of the NF membrane, did not significantly affect the microbial diversity under similar operation conditions.