Treatment of landfill leachates

Landfill leachate, which resembles concentrated mixed industrial waste water, threatens national groundwater supplies. Several processes drawn from industrial water treatment have been considered for renovating landfill leachate: biodegradation, chemical and thermal degradation, adsorption, reverse osmosis, and coagulation/precipitation. Since transporting leachate off-site entails considerable risk and expense, these technologies must be evaluated for their applicability to on-site treatment.Biodegradation has the greatest potential for removing the varied organic compounds found in leachate streams due to its flexibility and relatively wide application in waste-water treatment. Use of combinations of biological processes, such as sequential aerobic and anaerobic treatment, or of biological and physical processes, such as biologically activated carbon, may improve performance. Alternative chemical or thermal destruction processes are more energy intensive and require finer control than biological processes.Coagulation/precipitation, adsorption, and membrane processes have been studied for treating leachates to remove organic compounds, heavy metals, entrained oil, and colloidal material. Because these processes partition the leachate and, thus, concentrate toxic substances, further treatment of their residues is necessary. They are particularly suited for pretreating influent to a biological process or for polishing a biological effluent.Much work remains in applying these treatment processes to actual landfill leachates. Design of leachate treatment processes must be tailored to the site and will depend on the quantity and characteristics of treatment residues allowed under the prevailing regulatory environment. The variability of landfill leachates both from site to site and temporally within a site makes leachate treatment a challenging problem.     

Detoxification of Tunisian landfill leachates by selected fungi

Young landfill leachates (LFL) collected from Djebel Chekir (Tunisia) discharge area were found to be highly loaded with organic matter, ammonia, salts, heavy metals, phenols and hydrocarbons. Despite the possibility of their biodegradability, they represent a threat to the environment and show some resistance to conventional wastewater treatment processes. For these reasons, this study attempted to develop a biological process for the treatment of LFL using selected strains of Trametes trogii, Phanerochaete chrysosporium, Lentinus tigrinus and Aspergillus niger. Experiments were undertaken at different concentrations of the effluent up to 100%. COD removal efficiencies for P. chrysosporium, T. trogii and L. tigrinus were of 68, 79 and 90%, respectively, when LFL underwent a two-fold dilution. COD abatements were accompanied with an important enzyme secretion and a high reduction in the toxicity, expressed as percent bioluminescence inhibition (%BI < 20%). Above 50% of LFL, the effluent was toxic to these strains and caused growth inhibition indicating the sensitivity of these strains to concentrated LFL. Comparatively to the other tested strains, A. niger showed to tolerate raw LFL since it grew at 100% of LFL. However, this strain is inefficient in removing phenols and hydrocarbons. Consequently, toxicity abatement was very low (%BI > 70%).     

Use of advanced oxidation processes to improve the biodegradability of mature landfill leachates

Two advanced oxidative processes (Fe2+/H2O2/UV and H2O2/UV systems) were used for the pre-treatment of mature landfill leachate with the objective of improving its overall biodegradability, evaluated in terms of BOD5/COD ratio, up to a value compatible with biological treatment. At optimized experimental conditions (2000 mgL(-1) of H2O2 and 10 mgL(-1) of Fe2+ for the photo-Fenton system, and 3000 mgL(-1) of H2O2 for the H2O2/UV system), both methods showed suitability for partial removal of chemical oxygen demand (COD), total organic carbon (TOC) and color. The biodegradability was significantly improved (BOD5/COD from 0.13 to 0.37 or 0.42) which allowed an almost total removal of COD and color by a sequential activated sludge process. In addition, gel permeation chromatography (GPC) has showed a substantial agreement on the cleavage of large organic compound into smaller ones.     

Multivariate approach to the Fenton process for the treatment of landfill leachate

Fenton process has been widely used to treat landfill leachate. The "design of experiments" methodology was used to study the main variables affecting the Fenton process as well as their most relevant interactions. Results of two-level-factorial-design indicated that pH, COD, and the interaction of pH and COD gave negative effects, but Fe(II) dosage and H(2)O(2)/Fe(II) mole ratio showed positive effect, respectively. The quadratic model was derived based on the results of both two-level-factorial-design experiment and further runs of star points and center points. The response surface plots of quadratic model were obtained accordingly and the optimal conditions were derived from the quadratic model.     

High-energy oxidation process: an efficient alternative for wastewater organic contaminants removal

Radiation processing using electron beam (EB) has shown promising results in the treatment of organic water pollution. EB radiation is an additive-free process using short-lived reactive species, formed by the radiolysis of water, to carry out decomposition of organic pollutants. Studies have demonstrated the effectiveness of irradiation, alone or in combination with other processes, for the decomposition of refractory organic compounds in aqueous solutions, and in the removal or inactivation of microorganisms and parasites. Irradiation processes have been known for decades; however, their general application in the water field was impaired by the cumbersome and complexity of past existing technology. The technological picture is changing significantly in the last few years, with instrumentation that is significantly cheaper, easier and safer to use. Application of EB processing in the water sector promises a cost-efficient, by-products-less, and ultimately effective technology taking advantage of characteristics not available in others: total absence of chemical additives; capability of generating simultaneously both strong oxidants and reducers (hydroxyl radicals, hydrogen atoms, solvated electrons and others); capability of processing aqueous, colloidal, and opaque solutions; compatibility with existing technologies. This paper examines some of the few existing applications of this technology, which is still unknown, or poorly familiar, to most water professionals and researchers.     

Optimization of Fenton process for the treatment of landfill leachate

The treatment of landfill leachate by Fenton process was carried out in a batch reactor. The effect of operating conditions such as reaction time, pH, H2O2 to Fe(II) molar ratio, Fenton's reagent dosage, initial COD strength, feeding mode, the type of polymer, and temperature on the efficacy of Fenton process was investigated. It is demonstrated that Fenton's reagent can effectively degrade leachate organics. Fenton process was so fast that it was complete in 30 min. The oxidation of organic materials in the leachate was pH dependent and the optimal pH was 2.5. The favorable H2O2 to Fe(II) molar ratio was 1.5, and organic removal increased as dosage increased at the favorable H2O2 to Fe(II) molar ratio. The efficacy of Fenton process was improved by adding Fenton's reagent in multiple steps than that in a single step. Furthermore, the stepwise addition of both hydrogen peroxide and ferrous iron was more effective than that of hydrogen peroxide only. Sludge settling characteristics were much improved with the addition of the proper polymer. Temperature gave a positive effect on organic removal.     

Adsorption of landfill leachates onto activated carbon. Equilibrium and kinetics

The adsorption of stabilized leachates generated in a municipal landfill onto three commercial activated carbons has been investigated. Norit 0.8, Chemviron AQ40 and Picacarb 1240 have been used as adsorbents. Equilibrium experiments have been conducted to obtain the experimental isotherm profiles. Isotherms have been plotted based on the adsorption of general parameters, for instance chemical oxygen demand, total carbon, absorption at 410 nm and absorption at 254 nm. Different literature models and error functions have been used to adequately fit the experimental data. As a rule of thumb, three-parameter models do adjust experimental results better than two-parameter models. Norit 0.8 shows better adsorption characteristics than the rest of activated carbons, both in terms of contaminant level reduction of per unit mass of absorbent and in terms of the process kinetics.     

Pervaporation as an alternative to headspace

The use of pervaporation as an alternative to headspace is proposed. The analytical system involves the speciation of organomercury compounds in solid samples using pervaporation, which has been coupled for the first time to gas chromatography. The speciation of mercury as Me(2)Hg, Et(2)Hg, and MeHgCl has been carried out without any derivatization of the analytes, which, after separation from the solid matrix, are preconcentrated on a Tenax minicolumn prior to desorption and chromatographic separation on a semicapillary column (HP-1) prior to atomic fluorescence detection. No column degradation was observed. Linear ranges and detection limits slightly better than those obtained by headspace GC were observed for mercury species in solid samples. Excellent recoveries (between 95 and 107%) for mercury species added to complex solid samples were obtained by this extremely simple and easily automated setup.     

一种快速可变剪接模式搜索算法的研究

提出了一种快速可变剪接模式搜索算法--ASDT.该算法通过计算cDNA与基因序列的联配结构来寻找基因的可变剪接模式.ASDT计算中引入已知剪接信息,并采用增强后缀数组、块联配延伸和K最大参考路径等技术和方法来提高计算速度.与国外的BLAT软件的比较结果显示,在达到相同计算精度的前提下,ASDT的搜索速度是BLAT的2到16倍.根据ASDT算法开发的工具可以在以下网址获得: http://www.scbit.org/ASDT/.     

MBR-NF工艺在垃圾渗滤液处理中的应用

报告了采用膜生物反应器（MBR）-纳滤（NF）组合工艺处理高浓度垃圾渗滤液,该工艺充分发挥了MBR和NF单元的功能互补性,运行实践表明,对COD和氨氮的平均去除率均达99.5%,出水满足《生活垃圾填埋污染控制标准》的一级标准,运行费用（含折旧）为19.55元/m3,具有较明显的技术经济优势。     

MBR NF工艺在垃圾渗滤液处理中的应用

报告了采用膜生物反应器（MBR）－纳滤（NF）组合工艺处理高浓度垃圾渗滤液,该工艺充分发挥了MBR和NF单元的功能互补性,运行实践表明,对COD和氨氮的平均去除率均达99.5 %,出水满足《生活垃圾填埋污染控制标准》的一级标准,运行费用（含折旧）为19.55元/m3,具有较明显的技术经济优势。     

The traffic safety impact of alcohol abuse treatment as an alternative to mandated licensing controls

Driving records were compared for drivers who were convicted of multiple driving-under-the-influence offenses (DUI). Two groups of drivers were identified in four demonstration counties which offered a 12-month alcohol abuse treatment program as an alternative to mandatory license suspension or revocation. The first group participated in the program and thereby retained their driving privilege while the second did not participate thus receiving the mandated licensing action. Since legislation prevented drivers from being randomly assigned to treatment or licensing action, a third group of suspended or revoked drivers were identified in four systematically selected comparison counties. Analysis of covariance and survival rate analytical procedures were employed to analyze the driving records 12 months subsequent to their entrance into the alcohol abuse treatment program or receipt of the licensing action. In general it was found that the multiple offender alcohol abuse treatment program, during the period of treatment, demonstrated no advantages over mandatory licensing controls.     

Coagulation-flocculation as a pretreatment process at a landfill leachate nitrification-denitrification plant

The main aim of this research work was to study the possible application of coagulation-flocculation as a pretreatment process for young landfill leachate in order to prevent fouling in the ultrafiltration membranes employed for the separation of biomass in the biological plant. Jar-test experiments were carried out to determine the optimum conditions for the removal of turbidity colour and organic matter. The coagulants ferric chloride, aluminium sulphate and aluminium polychloride (PAX) were tested, along with different types of flocculants (anionic and cationic polyelectrolytes). Optimum pH values were around 4.0 and 6.0 for ferric chloride and aluminium sulphate, respectively. It was not necessary to alter the pH of the leachate when using PAX, as the optimum value was found to be similar to that of the leachate (around 8.3). Optimum dosages were 0.4 g Fe(3+)/L, 0.8 g Al(3+)/L and 4 g PAX/L, although there was not much difference in the results for lower dosage of PAX. The best results were found with this coagulant, obtaining 98% turbidity removal, 91% colour removal and 26% COD removal. When flocculants were also added, the results were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained. The volume of the sludge generated represents around 4.5-5.0% when using ferric chloride or aluminium sulphate, and 15% when using aluminium polychloride.     

The interprocess NIR sampling as an alternative approach to multivariate statistical process control for identifying sources of product-quality variability

We are presenting a new approach of identifying sources of variability within a manufacturing process by NIR measurements of samples of intermediate material after each consecutive unit operation (interprocess NIR sampling technique). In addition, we summarize the development of a multivariate statistical process control (MSPC) model for the production of enteric-coated pellet product of the proton-pump inhibitor class. By developing provisional NIR calibration models, the identification of critical process points yields comparable results to the established MSPC modeling procedure. Both approaches are shown to lead to the same conclusion, identifying parameters of extrusion/spheronization and characteristics of lactose that have the greatest influence on the end-product’s enteric coating performance. The proposed approach enables quicker and easier identification of variability sources during manufacturing process, especially in cases when historical process data is not straightforwardly available. In the presented case the changes of lactose characteristics are influencing the performance of the extrusion/spheronization process step. The pellet cores produced by using one (considered as less suitable) lactose source were on average larger and more fragile, leading to consequent breakage of the cores during subsequent fluid bed operations. These results were confirmed by additional experimental analyses illuminating the underlying mechanism of fracture of oblong pellets during the pellet coating process leading to compromised film coating.     

Hardenability: an alternative to the use of grain size as calculation parameter

Several austenizing treatments carried out on different types of quench-temper and carburizing steels confirm the relationship which exists between austenitic grain size and the treatment time and temperature parameters. A relationship has been established between the three variables, a regression plane linking them being obtained. A mathematical model is proposed which permits the treatment parameterP to be calculated theoretically, and making it possible to obtain from only chemical composition and austenizing temperature the data required to obtain the Jominy curve. The experimental results for diverse steels and the resulting structures agree with those obtained theoretically. A calculation programme has been developed in accordance with the model we present for both manufacture and quality control. Its industrial use has been widely verified.     

A semi-quantitative approach to risk analysis, as an alternative to QRAs

In quantitative risk analysis (QRA) risk is quantified using probabilities and expected values, for example expressed by PLL values, FAR values, IR values and F–N curves. The calculations are tedious and include a strong element of arbitrariness. The value added by the quantification can certainly be questioned. In this paper, we argue that such analyses often are better replaced by semi-quantitative analyses, highlighting assessments of hazards and barriers, risk influencing factors (RIFs) and safety improvement measures. The assessments will be based on supporting information produced by risk analysts, including hard data and analyses of failure causes and mechanisms, barrier performance, scenario development, etc. The approach acknowledges that risk cannot be adequately described and evaluated simply by reference to summarising probabilities and expected values. There is a need for seeing beyond the standard probabilistic risk results of a QRA. Key aspects to include are related to uncertainties in phenomena and processes, and manageability factors. Such aspects are often ignored in standard QRAs.     

Characterization of adsorption removal of hydrogen sulfide by waste biocover soil, an alternative landfill cover

Landfill is an important anthropogenic source of odorous gases. In this work, the adsorption characteristics of H(2)S on waste biocover soil, an alternative landfill cover, were investigated. The results showed that the adsorption capacity of H(2)S increased with the reduction of particle size, the increase of pH value and water content of waste biocover soil. The optimal composition of waste biocover soil, in regard to operation cost and H(2)S removal performance, was original pH value, water content of 40% (w/w) and particle size of ≤4 mm. A net increase was observed in the adsorption capacity of H(2)S with temperatures in the range of 4-35°C. The adsorption capacity of H(2)S on waste biocover soil with optimal composition reached the maximum value of 60±1 mg/kg at oxygen concentration of 10% (v/v). When H(2)S concentration was about 5% (v/v), the adsorption capacity was near saturation, maintaining at 383±40 mg/kg. Among the four experimental soils, the highest adsorption capacity of H(2)S was observed on waste biocover soil, followed by landfill cover soil, mulberry soil, and sand soil, which was only 9.8% of that of waste biocover soil.     

Feasibility of an in vitro microbiological model as an alternative to the rabbit eye model.

Ocular inserts of gentamicin sulfate with polyvinyl alcohol (PVA) 1.5%, 2.0%, and 2.5% and a combination of methyl cellulose 2% and Eudragit NE 30D 30%, 35%, and 40% w/w of methyl cellulose were fabricated by a casting technique. The inserts were sterilized by gamma radiation at 25 kGy and tested for sterility. The microbiological efficacy of the ocular inserts against Staphylococcus aureus ATCC 6538P and Pseudomonas aeruginosa NCIM 2200 was evaluated by developing an in vitro microbiological model and an in vivo noninvasive rabbit eye model. Parameters of the in vitro microbiological model were varied, and the results correlated with a noninvasive rabbit eye model. The in vitro model proved to be a viable alternative to the rabbit eye model in evaluating the microbiological efficacy of gentamicin sulfate ocular inserts.     

Grape bagasse as an alternative natural adsorbent of cadmium and lead for effluent treatment

This work investigated the utilization of grape bagasse as an alternative natural adsorbent to remove Cd(II) and Pb(II) ions from laboratory effluent. X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, nuclear magnetic resonance, thermogravimetric analyses, surface analysis, porosity and porous size were used for characterization of the material. Batch experiments were carried out to evaluate the adsorption capacity of the material. Parameters such as adsorption pH and contact time were optimized for the maximum accumulation onto the solid surface. The pH values found were 7 and 3 for Cd(II) and Pb(II), respectively, and contact time was 5 min for both metals. Adsorption capacity for metals were calculated from adsorption isotherms by applying the Langmüir model and found to be 0.774 and 0.428 mmol g(-1) for Cd(II) and Pb(II), respectively. The competition between metals for the same adsorption sites on grape bagasse was also evaluated, showing an increasing affinity for Pb(II) over Cd(II) when only these metals are present. The potential of this material was demonstrated by efficient metal removal from laboratory effluent using a glass column. The results indicate that the referred material could be employed as adsorbent for effluent treatment, especially due to its easy acquisition and low cost as well as the fast adsorption involved.