Multi-response optimization of Fenton process for applicability assessment in landfill leachate treatment

Fenton process, as a pretreatment method, was found to be effective in the primary treatment of mature/medium landfill leachate. However, the main problem of the process is the large amount of produced sludge that requires an accurate feasibility evaluation for operational applications. In this study, the response surface methodology was applied for the modeling and optimization of Fenton process in three target responses, (1) overall COD removal, (2) sludge to iron ratio (SIR) and (3) organics removal to sludge ratio (ORSR), where the latter two were new self-defined responses for prediction of sludge generation and applicability assessment of the process, respectively. The effective variables included the initial pH, [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage. According to the statistical analysis, all the proposed models were adequate (with adjusted R² of 0.9116–0.9512) and had considerable predictive capability (with prediction R² up to 0.9092 and appropriate adequate precision). It was found that all the variables had significant effects on the responses, specifically by their observed role in dominant oxidation mechanism. The optimum operational conditions obtained by overlay plot, were found to be initial pH of 5.7, [H₂O₂]/[Fe²⁺] ratio of 17.72 and [Fe²⁺] of 195 mM, which led to 69% COD removal, 2.4 (l sludge/consumed mole Fe²⁺) of SIR and 16.5 (gCOD removed/l produced sludge) for ORSR in verification test, in accordance with models-predicted values. Finally, it was observed that [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage had significant influence on COD removal, while Fe²⁺ dosage and [H₂O₂]/[Fe²⁺] ratio had remarkable effects on SIR and ORSR responses, respectively.     

Photocatalytic Degradation of Poly(Vinyl Alcohol) on Pt/TiO<Subscript>2</Subscript> with Fenton Reagent

In this research Fenton reagent (Fe²⁺/H₂O₂) was investigated as oxidants to degrade poly (vinyl alcohol) (PVA). The role of nano-TiO₂ photocatalyst was discussed as an additive in Fenton reagent (Fe²⁺/H₂O₂). Pt/TiO₂ composites were also synthesized by photo-reaction to be used as additive in Fenton reagent. The rapid degradation of PVA was obtained when Pt/TiO₂ composites served as photocatalyst. The different photocatalytic efficiency of Pt/TiO₂- Fenton reagent (Fe²⁺/H₂O₂) was studied compared with TiO₂- Fenton reagent (Fe²⁺/H₂O₂) during the degradation of PVA.     

Synthesis of a block copolymer of poly(3-hydroxybutyrate) and poly(ethylene glycol) and its application to biodegradable polymer blends

A block copolymer {P[(R,S)-HB-b-EG]} of atactic poly[(R,S)-3-hydroxybutyrate] {P[(R,S)-HB]} and poly(ethylene glycol) (PEG) was prepared by the ring-opening polymerization of -butyrolactone in the presence of a macroinitiator (PEG/ZnEt₂/H₂O) which had been produced by the reaction of ,-dihydroxy PEG ( _n=3000) with ZnEt₂/H₂O (1/0.6) catalyst. The block copolymer ( _n=10,500, _w/ _n=1.2) was an A-B-A triblock copolymer comprising atactic P[(R,S)-HB] (A) and PEG (B) segments. The miscibility, physical properties, and biodegradability of binary blends of microbial poly[(R)-3-hydroxybutyrate] {P[(R)-HB]} with the block copolymer P[(R,S)-HB-b-EG] has been studied. The glass-transition temperature (T _g) data showed that the P[(R)-HB]/P[(R,S)-HB-b-EG] blend was miscible in the amorphous state. The P[(R)-HB] film became flexible and tough by means of blending with P[(R,S)-HB-b-EG] block copolymer. The enzymatic degradation of blend films was carried out at 37°C and pH 7.4 in a 0.1M phosphate solution of an extracellular PHB depolymerase fromAlcaligenes faecalis. The enzymatic degradation took place solely on the surface of the blend films.     

Removal of H2S using molten carbonate at high temperature

Gasification is considered to be an effective process for energy conversion from various sources such as coal, biomass, and waste. Cleanup of the hot syngas produced by such a process may improve the thermal efficiency of the overall gasification system. Therefore, the cleanup of hot syngas from biomass gasification using molten carbonate is investigated in bench-scale tests. Molten carbonate acts as an absorbent during desulfurization and dechlorination and as a thermal catalyst for tar cracking. In this study, the performance of molten carbonate for removing H₂S was evaluated. The temperature of the molten carbonate was set within the range from 800 to 1000 °C. It is found that the removal of H₂S is significantly affected by the concentration of CO₂ in the syngas. When only a small percentage of CO₂ is present, desulfurization using molten carbonate is inadequate. However, when carbon elements, such as char and tar, are continuously supplied, H₂S removal can be maintained at a high level.To confirm the performance of the molten carbonate gas-cleaning system, purified biogas was used as a fuel in power generation tests with a molten carbonate fuel cell (MCFC). The fuel cell is a high-performance sensor for detecting gaseous impurities. When purified gas from a gas-cleaning reactor was continuously supplied to the fuel cell, the cell voltage remained stable. Thus, the molten carbonate gas-cleaning reactor was found to afford good gas-cleaning performance.     

Application of response surface methodology to the advanced treatment of biologically stabilized landfill leachate using Fenton’s reagent

A Fenton process that uses FeCl₂ as the alternative catalyst was employed to deal with the biologically treated landfill leachate. Data obtained revealed that this Fenton process can provide an equivalent pollutant removal as the Fenton process that uses FeSO₄ as catalyst. Central composite design (CCD) and response surface methodology (RSM) were applied to evaluate and optimize the four key factors, namely initial pH, Fe(II) dosage ([Fe²⁺]), H₂O₂/Fe(II) mole ratio ([H₂O₂]/[Fe²⁺] ratio) and reaction time, which affect the performance of the Fenton treatment. Chemical oxygen demand (COD) and color were selected as response variables. This approach provided statistically significant quadratic models, which were adequate to predict responses and to carry out optimization under the conditions studied. It was demonstrated that the interaction between initial pH and [H₂O₂]/[Fe²⁺] ratio has a significant effect on the COD removal, while the interaction between [H₂O₂]/[Fe²⁺] ratio and reaction time shows a large impact on color removal. The optimal conditions were found to be initial pH 5.9, [Fe²⁺] = 9.60 mmol/L, [H₂O₂]/[Fe²⁺] ratio = 2.38, reaction time = 5.52 h. Under this optimal scheme, the COD and color in the effluent were reduced to 159 mg/L and 25°, respectively, with an increase of BOD₅/COD ratio from 0.05 to 0.21.     

Treatment of MTBE‐Contaminated Waters with Fenton's Reagent

Methyl tertiary‐butyl ether (MTBE) is commonly used as a fuel additive because of its many favorable properties that allow it to improve fuel combustion and reduce resulting concentrations of carbon monoxide and unburnt hydrocarbons. Unfortunately, increased production and use have led to its introduction into the environment. Of particular concern is its introduction into drinking water supplies. Accordingly, research studies have been initiated to investigate the treatment of MTBE‐contaminated soil and groundwater. The summer 2000 issue of Remediation reported the results of an initial study conducted by the authors to evaluate the treatment of MTBE using Fenton's reagent. In this follow‐up study, experiments were conducted to further demonstrate the effectiveness of using Fenton's reagent (H₂O₂:Fe⁺²) to treat MTBE‐contaminated groundwater. The concentration of MTBE was reduced from an initial concentration of 1,300 μg/l (14.77 μ moles) to the regulatory level of 20 μg/l (0.23 μ moles) at a H₂O₂:Fe⁺² molar ratio of 1:1, with ten minutes of contact time and an optimum pH of 5. The by‐products, acetone and tertiary butyl alcohol, which are always present in MTBE in trace amounts, were not removed even after 60 minutes of reaction time. © 2002 Wiley Periodicals, Inc. *     

Decomposition of dichloromethane and in situ alkali absorption of resulting halogenated products by a packed-bed non-thermal plasma reactor

For an effective decomposition and removal of organic halogenated compounds, a packed-bed non-thermal plasma reactor with in situ absorption of the resulting halogenated products by alkaline sorbent incorporated was proposed. In the plasma reactor, α-Al₂O₃ particles of 1 and 3 mm (mean particle diameter) were packed as solid dielectric medium to enhance the plasma power density in the reactor. Further, alkaline sorbent of Ca(OH)₂ was doped onto the surface of α-Al₂O₃ particles, in order to remove halogenated products by in situ absorption with Ca(OH)₂. A high-voltage and high-frequency pulsed power of −15 to 15 kV and 1 kHz was applied to the wire electrode of the plasma reactor by means of a DC power source. In the present study, as the sample of an organic halogenated compound that is most popularly used, we selected dichloromethane (CH₂Cl₂), and 500 ppm of the initial concentration of CH₂Cl₂ was fed into the reactor accompanied by air at a fixed flow rate of 500 × 10⁻⁶ m³ min⁻¹ at room temperature. As a result, it was recognized that the amount of CH₂Cl₂ decomposed by non-thermal plasma in an α-Al₂O₃ particle bed increased with an increase in plasma input power. The ratio of decomposition of CH₂Cl₂ was almost 100% at 13 kV of electric power and 1 kHz frequency, and CO₂, CH₃Cl, COCl₂, HCl, and Cl₂ were observed as the major reaction products. On the other hand, when CH₂Cl₂ was introduced into the plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ were packed, the ratio of decomposition of CH₂Cl₂ became higher, compared to the case that α-Al₂O₃ particles were not doped with Ca(OH)₂. Moreover, there were no halogenated by-product gases detected in the outlet gas from the reactor. As the solid reaction products, CaClOH and Ca(ClO)₂·4H₂O were detected on Ca(OH)₂ by X-ray diffraction. From these findings, it was recognized that CH₂Cl₂ was decomposed more effectively without producing unwanted harmful halogenated by-products in the proposed non-thermal plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ sorbent were packed.     

Effect of Poly(dioxolane) as Compatibilizer in Poly(ɛ-caprolactone)/Tapioca Starch Blends

The influence of poly(dioxolane) (PDXL), a poly(ethylene oxide-alt-methylene oxide), as compatibilizer on poly(ɛ-caprolactone) (PCL)/tapioca starch (TS) blends was studied. In order to facilitate blending; PCL, PDXL and TS must be blended together directly; so that PDXL is partially adhered at the TS surface as shown by scanning electron microscopy. The molecular weight effect of PDXL on the PCL/TS blends showed that mechanical properties of PCL/TS/PDXL blends from low molecular weight (M _n=10,000) and high molecular weight (M _n=200,000) PDXL were rather dependent on TS content. The enzymatic degradability of PCL/TS/PDXL blends using α-amylase increased as the TS content increased but was independent on the dispersion of tapioca starch in the PCL matrix.     

Green Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Cellulose/Polyvinyl Alcohol Hybride Aerogel and Its Application for Dye Removal

A novel Fe₃O₄/cellulose–polyvinyl alcohol (PVA) aerogel was successfully synthesized by an eco-friendly and facile method in this work. Cellulose/PVA matrix was prepared through an environmental friendly physical cross-linking process and further in-situ decorated with Fe₃O₄. Series of Fe₃O₄ decorated aerogels were prepared and the effects of Fe₃O₄ nanoparticles (NPs) on the aerogels were systematic investigated. As-prepared aerogels exhibited desirable properties including nanostructure, relatively high porosity, improved mechanical and superparamagnetism. The TEM results showed that Fe₃O₄ NPs were integrated in the three-dimensional matrix of cellulose/PVA with a diameter of 9–12 nm. Furthermore, the mechanical strength of the aerogels was significantly enhanced after the introduction of Fe₃O₄ NPs. Meanwhile, the obtained Fe₃O₄/cellulose/PVA aerogel exhibited excellent adsorption performance toward methyl blue dye, and can be reused through fenton-like catalysts oxidative degradation of organic dye in H₂O₂ solution. Therefore, they will have a great potential application as eco-friendly and economical adsorbents.     

Properties and biodegradability of chain-extended copoly(succinic anhydride/ethylene oxide)

Chain-extension reactions were carried out using titanium-iso-propoxide (TIP) as a catalyst for a series of polyesters or copolyesterethers with low molecular weights (M _n =1500–10,000) synthesized by the ring-opening copolymerization of succinic anhydride (SA) with ethylene oxide (EO). The copolymers having aM _n from 25,000 to 50,000 of different properties were obtained. Both the melting point (T _m ) and the fusion heat (H), which indicate the crystallinity of the copolymers, rose with an increase in SA content in the copolymers. Semitransparent films were prepared by compression molding of the copolymers. The biodegradation of the copolymer films was evaluated by enzymatic hydrolysis by lipases and by an aerobic gas evolution test in standard activated sludge. The hydrolyzability of these copolymers by three kinds of lipases was affected by their copolymer composition SA/EO, form, andM _n . The copolyesterether (SA/EO=43/57,M _n =48,900) was more easily biodegraded by standard activated sludge compared to the polyester (SA/EO=47/53,M _n =36,300).Presented at the Pacifichem-95, December 17–22, 1995, Honolulu, Hawaii.     

Mathematical model analysis of Fenton oxidation of landfill leachate

The treatment of concentrated landfill leachate rejected from reverse osmosis (RO) with Fenton process was studied, and the system model was developed through the examination of reaction kinetics. The leachate is typically non-biodegradable with low BOD₅/COD ratio 0.01. The oxidation reactions of Fenton process was found to be a two-stage process, where a fast initial reaction (H₂O₂/Fe²⁺) was followed by a much slower one (H₂O₂/Fe³⁺). A simple and more accurate mathematics model based on COD and TOC removals has been derived successfully to describe the two-stage reaction kinetics. The two corresponding parameters involved in this model have been identified as the initial reaction rate and the maximum oxidation removal efficiency, respectively. It was found to be very useful for evaluating the performance of Fenton system and/or for process design using the two parameters under different experimental conditions.     

Stabilization of sewage sludge in the presence of nanoscale zero-valent iron (nZVI): abatement of odor and improvement of biogas production

The potential benefits of nanoscale zero-valent iron (nZVI) on sludge stabilization, either the abatement of odor or the improvement of biogas production, were investigated in this study. Two commercial-grade microscale iron powders were also utilized for comparison. Adding 0.10 wt% of nZVI in sludge during anaerobic incubation significantly reduced the concentration of H₂S in biogas by 98.0 % (96.2–98.9 %), probably attributed by reactions between sulfides and the neo-formed hydrous Fe(II)/Fe(III) oxides layer at the surface of ZVI nanoparticles. Meanwhile, the percentage of P in bioavailable fractions decreased from 76.8 to 52.5 %, possibly due to the formation of vivianite [Fe₃(PO₄)₂]. Furthermore, 0.10 wt% of nZVI in anaerobic digestion for 17 days enhanced the concentration of CH₄ in biogas by 5.1–13.2 % and improved the production of biogas and methane by 30.4 and 40.4 %, respectively. The amendment of iron nanoparticles during anaerobic digestion can not only effectively reduce H₂S in biogas, but also potentially boost methane production significantly.     

The use of waste basic oxygen furnace slag and hydrogen peroxide to degrade 4-chlorophenol

A new treatment method is developed to degrade 4-chlorophenol (4-cp) and its oxidation intermediates. The experimental results of this research demonstrate that 4-cp and its oxidation intermediates can be decomposed completely by basic oxygen furnace slag (BOF slag) with hydrogen peroxide (H₂O₂) in an acid solution. The factors that effect the treatment efficiency were studied including initial concentration of 4-cp, pH of the solution, concentration of H₂O₂ and amount of BOF slag. The BOF slags are final waste materials in the steel making process. The major components of BOF slag are CaO, SiO₂, Fe₂O₃, FeO, MgO and MnO. As the BOF slag in an acid solution, FeO and Fe₂O₃ can be dissociated to produce ferrous ion and ferric ion. Ferrous ion reacts with hydrogen peroxide to form “Fenton's reagent” which can produce hydroxyl radicals (OH^.). Hydroxyl radical possession of high oxidation ability can oxidize organic chemicals effectively. Results show that 100 mg/l of 4-cp is decomposed completely within 30 min by 438.7 g/l BOF slag with 8.2 mM hydrogen peroxide in pH=2.8±0.2 solution. The COD value of the solution is reduced from 290 to 90 mg/l. The factors studied which affect the 4-cp decomposition efficiency were the hydrogen peroxide concentration, BOF slag concentration, pH of the solution and initial concentration of 4-cp. Because large amounts of Fe₂O₃ and FeO are present in the BOF slag, the BOF slag not only has a high treatment efficiency, but also can be used repeatedly.     

Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

Sorbents synthesized from various types of ash (coal fly ash, coal bottom ash, oil palm ash, and incinerator ash) for flue gas desulfurization were investigated. The sorbents were prepared by mixing the ashes with calcium oxide and calcium sulfate using the water hydration method. The effects of various sorbent preparation variables, such as the hydration period, the ratio of calcium oxide to ash, and the amount of calcium sulfate, on the Brunauer-Emmett-Teller (BET)-specific surface area of the resulting sorbent were studied using a two-level full factorial design. The surface area of the sorbents obtained range from 15.4 to 122.1m²/g. Regression models were developed to correlate the significant variables to the surface area of the sorbents. An analysis of variance (ANOVA) showed that the model was significant at a confidence level of 95%. It was found that apart from all the individual variables studied, interactions between variables also exerted a significant influence on the surface area of the sorbent. From the activity test results, it was found that sorbents prepared from coal fly ash and oil palm ash have the highest SO₂ absorption capacity. Scanning electron microscope (SEM) analysis showed that the sorbent was composed of a compound with a high structural porosity, while an X-ray diffraction spectrum showed that calcium aluminum silicate hydrate compounds are the main products of the hydration reaction.     

Reducing H2S production by O2 feedback control during large-scale sewage sludge composting

Hydrogen sulfide (H₂S) production patterns and the influence of oxygen (O₂) concentration were studied based on a well operated composting plant. A real-time, online multi-gas detection system was applied to monitor the concentrations of H₂S and O₂ in the pile during composting. The results indicate that H₂S was mainly produced during the early stage of composting, especially during the first 40 h. Lack of available O₂ was the main reason for H₂S production. Maintaining the O₂ concentration higher than 14% in the pile could reduce H₂S production. This study suggests that shortening the interval between aeration or aerating continuously to maintain a high O₂ concentration in the pile was an effective strategy for restraining H₂S production in sewage sludge composting.     

Treatment of the biodegradable fraction of used disposable diapers by co-digestion with waste activated sludge

The results presented in this paper are part of a project aimed at designing an original solution for the treatment of used disposable diapers permitting the recycling of materials and the recovery of energy. Diapers must be collected separately at source and transported to an industrial facility to undergo special treatment which makes it possible to separate plastics and to recover a biodegradable fraction (BFD) made up mainly of cellulose. The methane yield of BFD was measured and found to be 280 ml CH₄/g VS_fed on average. 150 kg of dry BFD can be retrieved from the treatment of one ton of used disposable diapers, representing an energy potential of about 400 kW h of total energy or 130 kW h of electricity. As the treatment process for used diapers requires very high volumes of water, the setting up of the diaper treatment facility at a wastewater treatment plant already equipped with an anaerobic digester offers the advantages of optimizing water use as well as its further treatment and, also, the anaerobic digestion of BFD. The lab-scale experiments in a SBR showed that BFD co-digestion with sewage sludge (38% BFD and 62% waste activated sludge on volatile solids basis) was feasible. However, special attention should be paid to problems that might arise from the addition of BFD to a digester treating WAS such as insufficient mixing or floating particles leading to the accumulation of untreated solids in the digester.     

Chemical characterization of emissions from a municipal solid waste treatment plant

Gaseous emissions are an important problem in municipal solid waste (MSW) treatment plants. The sources points of emissions considered in the present work are: fresh compost, mature compost, landfill leaks and leachate ponds. Hydrogen sulphide, ammonia and volatile organic compounds (VOCs) were analysed in the emissions from these sources. Hydrogen sulphide and ammonia were important contributors to the total emission volume. Landfill leaks are significant source points of emissions of H₂S; the average concentration of H₂S in biogas from the landfill leaks is around 1700 ppmv. The fresh composting site was also an important contributor of H₂S to the total emission volume; its concentration varied between 3.2 and 1.7 ppmv and a decrease with time was observed. The mature composting site showed a reduction of H₂S concentration (<0.1 ppmv). Leachate pond showed a low concentration of H₂S (in order of ppbv). Regarding NH₃, composting sites and landfill leaks are notable source points of emissions (composting sites varied around 30–600 ppmv; biogas from landfill leaks varied from 160 to 640 ppmv).Regarding VOCs, the main compounds were: limonene, p-cymene, pinene, cyclohexane, reaching concentrations around 0.2–4.3 ppmv.H₂S/NH₃, limonene/p-cymene, limonene/cyclohexane ratios can be useful for analysing and identifying the emission sources.     

Attenuation of hydrogen sulfide at construction and demolition debris landfills using alternative cover materials

The attenuation of H₂S emissions by various landfill cover materials was evaluated using both laboratory and field experiments. The results demonstrated that cover materials consisting of selected waste products (compost and yard trash) and soils amended with quicklime and calcium carbonate effectively attenuated H₂S emissions and detectable H₂S emissions were only encountered in a testing plot using a sandy soil cover (average emission rate was 4.67 × 10^?6 mg m^?2 s^?1). H₂S concentration profiles in the cover materials indicated that H₂S was removed as it migrated through the cover materials. At the same depth in the testing area, the H₂S concentration in the sandy soil field plot was always higher than that of other testing plots because the sand (a) demonstrated less ability to remove H₂S and (b) exhibited a higher H₂S concentration at the base of the cover. Laboratory experiments confirmed these observations, with a combination of physical adsorption, chemical reactions, and biological oxidation, accounting for the enhanced removal. In addition to removal, the results suggest that some of the cover materials reduced H₂S generation by creating less favorable conditions for sulfate-reducing bacteria (e.g., high pH and temperature).     

Solubility and henry''s law constant for alcohols in water

A new correlation which provides reliable solubility values down to very, very low concentrations is presented for solubility of alcohols in water. The correlation is based on boiling point temperature of the alcohol and can be used for engineering studies involving health, safety and environmental considerations. Results for water solubility and Henry's law constant are provided for a wide variety of alcohols. Representative solubility values (parts per million by weight) are 74,000 for n-butanol (C₄H₁₀O) and 4.0 for 1-dodecanol (C₁₂H₂₆O).     

Hydrogen production from food wastes and gas post-treatment by CO2 adsorption

The production of H₂ by biological means, although still far from being a commercially viable proposition, offers great promise for the future. Purification of the biogas obtained may lead to the production of highly concentrated H₂ streams appropriate for industrial application. This research work evaluates the dark fermentation of food wastes and assesses the possibility of adsorbing CO₂ from the gas stream by means of a low cost biomass-based adsorbent. The reactor used was a completely stirred tank reactor run at different hydraulic retention times (HRTs) while the concentration of solids of the feeding stream was kept constant. The results obtained demonstrate that the H₂ yields from the fermentation of food wastes were affected by modifications in the hydraulic retention time (HRT) due to incomplete hydrolysis. The decrease in the duration of fermentation had a negative effect on the conversion of the substrate into soluble products. This resulted in a lower amount of soluble substrate being available for metabolisation by H₂ producing microflora leading to a reduction in specific H₂ production.Adsorption of CO₂ from a gas stream generated from the dark fermentation process was successfully carried out. The data obtained demonstrate that the column filled with biomass-derived activated carbon resulted in a high degree of hydrogen purification. Co-adsorption of H₂S onto the activated carbon also took place, there being no evidence of H₂S present in the bio-H₂ exiting the column. Nevertheless, the concentration of H₂S was very low, and this co-adsorption did not affect the CO₂ capture capacity of the activated carbon.