Removal of humic substances from landfill leachate by Fenton oxidation and coagulation

In this study, chemical oxygen demand (COD) was characterized as total organic constituents and the isolated humic substances (HS) were characterized as an individual organic contaminant in landfill leachate. It was found that the HS content of landfill leachate was 83.3%. The results of laboratory tests to determine the roles of HS in reducing the organic content of landfill leachate during Fenton process are presented. Furthermore, the performances of oxidation and coagulation of Fenton reaction on the removal of HS and COD from leachate were investigated. The change curves of HS removal were similar to those of COD. The HS removal was 30% higher than COD removal, which indicated that HS were mostly degraded into various intermediate organic compounds but not mineralized by Fenton reagent. The oxidation removal was greatly influenced by initial pH relative to the coagulation removal. The oxidation and coagulation removals were linear dependent with hydrogen peroxide and ferrous dosages, respectively. Ferrous dosage greatly influenced the coagulation removal of COD at low ratio ([H₂O₂]/[Fe²⁺] < 3.0), but not at extremely high ratio ([H₂O₂]/[Fe²⁺] > 6.0). The coagulation removal of HS was not affected obviously by oxidation due to both Fenton oxidation and coagulation remove high molecular weight organics preferentially. Higher temperature gave a positive effect on oxidation removal at low Fe²⁺ dosage, but this effect was not obvious at high Fe²⁺ dosage.     

Effect of ultrasound irradiation and Ni-loading on properties and performance of CeO2-doped Ni/clinoptilolite nanocatalyst used in polluted air treatment

In this research nanocatalysts containing 5, 10 and 15 wt.% of Ni, dispersed by sonication over CeO₂–clinoptilolite composite support were compared toward total oxidation of toluene. Their catalytic performance at different temperatures between 150 and 350 °C was studied based on the oxidative destruction of toluene. The results indicated that the activity of Ni/CeO₂–clinoptilolite nanocatalyst for toluene oxidation increased from 33 to 44% at 250 °C by employing sonochemical method in synthesis of catalyst. Meanwhile, the catalytic activity was also improved when Ni content was increased from 5 to 10 and 15 wt.%. With the aid of several characterization techniques like XRD, FESEM, PSD, EDX, BET and FTIR, the correlation between nanocatalyst structure and its activity was addressed. It is indicated that sonochemical method can lift the catalytic activity due to the better dispersion of catalyst active components and also higher surface area. Among sonicated samples, 15 wt.% Ni nanocatalyst showed the highest toluene oxidation due to the better dispersion of catalyst active components and hence to more effective catalytic sites.     

A novel pretreatment process of mature landfill leachate with ultrasonic activated persulfate: Optimization using integrated Taguchi method and response surface methodology

A novel advanced oxidation process (AOP) using ultrasonic activated persulfate oxidation was used to pretreat mature landfill leachate. The effects of different operating variables (e.g., the initial S₂O₈²⁻ concentration, pH, temperature, ultrasonic power and reaction time) on the oxidation performance were investigated regarding the total organic carbon (TOC) removal efficiency, and the variables were optimized using the integrated Taguchi method and response surface methodology (RSM). Based on the Taguchi method under L₁₆ (4⁵) arrays and a grey relational analysis, the most significant variables included the initial S₂O₈²⁻ concentration, temperature and reaction time. The concentrations of these variables were further optimized using RSM. Using the integrated optimization method, the optimal conditions included an initial S₂O₈²⁻ concentration of 8.5 mM, a reaction temperature of 70 °C and a reaction time of 2.46 h, which resulted in a TOC removal efficiency of 77.32%. The experimental results showed that the enhanced TOC removal from mature landfill leachate by sono-activated persulfate oxidation could be attributed to the combined effects of ultrasonic catalysis and sulfate radical-AOP. Overall, ultrasonic activated persulfate oxidation is a promising method for the pretreatment of landfill leachate.     

Low-dose irradiation by electron beam for the treatment of high-SOx flue gas on a semi-pilot scale—Consideration of by-product quality and approach to clean technology

Attention has been focused on the treatment of lignite-fired flue gas in order to use lignite in an environmentally friendly way – (i) low-CO₂ emission, (ii) production of a valuable by-product, (iii) no discharge of wastewater, (iv) direct removal of SO₃ (strong toxicity), and (v) treatment of high SO₂ concentration. Based on these criteria, electron beam irradiation with ammonia injection was tested on a semi-pilot scale: 800 Nm³ h^?1 flow rate, 5500 ppm SO₂, 70 ppm NO_x, 22% flue gas moisture, and 75–80 °C at the reactor outlet.As an energy-saving measure, a low dose (5 kGy) of irradiation was applied: the problem lay in the by-product quality. It is considered that (NH₄)₂SO₃ and NH₄HSO₃ produced by thermal reactions are oxidized to form (NH₄)₂SO₄ (fertilizer) by an electron beam. However, not all reactions were complete because the by-product contained small amounts of H₂SO₄ and NH₂SO₃NH₄ (herbicide), so a vegetable pot test was performed to study the by-product quality: no adverse effect was observed. It is inferred from the pot test that slightly acidic soil may protect vegetables from disease and a small amount of NH₂SO₃NH₄ probably affects woody species and not herbaceous species.It is concluded that the electron beam system is noted as a multi-component pollution control process (removal of NO_x, SO₃, SO₂ and dioxins) and this system will contribute to environmentally friendly use of lignite as well as agricultural productivity via fertilizer supply.     

Use of advance oxidation process to improve the biodegradability of olive oil mill effluents

In this study, recalcitrant total phenol (TPh) and organic matter removal were investigated at olive mill wastewater (OMW) in sequential Coagulation and Fenton system. This study focused on different operational parameters such as pH, H₂O₂, and Fe²⁺ dosages, and [Fe²⁺]/[H₂O₂] ratios. The optimum conditions were determined as; pH = 3; [Fe²⁺] = 2.5 g/L; [Fe²⁺]/[H₂O₂] = 2.5. A higher treatment efficiency was achieved at sequential Coagulation and Fenton system (COD, 65.5%) and TPh, 87.2%), compared to coagulation process (COD, 51.4%; total organic carbon (TOC), 38.6% and total nitrogen (TN) 52.1%). This study demonstrated that the Coagulation and Fenton process has a potential for efficient removal of phenolic pollutants from wastewater.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Pretreatment of municipal landfill leachate by a combined process

Biodegradability enhancement of landfill leachate using air stripping followed by coagulation/ultrafiltration (UF) processes was introduced. The air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen (NH₄–N) at air-to-liquid ratio of 3500 (pH 11) for stripping 18 h. The single coagulation process increased BOD/COD ratio by 0.089 with the FeCl₃ dosage of 570 mg l^?1 at pH 7.0, and the single UF process increased the BOD/COD ratio to 0.311 from 0.049. However, the combined process of coagulation/UF increased the BOD/COD ratio from 0.049 to 0.43, and the final biological oxygen demand (BOD), chemical oxygen demand (COD), NH₄–N and colour of leachate were 1223.6 mg l^?1, 2845.5 mg l^?1, 145.1 mg l^?1 and 2056.8, respectively, when 3 kDa molecular weight cut-off (MWCO) membrane was used at the operating pressure 0.7 MPa. In ultrafiltration process, the average solution flux (J_V), concentration multiple (M_C) and retention rate (R) for COD was 107.3 l m^?2 h^?1, 6.3% and 84.2%, respectively.     

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Enhanced NOx removal from flue gas by an integrated process of chemical absorption coupled with two-stage biological reduction using immobilized microorganisms

An integrated process of metal chelate absorption coupled with two stage bio-reduction using immobilized cultures has been proposed to continuously removal of NO_x, and the effects of SO₂, NO and O₂ concentration, gas/liquid flow rate on NO_x removal efficiency were investigated. Although nitrogen-containing components, such as Fe(II)EDTA-NO, NO₂^? and NO₃^? in the scrubbing solution, inhibited the bio-reduction of Fe(III)EDTA obviously, it was feasible to abate the inhibition effect by using the two stage bio-reduction system, and thus to improve NO_x removal efficiency. The removal efficiency decreased slowly with the increase of SO₂, O₂, NO concentration and gas flow rate, and increased with the increase of liquid flow rate. Continuously operating for 18 days, a high removal efficiency around 95% was reached by using the two-stage bio-reduction system with immobilized microorganisms, while the value decreased to 85% after 5 days of operation by using the suspended microorganisms, at a constant gas flow rate of 60 L/h containing 424–450 mg/m³ NO, 2428–2532 mg/m³ SO₂ and 3% O₂.     

An improved method of removal for high concentrations of NO by electro-scrubbing process

In the Ag(II)/Ag(I) redox mediator integrated scrubber system, NO reacts with the Ag(II) ions produced by the electrochemical oxidation of Ag(I) in an electrochemical cell present in the scrubbing solution (aqueous HNO₃ acid) to form NO₂. This NO₂ is then absorbed into the scrubbing solution and degraded to nitrate. Numerous experimental runs were carried out to evaluate the feasibility of the integrated system to treat industrial waste gases containing high NO_x levels. The results showed that the levels of NO and NO_x removal increased with increasing Ag(II) loading and contact time. Under optimized conditions, 93.5% and 73.3% of the NO and NO_x, respectively, were removed by a single stage gas scrubber with 1.62 g L^?1 Ag(II) operating at 25 °C and atmospheric pressure.     

7 mT static magnetic exposure enhanced synthesis of poly-3-hydroxybutyrate by activated sludge at low temperature and high acetate concentration

The effect of 7 mT (milliTesla) SMF (static magnetic field) on poly-3-hydroxybutyrate (PHB) production was studied at an acetate concentration of 260 Cmmol l^?1 and temperature of 10 °C. The SMF decreased the specific acetate uptake rate by 29%, but increased the maximum PHB content and the yield of PHB on acetate by 32 and 28% respectively. The ratio q_P/(q_S ? q_P), which described specific PHB production rate over the difference between specific acetate uptake rate and specific PHB production rate, was introduced for evaluation of the ratio of carbon flux into PHB synthesis and into the TCA (tricarboxylic acid) cycle. This value reached 2.3 when activated sludge culture was exposed to magnetic field of 7 mT, which was 1.1 times higher than the q_P/(q_S ? q_P) value obtained without magnetic exposure. Therefore, the SMF promoted diversion of more acetyl-CoA towards PHB synthesis and could offset adverse effects of high acetate concentration and low temperature. These results provide evidence that SMF enhances PHB production by activated sludge.     

Comparative response of two organic biofilters treating ethylbenzene and toluene after prolonged exposure

The response of two biofilters filled with an organic waste material for treating ethylbenzene and toluene was studied for 415 and 472 operating days, respectively. The peak elimination capacities (EC_MAX) recorded were 170 g m^?3 h^?1 for ethylbenzene (EC_MAX) and 138 g m^?3 h^?1 for toluene. Regarding the degradation profile through the biofilters, an increase in the inlet concentration displaced the degradation profile into the downstream section. A sudden decrease in the performance of both biofilters occurred when the moisture content (MC) of the packing material exceeded 37% for ethylbenzene and 30% for toluene. Thus, a recommended MC value was established in the 15–30% range. Given the bioreactor was operated at a low MC level, fungi prevailed over bacteria. Nevertheless, synergism was detected between both microorganism types for the mineralization of the aromatic hydrocarbons.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Removal of toluene vapour from air stream using a biofilter packed with polyurethane foam

Biodegradation of toluene vapour was investigated for 168 days in a polyurethane packed biofilter inoculated with a mixed microbial population. Biofilter consisted of five square cross-section modular units each of size 0.16 m × 0.16 m × 0.20 m and filled with the polyurethane foam cubes up to a height of 0.15 m. Inlet concentration of toluene was varied from 0.04 to 2.5 g m^?3 and the volumetric flow rate of toluene loaded air from 0.06 to 0.90 m³ h^?1.Depending upon initial loading rates, removal efficiency ranging from 68.2 to 99.9% and elimination capacity ranging from 10.85 to 90.48 g h^?1 m^?3 were observed during steady state operations. More than 90% removal efficiency was observed up to an inlet loading rate of 76.3 g h^?1 m^?3. High carbon recovery (>90%) indicated effective biodegradation in the bed. Low variation of pH (7.2–8.8) and pressure drop (45.8–76.3 Pa) was observed. The stability of the biomass was evident from the fast response of the biofilter to shutdown and restartup.     

Simultaneous photocatalytic treatment of Cr(VI), Ni(II) and SDBS in aqueous solutions: Evaluation of removal efficiency and energy consumption

Simultaneous photocatalytic reduction of poisonous Cr(VI) and Ni(II) ions, coupled with photocatalytic oxidation of sodium dodecyl benzene sulfonate (SDBS) were studied with a trace amount of commercial titania nanoparticles and by means of a direct-photo-irradiation reactor. The co-presence of metal ions and SDBS causes metal ions reduction as well as SDBS oxidation to enhance and energy efficiency to improve. XRD, XPS and FTIR analysis were used to characterize TiO₂ particles before and after usage with the aim of evaluating the mechanism of reactions. The effect of major operating parameters, pH and temperature, was investigated. Under conditions of [Cr(VI)]₀ = [Ni(II)]₀ = 5 mg/L, [SDBS]₀ = 10 mg/L, [TiO₂] = 40 mg/L, pH 6 and T = 35 °C; the removal efficiencies of 55.4%, 71.2% and 57.2% were obtained, respectively, for Cr(VI) and Ni(II) reduction, as well as for SDBS oxidation, after 110 min operation. The relevant kinetic model jointed with the Arrhenius equation was introduced. Pseudo-first-order reactions are relevant. Energy consumption (electrical and thermal) evaluations revealed that operations at higher temperatures provide significant cost reduction. Meantime, a criterion was proposed for a consistent assessment of this kind of processes.     

Feasibility of honeycomb monolith supported sugar catalyst to produce biodiesel from palm fatty acid distillate (PFAD)

Carbon coated monolith was prepared by sucrose solution 65 wt.% via dip-coating method. Sulfonation of incomplete carbonized carbon coated monolith was carried out in order to synthesize solid acid catalyst. The textural structure characteristics of the solid acid catalyst demonstrated a low surface area and pore volume. Palm fatty acid distillate (PFAD), a by-product of palm oil refineries, was utilized as oil source in biodiesel production. The esterification reaction subjected to different reaction conditions was performed by using the sulfonated carbon coated monolith as heterogeneous catalyst. The sulfonation process had been performed by using vapour of concentrated H₂SO₄ that was much easier and efficient than liquid phase sulfonation. Total acidity value of carbon coated monolith was measured for unsulfonated sample (0.5 mmol/g) and sulfonated sample (4.2 mmol/g). The effect of methanol/oil ratio, catalyst amount and reaction time were examined. The maximum methyl ester content was 89% at the optimum condition, i.e. methanol/oil molar ratio (15:1), catalyst amount (2.5 wt.% with respect to PFAD), reaction time (240 min) and temperature 80 °C. The sugar catalyst supported on the honeycomb monolith showed comparable reactivity compared with the sugar catalyst powder. However, the catalyst reusability studies showed decrease in FFA% conversion from 95.3% to 68.8% after four cycles as well as the total acidity of catalyst dropped from the value 4.2 to 3.1 mmol/g during these cycles. This might be likely due to the leaching out of SO₃H group from the sulfonated carbon coated monolith surface. The leaching of active species reached a plateau state after fourth cycle.     

An explosion of a tank car carrying waste hydrogen peroxide

On the Metropolitan Expressway in Tokyo, a tank car exploded because it was carrying hydrogen peroxide (H₂O₂) in a compartment in which copper chloride (CuCl₂) remained. Although the main cause of the accident was trivial, the background on the accident suggested that an induction period in the reaction led to a mistake. This report describes the experimental investigation of the catalytic ability of CuCl₂, and comparing it with two other copper(II) compounds (nitrate: Cu(NO₃)₂; and copper sulfate: CuSO₄) and three iron(III) compounds (chloride: FeCl₃; nitrate: Fe(NO₃)₃; and sulfate: Fe₂(SO₄)₃).The experiments were performed using a reaction calorimeter. During the experiments at 35 °C, 2×10⁻⁵ mol of copper compounds slowly reacted with H₂O₂ and generated a precipitate. The iron compounds allowed the hydrogen peroxide to violently decompose. A 1×10⁻⁴ mol solution of CuCl₂, however, produced a violent decomposition at 35 °C. At 15 °C, a moderate heat release occurred.Based on these results, the concentration and temperature dependence of the catalytic ability of CuCl₂ were postulated to contribute to the induction period observed in the accident.     

Evaluation of membrane bioreactor for hypersaline oily wastewater treatment

Produced water is a significant waste stream generated in association with oil and gas production. It contains high concentrations of hydrocarbon constituents and different salts. In this study, a membrane sequencing batch reactor (MSBR) was used to treat synthetic and real produced water. The MSBR was evaluated in terms of biodegradation of hydrocarbons in the synthetic produced water with various organic loading rates (OLR) (0.281, 0.563, 1.124, 2.248, and 3.372 kg COD/(m³ day)), cycle time (12, 24, and 48 h), and membrane performance. The effects of salt concentrations at different total dissolved solids (TDS) (35,000, 50,000, 100,000, 150,000, 200,000, and 250,000 mg/L) on biological treatment of the pollutants in the synthetic and real wastewater were studied. At an OLR of 1.124 kg COD/(m³ day), an HRT of 48 h and TDS of 35,000 mg/L, removal efficiencies of 97.5%, 97.2%, and 98.9% of COD, total organic carbon (TOC), and oil and grease (O&G), respectively were achieved. For the real produced water, removal rates of 86.2%, 90.8%, and 90% were obtained for the same conditions. However, with increasing salt content, the COD-removal efficiencies of the synthetic and real produced water were reduced to 90.4% and 17.7%, respectively at the highest TDS.     

Decolorization of synthetic Methyl Orange wastewater by electrocoagulation with periodic reversal of electrodes and optimization by RSM

Treatment of Methyl Orange (MO), an azo dye, synthetic wastewater by electrocoagulation with periodic reversal of the electrodes (PREC) was examined. Response Surface Methodology (RSM) was used to optimize the influence of experimental conditions for color removal (CR), energy consumption (ENC), electrode consumption (ELC) and sludge production (SP) per kg MO removed (kg(MO_r)) with optimal conditions being found to be pH 7.4, solution conductivity (к) 9.4 mS cm⁻¹, cell voltage (U) 4.4 V, current density (j) 185 mA cm⁻², electrocoagulation time (T) 14 min, cycle of periodic reversal of electrodes (t) 15 s, inter-electrode distance (d) 3.5 cm and initial MO concentration of 125 mg L⁻¹. Under these conditions, 97 ± 2% color was removed and ENC, ELC and SP were 44 ± 3 kWh kg(MO_r)⁻¹, 4.1 ± 0.2 kg(Al) kg(MO_r)⁻¹ and 17.2 ± 0.9 kg(sludge) kg(MO_r)⁻¹, respectively. With the enhanced electrochemical efficiency resulting from the periodic electrode reversal, the coefficients of increased resistance and decreased current density between the two electrodes in the PREC setup were 2.48 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.29 mA cm⁻² min⁻¹, respectively, as compared to 7.72 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.79 mA cm⁻² min⁻¹ as measured for the traditional electrocoagulation process. The rate constant of decolorization was also enhanced by 20.4% from 0.152 min⁻¹ in the traditional electrocoagulation process to 0.183 min⁻¹ in the PREC process. These performance characteristics indicate that the PREC approach may be more promising in terms of practical application, as a cost-effective treatment, than conventional electrocoagulation for textile dye removals.     

Growing Carbon Nanotube on Aluminum Oxides: An Inherently Safe Approach for Environmental Applications

Using micron-sized Al₂O₃ particles as carriers to grow carbon nanotubes (CNTs) under 700°C atmosphere of methane and hydrogen after pre-planted catalysts of Fe–Ni nanoparticles, those composite CNTs (CCNTs) have demonstrated several unique properties compared to CNTs—medium specific surface area and zeta potential, high adsorption capacity for metal ions, high recovery rate by acids, low decomposition heat for exothermal reaction, and so on. The adsorption behaviours of Pb²⁺, Cu²⁺ and Cd²⁺ in aqueous solutions by CCNTs are in good agreement with the Langmuir adsorption isotherm and second order kinetic model with maximum individual adsorption capacities of 67.11, 26.59 and 8.89 mg g⁻¹. The individual and competitive adsorption behaviours indicated that the preference order of adsorption were Pb²⁺ > Cu²⁺ > Cd²⁺ for aluminum oxides, activated carbon, commercial CNTs, and CCNTs as well as other researchers’ CNTs. We suggest that future development of CNTs to combine with metals and/or other materials, such as TiO₂, should consider attached to carriers or surface in order to avoid concerns on environment, health and safety. Thus, growing CNTs on Al₂O₃ particles to form CCNTs is an inherently safe approach for many promising environmental applications.