Hydrogen sulphide removal from landfill gas

Control of odours should be considered to be a fundamental issue in order to site, design and manage sanitary landfills. With regard to construction and demolition (C&;D) debris, landfilling was the mainly adopted solution in many European Countries; in particular, gypsum drywalls can produce high concentrations of hydrogen sulphide (H₂S) in landfill gas ranging from 7 ppm to 100 ppm. In some cases also dangerous concentrations until to 12,000 ppm were detected. In this paper H₂S removal efficiency in a lab-scale vertical packed scrubber was investigated. Hydrogen sulphide abatement was evaluated for inlet H₂S concentrations of 1000–100–10 ppm, adjusting scrubbing liquid pH in the range 9–12.5 by means of caustic soda (NaOH 2N solution). Moreover, best operating conditions for the system were defined as well as H₂S abatement along the tower and liquid recirculation effectiveness in case of inlet H₂S concentration of 10 ppm (typical odour concentration). Results showed that pH of 11.5 in scrubbing liquid could be considered the best value for removal of different inlet H₂S concentrations, also taking into account parasitical consumption of NaOH due to CO₂ absorption. Moreover, in case of continuous working of the system at H₂S concentration of 10 ppm, strong removal efficiency was already obtained with a packed bed height of about 70 cm. Significant performances were ensured after 1 h of constant activity, consuming about 3 ml of soda per cubic meter of polluted air. Subsequently liquid blowdown was necessary.     

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.     

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.     

An experimental study for H2S and CO2 removal via caustic scrubbing system

In this study, removal of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from simulated syngas has been studied on one column scrubbing system. Gas flow rate as a measure of gas residence time and superficial gas velocity, gas composition, inlet H₂S load, flow modes (countercurrent and cocurrent) and packing geometry were the parameters in the design and/or operation of an acid gas scrubber system. Better H₂S scrubbing efficiencies have been obtained in countercurrent flow mode than that of cocurrent flow mode. When accordingly designed, static mixer with its superior performance on H₂S removal overweighed to structured packings. The coexistence of CO₂ and H₂S has been shown to increase the sodium hydroxide (NaOH) consumption along the scrubber column thereby decreasing the H₂S removal efficiency at higher H₂S loads. The gas residence time as changing with the gas velocity was found to be more dominant on acid gas removal efficiency than the effect of superficial gas velocity within the experimented range. A gas residence times of equal or above 3 s were seemed to be closer to the optimum point.     

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.     

On–off control of aeration time in the simultaneous removal of ammonia and manganese using a biological aerated filter system

The biological aerated filter (BAF) system, a new alternative in drinking water treatment, was designed to remove NH₄⁺–N and Mn²⁺ simultaneously. This study aimed to control the aeration time in the BAF system for simultaneous NH₄⁺–N and Mn²⁺ removal to achieve the Malaysian effluent quality regulation for drinking water. The experiment was conducted under four strategies of S1, S2, S3 and S4. The results demonstrated that acceptable levels of NH₄⁺–N and Mn²⁺ were achieved over a 6 h aeration period (S1), producing effluent concentrations of 0.7 mg/L (93.2% removal) and 0.08 mg/L (79.6% removal), respectively. At the initial treatment of S1 and S2, the dissolved oxygen (DO) level rapidly increased until it reached a saturated concentration (6.8 mg/L DO) after 2 h period. Automatic on–off aeration time to maintain 3 mg/L DO set point (S4) resulted with a good effluent quality of NH₄⁺–N and Mn²⁺ compared with the 2 mg/L DO set point (S3) which did not meet the regulated standard limits. Through the automatic on–off aeration time, the saturated and excessive DO levels in the BAF system can be avoided consequently reduce the wastage of energy and electrical consumption for simultaneous NH₄⁺–N and Mn²⁺ removal from drinking water treatment.     

Fire and Explosion Characteristics of 3-Methyl Pyridine at 270°C with High Oxygen Concentrations

The mixture of 3-methyl pyridine (3-picoline) and steam is used in the production of vitamin B3 in the gas phase. The aim of this study was to investigate the influence of inert steam (H₂O) on the flammability characteristics of 3-picoline in the manufacturing process. Four practical vapour mixing ratios of 3-picoline/steam mixtures, 5, 10, 30 and 100 vol% 3-picoline, were selected in this study. A series of flammability tests were employed for determining their fire and explosion characteristics. Fire tests H₂O: 3-picoline 5,10, 30 and 100 vol% were carried out in a 20-L-Apparatus under simulated conditions of 760 mmHg, 270°C, together with high oxygen concentrations (42 and 21 vol%) used in the real process.The experimental results showed that the safety-related parameters and flammability hazard degrees were all able to be significantly reduced while substantial amount of steam was infused into the 3-picoline/steam system. While the steam proportion was up to 97 vol%, 3-picoline/steam would be non-flammable. As a result, dosing steam to the process is one of the effective methods to prevent the relevant processes from incurring fire and explosion hazards, not to mention its economical benefit.     

Refinery wastewater degradation with titanium dioxide,zinc oxide,and hydrogen peroxide in a photocatalytic reactor

This paper presents the photo-catalytic degradation of real refinery wastewater from National Refinery Limited (NRL) in Karachi, Pakistan, using TiO₂, ZnO, and H₂O₂. The pretreatment of the refinery effluent was carried out on site and pretreated samples were tested at 32–37 °C in a stirrer bath reactor by using ultra-violet photo oxidation process. The degradation of wastewater was measured as a change in initial chemical oxygen demand (COD) and with time. Optimal conditions were obtained for catalyst type, and pH. The titanium dioxide proved to be very effective catalysts in photo-catalytic degradation of real refinery wastewater. The maximum degradation achieved was 40.68% by using TiO₂ at 37 °C and pH of 4, within 120 min of irradiations. When TiO₂ was combined with H₂O₂ the degradation decreased to 25.35%. A higher reaction rate was found for titanium dioxide. The results indicate that for real refinery wastewater, TiO₂ is comparatively more effective than ZnO and H₂O₂. The experiments indicated that first-order kinetics can successfully describe the photo-catalytic reaction. The ANOVA results for the model showed satisfactory and reasonable adjustment of the second-order regression model with the experimental data. The ANOVA results also showed that pH is significant than reaction time and catalyst dosage of TiO₂; and in case of ZnO, reaction time is significant than pH and catalyst dosage. This study proves that real refinery wastewater reacts differently than synthetic refinery wastewater, oil field produced water or oil water industrial effluent.     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

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.     

Sensitivity analysis and optimization for gasoline vapor condensation recovery

Volatile organic compounds (VOCs) are easily evaporated and discharged from everywhere into the atmosphere, especially in various operations of gasoline. The emission of VOCs is always a significant environmental problem, and the control of VOCs pollution has been a hot topic in the field of air purification. In this paper, the condensation separation method for gasoline vapor recovery was investigated and four gasoline vapors of S1–S4 were selected for the sensitivity analysis and optimization of the condensation process, using the Model Analysis Tools from Aspen Plus. Generally, to control VOCs pollution efficiently, both the vapor recovery efficiency and the outlet vapor concentration of the condensation recovery system should be simultaneously considered. Then an optimized three-stage condensation process was proposed, whose condensation temperatures were optimized and designed at 1 °C, −40 °C and −110 °C, respectively. Further, based on the comprehensive consideration of both meeting the more strict VOCs emission standard and ensuring the condensation recovery system work stably and economically, it was recommended that the maximum total vapor recovery efficiencies for S1–S4 should be 99.73%, 99.79%, 99.82% and 99.19%, and the minimum outlet vapor concentrations be 2.87 g/m³, 2.75 g/m³, 3.04 g/m³ and 16.98 g/m³, respectively. Accordingly, the condensation temperature of the copious cooling stage should be set at −130 °C. Moreover, the total cooling duties for the single-stage and three-stage condensation processes were investigated and compared when the condensation temperature of the recovery system ranged from 20 °C to −110 °C. The total cooling duties of the three-stage condensation process for S1–S4 would be saved by 12.23%, 15.68%, 13.96% and 15.65%, respectively. Finally, a three-stage condensation system was developed for the industrial gasoline vapor recovery, which has performed well since its installation.     

Effects of applied voltage on hydrogen production rate of a single reactor BML with Clostridium sp.

This study aimed to explore the influences of single-chamber systems with different applied voltage on bio-hydrogen (H₂) production. The reactor used was the bio-electrochemically assisted microbial reactor (BEAMR) membrane-less (BEAMR-membrane-less, BML). The microbial dark fermentative H₂ production method was adopted. After the hot screening process and the DNA sequencing, the domesticated dominant microflora was Clostridium sp. This study discussed the influences of the cases with (continuous and intermittent) and without applied voltage separately. The results showed that, the H₂ production rate of the case with intermittent applied voltage (117 mL/h g VSS) of 0.24 V was increased of 1.7 folds higher than the without applied voltage (69 mL/h g VSS) and 1.3 folds higher than the case with continuous applied voltage (88.2 mL/h g VSS) of 0.24 V. The produced H₂ concentration with intermittent applied voltage was 18.9% (18.6–19.1%) higher than the without applied voltage, while there was no significant difference with continuous applied voltage.     

Performance of a pilot scale up-flow septic tank for on-site decentralized treatment of residential wastewater

The aim of this research was to study the on-site anaerobic treatment of a medium-strength residential wastewater in a pilot-scale up-flow septic tank (UST). The effects of three different hydraulic retention times (HRTs) of 24, 12 and 6 h on the UST performance were investigated. The UST removed 85, 77, and 86% of biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and total suspended solids (TSS), respectively, at steady state operation and with a 24 h HRT. Decreasing the HRT to 12 and then 6 h resulted in deteriorated effluent quality and significantly reduced reactor performance. The sludge showed a high specific methanogenic activity (SMA) of 15.2 mL CH₄ g^?1 VSS d^?1 with raw wastewater substrate. The solids accumulated in the tank by the end of the experiment had a VSS/TSS of 0.57, demonstrating significant stabilization. Overall, the UST is concluded to be a technically and economically promising alternative to conventional septic tanks for the on-site decentralized treatment of residential wastewater, particularly in the rural communities of developing countries.     

Inherently safer reactors: Improved efficiency of 3-picoline N-oxidation in the temperature range 110–125 °C

Alkylpyridine N-oxides are important intermediates in the pharmaceutical and agrochemicals industries. The N-oxides are produced via the homogeneously catalyzed oxidation of the respective alkylpyridines using a 50% excess of hydrogen peroxide. The competitive hydrogen peroxide decomposition produces oxygen in the flammable environment of alkylpyridines and thus forms a key hazard for this reaction. In this work, the N-oxidation was performed under pressure in the temperature range of 110–125 °C with different catalyst concentrations. It was shown that temperature had an undisputable positive effect on the N-oxidation efficiency. The accurate measurement of the pressure rise due to decomposition was difficult. However, only 5% of the added H₂O₂ decomposed when stoichiometric quantities were employed, even in the temperature of 110 °C. The N-oxidation was very efficient, even when the lowest concentration of catalyst employed in this study was used.     

Dilute Acid Hydrolysis of Cellulose and Cellulosic Bio-Waste Using a Microwave Reactor System

The dilute acid hydrolysis of grass and cellulose with phosphoric acid was undertaken in a microwave reactor system. The experimental data and reaction kinetic analysis indicate that this is a potential process for cellulose and hemi-cellulose hydrolysis, due to a rapid hydrolysis reaction at moderate temperatures. The optimum conditions for grass hydrolysis were found to be 2.5% phosphoric acid at a temperature of 175°C. It was found that sugar degradation occurred at acid concentrations greater than 2.5% (v/v) and temperatures greater than 175°C. In a further series of experiments, the kinetics of dilute acid hydrolysis of cellulose was investigated varying phosphoric acid concentration and reaction temperatures. The experimental data indicate that the use of microwave technology can successfully facilitate dilute acid hydrolysis of cellulose allowing high yields of glucose in short reaction times. The optimum conditions gave a yield of 90% glucose. A pseudo-homogeneous consecutive first order reaction was assumed and the reaction rate constants were calculated as: k₁ = 0.0813 s⁻¹; k₂ = 0.0075 s⁻¹, which compare favourably with reaction rate constants found in conventional non-microwave reaction systems. The kinetic analysis would indicate that the primary advantages of employing microwave heating were to: achieve a high rate constant at moderate temperatures: and to prevent ‘hot spot’ formation within the reactor, which would have cause localised degradation of glucose.     

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.     

Recycling of valuable chemicals through the catalytic decomposition of phenol tar in cumene process

The base catalyst LZ-2, which was the mixture of CaO and Na–NaOH/Al₂O₃·3H₂O, was chosen for the decomposition of phenol tar to generate valuable chemicals. The selectivity of LZ-2 for dimethyl phenyl carbinol, α-methyl styrene dimer and cumenyl phenol was 100%, 100% and 98%, respectively. Under the optimum operating conditions of catalyst 2.5 wt%, operating temperature 603.15 K and decomposition time 3.5 h, decomposition ratios of cumenyl phenol and dimethyl phenyl carbinol were 98.7% and 99.97%, respectively. In addition, the experimental repeatability demonstrated that the total yield of valuable chemicals still reached 90.1% after the catalyst being used five times. Mass and energy balance indicated that the catalytic decomposition was a high potential for the recycling of chemicals from phenol tar.     

A cost effective method for decentralized sewage treatment

The aim of this research was to upgrade the performance of a conventional septic tank (CST) for on-site treatment of sewage with negligible costs. Although CST is known as an inexpensive pre-treatment system, a complementary treatment is required to reuse its output effluent. In this work, the quality of treated wastewater reached to the standard level for irrigation by the innovational changes made in the structure of CST for converting it into an advanced septic reactor (ASR). The modification consists adding some pipe and trays without using any mechanical or electrical equipment.ASR was operated at ambient temperatures in laboratory and pilot-scale. The effects of up-flow velocities (V_up) of 0.4, 0.5, 0.7, 1 and 1.5 m/h and hydraulic retention times (HRT) of 36, 24 and 12 h on the ASR treatment performance were studied.For optimum V_up of 1 m/h and HRT of 24 h and biomass specific methanogenic activity (SMA) of 0.31 mg COD/g VSS d the maximum removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total suspended solids (TSS) were 86.2%, 79.4% and 95%, respectively.The results showed that ASR is an appropriate alternative for CST for sewage on-site treatment by a low cost modification.     

Achieving stable partial nitritation using endpoint pH control in an SBR treating landfill leachate

The feasibility of using endpoint pH control to achieve stable partial nitritation (PN) in an SBR for landfill leachate treatment was investigated. By imposing a fixed-time anoxia followed by variable-time aeration in an SBR cycle, successful partial nitritation was maintained for 182 days at a nitrogen loading rate of 0.30–0.89 kg/m³/day. The effluent NO₂⁻-N/NH₄⁺-N ratio and the effluent NO₃⁻-N concentration were 1.30 ± 0.22 and 16 ± 9 mg/L, respectively. High free ammonia (FA) and low dissolved oxygen (DO) concentrations were inhibition factors of nitrate formation. The termination of aeration at a suitable endpoint pH was the key to achieve an effluent NO₂⁻-N/NH₄⁺-N ratio close to the stoichiometric value. This endpoint pH control strategy represents practical potentials in the engineered application of combined PN–ANAMMOX processes.     

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.