فهرست مطالب bita ayati

Currently tons of dye produced per year, about the one sixth tons are converted into wastewater in various industries such as textiles and dyeing, which are among the toxic, carcinogenic and mutagenic wastes due to the presence of aromatic rings in their structure. This issue has attracted a lot of attention to the purification of such compounds. Ozone is one of the strong oxidizers which produces non-toxic compounds due to its decomposition. Ozone can convert many organic materials into simpler compounds through both direct and indirect oxidation mechanisms, including degradation of wastewater that contains double bonds components such as aromatic compounds and dyes. The purpose of this study was to investigate modeling, optimization and the interactions between parameters affecting the ozonation process in removal of Acid Orange 7 in order to achieve the highest removal efficiency for the highest possible initial dye concentration under the lowest ozone injection rate, no change in initial wastewater pH and the shortest reaction time by the use of response surface method. The RSM was performed using 4 parameters pH, initial dye concentration, ozone injection rate and time with 5 levels which ends up in 30 experimental tests. The results showed that correlation coefficients and adjusted correlation coefficients were 96.85 and 94.92, respectively, and p-value for model (less than 0.0001) and lack of fit (0.0507) were obtained as significant and non-significant, respectively. These results indicate the consistency and high reliability of the modeling results. Normal error, error independence and variance stability control were also checked which showed that the closeness between the actual and predicted values and the uniform distribution of the results obtained on the normal line indicates the uniform distribution of the error. The results and predictions of the software, the random distribution and distribution of the results indicate the suitability of the assumption considered by the software regarding the stability of the variance. Based on variance stability control, the effect of the experiments on the responses provided by the software. If one of the experiments is outside the range, this experiment will have a negative impact on the overall results of the software. In the case of experiments performed, this control was also well performed. Based on model equation the most important parameters are the injection rate of ozone (Q(O3)), pH, reaction time (T) and initial dye concentration [Dye], respectively, in which all parameters except the initial dye concentration have a positive effect on dye removal efficiency. After the related tests the optimum condition were the initial dye concentration of 480 mg/L, pH of 7.7, ozonation rate of 0.6 L/min and ozonation duration of 60 min which resulted in 90% dye removal efficiency. It was also found that the most effective factors were injectable ozone rate, time, pH, and dye concentration, respectively. The results showed that determining the appropriate domains can be of great importance in achieving the desired results from the response surface method. Also, the ozonation process is able to purify the dye from high initial concentrations to high removal efficiency, indicating the high strength of this applied process in the decomposition of complex organic compounds. Ozonation kinetic rate is based on pseudo first order which was increased from 0.3 to 0.6 by enhancing injected ozone rate from 0.2 to 0.6 L/min respectively and further increase of ozone injection rate didn’t had any effect on its kinetic rate.

Advanced oxidation processes (AOPs) are recognized as the most effective and capable available methods to remove and degrade different kind of dyes. Among various advanced oxidation processes, Fenton process is one of the most effective techniques that are used successfully to remove dyes without producing additional toxic by-products.

In the present study, all experiments were performed in a 500 mL rectangular plexiglass cubic reactor. The effect of different system parameters including pH, [Fe2+] to [H2O2] ratio, initial dye concentration, H2O2 concentration, stirrer velocity and temperature were examined and optimized using one- factor- at- a- time (OFAT) method.

The results obtained from this study showed that Fenton process can remove 96 percent of Acid Blue 25 from aqueous solution. The optimal condition using Fenton process included initial concentration of 150 mg/l, pH= 3, molar ratio of [Fe2+]/[H2O2] = 0.3, stir. vel.= 100 rpm, temperature 43°C and 10 min contact time.

Fenton process is suggested as a suitable method for the removal of Acid Blue 25.

There are different methods for soil stabilization, such as using windbreak, planting and use of mulch. The use of new soil stabilization methods, due to reduced environmental impacts, is a suitable alternative for oil mulch. Soil stabilization by using Nano polymer Polylatice creates a uniformly coherent cortex that is resistant to high wind speed and has less environmental degradation effects. In this research, the soil of the Hossein Abad area, near the salt lake of Qom, has been used for wind erosion test to verify the stabilization with the use of nano polymer Polylatice. After passing through a 2 mm sieve, the soils were stabilized with concentrations of 1, 1.5 and 2 L/m2 of Polylatice in trays with dimensions of 80*80*3 cm. These specimens were exposed to wind by three different velocities, including 10, 15 and 20 m/s, during 7 and 30 days and their stabilities were analyzed against wind. The concentration of dust of the Hossein Abad area in the 7 and 30-day stabilization decreased by 60 and 50 times at a wind speed of 20 m/s, respectively and as time passed by after adding mulch, the amount of particles deposited along the channel were also decreased significantly.

The aim of this study was to investigate the removal of acid orange 7 from aqueous solution using a new triple nanocomposite biochar/ZnO/SnO2. In this experimental study, weight percentages of ZnO, weight percentages of SnO2, pH, dye concentration and nanocomposite dosage as effective parameters on removal of acid orange 7 using one factorial method were analyzed. The maximum dye removal efficiency of 96.92% obtained at optimum conditions, 20% weight ratio for ZnO, 5% weight ratio for SnO2, pH = 7.1, 250 ppm dye concentration, 0.5 g/L nanocomposite dose after 60 minute. One of the highlights of the nanocomposite was its high power to remove dyes in a very short time. As after 2 minutes of testing, most of the dye (about 86%) was removed. It was also observed that the nanocomposite had the ability to reduce COD by 77.27% and TOC by 66.6% after 2 hours. Also, nanocomposite was reused until the fourth time, when the efficiency reduction for the first to fourth times was less than 10%. According to the results, the kinetics of the reactions for the nanocomposite were in accordance with the double exponential model and the Langmuir isotherm model was the most consistent with the observed data. Also, according to the thermodynamic studies, the dye adsorption on the surface of the nanocomposite was physical.

The purpose of this study was to compare the performance of Fe2+ activated persulfate and electro-persulfate process in Acid Blue 25 removal from aqueous solution. For this reason, the effects of different parameters including pH, dye, sodium persulfate and ferrous sulfate concentrations were investigated. The removal efficiency of 92% at the time of 60 min was obtained at pH= 3, dye concentration= 50 mg/L, sodium persulfate concentration= 500 mg/L and Fe (II) sulfate concentration= 100 mg/L for Fe2+ activated persulfate system and the removal efficiency of 95% at pH= 5, dye concentration = 200 mg/L, sodium persulfate concentration = 500 mg/L and ferrous sulfate concentration = 100 mg/L for electro-persulfate system by means of graphite materials as the neutral electrodes. COD removal efficiency in Fe2+ activated persulfate and electro-persulfate in the mentioned conditions were 90% and 89% in 180 minutes, respectively. Moreover, the result of process kinetics showed that using electrochemical process improved the reaction velocity from 0.0016 to 0.0487 mg/L/min. The comparison between these two-process showed that using electrochemical process improved dye removal efficiency by 4 times.

The textile industry wastewater causes serious environmental problems due to its high toxicity and color. Therefore, it is necessary to find an effective treatment technology for removing organic dyes from wastewater. Cavitation is one such modern technique which has been considered for the treatment of complex pollutants because of its ability to generate highly reactive free radicals. Up to now, researchers have mostly focused on qualitative interpretations and related scientific techniques, and there has been no quantitative cost analysis for pollutant control in textile industries for decision making purposes. Future studies need to focus on the cost analysis of more processes in textile wastewater treatment, such as advanced oxidation and combined and biological processes. Thus, this research was conducted with the aim of investigating and comparing various single and combined processes using the hydrodynamic cavitation (in a single system and with a specific contaminant) to remove reactive black 5 dye. Hydrodynamic cavitation (HC) was applied by using an orifice plate with a 7 mm hole diameter at the inlet pressure of 4 bars. Single processes, photocatalysis, photolysis, adsorption and combined processes, cavitation + photolysis, cavitation + photocatalyst and cavitation + photocatalysis were investigated in dye elimination and each of them was optimized by changing the various parameters (pH, TiO2 nanophotocatalyst concentration, irradiation power and dye concentration) and their best efficiency was obtained. In addition, considering the cost of energy and the nanophotocatalyst consumed by the processes, along with the process efficiency, processes were ranked by defining the index of efficiency to cost ratio. In the studied processes, efficiency increased as pH reduced, however, in the case of the photolysis process, efficiency increase at the highest level of the basic pH was significantly higher than acidic pH. Increasing the nanophotocatalyst concentration up to an optimum level resulted in efficiency increase. The decolorization rate increased as the irradiation power increased. The processes efficiency decreased with an increase in the initial concentration of the dye. In terms of efficiency, cavitation + photocatalysis, photocatalysis, cavitation + photolysis, photolysis, cavitation + photocatalyst, cavitation and adsorption processes, with the dye removal efficiencies of 83, 60, 52, 49, 43, 38 and 13% were placed first to seventh. This is while, considering both efficiency and cost consumption, photolysis process and then processes of cavitation + photolysis, cavitation and photocatalysis were ranked first to fourth, respectively with the best ratios. Hydrodynamic cavitation is a promising approach for dealing with industrial pollutants and the combination of this process with other advanced oxidation processes yields desirable results. Considering the parameters of energy and the cost of consumed nanophotocatalyst in the comparison of processes is very important and the output efficiency of the process should not be the only criterion. Paying attention to the substantial costs of nanophotocatalysts such as nanotitanium dioxide, combined techniques (e.g., the combination of cavitation with other advanced oxidation processes) lead to less consumption of nanomaterial and lower operational costs and are therefore cost-effective.

Activated sludge process is commonly utilized for the treatment of wastewater with the benefits of high efficiency and easy operation. However, during the biological treatment of wastewater, huge amounts of waste biomass (called as “waste activated sludge (WAS)”) are inevitably generated in the process. The WAS should be treated in order to reduce the water content of raw WAS, transform the highly putrescible organic matter into stable or inert organic and inorganic residue, and finally condition the residue to meet disposal acceptance regulations. But, WAS treatment and disposal, representing 50–60% of the total operating costs of the wastewater treatment. WAS is produced in massive volumes; specifically, more than 25,000 tons of WAS is produced in Iran per year. Anaerobic digestion is one the most applicable methods in WAS stabilization due to its ability to reduce WAS volume and produce biogases. A mixture of primary and secondary sludge (WAS) passes through anaerobic digestion, but this process is more difficult for WAS than primary sludge. However, the hydrolysis stage limits anaerobic WAS digestion. To optimize the general process of WAS anaerobic digestion and increase hydrolysis performance, it would be possible to pre-treat WAS by various mechanical, thermal, chemical, and biological methods. In this research the influence of ultrasonic bath pre-treatment was studied to observe the effects of ultrasonic density and sonication time on WAS solubilisation. The charactristics of ultrasonic wave producer was surface area of 240×137 mm2, frequency of 40 kHz, power of 265W. The effect of ultrasonic waves with these characteristics on WAS solubilization was investigated for the first time. Increases in soluble chemical oxygen demand and soluble polysaccharide concentration, as well as the decrease in volatile suspended solids, indicate that pre-treatment could cause WAS solubilisation. The cavitation produced by ultrasound waves radiation breaked down the bacterial cell wall and released the intracellular substances into an aqueous phase. Since polysaccharide is one of the main parts of extracellular polymeric substances (EPS), a polysaccharide concentration increase in the solution indicated that ultrasonication disintegrates WAS floc and the EPS value reduced in biological flocculation. Increases in ultrasonic density and sonication time caused more solubilisation, stronger cavitation arised with an increase in ultrasonic density and with increased ultrasonic density; more floc structure disintegration was achieved in less time. The best Pre-treatment efficiency was achieved in ultrasonic density 0.53 W/mL and 20 min. sonication time and it caused 20% increase in biogas production compared to the control sample. In addition to WAS pre-treatment for solubilisation, the ultrasonic bath pretreatment could improve WAS settling properties. After pre-treatment with the lowest energy in experiment rang, the diluted sludge volume index (DSVI) decreased by about 10% compared to the control sample; this reduction continued upon the energy increase. Reduction of EPS from around WAS floc reduced the negative charge of WAS floc and increased the WAS floc’s fall rate. Therefore, DSVI reduction resulting from ultrasonic bath pre-treatment could be due to the EPS concentration reduction around WAS floc. Likewise, the influence of pre-treatment on electrical conductivity was also examined for the first time. Given the change in WAS, electrical conductivity with ultrasonic bath pre-treatment, in addition to other tests like chemical oxygen demand and volatile suspended solids, electrical conductivity could also effectively assess WAS solubilisation.

In this study, TiO2/Fe3O4 and TiO2/Fe3O4/MWCNT as a new magnetic nanophotocatalytic materials were synthesized. For this, TiO2 nanoparticle were fixed on an inert surface by sonochemical method. X-ray Diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (DRS), vibration sample magnetometry (VSM) were used to characterize the magnetic nanocomposites. SEM analysis indicated that TiO2 and Fe3O4 nanoparticles were adhered to MWCNT. Ability of the nanocomposites to remove organic pollutants were investigated by photodegradation of Acid Red 14, Acid Blue 19, Reactive Red 77, and Methyl Orange dyes simulated conditions similar to sunlight. Furthermore, the removal efficiency of AR14 were investigated under direct sunlight irradiation, with an initial concentration of 50 mg/L by TiO2, TiO2/Fe3O4 and TiO2/Fe3O4/MWCNT nanocatalysts were 89.83, 21.19 and 86.27, respectively. According to the results, addition of carbon nanotubes to the TiO2/Fe3O4 magnetic nanocomposite, increased the efficiency of AR14 photodegradtion through change in energy gap visible waves and the scavenging role of carbon nanotubes. Also, The reusability of nanocomposites was assessed in five consecutive cycles of 6 hours, The results showed that after 5 cycles the degradation rate decreased only 7.79 %.

This study was conducted to evaluate sodium dodecyl benzene sulfonate removal using electrocoagulation/flotation and photocatalytic nano-TiO2 slurry systems. The parameters which are effective on the surfactant removal were investigated and optimized. Electrocoagulation/flotation system included meshed and mono-polar stainless steel electrodes which installed horizontally. According to the results, after 60 minutes in pH of 8, electrodes distance of 1 cm, initial SDBS concentration of 750 mg/L, SDBS and COD removal rates were achieved to 93.54 and 90%, respectively. In photocatalytic system, during 48 h, SDBS and COD removed 98.7 and 95%, respectively, while pH was around 8, initial concentration of SDBS was 300 mg/L and nano-TiO2 particles concentration was 0.5 mg/L. In the hybrid system, after 12 minutes, SDBS concentration reached to 329 mg/L which entered to the photocatalytic system that resulted in SDBS and COD removal efficiency of 99 and 96.27%, respectively. Compared to the single systems, by using the hybrid system, the removal efficiencies were improved.

Petroleum is the major source of energy and the activities related to the petroleum industry leading to high volumes of wastewater and emissions different pollutants to water systems. According to studies, world oil demand will increase to about 107 million barrels a day over the next two decades, and about 32 percent of global energy will be provided from Petroleum by 2030. Thus wastewater resulting from oil and refinery industry is increasingly rising and discharges into the environment, which is a serious threat to the world's water resources. A large amount of water is used to extract and to refine the petroleum in oil refineries, thus produce the large amounts of wastewater. The wastewaters containing various kinds of pollutants with different concentrations are of environmental problems due to high organic load and hard-biodegradable compounds. With the increasing drinking water standards and environmental stricter regulations relation to discharge of sewage, electrochemical technologies have gained their importance all over the world during the last two decades and now electrochemical processes such as recovery of metals, electrocoagulation, electro-flotation and electro-oxidation can be effective technologies in the field of different wastewater treatment. In the electrocoagulation process by applying an electric current to the cathode and anode electrodes in a conductive solution by dissolving anode, coagulants produced in situ and cause the flocs is that they are floating with bubbles of hydrogen gas generated at the cathode. The metal ion generation takes place at the anode, while hydrogen gas is produced at the cathode. The metal ions form flocculates which trap contaminants while the hydrogen gas floats these particles. In this study, the electrocoagulation process was carried out with the use of a cathode and an anode made of stainless steel to reduce pollution from synthesis wastewater. For this purpose, the various parameters are optimized separately in this system by one factorial method, and then use experiment design methods. The effects of five parameters including the electrode surface, initial COD concentration, current density, pH and NaCl concentration were evaluated in the range of 23.36 to 78.36 cm2, 100 to 2500 mg/L, 2 to 30 mA/cm2, 3 to 11 and 0.3 to 2 g/L, respectively, in the case of electrocoagulation process. The optimum conditions of electrode surface, initial COD concentration, current density, pH and NaCl concentration were achieved 23.36 cm2, 900 mg/L, 20 mA/cm2, 8.5 and 0.5 g/L, respectively, for this process with energy consumption of 7.3 kWh/kg CODRem and electrode consumption of 0.4 Kg Fe/Kg CODRem during 60 minutes. The results of the experimental design of response surface methodology were confirmed the results of OFAT method with acceptable obtained error for the electrocoagulation processes. Based on results from experimental design of response surface methodology in this process, current density, time, pH and concentration of sodium chloride, respectively, were the most influential parameters. Electro-coagulation process seems to be an economic and environmental friendly process to remove the pollutants from wastewater. It has been demonstrated that electrocoagulation process with the use of stainless steel anode and cathode is a very effective and operative method to degrade Petroleum pollution and reduce COD.

Many pollutants in industrial wastewaters, such as dyes, can't be removed easily by the conventional physical, biological and chemical purification processes, because of their complexity and intractability. Therefore, it is necessary to find an effective treatment technology that can degrade complex bio-refractory molecules or can breakdown them into smaller molecules which can be further degraded by conventional methods. Cavitation is one such recent technique which has been extensively studied for the treatment of complex wastewater due to its ability of generating highly reactive free radicals. Hydrodynamic cavitation has a potential of application on larger scale due to its capability in generating hydroxyl radicals at ambient condition, easy scale up and less material cost making it more economical to employ. The purpose of this study was application of hydrodynamic cavitation process for removing Reactive Black 5 and optimization the affecting parameters (pH, inlet pressure, hole diameter and initial concentration of dye) based on the amount of efficiency and energy consumption. Material and methods: In this research, removal of Reactive Black 5 with the use of hydrodynamic cavitation process was studied. 8.25 liters of colored solution was examined in each test. The cavitation was produced by orifice plate and pump. In order to optimize process, various trials were performed in pH of 3 to 11 and also using different orifice plates with hole diameter of 2, 3, 5 and 7 mm at inlet pressures of 2, 3, 4 and 5 bar and dye concentration of 30, 50 and 100 ppm. Due to the constant voltage of urban electricity, the electric current was measured as an indicator of energy consumption by ammeter. According to the results by reducing the pH, dye removal was increased and orifice plates with larger hole diameter in upper pressures had better efficiency. It was observed that increasing the initial concentration of dye resulted in decreasing dye removal efficiency. The orifice with 7 mm hole diameter at 5 bar inlet pressure yielded the highest efficiency, but by involving the amount of energy consumed and considering the process efficiency to energy consumption, the orifice with 7 mm hole diameter at 4 bar inlet pressure was chosen as the best. The pH of 3, orifice with 7 mm hole diameter at 4 bar pressure and initial concentration of 30 ppm (with regards to pump energy consumption obtained from measuring the electrical current and the efficiency of process) were selected as optimum conditions. In these conditions after 120 minutes, 38.21% dye removal was obtained using hydrodynamic cavitation. Hydrodynamic cavitation has a potential of application on larger scale due to its capability in generating hydroxyl radicals at ambient condition. It was found that the energy consumption was an effective factor in selecting the optimum conditions. By reducing the initial dye concentration and pH, dye removal was increased and orifice plates with larger hole diameter in upper pressures had better efficiency.

Surfactants are considered as chemical combinations with many environmental impacts such as eutrophication, foam generation, and oxygen reduction. This experimental study is conducted to evaluate the removal of Sodium dodecyl benzene sulfonate (SDBS) using unipolar electro-flotation and electro coagulation system. The experimental set up was installed as a cubic shape with effective volume of 735 ml and stainless steel mono-polar electrodes arranged in a horizontal fashion. Parameters evaluated individualy for the overall system optimization include: distance between electrodes (0.5-1.5 cm), surfactants initial concentration (50-1000 mg/L), pH (3-11), current density (0.5–1.5 A), and electric conductivity (950-3500 S/cmμ). Results obtained during the 1 hr operation time showed that the optimum surfactant and COD removal efficiency were about 94 and 90 percent, respectively. This optimum removal eficciencies were accomplished under the following condition: pH=8, distance between electrodes =1 cm, initial surfactant concentration = 750 mg/L, current density = 1 A, and EC = 1440 μS/cm . In addition, the energy consumption and anode dissolution were 45.03 kWh/kg and 1.04 kg Fe/kg for SDBS removal, respectively. In conclusion, the results obtained in this study support the application of electro-flotation and electro coagulation as an appoperiate system for the removal of surfactants such as detergent.

The petroleum refineries, water are used for different purposes, such as extraction of contaminants. Some of these pollutants such as petroleum and Methyl Tertiary Butyl ether (MTBE) can be noted that have less biodegradability than other organic compounds. Discharge of these pollutants into water, and the presence of them in drinking water make huge environmental concerns.
A sequencing airlift reactor (SBR) along with an internal riser is called sequencing batch airlift reactor (SBAR); it has a similar structure to SBR and purifies wastewater with a certain temporal cycle in a single reactor. The SBAR system, which is used along with granules to treat wastewater, is known as granule sequencing batch airlift reactor (GSBAR). Using this system for biodegrading requires a high concentration of biomass (aerobic granules. In recent years, several studies have been conducted on the use of aerobic biogranules. Mousavi et al., examined the removal of phenol with an initial concentration of 1000 mg/L from saline wastewater using GSBAR with aerobic granules 2 mm in size. The results indicated that 99% of phenol was removed. Bao et al., studied the effect of temperature on the formation of aerobic granules and on the removal of nutrients by SBAR system. The granules had an average diameter of 3–4 mm, density of 1.036 g/mL, sludge volume index of 37 mL/g, and sedimentation rate of 18.6–65.1 cm/min. The input load rate of COD, NH4–N, and PO4–P was 1.2–2.4, 0.122, and 0.012–0.024 kg/m3/day, respectively and the removal efficiency at low temperatures was 90.6–95.4, 72.8–82.1, and 95.8–97.9%, respectively. Taheri et al., examined the formation of aerobic granules in SBR for treating saline wastewater. In this study, the granules were 3–7 mm in size, had a fall speed of 0.9–1.35 cm/s, and density of 32-60 g/L. Using aerobic granules with a diameter of 1–2 mm to biologically restore 2, 4-di-chlorophenol with an initial concentration of 4.8 mg/L, Wang et al., achieved the removal efficiency of 95% and 94% for COD and di-chlorophenol, respectively. Siroos Rezaei et al. reported that COD removal efficiency of synthetic wastewater was 95% with the glucose carbon source in six 4-h cycles with a loading rate of 1500 mg/L in SBAR system using aerobic granules. The new granules had different diameters in the range of 0.5–5 mm, high sedimentation ability, and SVI of 100 mL/g. Ghaderi et al., investigated the performance of the biofilm reactor and SBR in removing formaldehyde from wastewater. The results revealed that removal efficiency of CODs less than 200 mg/L was 100% and removal efficiency of CODs between 200–450 mg/L was 90% after 48 h. The aim of this study was evaluating the ability of SBAR system in quick produce of granules and achieving high removal of petroleum and MTBE in a short time. For this purpose, 2 similar SBAR systems with Circular cross-section were used. Outer Cylinder's diameter and length was respectively 8cm and 110 and the internal riser's diameter and length was respectively 4 cm and 90 cm. In the first system (R1) petroleum was treated in 6 hours and in the second system (R2) MTBE wastewater was treated in 4 hours. In COD equivalent to 600 mg/L, the removal efficiency of R1 and R2 were equal to 81.1 and 84.2%. These values were respectively 82.8 and 90% in COD equivalent 500 mg/L. Consider to granules changes, optimal COD was respectively equivalent to 600 and 500 mg/L in R1 and R2. By reducing retention time to 5 and 3 hours in R1 and R2, removal efficiency of pollutants in optimal COD of each system was respectively 77.8 and 90 %. The first granules were observed in the seventh day of operating system. During this period, the size of the granules increased to 1.3 and 0.6 mm in R1 and R2. Density and velocity of the granules were in the range of 0.0252-1.1998 gr/mL and 3.02-3.32 cm/s in R1 and 0.05-0.06502 gr/mL and 0.4-0.9 cm/s in R2. SVI was in the range of 42-65 mL/g, pH and DO was in the range of 6.8-7.2 and 2-6 mg/L and ORP was always above 100 mV.

The present study used the adsorption process of activated carbon produced from agricultural wastes and the photocatalytic process of nano-ZnO to break down complex compounds available in removing Direct Blue 71 (henceforth, DB71). The two processes were done under three varied circumstances- adsorption/photocatalytic, photocatalytic/ adsorption, and simultaneous use of the processes. First, DB71 was exposed to activated carbon produced from walnut and almond shells and the efficiency achieved at equilibrium time (45 and 60 minutes) was 55 and 60 percent, respectively. Then, DB71 was exposed to different dosages of nano-ZnO to remove the dye completely. The result showed that amount of AC/ZnO in an optimum condition for two walnut and almond shell absorbents were 0.75/0.096 and1/0.096 g/L. Second, (photocatalytic/ adsorption) the complex compound of DB71 with a dosage of 0.024 g/L was broken down as a result of UV radiation. The experiment proceeded with different dosages of walnut and almond shells after achieving the efficiency of 50% in removing DB71 in the second process. The amounts of AC/ZnO were 0.75/0.024 and 1/0.024 for walnut and almond shells respectively under the optimum condition for the second process. In the third process advantages of the simultaneous use of photocatalytic and adsorption processes were taken in which different dosages of AC/ ZnO were used. Given the smaller dosages of nano-ZnO and less dye removal time, amounts of 0.75/ 0.288 g/L and 0.75/0.288 g/L were measured for walnut and almond shells. The findings show that photocatalytic/adsorption process was the more optimal process because of the less dosages of nano-ZnO, efficiency of removing DB71 and shorter dye removing time. Furthermore, the effect of the intensity of UV radiant on the efficiency and time of removing DB71 was also examined. The experiment revealed that removing COD in the optimum conditions were 47.22 and 49.6 and 62.23 and 63.15 percent using walnut and almond shell respectively both in the first experiment and the simulations use of adsorption and photocatalytic processes after 30 hours. While, in the second experiment (photocatalytic/ adsorption) 42.21 and 39.18 percent of COD were removed using walnut and almond shell respectively after 30 hours. The LC-mass test of photocatalytic/adsorption process also showed the degradation of DB 71 complex compounds.

The use of different synthetic dyes in textile industries has increased in recent decay, resulting in the release of dye-containing industrial effluents into natural aquatic ecosystem. Since most of dyes are usually very recalcitrant to microbial degradation, therefore dye removal from effluent is a main concern in many studies. Different process was used for the treatment of dye effluent. In the last few years, studies were focused on advanced oxidation process (AOPs) methods such as UV-ZnO, UV-H2O2, UV-O3 and UV-TiO2. Photocatalytic process such as UV-ZnO is an efficient method that treats non-degradable wastewater by active radicals. The photocatalysis needs a photo-reactor that contacts reactant, products and light. In recent years, different types of photo-reactors have been used for wastewater treatment. In some reactors, nano-photocatalysts are utilized in slurry form, and the other particles are coated on bed. In Photocatalytic reactors with fixed bed, nano-photocatalysts are immobilized on bed and do not need the separation unit, but the main disadvantage of this photo-reactors is the low mass transfer rate between wastewater and nano-photocatalysts. Consequently, Different optimal photo-reactors were developed for increasing mass transfer rate. In this study, a novel photocatalytic cascade disc reactor coated with ZnO nano-photocatalysts was applied and in order to increase mass transfer rate artificial roughness were created on the surface of disks. Applying artificial roughness changes mass transfer rate by providing vertical mixing, creating secondary currents and increasing the Reynolds number. This photo-reactor has a number of advantages that include eliminating the need for catalyst separation units as the catalyst is immobilized, creating the flow mixing by non-mechanical method, increasing the transport of oxygen from the gas phase to the photocatalyst surface by providing the flow cascade pattern. The photo-reactor was used in order to remove Reactive Yellow 81 (RY81) dye from textile industry effluent, by means of UV-ZnO process. RY81 is a reactive dye composed of 10 Benzene rings and two –N=N azo bonds. The effect of different operational parameters such as initial Concentration of dye, pH, Catalyst surface loading and flow rate in removal efficiency was investigated, and the optimal value of those parameters were 50 mg/L, 8, 40 gr/m2 and 80 cc/s, respectively. A rate equation for the removal of RY81 was obtained by mathematical kinetic modeling. The Langmuir-Hinshelwood kinetic model is one of the most common kinetic models that are used for studying the kinetics of heterogeneous photo-catalysis. The results of reaction kinetic modeling indicate the conformity of removal kinetics with Langmuir-Hinshelwood model, and the constants kL-H and Kads were obtained 7.17 mg L-1 hr-1, 0.122 mg-1 L, respectively.
One way of inserting various operational parameters to a rate equation is regression analysis. Therefore, in this study, nonlinear regression model was developed for prediction pseudo- first order rate constant as a function of initial concentration of dye, pH, catalyst surface loading and flow rate. This equation could properly predict (R2=0.95) the removal rate constant of RY81 removal in the photocatalytic cascade disk reactor under different operational conditions and a good consistency was observed between the calculated results and experimental findings.

Effluents bearing petroleum hydrocarbons must be treated prior to release into the environment due to the high toxicity of these compounds and the consequent hazards they pose to the receiving environment. The moving bed biofilm reactor (MBBR) is one of the several biofilm systems used in treating different types of wastewater that offers a good resistance to both toxic and hydraulic shocks. This study investigates the roles of the three air stripping, adsorption, and biodegradation mechanisms in the biofilm reactor using polyethylene sponge strips used as the biomass to treat the effluent from Tehran Refinery. Based on the results obtained, the optimum values of loading rate, retention time, and media filling ratio were equal to TPH=278 mg/L (COD=1000 mg/L), 22 hours, and 50 percent, respectively. Laboratory studies confirmed that each of the three mechanisms of air stripping, adsorption, and biodegradation may be involved in the removal of petroleum hydrocarbons by the MBBR system depending on hydrocarbon concentrations. More specifically, biological degradation was the dominant removal mechanism with lower loading rates (TPH=57 mg/l with a COD equal to 200 mg/l) while stripping became the dominant mechanism at higher loading rates (TPH=278 mg/l with a COD equal to 1,000 mg/l). It was found that under optimum conditions and at TPH=278 mg/L (and COD=1,000 mg/l), stripping removed 58%; biodegradation, 29%; and adsorption, 13% of the petroleum hydrocarbon content. It was observed that the removal of petroleum hydrocarbons by stripping and adsorption processes took place within the first process hour at the latest.

Removal of petroleum hydrocarbons from synthetic contaminated water using with photocatalytic process was conducted in the presence of nano TiO2 immobilized on the concrete plates. The solar photoreactor was consisted of storage tank of 60 L with floating pump, cascade system with 5 concrete steps, a 5 L weir on the top of the stairs and metalic chassis. The UV-A radiation of the sunlight was used instead of UV-A lamps as the irradiation source. The optimum parameters were pH of 5, TiO2 mass loading of 60 grm-2, UV equivalent irradiation time of 200 min, initial concentration of 100 mgL-1 and H2O2 concentration of 2000 mgL-1.The results demonstrated that under optimal conditions removal efficiency of chemical oxygen demand (COD), total petroleum hydrocarbons (TPH) and poly aromatic hydrocarbons (PAHs) were 70.48%, 67.63 % and 84.75% respectively. Also the results of GC-FID analysis indicated that most of PAHs were eliminated and only non-toxic aliphatic hydrocarbons were remained.

The aim of this study was to investigate MTBE removal efficiency using sequencing batch airlift reactor (SBAR) and to determine the share of aeration and adsorption processes during the operation. The present study was conducted with a new design of the system (cubic area and embedded baffle). The reactor was applied in 4-h cycles, which included 2 min filling, 210 min aeration, 5 min sedimentation, 8 min draw, and 15 min idle time. One week after start-up, the initial brown granules were observed. During the operation, some granules were formed with the size of 2–6 mm, average settling velocity and density of 0.66 cm/s and 0.06 g/mL, respectively. The results showed that COD removal efficiency was over 94 percent.

Everyday million liters of color wastewater are produced in different industries and cuases environmental problems. The textile industry significantly affects the environment, producing high volume of wastewater from water and chemicals used in processes including sizing, washing, bleaching, dyeing, printing, and finishing. The wastewater contains salts, acid, or alkali, washing solvents, other chemicals, intermediates, and residue dyes. In the presence of toxic colored substances in water light fails to penetrate the waters lower layers and consequently the photosynthesis of water plants and the level of dissolved oxygen decreases, and results in the death of aquatic life. Dyes are stable compounds that are not easily biodegradable; especially Azo dyes which are considered to be carcinogens that pollute the surface and groundwater.
Generally, the physical, chemical and biological methods or a combination of them have been used for treating textile wastewater can be mentioned as membrane filtration, and ultrasonic waves, electrocoagulation, adsorption, Fenton, photo-Fenton, ion exchange, electrolysis, coagulation, conventional, and advanced oxidation and photo-catalytic process.
In recent years, the ability of advanced oxidation processes in treating various hazardous wastes has brought this technology to the forefront of research. Among advanced oxidation processes, application of heterogeneous photo-catalysis by using semiconductors has been proved to be real interest as an efficient tool for degrading both aquatic and atmospheric organic contaminants. Semiconductors are photo-reactive metal oxides for contaminants eradication that refer to photo-catalysts. These methods mineralize and converse pollutants into CO2, H2O and inorganic ions, by the action of hydroxyl radical, which acts as a nonselective and strong oxidant of organics.
Because of the excellent properties and wide applications on nanomaterials, recent years, researchers start to focus on the nano-zinc oxide granule size lies in the 1-100 nms, because of having nanophase structure and char acteristics, it gets the surface effect and bulk effect and gains some special capabilities (on magnetism, light, electric and sensitivity etc.) and many new usages.
Photocatalytic reactors for water and wastewater treatment can be classified to slurry and immobilized systems. In the slurry reactors, the nano particles are freely dispersed in the water phase and consequently the photo-catalyst is fully integrated in the liquid mobile phase. Whereas the immobilized catalyst reactor design features a catalyst anchored to a fixed support and dispersed on the stationary phase.
The mail aim of this sudy was to compare removal efficiency of acid orange 7, one of the high consumed textile dyes, in slurry and immobilized methods using photocatalyst UV/ZnO process.
Methods and materials: In this study, after detrmination of the maximum absorption wavelength of acid orange 7 (Table 1), the initial experiments were done to determine the main role of photocatalyst process (Figure). Then the effect of different amounts of dye concentration and catalyst, pH, irradiation power and energy consumption were investigated and optimized for both slurry and immobilized systems by changing one papramter and keepig the others constant.
The Water Sealer Method (WSM) was used to immobilize the nano ZnO powder on concrete surface. The process began by complete mixing of 100 mL of selected concrete sealer (colorless liquid) with measured amounts of ZnO. To the cured concrete surface of one reactor, 10 mL of 10% (by mass) ZnO sealer solution was prepared and put into ultrasonic cleaner (Fungilab UE-6SFD) for 5 min to ensure the complete separation of nano particles. Then the solution was applied and allowed to be cured for at least 3 d.
Table 1 Characteristic of Acid Orange 7
Structure
Formula C16H11N2NaO4S
Molar mass 350.3243
λmax 487 nm
Solution pH 3
Slurry and immobilized photo-catalyst reactors
According to the Beer Lambert law, by measuring the absorbance of samples at the maximum absorption wavelength of the dye (487 nm) in a spectrophotometer, dye concentration and removal rate (Eq. 1) were calculated, where CR was color removal efficiency (%), C0 represented initial dye concentration, and C indicated instant dye concentration. In order to eliminate flocs errors, samples were filtered and centrifuged prior to placing them in the spectrophotometer.
(1)
The main equipments used in this study include a Kern PLS 360-3 digital scale with 0.001 accuracy and Metrohm 691 pH meter. The amount of dye in solution was measured by using a Hach DR-4000 spectrophotometer at a wavelength of maximum absorption of acid orange 7 (485 nm) and the calibration curve of dye concentrations, respectively. All experiments were performed according to the method of analysis of water and wastewater and repeated at least 3 times.
In summary, acid orange 7 could be successfully degraded and mineralized by nanophotocatalysis in both slurry and immobilized ZnO nanoparticle photocatalytic reactors.
The experiments in optimum conditions in both slurry and immobilized methods were shown that in pH of 7, catalyst concentration of 80 gr/m2 (10.32 gr/L) and 32 Watt UVc lamps, over 95 and 35 percent of 50 ppm dye was removed in slurry and immobilized methods, respectively. The amount of COD removal was higher in the slurry method (Table 2).
Table 2- Comparison of optimum conditions in the studied systems
Immobilized System Slurry System parameter
80 gr/m2 10.32 gr/L Catalyst Concetration
50 50 Dye Concentration (ppm)
7 7 pH
32 32 Power (Watt)
375 56 Time
4 6 COD Removal after 60 minutes
35 45 COD Removal after 375 minutes

The growing use of MTBE as a substitute for Tetraethyl lead and its adverse impacts on the environment warrant its removal from wastewater. Given the low efficiencty and the high cost associated with the chemical and physical processess commonly used for the removal of MTBE, which also release hazardous by-products into the environment, biological techniques have been explored as the more appropriate methods for its removal. This research seeks to investigate the feasibility of the SBAR system and aerobic biogranules for MTBE removal. For this purpose, a synthetic wastewater containing the materials needed for the microorganisms was used for the experiments and the pH level and DO were set to 7‒8 and 2‒5 mg/L, respectively. TEM was employed to characterize the granules. Results showed that over 90% of the initial COD (500 mg/L) was removed after 4h, which was attributed to the air stripping (28%) and sorption (1.5%) mechanisms. The resulting granules were brown in color, 2‒6 mm in size with a mean fall speed and a density equal to 0.65 cm/s and 0.055 g/ml, respectively. The superiority of the resulting granules to the flocs led to improved sedimentation in the reactor. Finally, TEM investigations showed that the sylyath and rotifer species formed the dominant populations in the granules.

Water contaminated with petroleum hydrocarbons has harmful effects on health, economy and environment. In this study, photolysis process for treating petroleum hydrocarbons was investigated. Hence different initial CODs with different UV-C radiation power were examined. Based on the energy consumption per unit of COD removed, COD of 350 mg/L and radiation power of 80 W were chosen as the optimum conditions. To improve model prediction, in addition to the aforementioned CODs, COD=1000 mg/L in 60 W was also tested. The findings indicated that photolysis can be considered as a suitable pretreatment process for the biological systems.

The removal of Acid Orange 7 by the photoelectrocatalytic process was investigated at ambient temperature under solar irradiation using graphite as the cathode and stainless steel coated with the ZnO/TiO2 nanocomposite as the anode. The microstructure of the ZnO/TiO2 coated electrode was characterized by the SEM test. The results revealed dye and COD removal efficiencies of 99% and 97%, respectively, over a period of 360 minutes. The best performance was achieved in 360 minutes with no aeration at a current of 1 mA/cm2, an initial dye concentration of 100 mg/L, an electrode surface area of 30 cm2, and an electrolyte concentration of 0.01 M; energy consumption under these optimum conditions was 0.15 KWh/ppm. It may be concluded that the photoelectrocatalytic process is well capable of removing organic compounds, especially textile effluents containing dyes and non-degradable contaminants, due to its ability to produce hydroxyl radicals, superoxide, etc. Thus, the technique may be recommended for use as a pre-treatment process to reduce operational costs.

Azo dyes constitute the largest class of dyes and contains one or various azo groups conjugated with aromatic systems such as acid azo dyes which have sulfonic groups causing strong attachment to the cationic groups of fibers. The characteristics of these materials are high color intensity and visibility in very low concentrations, complex chemical structures, and light resistance and hard to biodegradability, variability in pH range and above of these they have high carcinogenic and mutagenic potential. Generally, the physical, chemical and biological methods are considered as textile wastewater treatment techniques such as electrocoagulation, absorption, advanced oxidation, Fenton, photo-Fenton, photoelectrochemical and photoelectrocatalytic. Electro-Fenton is an indirect oxidation process and is based on in situ electrochemical generation of peroxide hydrogen due to electrochemical reduction of dissolved oxygen next to graphite cathode. In this process hydroxide radicals are generated by reaction of hydrogen peroxide and iron ions in acidic condition. Hydroxide radicals are the most powerful radicals with high oxidation potential lead to degrade organic matters into simple compounds like water and carbon dioxide. Recently carbonic material like carbon felt, graphite, activated carbon fibers, carbon nanotubes, carbonic sponge and graphite-PTFE are used to improve electro-Fenton process. Enhancement of surface area, reaction rate and electron transfer are the main reasons which Carbon nanotubes are used to improve electrochemical production of hydrogen peroxide in electro-Fenton process. Dye removal increased at initial reaction time by increasing current intensity, aeration rate and electrode surface due to enhancing electro-Fenton regents, meanwhile it decreased with increasing pH and electrolyte concentration. Reduction in dye degradation is usually caused by scavenging role of hydrogen peroxide and iron ions due to reaction of these compounds with hydroxyl radicals which decreased its concentration in reactor. Dye degradation increase by enhancement of Initial dye concentration from 35 to 100 mg/L but when initial dye concentration increased further to 200 mg/L, degradation rate was reduced. On the other hand energy consumption reduced by decreasing current intensity from 2 to 1 mA/cm2 and enhancing electrode surface from 30 to 90 cm2. It has been shown that carbon nanotubes coated on graphite cathode could enhance dye removal rate by increasing hydrogen peroxide concentration due to increase electrode surface area, electron transfer and reaction rate. The results showed that dye and COD removal efficiency was obtained 98% and 95% after 180 and 360 minutes respectively at the optimal condition of effective parameters such as current density of 1 mA/cm2, pH of 6.5, no aeration, initial dye concentration of 100 mg/L, electrode surface of 90 cm2, electrolyte concentration of 0.01 M, temperature of 25 ◦C and energy consumption of 0.13 KWh/ppm. Electro-Fenton process seems to be an economic and environmental friendly process to remove the toxicity of the persistent organic pollutants from water due to generation of hydrogen peroxide and hydroxyl radicals. It has been demonstrated that electro-Fenton process with the use of stainless steel anode and graphite cathode coated with carbon nanotube is a very effective and operative method to degrade Acid Orange 7.

Synthetic dyes and specially azo dyes are common pollutants found in textile and dyeing industries effluent. azo dyes are the most important class of synthetic dyes and and represent about 70% of all world dyes consumption. Textile effluent can cause considerable pollution and rise high health risk factors due to loos of 20% of dyes in process and large scale of dyes used in these industries. The characteristics of the textile wastewater are high color intensity and visibility in very low concentrations, complex chemical structures, and light resistance and hard to biodegradability, variability in pH range and above of these they have high carcinogenic and mutagenic potential.
Generally, the physical, chemical and biological methods were used for treating textile wastewater can be mentioned as electrocoagulation, adsorption, Fenton, photo-Fenton and photo-catalytic process.
In recent years, advanced oxidation technologies have been described as efficient procedures to obtain high oxidation yields from several kinds of organic compounds. These methods mineralize and converse pollutants into CO2, H2O and inorganic ions, by the action of hydroxyl radical, which acts as a nonselective and strong oxidant of organics.
Electro-Fenton is a common advanced oxidation processes which contains electrochemical production of H2O2 and Fenton process that makes each process more efficient. Its advantages are low operation cost, high potential for complete destruction and removal of organic pollutants into harmless compounds such as CO2, water and mineral salts. Electro-Fenton Process involves the reaction of a homogeneous organic contaminants with strong oxidants, H2O2 that produced by injecting air into water near the carbon electrode cathode and the iron ion as catalyst produce hydroxyl radical which eventually led to the decomposition of organic compounds.
In this study, electrochemical process was developed at ambient temperature in a 500 mL rectangular plexiglass cubic reactor which includes two electrodes, an anode made of 304 stainless steel and a graphite cathode placed 3cm from each other and a PM-3005D power supply. Air was blowing in the cathodic zone by an RS Electrical 610 air generator pump and an IKA RH-Bassic 2 magnetic stirrer was used to mix and homogenize the sample. The other equipments used in this study include a Kern PLS 360-3 digital scale with 0.001 accuracy and Metrohm 691 pH meter. The amount of dye in solution is measured by using a Hach DR-4000 spectrophotometer at a wavelength of maximum absorption of acid orange 7 (485 nm) and the calibration curve of dye concentrations, respectively.
In this study, several parameters including current intensity (0.3, 0.6, 0.9 and 1.2 A), aeration rates (0, 3.5 and 7 L/min), electrodes area (30, 60, 90 cm2), initial pH (2, 3, 6.5 and 9) and energy consumption were examined.
In order to maintain the flow of electricity in the cells, Na2SO4 (Merck) 0.01 M was used. All experiments were performed according to the method of analysis of water and wastewater.
3.1. Effect of current intensity
The influence of current intensity has been investigated in the range of 0.3 to 1.2 A., when current intensity was 0.3, dye removal efficiency was 71% after 120 min reaction. Increase of current intensity to 1.2 A could enhance dye removal efficiency to 94%, caused by increasing production of ferrous ions and hydrogen peroxide that results to enhance the production of hydroxyl radical. When the current intensity was increased further, excessive hydroxyl radicals would be consumed via following side reactions which may reduce the dye removal efficiency.
Fe2 OH0 → Fe3 OH- (1)
H2O2 OH0 → HO20 H2O (2)
OH0 → O2(g) 2H 2e- (3)
Due to the dye removal efficiency at current intensities of 0.6 and 1.2 A were approximately equal, the current intensity of 0.6 A was selected as the optimum level with lower power consumption than other cases (0.24 KWh/ppm).
3.2. Effect of air flow
Increasing the air flow rate from 0 to 3.5 L/min resulted in an increase of the acid orange 7 removal efficiency from 80 to 90 percent at 150 min. The removal efficiency remained constant when the air rate was increased to 7 L/min. The experimental results indicated that increasing air flow leads to increase hydrogen peroxide and enhance dye removal efficiency by improving production of hydroxide radicals, But further increase in air flow would lead to reduce removal efficiency by consumption of hydroxide radical with exceed hydrogen peroxide (reaction 2).
3.3. Effect of electrode surface
The results showed that when the electrode surface were 30, 60 and 90 cm2, the degradation percent of acid orange 7 after 300 min were 68, 89 and 97 percent, respectively. However by increasing time reaction, dye removal reaches to constant value. It was well known that the amounts of electro-Fenton reagents would be increased by enhancing electrode surface and result in increasing dye degradation.
3.4. Effect of initial pH Due to the direct production of hydrogen peroxide in situ, the highest dye removal efficiency was obtained at pH=2 because in this pH, H2O2 is more stable and could be produced more efficiently. Anyway, increase the initial pH lead to reduce dye removal efficiency in the first 60 minutes. Dye removal efficiency is decreased by increasing the pH to the neutral and alkaline ranges because of the formation of ferric hydroxide species, reduction in the ferrous ions reproduction and reduction in hydrogen peroxide generation. The results show that the dye removal were 76, 64, 62, and 55 percent, with initial pH of 2, 3, 6.5 and 9 at 60 min electrolysis respectively. However with increasing time reaction, efficiency of dye removal improved at initial pH of 6.5 to 95 percent at 180 min electrolysis. So initial pH of 6.5 was selected as optimum condition for reducing chemical material for releasing wastewater into the environment.
This paper has considered the electro-Fenton treatment of an azo dye with producing in situ hydrogen peroxide by oxygen reduction on graphite cathode. The effects of current intensity, air flow rate, initial pH and electrode surface were investigated. The experimental results showed that electro-Fenton process is able to decompose organic compounds without producing sludge as well as the oxidizing agent (H2O2) that produce only oxygen and water, so this process can be used for treatment or pre-treatment of wastewater containing toxic and non-biodegradable materials, especially textile effluents. From the obtained results, after 300 min of electrolysis, 90 percent dye removal was achieved under optimum condition (current intensity= 0.6A, pH=6.5, no aeration, electrode surface= 60cm2 and energy consumption= 0.24KWh/ppm), which shows electro-Fenton is the proper way to degrade acid orange 7.

In this study, bimetallic iron–nickel nanoparticles were obtained by chemical co-deposition of iron chloride with sodium boron hydride used as a strong reducing agent. The bimetallic nanoparticles thus obtained were then used to remove acid red 14 in a slurry system. Experiments were conducted to investigate such parameters as initial dye concentration, nano-particle dosage, pH, the time required for the nano-particles to be used after they are formed, the stirring speed, and the temperature required to reach optimum reaction conditions. Control experiments were subsequently performed under the optimum conditions thus determined to identify any other remaining factors involved. The optimum conditions included a temperature of 25±2 ºC, a newly synthesized nano-particle concentration of 0.05 g/L, an initial dye concentration of 200 mg/L, a pH level of 7.5, and a mixing duration of two minutes. The results indicated the high activity of the nanoparticles such that removal efficiencies equal to 79.39, 90.52, and 94.42 percent were achieved after 2, 30, and 240 minutes, respectively. Moreover, a COD removal of 72.61 percent was achieved after 4 hours of reaction.