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Mineral anions are among the most important toxic substances harmful to humans and animals even in low concentrations. Nitrate ions are considered important surface and groundwater pollutants for their high solubility in water. Nitrate is converted to nitrite and N-nitroso in the human body through certain reactions. N-nitroso combinations are considered carcinogenic and the primary cause of methemoglobinemia diseases. The existing nitrate in water resources is not easily separated for it is highly soluble and therefore the methods usually used for this purpose are very costly. Various methods can be used to remove or reduce the concentration of nitrate. Reverse osmosis, electrodialysis, electrocoagulation, ion exchange, and membrane processes are among the physicochemical methods of nitrate purification. Among the types of nitrate purification methods, biological processes with relatively high efficiency, the possibility of complete removal of the pollutant, and less harmful effects on the environment, are some of the most suitable options for the decomposition and removal of nitrate from water and groundwater. In a situation where the contaminated area is wide and it is not possible to pump water due to economic reasons or the large volume, treatment using in-situ methods will be a more suitable option. One of the types of in-situ biological treatment processes is the use of the permeable reactive bio-barrier (PRBB) method. PRBB is one of the novel and reliable methods used for in-situ groundwater remediation.  A PRBB is an emplacement of reactive media in the sub-surface designed to intercept a contaminated plume, provide a flow path through the reactive media, and transform the contaminant(s) into environmentally acceptable forms to attain remediation concentration goals down the gradient of the barrier. PRBB can degrade nitrate at a high rate under anaerobic conditions. In this research, different concentrations of four chemical substances including ZVI, nZVI, NaS2O3, and Na2S2O5 were used as Oxygen Capturing Compounds (OCC) in the removal of nitrate from polluted water in the PRBB process on a laboratory scale. Based on the obtained results, these substances affect the parameters of DO, pH, MLSS, turbidity, nitrate concentration, durability of DO, and ORP. After laboratory tests and taking into the opinion of experts, the qualitative effect of each parameter was calculated quantitatively and through the analytical hierarchy process (AHP), the best oxygen-capturing compound was selected. The results obtained from AHP (with an inconsistency ratio of 0.063), revealed that the priority of choosing OCC from three technical, economic, and environmental aspects is related to the concentrations of 750 mg/l ZVI, 240 mg/l Na2S2O3, 85 mg/l Na2S2O5 and 550 mg/l nZVI respectively. The concentration of 750 mg/l ZVI (the best OCC) during the experiments was able to reduce the DO from 7 to 0.05 mg/l in approximately 500 minutes and within the ideal range of the denitrification process (DO<0.05 mg/l). In addition, after the durability of DO tests, it was found that this substance has maintained its deoxygenation properties for longer than other used compounds. Also, based on the results, the concentration of 750 mg/l ZVI had a positive effect on the increase of MLSS and removal of nitrate. 

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Aims: The increasing development of microalgae applications has led to the concentration of new multidisciplinary studies to facilitate commercial cultivation of these organisms due to cost reduction and productivity enhancement. The aim of this study was the growth and quality optimization of Spirulina biomass by changing the dilution of medium and using the aeration cycle.
Materials and Methods: In this experimental study, the effect of concentration of Zarrouk medium (0 to 100% dilution) and aeration cycle on specific growth rate and dry weight, as well as the content of chlorophyll and carotenoids of Spirulina were investigated, using response surface method, central design. A total duration of 16 hours was aerated in any 24-hour period; the interval time between these aerated periods varied between 1 to 8 hours. The data were analyzed by SPSS 16 software, using multiple regression test.
Findings: The highest biomass (0.659mg/ml) was obtained at 80% concentration of culture media and aeration cycle of 2.75 hours and the highest specific growth rate (0.230 daily) was obtained at 60% concentration and aeration cycle of 4.5 hours. The highest aeration cycle (8 hours) resulted in a significant and simultaneous increase in the content of chlorophyll and carotenoids (11.65 and 2.67 mg/g, respectively).
Conclusion: The growth and quality optimization of Spirulina biomass can be accomplished by changing the dilution of the medium and using the aeration cycle.

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There are known techniques for cyanide remediation from contaminated soil such as soil washing, soil oxidation and biological degradation. However, there is very little research for electrokinetic remediation of cyanide from soil. This study investigates the application of electrokinetic remediation to contaminated soil with high clay content and low coefficient of permeability. The experiments were conducted with two electrodes as cathode and anode poles, which were placed inside the soil using the direct electrical current. Thus cyanide ions were transported to the anode pole and caused the remediation of the soil. The contaminated soil from tailing dam of Takab gold processing plant was used. Contaminated soil with the concentration of 420 mg/kg, distilled water and NaOH were employed in the electrokinetic cell. The experiments were conducted on the optimum moisture content of clayed soil at two voltage gradients (1.0 and 1.5 VDC/cm for the duration of 7 and 14 days) in order to assess the effect of voltage gradient when employing 1M NaOH solutions and distilled water at the anode pole. For each test, cyanide removal efficiency, the pH of the soil, moisture content, electrical conductivity and the electrical current and flow were determined. The measurements were conducted for the entire duration of electrokinetic experiments and at the end of the test. The results indicated that the cyanide removal obtained in 7 and 14 days was approximately 65% and 80%, respectively. The results also showed the pH of the soil was changed from 8.83 to 1-2 for the anode and to 12-13 for the cathode pole. The cyanide transported to the cathode and the pH were the most important dominant factors for cyanide remediation.

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Abstract: Two kinds of concrete sealers including epoxy and waterproof were used to immobilize TiO2 nano-particles on concrete surfaces for treating 25-500 mg/L synthetic phenolic wastewater using photocatalytic process. The reactor consisted of contaminated tank, photocatalytic and aeration zones. Irradiation of TiO2 was performed by UV-A lamps at different intensity (4.42- 8.9 mW.cm-2) placed 10 cm above the concrete surfaces. SEM and EDX analys is showed a uniform appearance of TiO2 catalyst on the concrete. In influent phenol concentration (100 mg/L), pH=7 and retention time (4 hr), the removal efficiency by epoxy sealer was more than 20% compared to the waterproof sealer because of hydrophobic effects. Reduction of removal efficiency was less than 2% for the epoxy sealer after several iterations of the process. Finally, the effects of intensity and wavelength of UV lamp and system pH in removal efficiency were evaluated.

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Abstract: Dyes and pigments are the major and important groups of chemical compounds with high amount of production and consumption amongst various environmental pollutants. For example, the annual imported amount of dye is over 7000 tons in Iran. Most of the dyes used in textile industries are considered either as inert or non-toxic, although some are not totally innocuous. The important fact is that most of them are made of carcinogenic chemicals that may be reformed as a result of metabolism. More than 50 percent of dyes consumed in different processes are discharged to wastewater, which in addition to changing the color of water, are preventing light penetration into the water and photosynthetic function that leads to destruction of aquatic ecosystem and some aquatic species. In recent years, increasing production and use of synthetic dyes, which have more complex structure and chemical stability as compared to natural dyes, more attention has been paid to their environmental pollution and importance of their treatment. Biological treatment is often the most economical alternative as compared to the physical and chemical treatment processes. But as most of dyes are hardly biodegradable, biological systems donot have capabilities in their removal. In expensive chemical processes, unexpected by- products and sludge are the main disadvantages. So, application of physical methods is preferred to control these kinds of pollutions. Different physical methods are also widely used, such as membrane–filtration processes and adsorption techniques. Adsorption is one of the most popular, flexible and effective methods that provides an attractive alternative for the treatment of colored water, especially if the sorbent is inexpensive and does not require an additional pre-treatment step before its application. It also does not result in the formation of harmful substances. Based on the aforementioned reasons, two adsorbents of sawdust and bentonite clay (absorbent aluminium phyllosilicate) were applied for the removal of cationic astrazon blue (F2RL) dye from wastewater regarding the two main factors of cost and availability in Iran, especially in the central provinces of the country. The parameters of pH, dye concentration and contact time were studied in this research. According to the study results, the optimum pH of 7 was found for the removal of dye for both sawdust and bentonite. Data analysis showed that increasing of the initial dye concentration resulted in the decreasing of removal efficiency. The maximum efficiency for the removal of dye from the solutions with the initial concentration of 25, 50 & 100 mg/L was 96.75, 91.11 & 79.26 percent for sawdust and 97.32, 96.78 & 94.62 percent for bentonite, respectively. The equilibrium time was 240 and 90 minutes for sawdust and bentonite, respectively. For the effect of adsorbent dosage on the removal of dye, experiments were carried out with two initial dye concentrations of 50 & 100 mg/L. By increasing of the adsorbent dosage, the maximum efficiency for the removal of dye from the solutions with the initial concentration of 50 and 100 mg/L increased from 53.46 to 97.06 percent and 49.76 to 96.83 percent, respectively, for sawdust, and from 90.78 to 99.64 and 86.44 to 99.46 percent, respectively, for bentonite clay. Analysis and calculation of separation factor (RL) of the result showed that adsorption of dye by sawdust and bentonite corresponds with Langmuir isotherm.

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There are different methods for treatment of composting leachate. Parameters dictating which method to be chosen include quantity and quality of the leachate, required amount of treatment and economical issues. Integration of ozonation and GAC adsorption into a single process is one of the attractive methods for post treatment of wastewater. Therefore, post treatment of composting leachate by means of ozonation and granular activated carbon (GAC) adsorption was considered as the main objective of this study. This study was conducted in laboratory scale and in batch mode. The set-up of batch system consisted of a Plexiglas column with 20 mm inner diameter and 800 mm height. The tall height of the column provides the required contact time between ozone and pollutants. Ozone was supplied to the column through a diffuser sited at its bottom. The outlet gas of the reactor may contain some residual ozone and can cause air pollution. Therefore, it is dangerous for the people working nearby the reactor. Thus, the ozone in the gas phase leaving the column was removed by KI solution. All experiments were conducted at room temperature (24 ±2°C). The leachate used in this study was obtained from the effluent of the Leachate Treatment Plant of Rasht Composting Facility (Guilan, Iran). All the chemicals employed for analysis were analytical grade and obtained from the reliable companies. In order to conduct the experiments, after complete determination of the specifications of GAC as an adsorbent, different dosages of GAC were added to 800 mL of leachate with the given initial concentration and pH in the column. The pH value of the solution was adjusted by Sulfuric Acid or Sodium Hydroxide as needed. Then the ozone gas was introduced into the column and the samples were taken in different intervals of time. After that required parameters of the samples were measured. Ozone generator (ARDA-COG 5S) with 5 gr/hr nominal capacity was used to produce ozone gas from pure and dry oxygen. Before starting each step of the experiment, the ozone generator was calibrated for ozone concentration. Pressure and flow rate of ozone gas produced was equal to 2 bara and 1 liter per minute, respectively. The results showed that integrated treatment of the leachate with ozonation and activated carbon adsorption, namely catalytic ozonation, was more effective than each process solely. In this study, COD removal rate of 44% in adsorption process, 57% in ozonation process and 80% in integrated process was achieved after 60 minutes. According to the results, in the integrated process, addition of the adsorbent (as long as it floats in the leachate) has positiveeffect on the removal of organic load. The pH value is another important parameter that affects the removal rate in the integrated process. It was found that removal of organic load is more evident at basic condition than at acidic condition. In this study, the maximum COD removal was achieved in the pH values between 8 and 9. Furthermore, in this process, ozonation along with adsorption process resulted in reactivation of activated carbon and avoided frequent GAC regeneration. After 5 times of the reuse of virgin GAC through a consecutive experiment, only 7% loss in COD removal was observed in the integrated process, while it reached to 95% for single adsorption process at the same condition. This can be explained either by the predominance of catalytic reactions rather than adsorptionoxidation reaction in the process or to the in situ regeneration of GAC.

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  Abstract: Hydroquinone is one of the most important phenolic compounds, which has a wide application in industries such as rubber, photo developing, cosmetic, and anti-oxidants. Because of its toxic effects, an efficient system should be provided for treating these kinds of wastewater. Therefore in this study, the performance of conventional and packed-cage RBC biological systems in treatment of wastewater containing hydroquinone, and parameters affecting the process were studied. In this study, the removal efficiency of hydroquinone was investigated in two different laboratory scale RBC systems. The first system was a two-stage RBC with rotating discs and the second one was a one-stage packed-cage RBC with bee-cell 2000 biofilm carriers. Each stage of the rotating discs RBC was consisted of 27 parallel plexiglas rotating disks with 15 cm in diameters. The packed-cage RBC had a net drum full of biofilm carriers with specific surface area about 650 m²/m³. Both systems had a total area of 2 m² and were fed by a peristaltic pump. During the startup, the reactors with sludge seed, daily dosage of 200 mg/L COD as glucose and synthetic wastewater was fed to each reactor. After increasing biofilm mass, the acclimation was started with stepwise substitution of glucose with hydroquinone (CODhdroquinone/CODtotal was increased about 10% in each step). After acclimation stage, the amount of COD was being increased stepwise up to 5000 mg/L. Both RBC systems as advanced biological processes had proper COD removal efficiencies for treating hydoquinone synthetic wastewater. Up to the maximum 90, 93 and 88 percent removal efficiencies were obtained in RBCI, RBCII and packed-cage, respectively for COD concentration of 1000 mg/L, hydraulic loading rate of 1.5 L/m³.d and optimum rotation speed of 10 rpm. Also, During the experiments up to 4000 mg/L influent COD, RBC with rotating discs had higher removal efficiencies (about 5%-15%) but at higher loading rates, packed-cage RBC had better results. The effect of hydraulic loading, and the rotational speed of disks in the performance of the both systems were studied. The results proved that the amount of hydroquinone removal increased with raising the rotational speed of the disks up to 10 rpm, and increasing hydraulic loading had a negative effect on the COD removal efficiencies in both conventional and packed-cage RBCs. Also COD concentration increased up to 10000 mg/L in one step whille the hydraulic loading rate and rotational speed were 1.5 L/m².d and 5 rpm, respectively. The results showed that conventional RBC had a better performance for the organic shock. For ensuring of hydroquinone biodegradation in the RBC systems carbon-13 NMR spectroscopy was also studied.

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Abstract: Water pollution due to toxic heavy metals has been a main cause of concern for the environmental engineers. Heavy metals are individual metals that negatively affect people's health. In very small amounts, many of these metals are necessary to support life. However, in larger amounts, they become toxic. Lead is one the important heavy metals that is applied in different industries such as manufacture of batteries, metal products and ammunition. Its standard limits in drinking water are 0.05 mg/L, because it affects all organs and functions of the body to varying degrees. The frequency and severity of symptoms among exposed individuals depends upon the amount of exposure. Lead entering the respiratory and digestive systems is released to the blood and distributed throughout the body. It is stored and may be released into the blood, re-exposing organ systems long after the original exposure. This is why the wastewater includes lead should be treated before discharging to the environment. Different kinds of physical, chemical and biological methods are used to remove lead. The main techniques are including precipitation, ion exchange, adsorption, membrane processing and electrolyte methods. Adsorption with many advantages is a proper method that is applied to treat heavy metal removal. In recent years, use of low cost materials as adsorbent for metal ion removal has been highlighted. Since natural absorbents are inexpensive and may be achieved without any cost and they are usually in abundance in nature, absorption of solute ions by these materials are a proper method to eliminate heavy metals from polluted waters and industrial wastewaters. In this study, following continuous column method, sawdust and ash, as two absorbents were used for removing lead. The experiments were carried out with the initial pH of 5 and different densities (50 and 100 ppm). In order to optimize the process of adsorption, three combined absorbents were also used which made from the above two absorbents with the ratios of 1:3, 1:4 and 1:6. Batch experiments were carried out in order to determine the parameters of adsorption. The results of sorption with sawdust have shown that Langmuir adsorption isotherm were suitable. Based on the results of the column experiments study, lead removal efficiency was more than 98 percent when combined absorbents were used. In batch experiments, the percent efficiency was 76 and 98 percent with sawdust and ash, respectively.

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Water scarcity has led to the search for alternative water resources. One solution is the recycling of wastewater for irrigation. Wastewater treatment is often based on biological systems such as activated sludge or other engineered units in urban areas. In rural areas, low-cost, environmentally-friendly alternative treatments such as constructed wetlands (CW), are more common. CWs are man-made planted systems that utilize natural processes to improve water quality for human benefit. Salinity in treated wastewater is often increased, especially in arid and semi-arid areas. Phytoremediation can be used to remove much of this problem. Phytoremediation is the use of plants for remedying water and soil pollution. This approach is based on plants that are especially tolerant to salt environments. Around 1% of all plant species are halophytes that can complete their life cycle in relatively high saline environments, as much as 200 mM NaCl or more. In the current study, we addressed the problem of soilsalinization due to the use of treated wastewater that is often more saline than fresh water, especially in desert environments. We aimed at testing the potential to recruit halophyte plants for salt phytoremediation in constructed wetlands. Therefore this study was performed to evaluate the ability of reducing salinity of wastewater by three halophyte plant species such as Frankenia, Atriplex and Festuca. The experiments were performed with different concentrations of saltwater. Reducing the electrical conductivity, salt removal and its uptake rate, the concentration of sodium stored in plant tissues at different levels of salinity, were analyzed. Also by matching the data with Michaelis- Menten and Lineweaver- Burk kinetic models, some results were obtained from each plant. The electrical conductivity decreased with increasing salinity levels in all three species. The highest salt absorption amount in Frankenia was in 4500 µs/cm about 20 percent, in Festuca was in 2600 µs/cm about 17 percent and Atriplex was in 5000 µs/cm about 14 percent. Of course reducing of salt uptake in each plant had its own reason for example; Atriplex plants due to having less compatible with wetland situation, Festuca plants due to facing with salinity stress and Frankenia plants because of salt replenishment faced with yield loss and withered state. Based on these results Frankenia, Festuca and Atriplex plants during the treatment with saline water, had the first order of kinetic equation with a correlation coefficient of respectively 97.7, 95.9 and 97.01, gradually with increasing of salinity these plants had the kinetic equations of 2, 0 and 1 order that as this result, Atriplex plants showed more resistance in salt uptaking. In reduction range also Atriplexand Frankenia had a better performance. The highest conformity of data in Frankenia plant related to Lineweaver- Burk and Atriplex plant related to Michaelis- Menten.

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High salinity wastewater is one of the main environmental issues. Using biological treatment systems to treatment this kind of wastewater is hard due to loss of microorganisms. Phytoremediation is one of the main methods to treat this type of wastewater, which is an environmental friendly and a low cost process. In this research we aim to study operation of two plants, including chrysopogon zizanioides known as Vetiver grass and Cyperus alternifolius know as umbrella, to simultaneous removal of salinity and organic loading. We assume five different combination of wastewater which are called statistical treatments and characterized by different amount of salinity and COD. Statistical treatments contain wastewater with Electrical conductivity 0,2.5,5,7.5,10 (ds/m) and 0,75, 150, 250, 300 (mg/L) COD respectively. Pure water is used as control treatment. Results show that in reactors with low level of salinity, both plants have better operation in removing of salinity and organic loading. For electrical conductivity above 5 and 7.5 ds/m, signs of salinity stress including Chlorosis and withering seen in leaves of both plants. For chrysopogon zizanioides, different statistical treatments results in different removal of organic loading range from of 60 to 12 percent. Salinity removal is ranged from 53 to 4 percent. For Cyperus alternifolius reduction in organic loading and salinity are respectively varied from 49 to 5 and 20 to 1 percent. Results of this study in laboratory scale shows that using phytoremediation method in constructed wetland for different combination of salinity and organic loading results in 17 and 15 percent reduction in salinity and wastewater for each unit of chrysopogon zizanioides and Cyperus alternifolius respectively. By increasing the level of salinity the trend of electrical conductivity is decreased. For the wastewater with 2.5 ds/m electrical conductivity, the most absorbing salinity absorbing is seen for both plants, which is 53 percent for chrysopogon zizanioides and 30 percent for Cyperus alternifolius. Reduction in capability of absorbing salt occurred for both plants due to completeness of salt aggregation capacity of the plant. By increasing the electrical conductivity of wastewater solution, wither and reduction in operation of the plant is seen as well. Increasing the salinity level results in decreasing the trend of organic loading reduction. COD removal for chrysopogon zizanioides is greater than Cyperus alternifolius in all reactors, which is related to natural characteristics of this plant, higher tolerance of salinity fluctuations and different phytoremediation mechanism. In statistical analysis of morphological characteristics of plants, the statistical population is all plants for different combination of wastewater and statistical controls. For each plant, results of different statistical treatments are compared to each other. The null hypothesis for independent tests assumes that the waste water treatment doesn’t have effect on morphological characteristics of the plant. So, rejecting this hypothesis means that all combination of wastewater doesn’t have the same effect on morphological characteristics. This hypothesis is considered separately for each of morphological characteristics by use of two sided independent sample T-test. These characteristics included dry weight, mean leaf area, mean stem diagonal and root volume. Results indicate that increasing salinity will affect the morphological characteristics with 95% confidence. Fitting the generalized linear regression shows that existing of organic loading doesn’t have meaningful effect on morphological characteristics, and level of salinity of wastewater affect the growing characteristics of the plant.

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Removal of petroleum hydrocarbons from contaminated soil using electrokinetic method or biological processes has been considered in recent century. The most limiting factors in the electrokinetic process are extreme changes in pH around the electrodes and non-polarity of some pollutants. On the other hand, the key factor of biological treatment is simultaneous presence of microorganisms, pollutants (carbon source of microorganisms), electron acceptors, and essential nutrients for microorganisms’ growth. But in fine-grained soils with low permeability, it is difficult to uniformly distribute bacteria, electron acceptors and nutrients, or making pollutants available for microorganisms. To solve these problems, bioelectrokinetic method is used to eliminate the limitations of both biological and electrokinetic processes in treatment of fine-grained soil contaminated with organic compounds. In this integrative approach, the biological method has a role in biodegradation of pollutants. Whiles, the electrokinetic process can direct and accelerate the transfer of pollutants and microorganisms. The aim of this study is determining the equations and conditions governing on bioelectrokinetic process in removal of crude oil from clayey soil. For this reason, the numerical method of FTCS finite-difference was applied for modeling the pollutant biodegradation and transmission in clayey soil under electric field. In order to develop and validate the model, the first step was to set up a bioelectrokinetic system in a laboratory scale. In this study, each test was conducted in cylindrical cell made of Plexiglas with the length and diameter equal to 55 and 5 cm respectively, for 35 days. They were performed in various conditions of pollution amount and electric field intensity in the presence of Pseudomonas Putida strain. On the other hand, after determining and combining the governing equations on the electrokinetic and biodegradation system, the numerical solution of the equation was coded using Matlab software. In suggested mathematical model, the parameters like initial concentration of crude oil, voltage gradient, time step and spatial step were assumed as variables and parameters related to reactor, soil and pollutant such as the length of reactor, soil porosity and tortuosity, ion mobility, diffusion coefficient and electroosmosis permeability coefficient were considered as constants. In continue, by comparison the result of numerical solution of the suggested model with the experimental results, the same trend was observed in changes in crude oil concentration between the two. Because of differences between the model results and laboratory data and to make more accordance between the two, the modifying factor was used as the factor of microorganism transfer under electric field. In this way, by addition of modifying coefficient in model, a better accordance between them was observed and this difference reduced to minimum. Modeling results showed that electroosmosis, diffusion and electromigration mechanisms, unlike biodegradation, had little impact on the transmission and removal of oil from soil. According to the numerical solution, similar to bioelectrokinetic data, increasing the initial concentration of oil and voltage gradient caused the increase in removal efficiency of oil. In addition, the model has been able to predict the residual crude oil concentration after bioelectrokinetic treatment with a good accordance.

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By developing of the consumerism and rapidly progress of industrial and commercial lifestyle in most of the countries, the solid waste production has been growth rapidly in the recent years. The leachate production starts shortly after the production of waste and cause the pollution of environment and especially contamination of the soil. Chemical processes are usually considered as the most effective processes for degradation of soil pollutants. In these processes, the chemical reagents are added to make the desired reactions take place. But it is sometimes necessary to increase the amount of reagents so that the reactions take place completely. This may cause chemical reagents to remain in the soil. Ozone, which acts as a powerful oxidizer, is capable of degrading organic pollutants in a short period of time without producing any toxic residuals. Nowadays ozonation has become one of the most favorable processes in soil remediation technologies. Ozone is used in the treatment of a wide range of pollutants. Due to the high diffusion coefficient of ozone, all of the present pollutants in soil are theoretically available for this oxidant. Since leachate contains a range of organic and inorganic pollutants, ozonation process is therefore can be a useful process in treating soils contaminated with leachate. In this study, application of ozonation process as an ex-situ method on the treatment of composting leachate polluted soil was studied in laboratory scale and in batch mode. Experiments were conducted using a cylindrical Plexiglas reactor with the diameter of 3 cm and the height of 60 cm. Ozone gas was continuously passed through a diffuser at the bottom of the reactor. Ozone generator with 5 g/h nominal capacity was used to produce ozone gas from pure and dry oxygen. Ozone content was measured with a digital ozone analyzer. A rotameter was also applied to measure the volume of gas injected to the reactor. The leachate used in this study has been collected from one of composting plant in north of Iran. The soil used in this study was mainly silica with the particle size of 0.12-0.3 mm. In order to pollute the soil; a certain amount of leachate was well mixed with the soil and then dried to the desired humidity. According to the results the maximum removal of soil organic content was obtained at pH=9 after 120 minutes ozonation with a flow of 200 ml/min. By increasing the initial organic content of the soil, the removal via ozonation has been also increased. In other word the soil with higher initial contaminations has shown better removal efficiencies compared with the one with lower initial pollutants. In this study, the presence of trivalent iron oxide caused 42% increases in soil organic content removal efficiency. In this research applying gas washing technique with acid also greatly enhanced the removal efficiency of ozonation process. According to the conducted experiments, after pre washing of ozone with acid, the removal of soil organic content with nearly 90% increase, reached to 21.2%. The results were also shown that, the change in the type of acid did not have a significant effect on the soil organic matter removal efficiency.

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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.