جستجوی مقالات مرتبط با کلیدواژه « لجن » در نشریات گروه « محیط زیست »

The chemical precipitation using lime, caustic soda and soda ash was investigated for the simultaneous removal of Cu and Zn from copper mine industrial wastewater by conducting jar tests in the present study. Jar experiments were performed with a set of polyethylene beakers (500 ml) in order to investigate the effect of two reaction parameters (precipitant doses and initial pH) on the removal of heavy metals. X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) equipped with X-Ray Energy Diffraction Spectroscopy (EDX) were used to identify the important chemical compounds and to study the surface morphology, chemical composition and particle size of the sludge samples. An increase in the removal of Cu and Zn was observed by increasing the precipitant dose (10-400 mg/L) for each reagent used. Removal efficiency of 90% were obtained for both heavy metal ions. The chemical precipitation efficiency was affected by pH. At high final pH levels (8<pH<10), Cu had higher removal efficiency than Zn by all precipitating agents. In the sludge produced, Zn and Cu were precipitated as amorphous hydroxides including Zn(OH)2 and Cu(OH)2. SEM images showed that the produced sludges have small size and compact structure. EDX analysis determined that in all sludge samples, the content of Cu was higher than Zn. Effluent treatment with soda ash resulted in the sludge production with lower volume and larger particle size. As a result, the use of this precipitating agent can be less expensive for sludge drying steps.

Coagulation is a process that increases the tendency of small particles in an aqueous suspension to attach to one another and to surfaces such as the media in a filter bed and is applied through mixing coagulants such as aluminum sulfate (alum), ferric chloride and polyaluminum chloride with raw water. Sludge containing coagulant is formed after coagulation and through sedimentation of natural turbidity. Presence of high amounts of coagulant in waterworks sludge, increases environmental risks and disposal costs. Coagulants in sludge have high economic value. Therefore, if these coagulants recover, not only sludge disposal risks but also expenses related to supply of fresh coagulant in water or wastewater treatment plant may decrease. In this paper, researches conducted by acid digestion method for coagulant recovery from waterworks sludge are investigated. Amounts of coagulant recovery, advantages and disadvantages and economic aspects of this method are studied. Results of the investigation showed that using sulfuric acid is the best option for conducting acid digestion process because it is cheap and available. Moreover, if the purpose of recovering process is to achieve a recovered coagulant with a similar quality to the commercial ones, acid digestion method will not satisfy related standards.

Sludge treatment in wastewater treatment plants is one of the most difficult challenges for professionals and officials (Heidari et al., 2014). The most important indicator of the presence of pathogens in the sludge and wastewater is the presence of coliforms (Tchobanoglous et al., 2003; Metcalf & Eddy, 2003). Ultrasound waves at frequencies of 20 to 200 kHz with high levels of energy is one of the new methods for disinfection of water and wastewater treatment plants (Foladori et al., 2010; Show et al., 2007; Pilli et al., 2011). The purpose of this study is to determine the effect of ultrasonic waves with a low wavelength to improve removal rate of total coliform and Escherichia coli in sludge and determine the optimum operating parameters of the ultrasonic method.

This study is a cross-sectional study that was conducted in a laboratory-scale batch. Accordingly, during two seasons, 12 samples were taken at an interval of 15 days. In this research, variables include ultrasound density (0.375, 0.75, 1, 1.3 and 2.5) in watts on ml and time (1, 5, 10, 15 and 30) in minutes. In this research the influence of these variables on the total coliform and E coli of sludge is measured. The ultrasonic device used in this study was a probe with a maximum output power of 750 watts and frequency of 20 kHz. All bacteriological tests were conducted using the MPN method in a few steps of possibility, confirmation and completion and they were performed using 15 tube methods with units of MPN per 100 ml. All the experiments have done in the Nano, Water and Wastewater laboratory of the Department of the Environment at the University of Tehran. All the experiments were performed on the basis of standard methods for water and wastewater experiments with No. 9221 (APHA, 2005).

With ultrasonic waves and through the destruction of the cell walls of pathogens, viruses and microbes and the disintegration of pathogens result in the disinfection of sludge. The high temperatures caused by cavitation can also be locally led for the elimination of pathogens. It seems that the hydrodynamic force and local high temperature zones caused by the cavitation phenomenon are the most important mechanisms influencing sludge disinfection process through applying ultrasonic waves. The results of this study showed that removal of total coliform and E. coli increased with an increase in the time and ultrasound density. The experiments determined that the optimum operating parameters are a sonification time of 30 minutes, ultrasound density of 2.5 W/ml in a frequency of 20 kHz. The removal rate of total coliform and Escherichia coli under these circumstances was more than 99 percent which is equal to the removal of 2 logs.

Based on the results of this research, ultrasound waves can remove coliform and disinfect the sludge and can increase the treatment rate.

Textile industry has a significant impact on the environment because large amount of water and chemicals is used in various processes of this industry such as sizing, scouring, washing, bleaching, dyeing, printing and finishing that leads to production of hazardous wastewater. This wastewater contains dying substances which remain visible even at low concentrations. Water clarity and dissolved oxygen decreases in the presence of even a small amount of dye. Azo dyes are considered to be carcinogenic that pollute groundwater and surface water (Khandegar and Saroha, 2013; Morshed et al., 2012; Merzouk et al., 2009). Dye removal by different physical, chemical and biological methods or a combination of them could be possible. Physical methods such as adsorption, membrane filtration and ultrasonic waves, chemical methods like ion exchange, electrolysis, coagulation, flocculation, conventional and advanced oxidation and biological methods by algae, fungi and bacteria have been mentioned in the literature (Wang et al., 2014; Oliveira and Airoldi, 2014; Pajootan et al., 2012). Recently, electrochemical method is considered as a convenient method for purification of industrial wastewater due to its versatility and adaptability to the environment. This method has advantages, for decolorization, such as simple operation, high performance and short retention time for removal of pollutants, and requires less chemicals (Yildiz, 2008; Yuksel et al., 2011). Electrocoagulation is a method in which coagulants are dissolved into solution from anode electrode (Fe or Al) by applying electric current. Besides, by electrolysis of water, hydrogen bubbles are generated at cathode. This tiny bubbles move upward collide with flocs and form a sludge blanket on the surface. Furthermore, these bubbles are very active and can alter surface and buoyancy properties of the solids. These changes are known to be electrochemical effects that do not exist in the other flotation techniques (Matis and Peleka, 2010; Parsa et al., 2011). Electrocoagulation has been used successfully for treatment of various industrial wastewaters such as plating (Adhoum et al., 2004), chemical and mechanical polishing (Drouiche al., 2007), textile (Khandegar and Saroha, 2013; Wei et al., 2012; Pajootan et al., 2012; Yuksel et al., 2011), olive oil (Tezcan et al., 2006), laundry (Wang et al., 2009), tannery (Feng et al., 2007), dairy (Şengil, 2006), pulp and paper (Khansorthong and Hunsom, 2009), and oil refinement (El-Naas et al., 2009). For instance, Khandegar and Saroha (2013) treated textile wastewater by electrochemical method. Under Optimum conditions, with dye concentration of 10 mg/L Acid Red 131 and using aluminum electrodes, dye removal efficiency of 98% was obtained. Pajootan et al. (2012) studied removal of Acid Black 52 and Acid Yellow 220 from wastewater by electrocoagulation. With dye concentration of 200 mg/L and aluminum electrodes removal efficiency was 90 and 98%, respectively for the mentioned dyes. The aim of this study was to assess the simultaneous performance of electrocoagulation and electroflotation techniques in an electrochemical system by using aluminium electrodes for removal of Acid Red 14 from aqueous solution. It was expected that the need for a gravity settling unit and as a consequence treatment cost would be reduced. In this study, the design of the reactor in a manner intended to take advantage of electrocoagulation and electroflotation methods simultaneously. Effect of four important parameters on the performance of electrochemical systems, including electrode surface area, interelectrode distance, electrical conductivity and current density was studied. The optimum values of these parameters were determined based on the amount of electrical energy and aluminium consumption and the best performance of coagulation and bubble generation. In this study, electrochemical process was developed at room temperature in a 5 L rectangular plexiglass cubic reactor which included two pure aluminium electrodes with monopolar and horizontal arrangment and a PM-3005D Megatek power supply. Considering that the generated hydrogen gas at cathode plays the main role of floating suspended particles, the cathode was placed above the anode. Before each experiment, the electrodes were sanded and then washed by diluted acidic solution and distilled water. The experiments were performed in batch mode. An Anionic dye, Acid Red 14, as the main pollutant with structural formula of C20H12N2Na2O7S2, containing an azo group and molecular weight of 502.4 was used to prepare the synthetic wastewater. The concentration of dye in solution was measured by using a Hach DR-4000 spectrophotometer at the wavelength of maximum absorption of the dye (λmax=515 nm). The other equipments used in this study included a Mettler PJ300 digital scale with accuracy of 0.001, Metrohm 691 pH meter, a Martini MI805 EC meter and an IKA RH-Bassic2 magnetic stirrer. NaCl (Merck) was used to obtain electrical conductivity in solution and synthetic wastewater was prepared with double distilled water. All measurements including dye concentration, EC and solids were according to water and wastewater standard methods (APHA, 2012). Parameters including electrode surface area (24.86, 52.86, 80.86 cm2), interelectrode distance (1, 1.5, 2 cm), conductivity (800, 1600, 3000, 4000, 5000 µS/cm) and current density (10, 20, 30, 40, 50, 60 mA/cm2) were examined. Specific energy and aluminium consumption were calculated in terms of (kWh/kg dye removed) and (kg Al/kg dye removed), respectively. These two responses and TSS of the separated sludge were the basis for determination of parameters optimum value. Effect of electrode surface area: Experiments were carried out at electrode surface area of 24.86, 52.86, and 80.86 cm2. Other parameters were kept constant. By increasing electrode surface, generated oxygen bubbles were trapped under anode and continued to stick together and form large bubbles. When these large bubbles were released from under the anode, they collided with hydrogen bubbles on their path upward and form larger bubbles that were not capable to floate the existing flocs. By increasing the electrode surface, due to lower electrical resistance of the system, the voltage required to achieve a constant electric current was reduced. It have to be noted that the lower anode dissolution results less production of sludge, hence lower disposal management costs. So the electrode surface of 24.86 cm2 with dye removal efficiency of 99% within less than 120 minutes, specific energy consumption of 193 kWh/kg dye removed, anode dissolution of 3.908 kg Al/kg dye removed and sludge TSS of 15050 mg/L was selected as the optimum value. Compared with conventional gravity settling tanks, this system has higher sludge TSS values. Effect of interelectrode distance: Experiments at interelectrode distances of 1, 1.5, 2 cm were carried out to assess the influence of this parameter. By increasing the distance between the electrodes, dye removal efficiency decreased due to the delay in forming coagulants and less mobility of the ions that were produced at the electrodes. By reducing the distance between the electrodes, the voltage required to achieve a constant electric current was reduced due to the reduction of electrical resistance. Aluminium dissolution with different interelectrode distances had close values; so interelectrode distance of 1 cm was selected as the optimum value for the following experiments. Effect of electrical conductivity: The electrical resistance decreases with increasing conductivity of the solution. Typically, the voltage required to achieve constant electric current decreases. Salts and ions are used to provide electrical conductivity. Deposition and corrosion caused by these ions on the electrodes make problems in the process, increase the electrical resistance and impose additional costs. It was observed that by enhancing the electrical conductivity and needing more time to completely separate the pollutant, the amount of aluminum in the separated sludge increased, taking into account turning of the sludge more into gray. The increasing of aluminum flocs that contain water, in the sludge causes the TSS to decrease. So the electrical conductivity of 1600 µS/cm with dye removal efficiency of 90% within less than 90 minutes, specific energy consumption of 130 kWh/kg dye removed, anode dissolution of 2.615 kg Al/kg dye removed and sludge TSS of 15050 mg/L was selected as the optimum value. Effect of current density: The rate of dye removal by increasing the amount of current density is greater. This phenomenon is because of the higher rate of production of coagulants and gases with increasing current density, which leads to faster coagulation, flocculation and separation of contaminants (Zodi et al., 2013). The lower current density leads to lower bubble generation. According to the observations, at low current density, due to the low volume of produced gases, the sludge was not floated well and after floatation it returned into the wastewater and the process of pollutant removal was more dependent on continuous separation of sludge. Thus at low current density, the efficiency of the process will be low in high pollutant concentration and load shock (Kobya et al., 2006). Optimum system performance was achieved at current density of 60 mA/cm2. This paper has considered the electrochemical treatment of an azo dye (acid red 14) with electrocoagulation and electrofloatation simultaneous processes. The experimental results showed that electrocoagulation and electrofloatation system has good performance for rapid removal of dye, so this system can be used for treatment or pre-treatment of wastewater containing toxic and non-biodegradable materials, especially textile effluents. The process can easily be controlled and equipments are safe. Tiny bubbles of the same size are generated. There are few needs to add chemicals. Also, good efficiency in hydraulic, organic and toxic shocks, reduction in the number of process units and in consequence decrease in the required area for treatment plant, and lower operation cost are the other advantages of this technique. The effects of electrode surface area, interelectrode distance, electrical conductivity and current density were investigated. From the obtained results, after 90 min of electrolysis, 90% dye removal was achieved under optimum condition of electrode surface area=24.86 cm2, interelectrode distance=1 cm, electrical conductivity=1600 µS/cm and current density=60 mA/cm2 with specific energy consumption=130 kWh/kg dye removed, anode dissolution=2.615 kg Al/kg dye removed and sludge TSS=15050 mg/L.

The present work has been performed to eliminate sewage dry sludge of Alborze city wastewater treatment plant by using them as fine aggregate in concrete. On this basis, at first the selected dry sludge was analyzed for XRD and XRF for crystalline phases and chemical composition, respectively. The results showed that more than 50% of the sludge is formed of SiO2 and it had more than 20% organic materials. The presence of organic materials can potentially decrease the performance of concrte, so, the dry sludge exposed to heating process. The crystalline phases of the sludge were evaluated after heating using XRF analysis. The results revealed the remove of organic materials and some changes in crystalline phases. Due to changes in crystals, formation of pozzolanic activity was measured using TGA analysis. To study the effects of dry sludge on concrete mechanical properties (compressive strength) two mix designs with water to cement ratios of 0.55 and 0.45 was produced. The sludge amount used in concrete was 0, 5, 10, 20 and 30%. The compressive strength was studied as an important factor in durability studies. Results showed that 90 days cured specimens containing 5, 10 and 20% dry sludge had 4, 8 and 22% decrease in compressive strength in comparison to control specimens.

Aluminum anodizing plants produce a significant volume of sludge in the final step of wastewater treatment. If this sludge is not disposed by the common methods, it produces several environmental problems, which is taken into account as an imposed cost. The object of this study is economical evaluation of aluminum anodizing plants sludge reusing, to prevent releasing it in the environment and reducing water and soil pollutions. Therefore it causes environmental conservation in one hand and a suitable economical saving can be achieved for these plants in the other hand. For this purpose, data gathering about aluminum anodizing process, the related wastewater treatment units, and various uses of the sludge was performed. It is found that if anodizing sludge uses as raw material in fire- brick preparation, annually 780 million Rials benefit can be achieved by this plant. Furthermore, if anodizing sludge uses as coagulant in municipal wastewater treatment, annually 820 million Rials saving can be obtained by municipal wastewater treatment plants.