مجله آب و فاضلاب
پیاپی 108 (خرداد و تیر 1396)

The presence of nitrate in groundwater resources has instigated increasing concerns among both managers and users of, especially, drinking and sanitation water. From among the different nitrate removal methods, the adsorption method has attracted more attention thanks to its high removal efficieny and economical operation. Commercial activated carbon ranging in mesh size from 30‒40 was utilized to remove nitrate from an aqueous solution. In order to enhance nitrate uptake, different acid, alkaline, and cationic surfactant post-treatments were examined. Alkaline post-treatment followed by cationic surfactant modification was found to yield the best efficiency. FTIR, SEM, and N2 adsorption/desorption were carried out to determine the physical and chemical properties of activated carbon. Kinetic tests revealed that adsortption reached its equilibrium state after 12 hiurs and that the pseudo-second order and Freundlich models. Based on the Langmuir model, maximum adsorption capacity was found to be 15.34 and pH had an insignificant effect on nitrate adsorption. Moreover, the highest decline in nitrate adsorption was observed in the presence of sulfate followed by chloride, phosphate, and carbonate. Based on the results obtained, the modified activated carbon accompanied by washing with sodiuym hydroxide and modified cationic surfactant post-treatment might be recommended for use in adsorption processes as a promising innovative technology for nitrate removal from drinking water.

The response surface statistical model developed via the central composite design (CCD) is a tool for optimizing manufacturing processes. Phrmaceutical plants depend on many such processes and i is essential to remove medicinal compounds from their effluents before they are discharged into the environment. The objective of the present study was to employ the response surface model for the optimization of the removal of the pharmaceutical compound ciprofloxacin from aqueous media via the electrochemical coagulation process. In this study, a reactor containing two iron electrodes used as the anode and two titanium ones used as the cathode was employed to remove ciprofloxacin from municipal effluents. The electrodes were connected in a monopolar fashion to a DC power supply. Parameters such as pH (4‒8), current (0.5‒1.5 A), initial ciprofloxacin concentration (15‒40 mg/L), and reaction time (15‒30 min) were introduced into the Design Expert software as the main design parameters. FT-IR analysis was conducted and SEM images were prepared while COD removal and changes in UV-VIS spectrum were determined under optimum conditions. Process modeling was accomplished using the response surface methodology (RSM) which is a statistical model for process optimization drawing upon central composite design (CCD). Modeling results showed that process efficiency was affected by the above parameters and that the optimum conditions for a process efficiency of 85.91% at an initial CIP concentration of 15mg/L would include pH=7.68, a current of 1.5 A, and a reaction time of 30 min. Under these conditions, COD removal efficiency would be 64%. FT-IR analysis and SEM images indicated changes during the process. Wavelength scanning also indicated reducing concentration of the contaminant due to mineralization. The results of the study indicate that optimization by RSM reduces the number of tests required and enhances their accuracy. It was also found that electrocoagulation has a high CIP and COD removal efficiency which makes it capable of being successfully exploited for the removal of organic pollutants from effluents before their discharge into the environment

Nanotechnology has nowadays found applications in a wide variety of fields including industrial effluent treatment. In this study, iron nanoparticles were synthesized via Ferric choloride reduction using sodium burohydrate to investigate the effects of retention time, nanoparticle concentration, BOD concentration, and pH on the efficiency of BOD removal from wastewater. To determine the optimum contact time, known quantities of the nanoparticles thus prepared were added to wastewater samples of two different concentrations with known values of BOD5 over peirods ranging from 15 to 180 minutes. In a second stage of the study, varying amounts of iron nanoparticles were added in two steps to wastewater samples with a fixed BOD5 concentration and allowed to remain over the optimum contact time to determine the BOD removal efficiency. Subsequently, fixed amounts of iron nanoparticles were added to wastewater samples with varying BOD levels and the BOD removal efficiency was determined. Finally, varying amounts of iron nanoparticles were added to wastewater samples with varing BOD levels over the optimum retention time to investigate the effects of pH variations in each stage on BOD removal efficiency and to determine the optimum pH level. Results indicated an optimum contact time of 45 minutes, an optimum iron nanoparticle content of 3 g for samples with BOD5 concentrations of 35 and 116 mg/l, and an optimum nanoparticle quantity of 5 g for samples with a BOD5 of 289 mg/l. The optimum BOD5 concentration was found to be 289 mg/l and the optimum pH was determined to be 3. At the optimum contact time and at high pollution loads, an acidid pH yields the highest contaminant removal with increasing nanoparticle additions.

Coagulation and flocculation techniques are appropriate methods for improving the quality of efflunets from wastewater treatment plants that help achieve higher standards of water reuse. In this study, PAC was used as the coagulant in the SBR treatment system of Yazd Wastewater Treatment Plant and the effects of mixing intensity during rapid and slow mixing steps were investigated on the improved efficiency of coagulation and flocculation processes. Meanwhile, constant and declining mixing speeds during the flocculation step were compared. For the purposes of this study, the Jar test unit was employed as a batch reactor. Results showed that from among the three mixer speeds of 100, 150, and 200 rpm in the rapid mixing tank, the 150 rpm mixing speed yielded higher removal efficiencies for turbidity, BOD, COD, and TSS. In addition, comparison of the constant speeds (20, 30, and 40 rpm) and the declining speeds (40 to 10 rpm) in the slow mixing stage showed that the declining speed yielded higher turbidity, BOD, COD, and TSS removal efficiencies than each of the three fixed speeds. Moreover, the lowest volume of sludge produced was 34 ml/L at a slow mixing speed of 30 rpm from among the constant speeds used in the slow mixing tank. Finally, it was found that the declining speed flocculation led to an improved sludge production of 26 mg/L.

Mesoporous silica adsorbents have been gaining increasing importance in the removal of heavy metal ions from water and wastewater. MCM-48 is a mesoporous silica adsorbent whose adsorption capacity of heavy metal ions can be drastically improved when it is modified by functional groups. The present study investigated the removal of lead and cadmium metal ions from aqueous solutions using the modified NH2-NH-NH-MCM-48. The nanoparticles were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The adsorption process was optimized by varying adsorbent doses from 0.125 to 10 g/l, the initial solution pH from 2 to 6, and the initial metal ion concentration from 5 to 60 mg/l. The equilibrium data were analyzed using the Langmuir and Freundlich isotherms using a nonlinear regression analysis. According to the parameters of the Langmuir isotherm, NH2-NH-NH-MCM-48 recorded a higher maximum adsorption capacity for both Cd(II) and Pb(II) than MCM-48. The maximum adsorption capacities of NH2-NH-NH-MCM-48 for Cd(II) and Pb(II) were calculated to be 82.7 and 119.24 mg/g, respectively. The results suggest that MCM-48 modified with the amine functional group to synthesize NH2-NH-NH-MCM-48 significantly improves its adsorption capacity so that it can be recommended as an effective adsorbent for the efficient removal of Cd(II) and Pb(II) metal ions from aqueous solutions.

Effluents from dairy plants inactivate the active water ecosystem as a result of reducing their dissolved oxygen content, thereby leading to the loss of aquatic life. The objective of this work was to use coagulants for optimizing the chemical oxygen demand (COD) reduction process employed in treating dairy effluents. An optimized composite formulation comprising natural and synthetic coagulants including pectin, sodium alginate, aluminum sulfate, and iron chloride was prepared and the coagulation temperature required to reduce the intended index was determined. Experiment design was accomplsihed using both the fraction of the full factorial statistical method and the Qualitek-4 software. The signal to noise approach was employed for data analysis. Optimum conditions were achieved at aluminum sulfate, sodium alginate, iron chloride, and pectin concentrations of 1.5, 0.03, 1.5, and 1 g L-1, respectively, as well as a temperature of 30 °C. While the COD reduction efficiency under optimal conditions was estimated to be 28.411%, a COD reduction efficiency of 29% was obtained in experiments under optimal conditions. Variation in iron chloride concentrations was identified to be the factor with the greatest contribution of 35% to reducing the effluent organic load. This is while changes in pectin concentration showed a lower contribution (1.8%) and sodium alginate had only a negligible impact of 8.8%. Finally, changes in aluminum sulfate concentration and coagulation temperature had impacts of 30.8 and 23.3%, respectively, on COD reduction. Compared to chemical coagulants, the natural ones exhibited lower effects on COD removal effiecincy.

Recent years have witnessed a growing interest in the optimal operation of water distribution networks (WDNs) as a result of their enhanced quality and reliability with due regard for the economic limitations faced. For this purpose, the present study was designed and implemeted to realize the two objectives of minimizing disinfection costs and maximizing reliability of water quality in water distribution networks using the multi-objective form of ACO algorithm as the optimization method. Different system analysis methods based on DDSM (demand driven simulation method) and HDSM (head driven simulation method) were also employed to investigate and compare the effects of constant versus time-dependent chlorine injection and pump speed. Results indicated that, compared to the condition with constant parameters of chlorine injectuion and pump speed, great improvements could be achieved in enhancing the reliability of water quality and reducing disinfection costs by using variable speed pumps (vsp) and time-dependent chlorine injection regimes without the need for buster pumps. Comparison of the analytical methods employed also indicated that application of HDSM led to reduced chlorine injection costs and improved reliability of water quality.

Water supply networks account for a major portion of the urban infrastructure requiring sizable funds for their construction and operation. This has encouraged many researchers to focus their efforts on optimizing water distribution networks. In most recent research in the field, stochastic meta-heuristic algorithms have been employed to address the problem. Given the many inadequacies of stochastic algorithms, the present study explored the application of a novel deterministic algorithm for minimizing pipe-sizing costs in water distribution systems (WDS). The algorithm used in this study is a modified version of the central force optimization algorithm called CFONet which is used for solving water distribution system problems. The performance of the proposed method was evaluated by optimizing pipe-sizing in two benchmark WDSs. For this purpose, both CFO and CFONet methods were written in MATLAB and interfaced with the hydraulic simulation model EPANET. Application of the two methods mentioned above to two different water supply systems revealed the superior performance of the proposed CFOnet over its CFO counterpart. Thus, CFOnet yielded an optimum response for the deisgn of a double ringed system equal to US$419,000 after 12,432 runs of objective function estimations. Moreover, the optimum design of a CAdo system was obtained to cost 126,535,915 In. Ruppes after 259,476 runs of objective function estimations. Comparison of the results obtained in this study with those reported in the literature on other stochastic optimization algorithms showed that the proposed method yields satisfactory solutions for WDSs optimization problems while it also enjoys the merits of a deterministic optimization method.

Dam reservoirs are commonly used for a variety of purposes including flood control; supplying drinking, irrigation, and industrial water; marine transport; fish culture; and recreation. It is therefore, essential to safeguard water qulity in order to ensure the sustianble and economical operation of dmas. This study was conducted to identify the relevant water quality indices for Shahid Rajaee Dam Reservoir (Mazandaran-Sari) and compare them based on abiotic (some of the physico-chemical) and biotic (Chlorophyl-a, Shannon, Saproby indices, microbes, and fungi) parameters. Sampling was carried out at four stations during different months in 2012-2013. The Water Quality Index was investigated using seven physicochemical parameters; the TSI trophic index based on nutrients, water turbidity, and chlorophyll-a; and the Shannon and Saproby indices. Maximum monthly values of TSI were obtained in July and August (eutrophic status) while minimum values belonged to September and February (oligotrophic status). Based on, water quality in the reservoir was classified in the “good” category in all the study months. Water quality assessment using Shannon and Saproby indices showed that July and August had the lowest water quality (moderately to highly polluted). The maximum fungal colony and coliform counts were observed in August and September at all the sampling stations. The study revealed that more reliable and comprehensively illuminating results can be achived if, especioally in the case of drinking water supplies, water quality investigations are conducted using both biotic and abiotic parameters. Overall, it is recommended that all human activities around the dam or upstream river tributaries be controlled and checked during the warm months of the year in order to prevent eutrophication, algal blooms, microbial activities, and organic phosphorus loading.

Located in an arid/semi-arid region, Iran calls for special attention to its water resources. More importance should, however, be attached to the groundwater resources due to their hidden nature and the excessive costs associated with their extraction as well as qualitative and quantitative monitoring. Due to the significance of the water resources for activities in the neighborhood of the Urumia Lake, the present study was designed to conduct a qualitative investigation of an aquifer in the area adjacent to the lake. Teh importance of water is especially foregrounded by the increasing daily human demands for drinking, irrigation, industrial activities, and home use. Shiramin area has an aquifer of approximately 34 square kilometers in area and is one of the plains bordering the Urmia Lake. The groundwater resources in Shiramin plain were evaluated by collecting samples from 18 points well distributed across the plain and subjected to analysis to determine 12 water quality parameters. A multivariate statistical analysis (namely, principal components analysis and factor score) was used and GIS and saturation index were also integrated. Four components were extracted as a result of applying Principal Components Analysis, one resulting from the impact of carbonate formations, one caused by water recharge, one due to the effects of sulfate and fluoride, and the fourth one due to the high factor loading of nitrate caused by human activities. Interpolation of the factor scores with GIS showed that the greatest area with positive factor scores was related to the first component and that the area covered by positive factor scores reduced moving from the first to the fourth component. Generally speaking, such factors as reduced rainfall, increased water extraction, and intensive agricultural activity accounted for the degradation observed in the water quality in Shiramin area so that samples collected upstream the plain and those from the plain end exhibited more positive values of saturation index with respect to their carbonate and halite rocks.

Hospital effluents are regarded as a kind of municipal wastewater laden with additional pollutants due to the variety of wards and therapeutic activities in a hospital. This makes the determination of kinetic coefficients and parameters of utmost importance for the successful operation and maintenance of hospital wastewater treatment facilities. Extended aeration activated sludge is one of the most important processes employed in such facilities. The present study is an effort to determine these parameters for the operation of such a facility operating in hot climate conditions. For this purpose, samples of both hospital raw wastewater and plant effluent were taken during a 6-month period from January to June 2014 to determine their BOD5, COD, TSS, PH, and Turbidity. Moreover, MLSS, MLVSS, and DO in the aeration tank as well as the sludge return ratios were measured. Such operation and maintenance parameters as θc, F/M, and SVI were then calculated and the equations of the modified Monod Model were used to calculate the values of the kinetic coefficients such as Y, K, KS, Kd, and µmax for the extended aeration activated sludge process at the hospital wastewater treatment plant as follows: K= 2.19 d-1, Ks=90.74 mg/l, Y = 0.39 g Biomass/g BOD5, Kd = 0.06 d-1, and µmax =0.85 d-1. The results obtained can be usefully exploited for designing similar extended aeration activated sludge processes for the treatment of hospital effluents, especially for those operating in hot climates.