Introduction: When there is no immediate access to dental laboratory for pouring dental impressions, impression materials with dimensional stability over time should be used. The aim of this study was to evaluate the effect of storage time on dimensional stability of casts poured from alginate impressions.Materials and Methods: In this experimental-laboratory study, a metal model containing two dies and acrylic impression trays were used to make five alginate impressions at each time interval using three different alginate brands [Hydrogum 5 (Zhermack), Elastic Cromo (Spofadental), and Alginmax (Major)]. The impressions were kept in a humid environment for 0, 24, 48, 72, and 120 hours and then poured with Type III dental stone. Five dimensions were measured in each cast with a digital caliper: ED (distance between the two dies), H1 (height of the smaller die), H2 (height of the larger die), D1 (diameter of the smaller die), D2 (diameter of the larger die). The results were compared among groups with two-way ANOVA and a post hoc Tukey test (a=0.05).Results: Dimensional stability of alginate impressions was dependent on both the material and time (p value<0.05); however, their reciprocal interaction did not exhibit any significant relationship at the same interval (p value>0.05). After 24 hours, dimensions of Elastic Cromo alginate only did not exhibit any statistically significant differences with the model (p value>0.05). After 48 and 72 hours Hydrogum5 alginate only did not demonstrate any significant dimensional differences with the model (p value>0.05). After 120 hours, Hydrogum5 alginate exhibited a significant difference with the model in H2 dimension.Conclusion: The results showed that Alginmax impressions must be poured immediately. Elastic Cromo impressions can be poured after 24 hours. The impression of these three kinds of impression materials did not exhibit any significant dimensional differences before 120 hours; however, they are not reliable for five-day usage.

Among the municipal and industrial wastewater treatment processes, the moving bed biofilm reactor (MBBR) technology has attracted much attention due to its ability to remove organic matter, nutrients, and some resistant compounds. In this study, technical performance and economic evaluation of a municipal wastewater treatment plant in Tehran, Iran, with the extended aeration activated sludge (EAAS) technology and its comparison with the MBBR technology were evaluated by process simulation using CapdetWorks software. The simulation results showed that the characteristics of the effluents from the wastewater treatment plant are in accordance with the FAO and Iranian Environmental Organization standards for green space irrigation. Also, economic analyses indicated that the total project cost of a wastewater treatment plant utilizing MBBR technology is approximately 14% less than that of EAAS technology, which could be due to the significant reduction in the volume of the moving bed biofilm reactor (649.2 m3) compared to the EAAS reactor (4148.1 m3). The results also indicated that the operating, maintenance, and chemical costs required in the MBBR method are 9.2, 16.4, and 18.3% lower, respectively, compared to the EAAS technology, whereas the amount of energy consumed in both technologies is almost the same. The effect of the media fill fraction (biofilm carrier) on the total project cost in the MBBR technology was also investigated. The results revealed that by increasing the media fill fraction from 30% to 70%, the total project cost decreases from $9.37 to $9.16 million, highlighting the significant role of the media fill fraction in the economic costs and performance of biofilm reactors.

Background & Objective: At the present time, increasing of nitrate ion in water resources observed most of cities and these conditions can cause various environmental health hazards. High nitrate concentrations in drinking water for infants fewer than 6 months could make in methemoglobinemia and Blue Baby syndrome. Hence, at present study, the rate of nitrate ions removal from aqueous using the aerated electrochemical process has been studied.Materials & Methods: This study was conducted a laboratory-scale experimental, which done in pilot study. Experiments were performed in a batch reactor (with an effective volume 1 L), with four iron electrode connected in parallel (bipolar mode). Electrodes using a bipolar power supply were connected to convert alternating to direct current electricity. In the first time, reactor was filled synthetic samples containing nitrate anion concentrations of 5, 50 and 100 mg. The reaction was started. The efficiency of the system in removal of nitrate under various condition, pH (3, 7, 10), voltages (10, 20, 30 and 40 V), initial concentration of nitrate (5, 50 and 100 mg/L) and reaction time (15, 30, 45 and 60 min) were determined.Results: Results obtained with synthetic solutions revealed that the most effective removal capacities of nitrate (96%) could be achieved at 40 V electrical potential, pH=10 and reaction time= 60 min for initial concentration of nitrate equal 5 mg/L. Also under these conditions, the amount of energy consumption was 0.0257 kwh/L.Conclusion: The results of this study showed that nitrate removal efficiency using aerated electrochemical technique has a direct correlation with pH, voltage and reaction time and reverse correlation with initial nitrate concentration. Moreover, it can be concluded that this process has the potential to be utilized for the effective and safe removal of nitrate from water and wastewater.

Many experimental studies have been conducted on development of the scour hole as a result of vertical jet impaction. Research has shown that aeration of the nappe flow in the model is much weaker than that in the prototype. Therefore, the influence of aeration on scour holes needs further study. Experimental investigation of the effects of air entrainment and tail water depth on the scour hole developed by a vertical submerged jet impaction is carried out in this study. The scour holes with and without air entraining conditions were investigated while hydraulic parameters like jet velocity and tail-water depth were kept constant. The results showed that air entrainment effectively reduces the scour depth and dimension. Variation of maximum relative depth and length of scouring i.e. ds/htw and Ls/htw versus tail- water Froude number parameter, i.e. Frtw were analyzed. By increasing the air concentration, maximum relative depth and length of scour hole reduced. The changes in scour hole dimension has a threshold. Results indicated that for Frtw more than 8.78, no meaningful effect on maximum scour hole depth (ds/htw) and length (Ls/htw) was seen for air concentration of less than 3.25 percent.

The treatment of pharmaceutical non-penicillin wastewater was conducted in the biological aerobic process. The oxygen transfer rate played the major role to reduce the organic pollutants of the wastewater by removing gases, oils, volatile acids and odor. The microbial culture used in the experiment was the ethanol producers, isolated form the wastewater. Optical density, COD and concentration of chemicals equivalent to carbohydrate were measured in a time period of 3-4 days of aeration. The propagation of bacteria was monitored and its growth rate was determined. Oxygen transfer rate and mass transfer coefficients were found to be affected by airflow rate, bubble size and agitation rate. Dissolved oxygen was shown as an indication of microbial growth and limitation of mass transfer. The dissolved oxygen was about 7.89 ppm from the starting point and then is dropped to 2 ppm by the end of the first day. After the second day of aeration the oxygen depletion was obviously observed since the DO meter showed 0.14 ppm. Aeration rate was 0.2-1.3 liters per minute for working volume of 3 liters and 5-10liters per minute for 15 liters aerated tank. Maximum optical density was obtained with high aeration rate at the first day of aeration, 0.95 g/l, as the aeration was reduced the cell propagation was also reduced. The maximum cell growth was obtained by the end of 3 days of aeration with minimum airflow rate. The maximum COD and carbohydrate reduction was 58 and 90 percent respectively with 1.15 liter/min airflow rate in the 3 liters aeration system. The bubble size affected the mass transfer coefficient (K__L.a), as the contract surface of gas exposure to liquid increased the mass transfer coefficient was increased. As the dissolved oxygen concentration dropped the K__L.a was also decreased. The values of K__L.a for the 5 and 10 liters/min airflow rate for 15 liters aerated tank were 0.055h^-1 and 0.3975h^-1 respectively.

Background and Objectives: Horizontal roughing filters (HRF) can properly remove suspended solids and microorganisms from surface water resources especially on filtration rates less than 1.5 m/h. This research was aimed at suspended solid removal efficiency of HRF during secondary wastewater effluent filtration. Methods: This experimental study was conducted by installing an HRF pilot system on effluent pumping station of Qom wastewater treatment plant based on aerated lagoon process. The pilot was a horizontal cylindrical column consisting of three compartments filled with river gravels in various sizes. Grab samples were simultaneously taken from HRF inlet and outlet in three filtration rates: 0.5 1 and 1.5m/h Results: The results indicated that filtration rate had a significant effect on the amount of total suspended solids in HRF effluent. During optimum operation of HRF removal efficiencies of three filtration rates (0.5 1 and 1.5 m/h) were 78.5 63.1 and 66.9 respectively. Conclusion: T-test analysis indicated that with a significance difference outlet effluent from HRF in all three flow rates met the standard requirements of Iran Environmental Protection Agency for irrigation and discharge to surface water.