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Sludge treatment and disposal processes in wastewater treatment plants account for a significant portion of the total treatment costs. One of the most expensive parts of sludge treatment is chemical conditioning. Study of the effect of process chain on the conditioning and dewaterability can effectively optimize and reduce operating costs and increase the quality of effluent sludge. This paper investigates the impact of aerobic digestion of waste sludge in Yazd wastewater treatment plant by SBR method on its dewaterability. For this purpose, the waste sludge sample of the plant was aerated in the laboratory at different residence times from 1.5 to 7 days. Then the dewaterability of the sludge was measured by two methods of Specific Resistance to Filtration (SRF) and Tests of Time of Filtration (TTF) in two cases with and without chemical conditioning with cationic polyacrylamide. The results showed that sludge aeration for up to 3 days without conditioning led to the best sludge dewaterability. The best results were obtained at 1.5 days aeration for the conditioning mode with polymer, which improved the dewaterability up to 4.5 times in the optimum polymer dosage. In this case, the polymer dosage decreased by 30% compared to the non-aerated conditioned sludge. It indicates the effect of digestion retention time on dewaterability. At the beginning of the process, the decomposition of cellular material improves the release of water from solid particles. Still, its continuation reduces the dewatering capability due to reduced particle size and conversion to colloidal materials.

Nowadays, the using of treated wastewater in diverse purposes such as agriculture, industry and irrigation is converted to an appropriate solution for water shortage. Despite the advantages of water reuse, due to various pollutants in wastewater and lack of complete treatment in accordance with the standards, it is always risky. Therefore risk assessment should be conducted in order to determine the reliability of system and offer solutions to enhance the reliability of wastewater treatment system. Risk is the possibility of occurrence an adverse event and the severity of the negative effects of it. In the present study, Bayesian network approach is used for risk assessment of wastewater treatment plant. In this method the possibility of an event can be obtained by creating cause and effect relationship between the components of the system. Wastewater treatment plant of industrial complex of Moorchekhort is selected for case study in this study. The fouling, corrosion and biofilm of using treated wastewater for industry have been determine as final events. The model input datas have been formed by experts, specialists and laboratory datas from wastewater treatment plant of industrial complex of Moorchekhort. The reliability of wastewater treatment system analyzed by Bayesian network model showed %70. The efficiency of Bayesian network in order to determine elements of failure and estimate the risk of wastewater treatment system that is not adapted to effluent standards for the industry is shown in this study.

The design and upgrade of sludge treatment systems generally depend on the decision made regarding the appropriate system from among the options available. The selection process has become increasingly important and complex due to recent technological developments that have led to increased diversity in the available options which offer a wide variety of capabilities. The multi-criteria decision making method is one of the techniques recently developed which takes into account all the criteria involved in the decision making process. The Ghods Town WWTP in the west of Tehran located in the vicinity of residential areas has given rise to claims by citizens due to the odors emitted by the sludge sand drying bed, which justifies the replacement of the present sludge dewatering system. For this purpose, the multi-criteria decision making method based on the fuzzy synthetic evaluation method was used to identify the optimal sludge dewatering system appropriate for the WWTP under consideration. Furthermore, weighting of the subjective (social, environmental, and administrative) criteria was accomplished using the analytical hierarchy process and the objective (i.e., economic) criteria were weighted using the entropy concept. In this method, the triangular fuzzy membership function was also used to take into account the uncertainty associated with each of the decision making parameters. Based on the results obtained, the belt filter press dewatering system and the filter press were identified as the preferred solutions.

Evaluation of a Biofilter System for Removal of Hydrogen Sulfide Gas (Case Study: Wastewater Pump Station of Khorramabad) Abstract The biofilter system is one of the methods commonly used for the removal of hydrogen sulfide as the main source of odors emitted from wastewater facilities. The system is based on using the contaminant material as bedding to feed microorganisms. To achieve the desirable removal efficiency, it is, therefore, essential to create the proper conditions for the bacteria to grow on the bedding. In this study, a pilot-scale biofilter made of compost and woodchip (with a compost/woodchip ratio of 5:1) was used as the bedding material at Khorrmabad wastewater pumping station to investigate the performance of the system under real conditions. The experiment was carried out over 75 days during which time the input and output H2S concentrations were measured on a regular basis. Moisture was adjusted between 40% and 60% throughout the experiment to provide optimal conditions for bacterial growth. The results showed that the concentration of H2S emitted from the pumping station during 24 hours varied greatly between 0 and 48 PPM. The maximum adsorption capacity of the biological bedding was recorded at 2.874 g/m3.hr and the mean efficiency of H2S removal including the startup time was 89%. The mean performance efficiency during the biological activity after the startup was recorded at 98%.

The total phosphorus (TP) concentration, as the primary limiting eutrophication factor in the Mahabad Dam reservoir in Iran, was studied, considering the combined impacts of climate change, as well as the scenarios on changes in upstream TP loadings and downstream dam water allocations. Downscaled daily projected climate data were obtained from the Beijing Normal University Earth System Model (BNU-ESM) under moderate (RCP4.5) and extreme (RCP8.5) scenarios. These data were used as inputs of a calibrated Soil and Water Assessment Tool (SWAT) model of the watershed in order to determine the effects of climate change on runoff yields in the watershed from 2020 to 2050. The SWAT model was calibrated/validated using the SUFI-2 algorithm in the SWAT Calibration Uncertainties Program (SWAT-CUP). Moreover, to model TP concentration in the reservoir and to investigate the effects of upstream/downstream scenarios, along with forecasted climate-induced changes in streamflow and evaporation rates, the System Dynamics (SD) model was implemented. The scenarios covered a combination of changes in population, agricultural and livestock farming activities, industrialization, water conservation, and pollution control. Relative to the year 2011 in which the water quality data were available, the SD results showed the highest TP concentrations in the reservoir under scenarios in which the inflow to the reservoir had decreased, while the upstream TP loadings and downstream dam water allocations had increased (+29.9%). On the other hand, the lowest TP concentration was observed under scenarios in which upstream TP loadings and dam water allocations had decreased (−18.5%).

The purpose of this study was to analyze the performance of Integrated Fixed Film Activate Sludge system in Amol industrial wastewater treatment plant to treat the food industrial wastewater. The capacity was 1700 cubic meters per day that includes physical and biological treatment, disinfection, sludge thickening, digestion and dewatering. The wastewater quality parameters were analyzed during winter 2010 and spring 2011. Using data, COD removal efficiency and kinetic coefficient such as yield coefficient (Y), half saturation coefficient (Ks), maximum substrate utilization rate (k) and endogenous decay coefficient (kd) were calculated and results indicated that except Ks other coefficient were in the range that was normally reported for conventional activated sludge. Under existing conditions at the wastewater treatment plant, COD removal efficiency range was between 98 to 99 percent. By using kinetic coefficient obtained in this study, effluent COD was estimated and sensitivity analysis was performed. The results showed that there is a direct relationship between the variation of kd and Ks with effluent substrate concentration, while the relationship between k and effluent substrate is reverse. Finally the effect of increasing sludge retention time (SRT) on COD removal efficiency was also investigated.