Naturally, microorganisms decompose the organic material existing in nature, both in the presence or absence of oxygen. The majority of materials such as poisonous chemical compounds, heavy metals, would prevent the treatment process from taking place, lead to the entry of these contaminants into the environment results in the emergence of numerous diseases. In the present study, using the TOXChem4.1 simulation model, attempts were made to simulate a wastewater treatment plant and then assess the dispersions of contaminants including 1,2-Dimethylnaphthalene, 1,3-Dinitropyrene, 1,6-Dimethylnaphthalene, 1,6-Dinitropyrene, and 17a-ethinylestradiol (EE2) in concentrations of a common scenario. The results of computer simulations showed that the EE2 contaminant is of the highest percentage of decomposition among others, due to its wider chemical structure. Consequently, it is clear that such contaminant is of the highest mass in the sludge exiting the treatment plant. In addition, the results of the simulations demonstrated that the highest volumes of gaseous pollutants take place in the modulation and initial sedimentation units.

In large cities, several hundred cubic meters of municipal wastewater is produced every day, which because of high levels of pollution, needs to be treated either for disposal or secondary use. Some of the most important indicators and pollutants that should be reduced to the standard range are VOC, TSS, TDS, BOD 5 , nitrogen, phosphorus, heavy metals, and pathogens. Wastewater treatment plants, which have different capacities and procedures depending on the type and characteristics of the infl uent and effl uent, have large budgets of several hundred million for their life cycle. These costs include construction, maintenance, operation, chemical and biological materials, energy, and amortization. The costs associated with these environmentally essential infrastructures vary according to their treatment processes. This issue leads environmental engineers and policymakers to economic evaluation of various methods. This study with the help of CapdetWorks2.5 software has discussed three different methods of Complete Mixed Activated Sludge (CMAS), Aerated lagoon, and Oxidation Ditch in wastewater treatment plants in terms of operating costs. Evaluation and implementation of the decision-making system were conducted using Analytic Hierarchy Process (AHP). The results of the analysis showed that aeration ponds are the most optimal option in terms of operating costs with a value of 47.3%. The other two studied methods, namely CMAS and Oxidation Ditch, have a value of 24.9% and 27.9%, respectively.

Industrial wastewater treatment is of high priority due to the presence of an extraordinary concentration of dangerous pollutants. Similar to urban wastewater treatment plants, there are plenty of options while designing industrial ones which need various analyses and researches to choose correctly. One of the most effi cient ways to solve this problem is to implement Economic and Sensitivity Analysis. This research has studied designing an industrial wastewater treatment plant utilizing three different biological treatment methods (including Sequential Batch Reactors (SBR), plug-fl ow activated sludge with a secondary clarifi er, and step aeration activated sludge with a secondary clarifi er). It also measures the sensitivity of performance cost parameters to factors affecting the suspended growth unit. The results of the economic analysis showed that using SBR has the highest construction cost of $ 70,200,000 and the highest total cost of 96,900,000. Sensitivity analysis showed that by adjusting design retention time and variance between heterotrophic microorganism decay rate and the reality, using activated carbon-based systems could signifi cantly reduce total annual costs.