Background: The purpose of this study was to model a real wastewater treatment plant in operation with GPS-X software. In the following, the verification of the output results of the software was done with the results of the effluent tests of the discussed sewage treatment plant. Then, the rate of return sludge, recycled sludge, and disposed sludge of the wastewater treatment plant was optimized by Modified Ludzack-Ettinger (MLE) method, so that it has the greatest effect on the quality of the effluent, especially chemical oxygen demand (COD) and nitrate (NO3) parameters.
Methods: First, using the available data of an operating wastewater treatment plant, the processes of the treatment plant were modeled in the software and the compatibility of the model with the existing treatment plant was checked. After the validation of the software, in order to check the parameters affecting the activated sludge process, including return sludge rate, excess sludge rate, and internal recirculation sludge rate in the treatment of organic matter and nitrogen, COD, NO3, and ammonia parameters were investigated as indicators of pollution. In addition, the MLE process for nitrogen removal was modeled in the software. After performing the modeling by changing the parameters and checking the resulting outputs, the results regarding the effect of increasing the sludge recirculation rate on the COD concentration in the effluent and the effect of increasing and decreasing the internal recirculation rate and the disposal sludge rate on COD removal were examined. In addition, the mutual effect of changes in internal sludge recycling and return sludge and the amount of excess sludge disposal on NO3 removal was shown by different graphs.
Findings: In this study, while validating the software, the results of the experiment design showed that the return sludge rate and the internal recirculation rate had mutual effects on each other in the removal of COD and NO3, and in the optimal mode of operation and design, the ratio of 0.54 for return sludge and one-time internal recycling and ratio of 0.021 for disposal sludge had the greatest effect on COD and NO3 removal target efficiency and increasing the effluent quality.
Conclusion: GPS-X software can be used in the modeling and optimization of wastewater treatment processes.
