Preparation of solids balances for municipal wastewater treatment facilities

Mass balance is a well-known method in many engineering applications including reactor design, process evaluation, and benchmarking. This method assumes and calculates the remaining stable the outputs and inputs of substances in a mass flow system. In environmental engineering field, preparation of mass balances is considered as a very important tool to compute the fluxes of substances compare operational conditions and check the general validity in wastewater treatment facilities (WWTFs). It is a very current way to compute the influent and effluent flows and their characteristics at wastewater treatment plants. However, application of mass balances on WWTP data is mainly difficult since the treatment processes are dynamic systems and the variability of the influent loading is unknown (Puig et al., 2008).Although mass balance calculations have been preferred to improve the quality of WWTF information (Meijer et al. 2002), getting reliable information from raw WWTF data is mainly not possible. For example, to establish a mass balance in the biological WWTFs having activated sludge units for process integrity, all in- and outgoing flows including the activated sludge composition and sludge production should be known (Puig et al., 2008). For process design including mass balances, the use of mathematical modeling of wastewater treatment processes has taken great attention based on engineering scale applications since 1990s and early 2000s. To evaluate and refine process configurations not only in the design of a particular unit process, but also in terms of plant-wide effects, some companies have developed simulation software programs such as BioWin (EnviroSim Associates Ltd., Flam borough, Ontario, Canada); GPS-X (Hydromantis Inc., Hamilton, Ontario, Canada); ATV-131 E (DWA, Germany) (WERF, 2010). The models are very useful to develop the steady-state mass balances of the integrated plant processes regarding the influent and effluent characteristics, kinetic and stoichiometric parameters, and the effects of sidestream loads.In this MSc. Thesis, a spread-sheet was developed by using Microsoft Excel to calculate the mass balance in biological WWTFs. It is capable to present how different wastewater treatment processes and their recycled flows affect the mass balance results. This research has been studied with three kinds of biological wastewater treatment processes -conventional activated sludge process, extended aeration activated sludge process, and A2/O process (BNR)- and flows. It has been computed with three iterations for each processes since there is no need for further iteration. The flows are 1000 cubic meter, 10,000 cubic meter, and 100,000 cubic meter. The constants and coefficients were chosen the same for all processes so it was suitable to comparison. It computed flow, BOD, TSS loads and recycle streams for conventional and extended aeration active sludge systems while flow, BOD, TSS, Org-N, NH4+-N, NO3--N, TN and TP loads were taken into account for biological nutrient removal system (BNR). In the calculations, medium strength domestic/municipal wastewater characteristics were used. The results showed that the conventional active sludge system is less stable than the other processes since its iteration differences exceeding 5 percent are higher than those in the other processes. The computing steps and the results are given in details and compared them for the treatment processes and flows examined in the thesis.