Exergetic evaluation of waste water and sludge treatment system with electrical generation of a processed food plant

An exergetic evaluation was carried out in a wastewater and sludge treatment plant with electric cogeneration that receives the tributaries of a sardine and tuna processing plant. A review was made of the historical data of operation of two years, the necessary technical information was collected to evaluate the plant and estimating the missing information through mathematical models and with a simulator of chemical and biological processes. The exergy balance of the subprocesses was carried out and determined that it is necessary to look for ways to increase the organic load that is removed in anaerobic processes and to improve the use of biogas energy; besides to reduce the consumption of electrical energy. To improve the operation of the UASB anaerobic reactor, its operation was modeled in the thermophilic environment and it was determined that the energy that could be extracted from the biogas is not enough to reach the operating temperature in this regime; Laboratory tests were performed and the real increase in biogas production was determined by increasing the operating temperature by a few degrees. The concentrations of GyA and SST fed to the UASB were determined close to the limit, so it was recommended to improve the operation of the DAF 1 and autoclave, the equalizing tank was cleaned regularly. With respect to the aeration system of the active sludge, a potential of 64% energy saving was determined by only performing an adequate cleaning of the diffusers. Optimizing the internal circulation recirculation was recommended to save energy and improve denitrification. The saving of money was compared of different options of use of biogas and it was determined that the most profitable option is to make a deep repair to the internal combustion engine already in place, in the place it was relocated sheltered from the acids that are generated in the biological reactors . The investment was estimated and would be paid in less than one year. The possibility of using biogas was valued as a substitute for fossil fuels and it is determined that more money is saved than with the previous option, so the detailed design must be followed. For the electric motors of the plant were determined which were the ones that should be changed by motors of premium efficiency and which is better to wait until they break down to replace them either by premium motors or high efficiency. The potential savings for each of these estimates is US $2,794, US $36 and US $1393 per year, respectively. The rigor analyzes in the CSTR were recommended in order to optimize the process. (Author)