Aerobic digestion processes of sewage sludgeAdvanced tools to optimize sizing and operation.

Laburpena

In the past years, WWTP designers and operators have sought for cost-effective and sustainable solutions for the treatment and disposal of sewage sludge minimizing the impact of its management on the overall performance of the mainstream water line. Following this main concern, the present work focuses on studying two different solutions based on aerobic-type digestion systems, namely single stage Autothermal Thermophilic Aerobic Digestion and Post-Aeration process, in order to optimize their design, obtaining clear guidelines for their operation and sizing at full-scale. With that purpose, these processes have been experimentally tested at pilot scale. The experimental results obtained were evaluated by means of stationary mass and heat balances, and later used as basis for the calibration of a dynamic mathematical model. In order to guarantee an accurate prediction of the experimental data, the dynamic model required of a protocol for the characterization of inlet sludge together with a reliable estimation of the composition of non-biodegradable organic matter in the feed sludge. . Thus, some additional ATAD and biodegradability tests were carried out at lab scale in order to quantify the heat potential of different samples of raw sewage sludge and gain more information regarding the fraction and composition of non-biodegradable organic matter, which severely affected the characterization of sewage sludge. Based on the results, a complete characterization protocol for the non-biodegradable and biodegradable fractions of sludge has been developed. Dynamic model calibration enabled the analysis of multiple scenarios for these processes considering a wide range of operating conditions. The results from this analysis provided with relevant clues for optimizing the design and operation of these processes, and even resulted in the development of simple tools for full-scale design of the Post-aeration process. Moreover, a new procedure for simplifying complex dynamic models has also been devised based on the stationary models used for the analysis of experimental data. The simplified models were demonstrated to provide an accurate description of the processes with very low data requirements. In summary, the results from this work proved the potential of using stationary and dynamic models as advanced tools to optimize the design and operation of aerobic digestion processes