Development of an optimization model for phosphorus recovery in wastewater treatment plants

• Main Author: Damalerio, Regina G.
• Format: text
• Language: English
• Published: Animo Repository 2022
• Subjects: Water—Phosphorus content; Sewage—Purification—By-products; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etdm_chemeng/15; https://animorepository.dlsu.edu.ph/context/etdm_chemeng/article/1011/viewcontent/Development_of_an_optimization_model2_for_phosphorus_recovery_in_w_Redacted.pdf
• Institution: De La Salle University

The current limited supply of phosphate rock ores poses a threat to the global food security since 95% of the phosphorus is utilized for food production. One sustainable alternative is to recover nutrients (phosphorus and nitrogen) from nutrient-rich sources such as wastewater and sludge. The problem lies on the selection of technologies while considering the total costs of a wastewater treatment plant (WWTP) since high recovery entails high WWTP costs. The study develops a lexicographic ε-constraint optimization model with total annualized cost (TAC) and overall phosphorus recovery as objective functions. The model can aid the decision-makers in determining possible combination of technologies and the corresponding trade-offs (high TAC and low TP recovery, and vice versa). Furthermore, the model can provide insights on the impact of different variables to the overall cost and TP recovery for different sink applications. Its capability was demonstrated using two case studies: one for wastewater treatment and one for phosphorus recovery from sludge. Literature review is carried out to search for available techno-economic data. Then, the proposed model was subject to topological, logical, and structural constraints. The 1st case study utilized Mixed Integer Quadratic Program (MIQP) while the 2nd case study used Mixed Integer Non-Linear Program (MINLP) due to the variable outgoing contaminant concentrations. Lexicographic ε-constraint method produced dominant solutions which is attributed to the use of constant flowrate values and variable technology efficiencies in determining the TAC and overall phosphorus efficiency. Lastly, sensitivity analysis provided insights on the impact of varying influent characteristics and land area requirements. Challenges include limited techno-economic data for various technologies and generation of dominating solutions. Therefore, recommendations for the study are as follows: improve the techno-economic data of the technology alternatives, consider evaluating the TAC and P-recovery for large-scale WWTPs (>100 m3/d), and improve the model such that it would provide non-dominating solutions.