Abstract
Resource recovery from municipal wastewater has been a prime focus for a decade. Although several recovery processes already exist in the market today, the high cost of material, inherent disturbance in the influent quality, lack of real time monitoring of critical parameters, and lack of a robust automation system may result in suboptimal performance. This work attempts to construct a model based predictive control for optimal operation of a struvite recovery unit in a full scale WRRF. A multi-parameter based predictive control has been developed by implementing an Economic Model Predictive Controller (EMPC) for optimal dosing of magnesium hydroxide in a struvite recovery unit. The EMPC used customized objective function for real-time optimization of performance and economical parameters of the crystallization unit. The effectiveness of the proposed EMPC controller is verified through tests conducted on the Benchmark Simulation Model No. 2 (BSM2d.). The results obtained from the simulator-based evaluation of EMPC demonstrate a significant improvement in resource recovery at reduced operational costs. The economic advantages of implementing an EMPC compared to proportional and constant magnesium dosage has also been enumerated.
Highlights
The Wastewater Treatment Plants (WWTPs) are consistently upgrading their processes to include more recovery operations and conform to its new terminology as Water Resource Recovery Facilities (WRRFs) (Regmi et al, 2019)
The remaining 25% of the data is chosen as validation data (t = 455 to t = 609) which was used to confirm the ability of model to predict PO4,EFF in the overhead stream of struvite recovery unit
The work demonstrates the advantages of a multi-parameter-based control strategy for optimal dosing of magnesium in a struvite crystal lization unit
Summary
The Wastewater Treatment Plants (WWTPs) are consistently upgrading their processes to include more recovery operations and conform to its new terminology as Water Resource Recovery Facilities (WRRFs) (Regmi et al, 2019). Struvite precipitation is one such process that gained popularity over the past decade (Jensen et al, 2015). Struvite (magne sium ammonium phosphate hexahydrate) has been of special interest due to its potential applicability as a slow-release fertilizer. The use of slow-release fertilizers (such as struvite) can offset the environmental deterioration caused by the excessive use of mineral-based fertilizers and eventually play a vital role in the modern eco-friendly sustainable agricultural sector (Rahman et al, 2014). Struvite can be precipitated by adding Magnesium Hydroxide (Mg(OH)2) to a stream rich in ammonium (NH4+) and phosphate (PO4− ) ions. In a typical WRRF, these nutrient-rich streams can be found in the supernatants of the anaerobic-digested sludge (Rahaman et al, 2008). A struvite recovery unit is often installed after the dewatering unit to recover the Nitrogen (N) and Phosphorus (P) before recycling the supernatant back to the biological reactors
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