Grantee Research Project Results
Final Report: Online Sensor for Wastewater Phosphorus Recovery
EPA Grant Number: SU839291Title: Online Sensor for Wastewater Phosphorus Recovery
Investigators: Winkler, Mari , Wei, Stephany
Institution: University of Washington
EPA Project Officer: Page, Angela
Phase: I
Project Period: February 1, 2018 through January 31, 2019
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2017) RFA Text | Recipients Lists
Research Category: P3 Awards , Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
Phosphorus discharge from wastewater treatment plants (WWTPs) can cause toxic algal blooms and hypoxic “dead zones” that threaten the biota in the surface waters. Phosphorus (P) removal from wastewater can be achieved by chemical precipitation or biological phosphorus removal (BPR). Chemical precipitation requires chemical dosage, produces extra sludge and does not allow for P recovery. BPR utilizes a special group of bacteria, the polyphosphate accumulating organism (PAOs), who store the phosphorus into their cells, hence removing it from the wastewater. Compared to chemical methods for P removal, BPR is the more cost effective and environmental friendly method as it does not require chemicals and the produced sludge can be utilized for P recovery. Phosphorus recovery (as fertilizer) is gaining importance as our global phosphorus reserve, which is essential for food production, is a non- renewable resource and projected to be depleted in the next 34-112 years. Therefore, P recovery at WWTPs can have a significant impact on extending the lifetime of phosphorus reserves. However, successful BPR process needs a stabilized microbial community and some BPR plants require external carbon dosage. If not carefully designed or optimized, these challenges can lead to system failure or expensive operational costs. As a result, chemical precipitation remains the dominant method of phosphorus removal despite the environmental consequences of wasting valuable phosphorus resources and producing extra chemical sludge for landfills.
This project aims to enhance sustainable practice in wastewater treatment by developing a new technology that simplifies BPR operations, reduces costs while increasing removal efficiencies and enabling P recovery. The biological P removal and recovery processes require routine monitoring of the key analyte, phosphate ions (PO43-). The amount of carbon dosage and fertilizer production are also based on the PO 3- concentrations. However, the only tested and reliable way of measuring PO43- are labor-intensive methods because no sensor exists yet that provides reliable online PO43- measurements. This project aims to create an engineering paradigm shift by developing a novel multi-sensor technology for PO43- quantification that enables real-time monitoring, controls and optimization of biological P removal and recovery process.
During BPR, PAOs store PO43- in their cells as polyphosphate while K+ and Mg2+ are utilized as counter ions. Therefore, the removal of PO43- is coupled with K+ and Mg2+. The proposed technology utilizes this coupled relationship to indirectly quantify PO43- using the commercially available K+/Mg2+ (hardness) sensors. This is done by collecting simultaneously signals from a multi-sensor array and measurements by conventional wet chemistry methods in a BPR bioreactor. These data are then used to train a novel machine learning algorithm for indirect quantification of PO43-. The multi-sensor array covers a wide range of environmental conditions (e.g., pH and temperature) and accounts for interferences of other ions present in the wastewater matrix, which leads to a biochemistry-informed algorithm for real-time PO43- quantification.
Summary/Accomplishments (Outputs/Outcomes):
The major milestones of Phase I included cultivation of stable community in a BPR bioreactor, installation of sensor hardware/software, and collection of baseline data for algorithm training in Phase II. A BPR bioreactor was successfully operated, achieving almost complete (98.4 ± 1.7%) phosphorus removal efficiency. Microbial analysis revealed a PAO-dominated (up to 43 % of total population) community. The sensor hardware and controllers were installed with real-time signal logging of a multi-sensor array. Baseline data collection showed a clear relationship between K+, Mg2+, and PO43-, which sets good basis for successful training of machine learning algorithm for quantifications of PO43- ions in Phase II.
Quantifiable benefits to People, Prosperity, and the Planet: Online phosphate monitoring enables real-time measurements of performance and notification of potential system failure, which prevents violations of discharge permits and pollution of the receiving waters. In addition, carbon dosage and aeration can be dynamically controlled to increase the BPR process efficiencies and reduce chemical usage. Online monitoring/controls will also advance P recovery and increase fertilizer production. Due to reduced costs and simplified BPR operations, the technology could drive more WWTPs to adopt or switch to BPR, thereby reducing harmful waste sludge from chemical precipitation. Using the reactor baseline data as an example scenario, the quantifiable benefits were estimated. With the multi-sensor technology implemented, the aeration time can be shortened by 37% in a bioreactor cycle while achieving the same P removal efficiency, which can translate to significant energy savings at full-scale facilities. P recovery takes place in a side reactor with a typical 12–20 hours of sludge holding time. Sufficient holding time is needed for PAOs to release PO43- from their cells to obtain a high P concentration liquid for recovery. Based on the P release rate obtained from the bioreactor biomass, we estimate that only 5 hours of holding time is needed to obtain a high concentration (200 mg P/L). By implementing the multi-sensor technology, this holding time can be automatically controlled and terminated once a desirable P concentration is attained. The reduction in holding time can translate to significant reduction in tank volumes and footprint consumptions at full-scale treatment facilities.
Conclusions:
The interdisciplinary team designed a multi-sensor technology that aims to create a paradigm shift in sustainable water management by enabling online monitoring and controls of the biological phosphorus removal and recovery processes. Under the scope of Phase I, the technical soundness of the technology was validated with a well-functioning BPR bioreactor and collected baseline data. The estimated quantifiable benefits demonstrated the potential for the technology to reduce aeration cost and footprint consumption at WWTPs. Other potential outcomes include increased fertilizer production and reduced chemical usage and waste sludge generation.
Proposed Phase II Objectives and Strategies: We plan to build upon the successes of Phase I to develop and implement control strategies in the bioreactor under Phase II. We will also partner with local wastewater divisions to test the technology under real wastewater conditions. We will examine the operational strategies that improve the P removal and recovery processes enabled by the multi-sensor technology and make final recommendations for implementations.
Supplemental Keywords:
sustainable water management, wastewater nutrient removal, resource recovery, online sensor technology, instrumentation and control, machine learning.Relevant Websites:
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.