(297c) Electrified Resource Recovery from Synthetic Anaerobic Digester Centrate: Impact of Anode Type on Operational, Design and Stream Variables

Eutrophication of natural water streams is an undesirable effect of nutrient-rich streams disposal into these water bodies and excessive use of fertilizers on agricultural lands¹. As a prevention act, the post-anaerobic digester liquid stream (centrate) in wastewater treatment plants (WWTP), due to its high loads of nitrogen (N) and phosphorous (P), is not permitted to be discharged into the natural water bodies. Hence, this centrate stream will be looped back to the head of the WWTP facility, and it will increase the nutrient content of the aeration tank influent^2,3. As stated in several literature studies, aeration tanks are one of the most energy-consuming processes in WWTPs and an increased nutrient load will result in increased energy consumption^4,5. Furthermore, the natural resources of P are anticipated to be depleted in the near future^2,3.

One approach that can simultaneously address all the aforesaid challenges is recovering nitrogen and phosphorous as a compound called Magnesium Ammonium Phosphate or struvite^1,6. Struvite is a commercial fertilizer product and has the added benefit of providing a sustainable P resource for the agricultural sector³. The process of struvite recovery from wastewater has been performed using several methods including chemical, biological, and electrochemical processes, to name a few⁷. This research focuses on the electrochemical pathway of recovering this valuable fertilizer product because of its sustainability, as renewable energy sources could be used for operating the electrochemical technology, as opposed to non-renewable resources for other methods⁸.

In this work, the performance of a planar three-electrode electrochemical cell in a batch configuration with two different anode types has been compared. Materials that have been utilized as the anode are graphite and sacrificial magnesium anode, while synthetic wastewater mimicking the real-world centrate has been used as the electrolyte. It is unknown how these different anodes affect or interact with the other parameters and impact the behavior of the system. Therefore, the aim of this study is to identify and compare the most influential stream, design and operational factors in the functionality of each process. Additionally, nutrient removal capability in the two systems will be compared and recovered solid products will be discussed. Figure 1 represents the main variables in the P percentage recovery for both anode types. Based on this statistical analysis, the most significant factors in the P recovery and the effect directions are distinct in each system. Our results suggest by choosing the optimum set of variables, high P recoveries with good solid product quality can be obtained from both types of systems.

References

(1) Galbraith, S. C.; Schneider, P. A.; Flood, A. E. Model-Driven Experimental Evaluation of Struvite Nucleation, Growth and Aggregation Kinetics. Water Research 2014, 56, 122–132. https://doi.org/10.1016/j.watres.2014.03.002.

(2) Guštin, S.; Marinšek-Logar, R. Effect of PH, Temperature and Air Flow Rate on the Continuous Ammonia Stripping of the Anaerobic Digestion Effluent. Process Safety and Environmental Protection 2011, 89 (1), 61–66. https://doi.org/10.1016/j.psep.2010.11.001.

(3) Holloway, R. W.; Childress, A. E.; Dennett, K. E.; Cath, T. Y. Forward Osmosis for Concentration of Anaerobic Digester Centrate. Water Research 2007, 41 (17), 4005–4014. https://doi.org/10.1016/j.watres.2007.05.054.

(4) Soares, R. B.; Memelli, M. S.; Roque, R. P.; Gonçalves, R. F. Comparative Analysis of the Energy Consumption of Different Wastewater Treatment Plants. International Journal of Architecture, Arts and Applications 2017, 3 (6), 79. https://doi.org/10.11648/j.ijaaa.20170306.11.

(5) Ghimire, U.; Sarpong, G.; Gude, V. G. Transitioning Wastewater Treatment Plants toward Circular Economy and Energy Sustainability. ACS Omega 2021, 6 (18), 11794–11803. https://doi.org/10.1021/acsomega.0c05827.

(6) Kékedy-Nagy, L.; English, L.; Anari, Z.; Abolhassani, M.; Pollet, B. G.; Popp, J.; Greenlee, L. F. Electrochemical Nutrient Removal from Natural Wastewater Sources and Its Impact on Water Quality. Water Research 2022, 210, 118001. https://doi.org/10.1016/j.watres.2021.118001.

(7) Balaguer-Barbosa, M. Recovery of Nutrients from Anaerobically Digested Enhanced Biological Phosphorus Removal (EBPR) Sludge through Struvite Precipitation. USF Tampa Graduate Theses and Dissertations 2018.

(8) Wang, Y.; Kuntke, P.; Saakes, M.; van der Weijden, R. D.; Buisman, C. J. N.; Lei, Y. Electrochemically Mediated Precipitation of Phosphate Minerals for Phosphorus Removal and Recovery: Progress and Perspective. Water Research 2022, 209, 117891. https://doi.org/10.1016/j.watres.2021.117891.