Polarity Switching As a Technique for Enhanced Electrochemical Treatment of Waste Activated Sludge for Nutrient Recovery
Authors: Adjei Jedidian , Abbasi Ehsan , Sahin Elif , Donneys-Victoria Dayana , Alvarez Pugliese Christian , Botte Gerardine G 
Published: August 2024

Traditionally, fertilizers have been produced with ammonia (which is produced from the Haber-Bosch process) as the main feedstock. The Haber-Bosch process which requires the reaction of atmospheric nitrogen with hydrogen at high temperature and pressure is energy and cost intensive [1]. Only about half fraction of reactive nitrogen in the produced ammonia fertilizers is used by the plants with the rest remaining in the soil as waste [2]. These ‘excess’ nutrients find a way into water bodies and wastewater treatment plants (WWTP) as run-offs and this poses a big threat to the nitrogen balance in the environment. This research aims to recover these nutrients primarily nitrogen and phosphorous to produce a low-cost fertilizer of at least compatible potency as commercial fertilizers.

Waste Activated Sludge (WAS), the solids obtained from the primary and secondary clarifiers in WWTPs contain a wide range of organic compounds as well as valuable nutrients such as phosphorus and nitrogen which can account for up to 4% and 9% of dry sludge, respectively [3]. The leachate from landfills can release these nutrients into the environment, raising serious environmental pollution concerns. Therefore, recovering nutrients from WAS presents a significant opportunity towards a nitrogen circular economy.

Most of the research in sludge treatment are exclusively focused on improving biological treatment processes like anaerobic digestion and composting which can take anywhere from a month to three months and thermal treatments such as pyrolysis and hydrothermal treatments [4] which are energy intensive and expensive. This work provides a novel approach to recover nutrients at low energy consumption with nickel based electrocatalysts [5].

The hypothesis here is that the alkaline medium will help break the floc structure of the sludge to release the proteins and other organic compounds which will then be hydrolyzed by the nickel oxyhydroxide (NiOOH) group formed on the electrode surface by application of a small voltage sufficient to form NiOOH. The NiOOH is consumed quickly on the surface of the electrode by the organic nitrogen present in solution [6]. Hence, alternating the polarity between two identical nickel electrodes will ensure that NiOOH is always present on the electrode surface. The approach square wave potential pulses also enhance the desorption of species and clean the surface of the electrodes, especially when dealing with a complex mixture of organics that can polymerize in the surface of electrodes during the oxidation/reduction process.

The effect of frequency of polarity oscillation, electrode surface area, pH and conductivity on nutrient recovery are being studied and results will be reported at the conference. Since sludge treatment accounts for a sizable portion i.e., close to 60% of wastewater treatment plant operational costs [7], WAS nutrient recovery could also provide economic benefits. This research highlights the potential for electrochemical approaches to address environmental concerns, improve resource efficiency and provide a sustainable solution for sludge management.

Acknowledgement

This work is funded by the National Science Foundation, EEC Division of Engineering Education and Centers, NSF Engineering Research Center for Advancing Sustainable and Distributed Fertilizer production (CASFER), NSF 20-553 Gen-4 Engineering Research Centers award # 2133576.

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