PhD Energy-efficient electrochemical phosphate recovery (EPR) – optimisation and upscaling

Updated: 22 days ago
Deadline: 29 Oct 2021

Topic background - Phosphorus (P) is an essential element for life, and our society is mainly dependent on the use of P derived products, including fertilisers and various other chemicals. The industrial source for P is phosphate-rich ores (phosphate rock). Known phosphate reserves are scarce, and their geographical spread is limited, with no substantial phosphate deposits found within the EU. Additionally, the quality of these deposits is decreasing over time due to increasing contamination with heavy metals. Therefore, phosphate was classified as a critical raw material (CRM) by the EU in 2014. Substantial amounts of phosphate can be found in our domestic and industrial wastewater originating from food production, consumption, and other manufacturing processes. Wastewater as a secondary phosphate resource is largely underexploited as the main focus of wastewater treatment plants (WWTPs) is phosphate removal. Therefore, WWTPs relies on either chemical phosphate removal (CPR) or enhanced biological phosphate removal process (EBPR).

Research challenges - Conventional P recovery processes from wastewater have severe limitations. EBPR recovers approximately 10-30% of the incoming phosphate load and requires Mg dosing for struvite precipitation. CPR involves adding Al or Fe salts to form insoluble aluminium - or iron phosphate, which can be recovered from the sludge. Electrochemical Systems (ES) are a suitable alternative to conventional phosphate recovery approaches. Previous research has shown that an ES can recover calcium phosphate (CaP) as hydroxyapatite or amorphous calcium phosphate. CaP recovery relies on the hydrogen evolution reaction at the cathode, which increases the local pH sufficiently for CaP precipitation. Contrary to CPR and EBPR, electrochemical phosphate recovery (EPR) does not require any chemical addition and solely relies on electrical energy. While EPR was proven at a laboratory scale with real wastewater and first steps have been made towards upscaling, further insights are needed into this technology for future upscaling and competitiveness.

Objectives and methodology - This PhD project will focus on optimising electrochemical phosphate recovery in terms of energy use and recovery efficiency of the system. Therefore, different system designs, material choices, and electrode materials and modifications will be investigated. The optimisation process will involve both experimental and modelling work. Another focus point will be the “harvesting” process and product quality of the recovered CaP product. Working under realistic conditions (real wastewater) and collaborating with the participating companies in the “Resource Recovery” theme will allow upscaling the electrochemical phosphate recovery process.

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