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.

Students requirements

• MSc degree in Environmental technology, chemical engineering, or equivalent with excellent grades
• Strong background in electrochemistry and hands-on experience with electrochemical workstation
• Ability to work independently in the laboratory and to rigorously design and perform experiments in a result-oriented and thorough manner
• A strong interest in carrying out multidisciplinary research in an international environment
• Excellent interpersonal skills to work effectively with team members from different backgrounds
• Good oral and written communication skills in English
• A strong interest in personal development and career growth
• A strong interest in advancing scientific knowledge into real-world application

Salary and working conditions are according to the collective labor agreement of the Cooperative Association of Dutch Universities (VSNU) for PhD students. Per 1-7-2021, the salary for a PhD student as determined by the collective labor agreement are (in Euros before tax per year): €34076 (year 1), €39732 (year 2), €41832 (year 3) and €43554 (year 4). PhD students are appointed by one of the three cooperating universities, but research is conducted at the Wetsus laboratory in Leeuwarden.

Wetsus

Wetsus, European centre of excellence for sustainable water technology is a facilitating intermediary for trendsetting know-how development. Wetsus creates a unique environment and strategic cooperation for development of profitable and sustainable state of the art water treatment technology.