Introduction
- Nitrogen (N) is one of the nutrients contained in high concentrations in sludge water from digested sludge dewatering. Conventional wastewater treatment plants require a lot of energy to remove nitrogen from the water and release it into the air in a form that is useless to us (N2). Our approach is to recover it as a fertilizer (ammonium sulphate solution) for use in agriculture.
- Phosphorus is a nutrient that is unevenly distributed worldwide and is a non-renewable resource. Compared to conventional wastewater treatment, more emphasis should be placed on phosphorus recovery rather than phosphorus removal. By precipitating P minerals such as struvite (NH4MgPO4-6H2O) or CaP, it is possible to recover phosphorus as fertilizer from waste streams with high phosphorus concentration such as sewage sludge concentrate and anaerobic digestate to realize the circular economy in the bioeconomy.
Technologies for the recovery of nutrients
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Transmembrane chemi(ab)sorption (TMCS) for nitrogen recovery: This recovery process is characterized by a high selectivity towards nitrogen and requires less space than conventional ammonia stripping. Here it is necessary for the nitrogen in the water to be converted into gaseous ammonia (NH3). A hydrophobic membrane then repels the liquid flow, but allows gaseous ammonia to pass through its pores to the other side of the membrane, where it is absorbed into sulphuric acid (H2SO4) and produces a fertilizer (NH4)2SO4.
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Wet and electrochemical processes for phosphorus recovery: Wet chemical and electrochemical processes are promising approaches for efficient and sustainable phosphorus recovery. Wet chemical processes extract phosphorus from wastewater through precipitation reactions or solubility changes by adding magnesium from external sources when the pH is adjusted to 8.5-9.5. Electrochemical phosphorus precipitation in the ePhos® process takes place in an electrolytic cell with an inert cathode and sacrificial anode made of magnesium. Water molecules are split by cathodic reduction, producing hydrogen (H2) and OH- ions. These increase the pH value of the waste water to pH 9, eliminating the need to adjust the pH by dosing alkaline solutions. Magnesium ions oxidize at the anode and react with the phosphorus and nitrogen contained in the water to form struvite.
Further information can be found here.
Offered services
- Sample production of fertilizers from different waste streams e.g. sludge water, digestate, separately collected urine, etc.
- Evaluation of the feasibility of nitrogen and phosphorus recovery
- Production of sustainable fertilizers with high P and N content
- Provision of solutions for different substrates for utilization
- Scale-up and process development
Susanne Zibek
Dr.-Ing.Coordination of Interfacial Processes / Lecturer
Ricardo Reyes Alva M.Sc.
Doctoral student, Bioraffinery-technology
Kuan-Po Liao M.Sc.
Doctoral student, Bioraffinery-technology