Continuous Phosphorus Recovery by Heterogeneous Nucleation: Challenges in Solid-Liquid Separation

Phosphorous (P) is an essential natural resource of limited availability. Furthermore, many countries, including Germany, have no access to P sources and are entirely dependent on P imports to cover their demand. Therefore the recovery of P is a topic of distinct importance. In the past decades a manifold of processes for P recovery from wastewater have been developed. The P-RoC-process (Phosphorus Recovery by Crystallization) is a technique developed by Competence Center for Material Moisture (CMM), KIT, based on crystallization of P on a Calcium-Silicate-Hydrate (CSH) substrate [1]. The feasibility of the approach has been shown on the lab scale and also as a semi-batch process on the pilot scale in a side stream of a municipal sewage plant. For full implementation of the process, a transition from semi-batch to a continuous process is desirable. However a crucial question still to be solved is the removal of the P-loaded substrate from the process. Challenges for the CSH separation are the particle size distribution that will result in a distribution in reaction kinetics and thus a difference in P coverage with particle size. Additionally comminution of the highly porous particles might also be an issue. ... mehrThe task at hand thus requires a separation unit that allows for classification as well as for separation of the particles. In this paper we present how the continuous classification and separation of P-loaded CSH is solved by using a hydrocyclone. For this cause an experimental setup was developed in order to realize the continuous P crystallization on CSH substrate and removal of CSH on the pilot scale.