Development of a fluidized bed reactor for phosphorus recovery from rubber industry wastewater through struvite formation: material selection and prototype†

A fluidized bed reactor for phosphorus (P) recovery from treated rubber industry wastewater through struvite formation was developed. The optimum conditions for struvite recovery and appropriate materials for fabricating the reactor were investigated. The results showed that pH 9 and a magnesium (Mg) : P molar ratio of 1.2 : 1 were the optimum ones. For the material selection part, struvite adhesion was tested on different materials (stainless steel, acrylic, epoxy resin fiberglass, vinyl ester resin fiberglass, aluminum, and galvanized steel). Stainless steel and acrylic had the lowest scale on the materials (0.11 ± 0.01 mg cm⁻² of the testing area and 0.23 ± 0.01 mg cm⁻² of the testing area, respectively), while galvanized steel had the highest scale on the material (0.69 ± 0.03 mg cm⁻² of the testing area). The reason was that different materials have different surface roughness and contact angles. Moreover, Cl⁻ concentration and pH also impacted struvite fouling. Therefore, stainless steel was selected for the fabrication of a struvite reactor. The reactor was operated at a hydraulic retention time (HRT) of 2 h without mixing equipment, which consumed less energy. The P recovery efficiency of the reactor was very high (93%), which was suitable for future applications.