Nutrients recovery from wastewater using integrated vacuum and direct contact membrane distillation

Abstract

Recovery of valuable nutrients such as phosphorus from waste streams is becoming increasingly important due to the limited and constantly depleting resources and increasing consumption. In this research, the potential of using enhanced membrane distillation (MD) system for producing phosphate-rich concentrate and ammonia-water permeate from waste streams is investigated for use in different agricultural and industrial applications. MD is a promising thermally driven technology that can utilize waste and low-quality heat sources as separation driving force. The proposed system involves in-series batch recycle coupling of a direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD). The investigation included different coupling configurations as well as both synthetic and real wastewater. Results showed better performance of the coupled system compared to individual units, and that the configuration of the integrated system was important. Dimensionless sensitivity analysis revealed that permeate flux is predominantly governed by feed temperature, followed by flow rate, pH, and concentration, with temperature elasticities an order of magnitude higher than the others. Results of the analytical modeling of the coupling effect using an approximate approach were consistent with the experimental data of this work as well as with data from the literature. An order of magnitude assessment of the specific energy requirement based on using waste and low-cost heat showed that the proposed integrated MD system can be significantly more energy efficient than nanofiltration (NF) for achieving the same phosphate concentration factor (CF).