Nutrient Recovery From Organic-Rich Wastewater Through Struvite Precipitation using Air Cathode Electrocoagulation Technology

Abstract

This study developed an innovative method for phosphate recovery contained in wastewater using air cathode electrocoagulation (ACEC) technology. This technique has the advantage of low energy consumption since it can effectively produce the struvite precipitate without any electrical-grid energy consumption. The experiments were conducted under recirculating batch mode by varying the recirculation rate and initial pH of wastewater to investigate their effects on the ACEC reactor performance. SEM-EDS and XRD analyses were performed to examine the morphology and structure of the produced crystals. The result showed that the precipitates exhibited in the form of crystals with irregularly shaped accompanied by a sharp at the surface and composed of Mg (6.67%), P (6.78%), N (1.66%), and O (47.41%). XRD chromatogram showed that the precipitate matched the reference pattern for struvite. The recirculation rate of 2.0 mL min−1 was determined as an optimum condition with nitrogen and phosphate removal, nitrogen and phosphate removal rate, and struvite precipitation rate was 14.7% ± 1.2%, 57.1% ± 1.1%, 22.9 ± 0.9 mg L−1 h−1, 18.6 ± 0.9 mg L−1 h−1, and 498 mg h−1, respectively. The recirculation rate affects the reactor performance through the magnitude of the hydraulic retention time of nutrients on the reactor and the potential electrical energy generated in the reactor. On the other hand, the reactor with initial pH 8 achieved the best performance with the nitrogen and phosphate removal of 24.6% ± 1.6% to 88.4% ± 3.8%, nitrogen and phosphate removal rate of 24.2 ± 2.1 mg L−1 h−1 and 35.3 ± 2.1 mg L−1 h−1, respectively, and the struvite precipitation rate of 900 mg h−1. Furthermore, when the initial pH of wastewater increased from 7 to 8, the struvite precipitation rate increased from 499 to 900 mg−1. However, increasing the initial pH of wastewater from 8 to 9 caused a decrease in struvite precipitation rate from 900 to 656 mg h−1. These results demonstrated that the recirculation rate and initial pH of wastewater control the process of the struvite precipitation process in ACEC technology.