Enhanced internal circulation for struvite crystallization in a novel air-lift circulation reactor with Venturi structure for ammonium recovery from wastewater

Abstract

Nutrient recovery as struvite from wastewater in is quite feasible. The mystery of ammonia loss has received much attention, and inadequate struvite purity is frequently present. A struvite fluidized bed reactor (FBR) was constructed and operating conditions were optimized in order to minimize ammonia nitrogen loss. The properties of the struvite produced by the reactor and the optimum operating conditions for ammonia recovery were also assessed. According to simulations, the Venturi tube increased turbulent flow energy to 4.5 × 10−2 m2·s−2. This significantly improved the mass transfer efficiency. A significant difference between the wall shearing rate (50–319 s−1) and the fluid shearing rate (2–10 s−1) prevented the crystal particles from colliding with the vessel wall. The reactor reached stable operation under conditions of N/P = 1:1 and pH = 9.0. The purity of the obtained struvite was 96.5 %, with an ammonia nitrogen conversion rate of 89.67 %, where the struvite crystals could grow to 82 μm within 24 h. It was concluded that the new FBR with air-lift internal circulation function was feasible for improving struvite crystal growth and purification. It is possible to achieve high ammonia nitrogen recovery efficiency at low cost.