Design and Optimization of Fluidized Bed Reactor Operating Conditions for Struvite Recovery Process from Swine Wastewater

Soomin Shim,Seungsoo Kim,Seunggun Won,Naveed Ahmed,Arif Reza,Changsix Ra

doi:10.3390/pr8040422

Abstract

Struvite crystallization using fluidized bed reactors (FBRs) is one of the most commonly used methods for nutrient recovery from different waste streams. However, struvite recovery from swine wastewater containing much higher solids using FBR has not been studied extensively. In this study, we therefore designed and optimized the key operating conditions parameters, i.e., pH (9.0, 9.5, and 10.0), circulation rate (CR) (1.5, 3.0, and 4.5 L/Lreactor·h), and hydraulic retention time (HRT) (1, 3, and 5 h) of FBR to ensure efficient nutrient removal and struvite crystallization from swine wastewater using response surface methodology (RSM) with central composite design (CCD) as experimental design. A magnesium/phosphorus (Mg/P) molar ratio of 1.3 was maintained with MgCl2 according to ortho-phosphate (O-P) concentration of influent and an air diffuser was set to supply air with 0.03 L air/Lreactor·min. The O-P recovery efficiency of over 91% was achieved through the entire runs. Among the operational parameters, pH did not show any significant effect on NH4-N recovery, particle size, and struvite production rate (SPR). The optimal CR over 2.94 L/Lreactor·h was found to be appropriate for efficient removal of nutrients and struvite crystallization. While optimizing the HRT, priority of the process operation such as the production of larger struvite particles or increased struvite productivity should be considered. Therefore, the optimal operational parameters of pH 9.0, CR > 2.94 L/Lreactor·h, and HRT of 1 or 5 h were chosen to obtain better responses through RSM analyses. The findings of this study would be useful in designing and operating either pilot- or full-scale FBR for struvite crystallization from swine wastewater.

Highlights

Struvite is magnesium ammonium phosphate and usually crystallizes when equimolar concentrations are achieved in alkaline conditions
The fluidized bed reactors (FBRs) eases the scaling problem in wastewater treatment plants and the size of the struvite crystal increases over time [13]
The formation of struvite was almost completed in the reaction zone, and, the O-P concentration in the recovery reactor was found to be low during the recovery process

Summary

Introduction

Struvite is magnesium ammonium phosphate and usually crystallizes when equimolar concentrations are achieved in alkaline conditions. It is sparingly soluble in alkaline solutions and soluble in acids [1]. The effectiveness of the struvite recovery process depends on the reactor type as well as its recovery efficiency and recovered product quality [10]. The MSR is simple in design and widely used in the industries It shows comparatively high phosphorus removal efficiencies, whereas high mixing intensity often produces fine and impure struvite crystals [12]. The FBR eases the scaling problem in wastewater treatment plants and the size of the struvite crystal increases over time [13]. Considering the above, we designed an FBR to mitigate the flushing out of struvite fines from the reactor

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Results

Conclusion