An overview of technologies to recover phosphorus as struvite from wastewater: advantages and shortcomings.

Phosphorus (P) is a significant limiting nutrient which is essential for all forms of lives. However, phosphate rock reserves are depleting rapidly due to population growth. At the same time, several countries have imposed legislative regulations on P-release into surface waters due to eutrophication. Nutrient recovery from wastewater can facilitate a sustainable, cost-effective and environment-friendly source of phosphorus. Although P-recovery as struvite from wastewater has been widely studied for a long time, there still exists a lot of challenges for widespread full-scale implementation. This paper presents a comprehensive analysis of the current state of the technologies for phosphorus recovery in the form of struvite. Fluidized bed reactors (FBRs) are widely used compared to continuously stirred reactors for P-recovery as struvite because of different solid and liquid retention time. Commercially available technologies were reported to accomplish about 80% P-removal efficiencies with a reasonable P-recovery for the most of the cases. The struvite production rate of various technologies varies from 0.89 to 13.7 kg/kg influent P. Nevertheless, these technologies are associated with several shortcomings such as high operational costs, high energy consumption, and large footprint. Increasing efforts focusing on the development of sustainable and commercially feasible technologies are expected in this sector as P-recovery is considered to be the future of wastewater engineering.

Impact of supersaturation ratio on phosphorus recovery from synthetic anaerobic digester supernatant through a struvite crystallization fluidized bed reactor.

Over the past few decades, several technologies have been developed to recover phosphorus (P) as struvite from wastewater. Although these technologies have achieved reasonable P-removal efficiencies, these technologies are associated with several shortcomings such as high capital and operating costs, longer crystallization time and production of low-quality product. This study focussed on the development of an efficient technology by designing a new fluidized bed reactor (FBR) and determining its optimum operating conditions. The supersaturation ratio is the most important process parameter for struvite recovery. This study exerted effort to establish a range of supersaturation ratios in order to achieve optimum P-removal and recovery with a lesser amount of fine crystals produced. Bench-scale FBR used in this study was able to accomplish 90% P-removal with 18% P-recovery. P-removal efficiency was observed to be increasing with an increase in the initial supersaturation ratio up to a value of 6.5. On the other hand, an increase in the supersaturation ratio resulted in a lower P-recovery efficiency with an increase in fines production. The supersaturation ratio from 5.5 to 6.0 was found to be optimum for efficient operation of the reactor.

Recovery of phosphorus from dairy manure: a pilot-scale study.

Phosphorus was recovered from dairy manure via a microwave-enhanced advanced oxidation process (MW/H2O2-AOP) followed by struvite crystallization in a pilot-scale continuous flow operation. Soluble phosphorus in dairy manure increased by over 50% after the MW/H2O2-AOP, and the settleability of suspended solids was greatly improved. More than 50% of clear supernatant was obtained after microwave treatment, and the maximum volume of supernatant was obtained at a hydrogen peroxide dosage of 0.3% and pH 3.5. By adding oxalic acid into the supernatant, about 90% of calcium was removed, while more than 90% of magnesium was retained. As a result, the resulting solution was well suited for struvite crystallization. Nearly 95% of phosphorus in the treated supernatant was removed and recovered as struvite.