Water Journal : Water Journal July 2012
environmental concerns refereed paper 56 JULY 2012 water technical features Abstract A new ultra-low phosphorus adsorption and recovery process was recently developed that integrates removal of phosphorus, recovery of the captured phosphorus, and in-situ regeneration of the adsorption media. Pilot testing of this integrated system in Japan and the US has demonstrated its ability to recover phosphorus as a high-grade fertiliser material while achieving ultra-low effluent phosphorus concentrations. This paper focuses on the results and findings of the pilot testing conducted in the US. Introduction Water quality professionals and environmentalists are becoming increasingly interested in treatment processes that not only remove phosphorus from surface water discharges, but also recover it for beneficial uses. A highly efficient adsorbent media has recently been developed along with a tertiary treatment process that integrates the removal of phosphorus, the recovery of the captured phosphorus, and the in-situ regeneration of the adsorption media. Long-term pilot testing of this integrated adsorption-and-recovery process in Japan, and now in the US, has demonstrated its capability to achieve ultra-low effluent phosphorus concentrations while recovering the phosphorus as a high-grade fertiliser material. The first US pilot testing of a new highly efficient phosphorus adsorption process has shown promising results in removing phosphorus to ultra-low levels as well as recovering the phosphorus for use as a high-grade fertiliser. Materials and Methods Adsorbent media A high-efficiency phosphorus-adsorbent media was developed through the work by Omori et al. (2007) and Midorikawa et al. (2008) in collaboration with the Japan Sewage Works Agency. The phosphate- specific adsorbent media is created from a mixture of metal oxide with ion exchange properties and a polymer manufactured using a new technique. The media consists of spherical beads with an average diameter of 0.55mm that have a unique structure, with a network of pores and fibrils with interior cavities to allow a high diffusion rate of phosphate ion inside the media. This adsorbent media can remove phosphorus from secondary effluent to low levels and has a breakthrough capacity greater than 4 g-P/L of resin at space velocities (SV) up to 20 hr-1. SV is calculated as the volumetric flow rate per unit volume of media and is the inverse of the empty bed contact time (EBCT). Integrated process Using this phosphorus-adsorbent media, a new process has been developed by Asahi Kasei that consists of phosphorus adsorption, phosphorus desorption for media regeneration, and phosphorus recovery processes as illustrated on Figure 1. During the adsorption process, phosphate ions are efficiently removed by passing influent through the media- filled column until the breakthrough point. During the desorption process, adsorbed phosphate ions are desorbed as the alkaline solution passes through the media column. During the phosphorus recovery stage, the phosphate in the alkaline solution is separated by adding calcium hydroxide, which precipitates phosphorus as calcium phosphate. The calcium phosphate solids and the alkaline solution are then separated and the alkaline solution can be reused for subsequent desorption cycles. The collected calcium phosphate is a hydroxyapatite with a composition similar to that of phosphate ore and a citric-soluble phosphorus content of 30% as P2O5. This indicates potential for use as a fertiliser. Pilot Testing Facilities Pilot testing of this system was conducted in Lawrence, Kansas, during the first half of 2010. The Lawrence Wastewater C Wallis-Lage, J Fitzpatrick, H Aoki, S Koh, I Midorikawa, A Omori, T Shimizu Pilot testing shows good results PHOSPHORUS RECOVERY WITH A NEW ULTRA-LOW ADSORPTION PROCESS Figure 1. An integrated system consisting of phosphorus adsorption, regeneration and recovery.
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