Simple technology for recycling phosphate from wastewater to farmland in rural areas

Abstract

A simple technology for phosphate (Pi) recovery has been developed using a bifunctional adsorption–aggregation agent. The bifunctional agent was prepared by soaking calcium silicates in hydrochloric acid solution. Importantly, recyclable calcium silicates were available almost free of charge from the cement industry and also from the steel industry. The acid treatment was essential not only for enhancing the ability of calcium silicates to remove Pi from aqueous solution but also for enabling the high settleability of removed Pi. On-site experiments using a mobile plant showed that approximately 80% Pi could be recovered from anaerobic sludge digestion liquor at a wastewater treatment plant. This technology has the potential to offer a simple, compact service for recycling Pi from wastewater to farmland in rural areas.

Handling the phosphorus paradox in agriculture and natural ecosystems: Scarcity, necessity, and burden of P

“…Basic slag from the Thomas process has been used as fertilizer for about 70 years, because it contained a high P 2 O 5 content of 10–15% w/w. However, the Thomas process had been replaced by other smelting processes using iron ores low in P. A large research and development project is currently been conducted by two leading steel companies in Japan to recover P from P-rich steelmaking slag, called dephosphorization slag (Ohtake and Okano 2015 ; Ohtake et al 2018 , this issue). Importantly, the rest after recovering P still contains valuable resources such as iron, calcium, and silicates.…”

“…The P recovery from steelmaking slag aims to recycle the rest as raw materials to the blast furnace, thereby improving the resource efficiency of the steelmaking process. Meanwhile, steelmaking slag can also be used as recyclable calcium silicates to prepare a bifunctional adsorption–aggregation agent for a simple phosphate recovery technology (Ohtake et al 2018 , this issue).…”