Hisao Ohtake

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

This special issue of Ambio compiles a series of contributions made at the 8th International Phosphorus Workshop (IPW8), held in September 2016 in Rostock, Germany. The introducing overview article summarizes major published scientific findings in the time period from IPW7 (2015) until recently, including presentations from IPW8. The P issue was subdivided into four themes along the logical sequence of P utilization in production, environmental, and societal systems: (1) Sufficiency and efficiency of P utilization, especially in animal husbandry and crop production; (2) P recycling: technologies and product applications; (3) P fluxes and cycling in the environment; and (4) P governance. The latter two themes had separate sessions for the first time in the International Phosphorus Workshops series; thus, this overview presents a scene-setting rather than an overview of the latest research for these themes. In summary, this paper details new findings in agricultural and environmental P research, which indicate reduced P inputs, improved management options, and provide translations into governance options for a more sustainable P use.

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

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.

Development of Phosphorus Recycling in Europe and Japan

This chapter will explore whether the differences in the process development for phosphorus recovery and recycling and its implementation in Europe and Japan are linked to the waste flows and the regulative framework. The main waste flows and their qualities are summarized for the two geographical areas. Then a comparative overview of the full-scale applications and their importance in relation to the potential is presented. The drivers for phosphorus recycling and the expected further development in Europe and Japan are described.

Heatphos Process for Recovering Phosphorus from Bio-P Sludge Before Anaerobic Digestion

Sewage sludge generated in Bio-P processes (also known as enhanced biological phosphorus removal processes) typically contains 3–5% of its dry weight as phosphorus (P). Approximately 60–80% of the P is stored as polyphosphate (polyP) which is a heat-labile polymer of inorganic phosphate (Pi). This chapter describes a simple technology, named “Heatphos,” for leaching polyP from Bio-P sludge by heating at 70 °C for about 1 h and recovering Pi from the leachate by the addition of CaCl2 without needing to adjust pH to a high value. Heating sludge for polyP leaching can also improve the digestive efficiency and thus biogas productivity in the subsequent anaerobic sludge digestion at both mesophilic (typically 35–40 °C) and thermophilic (50–60 °C) temperatures. The heat energy required for polyP leaching can be supplied from biogas generated by anaerobic sludge digestion. The demonstration plant with a capacity of treating Bio-P sludge of 0.36 m3/day has showed that P could be recovered from Bio-P sludge at a rate of approximately 10 kgP/day (c. 3.5 tP/a).

Phosphate Recovery Using Amorphous Calcium Silicate Hydrates

Amorphous calcium silicate hydrates (A-CSHs) can be chemically synthesized using abundantly available, inexpensive materials such as siliceous shale and calcium hydroxide. A-CSHs can serve as a bifunctional adsorption-aggregation agent for phosphate (Pi) recovery from aqueous solution. A-CSHs can also be prepared by soaking recyclable calcium silicates such as concrete sludge and steelmaking slag in a dilute hydrochloric acid solution. Since A-CSHs show high Pi removability, settleability, and filterability, they have the potential to offer a simple, cost-effective option to the recovery of Pi from Pi-rich waste streams. On-site experiments using a mobile, pilot-scale plant have showed that A-CSHs can recover approximately 80% Pi from a Pi-rich sidestream in a wastewater treatment plant. This chapter describes a simple process for Pi recovery from aqueous solution using A-CSHs as a bifunctional adsorption-aggregation agent.