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Chemical and heat treatment of sewage sludge can be used to recover valuable supplies of phosphorus, which is essential for many applications including fertilizers, medicines, and consumer products. The method developed by chemical engineers at Hokkaido University involves burning sewage sludge for electric power generation and then extracting phosphorus from the remaining ash. This is a promising approach to address the problem of diminishing supplies of phosphorus ores, which are becoming depleted and expensive.

The depletion and rising price of high-grade phosphorus ores have put pressure on industries that rely on these supplies, making it increasingly important to find new sources of phosphorus. Sewage sludge is currently burned for power generation and to reduce volume, leaving ash that is rich in phosphorus. Efficient methods for recovering this phosphorus are needed, as existing methods face challenges such as chemical contamination and expensive processing. The Hokkaido researchers have been investigating methods for recovering phosphorus and other elements from sewage sludge through heat treatment, with promising results.

By exploring the volatilization behavior of elements in sewage sludge ash under different chemical conditions, the researchers developed a method for separating phosphorus-containing compounds using a combination of chlorination steps with and without the presence of carbon. This effective method allows for the recovery of phosphorus in valuable forms such as phosphorus chloride, which can be converted to phosphoric acid by dissolution in water. The process they developed has lower energy requirements, lower CO2 emissions, and lower costs compared to conventional phosphorus recovery technologies from phosphate ores.

The total amount of phosphorus contained in secondary phosphorus resources in Japan, such as steel slag, livestock manure, and sewage sludge, is equivalent to about half of the total amount of phosphorus brought into the country. The researchers aim to study if their technique could help reduce the need for phosphorus imports, indicating the potential for their method to contribute to securing phosphorus supplies in the future. This innovative approach to phosphorus recovery from sewage sludge could provide a sustainable solution to the problem of diminishing phosphorus reserves.

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