Nitrogen Release and Fertiliser Value of Thermally‐Dried Biosolids

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Abstract
Nitrogen production from five thermally‐dried biosolids plants was measured in two contrasting soil types and compared with samples of undried digested sludge cake from the same treatment works, using a controlled laboratory incubation‐extraction procedure. Inorganic‐N was lost from the digested biosolids during high‐temperature drying by ammonia volatilisation. Nevertheless, the production of nitrate‐N in soil amended with thermally‐dried biosolids was similar to, or greater than, conventionally‐treated dewatered sludge. The results indicate that thermal conditioning significantly increases the mineralisable organic‐N content in digested biosolids. Soil properties had subtle effects on the patterns of nitrogen release, but did not significantly affect the overall accumulation of mineral‐N from the biosolids. The results showed that thermally‐dried anaerobically‐digested biosolids are potentially highly‐consistent products and effective replacements for inorganic‐N fertiliser in agricultural production.

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