Abstract
The nitrogen in the sludge mainly exists in the form of inorganic nitrogen and organic nitrogen.In this paper, the transformation of nitrogen during the hydrothermal carbonization of sludge was studied.The results showed that during the hydrothermal carbonization of the sludge, both the total nitrogen and theinorganic nitrogen in hydrochar decrease with the increase of the carbonization temperature. The reason isthat part of the inorganic nitrogen compounds in the sludge undergoes thermal decomposition to releaseNH3, and some organic nitrogen will be hydrolyzed to produce ammonia nitrogen into the liquid phase.
Highlights
The sludge produced by sewage treatment plants has soared worldwide in recent years
Sludge hydrochar can be used as a soil conditioner due to that inorganic nitrogen, such as ammonium nitrogen and nitrate nitrogen, is available for plant absorption and utilization
The content of organic nitrogen accounts for 88 % of the total nitrogen in the sludge. This is because organic nitrogen mainly contains protein nitrogen, pyrrole-N and pyridine-N
Summary
The sludge produced by sewage treatment plants has soared worldwide in recent years. At present, sludge production in China is estimated to reach 6 million dry tons every year [1]. Sludge is rich in nutrients (nitrogen, phosphorus, potassium, etc.) and available organics (such as protein, sugar, fat, etc.). The nitrogen in the sludge mainly exists in the organic and inorganic forms. After the sludge is hydrothermally carbonized, the produced hydrochar may have many kinds of applications. The sludge is rich in nitrogen elements, which can be transformed to form inorganic nitrogen or redox functional groups after hydrothermal carbonization. Sludge hydrochar can be used as a soil conditioner due to that inorganic nitrogen, such as ammonium nitrogen and nitrate nitrogen, is available for plant absorption and utilization. The sludge hydrochar has a good application in adsorption, and some of its surface nitrogen, oxygen and sulfur functional groups can be used to adsorb heavy metals in water [4].
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