Abstract
Hydrothermal carbonization (HTC) provides an attractive alternative method for the treatment of high-moisture waste and, in particular, digested sludge. HTC could reduce the costs and environmental risks associated with sludge handling and management. Although it is recognized that the dewaterability of hydrochars produced from digested sludge, even at mild temperatures (180–190 °C), is highly improved with respect to the starting material, the filterability of HTC slurries for the recovery of the solid material (hydrochar) still represents a challenge. This study presents the results of an investigation into the filterability of agro-industrial digested sludge HTC slurries produced by a C-700 CarboremTM HTC industrial-scale plant. The filterability of HTC slurries, produced at 190 °C for 1 h, with the use of acid solutions of hydrochloric acid, sulfuric acid or citric acids, was investigated by using a semi-industrial filter press. The use of sulfuric acid or citric acid solutions, in particular, significantly improved the filterability of HTC slurries, reducing the time of filtration and residual moisture content. The acid treatment also promoted the migration of heavy metals and phosphorus (P) in the HTC filtrate solution. This study demonstrates that P can be recovered via the precipitation of struvite in high yields, recovering up to 85 wt% by mass of its initial P content.
Highlights
Published: 20 August 2021The recent development of the agro-industry to satisfy increased demand for processed food and beverages requires new and sustainable technologies for agro-industrial waste management [1]
Due to the high environmental risks associated with heavy metal accumulation in soil [7], the direct soil application of sludge is a practice which is severely restricted in many European countries nowadays
Thermal energy for the Hydrothermal carbonization (HTC) process is provided by a diathermic oil boiler fed with methane, provided by the municipal network or biogas produced by the anaerobic digester located in the waste treatment plant in Mezzocorona
Summary
The recent development of the agro-industry to satisfy increased demand for processed food and beverages requires new and sustainable technologies for agro-industrial waste management [1]. Among the different strategies for the valorization of agro-industrial sludge, direct soil application, sludge drying, composting and the use of anaerobic digestion to produce energy are the most often used [6]. The sustainable processing of agro-industrial waste, which offers the opportunity to recover and valorize residual carbon, and to retrieve valuable nutrients such as phosphorus, which is considered a critical element in Europe [21], must include appropriate treatment of the waste products before disposal, in order to avoid sanitary problems and the risk of environmental pollution [22,23].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
