Hydrothermal carbonization of sewage sludge: A critical analysis of process severity, hydrochar properties and environmental implications

The impact of hydrothermal carbonization on the surface functionalities of wet waste materials for water treatment applications

“…This is different from lignocellulosic biomass, in which carbon content almost always increases after HTC with increasing temperature (Wilk et al 2019). HTC treatment increased the highest heating value (Tasca et al 2019;Zhou et al 2019); however, ash concentration could be problematic, leading to slagging and fouling issues upon combustion. Despite the wide range of studies on the HTC of wet waste materials, studies examining these materials for higher value applications, such as water treatment, along with in-depth surface studies, are lacking.…”

“…Traditionally, these wet waste materials are disposed in landfill, incinerated, or utilized as fertilizers; however, this is problematic because of contaminates (e.g., heavy metals, ash, pharmaceuticals, personal care products (PPCPs), and pathogens), bans on landfilling combustible materials, and eutrophication/acidification from nitrogen and phosphorus leeching. The high moisture content, up to 97% w/v (Tasca et al 2019), also makes transportation costly and limits the disposal of these materials to facilities in proximity to the waste source.…”

“…The result is a solid carbonaceous material, an organic rich water phase and small amounts of gas (CO 2 , CH 4 ). The physicochemical properties of the final products depend on the reaction conditions, precursor, and pH, allowing a high level of tuneability (Latham et al 2014;Tasca et al 2019;Zhou et al 2019). Additionally, HTC treatment sterilizes the waste materials, removes water soluble species, stabilizes heavy metals (Fan et al 2017;Tasca et al 2019), allows the recovery of phosphorus and nitrogen (Becker et al 2019), and breaks down pharmaceuticals (vom Eyser et al 2015(vom Eyser et al , 2016.…”

“…There is a wide range of studies examining the HTC of sewage sludge (Tasca et al 2019), biogas digestate (Rodriguez Correa et al 2017), paper mill sludge (Mäkelä et al 2015;Mäkelä and Yoshikawa 2016), human excrement (Fakkaew et al 2018), chicken litter, and swine manure (Ro et al 2018;Zhou et al 2019) for energy applications (Fakkaew et al 2018;Ro et al 2018;Zhou et al 2019) and soil amendments (Melo et al 2018). In general, HTC reduces the water content of these solid materials, while concentrating insoluble inorganic species (ash) (Gasco et al 2018;Tasca et al 2019;Zhou et al 2019). Carbon content in the final solid product is dependent on the precursor and not the reaction conditions (Zhou et al 2019).…”

A Comprehensive Review on Hydrothermal Carbonization of Biomass and its Applications

“…Despite a complex process, which involves the conversion of carbon-rich compounds at relatively high temperatures and pressure, it is a highly sustainable process for the purpose of preservation of resources. Hydrochar, the solid product of HTC, is hydrophobic and non-toxic that can be used as activated carbon, solid-fuel and adsorbent for wastewater treatment [57,151].…”