Thermal Disposal of Post-processing Water Derived from the Hydrothermal Carbonization Process of Sewage Sludge

Abstract

Hydrothermal carbonization is a suitable method for sewage sludge management due to great improvements in its dewaterability and the successful application of its solid product, hydrochar, in different sectors. However, the resulting liquid product requires special treatment due to the amount of undesirable compounds it contains. The main purpose of this work is to study the use of distillation as a method of post-processing liquid purification. In addition, the influence of vacuum depth on the properties of liquid products was investigated. A number of chemical and physical parameters were determined to confirm the validity of this treatment method: TOC, COD, total nitrogen Kjeldahl content, ammonium nitrogen content, phosphorus, magnesium, calcium, selected heavy metals content and phenol index. Distillation under atmospheric pressure caused reductions in the following parameters: COD, TOC, phenol index, heavy metals, chlorine by more than 90%: removal of 95% COD and TOC, 99.5% of PO4-P, 93% of Phenol, over 90% of heavy metals, and over 97% of free and total chlorine. In the case of distillation under -0.3 bar pressure, the following reductions were obtained: 97% of COD, 98% of TOC, 99.9% of PO4-P, 94% of Phenol, c.a. 98% of heavy metals, and more than 98% of free and total chlorine. Decreasing the pressure to − 0.5 bar did not producee any significant effects as the results were similar to distillation under atmospheric pressure. Both methods, distillation and distillation under lower pressures, can be used as an appropriate method of post-processing water utilization. Graphical Abstract: (Figure presented.)