Anaerobic digestion of liquid products following hydrothermal carbonisation of faecal sludge at different reaction conditions

Abstract

a b s t r ac tThe hydrothermal carbonisation (HTC) conversion of wet wastes, such as sewage sludge, generates a carbon-rich material (called 'hydrochar'), and an aqueous fraction with a small release of gas. The liquid fraction is high in soluble chemical oxygen demand, from 10 to 50 g/L, and could not be discharged to the natural environment without treatment. This study investigates the anaerobic digestibility of this HTC liquid stream from different HTC temperatures and retention times (140°C-200°C for 30-240 min). It is focused on biogas production in order to improve the energy input of the HTC process and to improve process sustainability. The results demonstrated that liquid products from the lower HTC temperatures gave better biogas production. The biogas yield from the 140°C HTC filtrate digestion was 0.

Coupling Hydrothermal Carbonization with Anaerobic Digestion for Sewage Sludge Treatment: Influence of HTC Liquor and Hydrochar on Biomethane Production

“…As reported in Figure 3, the highest methane production was reached after 25 days and accounted for 76 ± 20 mL CH4 g −1 COD, a significant increase compared to test #2: in literature the biomethane yield of HTC liquor from sewage sludge ranges between 3 and 227 mL CH4 g −1 COD, depending on the kind of feedstock, the HTC operative conditions, the AD operative conditions and the efficiency of the solid/liquid separation [29,[46][47][48]. Similar data to those here obtained were found by Nyktari et al [49].…”

Process Waters from Hydrothermal Carbonization of Sludge: Characteristics and Possible Valorization Pathways

“…This fact is mainly attributable to the presence of some metals (e.g., Al and Fe- compounds) in the initial feedstock that can favor the P precipitation. A practical operation mode is to dilute HTC process waters with digestate from the AD reactor, both to allow nutrient recycling and to reduce AD inhibition [ 125 ]. Problems related to the presence in HTC process waters of inhibitors to the AD, such as phenols, can be further solved with an appropriate AD inoculum adaption [ 126 ].…”

A Review on Sewage Sludge Valorization via Hydrothermal Carbonization and Applications for Circular Economy

“…Nyktari et al investigated the biogas rates from LFHTC of sludge at temperatures 140° -200° and retention times 30-240 min. and found out that higher biogas production is achieved at lower HTC temperatures (Nyktari et al 2017).…”

“…Additionally, the fact that the liquid phase of HTC process (LFHTC) is also being assessed in recent research studies (Nyktari et al 2017) (Villamil et al 2018) (Villamil et al 2019) (Xu et al 2020) as feeding material due to high organic and nutrient content is encouraging in pursuit of circular economy.…”