Treatment of Liquid By-Products of Hydrothermal Carbonization (HTC) of Agricultural Digestate Using Membrane Separation

Abstract

Agriculture affects both the quantity and the quality of water available for other purposes, which becomes problematic, especially during increasingly frequent severe droughts. This requires tapping into the resources that are typically neglected. One such resource is a by-product of anaerobic digestion, in which moisture content typically exceeds 90%. Application of hydrothermal carbonization process (HTC) to this residue could partially remove organic and inorganic material, improve dewatering, decrease the overall solid mass, sanitize the digestate, change its properties, and eliminate problems related with emissions of odors from the installation. However, a significant gap still exists in terms of the dewatering of the hydrochars and the composition of the effluents. This work presents results of experimental investigation focused on the removal of organic compounds from the HTC effluent. Results of qualitative and quantitative analysis of liquid by-products of HTC of the agricultural digestate showed that acetic acid, 3-pyridinol, 1-hydroxyacetone, and 1,3-propanediol were the main liquid organic products of the process. Application of ultrafiltration process with the use of 10 kDa membrane for liquid HTC by-product treatment allows for the reduction of chemical oxygen demand up to 30%, biological oxygen demand up to 10%, and dissolved organic carbon up to 21%.

Experimental and Computational Evaluation of Heavy Metal Cation Adsorption for Molecular Design of Hydrothermal Char

“…Hydrochar OFG abundance tends to decrease with increasing reaction conditions such as reaction time, temperature, and water-to-biomass ratio [46][47][48]. For many feeds [50][51][52][53][54], HTC can be performed over the temperature range from 160-180 • C and at reaction times <12 h to promote formation of OFGs. More aggressive conditions (≥200 • C) are preferred for other applications [55].…”

Cascade Membrane System for Separation of Water and Organics from Liquid By-Products of HTC of the Agricultural Digestate—Evaluation of Performance

“…This effect has been observed for all analysed cases regardless of the membrane cut-off or its material (Figure 4). Overall, it could be stated that proper configuration of the cascade of membranes significantly outperformed single ultrafiltration membrane, investigated in the previous study [84].…”

“…This effect has been observed for all analysed cases regardless of the membrane cut-off or its material (Figure 4). Overall, it could be stated that proper configuration of the cascade of membranes significantly outperformed single ultrafiltration membrane, investigated in the previous study [84]. The use of microfiltration enables the separation of both colloids and fine suspensions, as well as some macromolecular compounds and microorganisms.…”

“…Literature sources suggest positive influence of HTC treatment on subsequent membrane separation, with the possible effect of synergy [83]. Promising results were obtained by the authors of his manuscript on ultrafiltration of the HTC effluent, with a significant reduction of COD in the permeate [84]. This study is a consequent follow-up, and its purpose is further optimisation of membrane separation of organic fraction of HTC effluent, using different configurations of a cascade membrane system.…”

“…Lack of literature sources on membrane separation of organics and water in HTC effluent makes direct comparison difficult. Urbanowska et al [84] reported COD removal efficiency close to 30% for membrane purification of post HTC effluent, using a single ultrafiltration membrane. Owing to the use of membrane cascades in this study the efficiency was almost doubled (see G in Figures 4 and 5).…”