Abstract
Granular activated carbon (GAC) adsorption, as well as ozonation in combination with biodegradation was investigated in order to remove refractory organics from biologically pre-treated process waters (PW) produced by the hydrothermal carbonization (HTC) of spent grains and fine mulch. Kinetic tests revealed that the organics in spent grains PW had much lower molecular weights than organics in fine mulch PW. Moreover, isotherms showed that they were more strongly adsorbable. This was confirmed in GAC column experiments, where the breakthrough curves could be predicted fairly well by a dynamic adsorption model. On the other hand, ozonation had a stronger effect on fine mulch PW with respect to an enhancement of the aerobic degradability. Thus, the type of input material determines the properties of soluble reaction products from the carbonization process that must be accounted for when selecting the most suitable post-treatment method for HTC PW. However, adsorption on granular activated carbon should always be the final stage.
Highlights
Hydrothermal carbonization (HTC) is a process where biomass is transformed into a material comparable to brown coal
High organic contents were reflected by chemical oxygen demand (COD) and total organic carbon (TOC) concentrations, which were in the g/L range
From the data presented it can be concluded that activated carbon adsorption cannot be considered an appropriate post-treatment process for fine mulch process water (PW), while it should be considered as a promising treatment option for spent grains PW after an anaerobic and aerobic biological stage
Summary
Hydrothermal carbonization (HTC) is a process where biomass is transformed into a material comparable to brown coal. In contrast to natural processes that require many years, HTC takes less than. The HTC process is performed with biomass suspensions in a pressure vessel at 180 to 260 ◦ C and resulting water vapor pressures of 15 to 60 bars [2]. The PW is acidic for most input materials. It contains a portion of 15% to 25% of the input organic carbon [3] resulting in chemical oxygen demand (COD) loads of 4900 to 78,700 mg/L and biochemical oxygen demand (BOD) loads of 1700 to 42,000 mg/L [2]
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