Modelling GAC adsorption of biologically pre-treated process water from hydrothermal carbonization

Abstract

Granular-activated carbon (GAC) adsorption of biologically pre-treated process waters from hydrothermal carbonization (HTC) of different materials was investigated. Overall, isotherms showed that most of the dissolved organic substances are strongly adsorbable while the non-adsorbable fractions are small. The equilibrium data were modelled by using five fictive components to represent the organic matter. Mean film transfer coefficients and mean intraparticle diffusivities were derived from short-column and batch kinetic test data, respectively. Breakthrough curves in GAC columns could be predicted satisfactorily by applying the film-homogeneous diffusion model and using the equilibrium and kinetic parameters determined from batch tests. Thus, the approach is suited to model GAC adsorption of HTC process water under technical-scale conditions.

Options for Removing Refractory Organic Substances in Pre-Treated Process Water from Hydrothermal Carbonization

“…If one assumes that column capacities of 130 mg DOC/g (≈ 390 mg COD/g) for spent grains, and 60 mg DOC/g (≈ 180 mg COD/g) for fine mulch organics, could be realized when reducing the actual COD concentrations (as shown in Table 2) to 200 mg/L by a large-scale adsorber, the carbon usage rates for the PW studied would be on the order of 1.5 and 7.6 kg/m 3 , respectively. In the preceding study [16] on the post-treatment of HTC PW, sugar beet residuals, food leftovers, and spent grains were used as input materials. The refractory organics had low to medium molecular weights, and capacities of up to 200 mg DOC/g (≈ 600 mg COD/g) were estimated for activated carbon columns.…”

“…In a preceding study, Fettig and Liebe [16] demonstrated that adsorption onto activated carbon was suitable for the removal organics from PW remaining after anaerobic and aerobic degradation. This approach was refined in our study by applying adsorption and ozonation to two different types of HTC PW, in order to develop and evaluate appropriate disposal options.…”