Removal of dissolved organic compounds in fixed-bed columns: Evaluation of low-rank coal adsorbents

Abstract

Characterisation of a range of Victorian low-rank coal (VLRC) based and commercial adsorbents under continuous flow conditions was conducted in down flow fixed-bed columns. The effect of bed depth, hydraulic loading and initial concentration of the adsorbate 4-nitrophenol (4-NP) was studied. Prediction of the performance of the columns using bed-depth/service time analysis showed good agreement with the experimental results. The VLRC-based activated carbons gave lower service times for removal of 4-NP compared with the coconut-based commercial activated carbon Picactif. However, they showed comparable efficiency in terms of bed volumes treated and carbon usage rate (CUR). The VLRC-activated power station char (APSC) showed the lowest CUR of 0.57 g/L in comparison with 0.62 and 3.61 g/L exhibited by the commercial carbons Picactif and Hydraffin, respectively. The power station char (PSC) and Auschar gave poor CUR of 11.23 and 75.36 g/L, respectively. Three adsorbents were evaluated for the removal of natural organic matter (NOM) from aqueous solution. The breakthrough behaviour indicated that the pore size distribution of the adsorbents is an important physical characteristic for the adsorption of the NOM. There was a non-adsorbable fraction of the NOM that was a function of the type of adsorbent. In the presence of NOM, Picactif gave longer service time for the removal of 4-NP compared with APSC, consistent with the trend obtained in the absence of NOM. However, lower breakthrough times (at 10% C 0) of 44 and 47% were obtained for APSC and Picactif, respectively. Further removal (35%) of 4-NP was achieved over extended operation of the beds, however more frequent backwashing was required as a result of the biological growth exhibited in the presence of NOM.