Mixed- and plug-flow performances of an anaerobic biofilter treating 2-ethylhexanoic acid |
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Authors: | Chua H Yap M G S Ng W J |
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Institution: | 1.Department of Chemical Engineering, National University of Singapore, 10 Kent Ridge Crescent, 0511, Singapore ;2.Department Civil Engineering, National University of Singapore, 10 Kent Ridge Crescent, 0511, Singapore ; |
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Abstract: | The performance of a 20-L anaerobic biofilter treating 2-ethyl-hexanoic acid (2-EHA) operating with the effluent recirculated
was compared with that of the same biofilter operated without any recirculation. The recirculation of effluent was at a rate
of 60 L/h through the biofilter. Tracer experiments were carried out to study the hydrodynamics in the biofilter under different
modes of operation. The dispersion number (D/UL) obtained from these tracer experiments for the biofilter operated with and
without effluent recirculation were 0.65 and 0.06, respectively. These values show that the recirculation was effective in
achieving a mixed-flow pattern in the biofilter, whereas the biofilter operated without recirculation was essentially a plug-flow
column with a moderate level of axial dispersion.
The feed consisted of 2-EHA at a concentration of 8200 mg/L, which is equivalent to a COD of 20,000 mg/L. The optimal performance
of the mixed-flow biofilter was at a hydraulic retention time (HRT) of 1.1 d, with a COD removal efficiency of 92.8% and a
biogas production rate of 6.44 L/L biofilter vol/d. The biofilter failed at 0.83 d HRT, as a result of washout of biomass
at this high hydraulic loading rate. By comparison, the optimal performance achieved for the plug-flow system was at 2 d HRT.
The COD removal efficiency was 74.1%, and biogas production rate was 2.13 L/L biofilter vol/d. When the HRT was lowered to
1.5 d, failure occurred owing to inhibition as indicated by the low methane yield of 0.192 L/g COD removed. The superior performance
of the mixed-flow mode can be attributed to the presence of the recycle stream, which diluted and evenly distributed the feed. |
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Keywords: | Index Entries" target="_blank">Index Entries Mixed- and plug-flow anaerobic biofilter 2-ethyl-hexanoic acid degradation branched-chain fatty acid biofilter performance tracer studies |
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