Biofiltration of paint solvent mixtures in two reactor types: Overloading by polar components

Abstract

Steady-state performances of a trickle bed reactor (TBR) and a biofilter (BF) in loading experiments with increasing inlet concentrations of polar solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone and n-butyl acetate, were investigated, along with the system's dynamic responses. Throughout the entire experimentation time, a constant loading rate of aromatic components of 4 g(c)·m(-3)·h(-1) was maintained to observe the interactions between the polar substrates and aromatic hydrocarbons. Under low combined substrate loadings, the BF outperformed TBR not only in the removal of aromatic hydrocarbons but also in the removal of polar substrates. However, increasing the loading rate of polar components above the threshold value of 31-36 g(c)·m(-3)·h(-1) resulted in a steep and significant drop in the removal efficiencies of both polar (except for butyl acetate) and hydrophobic components, which was more pronounced in the BF; so the relative TBR/BF efficiency became reversed under such overloading conditions. A step-drop of the overall OL(POLAR) (combined loading by polar air pollutants) from overloading values to 7 g(c)·m(-3)·h(-1) resulted in an increase of all pollutant removal efficiencies, although in TBR the recovery was preceded by lag periods lasting between 5 min (methyl ethyl ketone) to 3.7 h (acetone). The occurrence of lag periods in the TBR recovery was, in part, due to the saturation of mineral medium with water-soluble polar solvents, particularly, acetone. The observed bioreactor behavior was consistent with the biological steps being rate-limiting.

Biofiltration of a styrene/acetone vapor mixture in two reactor types under conditions of styrene overloading

“…Preferential utilization of more water-soluble ketones in the presence of aromatics was, thus observed in previous studies (Cai et al 2006;Paca et al 2012a). However, consistently <100% acetone removal observed in the current study in both the reactors while styrene was removed completely at similar (low) concentrations indicated that the biochemical acetone degradation fluxes could be comparable to those of its mass transfer.…”

“…A higher styrene removal efficiency observed in the BF compared to TBR provided the evidence for mass transfer being rate-limiting, at least for styrene removal. This difference could be explained by a smaller packing particle size in the BF leading to a larger effective mass transfer surface area, as shown by Paca et al (2012a). Corroborating this observation, Mathur and Majumder (2008), as well as Paca et al (2009), showed that the styrene elimination capacity could be increased by an order of magnitude by using a packing made of activated carbon, which was an effective styrene absorbent facilitating its mass transfer.…”

“…In previous similar study with multiple aromatic and polar compounds, this feature was not observed . In particular, the acetone removal was negatively affected by increasing loads of toluene and xylenes in the presence of esters and ketones, apparently due to multiple substrate interactions (Paca et al 2012a). Table 1 shows the comparison of BF and TBR performance at the same substrate loadings, conducted at the upper threshold value for BF, as explained above.…”

“…In the first of these studies, polar solvents (ketones and esters) were the minor component whereas the loading of the major component, aromatic hydrocarbons, was gradually increased until overloading, then monitoring the long-term effects of overloading ). In the second study, a reciprocal loading pattern was applied, i.e., with a constant low amount of the same polar solvents under increasing loading by the same aromatic hydrocarbons (Paca et al 2012a). These two studies documented a number of substrate interactions, thus necessitating a further reduction in the system's complexity.…”

A two-stage combined trickle bed reactor/biofilter for treatment of styrene/acetone vapor mixtures

“…Mass transfer could be rate-limiting, e.g., for biofiltration of hydrophobic pollutants from the gas phase thus justifying the preferential use of BFs. [2,3] On the other hand, mass transfer of water-soluble substrates may be significantly improved in TBRs and other water-inundated reactors. Our previous studies confirmed different removal characteristics of individual pollutants in trickle-bed reactors and biofilters treating mixtures of hydrophobic and polar pollutants including styrene and acetone [1,4] as well as a paint solvents mixture.…”