Trickle Bed Reactors
Trickle beds (Figure 8) with countercurrent flow of gas and liquid are used on a large scale for vinegar production, as biofilters for gas clean-up and deodorisation, for water purification and for ore leaching. Trickle beds can be operated with or without recycling, but recycling allows higher loading and gives better flow distribution, which is even more critical than in submerged packed bed operation. Cleaning is again possible by flooding the filter and proceeding as with submerged fixed bed reactors. In the case of gas purification, the gas is cleaned in a single passage and the liquid is there both as an absorption fluid and as nutrient supply to the biomass on the packing (usually wood shavings or bark). Excess biomass is settled out of this stream and no other cleaning is needed.
Figure 8. Trickle bed reactors
(a) trickle bed or biofilter; (b) waste water trickling filter, (adopted by ref. 5).