Optimizing nutrient supply in a rotatory-switching biofilter for toluene vapor treatment

Abstract

The influence of nutrient conditions on the degradation of toluene vapor in a rotatory-switching biofilter (RSB) was investigated. The biofilter consists of four segments connected in series, each with a packing layer made of polyvinyl formal. The influent airstreams including toluene vapors were passed through segments 1–3 as up-flow with a toluene concentration of 0.9–1.2 g m−3 and with an empty-bed retention time of 26–52 sec. Nutrient solutions were fed to all packed segments once a day by means of immersion. The nutrient solution was used repeatedly and replenished by the addition of (NH4)2SO4. The result at 155 days showed nitrogen depletion was particularly obvious and the lack of nitrogen affected toluene removal. By adding 161 g of nitrogen solution per volumetric cubic meter of reactor, toluene removal efficiency was immediately increased to greater than 99%. With long-term biofilter operation, 21%–32% of ammonium was utilized for nitrification because of the growth of nitrifying bacteria such as Nitrosomonas sp. Based on the carbon-nitrogen balance, the daily nitrogen demand for toluene removal was estimated 2.1 g day−1 at a toluene load of 70 g m-3 hr−1. Implications: Biofilters are considered as an alternative technology to control waste volatile organic compound (VOC) gases from various industries. In recent years, a major challenge has been to update the designs of biofilter systems and achieve their operational optimization (e.g., biomass control, nutrient supply). This paper describes the application of a newly designed biofilter, the rotatory-switching biofilter (RSB), which involves repeated use of nutrient solution. The results demonstrate how performance of biofiltration processes can be improved by the supply of nitrogen, and provide key knowledge for improving the performance of biofiltration processes by optimizing nutrient supply.