Prevention of clogging in a polyurethane foam packed biotrickling filter treating emissions of 2-butoxyethanol

Biotrickling filter (BTF) tend to accumulate biomass leading to clogging and a subsequent increase in pressure losses and energy demands at high volatile organic compound (VOC) loadings under long-term conditions. Besides higher pressure losses and energy demands, the treatment performance gradually declines due to inhomogeneous gas distribution within the biofilm. Clogging prevention techniques are highly interesting regarding the design of BTFs, high performance levels, energy efficiency and corresponding costs.Squeezing out and backflushing as clogging prevention techniques with optional addition of auxiliary gas injections and chemicals were tested under various conditions. Five BTFs equipped with 17.6 L of different Poret® PPI10 PU foam structures were used to analyze removal efficiencies of both biomass and 2-butoxyethanol as VOC, testing different clogging prevention techniques in comparison to two reference systems without prevention steps. Up to 109.5 g organic dry matter were removed (270 s of gas injection, 0.2 w% sodium hydroxide). With removal efficiencies of 91.7% and 72.8% and corresponding elimination capacities of 36.6 and 56.2 g C·m⁻³·h⁻¹ the highest performance levels were achieved at specific loadings of 39.9 and 77.1 g C·m⁻³·h⁻¹ at 12.6 s of empty bed residence time (EBRT), using a PU foam cylinder as package material. Removal efficiencies were evaluated in a pilot system with 2.1 m³ of package volume and 8.9 s of EBRT for treatment of air containing 95% 2-butoxyethanol and 5% styrene according to a waste gas problem in aviation industries. Even though additional installations like a compressor and different valves were necessary, total construction costs, total operational costs and energy costs for the BTF with clogging prevention techniques were reduced by nearly 10%, 20%, and 40% compared to conventional BTFs. Variations in microbial community over time were also tested.