Feedforward control application in aerobic and anoxic biotrickling filters for H2S removal from biogas

Abstract

BACKGROUND Feedforward control was implemented at laboratory scale in an aerobic and an anoxic biotrickling filter (BTF) operating under fluctuating H2S loading rate (LR) conditions in order to show the capabilities and added value of this control strategy. Dynamic, long-term tests with variable H2S LR were performed to simulate disturbances in the inlet gas concentration with and without the implementation of a feedforward control loop based on trickling liquid velocity (TLV) and nitrate feeding rate manipulation for the aerobic and anoxic BTFs, respectively. RESULTS An average LR of 80 g S-H2S m–3 h–1 with peaks and valleys of 141 and 28 gS-H2S m–3 h–1 were tested. At the highest H2S LR, a 68.4% and 62.6% reduction of maximum outlet H2S concentration, and 50.0% and 26.6% reduction of H2S cumulative mass emitted were reached in the aerobic and anoxic BTFs, respectively, thanks to the application of feedforward control strategies. The sulfate selectivity in the aerobic BTF was enhanced up to 100.6 ± 5.0% under controlled conditions. In the anoxic BTF the sulfate selectivity was kept constant at 32.8% ± 0.8%. CONCLUSION Despite demonstrating that the feedforward controller significantly reduced the impact of disturbances, the utilization of TLV as manipulated variable in the aerobic reactor showed performance problems. However, the feedforward control through nitrate addition was shown to be an adequate, robust strategy for reducing the impact of load perturbation in anoxic BTFs.