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BACKGROUNDFeedforward 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.RESULTSAn 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%.CONCLUSIONDespite 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. © 2018 Society of Chemical Industry

BACKGROUND: A high H 2 S elimination capacity has been achieved by anoxic biotrickling filters but accurate control of the nitrate dosage is required. Different control strategies have been used in biotrickling filters but proportional-integral-derivative (PID) control studies have not been reported to date. The aim of this study was to demonstrate the stability and robustness of PID control in an anoxic biotrickling filter. RESULTS:Three PID tuning methods were tested: Ziegler-Nichols, Approximate M-constrained integral gain optimization (AMIGO), and maintained oscillation. The best results were obtained using PID control by the maintained oscillation method, where the system reached stabilization 0.41 h after the H 2 S inlet step. Moreover, the nitrate consumption was 15.4% lower than that without control. CONCLUSION:The biotrickling filter operated with a PID control strategy proved to be highly stable and robust against the perturbations and disturbances evaluated. The control system was able to operate satisfactorily to a change in the set-point of the outlet H 2 S concentrations from 25 to 200 ppm V . The desulfurized biogas could be fed directly to an internal combustion engine or solid oxide fuel cell (SOFC) equipped with a zeolite clean unit.

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Biotrickling filters’ control for H2S removal has special challenges because of complexity of the systems. Feedback and feedforward control were implemented in an anoxic biotrickling filter, operated in co-current flow mode and using nitrite as an electron acceptor. The feedback controller was tuned by three methods—two based on Ziegler-Nichols’ rules (step-response and maintained oscillation) and the third using the Approximate M-constrained Integral Gain Optimization (AMIGO). Inlet H2S staircase step perturbations were studied using a feedforward control and the effect of EBRT considered by feedback control. The tuning method by maintained oscillation shows the lower errors. The selected controller was a PI, because unstable behavior at the lowest H2S inlet loading was found under a PID controller. The PI control was able to maintain an outlet H2S concentration of 14.7 ± 0.45 ppmV at three EBRT, studied at 117 s, 92 s and 67 s. Therefore, desulfurized biogas could be used to feed a fuel cell. Feedforward control enhances BTF performance compared to the system without control. The maximum outlet H2S concentration was reduced by 26.18%, although sulfur selectivity did not exceed 55%, as elemental sulfur was the main oxidation product.