Integration of a nitrification bioreactor and an anoxic biotrickling filter for simultaneous ammonium-rich water treatment and biogas desulfurization

Abstract

A preliminary assessment has been carried out on the integration of an anoxic biotrickling filter and a nitrification bioreactor for the simultaneous treatment of ammonium-rich water and H₂S contained in a biogas stream. The nutrient consumption in the biotrickling filter was as follows (mol^-1 NO₃^--N): 6.3·10^-4 ± 1.2·10^-4 mol PO₄^3--P, 0.04 ± 0.05 mol NH₄⁺-N and 0.04 ± 0.03 mol K⁺-K. Furthermore, it was possible to supply a mixture of biogenic NO₃^- and NO₂^- into the biotrickling filter from the nitrification bioreactor to obtain a maximum elimination capacity of 152 gH₂S-S m^-3 h^-1. The equivalence between the two compounds was 1 mol NO₃^--N equal to 1.6 mol NO₂^--N. The biotrickling filter was also operated under a stepped variable inlet load (30-100 gH₂S-S m^-3 h^-1) and outlet H₂S concentrations of less than 150 ppm_V were obtained. It was also possible to maintain the outlet H₂S concentration close to 15 ppm_V with a feedback controller by manipulating the feed flow (in the nitrification bioreactor). Two stepped variable inlet loads were tested (60-111 and 16-102 gH₂S-S m^-3 h^-1) under this type of control. The implementation of feedback control could enable the exploitation of biogas in a fuel cell, since the H₂S concentrations were 15.1 ± 4.3 and 15.0 ± 3.4 ppm_V. Finally, the anoxic biotrickling filter experienced partial denitrification and this implied a loss of the desulfurization effectiveness related to SO₄^2- production.

Keywords: Anoxic conditions; Biogas; Biological desulfurization; Nitrate equivalent; Nitrification; Nitrogen removal optimization.