Mathematical modeling to optimize control strategies in an industrial biotrickling filter for biogas sweetening

Burning biogas in a combined heat and power (CHP) plant is a promising option to reduce the emissions and the operational cost of a WWTP. However, the biogas generated in anaerobic digestion facilities in WWTPs contains average concentrations of H2S in the range from 0.1 to 0.5 vol.% which has to be removed to avoid corrosion, unnecessary production of by-products, and SO2 emissions. In a biotrickling filter (BTF), the H2S is absorbed and removed in a packed column where biomass is immobilized, being a liquid phase continuously recirculated from the bottom of the reactor. Advances in mathematical modelling of biofilters have allowed improving the knowledge of the phenomena and interactions involved in the biological desulfurization of biogas (Almenglo et al. 2013). The principal limitation for the long term operation of BTF in biogas sweetening is the accumulation of elemental sulphur due to oxygen mass transfer limitations. Apart from reducing the removal efficiency, this accumulation increases pressure drops, thus it increases the operation cost to blow the air through the bed, and force frequent maintenance tasks to replace or wash the packing material. In the present study, the dynamic model developed and validated by Rodriguez (2013) has been used to evaluate different control strategies and optimize the performance of a BTF located in the WWTP of Manresa (Barcelona). Particularly, the use of different kind of packing materials (organic and inorganic) has been evaluated to determine in different operation conditions which removal efficiency (RE) and sulphur accumulation could be expected, i.e time period of operation before the forced shutdown. Additionally, an optimal distribution of different particle sizes of materials has been proposed to reduce sulphur rate production, affecting minimally the abatement efficiencies currently obtained.