Design and Verification Modelling on Sulphate Reduction in Gas-lift Reactors

Two mathematical models for, respectively, the design and verification of gas-lift reactors aimed at sulphate removal from wastewater are proposed. Once the effluent sulphate concentration is fixed and the influent wastewater characteristics are assigned, the steady-state design model gives explicit mathematical relationships to determine the bioreactor volume and the effluent concentrations of substrates (acetate and hydrogen) and products (methane and sulphide). Due to the availability of explicit relationships, the model application is very easy and fast and requires no iterative procedures. The verification model is aimed at predicting the gas-lift reactor performances and takes into account the same substrates and biochemical processes as the design model. Once the reactor volume and the sludge recycle flow are fixed and the influent wastewater characteristics are assigned, its application gives the substrate, product and biomass concentrations in the reactor effluent. The verification model can also be applied in dynamic conditions. Model simulations show that methanogenic bacteria (MA) prevail over sulphate reducing bacteria (SRB) and homoacetogenic bacteria (HB) when the volume of the gas-lift reactor is not sufficient to enable the growth of all bacteria. This implies that no sulphate removal can be performed by an undersized H2/CO2 fed gas-lift reactor, making clear the need of a reliable design procedure to determine the proper reactor volume.