Bitter substances recovery from hot trub: A study of polymeric membranes performance in a sequential mode with fouling investigation

Crossflow membrane technologies were used to clarify and concentrate the raw extract of bitter substances from hot trub, a brewing by-product, seeking to produce an alternative route for hop products via a study performance and fouling investigation. Microfiltration was performed in concentration (MF/CO) and diafiltration (MF/DF) operation modes, feeding with extract composed of lupulone/analogs (similar to 6 mg/g), iso-alpha-acid (similar to 4 mg/g), and humulones/analogs (similar to 2 mg/g). The MF/CO had similar to 69 % bitter substances permeation, while the MF/DF exhibited an increase of about 22 % in relation to MF/CO only (achieving 81-92 % the bitter substances permeation), being colupulone and n-+adlupulone presenting minor retention (<16 %). Adding the diafiltration step had not modified the profile of permeate fluxes curves, which was close to the exhibited by MF/CO. Concerning the sequential nanofiltration approach, six commercial membranes with different thin-film features and nominal molecular weight cut-offs ranging from 1000 to 150 g/mol (NP010 >= UA60 > NP030 > XN45 > NF9 > HL) were tested, operating with a clarified extract from MF/DF. XN45 and HL membranes presented higher bitter substance retention with less flux decay (similar to 42 %) than others. Membrane surfaces were altered after filtrations in relation to chemical profiles, morphology, and hydrophobicity, indicating a foulant layer formation. Different compositions and morphology of foulant layer were observed, being proteins the principal fouling agent for microfiltration while bitter substances were the main agent for nanofiltrations.

Automated summary

This study used crossflow membrane technologies to clarify and concentrate bitter substances from brewing by-products. The performance and fouling investigation showed that microfiltration achieved a high permeation of bitter substances, and adding a diafiltration step further increased the permeation. Sequential nanofiltration with different membranes also showed promising results in retaining bitter substances with less flux decay.