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

• MF was carried out at concentration (MF/CO) and diafiltration (MF/DF) operation mode. • MF/DF presented better bitter substances permeation ∼81 % than MF/CO with ∼69 % • NF membranes allowed high bitter substances retention (>90 %) in particularly NF90, XN45, and HL. • NF90 showed severe fouling leading to low permeate fluxes (from ∼34 to 11 L.h−1.m−2) • Proteins and bitter substances were the main fouling agent of MF and NF processes. 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 (∼6 mg/g), iso -α-acid (∼4 mg/g), and humulones/analogs (∼2 mg/g). The MF/CO had ∼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 (∼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. [ABSTRACT FROM AUTHOR]