Dewatering of brewer's spent grain using a membrane filter press: A pilot plant study

In Portugal, brewer's spent grain (BSG) is produced in huge quantities as a by-product with moisture of 70-80%. Under environmental conditions, because of its high moisture and fermentable sugar content, BSG becomes an environmental problem after a short time (7-10 days). Thus, it must be transported to animal farms to be consumed within that period of time. In this paper, the application of a new technology of membrane filter press to achieve higher drying levels of BSG cake was studied. BSG, after being mixed with water, was filtered, water-washed, membrane-squeezed, and vacuum-dried reaching lower moisture levels (20-30%). The process cycle is approximately 115-180 min. Filtration was carried out at different feed pressure (3-5 bar) and different slurry concentrations (10-30 kg/m³, dry weight) with and without diatomite filter aid precoat. Specific cake resistance, α, was found to increase with feed pressure increase and to decrease with slurry concentration increase with average values 1.86 × 10¹² and 2.25 × 10 ¹³ m/kg for cakes produced with and without filter aid precoat, respectively. Cake dewatering via membrane squeezing was applied using hot water (65°C) and cake moisture was dropped from ∼80% before squeezing to 51% after squeezing. Five minutes were found to be enough for that stage to be accomplished. With vacuum application over the hot cakes for 30min, cake moisture decreased to ∼20% for cakes with an average thickness, 0.7cm. The produced cake loses more moisture by storing in open air (on the shelf), reaching an equilibrium value of 10.1% in less than 2 days. No bacterial activities were observed on the cake by storing for a 6-month period on the shelf. The drying levels achieved allow the cake to be stored in open air without bacterial activities facilitating its use as animal feed, at any time, and as a start material for other related BSG uses.