Valorization of wood processing effluent for biotechnological reduction of volatile organic compounds in pinewood

Abstract

This study focused on using medium density fiberboard (MDF) effluent as a culture medium for Pseudomonas putida PX1 (P. Putida) for reducing volatile organic compounds (VOC) in pinewood. This process effluent stream is rich in wood extractives and primarily composed of various carbohydrates, polyphenols (lignans and stilbenes), and organic acids, particularly fatty and resin acids. In a first step, a general workup procedure for MDF effluent was developed by removing and recovering growth inhibiting substances, such as resin acids by centrifugation and membrane filtration, followed by recovery of valuable bioactive compounds, particularly lignans and stilbenes, by adsorption. Using this approach, a scalable, fixed-bed adsorption system packed with polyvinylpolypyrrolidone (PVPP) was developed to remove and selectively recover polyphenols (lignans and stilbenes) from MDF effluent. The capacity of the PVPP for 7-hydroxymatairesinol (HMR) as a model lignan was determined as 37.4 mg g−1 at 1% breakthrough. However, highly polar substances, such as sugars, sugar alcohols, small organic acids, and salts, were not retained on the column and remained in the flow-through for further use as a cultivation medium for P. putida, a VOC degrading soil bacterium. P. putida was successfully cultivated in this residual carbohydrate rich effluent stream. It was shown that a wide range of substrates in the effluent stream in addition to C5-and C6-sugars, such as glycerol, acetate, succinate, and citrate, were efficiently metabolized without adding other nutrients. In a further step, P. putida cultures were applied to pinewood strands, markedly reducing VOC. To address requirements for industrial fiberboard production, the potential for seasonally varying MDF effluent in a year-round cultivation process of P. putida to reduce VOC in pinewood strands was investigated Seasonal variations with abundant fermentable carbon sources during colder periods and few carbon sources during warmer periods were observed across four years. VOC reduction in pinewood strands with P. putida after mixed substrate fermentation under controlled conditions showed very promising results for industrial application. Total VOC (TVOC) emissions decreased by more than 55% in only 3 h. Most aldehydes and terpenes were effectively reduced by 67%–100%,except for Δ-3-carene and α-terpinolene, which decreased by 20%–22%. Combined, ourresults identify a promising approach to reuse the currently unused MDF effluent stream in ayear-round biotechnological process to produce VOC-reduced wood products, such as oriented strand boards (OSB).