Adsorption and Ultrafiltration as Techniques for Value Addition to Plant-Based By-Products

Abstract

The growth of the global population to 8.5 – 10 billion people by 2050 entails an increased demand for food in the forthcoming decades. Our incumbent world food system is marked by tremendous inefficiencies in the utilization of agricultural commodities for food production. The accumulation of vast quantities of solid and liquid food processing by products along the food supply chain poses a serious environmental burden. The expansion of food production to cope with the growing demand for food proliferates the generation of by products and exacerbates the adverse externalities associated with existing by product management strategies. Hence, the food system faces the conflicting pressure to deliver the predicted demand for food by means of an environmentally sustainable development. In this context, efforts focusing on the exploitation and valorization of underutilized natural resources become of utmost importance. However, the specificity of food by products in accordance with the processed commodities depicts a central challenge for the design of reutilization processes to derive added value from unused material. This work shows applications of adsorption and ultrafiltration processes aimed at the complete utilization of diverted resources and the recovery of higher added value compounds that capitalize on the unique properties of the by products studied. Pigeon pea husk (PPH) possessed promising merits as low cost adsorbent for the removal of atenolol (ATN) and trimethoprim (TMP) that are among the most abundantly occurring pharmaceuticals in Indian water bodies. Detailed investigations of the mass transfer mechanism using the external mass transfer model (EMTM) and description of adsorption equilibrium state based on the Akaike information criterion (AIC) revealed the governing mechanisms of the adsorption processes. Moreover, olive pit derived activated carbon (OPAC) exhibited the technological suitability for the adsorption of hydroxytyrosol (HT), a potent antioxidant found in olive mill wastewater (OMWW), by matching the adsorption capacity of a commercial activated carbon (CAC). The rigorous examination of the adsorption behavior of HT onto OPAC, including the description of adsorption kinetics by means of the pore volume and surface diffusion model (PVSDM), demonstrated a promising complementary approach for the exploitation of solid and liquid by products arising during the production of olive oil. Ultrafiltration of polysaccharides with distinct conformation in aqueous solutions and comparable molecular weight, namely rigid rod like and randomly coiled pullulan, differed significantly in terms of their rejection yield, illustrating a decisive effect of polysaccharide conformation on ultrafiltration separation performance. Additionally, the observations indicated that molecular weight cut off (MWCO) offers limited suitability as selection criteria for membranes intended for polysaccharide filtrations. Overall, the presented applications of adsorption and ultrafiltration processes provide encouraging prospects for their incorporation into integrated processes aimed at the valorization of various food by products. Further collaborative efforts from diverse research fields, such as physics, chemical engineering, food science and process engineering, will facilitate the development of holistic valorization concepts to expedite the complete reutilization of food by products.