Production of Membranes from Agricultural Wastes
Research studies have focused on the adsorptive materials made from agricultural wastes due to their low cost, abundance and ecological friendly nature. Porous mixed matrix membranes (MMMs) were prepared by particles of banana peel, tea waste and shaddock peel as fillers in polyethersulfone (PES) (Lin et al., 2014). The prepared MMMs were applied in the adsorption of methylene blue (MB) and methyl violet 2B (MV) dyes using either a batch or flow process. Moreover, desorption took place so as to regenerate membranes. According to the results, the saturated dye adsorption capacities for MMMs were equal to 294-340 mg/g for MB and 308-370 mg/g for MV in a batch process. Desorption reached 95% leading to membrane regeneration. In flow type operation, high dye removal and recovery efficiency could be retained after three adsorption/desorption cycles.
Agricultural wastes can be used as raw materials for the production of fertilizers, membranes, biosorbents or activated carbons for the removal of dyes, organic molecules and heavy metals. Different types of agricultural wastes, i.e., deoiled soya, coconut shell, neem leaves, hyacinth roots, rice husk, rice straw, rice bran, lemon leaf, tea waste, potato plants wastes, tomato wastes, sesame hull, garlic peel, peanut hull, carrot stem, carrot leave, barley straw, banana stalk, olive stones, almond shells, peach stones, apricot stones, cherry stones, grape seeds, Trapa natans husk, bamboo, doum-palm seed coat, walnut shells, rose seed, pine sawdust and coir pith are ideal raw materials for different industrial applications due to their low cost, non-toxic content and their abundance. The final products derived from agricultural wastes have shown equal or even better properties compared to conventional products concerning separation, adsorption and fertility.
Most of the projects related to sustainable use of AW are focused on the development of innovative technologies of wastes treatment as well as, of innovative technologies for the improvement of production processes which further produce “cleaner” wastes. Treated wastewaters or composted sludges produced by these technologies could potentially be used for irrigation and/or fertilization of crops after evaluation and definition of specific terms and conditions regarding their suitability to support plant growth, without causing phytotoxicity and environmental problems, in general. In addition, relevant studies have proven that natural zeolites can be very effectively used as a slow release fertilizer and cultivation yields can be highly increased thanks to its capacity to hold water and equilibrate the root environment particularly when they used with AW. Successful application cases have been reported in many countries but not in European member states. Despite unique properties of zeolites, it is evident that zeolites have little been involved in waste reuse processes. Thus, any technology based on natural zeolites should imply experimental research.