The literature on membrane distillation and forward osmosis for treating natural and recovered wastewaters is reviewed. There is renewed interest in these membrane technologies as alternatives to pressure driven processes such as reverse osmosis, which are expensive in both capital and energy, and generally require pre-treatment of the feed water. Membrane distillation with hydrophobic microfiltration membranes can make use of low-grade heat energy, and give higher yields of product water from concentrated feed waters. Forward osmosis uses hydrophilic membranes akin to reveres osmosis, and needs a draw solution that is appropriate in the product water. or must be recovered and reused in large-scale operation. Although they show great promise as simple low energy systems, no large-scale installation of either process exists as yet. Membrane distillation has considerable potential for desalination to produce drinking water, whereas FO is currently confined to small-scale systems, especially as a source of energy drinks in emergency situations.

Easy-to-handle and effective methods of juice clarification and concentration by membrane technologies are still under exploration. The current article presents results of research on the technological development of an alternative natural sweetener of high biological value and improved organoleptic properties. Sorghum saccharatum stem juice is used in research. It is pre-clarified enzymatically with α-amylase and glucoamylase, clarified by ultrafiltration, and concentrated by the direct contact membrane distillation in various temperature ranges. The study shows the efficacy of membrane methods for improving juice purity, total soluble solids ( TSS), and total sugar (TS) content in the syrup obtained. Clarification depends on membrane characteristics at the beginning of the process, as there are no differences at the end of it. Juice concentration at high-temperature differences allows to accelerate the process by approx. 60% comparing to low-temperature differences. A lower temperature difference ( ΔТ = 20–30°С) in the concentration process results in a longer process and syrup acidisation, whereas a higher temperature difference ( ΔТ = 70°С) affects physicochemical properties of syrup due to local overheating and formation of Maillard reaction products. The juice concentration at ΔТ = 50–60°С allows to obtain high values of total soluble solids without significant degradation of physicochemical and organoleptic properties.