Wastewater represents an alternative to freshwater if it can be treated successfully for re-use applications. Promising techniques involve photocatalysis, photodegradation, adsorption, bioreactors, nanocomposites, nanofiltration and membranes. Keywords: Wastewater Treatment, Biohydrogen Production, Bioethanol Production, Biological Wastewater, Carbon Nanotubes, Dairy Wastewater, Graphene-based Nanocomposites, Hormones in Wastewater, Malachite Green Removal, Membrane Bioreactors, Nanocomposites, Nanofiltration, Nanomembranes, Nanotubes, Organic Pollutants, Pesticides Removal, Photocatalysis, Photodegradation, Reversed Osmosis, Textile Wastewater.