**1.Introduction**

 Wastewater, which is the biggest waste stream from municipalities, petrochemical, pharmaceuticals, food, textile, agricultural, polymer and paper industries and so on contain high contaminants of oil and salts of organic and inorganic compounds [1–5]. This strikes as a major ecological problem with high environmental impacts when discharged into the ecosystem without proper treatment. Furthermore, the industrial revolution associated with demographic growth have increased the demand for freshwater supply, which is depleting the natural fresh water supply sources [3, 5], although wastewater can be treated through various physical, chemical and biological strategies [1–3]. Unfortunately, the current conventional wastewater treatment methods cannot eliminate the contaminants. In addition conventional wastewater treatment can be expensive. Therefore, the quest for clean water and

 clean environment has resulted in various environmental protection agencies setting stringent discharge limits [3, 4]. Conversely, there are always variations in wastewater qualities which have different impacts on the environment [2–4], where a proper wastewater treatment incorporated with primary, secondary and advanced treatment strategies seems to more viable [1, 3, 4]. The primary treatment involves separating the solids from the liquids via filtration or sedimentation, whereas the secondary treatment removes the dissolved solids and other contaminants through chemical precipitation and biological process [4, 6, 7]. Then UV light or membranes are used for further treatment [1, 2, 5]. After which, the treated water can be profitable to farmers as well as the environment positively in sustainable manner viz. irrigation, and agricultural purposes. In this study, evaluating the streamline flow of innovative wastewater treatment technologies for reuse and subsequent sludge generation as an energy source is being addressed. The biological treatment is presented in section one, followed by membrane technology and lastly the advanced oxidation process. The current limitations and future prospects of each technology are also presented.
