Performance of wastewater treatment during variable temperature

The general aims of the biological treatment of wastewater (BTW) are to convert (i.e., oxidizes) dissolved and particulate decomposable elements into satisfactory end products. Biological process produces huge quantity of biological wastewater sludge composed of water, microorganisms, and organic and inorganic constituents, for example, phosphorus (P) and nitrogen (N₂) as well as many contaminants such as substantial metals, organic pollutants and pathogen in waste sludge. BTW is affected by various factors, among which temperature is the major one. In coldest and hottest regions, there are enormous challenges, and it is difficult to understand what the optimal treatment of wastewater is, particularly if the temperature is changed from less than 4 °C and more than 70 °C. This article presents an exhaustive review of previous studies and suggests a direction for future developments. It is expected that this study will make understanding of behavior of the biological treatment during extreme circumstances.