Selecting the wastewater treatment according to settlement size

The approach to the problem of wastewater treatment considering the size of the settlement is the following: settlements are grouped according to size - number of inhabitants, therefore it is a grouping according to the amount of water that settlements consume. The type of the wastewater treatment process is conceived in comparison to the size of the settlement. It will start from the large settlements (there are calculated settlements with over 20, 000 inhabitants), followed by purification processes for smaller settlements (5, 000 to 20, 000 inhabitants), and at the end solutions for processes of wastewater treatment in small settlements (less than 5, 000 inhabitants) will be considered. Wastewater from large settlements is usually processed in a centralized wastewater treatment plant. As for the treatment of wastewater from other settlements that we're not covering with an existing wastewater treatment plant, these settlements are using the following types: pre- treatment, primary treatment, secondary treatment, and tertiary treatment. For the group of the smallest settlements, up to 1, 000 inhabitants, a solution for wastewater treatment in these settlements should be sought through the implementation of large septic tanks, combined with subsequent purification of effluents from such tanks, such as sand-gravel filters. Natural treatment systems are recommended for the treatment of wastewater from small settlements (less than 500 inhabitants).