Effluent Disposal

Treated wastewater effluent, if not reused, is disposed off either on land or within water bodies. Discharge into water bodies is the most common disposal practice. It takes advantage of the self-purification capacity of natural waters to further treat the effluent. Therefore, wastewater effluent discharge must be based on sound engineering practice if the receiving environment is not to be adversely affected. Excessive quantities of organic material might cause rapid bacterial growth and depletion of the dissolved oxygen resources of the water body. Further, changes in pH or concentrations of some organic and inorganic compounds may be toxic to particular life forms. Accordingly, outfall structures must be designed for adequate dispersal of the effluent within the receiving waters in order to prevent localized pollution. Depending on the characteristics of the receiving waters, several factors are considered for proper mixing and dispersal of effluent. These factors involve flow velocity, depth stratification due to salinity and temperature, shape, reversal of current and wind circulation. The temperature and salinity of the effluent should also be taken within consideration. The disposal area should be downstream from any location while water is to be withdrawn for human consumption. This section addresses major considerations which need to be taken within account while treated wastewater effluent is discharged within water bodies, including rivers and streams, lakes, and oceans and seas. Specific mathematical models devised to assess the effect of effluent discharge on receiving bodies and to aid in the design of outfalls will not be discussed here.