modern Wastewater Treatment Methods
& Disposal techniques
Satisfactory disposal of wastewater, whether by surface, subsurface methods or dilution, is dependent on its treatment prior to disposal. Relatively simple wastewater treatment technologies can be designed to provide low cost sanitation and environmental protection while providing additional benefits from the reuse of water.Adequate treatment is necessary to prevent contamination of receiving waters to a degree which might interfere with their best or intended use.
The whole process consists of consists of applying known technology to improve or upgrade the quality of a wastewater. Generally the steps may involve collecting the wastewater in a central, segregated location, and subjecting the wastewater to various treatment processes.

Physical, Chemical and BiologicalWastewater Treatment Methods:
Chemical:
-Neutralization
-Chlorination
-Coagulation
-Ozonation
-Adsorption
-Ion Exchange

Physical:
Sedimentation (Clarification)
-Aeration
-Flotation and Skimming
-Equalization
-Screening
-Filtration
-Degassification

Biological:
Aerobic :
-Activated Sludge Treatment Methods
-Oxidation Ponds

Anaerobic :
-Anaerobic Digestion
-Lagoons

Preliminary Treatment:
preliminary treatment is used to protect pumping equipment and facilitate subsequent treatment processes. Screens -- rack, bar or fine, Grit chambers, Pre-aeration tanks etc are used.

Primary Treatment:
most of the settleable solids are separated or removed from the wastewater by the physical process of sedimentation. The main aim is this stage is to reduce the velocity of the wastewater sufficiently to permit solids to settle and floatable material to surface

Secondary Treatment:
Secondary treatment depends primarily upon aerobic organisms which biochemically decompose the organic solids to inorganic or stable organic solids. Trickling filters with secondary settling tanks, Activated sludge and modifications, Intermittent sand filters etc are used.

Chlorination:
It involves the application of chlorine to the wastewater. The purposes are:
Disinfection or destruction of pathogenic organisms, Prevention of wastewater decomposition etc.

For more details, refer these links:
http://water.me.vccs.edu/courses/ENV149/methods.htm
http://oasDSD/publications/Unit/oea59e/ch25.htm#TopOfPage