There are three principal ways you can achieve the best results in the treatment of sewage, at the lowest cost. This article takes a look at what these are:


1. Wastewater Stabilization Ponds:


This method involves (a) aerobic, (b) anaerobic and (c) aerobic cum anaerobic oxidation ponds. Oxidation Ponds are also known as Facultative Ponds. In these ponds, photosynthesis (sunlight and oxygen are needed) mainly causes purification. If anaerobic bacteria can do the job, then sunlight and oxygen are not needed for the treatment of sewage.


2. Biological Treatment:


Biological treatment comes midway between waste stabilization ponds and conventional secondary treatment. Purification is wholly biological here and air is supplied by surface acting aerators to treat wastewater. 90% organic removal is possible in a few days.


This is a system similar to aerated lagoons, but the physical layout is different. Here, the channel is oval shaped to facilitate adequate velocity in the liquid. This in turn will keep the biological solids in suspension which results in a better reaction which is needed to treat wastewater. A special system of aerators supply air, hence oxygen is available in plenty for the treatment of sewage.


Biological treatment consists of a series of adjacent discs, partly submerged and slowly rotating in sewage to facilitate the growth of bacteria (on the discs) that stabilize the organic matter. The process is wholly biological in nature.


3. Chlorination:


Chlorine is used in sewage treatment to disinfect, remove odors and reduce Biochemical Oxygen Demand (BOD). In sewage, organic matter will consume a large quantity of chlorine first. The remaining chlorine will kill bacteria. So, disinfecting doses for the treatment of sewage will be much larger.


The normal chlorine dosage that may be sufficient to treat sewage is as follows:


Raw Sewage -- 20 to 25 mg/l 
Settling Tank Effluent -- 20 mg/l 
Trickling Filter Effluent -- 15 mg/l 
Activated Sludge Effluent -- 8 mg/l 
Sand Filter Effluent -- 8 mg/l