Odour at a Sewage Treatment Plant (STP) site, poor quality of treated water (coloured and smelly) are common laments with most STPs. Though there has been huge advancements in the technologies adopted in modern STPs, problems continue to remain. With the increasing focus on hygiene and the need to reuse water to conserve this precious resource, a solution to this vexing problem is the need of the hour.

Many solutions in the form of adding bio-cultures / nutrients to enhance the performance of STPs have been attempted but they have not produced consistent and sustained results. A better understanding of what are the causes of poor performance and what really happens in an STP could help in finding a lasting solution.


  • Excess load: Most STPs are designed for a certain operating load but the actual input is higher than what was initially planned, putting a stress on the equipment and infrastructure.
  • Higher Organic & Inorganic Load: Higher proportion of fats/ oils and use of strong cleaning chemicals / personal care items tend to impair the performance of bacteria which are the heart of any STP
  • Power shutdowns: Power outages result in stoppage of air blowers / diffusers which are required to run on continuous basis to provide oxygen to bacteria that treats the sewage. Lack of oxygen results in dramatic drop in population of beneficial bacteria

The above can be categorized as problems due to external challenges.


All the wastewater from various sources is received at a common collection tank. At the collection tank, the waste separates into three parts:

  • The heavier portion called sludge settles at the bottom and this is largely organic load
  • Fats and oils which is lighter than water accumulate at the top as scum layer
  • The rest is liquid effluent containing organic load mainly

Sewage is then transferred to the next stage of the process which is the aeration stage. This is the heart of the plant where the beneficial bacteria live and break down the sewage.


  1. The sludge that settles at the bottom, tends to accumulate and needs to be disposed periodically. The disposal of this sludge is not only expensive, it is a messy affair too due to its unbearable stench.
  2. Fats / oils being light float upwards and are carried over into the aeration tank. These are harmful to the beneficial bacteria and impair their performance

The pain points above are operational and these problems can be termed as internal challenges.

Tomorrow let’s see the solution to these pain points!