Organo Editorial

Why do STPs Smell?

Controlling odour is one of the most important and yet most challenging aspects of a sewage treatment plant. Foul smells are often a source of igniting objections from the neighbor's. However, as levied from the Telangana govt it is mandatory to install STP in a housing community with an area of more than 10,000sqm.  

To understand how to tackle the smell, let us first understand what causes the odour at sewage treatment plants? 

The typical odour is associated with rotten eggs, ammonia, or garlic, referred to by multiple people. Sometimes the odour is described as earthy or organic. Foul smell at treatment plants originates from the anaerobic decomposition of organic compounds.  

A natural by-product of anaerobic digestion is Hydrogen sulphide (H2S), which gives off a strong smell of rotten eggs. It has low solubility in wastewater; hence it releases into the atmosphere, producing an offensive odour. Another critical aspect to understand is that not all odour is created equally; they vary in intensity. Also, weather conditions intensify the odour. For instance, temperature inversions, wind velocity and wind directions play a significant role in odour emission drifting. It is typically worse at higher temperatures. Hence, one might complain of the odour often during summers.  

As this is a reviling problem in most communities, the first step in solving any odour is identifying the problem.  

1.  Odour can be coming from raw wastewater exposed to air at the influent pump station and primary stages 

2.  It can also be due to the build-up of sludge over a period. When the foul smell begins, it implies that the STP needs to be emptied, which ideally should be done once a year. Sometimes, the waste water contains elements that cannot be broken down in a treatment plant.  

It is highly advisable to educate the users to avoid dumping items such as sanitary napkins, food waste and diapers into the WC. Often air vents are installed if the problem is persistent. It may be due to blockages or air not circulating efficiently with the system. 

Lastly, one of the significant reasons for STPs not working correctly is the fluctuations of input loads which the amount of wastewater entering the STP at a particular time. The flow of sewage in a residential community is never uniform. It varies with peak flows in the morning (residents getting ready to go to work), very low oral most no flows later in the day, with another rise in the evening. , it results in a situation called "sewage in sewage out". It takes a longtime for the STP to stabilize and provide treated water by causing a foul smell. It is advised not to compromise on the equalizer tank capacity and uniformly distribute the wastewater flow.  

Hence, it is essential to understand the STP must be sized as per the requirement, maintained well by experienced supervisory staff. If all the measures are considered for a well-maintained STP, there are very few chances to smell.  

STOP – THINK – FLUSH 

source: https://tataandhoward.com/2018/05/please-do-not-flush/)

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