Q & A

Sewage FAQs

Domestic sewage are often discharged by tankers into rivers and other waterbodies, creating tremendous pollution.  

What are small Sewage Treatment Plants?

Small Sewage Treatment Plants (STPs) are those that fall under the category of 1 KLD to 250 KLD. These are fully automatic systems that can be placed in underground tanks or even in existing septic tanks. The treated water from these plants beats the threshold set by the government by a very high degree. The operation and maintenance costs of these plants are very low compared to the expense of having trucks regularly collecting sewage. For example, the operation costs for an EcoTec STP system in a 50 apartment building is about Rs. 150 a day, and there is no need for an operator. The treated water can be used for flushing after disinfection.

What standards apply to these STPs?

When it comes to small plants, at present there are no standards available in India or government stipulations. Vendors have some patented media and membranes, which are widely sold as proprietary technology, but they are not transparent on the functioning of such proprietary systems. This means there is very little information available to understand these claims. The systems that use standardised designs such as SBR or MBR are more reliable.



What are the different STP solutions available?

The most popular aerobic treatment systems are FBR, MBBR, MBR and SBR. Apart from this, septic tanks are also available and some of them are also popularly known as Dewats. Aerobic systems use air and microbes in an aerated environment, which digest the waste in the water and produce sludge and treated water to different quality depending on the system. Dewats use oxygen-devoid conditions to remove waste from water and require large volumes of water.



Why do STPs fail so often and there are so many tanker lorries disposing sludge everywhere?

Badly designed sewage treatment tanks are the main cause of failure of treatment. Collection tanks are not designed scientifically. Collection tanks do not receive water evenly; most of the water comes in three hours in the morning and three hours in the evening. The tank not only receives water but also settling particles and floating material. These particles over time reduce the tank’s capacity. The collection tank has to be designed factoring in details such as the interval for removing the settled and floating sludge. Second, people often end up with a sewage treatment plant that is either too small or cannot withstand small variations in flow. Due to overloading, many diffusion systems fail within three of installation. Operators continue to operate the plant, but the sewage is not being treated.

What are the common issues faced by users of improper STPs?

The collection tank gets filled up often and tankers have to come frequently to empty the overflowing tanks. The treated water starts smelling foul within hours of storage for reuse. There is high consumption of treatment chemicals and electricity, which is unlikely if the plant is functioning properly. There is a large volume of stinking sludge produced from the STP. A properly designed tank should be able to handle the household waste that comes from a residence or community.



Why are there so many substandard plants?

Property developers use the facade, garden, landscape, roads, lights, swimming pool, etc. as selling points. Nobody sells real estate using STPs. When a property is developed, plumbing and sewage treatment and disposal gets least priority, as it all lies underground and does not show its real self until the surrounding start to stink. By this time the developer is no longer around and the residents and their associations have to deal with the sewage issue. Developers invariably choose plant that are cheaper and capable of treating only partial volumes in a partially occupied property. Only after full occupancy, does the association face the reality, by which time the STP plant’s warranty is over.



How could builders and end-users choose better STPs?

Builders always want to please customers by installing systems that buyers see as value for money. When buyers become aware and ask about STPs, builders will start to give them the best. While investing in a property, insist on a good STP. Resident’s Associations and online forums should start to blog about STPs.

Builders should buy in at the time of design and construction, opting for modulised STP so that there is cost saving in plumbing as well as space saving.

Can STPs be rented?

Yes, it is now possible. Builders and residents’ associations are suspicious about the performance claims from different STP companies. By renting an STP, there is no need for high capital investment and they have to pay only for the service provided.

The service becomes pay as you use, like electricity or water. Moreover, users can decide to move to a different STP provider.


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Printable version | Oct 23, 2021 11:43:21 AM | https://www.thehindu.com/features/homes-and-gardens/q-and-a/sewage-faqs/article6727954.ece

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