STP Issue Status

Here's what we know so far:

Foul smell in STP treated water arises primarily from two reasons: 

• Gases released by anaerobic bacteria - Typically a rotten smell and primarily H2S and some ammonia etc.
• Residual chlorine or potentially chloramines formed when chlorine does not react fully in STP water: This will have a medicinal chlorine smell that is typical of swimming pools. Chlorine is deliberately injected into water to destroy bacteria. There are also other options to kill bacteria - UV/Ozone etc.
  

STP water typically has two main types of bacteria: aerobic and anaerobic. When the STP water is well aerated (has dissolved oxygen) the aerobic bacteria (good bacteria) thrive and they cause no smell. They dominate anaerobic bacteria. Once they eat up the oxygen, anaerobic bacteria, which do not like oxygen, "take over". These decompose organic material to form odorous gases.

The water coming to our flush tanks goes through the following process: 

HoH Central STP Water
         ↓
   Incoming Tank
     (Tank I)
         ↓
   Local LE Treatment Plant (LETP)
(Filters + Chlorine dosing)
         ↓
   Treated Water Tank
      (Tank T)
         ↓
LB (Lower Basement) Tank - One per building 
         ↓
Overhead Tanks (OH Tank)
(in each building)
         ↓
     Flush Tanks

So the key factors that can affect the foul smell are:

• Quality of incoming water from HoH STP
• Extended storage of STP water in Tank I 
• Bad design or improper capacity of LETP - this plant is maintained by Konark who also commissioned the plant
• Extended storage of STP water in Tank T
• Extended storage of STP water in OH Tanks
• Accumulated biomass in pipes 
• Lack of aeration in any of the tanks as that allows anaerobic bacteria to grow
• Stagnant water in flush tanks

Aralia society had a similar issue and we spoke to their MC. They have managed to solve the problem to an 80% extent by taking the following steps:

• Regular tank cleaning
• Reduce the amount of water in overhead tanks (so that OH water does not sit for too long)
• Advising resident to flush their toilets frequently and not allow water to sit for more than one day. According to them this causes some sort of a back draft that can affect other flats too - not sure exactly how this works.

Eagleridge to had the same problem, but their MC eventually decided to shut down the plant completely and switched to clean water. This is a brute force method and we are not at this stage yet.

Here are some reports of tests we have done to check water quality in 

• Output of LETP
• Water in OH tank in GD
• Water in incoming Tank I (this water comes from HoH STP)

Treated Water

STP Water

Treated Water - Output of LE STP

OH Tank Water

Note: The Konark report says the permissible limit for BOD (which is a measure of dissolved oxygen - lower is better) and hence is 30 but some states have a more stringent limit of 10.

Steps Taken Recently: 

• Manual addition of hypo (chlorine) in OH tank and treated water Tank I - chlorine kills bacteria
• Reduced the level of water in OH tanks - this is automated so just a level setting change
• Cleaning of OH tanks

This was done just over a week ago and led to immediate improvement but the problem has reappeared after that in some flats in esp. Glendale and GD does seem to be far more impacted by the problem, for reasons as yet unknown.

Here are the next steps to work towards a roadmap: the first three are meant for immediate relief in Glendale.

1. GD OH tank will be cleaned again tomorrow - for immediate relief . 
2. Cleaning of strainers in all GD Flats that have strainers (partially done - blocked due to wood work in many flats)
3. We have increased the chlorine dosage in Tank T and OH Tank in GD. Addition of Chlorine in Tank T has been automated as on 12 Apr.
4. Open the cover to the GH OH tank (it's about 2 feet wide) and cover it with a mesh. Not exactly aeration but to release gases more effectively. This is a minor step.
5. We will monitor the odor situation in 4 GD flats that we have identified and visited today.
6. We are exploring cleaning of the pipe that transports water from Tank T to OH tank in GD - since GD is most affected. This has been done.
7. We decided to add an aeration pump to GD OH tank - as this is expected to oxygenate the water and prevent anaerobic bacteria. Quote awaited.
8. HoH has pointed out that the LETP is injecting chlorine before filtration - they recommended adding it AFTER filtration. This is being worked on ->  Addition of Chlorine in Tank T has been automated as on 12 Apr.
9. We had asked Thermax to visit LE and examine our plant and it's design/fit for purpose including capacity. Their technical team has conducted a visit and we are expecting a report and recommendations from them. 
10. As part of #8  - there was a thought process to add a further layer of UV/Ozone treatment but this will need to be evaluated.
    
    Note: There is a thought process that we should add the good bacteria in Tank T and aerate it (add oxygen to water) so that bad bacteria do not get a chance to work. Point #7 is also impacted by this as chlorine will kill both good and bad bacteria.