Septic tank effluent FM discharge to gravity sewer - Odor control?

[Spartan5]

I am working on the design of a STEP collection system to serve 250 existing homes. The collection system will be discharging to a conventional gravity sewer system.

I expect that given it is septic tank effluent to begin with in a small diameter collection system that sulfide generation will be excessive and will cause a significant odor problem at the discharge point.

I have considered a few options at this point. The first is to detain/equalize some of the effluent and aerate it prior to repumping it to the discharge point. The cons of this idea are:

1. One of the nice features of the STEP system is that there is limited need for redundancy/fail safe at each of the STEP tanks at each residence. However, once I detain that flow somewhere I need to remump it with larger pumps, backup generators, etc. It adds a significant "mission critical" aspect to the project. There is also the potential for odor generation at this site which would have to be mitigated as well.

2. I have no means of quantifying the amount of sulfide generation to expect. I have a feeling that the amount of sulfide generated is going to vary significantly throughout the day. Also, while I have found a great deal of information in the EPA Design Manual Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants, it mainly deals with the prevention of sulfide formation, not reduction of existing sulfide. This makes design and sizing of this system difficult. Due to the uncertainty involved it will be easy to spend way more money than is actually necessary to solve the problem.

Another idea I have considered is hydrogen peroxide injection prior to discharge. This idea has merit because it is easily scalable to match the actual treatment requirements of the effluent after the system is brought online and can be metered based on the flow rate of the effluent. However, it is a hazardous substance which will require specialized facilities. It will also add a significant cost to the operation and maintenance of the STEP collection system.

I am looking for any alternative ideas others might have or for any insight on the concepts I am considering.

 

[alexcmmi]

http://www.purafil.com/Products/purafil-water-wastewater-air-filters.shtml

MOLE Manhole scrubber.

Never used one, but if you do, let me know how it works...

 

[bimr]

Unless your discharge manhole is immediately adjacent to a residence, there should not be a big concern. Why are you concerned with this?

Is it possible to locate the manhole away from residences?

 

[Spartan5]

Unless your discharge manhole is immediately adjacent to a residence, there should not be a big concern. Why are you concerned with this?

Is it possible to locate the manhole away from residences?

I should have been clearer in the first post. It's an existing gravity sewer. The tie in point is in the middle of a residential subdivision.

 

[civilperson]

Manholes may be sealed by gaskets to prevent venting until out of the critical area of residences. Forced air bubbling in the septic tanks will lessen the odor problem.

 

[bimr]

Here is a report that you may find useful:

http://www.dewberry.com/uploadedFil...Affluent Existing Neighborhood_permission.pdf

Since you have great concerns regarding the potential for odors, it is recommonded that you contact the suppliers of this equipment to see if they can quantify the odor problem.