What options can be considered for alleviating pollution from combined sewer overflow?

Question

other than separate sewers

Answer 1

doh! i was going to say separate sewers. stupid wasting all that lovely rainwater....

overflow into a reed bed? this could be the 'polishing' process normally, to reduce nitrates, and would hold a good deal of poo in a storm surge, it would stink for a week or 2 til the bugs cleared it but not as bad as letting it into the river!

Answer 2

Combined Sewer Overflows (CSO) abatement is very complex.  One solution does resolve every other problems.  Before you can decide on a particular alternative your engineers (if you are a municipal authority) need to go through engineering study of your system.

You need to characterize your system in terms of rainfall analyis; know how much of the rain result in runoffs and eventually overflows; know the hydraulic of your sewer system; know what amount of the overflows result in water quality violations.

Also, the EPA Control Policy, and the CSO Long Term Control Guidance should give you enough information.  Calculate how much of your wet weather is captured to see if you meet the "presumptive approach"  of 85% capture, or "4 - 6 overflows" on annual average.

Sewer separation or other means may not fit your system. You really need to have a good engineering evaluation before you can decide which alternatives to use.

Answer 3

Clearly, combined (sanitary and storm) sewers are the problem.  Any treatment facility will be overwhelmed every time there is substantial rain.  By separating sanitary and storm water, you make possible the building of an efficient treatment facility for the sanitary sewage at a reasonable cost.

That said, however, if the reality is that there is no money to do the re-piping and the overflow pollution problem is urgent and acute, there is a potential "band aid" approach.

1.  Mandate by by-law that all homeowners and building owners whose roof gutters discharge into the public sewer disable the systems so that rainwater is discharged onto the surface.  Where this is impossible in built-up areas, owners will be required to pay an off-set fee for a waiver.  Many buildings will be able to meet the requirement by installing retention ponds on their property.

2.  Build retention ponds throughout the municipality.

3 Disable street drains and redirect water from the streets into the ponds.

In other words, take action to largely convert your combined sewers into exclusively sanitary sewers.  Then deal with the surface water as surface water.

For further ideas on how storm water can be handled without sewers, you might contact the City of North Port, Florida -- a city that "enjoys" torrential summer rains, lies on very flat, low land, and has virtually no storm sewer system.  It controls storm water with a series of "dry canals", dry retention ponds, year round ponds and well-engineered landscaping.

Since you don't say the size of your community, where it is located nor how densely populated, I can only guess.  If your community is relatively small and is currently just using a sewage lagoon which overflows in rainy season, I would think your cheapest option is to build another, much deeper, lagoon to take the (screened) overflow.  Aeration of this second lagoon would probably make its overflow, if any, reasonably safe.

In the meantime, start budgeting for that new, segregated sewer system.

Good luck.