Tell me about the sewer

Factual Questions
1

Millions,
So it was dumping yesterday in San Francisco and I was wandering towards the bus stop and started thinking about the gutters. Yes, my mind was in the gutters, ladies and gentlemen. I just started contemplating how genius the whole idea of a sewer system is. It’s like traffic regulations; one of those things I’ve lived with all my life, taken for granted, but have never really stopped to think about. All those gutters, the water rushing off meaningfully underground, then that water going…somewhere else.

See. The thing is: I don’t know the first thing about the sewer system. I raced little tin foil boats in the gutter when I was a whippersnapper, but my expertice more or less ends there. Things like, who first devised one? and does the water really just go straight into the ocean, like those crude spray painted admonishments say it does? I just want to learn a little about the sewers.

2

the first result on a google for “sewer” is excellent (not being snide, it is)

3

Good ol’ How Stuff Works. Good ol’ google. I’d stupidly assumed that googling sewer would lead me into…webpages unfit for my pristine peepers.

4

Well what you describe are technically “storm drains” which are usually, but not always, seperate from sewars, which carry human waste. Some places have combined storm drain/sewer systems, like parts of San Francisco.

Storm drains usually channel rainwater from the roads and dump it right into the nearest convenient river. Usually they just flow downhill but they may have pumps in certain places. Sewars carry contents to a treatment plant where it is cleaned up a bit before fertilizing next year’s Cheerios.

5

Watch for a show on the discovery channel called Dirty Jobs. In one episode the host goes down in to the San Francisco sewer system. Then you can actually see what’s down there.

6

If only I had cable…
Actually, that sounds interesting enough to break into my neighbor’s house and watch. By the by, our sewer system was working…poorly yesterday. Standing water anyone?

7

Quite a few years ago I backpacked through Africa. You don’t really appreciate our urban sewerage systems until you visit a few large cities with open sewers. Yes, ladies and germs, between the sidewalk and street with no covering.

8

First off, distinguish storm sewers from sanitary sewers. The oldest systems still have them flowing into a single system, but they are rapidly trying to replace all such systems. Storm sewers, of course, simply take runoff from rain, snowmelt, etc., and route it into the appropriate drainiage, usually a stream or river.

At one time, sanitary sewers often emptied directly into rivers and streams, which diluted the sewage and processed it by aeration, fragmentation, and absorption of particulates in the course of its flow.

Individual plumbing, shared systems, and the smallest of community systems will feed into a septic tank and leach field, which allows for natural decay of the organic parts of the sewage and then its spreading into the subsoil, which finishes the purification process by absorbing water and nutrients.

Typically, community systems flow into primary, secondary, and tertiary treatment facilities, the level of sewage load mandating whether the latter units are needed. At minimum, there will be an aeration pond, gently agitating the sewage to encourage oxygen to enter it and feed the bacteria and such breaking down the organic wastes, and then the results will be processed through a large sand filter area before being fed into a stream. In larger communities, processing may need to be far more complex than this, and design and construction of such treatment facilities is a major aspect of civil engineering businesses.

Normally, sewer laterals and mains themselves are built at a very slight incline off the perfect horizontal, to permit downhill flow of the sewage. These are gravity sewers. Where this is not feasible, individual home or neighborhood “grinder pumps” or “injection pumps” are installed, which pulverize solids and lift and pump the result down force mains. These are typically of smaller dimension than gravity sewer mains, into which they typically empty, and are slightly pressurized by the output of the pumps.

9

Yeah…I hear someone else talked about sewage treatment once.

http://www.straightdope.com/mailbag/msolidwaste.html

10

“Sanitary” sewers ain’t. :rolleyes:

Seriously sewer technology and (un)sanitary waste disposal is a major engineering discipline.
Operating a sewage treatment plant is not for the easy-queasy person. :wink:
Properly run the effluent returned to the enviornment is drinking water quality! :slight_smile:

11

Polycarp caught my miscue. I suppose what I was really most curious about were the storm drainage system as opposed to the sewers of the waste evacuating variety. And Una, thanks for the research on the more grisly type of sewer—actually think it was one of the first SD articles I read, back when I happened upon the wondrous world of Cecil while trying to figure out why my hands & genetalia could be tingling from MSG overload.

12

This site says the first evidence of sewers is from the Orkney Islands (northern Scotland) and goes back more than 5000 years.

13

Related: Is there any sort of filtration system between storm sewers & their final destination (rivers/oceans)? Anything that at least filters out solids washed down through the gutters (cigarette butts, bottle caps, etc.)?

14

If the storm sewer is separate from the “sanitary” sewer, then IME there is nothing at all. Typically, there may be bars at the final exit to try to keep people or animals out, but not to filter out debris. In this metropolitan area, I can assure you that nearly 100% of the storm sewers dump into the rivers with no treatment or filtering.

15

OK, a wastewater engineer who I just phoned here at work tells me that in the EC, there are some cities that have separate systems using crude settling ponds/basins and gravel beds to catch debris, but he does not know of anything in the US like that.

16

There’s a great, green, “alternative” waste water treatment system that has been at work (and play) for the city of Arcata, California (home of my alma mater, Humboldt State University) for many years.

A triple-yolked “good egg”, in that it naturally processes waste water back into circulation, while simultaneously creating much needed wetland habitat and recreational facilities for residents.

While not an applicable solution for every city, last I heard it was receiving a lot of attention as a model for similar systems internationally.

17

A few years ago, I did some technical writing for a “waste water treatment facility;” in other words, a sewer plant. The particular plant was involved in a massive rebuilding effort and as part of that effort, a storm drain system was incorporated for the plant itself, not for the community. Basically, it was just a huge holding pond that was located under a massive concrete slab that eventually served as the foundation for a new settlement tank. The idea was that solids would settle out; when the pond level exceeded a certain amount, automatic pumps would fire up and the excess water would be pumped to the top of an elevated structure, where it would then run down what looked like a very large staircase and thence into a local creek; the idea was that the stair steps would aerate the water, rendering it safe for introduction to the creek. In the event of an emergency, treated sewage water could also be run through the aeration part and then into the creek. IIRC, the system was actually a study project; I would guess that the cost of incorporating such a system for a municipality would be prohibitive.

The entire plant was supposed to be state-of-the-art when the rehab was finished; it is an impressive facility today—lots of slicking up for public relations, but still a very efficient operation. I enjoyed writing the processes for the plant and I learned a lot more about sewage disposal than I had ever thought to. Like most things we take for granted, there is a very impressive amount of engineering and technology behind sewage disposal. I’m glad I had the opportunity.

18

Actually, since enforcement of the Phase II Stormwater regulations (part of the Clean Water Act) began a couple of years ago, cities are now being required to “treat” their stormwater before discharging it. Both new construction and existing development are included.

Look at your state’s DEQ site and search for “best management practices”. This details all of the things one can do to lessen the pollution in stormwater discharges.

Since governments in my area already require stormwater detention facilities to knock the peak off of stormwater flows, it makes sense to modify the design of the outlet structures so that they also function as settling basins.

In tight spots, grit- and trash-separating chambers can be installed at each inlet. For an example, I give you the stormceptor.

Slowly, you will see these regulations expand so that one day the treatement of stormwater will be commonplace.

Interesting aside: Poly is correct in that most “combined” systems are considered a no-no, and many cities have spent oodles trying to separate stormwater from wastewater. However, one city discovered that by continuing to treat the stormwater as well as the wastewater, they could satisfy their Phase I and II stormwater requirements better than if they had implemented Best Management Practices.

19

Although to be exact, the effluent is usually returned to the natural water system. For example, a plant my brother designed flows out into a local creek. That water authority then uses a separate treatment plant to feed water into the local tap water system.

My bro’s treatment plant was not yet online when I visited it, so I can’t comment on the queasy factor. They are gonna smell, of course, but they are also critical for our health and the health of our environment.

In my area, we have separate storm drains. The county has clearly marked the drain holes so that people don’t dump stuff into them. Most storm drains in my area dump into the SF Bay, which I believe* can handle most major storms. I mean, Alviso hasn’t flooded in 20 years! Ironically, the so-called “Alviso Yacht Harbor” is full of mud. :smack:

20

Spingears, I agree that “sanitary sewer” is something of a misnomer, considering what they carry. But as I understand it, the usage is a contraction for “sanitary disposal of waste via sewer,” as opposed to “let it run into the creek out back and cause typhoid” or “dump it all into a cesspool” or equally unsanitary means of disposing of unsanitary waste.

For the record, a lot of my work during the 1990s was on getting funding for small-town wastewater collection and treatment systems … i.e., sanitary sewers and treatment plants, taken as a unit. We had some interesting experiences.

Canton, New York, had to build a complete new treatment plant, at a cost far higher than they could pay. We got them some grant money, some long-term low-interest loans, but the creative part of how they helped finance it was to design the plant alongside the river in the middle of a large area of vacant land, buffering the treatment plant with a golf course, fees from which have helped pay for the plant. (This innovative approach to helping underwrite the cost got them a grant to design and build the course, IIRC.) They’re now putting in a bike/hike trail system around the edge of the golf course, past the treatment plant, connecting with the local university’s trail system and a couple of regional interurban trails.