Sanitary Sewer Collection Systems

[viktom]

Dear All,

I am currently working on design of sanitary sewage collection systems for an upcoming industry and have no great idea for the same. The industry is spread over 4km by 4 km and source of sewage generation is also quite spread out over entire area. It is proposed to be collected and treated in a Centralized Sewage treatment Plant. The site has water table around just 4 m from ground level. Providing a common gravity sewer line makes it too deep, and may not be recommended

We are planning to provide combination of gravity and pumped mains. Around 6-8 pumping stations are anticipated. which will collect sewage from closeby areas under gravity. Now , each pumping station if feeding to another pumping station(...cascading...)which in turn feed other and finally feeds to Centralized treatment. The max sewage generation per day would not be more than 1000 m3/day

Could you please advise if this concept Okay from your experience. or what is generally being practiced in an industry.

a) Can there be one forced main and each pumping station pumps connects to that main.

b) Whether individual pipes from various lifting stations to central plant would be a better idea.

 

[bimr]

Additional information is necessary:

1. What does the topo look like?
2. What does the climate look like?
3. Will the streets be public or is the entire site private?
4. Is the site connected with pipe racks?
5. Is the wastewater all domestic or residential in nature?
6. Is this an around the clock plant operation, or does it only happen during the day.

It is hard to come up with a plan without knowing the above.

A system with small lift staions, maybe step systems on the upstream side transitioning to a gravity system close to the treatment plant would probably be most practical. You have enough flow for an 8-12” gravity pipe at the discharge end.

 

[civilperson]

A system with low pressure pipes from sumps in each building can be built to follow the grade to a central collection gravity flow system. These use grinder/pumps and 2" diameter PVC lines with float level switches. Very cost effective compared to excavation in rock or water saturated sands.

 

[BADMANWINS]

Based on the info, I would generally agree with civilperson with the exception of specifying a pipe size. The pipe sizing must be done based upon the flowrate of the pumps and maintaining a minimum velocity (in US generally 2 ft/sec) and also attempting to minimize retention times (i.e, not allowing the wastewater to turn septic. The pump manufacturer might even be able to help you size the pipes and determine if intermediate pump stations are required, odor control facilities, etc.........

 

[viktom]

Thanks Bimr,

Following is the lil more info as desired by you.:

a) The ground RL varies from 3.9 to 5.9. The location of Sewage treatment plant is against the gravity slope.
b) This is for middle east.., where the temp can go up to 50 Deg C in summer and 10 degrees in winter.
C) the streets are all private. Only one industrial plant for which these facilities expected.
d) Yes connected with pipe racks.
e) There is no residential block in this industrial area. The waste water is gonna be a combination of grey and black water.
f) The plant operation will be 24 hour opn.

As indicated by you, we are planning to have lift stations pumping to gravity lines. As the lengths are going to be too high, we can not have gravity lines, which will make them deeper and water table is too high. I was wondering what is usually being practices in industries:

a) Cascading lift stations (one feeding to other)?
b) Can there be one forced main and each pumping station pumps connects to that main.
c) Whether individual pipes from various lifting stations to central plant.

 

[viktom]

The site is on a desert close to sea shore

 

[bimr]

Tkere really is no usual practice. Each individual waste source is probably going to require the development of a best route to a treatment facility. You may use some features of A, B, and C.

A system with small lift stations, on the upstream side transitioning to a gravity system closer to the treatment plant would probably be most practical.

You may require some temporary lift stations while your facility is being built out.

You should arrange your plant layout to minimize the number of pumps, especially repumping.

 

[francesca]

Cascading lift stations is less desirable than a common forcemain with individual lift stations. From a maintenance an electrical cost point of view, as well as initial pump capital cost, it's cheaper to pump the sewerage only once. If your overall terrain change is small, this is much cheaper initially and overall than cascading lift stations.

 

[BRIS]

Practice in the ME is to tunnel and keep 0&M to a minimum. Otherwise Bimr and Francesca both offer good advice (as usual).

The local department of drainage affairs probably has some strong views and good advice.