Designing a Sequential Batch Reactor (SBR)

Collection tank with required storage capacity, sedimentation basin/tank if wastewater contains suspended solids, SBR with sufficient retention time for entire duration of process (treatment process, coagulation, flocculation, pH adjustment/balancing), effluent discharge, sludge thickening, sludge dewatering, sludge disposal.

Make sure that your transfer pump from the collection tank to the sedimentation basin has a higher flow rate than your influent flow. If your process is a biological one, then ensure your SBR is twice as large as required as half the reactor will be occupied by bacterial sludge.

Is there any excel spread sheet or thumb rule for sizing of the various treatment plant units based on the TSS, BOD, SRT and the SBR cycle period etc.

If so kindly advise.

Regards

emendy

That will depend upon the type of waste you are processing. Please provide all the relevant details such as influent flow rate, floor space, waste concentration etc and I'll help walk you through this.

The plant requirements are as under.Plant design to cater for max value of the influent parameters.Plant capacity 35 MLD with Peak factor 2.25. Site Area available for the plant is 20000sqm

------------------Influent ////////////////////////Treated sewage requirement

BOD5@20deg cel ///150-250mg/lit /////////////<=20mg/lit

suspended solids ///250-550mg/lit /////////////<=30mg/lit

COD /////////////////300-700mg/lit /////////////<=10mg/100lit

faecal coliform//////1 X10^7MPN/100ml////////<=100MPN/100ml

Regards

emendy

So you have a high flow rate with low TOC level and a floor area of 2 hectares.

1. For the collection tank, at least 10 hours normal flow storage time is suggested. This will give you a retention time of slightly less than 4½ hours during peak flow. This will ensure that you always have enough storage capacity.
2. For your sedimentation basin, go for 2 hours retention. Design it wide and deep rather than long so as to achieve a much lower water velocity for more effective sedimentation. A total tank volume of 3,300m³ minimum will give you a retention time of > 2.25 hours normal flow and 1 hour peak flow. Remember to add in a sludge pump to drain out the settled sludge.
3. Given your low TOC level, 4 - 6 hours aeration is sufficient. 26,300m³ will give you more than 9 hours retention time for normal flow and 4 hours peak flow. This should be sufficient for the entire process for the most part. You may need to add in nitrates and phosphates as nutrients, although I personally doubt it since it's domestic sewage, which already contains these nutrients. Given the volume of the tank, make it slightly less shallow than the maximum depth your blowers can handle. Talk to your suppliers on this. You may also need to supplement the blowers with mixers to better aerate the water. Remember: half the tank will contain sludge, so you need to make the tank twice as large as required for the retention time. You will also need 2 SBRs; at any one time, one will be operating while the other is undergoing decanting and sludge wasting.
4. For such a large volume of water, I'll assume you're using chlorination to reduce costs. In this case, you'll need a minimum of ½ hour contact time. 1,700m³ will give you slightly more than ½ hour contact time for peak flow and 1.125 hours contact time for normal flow. Use a separate chlorination system as you do not want to poison your bacteria.
5. Since this is domestic sewage, you'll probably not require pH balancing. If you do, 850m³ will be sufficient as it will give you ¼ hour contact time at peak flow and > ½ hour contact time at normal flow.
6. At least 2 hours retention time (6,600m³) at peak flow will be required for the sludge thickener. It's best you talk to your supplier for the filterpress sizing.

I hope this helps.

Hi,

I am currently interning in a firm looking to expand to sewage treatment. I have a few questions and I would greatly appreciate your expert advice and guidance.

1. Could explain in more detail how you calculated the retention times based on the influent and effluent qualities?

2. How do you calculate the size of the different compartments based on retention times?

3. How do I modify the cycle to include nitrogen removal?

4. How do I modify the cycle to include phosphorous removal in addition to nitrogen removal?

Thank you so much in advance!

could help you mail me on viksurs@gmail.com with all your details

The SBR technology I am familiar with used two tanks. It could be expanded to more if required The design involved the complete cycle time being used for the operation at maximum design conditions.

Constraints

1 One tank had to always be filling. There was a very small pH control tank that feed the SBR train. If the SBR train was not available to accept design flow the plant shut down.

2. The time to fill one tank has to be long enough (tank big enough) while one tank was filling the other tank had to sequence through the steps

3. The steps were aeration (could be started during filling), The aeration time for your conditions will drive the size required. Additive mixing (polymer if needed), Flocculation, settling and decanting.

The settled floc was managed by biologists that watched the age population and type of biologicals. Too old, too much or too much of the wrong things resulted in Blowdown, and possibly reseeding the SBRs They also added nutrients (usually nitrogen and phosphorus for our particular applications.

Note the decant layer was a small percentage of the total volume and the space required for flock retention was much larger than most expected (making the volume of each SBR about twice the volume required for the flow.

The general observations that it worked better than expected. The floc settling step has a very distinct clear layer of decant that was the effluent at the end of each step.

Hope this helps.

Paddler