Neerajee

I have some experience designing extended aeration process.
Typicall nominal HRT ranges from 2 to 2.5 days. Actual HRT ranges from 1 to 1.25 days (including RAS flow). If you are designing for a cold region the water temperature in the basin can decrease 5 to 8 degress C. As result you may loss denitrification and potentially nitrification if the temperature drops to less than 5 degres C.

Yes you can achieved both nitrification and denitrification if the control valves in the aeration chains are cycle on and off.

The purpose of extended aeration is to diggest the sludge so that it will produce less odurs. In some extended aeration process, the SRT is around 35 to 50 days to ensure that aerabic digestion of the sludge will occur. The disadvantage of long SRT is that the sludge settleability becomes poor.

typically extended aeration process is achieved in an earthen basin with slopes 2:1 or 3:1. If you use slope 2:1 make sure the slopes are stable.

In addition, the clarifiers have to be larger to account for the poor sedimentation properties of the floc (i.e. pin floc). Some suppliers of clarifiers would like to use integral clarifiers at the end of the earthen basin. However, if maintenance is needed, the bioreactor has to be out service for a period of time. To avoid this disadvantage, I would suggest to use separate clarifiers so that the bioreactor is not taken out of service.

There are well known aeration equipment to maintain the required mixing such as membrane tube difuser provided by Parkson. I like this system because you can pull the diffusers out the water without stopping the process. This mean that you can take one lateral out of service mainwhile the others laterals are operating.

Keep in mind that Enhance Biological Phosphorus Removal can not be achieved in extended aeration process because the excessive aeration deplects glycogen reserves through the aerabic stages, which, in turn, limits the PHA storage in the anaerobic zone, thereby reducing EBPR efficiency.

My personal preference is to use conventional activated sludge processes with SRT less than 14 days so that you the foot print of the bioreactor and clarifiers is smaller and therfore you can use concrete tanks. Sludge treatment should be conducted in the typical way of aerobic or anaerobic disgestion followed by dewatering and disposal.I understand that for small to medium size facilities extended aeration facilitate the sludge management since the sludge can be disposed in a sludge lagoon and dewatered every three years using drying beds or geotubes. However, you have to eal with odor problems during the dewatering stage.

Regards!
Risk

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Thanks for your information, Risk.
Anyway can anyone advise me more about hydraulic detention time and SRT for extended aeration design of this kind of high BOD loading wastewater?
Please?

Neerajee
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Neerajee,
You can go with a less conservative loading rate (up to 0.8kgBOD/m3/d).

As stated before a HRT of no more than 36 hours is common. (do not include RAS flow in calculations)

The SRT will depend on the type of extended aeration plant. Are you proposing an aeration tank followed by a clarifier or perhaps an SBR type?

Your wastewater temperature (lowest) will determine your SRT if you wish to nitrify. You can find numerous versions of the formula to calculate your SRT based on temperature on the internet. The rule of thumb is the aerobic portion of the aeration system should provide at least 10 days at 20 degree C. If only 40% of the tank is aerobic (ie oxidation ditch) then 10days/40% = 25 days SRT.

Cheers
Logged

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Thanks Goff

My aeration tank is followed by a clarifier.
The purpose of extented aeration design is to minimize odour problem by including digestion process in the aeration tank.
The high hydraulic detention time came from calculating aeration tank volume using sludge age; Y(So-S)/(1/SRT+kd) = XV. The higher sludge age is, the bigger aeration tank volume is. I used criteria above and got tank volume of around 2500 m3. How can I reduce my aeration tank size?

Thanks advance for any help.
Neerajee
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Neerajee,
Ignoring other factors aeration tank volume is a function of the influent load. Your load strength is about 4 to 5 times that of domestic sewage and so you will get a large tank volume.

Can you consider some form of pre-treatment?

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Before the influent reaches the Aeration tank have you thought of any process(unit operation)?If yes can you present your scheme.What I feel is You can add some bio enzymes to reduce the BOD Load.And secondly Please put the streams into the Anaerobis digestor and then to UASB AND then pass it through two stage aeration with 3 days retaintion.This feedback is as per your BOD 1400 and desired BOD 20.U can achieve this surely.
If u have a pilot plant you can start accordingly and arrive a figure.
Regards
Amaresh
Please get back with your results ......all the best...

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Neerajee:
It seems to me that you are working on a school exercise and not in a real problem. I believe this is industrial waste; low flows, high BOD. However, you don’t mentioned.
It seems to me that you this is the first time that you are designing a bioreactor. A 2500 m3 is a small reactor in my opinion. If you building concrete tanks the cost could range about 10 million.
You are using very high MLSS, hopefully you are in a warm country so that you can settle the sludge in a convetional clarifier designed with typical criteria. I also hope that put enough diffusers so that you can maintain the biomass in suspension.
If the size of the bioreacotr is larger than what you wish, use a membrane bioreactor with a SRT of 200 days or more. An MBR will reduce the tank size. Contact Zenon, they may even have a portable plant and potentially the cost would be less than 10 million.
Regards!
Risk
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Dear all,
Thank you all valueble advices.
It’s really helpful.
Regards,
Neerajee

仅靠生化很难达到20mg的要求吧

呵呵，我的洋文不好呀，看不懂，呜呜呜呜，有人翻译么，谢谢了