12 hours is not a large time gap. However, in order to maintain levels, you can have a pump based recycle of the wastewater (capacity of pump should be such that it should be able to keep the contents stirring slowly, not vigourously) inside the tank to keep the contents agitated, and circulating. The surface oxygen exchange will suffice.
Dont worry. Having a 12 hour downtime doesnt kill the bacteria, it just starves them. Once you restart the process, just make sure to add a bit of additional culture, urea and dap.
Wastewater aeration is the process of adding air into wastewater to allow aerobic bio-degradation of the pollutant components. It is an integral part of most biological wastewater treatment systems. Unlike chemical treatment which uses chemicals to react and stabilise contaminants in the wastewater stream, biological treatment uses microorganisms that occur naturally in wastewater to degrade wastewater contaminants.
Probably a pre- aeration treatment chemical like H2O2 or other oxidants like, ozone, c hlorine dioxide injected at headworks, equalization tank, to Then you will have to look at cost effectiveness.
Best way try adding Algal or Spirulina cultures instead of chemicals
Rejuvenation of the Drains Ponds Lakes & Rivers by Accelerated Bio-Remediation thru insitu deployment of Nano Biotech Product, Invented Developed and Made in India to Accelerate Sh.Narendra Modi’s Make in India Initiative Join our Face-book Group now with more than 28000 Members Bio-Remediation of Rivers Lakes Ponds & Drains By TechAirMart.com https://www.facebook.com/groups/techairmartbioremediation/ Mahesh Uppal +919278200108
If you can use surface aerators specialize in agitation & aeration (like they do in fish farms ) mybe it will be sufficent for keeping the organizm population in a stable condition, best consult manufacturares
I have seen Diatoms do a very good job for this situation as well as a simple Surfactant which will break up the O2 into smaller particles giving the O2 more surface area and more available for the aerobic microbes.
12 hours is not long time.Try to keep D.O at least 2.0 mg/l at shut down. Hydrogen sulfide is always a problem if MLSS are high & D.O. is less than 2.0 at shut down.I have used Sodium Nitrate many times on large and small plants for H2S control. It will release and dissolve fast. Fertilizer 16-0-0. It would take as much as 30 mg/L at first then back off to 10-20 mg/L. Hydrogen Sulfide gas is a strong wind that will have every elected official calling you. Hand held H2S meters are low cost. Plan ahead and have many bags on hand. Always use caution when H2S is too strong you can not smell it. Good luck.
You can use peroxide, but as mentioned by Leah it is a biocide. If you can use at low concentrations and it will provide oxygen. (It is used for in rivers if there has been a pollution event to aerate). If you are having to lose the blowers, is it possible to use some temporary surface aeration instead, such as floating aerators?
I agree with Leah and Marina and I would like to add to stop feeding wastewater in the aeration tank for at least 8 hours prior to the planned 12 hour shutdown. This will minimize oxygen demand and decay.
Instead of pure oxygen you could also add nitrate preferably as Ca(NO3)2 with sufficient mixing to supply chemical oxygen to the bacteria.
Both Hydrogen Peroxide and Ozone will kill your bacteria. You would be better off not aerating. You may have some die-off, but we have had periods of 8 - 9 hours with no aeration in an Activated Sludge plant with Nitrification, with little ill effect. Or, get a couple of Oxygen tanks for welding and hook up some kind of diffuser. Be careful of the explosive hazard though.
One of the alternatives for introduction of oxygen into the WWTPs is application of pure oxygen instead of air.
You could investigate the possibility to rent a mobile liquid oxygen tank and determine the necessary dose, if there are some liquid air supplier nearby.
The only two chemicals i know of that might work are ozone and/or hydrogen peroxide. don't know how this will affect plant as i have never heard of it being used before. if the tank is being mixed, you might try just using an air compressor to feed air into the system. hope this helps in some way.
Ozone and peroxide if uncontrolled will kill your bacteria. It best not even to go there. I agree will Marina's proposal and supported by Bruno. Ensure that you have sufficient nitrates present and if need be supplement this with Ca(NO3)2 as suggested by Bruno. You will save cost for the same results by using pure oxygen or additional mechanical aeration.