Q & A > Question Details
We experienced an aromatics leak to the cooling water system one month ago. When we routed the contaminated water to our waste water treatment, it didn’t show any significant change. However, recently we experienced low F/M in our aeration basin. Is it normal to have this delayed response of about 30 days after introducing aromatics contaminated water to the waste water treatment plant?
 
Answers
29/10/2020 A: Joel Kaye, Retired from UOP & Tesoro, kaye13@gmail.com
In my experience a poisoning event will have a quicker impact, such as within several days. Of course this will be different for different systems. Futhermore, aromatics tend to be a common feed in wastewater, and often swing. While it will spike the COD, it generally won't poison the aeration basin.
15/10/2020 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Typically any deleterious effects of a 'not normal' effluent in the feed to wastewater treatment systems first appear almost overnight as the contaminant concentration reaches the critical level' for the contaminant.
Processing that depends on biological reactions can die off in a few hours, while chemical-based ones will die down as the concentration of the bad actor increases. Aromatics at low concentrations do not kill activated sludge units, while phenols will kill the bugs.
No long delay is likely.
14/10/2020 A: Prakash Pimparkar, Environmental Consulting Services , prakash.pimparkar@yahoo.in
This is called shock loading of the WWT plant. Any abnormal loading will stress the biomass and will result in reduced activity and eventual dead mass if continued for 4 to 6 days. The extent of damage also depends on the type of system MBBR. Packed media where biomass is attached to the media surface has more resilience than free floating activated sludge systems
The biomass will rejuvenate after about a fortnight. The operator has to ensure proper nutrient (N and P) supply and avoid large pH changes in the system.
the problem with aromatics is that they are more soluble in water compared to other hydrocarbons ( 2000 to 3000 mg/l ) and so can not be skimmed off in API or TPI or other pretreatment and so they increase the BOD/COD loads.
The operator may increase recycling to improve MLSS in the aeration tank by operating a standby sludge recycle pump. If recycle is not available, you can add biomass from an external source by dumping waste sludge to the aeration tank. This is a quick solution to be done under expert supervision.
13/10/2020 A: Daniel Kemp, Spectrum Water Technology, dkemp@spectrumwater.com
This is unlikely. F/M is a measure of your current BOD loading relative to your current biomass in your aeration tanks. The aromatics contaminated water is long gone and not in this calc, unless you have a 30 day retention time in the EQ tank.