At the moment I'm running a small biological simulation on treating water from a rubber glove factory.
The problem is the bacteria seem to die off after a few days. The residual COD first goes down, then goes up again. The biomass continuously decreases.

I've found out that the white foam might indicate that surfactants are involved. I've gone throught the forum threads but didn't find any information on the surfactant they use. It's an ethoxylated acetylenic diol.
Could this surfactant cause the problem?

I'm currently using Poly Aluminum Chloride and anionic polymer in the pretreatment to remove suspended solids before the biological system.
Is there any way I can remove/neutralize the surfactant in the pretreatment?

They also use alkyl trimethyl ammonium bromide and ethylene oxide which might cause problems.
Is there any way I can remove/neutralize these chemicals in the pretreatment?

Thanks for your help.

Unfortunately I have no choice in changing the surfactant, since the wastewater is coming from an existing factory where they use this surfactant.

I am dosing nutrients and am currently running at 24 hrs retention time.

Thx. Yeah I know these two compounds might be a problem.

But I know that other factories, where we also use a biological system, also use this quaternary ammonium compound. But there it is no problem.

First time I see the ethylene oxide pop up though.

At this moment I'm more worried about the surfactant, but can't find much information on it.

EO is used to disinfect. It is also used in autoclaves for killing living things.  It is used to sterilize in the rubber glove plants I have encountered this before. It is not good and will likely always kill and reduce bacteria as that is what it is edsigned to do.

It might help if you would describe the physical and mechanical details of the biological simulation that you are running. If it takes a few days to affect the biological system you are operating, then the problem may be due to some other factor than feed composition. For example, determining the SOUR may provide a clue to how acute the toxicity of the feed is. Access to a respirometer may provide important clues.

Have you been continuously monitoring the DO during the simulation? Surfactants may be difficult to biodegrade and may be responsible for the higher COD after sorbing on biological surfaces initially. SOUR would be a better indicator of biological health than effluent COD. If you are using a fill and draw bench test (similar to a SBR), be sure to consistantly waste sludge to maintain an optimum sludge age and that the DO is adequate after feeding.

I would check the operation of your simulation before concluding that one of the chemicals used in the plant is preventing biological treatment of this wastewater. Many toxic chemicals may be processed if their concentrations are not above a critical threshold. Also, white foam is indicative of surfactants, but not necessarily that the surfactants are biocidal.

grrun    

I can't measure MLSS or MLVSS here. It's basically a simple aerated aquarium. I'm using slow fill, settle then draw method.

DO is always quite high.

The sludge volume decreases very fast. I think it halves about every day. So no need to waste sludge.

The client now mentioned they also use glutaraldehyde, another biocide.

grrun wrote on Sep 20^th, 2005, 2:51am:

Let us change the approach to this problem from speculating, "What is in this wastewater that is preventing me from treating it?" to "How I can treat this wastewater!" You have provided the necessary nutrients and have observed that the volume of sludge has decreased with time and so you do not think that wasting sludge is beneficial. However, I believe that consistent sludge wasting may be the solution to your problem. Activated sludge is not a uniform population of micro-life, but a diverse mixture of a myriad of life forms. Consistent sludge wasting is the way to maintain a constant population distribution of microbes.

The concept of Sludge Age and acclimatization is the way to biologically treat this waste. You should be less concerned about the die-off of your AS and more concerned about the survivors because the survivors are the ones that will multiply and consume the wastes. This may take some time, but it will help you determine the parameters necessary for a proper design. Sludge Age will help maintain a consistent population distribution of microbes.

Unfortunately, I cannot tell you what Sludge Age is necessary to treat your wastewater, but I usually start with 10 days (10% wasted AS per day). This is a trial and error process, but you will probably find that your optimum Sludge Age will be >5 days and <25 days.
After you determine an optimum, acclimated Sludge Age; you may want to explore other variables such as cycle times for filling, aeration, settling, and decanting.

One caution; be sure that your sludge is well mixed after decanting and before wasting. Forget about trying to maintain a predetermined concentration of MLVSS and allow the AS to increase or decrease with the available food supply. The MLVSS concentration is important for designing sludge processing, not for operational control.

Sincerely, grrun     8)

Dear Prody

I agree with Grrun.  The sludge age is important parameter for getting effective efficiency.  As you mentioned that for initial days you are getting higher efficiency and then it goes down with operation period, I think apart from the toxicity of some chemicals, availability of essential nutrients (Macro and micro) may be limiting the growth of the microorganisms in the reactor.  Kindly ckeck up whether these are available in the wastewater.

I think, if you can provide conditions in the reactor which are conducive for microbial growth and sustanance, you will get the steady removal efficiency.

M.M. Ghangrekar

# ethylene oxide issue
yes it is used for sterilization - the effect is due to its high reactivity with 'active hydrogen', i.e. -OH, -NH, -SH groups. However, this also means it has only a short term effect because surplus ethylene oxide is reacting with water forming polyglycols. Therefore no adverse effect has to be expected in wastewater treatment.

# removal of nonionic surfactants
the name 'surfactants' stand for 'surface active substances', i.e. it tends to accumulate at interfaces and can therefore be removed by adsorption.
Ethoxylation makes the practically insolube 'acetylenic diols' compatible with water.
Eventually the surfactants are already removed by this mechanisms due to the PAC treatment.
Also in light of potential toxic effect of other  organic contaminants you should try adsorption by clays or alternatively powdered activated carbon. This should also remove the cationic surfactant.

# biodegradation
by similarity it has to be expected that the polyethyleneglycol chains are degraded leaving short chain oligomers with low aqueous solubility, i.e. these will accumulate in the sludge.

Kind regards
T. Sobisch

our client also have this problem we are resolving. surfactant comes from dishwashing from a large consessionaire company. so PAC is the solution?

Dear Prody,
I would suggest you consider the use of bioaugmentation as a means of dealing with the surfactants. We have done this in the past for pubber glove manufacturing and it works very well.

Best regards,
Cgillen

Dear Brent Cowan,

degradation products of nonylphenol-type (alkylphenol-type) nonionic surfactants, i.e. nonylphenol and nonylphenol mono- and diethylene glycols are accumulating in the sludge. Related studies were already done in the 70th.

Kind regards
T. Sobisch