analytical testing - whitish foam at urban drainage site

Question from Akin Babatola
Lab/Environmental Compliance Manager
WWTF City of Santa Cruz

I have the responsibility for assessing the possibility that a whitish foam
observed at an urban drainage site about once a year (after major storms)
is a surfactant.
Is there a combination of standard tests you might suggest?
Also, are there any common candidates among urban surfactants that might
behave this way?

Answer

Possibly, the whitish foam observed is not caused by surfactants. A natural
foam formation is often observed at lakes and minor creeks in mostly
unaffected environments. The foam formed used to be very stable and has a
batting-like appearance. The precise origin of the foam forming substances
seems to be unknown. It seems to be associated with degrading natural
organic matter, maybe degradation of resins plays an important role. The
foam is formed at the beaches of the lakes during stormy weather due to
breaking of the weaves or by turbulence of streaming water.

If the cause of foaming is man-made especially proteins, eventually from a
dairy or a food farm, may be the cause too.

To analytically tackle the problem you might start with more simple tests.

Sampling of the foam and dry it. Surfactants will be soluble and
therefore extracted with alcohol, proteins should not be extracted,
denaturation should take place.
Sampling, enrichment from the water column, adapt the standard procedure
which exists for this purpose - an air stream saturated with ethyl
acetate is bubbled through the water sample with an ethyl acetate layer
on top. The surfactants are transferred to the ethyl acetate phase.
Again proteins should be denatured at the phase boundary.

After removing the alcohol or ester you may dissolve it in water for
further testing.

physico-chemical testing
measurement of surface tension as function of concentration. At higher
concentration you will observe a minimum or constant value of surface
tension in the range below 40 mN/m. If you remove the upper layer by
suction the surface tension of the solutions of concentrations near but
below the minimum should read approx. the same value as before suction.
Otherwise the low values are caused by a highly surface active component,
mostly not a surfactant.

analytical testing
standard procedure for
anionic surfactants - determination of methylene blue active substance,
cross contamination of humic like materials causes higher values than
present.
nonionic surfactants - determination with draggendorf reagent
cationic surfactants - not necessary, because these strongly adsorb to
soil, particulates etc., it is not likely that they will have residual
concentrations causing foaming

The most common surfactant is alkyl benzene sulfonate, which might be
determined directly by HPLC in a specialized laboratory.

As a general hint - you may contact a specialized lab at your location,
which is dealing with the level of surfactants in streams or wastewater.

Invitation to email further comments!

Back from POWTECH 2004

Thank you all for interesting contacts and discussions at POWTEC/PARTEC in Nürnberg

Presentations at PARTEC 2004

PARTEC 2004 International Conference for Particle Technology

Nuremberg, Germany 16 - 18 March

Thursday March 18 at 12:10
paper 25.6 - subtopic Adhesion & Surface-Particle Forces

Characterization of interparticle forces in dispersions by analytical centrifugation
Titus Sobisch, Dietmar Lerche
L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin Germany, info@lum-gmbh.de

condensed preprint at the Preprint Server of Chemweb.com shifted to the Preprint Archive
Chemistry Preprint Archive, Volume 2003, Issue 7, July 2003, Pages 198-218

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow and packing behaviour and processes at the solid-liquid interface, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields such as nanomaterials, coating, paper making, ceramics, sludge dewatering, to name just a few.
The present work reports on the use of analytical centrifugation for investigation of the packing and compression behaviour to characterize the colloidal stability and microstructure in aqueous dispersed systems. To this end interactions have been studied in monodisperse silica dispersions and in dispersions of cellulose fibres.
Packing density, obtained after compression, is related to the total interparticle potential energy. By using different additives interaction between particles can be shifted from nearly hard sphere behaviour to strong attraction which results in flocculated systems. Both substrates differ in particle shape, swelling, surface charge density and exhibit therefore different packing behaviour. Additional information could be obtained about the strength and elasticity of particle networks by analysing the relative change in sediment volume after increasing/decreasing the excess pressure.
The multisample technique applied implies the potential for more systematic studies for targeted colloidal stability.

Wednesday March 19 at 17:10
paper 20.6 - subtopic Filtration

Identification of particle size distribution based on transmission profiles measured by photocentrifuges

Stefan Berres, Raimund Bürger
Universität Stuttgart, IANS, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Dietmar Lerche

The particle size distribution of a suspension of fine particles of the same material and with a continuous size distribution is calculated from an extinction profile measured by a photocentrifuge. Photocentrifuges provide a useful tool for the characterization and quality control of suspensions. While visual inspection of the light extinction curve under centrifugal segregation allows a qualitative description, a rigorous formulation, for example as an optimization problem, gives access to a quantitative characterization. The aim of parameter identification formulated as an optimization problem is to minimize a cost function, which indicates the distance of parameter-dependent simulations from measurements. The dependence of the model solution on the parameters is induced by continuum mechanic model equations describing the continuity of mass of the solid phases. As a result, particle size distributions can be obtained from extinction profiles by computational postprocessing if basic fluid and material properties are known. Thus, the utility of photocentrifuges for recovering physical properties of suspensions from light permeability measurements is highlighted.

Water and Wastewater.com Help Forum - SBR settling question

Water and Wastewater.com Help Forum - SBR settling question

A very puzzling discussion - SBR settling question

Hello,
I run an SBR and have had a baffling situation since I began there about a year ago. Maybe someone has had something similar.
Settling in a settleometer, cylinder, bucket, square bucket and just about everything else I've tried settles to about 40% after 30 minutes with an SVI around 100-125. All that's great except that the actual settling in the SBR is always around 80%(ie an 11 foot blanket in a 14 foot volume of water). In addition, the blanket always follows the decanter down during decant. In other words, 30 minutes into decant, there's still at least 3 feet of clear water.
It's not really a major problem but it drives me nuts! I can take a square bucket worth of MLSS out of the tank(the same surface to volume ratio as the SBR) when it goes into settle, don't stir it and set it right next to the tank. The SBR settles to 80% and the bucket settles to 40% in 30 minutes.
Any ideas why or what to do? The only thing I wonder is some sort of electrical grounding issue but I'm not sure.
Thanks for any input.
Jeff

Re: SBR settling question

Dear Jeff, Dear Victor Santa Cruz,

if I got it right, you meant that settling in the SBR is always worse (only 20 % of clear water layer).
This is contrary to what one could expect comparing Sludge Volume Index and sludge settling in a real basin.
Wall effects as mentioned by Victor Santa Cruz would cause poorer settling in the measuring cylinder! Further, same surface to volume ratio does not ensure compareability. Besides wall effects "sludge excess pressure" (proportional to the mass of solids/area) has to be taken into account.
However, all this would justify more extensive settling in the basin.
I see two possible explanation.
You have a kind of upflow in your SBR not present in the bucket. However, this seems a little bit mysterious.
More likely, sampling for MLSS and SVI is not representative.
Possibly, in your SBR is a concentration gradient.
So I would suggest to do sampling at various depth and determination of MLSS and SVI.
Would be nice if you could share your findings with the help forum.

Kind regards
T. Sobisch


Re: SBR settling question

Thanks for the responses.
Yes, you're right. I have 2 to 3 feet of clear water on top of my blanket but in ANY SVI test I have about 50% to 60% of the volume as clear water after 30 minutes alone. I'm pretty certain we get a representative sample. Always at the end of react and from varying depths and locations. Also, I can put the MLSS in any container and the more it resembles the actual SBRs (dimension-wise), the better the SVI..(makes sense to me)..That is until I look at the true settling IN the SBR and then I'm lost again!
The other very baffling part is the fact that, after an hour of settling I get 2 to 3 feet of clear water on top. However, after only 30 minutes of Decant, the tank's dropped almost 2 feet and I STILL have 2 to 3 feet of clear water on top. It's almost like as soon as decant starts, then the settling really starts hauling! That, combined with the consistant SVI and blanket discrepency makes me wonder if there's some kind of static charge that is grounded out when decant starts.
I talked to one of our state's operator trainers and he said he heard of this situation only one other time and it was in an SBR. Unfortunatly, he didn't know the outcome.


Re: SBR settling question

Dear Jeff,

the static charge hypothesis is not quite clear. If it is related to wall effects it would play a minor role only. If it is related to a sedimentation or streaming potential I could not see why it should be different in a separate sample. In every case charge effects can only be important if the conductivity is low. So could you check this?
It seems to me that the problem is related to the unability of taking an 'undisturbed sample'. So far I cannot image what is the origin of the 'hindered' settling of the undisturbed sludge body. However, when doing the sampling or when starting decanting the hindering is abolished. Maybe this offers the opportunity for a specialised technique - namely slurping of the clear water from the surface at one point?
I am curious about the story being continued.

Kind regards
T. Sobisch

Water and Wastewater.com Help Forum - Ammonia Removal

Water and Wastewater.com Help Forum - Ammonia Removal

"I work at a military installation in the midwest and we have been required to test for ammonia since last year and we have been consistently at or over our levels ever since. It is a 3 MGD, primary clarifiers, 4 standard rate tricking filters, anaerobic digesters, secondary clarifiers, sand filtration. We have tried various biological parameters (PH, breakpoint chlorination, lime, etc.) with little success. We even added mechanical aerators to our chlorine contact chambers but the effects were minimal. Was wondering if someone else could offer some suggestions for our nagging ammonia problems. "

Answer
Dear Moeagle,
as a pacifist I would say the only sustainable solution to your problem is to shut down the military installation.
As a chemical engineer I like to remark that you have an oversupply of nitrogen nutrients.
Ammonia liberates when the pH gets alkaline. Therefore application of lime is contra productive. Further, I cannot see how chlorination should improve the situation, it would be more straight forward to add hydrochloric acid directly. Would not recommend that either.
Using an active sludge process one would establish a working nitrification/denitrification process.
Given your configuration I would suggest to include a trickling filter filled with bark mulch (a substrate deficient with nitrogen nutrients) in front of your process.

Kind regards
T. Sobisch

Victor Santa Cruz
Moeagle/Sobisch:

The addition of Cl transforms NH3-N into mono/di chloramines and there comes a point in the disinfections process (primarily) where endpoint chlorination occurs. This is one process to reduce ammonia in wastewater treatment plant effluents. Air stripping is one way to reduce ammonia. A step or cascading effect removes some of the ammonia. Depending on the constituents present in the primary influent such as alkalinity, DO, and BOD nitrification may or may not occur. You will lose alkalinity with nitrification and the minimum alkalinity that must be present in your primary influent should be ~70 mg/L. Trickling filters are capable of removing some of this ammonia.

Further comments ???