Any one have a procedure for how to take a very dry sample 90% solids and mix it with water and extract the liquid and do the a membrane filtration analysis for fecals.  Yes, I know how to do the test but I can't find a method or procedure for preparing the sample.  Do I blend it, stir it, homogenize it?  All the methods seem to be tailored for water or sewer.  The MTF technique just state to inoculate the tubes but it doesn't give any idea on what the best method is for inoculating the tube.  The solid stays intact in the tube and doesn't rehydrate.  Any thought on this subject or SOPs would be nice.

We do the MF technique for fecal coliform on our sludge. It is 24 %TS and we weigh about 1 gram wet weight into a 100 ml dilution blank and homogenize until dispensed. It does not take long and does not generate heat to kill the bacteria. We then filter various amounts so as to get a good count. We are producing a class B sludge so the counts are high enough so that the solids do not interfer with growth. We have compared favorably with the MPN procedure.

Victor wrote on Mar 30^th, 2010, 1:46pm:


Victor do you think MPN is better because you would have concerns over turbidity/discoloration on the filter?  The product  need to test is a pellet about the size of popcorn kernels.  I spoke with someone at a commercial lab and they mix it with a spatula then then extract the water with a pipettor and  filter it.  I am concerned that bacteria could be locked up on the inside of the pellet and never actually be exposed to the aqueous soln.  

I have a similar concern for MPN.  If I put the pellet directly in the tube then the inside of the pellet never comes in contact with the solution.  I suppose this wouldn't really effect the formation of gas but I would appreciate your thought on the subject.

And I will PM you for how to treat the sample prior to inoculation.  thanks for the help.

Yes, I do agree about MTF over MF in this particular application.  Due to the nature of the solids and the greater difficulty in a truley homogenous blend I think the MTF will give better results.  Email is on its way.

I agree with Victor that the MTF might be better than MF if the bacterial count is low and the %TS is high. With the MF technique you can only filter a finite amount of sample or you will blind the filter with solids and no colonies will grow. Metals toxicity will also affect the colony growth.
You still have to crush the pellets and get them in suspension to get a representive sample on the filter or into a tube to be able to get good results. Check for reprducibility of you analysis on the same sample.