Sand is cheap :) Cottonwool too.

Civil water treatment uses sand filters as the 2nd stages (starting with gravel filters that seem to be a bit over-engineered for your samples).

So get (washed) sand and build a coarse filter stage that will eliminate a significant amount of the dung. Filter size etc. depends on the size of your samples but is easily adapted. And cottonwool should be great to prevent the sand from exiting the filter - adding another filter stage.

If there are any concerns about contamination: rinse the filter with de-ionized water prior filtering. The only thing to be considered is an eventual dilution of the samples. - If this is an issue.

Curious question.  In centrifuging, you are probably removing some material, but also breaking it up.  Are you using several lagoons, sampling the third stage, or just collecting from a single collection point?  If you are running fecal coliform, fecal strep, etc., you are probably going to have to dilute the sample by many thousands to get a readable Petri dish.  Most of what I know was based on using Millipore supplies.  They have a filtering apparatus with vacuum pump, but vacuum pumps can only pull so much.  I dint know how strong the filters are if you made a pressurized system with compressed air to force the waste water through.  However if your intent is say total nutrient content, solid vs liquid, your approach in separating may be different.  The gravel and sand suggested is helpful for filtering out solids, unless you intent is also measuring them.  They make various materials for filtration of sediments, I call hem filter fabrics, woven, non woven, needle punched and non needle punched.  This was pretty good at filtering out sediments delivered from a small gully or wildfire.  The filtering fabric fences might help you separate the coarser materials from the fines, for disposal, measuring or sampling.  Many procedures require this filtration to prevent plugging up analysis equipment, and are standard methods.  You might try filtering smaller samples or using bigger filters.  If you are used to filtering a gallon, find a way to get a good mixed sample and filter 100 ml.  Consult with a water or wastewater lab, maybe they know some sampling tricks.  One other thought, they make porous ceramic caps you can put on plastic pipes to get groundwater samples.  They are probably similar to the small tools that survivalists use for filtering streams so they can drink to remove solids, many contaminants.  Perhaps the plastic pipe with ceramic cap could be pressurized to remove old sample, and then vacuum to pull in new sample, and they may not need to be refiltered if the ceramic was 0.45 microns.  We used this sampling tool in Missouri, and Sopper and Kardos at Penn State may have used this too back in the 1970s in their wastewater irrigation projects that we also tried in Missouri with a paper I uploaded into Researchgate.

I agree with most of what has already been stated. If you were to say what you are going to do with the samples you may get better answers.

You are correct. I am going to be measuring nutrient levels (anions and cations) and DOC and TON. That is all. As of yet I am not looking at the sediment. But in the future maybe so will need to think about that later on.

You could try using depth filters such as glass fibre or cellulose pads rather than membranes but be aware that they both have the potential to purturb your sample. The GF filters would either release  or sorb nutrients caions. Organic matter may be released or sorbed onto paper filters.

In my opinion whatever you do your results will be defined by the method you use. The best you can do is to minimise the errors and then be very specific about the filtration method when you publish, recognising the potential errors.

Finally, have you thought of trying to reduce the volume you need to filter by using analytical methods with reduced volume requirements. Alittle innovation can often achieve this.

(1)Filter dirty water with cotton and than  with   0.45 mili micron cellulose paper.  (2) Attempt should be made with UV technology also.

MORINGA seeds may help you in the process of fast filteration

Have you tried two steps filtration? We don't really know what sizes of particles clog your 0.45 micron filter. Clogging could be due to larger particles. So if you make a king of coarse filtration of your samples, let's say 10 micron, big particles will removed (it could be 80% of particles). Your second step of filtration at 0.45 micron will be faster.

During my Ph. D. I used to collect raw surface water (I needed important quantity for my lab experiments). I made a set-up for prefiltration of raw water on 10 micron sediment prefilter that removes large particles and my later filtration on 0.45 micron was faster. Try something like that.  Good luck!

Filter previousl on paper of 8 um an t then with your membrane wit low pressure.

,

Thank you all. These ideas have all been fantastic!!!! I'll see what I choose 

You can use successive white sand filters with different grain sizes starting with larger grain sizes and ending with smallest grain size.

Best wishes

From my point of view, in can be slow freezing and then melting, like:

1. Menin B.M., Lyubarsky V.M., Fomin N.V, G.I. Kravtzov. Plant for Treatment of

Sediment of Natural and Waste Waters. UK Patent GB 2 200 625 B, 1990.

2. Menin B.M., Lyubarsky V.M., Fomin N.V, G.I. Kravtzov. Plant for Treatment of

Sediment of Natural and Waste Waters. Patents Nr. DE 3690729 C2,

BUNDESREPUBLIC DEUTSCHLAND, 1990.

3. Menin B.M., Lyubarsky V.M., Fomin N.V, G.I. Kravtzov. Plant for Treatment of Sediment of Natural and Waste Waters. US Patent 4,786,407, 1988.