Measuring Percent Solids

A Centrifuge, if this is something that needs testing from time to time you can get them pretty cheap

do you want to measure the average solids just once, or repeatedly. Do you want solids by volume or solids by weight. These are necessary before a solution could be considered.

We'd like to measure the solids by weight, on a daily basis.

Are you trying to determine the amount of volitile or non-volitile solids? There is a standard procedure (check "Standard Procedures for Testing of Wastewater"), where a sample is dried in an oven to determine amount of solids. The dry weight is compared to the wet weight, yielding the % solids. This test usually takes a few hours, depending upon relative humidity. You can spped the process by placing a dessicant within the oven. Since you only need the results once a day, this should be adequate for you needs.

If truly your system is well agitated and unstratified, then it is assumed that the concentration gradient of the components (of the manure) in the tank is zero ( i.e. ∂C/∂x≈0) and same is applicable for the stereometry of the system i. e gradients along other coordinates y and z are zero. By this condition, any result you obtain using drying to constant weight in the oven should give you a fair representation of the percent Total Solids. Mind you, you must arrest any possible bio- and pyro-degradation of your sample. Effects of these degradations, amongst other, are loss of volatile alkaloids and the bio-degradables, which the microbes might have employed in bio-mass formation. The indications here, are that your drying to constant weight should be as fast as possible else material balance errors may result. At the, end you can compare wieght to weight or weight to volume,....whichever! Even, if you want to go further to carry out proximate or ultimate analyses, the AOAC methodologies are ample.

Good Luck,

Soji, Ibadan, Naija

I was enjoying a cheese sandwich until I read this topic......

Stir it up thoroughly.

Take a known (but small) amount of the mixture.

Force it through a very fine filter (but weigh the filter pad first).

Weigh the result, then deduct the weight of the original filter pad.

This gives the weight of solids.

Do this a number of times by taking a sample from different parts and levels of the tank. This will give you an average figure. If the density varies (with depth perhaps) one of the samples should be close to the overall avarage.

One sample then taken from the same place and depth in furure tanks should give you a realistic result.

If you know the size or weight of the tank, then you will be able to estimate the amount of solids. ie, if half the sample is solids, then half the tank is solids.

Wash your hands.

Here is a simple setup "good enough for the purpose" - a quick&dirty technique...

Get one of the 2-cup size press-on type coffee maker utensil (the one that you put ground coffee and water and press on the piston with filters - original Sweedish design).

Weigh your dry coffee maker with the piston (dry)- W_a.

Stir your testing material (manure) and fill about half of the coffee maker jar. Weigh the whole cup (with the filtered water)- W_b.

After pouring the filtered juice, pull the piston out, empty the filtered stuff (crumble it for quicker drying) and the coffee maker parts in a pan and weigh it(W_c). Dry it in an oven at 120 degree centigrade for 4-5 hours until everthing dries. Weigh the pan again- W_d. Done with testing... wash the tools and your hands. (higher temperatures can be used for quicker drying- as long as you dont burn the filtered stuff and the plastic handles of the coffee maker).

Now is the calculation:

W_b - W_a = W_wet (Weight of the tested material)

W_{c -}W_{d ⁼} W_dry (Weight of the dry material)

W_dry^/W_wet = %solids (by weight)

Good enough precision +/- 3 or 5% (depending on the filter and fines in the juice)

Once you get the hang of it, you may not need to dry it. Just weighing the filtered stuff and estimating its dry weight may be OK (auto-calibration for wetness of the filtered stuff - "by-eye method").

PS: Don't use that coffeemaker for its originally intended purpose - coffee may have a funny aroma....

glad to help - someone dealing with waste.....

Thanks for pointing out the need for dessication.

a few things to note here, manure solids are organics that range from slightly lighter to slightly heavier than water, they are notorious about sealing filtering materials, and his wastewater is probably really high in solids that cover a large range of sizes.

Typically, he might use filters of a known mass assisted by vacuum to remove most of the water from a known mass of the wastewater, wash the samples with clean water through the filters, then oven dry the filters with the samples. The difference in mass is the TSS or Total nonvolatile Suspended Solids, depending of drying temperaure and time. Drying the remaining filtered wastewater would give the Total Dissolved Solids. The TSS could be loosely correlated to the Turbidity, and Turbidity used for continuous monitoring of the flow stream (with corrective correlation, QA/QC, samples drawn at a statistically significant frequency). Dissolved solids could be correlated to the electrical conductivity.

Perhaps this is too simplistic, but a measurement of specific gravity should give you a relative value for solids concentration. If you weigh an empty 1 pint container and fill it with a sample, then the total weight minus the container weight is the weight of exactly one pint of manure. One pint of water weighs 1.041 pounds at 70 F. The difference should be (approximately) the solids. Make sure you correct properly for change in density of water at different temperatures. For example,

45F 1.043

50F 1.042

55F 1.042

60F 1.042

65F 1.041

70F 1.041

75F 1.040

Does anyone know of a good way that this could be done on-line, i.e. without taking a sample away to the lab? It would be ideal if it could be measured in the tank, but also acceptable to have it measured in a pumped recirculation line.

The most obvious solution I can think of is using a coriolis mass flow meter...

Which is just a bent tube for want of a more detailed description!

As it measures mass flow, if you know the volume flow rate of the pump you can adjust the output to read in gms per litre or kg per litre etc....

Knowing that 1 kg = 1 litre of water etc... the solids in the water can be measured as the density difference...

Can't they?? its a bit early in the morning for me???

John.

Reply # 11 is also a quicker and OK solution - w/precision good enough for the purpose.

Regarding on-line issue: If one manages manure, he/she has to literally handle it some way in practical applications. An on-line solution can be devised; but, may not be practical (and costly) for small scale farm settings.

*** Replier #8

I would think that might work for thicker sludges, but slurries with fine suspended particles could be more challenging. Mass wouldn't really change that much.

Anyone else know of a way to measure percent solids in-line?

-Dan

hi,

this one is a practical solution n very easy to practice. if the manure is a repetitive type:

1. have the specific gravity of the manure measured once. it is a simple procedure n can be done in a local lab.

2. whenever needed, measure the density of the slurry. take a bottle of known volume n fill it up with the slurry. weigh the net contents. weight divided by vol gives u the density.

3. apply this simple formula (Brogniart's equation) to know the weight of solids in the slurry:

W = ((D-1)*SG)/D

Density in grams/cc ...gives you the result in "grams of solids available per cc of slurry". this factor can be multiplied by the total available slurry volume to arrive at total available solids!!

this is routinely used in ceramic industry for every day checks!

===> If the manure is different everytime, the specific gravity will have to be measured each time to apply the above formula.