MATHMATICALLY, I EXPECTED A 6 FOLD WEIGHT REDUCTION AFTER DRYING WET
SLUDGE CAKE AT 15% DRY SOLIDS CONTENT TO DRY SLUDGE AT 90% DRY SOLIDS
CONTENT. HOWEVER, AFTER EXTENSIVE TRIALS THE WEIGHT REDUCTION IS 10
FOLD. WHY THE DIFFERENCE AND EXPLAIN THE "MISSING WEIGHT/VOLUME
PLEASE? EG 100 TONNES OF WET SLUDGE CAKE AT 15% DRY SOLIDS CONTENT IS
THE EQUIVALENT OF 15 TONNES AT 100% DRY SOLIDS CONTENT. IF DRYING TO
90% , 16.66 TONNES SHOULD REMAIN.HOWEVER ONLY 10.16 TONNES REMAIN. A
DIESEL FIRED ROTARY DRYER IS USED OPERATING AT 250 DECREES CELCIUS
APPROX. NO BURNING OF THE MATERIAL OCCURS. THE AIR TEMPERATURE EXITING
THE DRYER IS APPROX 130 DEGREES c. NO ASH RESIDUE IS EVIDENT, NO DUST
CARRY OVER POST BAG FILTER EVIDENT (THE 10 FOLD REDUCTION INCLUDES THE
DUST COLLECTED FROM THE BAG FILTER)THE EMISSIONS ARE SIGNIFICANTLY AND
CONSISTENTLY BELOW LIMITS ETC. NO BURNING SMELLS EVIDENT. NO PLUME IS
EVIDENT 99% OF THE TIME AND WHEN IT IS EVIDENT ITS A CLEAN WHITE STEAM
VAPOUR. IS THE MATERIAL LOST THROUGH VOLOTILISATION AND HOW IS IT
QUANTIFIED. THE SLUDGE THAT IS DRIED ORIGINATES FROM A BIOLOGICAL
WASTEWATER TREATMENT PLANT AND IS NON HAZARDOUS.

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Request for Question Clarification by pafalafa-ga on 25 Feb 2004 16:20 PST

Do you know how the solids content of the sludge cake is determined in
the first place?  The technique may impact the answer to your
question.

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Clarification of Question by watertower-ga on 26 Feb 2004 13:37 PST

A MOISTURE BALANCER UNIT IS USED TO MEASURE THE DRY SOLIDS OF THE WET
CAKE AND THE SAME UNIT IS USED TO MEASURE THE DRY SOLIDS CONTENT OF
THE DRIED SLUDGE PRODUCT. THE WET CAKE IS WEIGHED ON A WEIGHBRIDGE
PRIOR TO DRYING.tHE DRIED SLUDGE PRODUCT IS WEIGHED ON THE SAME
WEIGHBRIDGE. THE DRY SLUDGE PRODUCT IS PNEUMATICALLY CONVEYED
AUTOMATICALLY TO AN ENCLOSED BAG FILLING PLANT AND THE DUST FROM THE
BAG FILTER IS ADDED TO THESE SAME BAGS. ANY MORE QUERIES PLEASE DONT
HESITATE TO ASK.

I'm not an expert on this, but basic conservation tells
me that either
1. Measurements were incorrect 
or 
2. Something other than water left what was weighed

In case 1, the only idea that comes to mind is that
I would want to verify that the 15% really corresponds
to the ratio of the masses (not the ratio of the volumes).
If you're not certain about this, you might want to look
into the meaning of the 15%.

In case 2, the only idea is that an organic process could
occur in the material.  As a result of the process, a 
chemical reaction produces a gas which then escapes during
the drying process.  The mass of this gas is then removed
from what you weigh at the end.