Principles of Food Sanitation

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reproducible, and correlates highly with
standard BOD 5 and COD tests, but it is dif-
ficult to conduct, and requires sophisticated
laboratory equipment. This test can be effec-
tively conducted where total solid matter is
mostly organic and if the operation has a
large volume. However, the cost of perform-
ing TOC analysis is frequently prohibitive
for smaller and/or seasonal processing
plants.
Residue in Wastewater. Residue can be
considered pollution because it affects the
measurements that have been previously dis-
cussed. Residues of evaporation (total
solids) and the volatile (organic) and fixed
(ash) fractions are routinely recognized.
Settleable solids(SS) settle to the bottom
in 1 hour. They are usually measured in a
graduated Imhoff cone and reported as
mL/L SS. Settleable solids are an indication
of the amount of waste solids that will settle
out in clarifiers and settling ponds. This
examination technique is easy to perform
and can be conducted at field sites.
Total suspended solids, sometimes referred
to as nonfilterable residue, are determined by
filtration of a measured volume of waste-
water through a tared membrane filter (or
glass fiber mat) in a Gouch crucible. The dry
weight of the total suspended solids (TSS) is
obtained after 1 hour at 103 to 105ºC.
Total dissolved solids(TDS), or filterable
residue, is determined by the weight of the
evaporated filtered sample or as the differ-
ence between the weight of the residue on
evaporation and the weight of TSS. These
pollutants are difficult to remove from
wastewater, so knowledge of them is essen-
tial. Treatment requires microorganisms,
which are normally present, for conversion
to particulate matter, i.e., microbial cells.
Fats, oil, and grease(FOG) are detrimental
to biota and are unaesthetic. Interchange of
air and water is reduced through the thin
film created by FOG, which is detrimental to


fish and other marine life. Water fowl are
also affected by heavy oil films. These com-
pounds increase oxygen demand for complete
oxidation.
Althoughturbidityis not a pollutant, it is
caused by the presence of suspended matter
(organic matter, microorganisms, and other
soil particles). Turbidity is an optical prop-
erty of the sample, which causes light to be
scattered and/or absorbed, rather than trans-
mitted. It is measured by a candle turbidime-
ter. This measurement is not an accurate
indication of suspended matter that has been
determined gravimetrically because the lat-
ter method involves particle weight, and the
former relates to optical properties.
In waste material,nitrogen can exist in
forms ranging from reduced ammonium to
oxidized nitrate compounds. High concen-
trations of the nitrogen forms can be toxic to
certain plant life. The most common forms
of nitrogen found in wastewater are ammo-
nia, proteins, nitrites, and nitrates. The
reduced forms, i.e., organic nitrogen and
ammonia, can be measured by the total
Kjeldahl nitrogen (TKN) method. Other
tests are necessary to measure the oxidized
forms, i.e., nitrate and nitrite.
Phosphorusoccurs in wastewater as phos-
phate in the forms of orthophosphate and
polyphosphate. This element is present as
either mineral or organic compounds.
Although trace amounts of soluble phos-
phates occur in natural waters, too much is
detrimental to marine life. Routine analyses
measure only soluble orthophosphate. Analy-
ses for total phosphates, polyphosphates, and
precipitated phosphates are accomplished by
converting the polyphosphates and precipi-
tated phosphates to orthophosphate by acid
hydrolysis, with subsequent testing for
orthophosphate by colorimetric methods.
With the required chemical reagents and a col-
orimeter or spectrophotometer, these tests may
be performed through a trained technician.

Waste Product Handling 217
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