Environmental Express Joe Boyd · 2013. 10. 1. · SM 2540C, ASTM D5907-03, USGS I-1750-85 Total...
Transcript of Environmental Express Joe Boyd · 2013. 10. 1. · SM 2540C, ASTM D5907-03, USGS I-1750-85 Total...
Environmental Express
Joe Boyd
Solids and BOD Analyses: Pitfalls and Troubleshooting
Solids Analysis
September 26, 2013
Total Dissolved Solids
SM 2540C, ASTM D5907-03, USGS I-1750-85
Total Suspended Solids
SM 2540D, USGS I-3765-85
Settleable Solids
SM 2540F
Total Solids
SM 2540B
Total Dissolved Solids (TDS)
September 26, 2013
Method Summary:
An aliquot of sample is
filtered through a glass
fiber disk. The filtrate is
collected in a pre-weighed
evaporating dish. The
liquid is evaporated at
104˚C and the dish then
placed in an oven at
180˚C. The dish and
residue are weighed with
the mass of the residue
determined by difference.
Total Dissolved Solids (TDS)
Equipment Specification
September 26, 2013
Filter
Evaporating dish
Vacuum filtration device
Oven
Weight stability
Binderless Glass Fiber, 1.5µm pore size
Platinum, porcelain, or silica glass; 100mL vol.
Variety of options
104˚C and 180˚C
+/- 0.5mg of previous weight
Total Dissolved Solids (TDS)
September 26, 2013
Potential problems with evaporation dish
The lighter the better.
• Platinum is the lightest material but the most expensive.
• Typical weight of porcelain dish is ~ 80g.
Porcelain is porous.
• High humidity can affect weight stability.
• Allow the same cooling / desiccating time each time the sample is
weighed to achieve consistent results.
• A 1-hour wait time in the desiccator is generally sufficient.
• Obtain the initial weight of the dish immediately prior to use.
Total Dissolved Solids (TDS)
September 26, 2013
Why two temperatures and why are they important?
The initial evaporation step at 104˚C allows sample
evaporation without any splattering.
Drying at 180˚C drives off all mechanically occluded
water and most of the water of crystallization.
• Samples of high sulfur content may retain more water than
normal
The 180˚C temperature also drives off carbon dioxide
and converts bicarbonates to carbonates.
• Too high of a temp may cause further conversion to oxides.
Some organic matter may be lost at 180˚C but the
temperature is a good compromise between complete
water removal and minimal volatile loss.
Total Dissolved Solids (TDS)
September 26, 2013
What is the right sample volume for this test?
Standard Methods states “Choose sample volume to yield
between 2.5 and 200 mg dried residue”.
• The lower limit is 5x the allowed variance between weights
giving sufficient weight differences between initial and final
weights.
• The upper limit allows for a timely and complete removal of
water from the crystals in the sample.
• Amounts greater than 200mg may layer in the dish trapping water.
Typically 100mL is a good volume to start with but the
method does not dictate what you must use.
Total Suspended Solids (TSS)
September 26, 2013
Method Summary
An aliquot of sample (no
more than 1-L) is passed
through a pre-washed,
pre-weighed filter. The
filter is then dried at
104˚C. After drying the
filter is re-weighed and
the TSS is calculated.
Total Suspended Solids (TSS)
Equipment Specification
September 26, 2013
Filter
Vacuum filtration device
Oven
Weight stability of filter
Binderless Glass Fiber,
1.5µm pore size, pre-
washed and weighed
Variety of options
104˚C
+/- 0.5mg of previous
weight
Total Suspended Solids (TSS)
September 26, 2013
Potential problems with the filter paper
Preparation is the key
• Wash, dry, desiccate, weigh. Repeat dry through weigh steps
until a weight-stable filter is achieved.
• Prepared filters such as the ProWeigh® can solve filter preparation
problems.
• New documentation for DoubleWeigh® filters.
Shows weight stability of filter for audit trail.
Many auditors and auditing bodies now requiring this type of
documentation.
Total Suspended Solids (TSS)
September 26, 2013
Date/Time Box ID Identifier Weight 1 Weight 2 Lot #
Sep 11 2013
04:38:26:743AM a00000 D5984 0.1245 0.1245 600006
Sep 11 2013
04:38:34:493AM a00000 D5985 0.1215 0.1215 600006
Sep 11 2013
04:38:43:243AM a00000 D5986 0.1195 0.1195 600006
Sep 11 2013
04:39:12:760AM a00000 D5987 0.1186 0.1188 600006
Sep 11 2013
04:39:21:260AM a00000 D5988 0.1223 0.1221 600006
Sep 11 2013
04:39:50:777AM a00000 D5989 0.1186 0.1187 600006
Sep 11 2013
04:39:59:277AM a00000 D5990 0.1182 0.1182 600006
Sep 11 2013
04:40:29:793AM a00000 D5991 0.1203 0.1205 600006
Sep 11 2013
04:40:38:543AM a00000 D5992 0.1214 0.1213 600006
Sep 11 2013
04:41:10:560AM a00000 D5993 0.1211 0.1214 600006
Total Suspended Solids (TSS)
September 26, 2013
Filter Paper Continued…
Consistency in pore size
1.5µm is the industry
standard pore size for
filters used for TSS
analysis.
Once you analyze a sample
for TSS using a filter with a
particular pore size you
MUST stick with that size.
What filter has the edge?
Frayed edges can cause loss
of filter material during
analysis resulting in biased
results.
Total Suspended Solids (TSS)
September 26, 2013
Filter Paper Continued…
Filters that stick to the pan indicate a high organic
content.
• Wash the filter well with DI Water after sample filtration to
remove any residue that is stuck to the bottom of the filter.
Orientation of the filter
• There is an “up” and “down” side to the filters. Ensure they
are oriented correctly prior to filtration.
Total Suspended Solids (TSS)
September 26, 2013
Shake it up!
The key to obtaining a representative aliquot of sample
is to thoroughly mix the sample.
• Constant sample movement helps.
• Look for fine silt stuck to the bottom of containers.
• Remove debris that would not be considered part of a typical
water sample such as sticks and leaves.
Total Suspended Solids (TSS)
September 26, 2013
What is the right sample volume for this test?
Try to limit the sample size to yield no more than 200mg
of residue.
Experience with the sample is your best guidance.
• Typical sample volumes are:
• Mixed Liquor: 1 – 10 mL
• Influents: 25 – 50 mL
• Effluents: 300 – 700 mL
• Storm water: 500 – 1000 mL
Unlike TDS, Standard Methods dictates a sample volume
of 1-L as the largest volume one can use.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Standard Methods 5210B
A known volume of sample has its initial dissolved oxygen content recorded. After a five day incubation period at 20˚C the sample is removed from the incubator and the final dissolved oxygen content is taken. The BOD value is calculated from the depletion and the amount of sample used.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Equipment / Reagents
BOD bottles
Incubator
Dilution water
Seed
Standard
DO Meter
Specifications
Hold 300mL, seal tight, no
oxygen migration
Hold temp of 20⁰C
Contains the 4 required
nutrients and is aerated
Viable and active
GGA with TV of 198mg/L
Membrane electrode or
optical luminescence
Biochemical Oxygen Demand (BOD)
September 26, 2013
Bottles – Glass or Plastic?
Glass is traditional but can
crack, chip, break, and are
a pain to clean.
If not cleaned properly can
lead to poor results.
Plastic bottles are
designed for 1-time use –
no washing!
Lighter, can fit more in an
incubator.
EPA approves both styles.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Dilution Water
Choose your water type carefully.
• Distilled water is not always the best choice as certain metals
and volatile organics may distill over.
• Deionized water is a popular choice but proper maintenance of
your resin tanks is key.
• The oxygen depletion after 5 days must be < 0.2mg/L.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Seed
Choosing your seed source can make or break your test.
• The safest route is generally to purchase a commercially
available freeze dried seed.
• These are generally very consistent from one batch to the next and
provide predictable results.
• If you have a source of seed material (i.e. wastewater
treatment plant), research where you take your seed from.
• Should be a consistent part of the plant (NOT influent).
• Ahead of any disinfection area.
• Primary or Secondary Effluent are generally good places.
• A good Seed Correction Factor (SCF) should be between 0.6 –
1.0 mg/L.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Seed Continued…
Too high of a SCF
• Check your water quality to ensure no contamination.
• Check other labware such as bottles, pipettes, tubing, etc for
cleanliness.
• If you are providing your own seed look for changes in the seed
source that could affect the strength of the seed and make
adjustments.
• If the GGA is within range increase the amount of rehydration
water used in the commercial freeze dried seed or check your
seed source and potentially dilute it with DI Water.
• This process is approximately linear (especially with the
commercial seeds) so if you need to reduce your SCF by 20%
increase the rehydration water by 20%.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Seed Continued…
Too low of a SCF
• Check your water quality to ensure no contamination.
• Check other labware such as bottles, pipettes, tubing, etc for
cleanliness.
• If you are providing your own seed look for changes in the seed
source that could affect the strength of the seed and make
adjustments.
• If purchasing a commercial freeze dried seed reduce the
amount of rehydration water by the same factor you want to
increase your SCF.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Standard
The standard used for BOD analysis is Glucose /
Glutamic Acid, better known as GGA.
• This is made by adding 150mg of glucose and 150mg of
glutamic acid to distilled or DI Water and diluting to 1-L.
• The true value of the GGA standard is 198 mg/L of BOD.
• As this is a demand standard there is an acceptable range defined
by the method of +/- 30.5 mg/L.
• If making this standard up in the lab it is important to
desiccate the glucose and glutamic acid prior to weighing out
so it does not absorb moisture which can affect the weight.
• Commercially available, premade vials of GGA are available.
Biochemical Oxygen Demand (BOD)
September 26, 2013
Standard Continued…
If your SCF is within range but your GGA results are high,
decrease the amount of seed in your GGA and/or
samples by 1-2 mls.
If your SCF is within range but your GGA results are low,
increase the amount of seed in your GGA and/or samples
by 1-2 mls.
Biochemical Oxygen Demand (BOD)
September 26, 2013
The biggest issue with the BOD test, however, is
that the holding time for samples is 48 hours and
the test takes 5 days.
By the time you find out if your test is valid it is too late
to do anything about it.
One must give the utmost care to each step of your
procedure to avoid the possibility of invalid data.
Questions?
December 26, 2012
Joe Boyd
Environmental Express
800-343-5319