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.


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


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.


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.


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.


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


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.


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


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.


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.


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.


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.


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


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.


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.


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.


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%.


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.


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.


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.


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

[email protected]

800-343-5319

mailto:[email protected]

environmental express joe boyd · 2013. 10. 1. · sm 2540c, astm d5907-03, usgs i-1750-85 total...

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