ENGI 9628

Environmental Laboratory

Lab #2

Solids Determination

Faculty of Engineering & Applied Science

SOLIDS DETERMINATION

PURPOSE

Using Standard Methods for solids determination.

THEORY

Total solids refer to the matter that is suspended or dissolved in water. When a water sample is evaporated, there is often a residue left in the vessel—these are the total solids. The solids in water have different attributes and sizes. The suspended particles in water can be retained on a filter with a 2.0-µm or smaller pore size, while dissolved solids are small enough to pass through a filter of that size.

“Total solids” is the term applied to the material residue left in the vessel after evaporation of a sample and its subsequent drying in an oven at a defined temperature. Total solids includes

“Total suspended solids”: the portion of total solids retained by a filter (2µm or smaller), and “Total dissolved solids”: the portion of the total solids that passes through the filter. Ref (1)

“Fixed solids” is the term applied to the residue of total, suspended, or dissolved solids after heating to dryness for a specified time at a specified temperature.

“Volatile solids” is the term applied to the weight loss on ignition. It is sometimes assumed to represent the organic fraction of the solids bat isn't an accurate measure of organic matter.

“Settleable solids” is the term applied lo the material settling out of suspension within a defined period. This test is ordinarily conducted in an Imhoff cone, allowing a one-hour settling period under quiescent conditions. Results axe measured directly and reported in terms of milliliters per liter of settleable matter Ref (1).

The volatile and fixed components in the total, suspended and dissolved solids may be determined by igniting the solids at 550°C. Organic matter at this temperature is converted to CO2 The amount of solids remaining after ignition is termed the fixed portion of the solids and represents the inorganic fraction. The loss in weight upon ignition is termed the

Page 2 of 8

“volatile” portion and is assumed to represent the organic fraction of the solid.

APPLICATIONS OF SOLIDS DATA IN ENVIRONMENTAL ENGINEERING PRACTICE (Ref 2)

Water Supplies

Dissolved solids are the major concern in water supplies therefore the total solids determination is of greatest interest. Solids may affect water or effluent quality adversely in a number of ways. Waters with high solids generally are of inferior palatability and may induce an unfavorable physiological reaction in the transient consumer Ref (1). Highly mineralized waters are also unsuitable for many industrial applications.

Polluted Waters and Domestic Wastewaters

The settleable and suspended solids determinations are of greatest interest in assessing the strength of domestic wastes and lightly polluted waters. The determination of settleable matter is of particular importance in the analysis of wastewater since it relates to the design and operation of primary settling basins. It is also widely used to determine the efficiency of sedimentation units. The suspended solids and volatile suspended solids tests are used to determine the strength of domestic and industrial wastewaters.

Industrial Wastes

All tests of solids are of interest in this case as industrial wastes include such a variety of materials that analyses for exploratory purposes should include all possible determinations. Many industrial waste waters contain high amounts of dissolved inorganic salts, and their presence is easily detected by the total-solids test.

Sludges

The total and volatile solids determinations are important in the analysis of raw and digested sludges. They are used in the design and operation of sludge digestion, vacuum-fitter, and incineration units.

SCOPE AND APPLICATION

These methods are suitable for the determination of solids in potable, surface, and saline waters, as well as domestic and industrial wastewaters in the range up to 20,000-mg/L (Ref 1).

Page 3 of 8

INTERFERENCES

In general it is best to exclude unrepresentative particles such as leaves, sticks, fish, and lumps of fecal matter from the sample.

APPARATUS

(a) Evaporating dishes (b) Water bath - capable of evaporating a water sample (c) Drying oven - equipped with a thermostatic control capable of maintaining a

temperature of 103-105 °C + 2°C. (d) Drying oven - equipped with a thermostatic control capable of maintaining a

temperature of 178 -182°C (e) Muffle furnace - for operation at 550+50°C. (f) Dessicator - provided with a desiccant. (g) Filtration apparatus and vacuum pump. (h) Glass fiber filter disks - suitable for filtration apparatus being used. (i) Volumetric pipets (j) Aluminum pans or porcelain crucibles - of appropriate size to hold filter papers. (k) Analytical balance (l) Tweezers (m) Finger thimbles (n) Imhoff cones and stand

SAFETY

Muffle Furnace: The muffle furnace is maintained at 550 °C. Combustible materials may burst into flames instantly at this temperature. Wear safety glasses, asbestos gloves and face shield. Handle all hot items with tongs.

PROCEDURE

(A) Sample Preservation

Begin analysis as soon as possible to minimize the possibility of chemical or physical change during storage. Resistant glass bottles are preferred for sample storage since this will reduce the solvent action on the glass, which causes an increase in the mineral content of the sample. Plastic bottles are satisfactory provided that the material in suspension in the sample does not adhere to the walls of the container Store samples likely to contain iron or manganese so that oxygen will not come in contact with the water.

Page 4 of 8

(B) Determination

Note: Handle dish with tongs or finger thimbles only when removing from oven/furn

(1) Total Solids Dried at 103-105°C (Method No 2540 B)

(a) Ignite a dean evaporating dish at 550°C for l hour in a muffle furnace.

(b) Cool in a dessicator to room temperature (approx. 1 hr) and then weigh to obtain the tare weight,

(c) Choose a sample size that will yield a minimum residue of 20 mg to 200 mg (usually 50 mL is sufficient). Pipet the well mixed sample into the previously tared dish.

(d) Place the dish in a drying oven at 9S°C or water bath and evaporate to dryness.

(e) Dry the evaporated sample for at least 1 hr. at 103 to 105°C in a drying oven.

(f) Cool the dish in a dessicator to room temperature and weigh.

(g) Repeat cycle of drying, cooling, desiccating and weighing until a constant

weight is obtained or until weight change is less than 4% of previous weight or

0.5mg, whichever is less.

Calculation:

mLVolSampleBALsolidstotalmg

.,1000)(/ ×−

=

Where: A = weight of solids + dish after drying in mg. B = initial tare weight of dish in mg.

(2) Total Dissolved Solids Dried At 180°C (Method No 2540 C)

(a) Preparation of glass fiber filter disk:

Page 5 of 8

Place the disk on the membrane filter apparatus. Apply vacuum and wash the disk with three successive 20-ml portions (approximately) of distilled water.

(b) Ignite a clean evaporating dish at 550°C for 1 hour in a muffle furnace.

(c) Cool in a dessicator to room temperature (approx. 1 hr) and then weigh to obtain the tare weight.

(d) Choose a sample size that will yield a minimum residue of 20 mg to 200 mg (usually 50 mL is sufficient). Pipeite the well-mixed sample into the vacuum funnel.

(e) Using a wash bottle with distilled water, rinse the sides of the vacuum funnel to remove any remaining residue.

(f) Transfer total filtrate (with washings) to a weighed evaporating dish and evaporate to dryness on steam bath or in a drying oven.

(g) Dry the evaporated sample for at least 1 hr. at 17S to 182 °C in a drying oven.

(h) Cool the dish in a dessicator to room temperature and weigh.

(i) Repeat cycle of drying, cooling, desiccating and weighing until a constant weight is obtained or until weight change is less than 4% of previous weight or 0.5mg, whenever is less.

Calculation:

mLVolSampleBALsolidsdissolvedtotalmg

.,1000)(/ ×−

=

Where: A = weight of dried residue + dish after drying in B = initial tare weight of dish in

(3) Total Suspended Solids Dried at 103-105°C (Method No 2540 D)

(a) Preparation of glass fiber filler disk: Place the disk on the membrane filter apparatus. Apply vacuum and wash the disk with three successive 20-mL portions (approximately) of distilled water.

Page 6 of 8

(Prepare individual disks for each sample, plus one blank and several "spares"). Remove the disk and place in a porcelain crucible or aluminum pan. Dry in an oven at 103 to 105°C for one hour. Cool in a dessicator to room temperature and weigh immediately before use.

(b) Place the weighed filter disk on the membrane filter apparatus and pipette a well-mixed sample into the vacuum funnel.

Note: The volume of sample taken for filtration will depend upon the concentration of suspended matter in the sample, and should be as large as practical (as a guide use 20 to 50 mL for sewage. 50 to 100 mL for surface waters).

(c) Using a wash bottle with distilled water, rinse the sides of the vacuum funnel to remove any remaining residue. Carefully remove filter and place it in porcelain crucible or aluminum pan. Dry in an oven at 103 to I05cC for an hour Cool in a dessicator to room temperature and weigh.

Calculation:

mLVolSampleBALsolidssuspendedtotalmg

.,1000)(/ ×−

=

Where: A = weigh of filter & solids in mg

B = weight of filler in mg

(4) Fixed and Volatile Solids Ignited at 550°C (Method No 2540 E)

(a) Place the dish and solids previously used to determine total solids, dissolved solids or suspended solids in a preheated 550°C muffle furnace and heat lo a constant weight (for 5 to 20 minutes).

(b) Allow the dish to cool partially in air until most of the heat has been dissipated. Transfer to a dessicator and allow to cool to room temperature. Weigh the dish as soon as it has cooled completely.

(c) Repeat cycle of drying, cooling, desiccating and weighing until a constant weight is obtained or until weight change is less than 4% of previous weight or 0.5mg, whichever is less.

Page 7 of 8

Calculation:

mLVolSampleBALDSorSStotalsolidsvolatilemg

.,1000)(/),( ×−

=

Where: A = weight of solids + dish before ignition in mg. B = weight of solids + dish after ignition in mg.

mLVolSampleCBLsolidsfixedmg

.,1000)(/ ×−

=

Where: B = weight of solids + dish after ignition in mg

C = initial tare weight of dish in mg

(5) Saleable Solids (Method No 2540 F)

(a) Fill anlmhoff cone to the one-liter mark with a thoroughly mixed sample. Allow to settle for 45 minutes, then gently swirl the sides of the cone with a rod.

(b) Allow to settle for an additional 15 minutes, and record the volume of settleable matter in the cone as mL/L.

Note: Where a separation of settleable and floating materials occur, do not estimate the floating material.

REFERENCES

(1) Standard Methods for the Examination of Water and Wastewater, l9th Edition, 1995

(2) Sawyer & McCarty, Chemistry for Environmental Engineers, 3rd Edition, New York: McGraw-Hill.1978. PP 454-463.

Page 8 of 8