### where:
A weight of dried residue  dish, mg, B weight of dish, C weight of wet sample  dish, mg, and D weight of residue  dish after ignition, mg.

5. Precision and Bias



### Precision and bias data are not now available. 6. Bibliography

G OODMAN , B.L. 1964. Processing thickened sludge with chemical conditioners. Pages 78 et seq. in Sludge Concentration, Filtration and Incineration. Univ. Michigan Continued Education Ser. No. 113, Ann Arbor. GRATTEAU , J.C. & R.I. D ICK . 1968. Activated sludge suspended solids determinations. Water Sewage Works 115:468.



## 2550 TEMPERATURE*

2550 A. Introduction

Temperature readings are used in the calculation of various forms of alkalinity, in studies of saturation and stability with respect to calcium carbonate, in the calculation of salinity, and in general laboratory operations. In limnological studies, water temperatures as a function of depth often are required. Elevated temperatures resulting from discharges of heated water may have signi fi cant ecological impact. Identi fi cation of source of water supply, such as deep wells, often is possible by temperature measurements alone. Industrial plants often require data on water temperature for process use or heat-transmission calculations.



## 2550 B. Laboratory and Field Methods

1. Laboratory and Other Non-Depth Temperature Measurements



### Normally, temperature measurements may be made with any good mercury- filled Celsius thermometer. As a minimum, the thermometer should have a scale marked for every 0.1 ° C, with markings etched on the capillary glass. The thermometer should have a minimal thermal capacity to permit rapid equilibration. Periodically check the thermometer against a precision thermometer certi fi ed by the National Institute of Standards and Technology (NIST, formerly National Bureau of Standards)* that is used with its certi fi cate and correction chart. For fi eld operations use a thermometer having a metal case to prevent breakage.

A total immersion thermometer is designed to indicate temperatures correctly when the bulb and the entire liquid column are exposed to the temperature being measured, except for a minimal emergent length. A partial-immersion thermometer has a line around it at the immersion distance from the bottom. It indicates correctly when the bulb and the liquid column to that line are exposed to the temperature being measured and the emergent stem is at ambient temperature. 2. Depth Temperature Measurements


### Depth temperature required for limnological studies may bemeasured with a reversing thermometer, thermophone, or thermistor. The thermistor is most convenient and accurate; however, higher cost may preclude its use. Calibrate any temperature measurement devices with a NIST-certi fi ed thermometer before fi eld use. Make readings with the thermometer or device immersed in water long enough to permit complete equilibration. Report results to the nearest 0.1 or 1.0 ° C, depending on need.

The thermometer commonly used for depth measurements isof the reversing type. It often is mounted on the sample collection apparatus so that a water sample may be obtained simultaneously. Correct readings of reversing thermometers for changesdue to differences between temperature at reversal and temperature at time of reading. Calculate as follows:

 T 

#  ( T 1

 t ) ( T 1  V 0 )
K 

# 

 

#  1  T 1

 t ) ( T 1  V 0 )
K 

#   L



### where:  T correction to be added algebraically to uncorrected reading, T1 uncorrected reading at reversal, * Approved by Standard Methods Committee, 2000.

* Some commercial thermometers may be as much as 3 ° C in error. TEMPERATURE (2550)/Laboratory & Field Methods 2-61t temperature at which thermometer is read, V

0 volume of small bulb end of capillary up to 0 ° C graduation, K constant depending on relative thermal expansion of mercury and glass (usual value of K 6100), and L calibration correction of thermometer depending on T1

. 

### If series observations are made it is convenient to prepare graphs for a thermometer to obtain  T from any values of T 1 

### and t. 3. Bibliography

WARREN , H.F. & G.C. WHIPPLE . 1895. The thermophone

—A new instrument for determining temperatures. Mass. Inst. Technol. Quart. 8:125. S VERDRUP , H.V., M.W. J OHNSON & R.H. FLEMING . 1942. The Oceans. Prentice-Hall, Inc., Englewood Cliffs, N.J. AMERICAN S OCIETY FOR T ESTING AND M ATERIALS . 1949. Standard Specifi cations for ASTM Thermometers. No. E1-58, ASTM, Philadelphia, Pa. REE , W.R. 1953. Thermistors for depth thermometry. J. Amer. Water Works Assoc. 45:259.



## 2560 PARTICLE COUNTING AND SIZE DISTRIBUTION*

2560 A. Introduction

1. General Discussion



### Particles are ubiquitous in natural waters and in water and wastewater treatment streams. Particle counting and size distributionanalysis can help to determine the makeup of natural waters, treatment plant influent, process water, and finished water. Similarly, it can aid in designing treatment processes, making decisions about changes in operations, and/or determining process ef fi ciency. Methods for measuring particle size distribution included herein depend on electronic measurement devices because manual methods are likely to be too slow for routine analysis. However, when particle size analysis is to include size distribution of large (  500-  m) aggregates, use direct microscopic counting and sizing. Principles of various types of instruments capable of producing both size and number concentration information on particulate dispersions are included. Unless explicitly stated otherwise, the term “ size distribution” means an absolute size distribution, i.e., one that includes the number concentration or count.

In most particle-counting instruments, particles pass though a sensing zone where they are measured individually; the onlyexception included is the static type of light-scattering instrument. Instruments create an electronic pulse (voltage, current, or resistance) that is proportional to a characteristic size of the particle. The instrument responses (pulse height, width, or area) are classi fi ed by magnitude and counted in each class to yield the particle size distribution. 2. Selection of Method


### Three instrument types are included: electrical sensing zoneinstruments, light-blockage instruments, and light-scattering instruments.

Select instrument consistent with expected use of the particle size analysis. Instruments vary in the particle characteristic being sensed, lower and upper size limits of detection, degree of resolution of the size distribution, particle number concentration range that can bemeasured accurately, amount of shear to which a sample is subjected before measurement, amount of sample preparation, operator skill required, and the ease with which data can be obtained and manipulated into the desired forms. See Sections 2560B.1, C.1, and D.1, and manufacturers ’ literature for information on characteristics of each type of instrumentation.

Some instruments can be set up for either continuous- fl ow or batch sampling. Others can be used only for batch analysis. For instruments usable in both modes, check that no systematicdifferences in particle size distributions occur between continuous- fl ow measurements and batch samples taken at or near the intake point for continuous- fl ow samples.

3. Sample Collection and Handling



### a. Batch samples: Use extreme care in obtaining, handling, and preparing batch samples to avoid changing total particle count and size distribution.

Choose representative times and locations for sampling. Ensure that particles are not subjected to greater physical forces during collection than in their natural setting. Collect samples from a body of water with submerged vessels to minimize turbulence and bubbleentrainment. If sampling from particular depths, use standard samplers designed for that purpose. For fl owing systems, make sure that the velocity into the opening of the sampling device is the same as that of the fl owing stream (isokinetic sampling) and that the opening * Approved by Standard Methods Committee, 2000. Joint Task Group: 20th Edition

—Desmond F. Lawler (chair), Erika E. Hargesheimer, Carrie M. Lewis, Nancy E. McTigue, Theodore S. Tanaka, John E. Tobiason, Mark R. Wiesner. 2-62 PHYSICAL & AGGREGATE PROPERTIES (2000)