1. General Discussion
Particles are ubiquitous in natural waters and in water and wastewater treatment streams. Particle counting and size distribution analysis 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 determining process efficiency. The particle size distribution methods included herein depend on electronic measurement devices because manual methods are likely to be too slow for routine analysis. However, when particle size analysis includes a size distribution of large (>500-μm) aggregates, use direct microscopic counting and sizing. The principles of various 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 through a sensing zone where they are measured individually; the only exception included is the static light-scattering instrument. Instruments create an electronic pulse (voltage, current, or resistance) that is proportional to a characteristic particle size. The instrument responses (pulse height, width, or area) are classified by magnitude and counted in each class to yield the particle size distribution.