the more qualitative biological and physical determinations. The quantitative methods of analysis are either gravimetric, volumetric, or physicochemical In the physicochemical methods, properties other than mass or volume are measured. Instrumental methods of analysis such as turbidimetry, colorimetry, potentiometry, polarography, adsorptio spectrometry, fluorometry, and nuclear radiation are representative of the physicochemical analyses Details concerning the various analyses may be found in Standard Methods, the accepted reference that details the conduct of water and wastewater analyses are defined and are listed below in order of increasing leve vel must be specified Several detection limits Units of Measurement for Physical and Chemical Parameters The results of the analysis of wastewater samples are expressed in terms of physical and chemical terms of measurement. The most common units for these measurements are, for example, kg/m, %by volume or by mass), pg/L, ng/L, ug/L, mg/L, g/L, ppb, ppm, mol/L, eq/L, meq/L and so on. The concentration of trace constituents is usually expressed as micrograms per liter(ug/L)or nanograms per liter(ng/L) For dilute systems, such as those encountered in natural waters and wastewater, in which one liter of sample weighs approximately one kilogram, the units of mg/L or g/mare interchangeable with ppm. The terms"parts per billion"(ppb) and"parts per trillion(ppt)are used interchangeably with ug/L and ng/L, espectively 2-3 Physical Characteristics The most important physical characteristic of wastewater is its total solids content, which is composed of floating matter, settleable matter, colloidal matter, and matter in solution Other important physical characteristics include particle size distribution, turbidity, color, transmittance, temperature, conductivity and density, specific gravity and specific weight Odor, sometimes considered a physical factor, is discussed in the following section Solids Wastewater contains a variety of solid materials varying from rags to colloidal material. In the characterization of wastewater, coarse materials are usually removed before the sample is analyzed for solids. The various solids classifications are identified in Tab 2-3. The interrelationship between the arious solids fractions found in wastewater is illustrated graphically on Fig. 2-1. The standard test for ttleable solids consists of placing a waste water sample in a l-liter Imhoff cone and noting the volume of lids in millimeters that settle after a specified time period (1 h Evaporation Typically, about 60 percent of the suspended solids in a municipal glass fiber TS solids (ts) are obtained by TSS= total susp evaporating a sample of wastewarer IDS- total disc to dryness and measuring the mass of fitrate FSS= fixed susE of the residue. As shown on Fig 2-1, VDS- volatile dis a filtration step is used to separate rys- toted diss the total suspended solids (TSS) TFS total fixed from the total dissolved solids (TDS). Filters with nominal pore from 0. 45 um to about 2.0 um have been used for the TSs FSS Fig. 2- Interrelationships of solids found in water and wastewater In much of the water TFS the solids through the filter are called dissolved solids.2-4 the more qualitative biological and physical determinations. The quantitative methods of analysis are either gravimetric, volumetric, or physicochemical. In the physicochemical methods, properties other than mass or volume are measured. Instrumental methods of analysis such as turbidimetry, colorimetry, potentiometry, polarography, adsorption spectrometry, fluorometry, and nuclear radiation are representative of the physicochemical analyses. Details concerning the various analyses may be found in Standard Methods , the accepted reference that details the conduct of water and wastewater analyses. Regardless of the method of analysis used, the detection level must be specified Several detection limits are defined and are listed below in order of increasing level. Units of Measurement for Physical and Chemical Parameters The results of the analysis of wastewater samples are expressed in terms of physical and chemical terms of measurement. The most common units for these measurements are, for example, kg/m3 ,%(by volume or by mass), pg/L, ng/L, µg/L, mg/L, g/L, ppb, ppm, mol/L, eq/L, meq/L and so on. The concentration of trace constituents is usually expressed as micrograms per liter (µg/L) or nanograms per liter (ng/L). For dilute systems, such as those encountered in natural waters and wastewater, in which one liter of sample weighs approximately one kilogram, the units of mg/L or g/m3 are interchangeable with ppm. The terms "parts per billion" (ppb) and "parts per trillion"(ppt) are used interchangeably with µg/L and ng/L, respectively. 2-3 Physical Characteristics The most important physical characteristic of wastewater is its total solids content, which is composed of floating matter, settleable matter, colloidal matter, and matter in solution. Other important physical characteristics include particle size distribution, turbidity, color, transmittance, temperature, conductivity, and density, specific gravity and specific weight. Odor, sometimes considered a physical factor, is discussed in the following section. Solids Wastewater contains a variety of solid materials varying from rags to colloidal material. In the characterization of wastewater, coarse materials are usually removed before the sample is analyzed for solids. The various solids classifications are identified in Tab 2-3. The interrelationship between the various solids fractions found in wastewater is illustrated graphically on Fig. 2-1. The standard test for settleable solids consists of placing a wastewater sample in a 1-liter Imhoff cone and noting the volume of solids in millimeters that settle after a specified time period (1 h). Typically, about 60 percent of the suspended solids in a municipal wastewater are settleable. Total solids (TS) are obtained by evaporating a sample of wastewarer to dryness and measuring the mass of the residue. As shown on Fig. 2-1, a filtration step is used to separate the total suspended solids (TSS) from the total dissolved solids (TDS). Filters with nominal pore sizes varying from 0.45 µm to about 2.0 µm have been used for the TSS test (see Fig. 2-2). Fig. 2-1 Interrelationships of solids found in water and wastewater. In much of the water quality literature, the solids passing through the filter are called dissolved solids