Testb Description
Total solids (TS) The residue remaining after a wastewater sample has been evaporated and dried at a
specified temperature (103 to 105°C) Total volatile solids (TVS) Those solids that can be volatilized and burned off when the TS are ignited (500 6 50°C) Total fixed solids (TFS) The residue that remains after TS are ignited (500 6 50°C)
Total suspended solids (TSS) Portion of the TS retained on a filter (see Fig. 2–3) with a specified pore size, measured after
being dried at a specified temperature (105°C). The filter used most commonly for the determina- tion of TSS is the Whatman glass fiber filter, which has a nominal pore size of about 1.58 mm Volatile suspended solids (VSS) Those solids that can be volatilized and burned off when the TSS are ignited (500 6 50°C) Fixed suspended solids (FSS) The residue that remains after TSS are ignited (500 6 50°C)
Total dissolved solids (TDS) (TS 2 TSS)
Those soilds that pass through the filter, and are then evaporated and dried at specified temperature. It should be noted that what is measured as TDS is comprised of colloidal and dissolved solids. Colloids are typically in the size range from 0.001 to 1 mm.
Total volatile dissolved solids (VDS) Those solids that can be volatilized and burned off when the TDS are ignited (500 6 50°C) Fixed dissolved solids (FDS) The residue that remains after TDS are ignited (500 6 50°C)
Settleable solids Suspended solids, expressed as milliliters per liter, that will settle out of suspension within a
specified period of time (see Fig. 2–4)
a Adapted from Standard Methods (2012).
b With the exception of settleable solids, all solids values are expressed in mg/L.
Figure 2–4
Imhoff cone used to determine settleable solids in wastewater.
Solids that accumulate in the bottom of the cone after a 60-min settling time are reported as mL/L.
1 L 1 L 1 L
Figure 2–3
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 (Tchobanoglous and Schroeder, 1985).
Settleable solids
Imhoff
cone Sample Evaporation TS
Filter (glass fiber)
Evaporation
TSS
Muffle oven
VSS
TVS
FSS
TS
Evaporation
TDS
Muffle oven
VDS
TFS FDS
TS TSS TDS VSS FSS VDS FDS TVS TFS
=
=
=
=
=
=
=
=
= total solids suspended solids total dissolved solids volatile suspended solids fixed suspended solids volatile dissolved solids fixed dissolved solids total volatile solids total fixed solids Filtrate
in a 1-liter Imhoff cone (see Fig. 2–4) 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 wastewater to dryness and measuring the mass of the residual residue. As shown on Fig. 2–3, a filtration step is used to separate the total suspended solids (TSS) from the total dissolved solids (TDS). The apparatus used to determine TSS is shown on Fig. 2–5.
2–3 Physical Properties 75
Total Suspended Solids. Because a filter is used to separate the TSS from the TDS, the TSS test is somewhat arbitrary, depending on the pore size of the filter paper used for the test. Filters with nominal pore sizes varying from 0.45 mm to about 2.0 mm have been used for the TSS test (see Fig. 2–6). More TSS will be measured as the pore size of the filter used is reduced. Thus, it is important to note the pore size of the filter paper used when comparing reported TSS values.
It is also important to note that the TSS test itself has no fundamental significance.
The principal reasons that the test lacks a fundamental basis are
1. The measured values of TSS are dependent on the type and pore size of the filter
used in the analysis.
2. Depending on the sample size used for the determination of TSS, auto filtration,
where the suspended solids that have been intercepted by the filter also serve as a filter, can occur. Auto filtration will capture smaller particles than otherwise possible and cause an apparent increase in the measured TSS value over the actual value.
3. Depending on the characteristics of the particulate matter, small particles may be
removed by adsorption to material already retained by the filter.
4. Because the number and size distribution of the particles that comprise the measured
value is unknown, TSS is a lumped parameter.
Nevertheless, TSS test results are used routinely to assess the performance of conven- tional treatment processes and the need for effluent filtration in reuse applications. The TSS test is one of the two universally used effluent standards (along with BOD) by which the performance of treatment plants is judged for regulatory control purposes.
Total Dissolved Solids. By definition, the solids contained in the filtrate that pass through a filter with a nominal pore size of 1.2 mm or less are classified as dissolved (Standard Methods, 2012). Yet it is known that wastewater contains a high fraction of colloidal solids. The size of colloidal particles in wastewater is typically in the range of 0.01 to 1.0 mm. It should be noted that some researchers have classified the size range for colloidal particles as varying from 0.001 to 1.0 mm, others from 0.003 to 1.0 mm. The size range for colloidal particles considered in this text is from 0.01 to 1.0 mm. The number of colloidal particles in untreated wastewater and after primary sedimentation is typically in the range of 108 to 1012/mL. Because the distinction between colloidal particles and truly dissolved material has not been made routinely, it has led to confusion in the analysis of treatment plant performance and in the design of treatment processes.
Figure 2–5
Vacuum filtration apparatus used for the determination of total suspended solids. After wastewater sample has been filtered, the preweighed filter paper is placed in an aluminum dish for drying before weighing.
(a) (b)
Figure 2–6
Micrographs of two laboratory filters used for the measurement of suspended solids in wastewater: (a) polycarbonate membrane filter with a nominal pore size of 1.0 mm and (b) glass fiber filter with a nominal pore size of 1.2 mm.
Volatile and Fixed Solids. Material that can be volatilized and burned off when
ignited at 500 6 50°C is classified as volatile. In general, volatile solids (VS) are presumed to be organic matter, although some organic matter will not burn, and some inorganic solids break down at high temperatures. Fixed solids (FS) comprise the residue that remains after a sample has been ignited. Thus, TS, TSS, and TDS comprise both fixed solids and volatile solids. The ratio of the VS to FS is often used to characterize the wastewater with respect to amount of organic matter present.
Particle Size and Particle Size Measurement
As noted above, TSS is a lumped parameter. In an effort to understand more about the nature of the particles that comprise the TSS in wastewater, measurement of particle size is undertaken and an analysis of the distribution of particle sizes is conducted (Tchobano- glous, 1995). Information on particle size is of importance in assessing the effectiveness of treatment processes (e.g., secondary sedimentation, effluent filtration, and effluent disinfection). Because the effectiveness of both chlorine, ozone, and UV disinfection is dependent on particle size, the determination of particle size has become more important, especially with greater effluent reuse in the western United States.
Information on the size of the biodegradable organic particles is significant from a treatment standpoint, as the biological conversion rate of these particles is dependent on size (see discussion in Sec. 2–6, which deals with biochemical oxygen demand). Methods that have been used to determine particle size are summarized in Table 2–5. As reported in Table 2–5, the methods can be divided into two general categories: (1) methods based on observation and measurement and (2) methods based on separation and analysis tech- niques. The methods used most commonly to study and quantify the particles in wastewater
Table 2–5