Geoscience Reference
In-Depth Information
matter that is collected and passes through sewers. This includes both solid and liquid con-
taminants, originating from human wastes as well as surface water runoff.
To understand the nature of the fluorescence spectra of treated and untreated wastewa-
ters, it is important first to consider the composition of sewage and wastewaters. Owing to
the complexities associated with their origin, wastewater composition varies enormously
and the exact composition of a particular wastewater sample is dependent upon a num-
ber of key factors, such as geography and the nature of the inputs entering the system.
Inputs can exhibit both physical and aggregate properties (e.g., suspended particulates).
All wastewaters contain some metal ions, such as aluminium, copper and iron at varying
concentrations (µg L
-1
to mg L
-1
) as well as inorganic nonmetallic constituents (e.g., chlo-
rine, phosphate, and nitrate ions). Aggregate organic constituents including humic acid and
fulvic acid, tannins, lignin-related material and a variety of surfactants are also present.
Moreover disinfection by-products and pesticides are always present to some degree. Many
wastewaters have a complex microbiota including bacteria and viruses, as well as plankton
and algae.
Crude sewage is composed of a heterogeneous mixture of compounds including fulvic
acids, proteins, carbohydrates, and lipids (with varying contributions from organic sur-
factants), nucleic acids, and volatile fatty acids (Ahmad and Reynolds,
1995
). It is a mix-
ture of domestic waste, industrial discharges, and the domestic elements from industrial
premises such as kitchen and toilet wastes, in addition to surface runoff and storm flow.
Composition of domestic sewage varies depending on the age and type of sewerage system
in the catchment (separate or combined), time of day (Reynolds and Ahmad,
1997
), pre-
vailing and prior weather conditions, and type of incoming sewer (gravity or pumped). This
complicated matrix is best summarized by Eaton et al. (
2005
) in the latest (21st) edition of
Standard Methods for the Examination of Water and Wastewaters
.
The complex composition of wastewaters implies that the observed fluorescence prop-
erties are a manifestation of innumerable types of fluorophores, including humic and fulvic
acids and lignin-derived substances. In addition to these fluorophores there are variable
amounts of steroids, phenols, nonvolatile acids, oils, and trace quantities of surface-active
agents (Waggot and Butcher,
1976
). Therefore, the spectral shape of the fluorescence spec-
tra obtained from sewage and wastewater samples will be a composite of the overlap-
ping contributions from a variety of these fluorophores and devoid of any sharp features.
The interpretation of fluorescence spectra from wastewater samples is further complicated
by variations in chemical and physical parameters that are known to affect fluorescence,
namely pH, metal ion content, temperature, and suspended solids (Reynolds and Ahmad
1995a
). This latter point is important as it is widely accepted that the fluorescence spectral
properties observed at any one point in time, and from a particular site, are “quenched.”
Given the diverse nature of wastewater composition the direct comparison of fluorescence
intensities of samples from different locations is problematic.
Up until the mid-1990s the fluorescence properties of wastewaters and sewage wastes
were poorly understood. Bari and Farooq (1984) first reported the use of fluorescence in
their investigation of the treatment efficiency of potassium ferrate and ozone, in various
