102 ENVIRONMENTAL ENGINEERING
A BDFigure 5-10, Millipore filter apparatus for coliform measurement. The procedure is
illustrated in the sequence of photos starting at top left: (A) Millipore filter is put on
filter support; (B) funnel is replaced; (C) measured sample is poured into funnel; (D)
suction is applied using laboratory vacuum; (E) suction is released and filter removed;
(F) filter is centered on growth medium in Petri dish; (G) Petri dish is incubated at
35°C for 24 h; (H) coliform colonies are counted using a microscope.
wastewater because some pathogens are more resistant to disinfection methods than
coliforms.)
HEAVY METALSHeavy metals such as arsenic, copper, and mercury can harm aquatic organisms, or
bioaccumulate in the food chain, even if the metal concentration in water is relatively
low. Consequently, the method of measuring metals in water must be very sensitive.
There are a large variety of methods available to measure metals in water samples,
and the choice of method often depends on the desired sensitivity as well as cost.
Heavy metals are usually measured using flame, electrothermal (graphite furnace), or