The protozoa are the predominant small animals with all forms from the
Phytomastigophora to Suctoria. The free-swimming ciliates predominate at the
slime surface, while the stalked ciliates predominate in the lower regions. The
primary function of protozoa is not to stabilize the waste, but to control the bacterial
population in the system.
Higher animals including worms, snails, and insect larvae feed on the lower forms
of microorganisms in the microbial slime system and live in the upper aerobic areas.
As a result, these higher animals can help to keep the bacterial population in a state of
high growth or rapid food utilization. Filter flies are nuisance organisms in the
trickling filters. Much of the early study of trickling filter populations was aimed
at the control of these nuisance organisms by flooding, chlorination, and the use of
various pesticides.
A comprehensive description of the organisms found in trickling filters has been
presented by Cooke [94], whose listing of various organisms can be found from
Ref. (103).
Trickling filters and similar microbial slime systems are short-term retention
devices that should not be expected to act as effective reduction devices for
S. typhosa, S. paratyphi, and M. tuberculosis. This is true also of pathogenic
protozoa, such as Entamoeba histolytica [96].
When loaded lightly with carbonaceous substances, the trickling filter does some
nitrification because of the presence of Nitrosomonas and Nitrobacter. However,
when heavily loaded with carbonaceous matter, nitrification in a trickling filter or
similar system may be absent or nominal.
5 Theories and Mechanisms
5.1 Transfer of Oxygen in Slime Layer and Liquid Film
The relationships of the supporting medium, the biological slime film, the waste
liquid, and the atmosphere, as illustrated in Fig. 3.12, have challenged the kinetic and
mathematical skill of environmental engineers for many years. It was generally
believed [36, 103] that the slime layer had an aerobic zone and an anaerobic zone,
defined by the depth of penetration of oxygen in the slime layer. Further studies
[72, 73] have reported that the biological slime film does not always consist of an
aerobic layer and anaerobic layer. With dilute substrate, the respiration was found to
be substrate-limited, and high concentrations of oxygen were found throughout the
slime mass. More concentrated substrates increased oxygen utilization; however,
oxygen concentrations simply approached zero in the depth of the slime but were
still above zero. A new term “anoxic” has been used by many environmental
engineers to define an environment in which the dissolved oxygen concentration
ranges from 0 to about 1 mg/L. Accordingly it is believed that there would only be an
aerobic zone in the slime layer when the substrate concentration is low and there
could be an aerobic zone and an anoxic zone in the slime layer when the substrate
116
L. K. Wang et al.
Phytomastigophora to Suctoria. The free-swimming ciliates predominate at the
slime surface, while the stalked ciliates predominate in the lower regions. The
primary function of protozoa is not to stabilize the waste, but to control the bacterial
population in the system.
Higher animals including worms, snails, and insect larvae feed on the lower forms
of microorganisms in the microbial slime system and live in the upper aerobic areas.
As a result, these higher animals can help to keep the bacterial population in a state of
high growth or rapid food utilization. Filter flies are nuisance organisms in the
trickling filters. Much of the early study of trickling filter populations was aimed
at the control of these nuisance organisms by flooding, chlorination, and the use of
various pesticides.
A comprehensive description of the organisms found in trickling filters has been
presented by Cooke [94], whose listing of various organisms can be found from
Ref. (103).
Trickling filters and similar microbial slime systems are short-term retention
devices that should not be expected to act as effective reduction devices for
S. typhosa, S. paratyphi, and M. tuberculosis. This is true also of pathogenic
protozoa, such as Entamoeba histolytica [96].
When loaded lightly with carbonaceous substances, the trickling filter does some
nitrification because of the presence of Nitrosomonas and Nitrobacter. However,
when heavily loaded with carbonaceous matter, nitrification in a trickling filter or
similar system may be absent or nominal.
5 Theories and Mechanisms
5.1 Transfer of Oxygen in Slime Layer and Liquid Film
The relationships of the supporting medium, the biological slime film, the waste
liquid, and the atmosphere, as illustrated in Fig. 3.12, have challenged the kinetic and
mathematical skill of environmental engineers for many years. It was generally
believed [36, 103] that the slime layer had an aerobic zone and an anaerobic zone,
defined by the depth of penetration of oxygen in the slime layer. Further studies
[72, 73] have reported that the biological slime film does not always consist of an
aerobic layer and anaerobic layer. With dilute substrate, the respiration was found to
be substrate-limited, and high concentrations of oxygen were found throughout the
slime mass. More concentrated substrates increased oxygen utilization; however,
oxygen concentrations simply approached zero in the depth of the slime but were
still above zero. A new term “anoxic” has been used by many environmental
engineers to define an environment in which the dissolved oxygen concentration
ranges from 0 to about 1 mg/L. Accordingly it is believed that there would only be an
aerobic zone in the slime layer when the substrate concentration is low and there
could be an aerobic zone and an anoxic zone in the slime layer when the substrate
116
L. K. Wang et al.