of filter media used for the anaerobic carbonaceous oxidation of organic matter in
wastewater. The wastewater flows upward through the column, contacting the media
on which anaerobic bacteria grow and are retained. Because the bacteria are retained
on the media and not significantly washed off in the effluent, mean cell residence
times on the order of 100 d can be obtained. Anaerobic filtering appears to be a
viable process for the pretreatment of high-temperature and high-strength industrial
wastes. It achieves high carbonaceous removal at relatively low operating cost and
low sludge production compared to aerobic biological systems. Besides, it also
produces methane as a useable end product according to Eq. (3.25).
The emphasis of this chapter is on the principles of well-established aerobic
attached-growth systems and the design of trickling filters. The design of rotating
biological contactors, anaerobic filters, and activated biofilters is presented in detail
elsewhere.
4.3 Microbiology and Ecology
A conventional microbial slime system is designed to contain an air-renewable
surface to which a wastewater stream containing organic substrate and minerals is
applied. Microorganisms can metabolize the substrate in wastewater with net production of energy for growth or sufficient energy to maintain the existing population.
Although the system is classed as an aerobic treatment device, it is not truly aerobic,
but rather must be considered as facultative because the great majority of microorganisms in the system are facultative bacteria, such as Pseudomonas, Alcaligenes,
Flavobacterium, Micrococcus, and so on, which live aerobically as long as dissolved
oxygen is present and anaerobically when the oxygen is almost depleted. Aerobic
bacteria, such as Bacillus, are found in the upper, aerobic slime surfaces [92]. When
an anoxic or anaerobic zone is formed in a thick slime layer, the obligate anaerobe,
such as Desulfovibrio, and some other sulfur-reducing bacteria have been isolated
from the slime-medium interface [93]. Under such circumstances the microbial slime
system can develop odors, and conceivably sloughing can occur as the result of gas
generation in the interior slimes.
Fungi are aerobic microorganisms living in the aerobic zone of the slime and also
decomposing the organic substrate in the wastewater. The contribution of fungi is
significant only under low pH conditions or with unusual industrial effluents because
the fungi cannot compete successfully with the bacteria for their food under normal
environmental conditions.
Algae growing on the surface of a microbial slime system, such as trickling filter,
are usually an inconsequential element of the microorganism’s population, limited to
illuminated surfaces. Algal microorganisms on a slime system are clearly tolerant of
organic substances and high levels of carbon dioxide. Although algae add oxygen to
the wastewater, they have been charged with responsibility for bed clogging and are
considered to be troublesome from an operational standpoint [95].
3 Biological Processes
115
wastewater. The wastewater flows upward through the column, contacting the media
on which anaerobic bacteria grow and are retained. Because the bacteria are retained
on the media and not significantly washed off in the effluent, mean cell residence
times on the order of 100 d can be obtained. Anaerobic filtering appears to be a
viable process for the pretreatment of high-temperature and high-strength industrial
wastes. It achieves high carbonaceous removal at relatively low operating cost and
low sludge production compared to aerobic biological systems. Besides, it also
produces methane as a useable end product according to Eq. (3.25).
The emphasis of this chapter is on the principles of well-established aerobic
attached-growth systems and the design of trickling filters. The design of rotating
biological contactors, anaerobic filters, and activated biofilters is presented in detail
elsewhere.
4.3 Microbiology and Ecology
A conventional microbial slime system is designed to contain an air-renewable
surface to which a wastewater stream containing organic substrate and minerals is
applied. Microorganisms can metabolize the substrate in wastewater with net production of energy for growth or sufficient energy to maintain the existing population.
Although the system is classed as an aerobic treatment device, it is not truly aerobic,
but rather must be considered as facultative because the great majority of microorganisms in the system are facultative bacteria, such as Pseudomonas, Alcaligenes,
Flavobacterium, Micrococcus, and so on, which live aerobically as long as dissolved
oxygen is present and anaerobically when the oxygen is almost depleted. Aerobic
bacteria, such as Bacillus, are found in the upper, aerobic slime surfaces [92]. When
an anoxic or anaerobic zone is formed in a thick slime layer, the obligate anaerobe,
such as Desulfovibrio, and some other sulfur-reducing bacteria have been isolated
from the slime-medium interface [93]. Under such circumstances the microbial slime
system can develop odors, and conceivably sloughing can occur as the result of gas
generation in the interior slimes.
Fungi are aerobic microorganisms living in the aerobic zone of the slime and also
decomposing the organic substrate in the wastewater. The contribution of fungi is
significant only under low pH conditions or with unusual industrial effluents because
the fungi cannot compete successfully with the bacteria for their food under normal
environmental conditions.
Algae growing on the surface of a microbial slime system, such as trickling filter,
are usually an inconsequential element of the microorganism’s population, limited to
illuminated surfaces. Algal microorganisms on a slime system are clearly tolerant of
organic substances and high levels of carbon dioxide. Although algae add oxygen to
the wastewater, they have been charged with responsibility for bed clogging and are
considered to be troublesome from an operational standpoint [95].
3 Biological Processes
115