i.e., chlorination or use of other oxidative chemicals or precipitation chemicals, to
destroy all filamentous organisms that are not protected by activated sludge flocs.
However, these methods are not very selective on microorganisms and can terminate
the whole biological activity [11].
The most important parameters of activated sludge system are HRT and the
operating temperature. These parameters need to be carefully determined to ensure
the breakdown of resistant organic substances. Additionally, separate compartment
or selector is commonly used to prevent and control filamentous growth. The
selector provides the selective growths of floc-forming organisms by providing
high F/M ratios at a controlled dissolved oxygen level. The contact time is generally
10–30 min.
The anoxic selector, which requires the presence of nitrate in the water, is often
chosen in activated sludge systems for nitrification purposes. It reduces the oxygen
requirements since nitrate-nitrogen is used as a terminal electron acceptor for the
oxidation of influent biodegradable organics and reduces the consumption of alkalinity during nitrification, by means of recovered alkalinity in the anoxic zone.
Anoxic selectors can also be quite effective in controlling filament growth [11].
In fixed-film aerobic processes such as trickling filters, the biomass grows as a
film on the surface of packaging medium and the wastewater is evenly distributed
across it. The trickling filter medium typically consists of rocks or various types of
filling materials, such as slats, or plastic materials. The wastewater is distributed over
the surface of media by a rotating arm. Rock filter diameters may range up to 60 m.
As wastewater trickles through the bed, a microbial growth establishes itself on the
surface of the stone or packing in a fixed film. The wastewater passes over the
stationary microbial population, providing contact between the microorganisms and
the organics. Oxygen is provided from the bottom to the biomass by blowing outside
air. The treated wastewater is collected under the media and directed to a sedimentation tank where a part of the liquid can be recycled to dilute the strength of the
incoming wastewater (Fig. 8.4).
Anaerobic Treatment
Anaerobic processes are commonly used for the treatment of industrial wastewaters.
Whereas aerobic processes effectively treat low-strength wastes, anaerobic processes
more effectively treat high-strength wastes. These high-strength wastes have COD
levels greater than 2,000 mg/L. Anaerobic digestion occurs in a heated reactor with
the absence of molecular oxygen that results in methane and carbon dioxide production [29]. In comparing anaerobic processes and aerobic processes, anaerobic
processes have distinct advantages including energy and chemical efficiency and
low biological sludge yield, in addition to the possibility of treating high-strength
wastewaters with a COD of 5,000 up to 40,000 mg/L, with the requirement of only a
small reactor volume [56]. The specific biomass loading of typical anaerobic processes treating soluble industrial wastewaters is approximately 1 kg COD utilized
per kg biomass-day. There is a wide range of anaerobic reactors with different
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destroy all filamentous organisms that are not protected by activated sludge flocs.
However, these methods are not very selective on microorganisms and can terminate
the whole biological activity [11].
The most important parameters of activated sludge system are HRT and the
operating temperature. These parameters need to be carefully determined to ensure
the breakdown of resistant organic substances. Additionally, separate compartment
or selector is commonly used to prevent and control filamentous growth. The
selector provides the selective growths of floc-forming organisms by providing
high F/M ratios at a controlled dissolved oxygen level. The contact time is generally
10–30 min.
The anoxic selector, which requires the presence of nitrate in the water, is often
chosen in activated sludge systems for nitrification purposes. It reduces the oxygen
requirements since nitrate-nitrogen is used as a terminal electron acceptor for the
oxidation of influent biodegradable organics and reduces the consumption of alkalinity during nitrification, by means of recovered alkalinity in the anoxic zone.
Anoxic selectors can also be quite effective in controlling filament growth [11].
In fixed-film aerobic processes such as trickling filters, the biomass grows as a
film on the surface of packaging medium and the wastewater is evenly distributed
across it. The trickling filter medium typically consists of rocks or various types of
filling materials, such as slats, or plastic materials. The wastewater is distributed over
the surface of media by a rotating arm. Rock filter diameters may range up to 60 m.
As wastewater trickles through the bed, a microbial growth establishes itself on the
surface of the stone or packing in a fixed film. The wastewater passes over the
stationary microbial population, providing contact between the microorganisms and
the organics. Oxygen is provided from the bottom to the biomass by blowing outside
air. The treated wastewater is collected under the media and directed to a sedimentation tank where a part of the liquid can be recycled to dilute the strength of the
incoming wastewater (Fig. 8.4).
Anaerobic Treatment
Anaerobic processes are commonly used for the treatment of industrial wastewaters.
Whereas aerobic processes effectively treat low-strength wastes, anaerobic processes
more effectively treat high-strength wastes. These high-strength wastes have COD
levels greater than 2,000 mg/L. Anaerobic digestion occurs in a heated reactor with
the absence of molecular oxygen that results in methane and carbon dioxide production [29]. In comparing anaerobic processes and aerobic processes, anaerobic
processes have distinct advantages including energy and chemical efficiency and
low biological sludge yield, in addition to the possibility of treating high-strength
wastewaters with a COD of 5,000 up to 40,000 mg/L, with the requirement of only a
small reactor volume [56]. The specific biomass loading of typical anaerobic processes treating soluble industrial wastewaters is approximately 1 kg COD utilized
per kg biomass-day. There is a wide range of anaerobic reactors with different
346
D. Kaya and Y.-T. Hung