Page 61 - Industrial Wastewater Treatment, Recycling and Reuse

44 Industrial Wastewater Treatment, Recycling, and Reuse

Biomass recycling (external separation)
5. Sedimentation by chemical or physical separation
– Anaerobic contact process (flocculation/lamella separator)
– Centrifugation
6. Flotation
The scale-up of anaerobic wastewater treatment has not been studied in a
systematic way. Adequate information on scale-up and designing of anaer-
obic reactors with integrated provision for biomass retention (e.g., UASB
reactors, fixed-bed and fluidized-bed reactors) is not available.

1.4.8.3 Biological Treatment: Combination of Aerobic and Anaerobic
Operations
Aerobic treatment is more suitable for low-strength wastewaters, while
anaerobic treatment is more suitable for high-strength wastewaters. There
are a number of advantages and disadvantages associated with each of these
processes that are well documented. In order to maximize the impact, many
variations in the form of combined operations involving both aerobic and
anaerobic treatments exist. One variation includes sequencing of the two
methods, recycling of sludge, and optimizing the benefits of both the oper-
ations, resulting in better-treated water quality along with reduced sludge
generation. One such scheme is schematically shown in Figure 1.17.Itis
to be noted that such sequencing can be highly useful in cases where one
fraction of the wastewater can only be aerobically degraded and the other
only anaerobically degraded. A sequential operation can also help in substan-
tial nitrogen removal in the process. It can also result in a reduced odor prob-
lem. Some designs suggest combination of anaerobic+aerobic or anaerobic
+aerobic+anaerobic for further improved efficiency. A typical commercial
example of such a combination of processes is distillery wastewater treat-
ment, which is conventionally done using an anaerobic process for gener-
ation of biogas followed by aerobic treatment for meeting wastewater
standards, utilizing high-strength wastewaters for anaerobic treatment fol-
lowed by low-strength wastewaters for aerobic processes (Pant and
Adholeya, 2007).
1.4.9 Hybrid Separations

The chemical industry can be conveniently defined as a combination of
reaction and separation processes. Technologies for process improvement
should involve improvement in any or both of these operations, either in
isolation or in the form of process integration. Thus, new research is needed