Page 52 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 35

area of MBRs. The MBR process essentially has an in-line combination of a
biological wastewater treatment-activated sludge process with a membrane
process, the two stages working in tandem to treat wastewater biologically
and to separate biomass physically from the wastewater in a single step. In the
polluted effluents from industrial sources, such as petroleum refineries, plas-
tic/coke oven industries, and phenolic resin manufacturing processes,
organic chemicals (up to several grams per liter) can be removed by cells
immobilized on microporous hollow fibers forming a membrane-attached
biofilm-microporous membrane bioreactor (MMBR) for biodegradation
applications. Further, different engineering designs are available, such as sus-
pended basket or crossflow tubular MBRs for specific applications, which
may enhance overall process performance. Compared to other membrane
separations, the engineering principles underlying MBRs are mature
enough to ensure reliability. MBRs have been used to treat a wide range
of municipal and industrial wastewaters and currently are believed to be
installed at more than 1000 sites in Asia. Adequately reliable equipment
and technological support are commercially available to meet existing and
developing demand.

1.4.5 Cavitation
Although various physico-chemical and biological methods are available to
treat wastewater, many of the conventional treatment techniques employ
large quantities of chemicals for treatment. Subsequent disposal of these che-
micals poses problems in the conventional treatment methods. The cavita-
tion method is a relatively recent physico-chemical method for treating
wastewater. There are certain organic pollutants, especially in dye/pig-
ment/textile wastewaters that are considered refractory compounds—difficult
to remove/degrade by using conventional methods of chemical/biological
treatment. For such pollutants, newer techniques have to be explored, such
as cavitation, where extreme conditions generated by collapsing cavities
can break down pollutants and organic molecules. Typically, hydrodynamic
and sonochemical or acoustic cavitation are found useful in destruction of
organics. Cavitation generates strong oxidizing conditions due to production
of hydroxyl radicals. The impact of cavitation processes can be dramatically
increased by combining them with other oxidation processes employing cat-
alysts or additives. This process can work very well, especially in treating
wastewaters containing refractory pollutants and/or having unusually high
COD. Newer, specially designed devices such as the vortex diode can provide