Page 54 - March 2020 - WT Site

Membrane bioreactors can be used to reduce the footprint of an d) Levy costs are reduced
activated sludge sewage treatment system by removing some of
the liquid component of the mixed liquor. e) Direct use as process water is possible in various applications
f) Direct post-purification is possible via reverse osmosis for
There are two Membrane Bioreactor configurations: internal/ the removal of salts or recalcitrant organic compounds
submerged, where the membranes are immersed in and integral
to the biological reactor; and external/side stream, where g) The quality of the MBR permeate is greatly determined by
membranes are a separate unit process requiring an intermediate the quality of the influent
pumping step. The internal/submerged the membrane is installed
in either the main reactor or in separate tank. These membranes h) Dissolved substances, primarily high calcium contents and
can incorporate and online backwash system to prevent the aluminum salts can also cause damage to the membranes
membrane surface fouling; by pumping membrane infiltrate i) Maintenance cleaning with higher chemical concentration
back through the membrane. Whereas in External/side stream; and intensive chemical cleaning
the filtration components are fixed externally to the reactor. The
biomass is pumped through membrane module in series and back j) In comparison to the conventional activated sludge process
to the bioreactor. Cleaning and soaking of the membranes can be (ASP) which typically achieves 95 percent, COD removal can
undertaken in place be increased to 96 to 99 percent in MBRs
Review: 3. Trickling Filter

a) Advantages of MBRs over conventional processes include Trickling filters are advanced biological wastewater treatment
small footprint, easy retrofit and upgrade of old wastewater technologies used for efficiently treating wastewaters with high
treatment plants
to extremely high organic contamination levels. Of all biological
b) It is possible to operate Membrane Bioreactor processes at treatment systems, these can hold the most contaminant-eating
higher mixed liquor suspended solids (MLSS) concentrations microbes in the smallest area, which makes them space-saving
compared to conventional sedimentation systems, thus and energy-efficient technologies ideal for treating wastewaters
reducing the reactor volume to achieve the same loading rate with medium to very high BOD. It consists of a fixed bed of
rocks, coke, gravel, slag, polyurethane foam, sphagnum peat
c) Discharge is possible in vulnerable areas moss, ceramic over which sewage or other wastewater flows

56 Water Today - The Magazine March 2020