Page 436 - Industrial Wastewater Treatment, Recycling and Reuse

408 Industrial Wastewater Treatment, Recycling, and Reuse

energy, due to the fact that it provides a lower level of membrane surface
shear and operates at lower permeate flux. This results in higher membrane
surface requirements.

10.3.1 Integration Philosophy of Membrane with Anaerobic
Bioreactor

The success of anaerobic wastewater treatment can be attributed to an effi-
cient uncoupling of the solids’ residence time from the hydraulic residence
time through biomass retention, which is usually accomplished through bio-
film and/or granule formation. With this strategy, high concentrations of
biocatalysts are obtained, leading to high volumetric treatment capacities
for a wide variety of wastewaters. At present, close to 80% of the full-scale
anaerobic installations are sludge bed reactors in which biomass retention is
attained by the formation of methanogenic aggregates. Granule formation is
a complex process that involves physicochemical as well as biological inter-
actions. In situations where biofilm or granule formation cannot be guaran-
teed, such as extreme salinity and high temperatures, or when complete
biomass retention must be ensured, membrane-assisted physical separation
can be used to achieve the required sludge retention. MBR technology
ensures biomass retention by the use of micro-filtration or ultra-filtration
membranes. Given that biomass is physically retained inside the reactor,
there is no risk of cell washout, and the sludge retention is not dependent
on the formation of biofilms or granules. In addition, MBRs offer the pos-
sibility of retaining specific microorganisms that, in the generally applied
upflow reactors, would wash out. MBRs also appear suitable for the treat-
ment of wastewaters with high organic suspended solids content, because
particles are confined inside the reactor, allowing their degradation. As per-
meate is free of solids or cells, water would require fewer post-treatment
steps if reusing or recycling is of interest.

10.3.2 Trends in AnMBR Research

Today the wastewater treatment discharge norms are becoming more and
more stringent, and the demand for recyclable-quality treated water is grow-
ing. In such circumstances, conventional anaerobic processes are facing lim-
itations, and growing interest in AnMBR is observed. The trend is obviously
illustrated by the number of publications on both processes, conventional
UASB and AnMBR (Figure 10.5). Starting from the early 2000s the growth