An innovative greywater treatment system for urban areas ... - SuSanA

2.1.5 TREATMENT TECHNOLOGIES
Generally there are different treatment technologies for greywater available. A
compendium of common biological wastewater treatment methods is listed in Table 4, based
on the characteristic features.
Table 4: Comparison of biological wastewater treatment processes based on distinctive features;
(Heinrich & Heinrich, 2008)
Treatment
method
Criteria
Cleaning
capacity
Space
requirements
Level of
technology and
automation
Operating and
maintenance
expense
Trickling filter
good -
satisfactory
Biological
contactor
good
good -
satisfactory
good -
satisfactory
This study is specifically limited to the MBR technology and cannot explain all different
treatment technologies (for more detailed information see introduction, hypothesis 1-3). It is
not possible to go into particulars and describe all advantages and disadvantages of
greywater treatment plants. But a short overview of membrane bioreactors strengths and
weaknesses is given.
The MBR technique in Figure 5 with submerged membrane modules MBR represents a
combination of activated sludge process and membrane filtration under low pressure
conditions. Thereby the membrane filtration (ultrafiltration) replaces the conventional
secondary clarification in the settling tank, the sand filtration and the disinfection. In activated
sludge the bacteria degrade the organic contaminants from the greywater under aerobic
conditions. And the permeate is filtered with a slight negative pressure through the
membranes (Paris, 2009b).
Figure 5: Technical principle of membrane bioreactor; (Bérubé, 2010; modified)
good very good very good
low low low very low low very low very low
enineered engineered
Aerated fixed
bed reactor
strongly
engineered
Fluidised bed
strongly
engineered
Activated
sludge
treatment
strongly
engineered
Sequencing
batch reactor
(SBR)
strongly
engineered and
automated
Membrane
bioreactor
(MBR)
strongly
engineered and
automated
high low fairly high low very high low very high
In contrast to the conventional activated sludge process, in a membrane bioreactor the
secondary clarification is substituted by a membrane filtration. In general the MBR
technology achieves higher removal efficiency than other possible methods such as SBR,
biological contractors or the conventional activated sludge treatment. For reuse applications
it provides further advantages, since the outlet of a MBR plant is considered as disinfected.
By the use of ultrafiltration membranes, an effective retention of bacteria is ensured, because
of the pore diameter of less than 0.2 µm and the permeate is free from suspended solids.
The disadvantage of the MBR process lies in the two- to threefold higher energy and higher
maintenance costs in comparison to SBR. The higher energy consumption results from the
intensive ventilation needs for the membrane surface cleaning air, in order to prevent
blockage of the membrane. (Cornel & Wagner, 2009)
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