Water Recovery from Sewage Using Forward
Osmosis
K.Lutchmiah, K.Roest, D.J.H.Harmsen, E.R.Cornelissen and L.C.Rietveld
[email protected]
Fine Sieving
Wastewater
Reconcentration
System
FO
Retentate
Concentrated
sewage
High quality
water
BACKGROUND
The amount of fresh water per person is decreasing. Therefore interest into alternate, low cost
solutions i.e. water recovery from wastewater, is growing.
Renewable energy
Renewable
energy
Forward Osmosis (FO) has the potential to produce high quality water which can be used as
• industrial process water
• (indirect) source of potable water etc.
Digestate
Digestate
Anaerobic digestion
Dry Anaerobic digestion
Figure 1: Schematic overview of the Sewer Mining concept. FO is coupled to
i) a reconcentration system to produce high-quality water and to ii) an
anaerobic digester to convert the subsequent concentrated sewage into
renewable energy.
SEWER MINING CONCEPT
Figure 1 summarises the different processes involved in the Sewer Mining Concept. This poster
focuses primarily on the FO unit, which extracts water from sewage by means of osmosis.
AIM
• Investigate the influence of settled sewage on FO performance vs deionised water (DI)
• Investigate the fouling propensity of the FO membrane by inducing fouling.
RESULTS
The short-term experiments, which lasted 6 hours were all performed in a U-tube, lab-scale
setup (Figure 2). Figure 3 illustrates the influence of the different feed types. The feeds used
were settled sewage and DI water, and the draw solution 0.5 M NaCl. Stable FO water fluxes
were obtained. Produced values (> 4.3 LMH) with settled sewage as feed were approximately
20% lower than with DI water as feed (5.2 LMH) using 0.5 M NaCl.
Figure 2: Experimental U-tube setup.
Figure 4 demonstrates the results from the fouling test. The test attempted to induce fouling
by increasing the draw solution concentration. Fouling is evident when comparing water flux
values of a fresh membrane (virgin) with a membrane used for the full series.
5
2
Water Flux [L/m .h]
6
4
3
Results from the Scanning Electron Microscopy (SEM) of the fouled membrane, show cracks in
the support layer due to possible drying-out of the membrane (Figure 5A), while Figure 5B
confirms the thin fouling layer on the membrane. This layer could be simply rinsed off showing
that fouling was, in this case, reversible.
2
Settled Sewage-NaCl (0.5M)
1
DI-NaCl (0.5M)
0
1
2
3
4
5
6
Time [h]
Figure 3: Water flux over time with feed solutions (i) DI water [grey] and (ii)
settled sewage [black], 0.5 mol/L NaCl as draw solution (temperature
normalised to20°C; membrane orientation: active layer facing feed side).
CONCLUSION
16
FO membranes can be used in the recovery
of water from settled sewage resulting in low
fouling propensities.
Water flux (L/m2.h)
14
12
10
8
6
DI water
4
Settled Sewage: Accumulated Fouling
2
Settled Sewage: Fresh Membrane
Fouling of the membrane was found to be
reversible during short-term experiments.
0
0
1
2
3
4
5
NaCl concentration (M)
Figure 4: Water flux with feed solutions (i) DI water [grey] and (ii) settled
sewage – accumulated fouling from low to high NaCl concentrations [pink],
(iii) settled sewage – fouling per fresh membrane [open], 0.5–4.5 mol/L NaCl
as draw solution (temperature normalised to 20 WC; membrane orientationactive layer facing feed side).
Figure 4: SEM micrographs of the FO membrane surface: (A) Image of the
fabricated mesh within the membrane (magnification ×100, accelerating
voltage: 6 kV). Cracks in the surface can be observed, possibly caused by
drying out of the membrane. (B) Image of the fouled, dull layer of the
membrane (magnification ×100)
Section Sanitary Engineering
Department Water Management
Faculty of Civil Engineering and Geosciences
Delft University of Technology