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Membrane Processes for Reclamation of Municipal Wastewater 451
5.2. Description of Overall Process
An MF/RO pilot plant with the capacity of 20 m 3 /day was used in this study. The overall
pilot plant process and pilot operation had been described previously in detail (14). The RO
unit contained six elements of membranes installed in series as single stage configuration.
Operating conditions of the RO unit are shown in Table 10.11. For each RO membrane, the
pilot plant was continuously operated over 2 weeks at Bedok Water Reclamation Plant,
Singapore.
During the study, online TOC of RO permeate was monitored using a model 820 Sievers
portable TOC analyzer and online measurements of conductivity were conducted by a model
Ecomet C75.
5.3. Plant Performance
Figure 10.8 shows TOC of RE4040-FL RO permeate as a function of time over 360 h (or
15 days) in Test 1. It should be pointed out that the plant operation had been stabilized over 3
months before the online TOC measurements were conducted (14). It can be seen that the
permeate TOC fluctuated regularly between 36.2 and 65.7 ppb. Figure 10.8 also illustrates
that the peak valley of TOC appeared daily. It might be due to high and low loading of
influent to the wastewater treatment works, which subsequently produced the secondary
treated effluent with high and low TOC, respectively. Also it is well understood that the
pattern of the TOC peak valley is consistent with the daily life of human beings as the raw
sewage is from domestic sources.
Figure 10.9 shows TOC of RE4040-FE RO permeate as a function of time over 340 h (or
14 days). It can be seen that the TOC level dropped significantly over the first 48 h at
operating pressure of 70 psi. After the stabilization of plant operation, the permeate TOC over
26 h at operating pressure of 107 psi in Test 2 was in the range of 30–36 ppb. The low TOC
level of the reclaimed water does not appear to be reported previously for the application of
RO in the reclamation of municipal wastewater. In Test 3 at 70 psi, the permeate TOC over
260 h (or 11 days) fluctuated between 32 and 44 ppb, which was lower than that of RE4040-
FL membrane as shown in Fig. 10.8. The RE4040-FE RO permeate with the low TOC level
greatly benefits the special application where the reclaimed water from municipal wastewater
is to supply for the electronics industry to further produce ultrapure water.
Table 10.11
Operating conditions of the RO unit for different membranes (15)
Parameter RE4040-FL RE4040-FE
Test 1 Test 2 Test 3
Flux rate (gallon/ft 2 day) 10 15 10
Feed flow (m 3 /h) 1.7 2.3 1.7
Recovery (%) 50 55 50
Operating pressure (psi) 60 107 70