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Membrane Processes for Reclamation of Municipal Wastewater 459
expected TDS concentration in permeate at 22 and 25.4 L/m 2 h would be 1/1.3 and 1/1.5 times
that at 17 L/m 2 h, respectively. As a result, TDS concentration in the permeate at 22 and 25.4
L/m 2 h compared to that at 17 L/m 2 h would be reduced by 23 and 33%, respectively. On the
other hand, based on the measured TDS results as shown in Table 10.5, measured the
reduction of TDS in the permeate at 22 and 25.4 L/m 2 h compared to that at 17 L/m 2 h was
calculated as 25 and 30%, respectively, which matched the expectation. TDS rejections of the
RO system at 17, 22, and 25.4 L/m 2 h can be calculated as 98.6, 98.7, and 98.5%, respectively.
6.3.4. Comparison of the MBR-RO Process to the ASP-MF-RO Process
In order to compare the new MBR-RO process with the ASP-MF-RO process, an MF-RO
pilot was operated with the secondary treated effluent that was from the conventional ASP
during 10–15 September. 0.1 mm MF membrane (PVDF hollow fiber) and the same RO
membrane were used. The operating conditions of the RO pilot remained the same as that in
the MBR-RO process. Analytical results of MBR product and MF permeate are given in
Table 10.17. The results show that NH4 N; NO3 , TOC, and pH of the MBR product were
lower than that of the MF permeate, which was in agreement with previous studies (38, 45). It
could be attributed to better performance of MBR than ASP on the reduction of the
biodegradable components. The lower concentration of NO3 in the MBR effluent suggested
that the MBR process included a greater degree of denitrification than the ASP. It was due to
the much higher mixed liquor suspended solids (MLSS) concentration and anoxic volume
ratio in the MBR than in the ASP. It should be pointed out that the better performance of the
MBR product than the MF permeate was due to differences in the biological treatment
efficiency of the MBR process as opposed to the physical separation process.
Figure 10.14 shows the online TOC of both RO permeates at the RO pilot. TOC level of the
RO permeate from the ASP-MF-RO process fluctuated in the range of 33–53 ppb while the
TOC level from the MBR-RO process during 16–22 September was in the range of 24–33
ppb, which was similar to the TOC level in May–June. The results showed that TOC level of
RO permeate from the new MBR-RO process was not only lower, but also less fluctuated than
that from the ASP-MF-RO process. The lower TOC level for the MBR-RO permeate was due
to the lower TOC of RO feed (MBR product) in the MBR-RO process than that in the ASP-
MF-RO process as shown in Table 10.17, i.e., because of the higher TOC removal efficiency
of the MBR process.
Three samples for each stream of RO feeds and permeates in the ASP-MF-RO and the
MBR-RO processes were analyzed. The ranges of RO feeds, permeates, and rejections are
Table 10.17
Comparison of quality of MBR product and MF permeate (33)
Parameter MBR product MF permeate
NH4–N (mg/L) 0.05–0.62 0.97–2.57
NO3 (mg/L) 17.6–22.8 25.2–42.2
TOC (mg/L) 4.9–5.1 6.8–6.9
pH 6.2–6.4 6.7–6.8