Membrane and Desalination Technologies - TCE Moodle Website

Membrane Processes for Reclamation of Municipal Wastewater 439
loaded UF elements were flushed with town water. Then, the initial performance of UF
membranes was tested with town water and the normalized flux was 330 L m 2 h at 0.1 MPa at
20 C. Before and after the trial, the membrane integrity test was performed using the pressure
decay method. The results showed the membrane integrity was good.
Trial runs on various concentrations of alum dosage at different water recoveries were
conducted. The common and variable operating conditions of the plant are given in
Tables 10.1 and 10.2, respectively. The plant was later continuously operated for 4 weeks
under the conditions showed in Test 5 of Table 10.2. Transmembrane pressure (TMP) and
normalized flux of UF membranes as a function of time were observed. Product quality and
chemical consumption were determined. An energy meter was purposely installed to monitor
the energy consumption.
3.3. Plant Performance
3.3.1. Permeate Quality of UF Membrane
Table 10.3 shows typical characteristics of the raw feed water in the study. The raw feed
water contained a wide range of suspended solids and colloidal substances. The microstrainer
was required to remove large suspended solids for protecting the UF membranes.
The UF membranes further removed smaller suspended solids and colloidal substances.
Table 10.4 shows the permeate quality of UF membrane during the study and the target
quality for RO feed (19). It can be seen that the average silt density index (SDI) and turbidity
were 1.6 and 0.13 NTU, respectively. Particle (1–15 mm) was 2 counts/mL in average. Both
fecal coliform and total coliform in the permeate were not detectable. Total bacteria were
69 cfu/mL in average. Total suspended solid (TSS) was lower than 2.5 mg/L (detectable
Table 10.1
Common operating conditions of the plant (13)
Parameter Value
Feed flow (m 3 /h) 4.9–5.0
Backwash flux (L/m 2 h) 250–300
Backwash duration (s) 30–40
Backwash frequency (time/h) 2–4
CEB interval (day) 1–3
Table 10.2
Variable operating conditions of the plant (13)
Parameter Test 1 Test 2 Test 3 Test 4 Test 5
Alum dosing concentration (mg/L as Al) 4.8 1.3 0.6 2.5 2.5
Water recovery (%) 87.5 87.5 87.5 87.5 90.1