04.02.2013 Views

The MBR Book: Principles and Applications of Membrane

The MBR Book: Principles and Applications of Membrane

The MBR Book: Principles and Applications of Membrane

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Case studies 219<br />

In this UNR configuration, the <strong>MBR</strong>s are placed downstream <strong>of</strong> sequential<br />

anoxic (AX) <strong>and</strong> anoxic/anaerobic (AX/AN) basins, converted from existing clarifiers,<br />

which promote denitrification <strong>and</strong> enhanced biological phosphate removal<br />

(EBPR) as well as acting as equalisation chambers. <strong>The</strong> anoxic treatment is preceded<br />

by screening, originally a 3 mm-step screen which was subsequently replaced with a<br />

3.2 mm centre flow b<strong>and</strong> screen, followed by degritting in an aerated grit chamber.<br />

<strong>The</strong> aerobic part <strong>of</strong> the UNR process is operated at a low dissolved oxygen (DO)<br />

concentration using the SymBio ® process to promote SNdN. <strong>The</strong> SymBio ® zone is fitted<br />

with Sanitaire fine bubble aeration equipment <strong>and</strong> is fed air at a controlled rate<br />

based on the measured DO <strong>and</strong> biological potential activity (BPA) – a parameter based<br />

on the level <strong>of</strong> the energy transfer co-enzyme nictotinamide adenine dinucleotide<br />

hydrogenase(NADH). Submersible pumps continuously recycle mixed liquor to the<br />

aerated reactors, which are partitioned into <strong>MBR</strong>s <strong>and</strong> SymBio ® zones, at roughly<br />

four times design flow, that is 9.1 MLD. <strong>The</strong> retained sludge is returned to the anoxic<br />

basin as thickened sludge to complete an internal recycle loop for denitrification. To<br />

control sludge age, mixed liquor is periodically wasted from the system <strong>and</strong> pressed<br />

before disposal <strong>and</strong> the filtrate is returned to the head <strong>of</strong> the plant for treatment. <strong>The</strong><br />

process schematic is shown in Fig. 5.8.<br />

Process operation <strong>and</strong> performance <strong>The</strong> <strong>MBR</strong> plant controls include relaxation. <strong>The</strong><br />

supervisory control <strong>and</strong> data acquisitions (SCADA) system allows the operator to<br />

adjust the relax frequency <strong>and</strong> duration. Typically, the system is set to relax for<br />

1–2 min out <strong>of</strong> each 10–20 min filtration cycle. <strong>Membrane</strong> performance is optimised<br />

by automatically matching permeate flow to hydraulic dem<strong>and</strong> while minimising<br />

changes in flux. Hydraulic loading rate is estimated from the liquid level in<br />

the AN/AX basin, which then determines the mode <strong>of</strong> operation <strong>of</strong> the <strong>MBR</strong>, which<br />

can be anything from zero to peak flow. Using the real-time NADH <strong>and</strong> DO signals, the<br />

SymBio ® process controller automatically adjusts the speed <strong>of</strong> a dedicated blower to<br />

keep the MLSS (predominantly between 10 <strong>and</strong> 22 g/L) DO concentration between<br />

Influent<br />

Washed<br />

compacted<br />

screenings<br />

Irrigation<br />

or pond<br />

Fine screening<br />

1/8�<br />

Grit<br />

UV<br />

Grit<br />

removal<br />

Permeate<br />

AX<br />

basin<br />

Internal recycle<br />

Figure 5.8 Running Springs plant, schematic<br />

<strong>MBR</strong>1<br />

symBio1<br />

<strong>MBR</strong>2<br />

symBio2<br />

AN/AX<br />

basin<br />

P

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!