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The MBR Book: Principles and Applications of Membrane

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Case studies 225<br />

to be treated to a 10/10 (BOD/TSS) st<strong>and</strong>ard or better. <strong>The</strong> flow rate to be treated was<br />

a maximum <strong>of</strong> 0.012 MLD. Given the very low flow <strong>and</strong> relatively tight discharge<br />

consent, an <strong>MBR</strong> plant was <strong>of</strong>fered as the most attractive process option based on the<br />

comparatively low capital <strong>and</strong> whole life costs <strong>of</strong> the <strong>MBR</strong> over that <strong>of</strong> conventional<br />

activated sludge treatment with tertiary treatment polishing. Colloide Engineering<br />

Systems was commissioned to provide the plant by the developer on a design <strong>and</strong><br />

build contract. <strong>The</strong> plant was installed <strong>and</strong> commissioned in August 2004.<br />

<strong>The</strong> reactor comprises a pre-existing elliptically shaped concrete tank divided into<br />

two sections, each <strong>of</strong> 2 m 3 volume (Fig. 5.13a). <strong>The</strong> first compartment is used as an<br />

inlet section for settlement <strong>of</strong> gross solids; settlement comprises the only pretreatment<br />

used at this site. <strong>The</strong> wastewater is allowed to flow to the second chamber via an interconnecting<br />

pipe fitted near the top <strong>of</strong> the tank. <strong>The</strong> tank is installed below ground,<br />

with its top at ground level. <strong>The</strong> membrane assembly comprises two 10 m 2 Sub Snake<br />

modules, providing a total membrane area <strong>of</strong> 20 m 2 . <strong>The</strong> modules are mounted in a<br />

PVC frame which also holds a tubular fine bubble air diffuser, positioned directly<br />

below each membrane module. This complete membrane assembly is immersed in<br />

the second chamber <strong>of</strong> the tank. A float switch is also mounted in this chamber to<br />

control the water levels. A control kiosk is positioned above ground adjacent to the<br />

wastewater treatment tank with a duct running between the tank <strong>and</strong> the kiosk.<br />

<strong>The</strong> kiosk houses a 0.2 kW air blower delivering air to the diffusers, the permeate<br />

suction pump discharging treated water <strong>and</strong> all process control equipment.<br />

<strong>The</strong> system is operated at a TMP <strong>of</strong> 0.4 bar (4 m head), which provides a flux <strong>of</strong><br />

20–30 LMH. A filtration cycle <strong>of</strong> 6 min on/2 min relaxation is employed, with a cleaning<br />

cycle time estimated as being 6–12 months, using 200 ppm sodium hypochlorite.<br />

No coarse bubble aeration is used, fine bubble aeration being provided at a rate <strong>of</strong><br />

10 m 3 /h to the total membrane assembly, yielding a SAD p <strong>of</strong> 20 m 3 air per m 3 .<br />

<strong>The</strong> plant has generally operated very well. <strong>The</strong> hydraulics <strong>of</strong> the system have<br />

never been an issue with this plant, <strong>and</strong> the membranes remove practically all<br />

Control<br />

panel<br />

Power<br />

supply<br />

Effluent in<br />

Air blower<br />

Treated<br />

effluent out<br />

Treated effluent<br />

pump<br />

(a) (b)<br />

Figure 5.13 <strong>The</strong> Fisherman Cottages <strong>MBR</strong>: (a) schematic <strong>and</strong> (b) in situ. <strong>The</strong> membranes are in the<br />

second <strong>of</strong> the two underground concrete tanks in the picture, only the kiosk housing the control equipment<br />

is mounted above ground

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