Page 290 - Membranes for Industrial Wastewater Recovery and Re-Use

Case studies 259

Figure 5.19 Mass balance aroirrld Pasfrost reclamation facility (data in 171 year-’)

The flow is then passed to a 11 000 m3 activated sludge plant operated at a
specific loading rate of 0.1 kg COD kg VSS-l day-’ to polish and re-aerate the
flow. After sedimentation the effluent is treated in two serial steps by
ASTRASAND”’ up flow monomedia continuous depth filters. The first set of filters
act as a roughing stage and comprise two 5 m2 filter beds operating at a
hydraulic filtration velocity of 10 m3 m-2 h-l. The second stage incorporates
a polymer dose to help flocculate and capture the remaining solids as they pass
through two 10 m’ filters.
Flow is either directly pumped after chlorination for second-grade operations
such as machine washing and cooling or is pumped to the membrane filtration
treatment plant. The first membrane stage is a semi dead-end hollow fibre
ultrafiltration membrane plant supplied by Norit X-flow designed to deliver an
overall flow of 40 m3 h-’ (Fig. 5.21). The hydrophilic membranes are
manufactured out of PESJPVP blend and have a pore size rating of 50 kDa. The
membranes operate over a pressure range of 0.3 to 1 bar which delivers a mean
flux of 45 LMH. Cleaning of the membranes occurs by a periodic backflush of
permeate and a regular chemical clean.
The final stage of treatment is a two-stage reverse osmosis plant containing
spiral-wound neutrally-charged polyamide LFCl membranes supplied by
Hydraunautics. The plant is designed to deliver a net production of 20 m3 h-l at
a recovery of 70%. The membranes operate over a pressure range of 8-10 bar,
delivering a mean flux of 30 LMH. As an extra precaution the permeate is passed
through a UV plant to ensure the water is sterile. The final effluent is then mixed
with the ground water and pumped into the production process. RO concentrate
is discharged with the excess flow.

5.9.3 Performance
The plant has been operated since mid-2000 and has suffered no overall
problems with effluent quality. Incoming wastewater is ultimately reduced in