Page 289 - Membranes for Industrial Wastewater Recovery and Re-Use

258 Membranes for lndiistrial Wastewater Recovery and Re-use

of the groundwater has also deteriorated (Table 5.12) such that the Flemish
government has forced companies in the region to severely reduce abstraction
volumes.
To maintain production and enable any future expansions requires both
conservation and reuse to be considered. Specific items adopted at the Pasfrost
site include:

0 Partial reuse of wash water for low-grade application which has decreased
the specific water use from 5 down to 3.5 m3 tonne-' of product.
0 Steam peeling instead of caustic peeling to reduce the salt concentration in
the waste water.
0 Anaerobic pretreatment and extension of aerobic treatment producing a
more stable effluent suitable for further treatment and reuse.

By reusing treated wastewater the groundwater demand has been reduced by
50%, equating to a specific water consumption of 2 m3 tonne-' of product.
Specific concerns with the requirements of a reclamation plant were the need to
handle feedwaters with highly variable organics levels, minimise operational
costs and achieve high membrane life expectancy. A core element to the design of
the reclamation facility was the ability to deliver a constant quality feed to the
advanced treatment processes.
Overall, introduction of the reuse options has reduced the groundwater
requirement to 100000 m3 y-' with 200000 m3 y-l coming from reuse of
partially-treated wastewater and 100 000 m3 y-l from the advanced water
treatment plant (Fig. 5.19). Discharge from the site is 100 000 m3 y-' of which
50% is evaporation and 50% is discharge from the treatment works.

5.9.2 Description of plant
The flow initially passes through a screen and a heat exchanger to raise the
average temperature from 20 to 30°C as a pretreatment for the anaerobic stage.
The anaerobic reactor is a 5000 m3 UASB operated at a specific loading rate of
3-6 kg COD m-3 d-l enabling a total of 30 000 kg COD to be treated per day. The
produced biogas is used for heating the incoming flow and has an equivalent
steam rating of 70 tonnes day-' based on the production of 5000-6000 m3 d-l
of biogas during high loads.

Table 5.12 Groundwater quality and guidelines for drinking water quality
Parameter Groundwater WHO guidelines
PH 8.3 6.5-8.5
S042- (mg I-') 126 400
HC03-(mg 1-') 552
C1- (mg 1-I) 550 250
Conductivity (ms cm-l) 2.6 0.25
TH (mmol 1-I) 0.3