Page 291 - Membranes for Industrial Wastewater Recovery and Re-Use

q Depth .

Biogas
Depth filters filters
Biogas
ade
Zm grade
Activated sludge
wastewater Screen Actrdated sludge Process water
water
Screen
UASB +
sludge sludge sludge
sludge
I UF RO
I
I Process
water

Figtire 5.20 Processflow diagram ojthe Pasjrost water recyrlingplant

Figure 5.2 1 (a) Ultrafiltrationand (b) bioreactorsat Pasjrost

COD concentration from 12000 mg 1-1 to a non-detectable level by the
treatment train (Table 5.13). Final product water quality also shows non-
detectable levels of turbidity and coliform concentrations. The recycle water
contains a lower concentration of conductivity, iron and total hardness but is
slightly higher in NH4+-N and HC03-compared to the existing groundwater.
The main operational difficulty has been in maintaining flux rates through the
UF plant throughout the year. During winter periods (vegetables and
Schorseneer) UF fluxes deteriorate to 50% of the design flow. Diagnostics of the
membrane surface reveal spots attributable to a variety of humic acids. Chemical
cleaning protocols have been changed to use enzymatic cleaners but the overall
problem remains. During the winter period the water consumption is reduced
and so it was decided to operate at reduced fluxes, which seem to ameliorate the
problem. In the summer the UF fluxes can be increased to 50-60 LMH and as a
consequence RO capacity has been increased by 40% to 30 m3 h-' without
additional investment in UF plant.
Operation during the initial phase of the project has yielded a net plant flow of
20 m3 h-l while the infrastructure is designed to produce 40 m3 h-l and so lost