Page 103 - Membranes for Industrial Wastewater Recovery and Re-Use

lndustriul waters 8 3

Typically, when reclaimed water is considered as a water source for cooling
water, alternative sources such as surface water, groundwater, estuarine, or
seawater may also be available locally. Thus the incentives for using reclaimed
water are specific to the situation. When reclaimed water is used in lieu of surface
or groundwater, the higher quality water sources can be preserved for other
applications, such as drinking water. On the other hand, when reclaimed water
is used in lieu of estuarine or seawater the impetus is usually related to discharge
limitations.
Depending on the water source, water quality can vary seasonally.
Groundwater tends to have fairly consistent characteristics, whereas the quality
of surface water, estuarine water, seawater, and reclaimed water can be
influenced by patterns of rainfall, runoff and evaporation, leading to significant
seasonal variations in oxygen demand and suspended material (Fig. 3.5),
nutrient levels (Fig. 3.6) and chloride (Fig. 3.7). Although water quality is
source specific, the variation in wastewater characteristics and treatment
alternatives means that similar trends arise with all reclaimed water sources.
Levels of dissolved minerals associated with estuarine water are shown for
sodium and chloride in Fig. 3.8 and for calcium, magnesium, potassium, and
sulphate in Fig. 3.9. Dissolved solids levels in estuarine waters are almost two
orders of magnitude higher and sulphate and magnesium levels one order of
magnitude higher than those levels associated with freshwater or reclaimed
water. Typically, the mineral content of seawater can be two- to three-fold
higher than that associated with estuarine waters. These water quality
characteristics influence the extent of treatment required to allow for use of
recirculating systems.
Another characteristic of reclaimed water that is different from fresh or
saline water sources is the potential presence of a disinfectant residual.
Reclaimed water is treated to meet requirements pertaining to microbiological
safety. As such, disinfection is a key component of the treatment system. When
chlorine is used for this duty, residual chlorine is usually present in the reclaimed

OJ I
Jan-01 Mar-01 May-01 Jul-01 SepOl Nov-01
C-BOD5 .---. . . TSS
Figure 3.5 Seasonal iuriutions in five-duy carbonaceous biocliernicul oxygen deniand (C-BOD5) and
suspendedsolids (TSS)for a recluimed water (data from St. Petcrsburg, Florida)