Page 22 - Membranes for Industrial Wastewater Recovery and Re-Use
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Introduc~troti  3

           repurification  plant and, more directly, on the reuse options. Hence, reclaimed
           greywater for reuse  in buildings  is  invariably  employed  exclusively  for toilet
           flushing, where the risk to human health through exposure to the contaminated
           water is considered minimal. Large-scale municipal wastewater reclamation and
           reuse schemes are predominantly aquifer recharge, such as the well-established,
           flagship Water Factory 2 1 plant in Orange County, California (Wesner, 1987) or
           turf grass irrigation schemes.
             In  the  case  of  industrial  water  recycling  the  issue  is  notionally  more
           straightforward.  As long as recycling can reliably and cost-effectively provide
           water of a quality  appropriate  to  its designated use, then there should be  no
           barrier  to its introduction  and deposition of  the existing freshwater supply. Of
           course,  and as already  mentioned, the cost  benefit may  be  largely  or  wholly
           determined by statutory requirements: there are, for example, a number of power
           plants  throughout the world  that have  a zero liquid  discharge imposed  upon
           their  operation  (Section  5.3). Under  such  extreme  conditions,  wastewater
           recovery  and reuse  is  no  longer  an  option  but  an absolute  necessity  - and
           inevitably  incurs  cost  penalties  due  to  solid  waste  generation  and  energy
           expenditure.  In  other  cases, the  decision  to  recycle  is  motivated  entirely  by
           economics;  the  total  cost  of  purification  to  provide  a  water  of  a  quality
           commensurate with or better than that of  the freshwater supply is perceived as
           being less than the total cost of  freshwater and waste discharge. Perception  in
           this instance relates entirely to the acceptance of the technology, rather than to
           the use of water employed for duties considered unsavoury.
             Given the apparently  less restrictive constraints imposed on the recycling of
           industrial wastewater compared  to that of  domestic wastewater, it is perhaps
           surprising that the former has received far more attention, has attained a much
           higher  profile  and  has  achieved  more  widespread  implementation  than  the
           latter. There exist  a number of  domestic and municipal wastewater recycling
           schemes, from single households through to large buildings, as well as municipal
           or  industrial  wastewater  reclamation  for  irrigation.  Similarly,  a  number  of
           municipal wastewater reclamation schemes exist whereby the polished effluent
           is reused for cooling, which represents around two-thirds of  all industrial water
           use, or other activities demanding low-grade process water such as for washing
           or transporting. Direct “closed-loop” industrial water recycling, whilst limited in
           technical  and economic viability  in many instances, is nonetheless  attracting
           greater interest and being more widely applied. Indeed, it is already established
           practice for specific industrial processes where other resources are recovered in
            addition to the water, such as pulp solids in paper manufacturing (Sections 3.2.5
            and 5.4-5.6) and paint pigments (Section 5.10) in electrophoretic painting.
             Two  factors  mitigate  against  widespread  “closed-loop”  industrial effluent
           reuse.  Firstly,  most  industrial  processes  involve  a  number  of  individual
           operations that give rise to wastewaters of  a certain compositional range. These
           individual effluent streams are generally combined to give a wastewater whose
            resultant temporal variation  in quality is immense, representing  a significant
            challenge to any treatment process  that is to provide water of  a reliably high
            quality. Secondly, it is invariably the case that conventional sewage treatment
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