Page 237 - Membranes for Industrial Wastewater Recovery and Re-Use
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206  Membranes for Industrial  Wastewater Recovery and Re-use

          sizing agent. Operating cost is assumed to be €0.1 per m3, based on the same
          assumption of a cost recovery as the IJF plant.
            Membrane  treatment for  recovery  of  wastewater from printing paste  (European
          Commission, 2001). Capital cost for a 60 m3 day-l  plant is €0.82 per m3 based
          on  a  10-year depreciation  period  at an interest  rate of  0%. The  installation
          comprises coagulation/precipitation  pretreatment followed by a microfiltration
          unit  using  a  polypropylene  membrane  and  a  tube  settler  to  remove  the
          suspended solids. Operating cost, including external disposal of  the concentrate,
          the principal contribution to opex, is about €4 per m3.
            Membrane treatment for recovery of  wastewater fromfinal washing. Capital cost is
          assumed to be €0.33  per m3 for an ultrafiltration installation of  250 m3 dayp1.
          Operating cost is assumed to be €0.25 per m3.
            Centralised biological wastewater treatment plant (European Commission, 2001).
          Capital  cost  is  taken  at  €1.25  per  m3 for  a  2500  m3 dayp1 plant  (10-year
          depreciation at an interest rate of 6.88%). The investment cost given in the paper
          (European  Commission,  2001)  was  €1.50  per  m3, although  this  included
          further purification  (by reverse  osmosis) of  the  effluent  for  reuse.  The  plant
          comprises  equalisation,  neutralisation,  and  activated  sludge  treatment  in  a
          special system of  loop reactors  and clarifiers, adsorption  to remove  dyestuffs,
          flocculation/precipitation  and removal of  sludge, and filtration  in a fixed-bed
          gravel filter to remove  suspended  solids. Also included  is the treatment of  the
          sludge in a thickener  and decanter and thermal regeneration  in a rotary kiln.
          Operating cost is taken at €0.6 per m3, based on the above, including ash disposal
          and ignoring heat recovery.
            Reverse  osmosis for  polishing  the  treated  wastewater  (European  Commission,
          2001).  Capitalcostistakenat€0.2Sperm3 fora 1500m3 day-'  plant.Investment
          comprises the reverse osmosis plant consisting of  10 modules containing 4 spiral
          membrane elements each. Included is a storage tank conditioned with ozone to
          control biological growth. Operatingcost is taken at €0.1 per m3.

          Results
          Base  case:  targeted  minimum  flow  rate,  discharge  to  sewer.  For the base case it is
          assumed  the company  is  required  to  meet  stricter  consents  for  discharge  to
          sewer. In the first instance a large central wastewater treatment plant can be
          envisaged for the treatment of the overall wastewater.
            The result of the base case reveals that 12 10 m3 day-l  of fresh water is needed
          with all effluent from the cooling process being recycled  (350 m3 day-l  waste
          from a 1560 m3 dayp1 feed). No other effluents are identified for reuse taking into
          account  minimum  operating  cost.  The  effluent  of  the  central  wastewater
          treatment plant meets the strict discharge consents for both SS and BOD. Only
           378 m3 day-'  needs to be treated in the central plant, the remaining  effluents
          being discharged directly to sewer. The daily cost of this base case is €6387,60%
          of this being due to the external treatment of the concentrated waste.

          Scenario  I:  targeted  minimum  flow  rate,  all purification  techniques  permitted. For this
          case it is presumed the company was seeking alternative ways of minimising the
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