26 Successful Operation of a Permasep Permeator Reverse-Osmosis System on Biologically Active Feed Water Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 21, 1981 | doi: 10.1021/bk-1981-0153.ch026
H. W. POHLAND and G. E. BETTINGER Plastic Products Division, E. I. du Pont de Nemours and Company, Inc., Wilmington, DE 19898 A "Permasep" permeator reverse osmosis (RO) installation, capable of producing 1500 cubic meters of product water per day, was successfully operated for six months with RO feed water drawn from an estuary and having 1200 to 1400 mg/l total dissolved solids (TDS). The plant shown in Figure 1 consists of a water pretreatment plant and four separate blocks of "Permasep" units. A l l blocks are fed by the same high pressure pump, and each block consists of 4-inch modules, reject-staged in a 2 to 1 ratio. The total conversion is about 70 percent -- this means that about 70 percent of the feed water is converted to product, with 30 percent discarded as a brine stream. Reject staging was used to achieve flow rates necessary to counteract the effects of concentration polarization. During this initial period local water authorities completed a dam, cutting the sea connection to the estuary and causing a gradual drop in the RO feed water to 250 mg/l TDS. With this drop in TDS was a marked decrease in overall plant performance, as evidenced by a drop in productivity (Figure 2a) (flux) and an increase in the salt passage (Figure 2b). Normal cleaning measures temporarily restored the flux and halted the rise in salt passage. However, as shown in these figures, the plant soon began to deteriorate and periodic cleanings were used to attempt to maintain productivity. After 24 months of operation a thorough analysis of the plant performance was made. No changes in the water pretreatment were observed; the Langelier Saturation Index (Ref. 1) had been kept negative with the changing water analysis; and the s i l t density index (SDI), a measure of suspended solids, was consistently below 2.5, well within the "Permasep" Guideline of SDI max. = 3.0. These findings ruled out scaling, iron, or colloidal fouling as the source of difficulty. Red slime deposits, which appeared to be biological in origin, were observed in one disassembled permeator. A microscopic examination of the slime revealed a heavy growth of a 0097-6156/81/0153-0399$05.00/0 © 1981 American Chemical Society
In Synthetic Membranes:; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
400
SYNTHETIC
MEMBRANES:
AG
Media
Fitter
Lake Water
DESALINATION
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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 21, 1981 | doi: 10.1021/bk-1981-0153.ch026
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The product is further treated in a degasifier and mixed bed ion exchanger.
High Pressure Pump
4 RO Blocks Refect Staged. 2:1 Taper Figure la.
3
Plant flow diagram of a 1500 m /D RO plant
IMdM
AG
2 1 Tap*r
Figure lb.
3
Plant flow diagram of a 1500 m /D RO plant
In Synthetic Membranes:; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
26.
POHLAND AND BETTINGER
Permasep
Permeator
RO
System
200-1
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 21, 1981 | doi: 10.1021/bk-1981-0153.ch026
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