Potable water design considerations

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

There are obviously situations which demand considerable over-design of a cathodic protection system, in particular where regular and efficient maintenance of anodes is not practical, or where temporary failure of the system could cause costly damage to plant or product. Furthermore, contamination of potable waters by chromium-containing or lead-based alloy anodes must lead to the choice of the more expensive, but more inert, precious metal-coated anodes. The choice of material is then not unusual in being one of economics coupled with practicability. 

Redondo, J. A. and E. Lanari (1997). Membrane selection and design considerations for meeting European potable water requirements based on different feedwater conditions. Desalination, Proc. 1997 Workshop on Membranes in Drinking Water Production, June 1-A, L Aquila, Italy, 113, 2-3, 309-323. Elsevier Science B.V., Amsterdam, Netherlands. 

Although modem plants are designed to export as little waste water as possible and attempts are made on the premises to recondition the waste water for cooling or boiler feed water service, almost all coal-to-methanol plants still have a considerable demand for raw water. Main consumers are cooling and boiler feed water supply systems, whereas other services such as potable water and water for general operating purposes account for only a small portion of the demand. 

PP pipes can normally be produced on plants which are designed to process HOPE. However, some special considerations are needed since PP degrades faster and is more sensitive to oxidation. PP has a similar heat capacity to HDPE with a lower thermal eonduetivity. Consequently, the output in the case of PP is 15% lower than that for HDPE. Applications for PP pipes include potable water supply, domestic waste systems, under-floor heating circuits, chemical effluent disposal systems and thermal spring conduits. 

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