Water treatment pretreatment

J. C. Kruithof, J. C. Schippers, P. C. Kamp, H. C. Fohner, and J. A. M. H. Hofinan, Integrated multi-objective membrane systems for surface water treatment pretreatment of reverse osmosis by conventional treatment and ultrafiltration. Desalination 117, 37 8 (1998). 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

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. 

Water pretreatment plant Waste water treatment plant... 

For most smaller operators, the waste water discharge from pretreatment equipment, blowdown receivers, and FSHR equipment typically discharges into a city sewer. Most larger factories, process plants, and power stations, on the other hand, incorporate some form of waste water treatment facility to balance the pH level, remove oils and pre-cipitable solids, or otherwise reduce the contamination load before the discharge of water from the site. 

To limit the potential for waterside problems throughout the steam-water system cycle a balance of water treatment processes is required with external items of capital equipment providing primary duty for FW pretreatment and internal specialty chemicals providing a supporting, polishing function. 

The more extensive use of pretreatment equipment generally is a commendable approach, although it is difficult to externally overtreaf boiler MU and FW, it also is pointless to spend limited capital resources installing sophisticated equipment to provide high-purity water and then to subsequently add dissolved solids back into the FW or BW with an inappropriate, internal chemical program. Both external and internal water treatment programs must be compatible and mutually beneficial ... 

When considering the need for capital pretreatment equipment, sufficient care should be taken not to propose any particularly sophisticated external or internal water treatment regimen that of itself creates restrictive operational BW control limitations—where boiler design, steam usage, and common sense dictate no necessity for such limitations to be imposed. The overall water treatment program should not be overdesigned but should properly match the needs of the project. 

Nevertheless, it was perhaps only 25 to 30 years ago that significant improvements in limiting deposits through improved water treatment were made available to general industry. Until then many operators in hard-water areas had to contend with no pretreatment softening of MU... 

In all cases, and irrespective of the types of pretreatment equipment employed and the degree of boiler operational control provided, additional and complementary support through the use of suitable internal chemical water treatment programs is always needed to limit waterside deposition. 

Despite the rhetoric surrounding the subject of magnetic water treatment, some useful information can be gleaned from technical papers and supplier s literature (extracts of which are reported below), which may help the reader form an informed opinion on the benefits or otherwise of this form of pretreatment. 

Kim HA, Choi JH, Takizawa S (2007) Comparison of initial filtration resistance by pretreatment processes in the nanofiltration for drinking water treatment. Separ Purif Technol 56 354-362... 

According to the vendor, costs for sediment removal, dewatering, water treatment, and segregation by particle size are approximately 250/m or less. For removal only, costs are 100/m or less. These estimated costs do not include mobilization and demobilization and/or supplying temporary enclosures (used in pretreatment) if none are available at the site (personal communication Roger Carr, Eriksson Sediment Systems, Inc., May, 1997). 

Specifications for the equipment (storage tanks, heat exchangers, pumps, valves and piping components) to be used for water treatment and pretreatment... 

Additional work must be completed before these hydration inhibitor treatments will be widely used. However, it appears that combined FPL/inhibitor pretreatments have the potential of producing water stable aluminum oxides with structures that promote mechanical aspects of adhesion in a relatively simple manner. Since mechanical adhesion mechanisms are not greatly affected by water, these pretreatments show promise as a means of increasing the durability of metal/polymer adhesion systems in wet environments. 

WATER TREATMENT (Boiler). One of the most critical and exacting requirements for pretreating water prior to industrial use is found in connection with the operation of modem boilers. Many of the basic principles of water treatment are encountered for this application.1 The advantages of modern boilers can be realized to the fullest only if proper attention is given to water treatment. No boiler can operate efficiently or dependably if its heat-transfer surfaces arc allowed to foul with scale or if corrosion is peimitted to occur. 

All cooling water treatment programs, whether designed in-house or via a water treatment service company, continue to focus on the minimization of hard water crystalline scales and sludges in the system as a major criteria for success. Program techniques employed are either pretreatment processes, such as lime-soda softening or ion exchange, the use of sulfuric acid or polymer-based chemicals that operate in an alkaline environment, or combinations of some or all of these processes. 

While specifying some acceptable parameter is a sensible practice to be applauded, it will not generally work if the owner or operator also seeks to impose rules on what is or is not an acceptable chemical treatment program, or also fails to fully involve the successful water treatment vendors early on in the pretreatment and start-up programs. 

Photochemical operations offer several routes of hydroxyl radical formation by UV irradiation. The formation of hydroxyl radicals by irradiation of samples doped with hydrogen peroxide or ozone is the state-of-the-art in water treatment. Two comprehensive reviews cover the historical development of the UV photo-oxidation technique as a pretreatment step in the inorganic analysis of natural waters, its principles and the equipment available, and its principal applications in the analytical field.3,4 They include tables summarizing the elements determined, the analytical techniques used, and the sample matrices studied. 

---