Concentration Cycle Research Articles

A case study on the wastewater reclamation and reuse in the semiconductor industry

The semiconductor factory generally requires ultra pure deionized water to rinse their integrated circuit (IC) crystal chips in Taiwan. When tap water is used as the source of deionized water supply system, the reject from the devices of producing pure water (e.g. reverse osmosis , RO) usually contains less inorganic and allowed to be reused as make-up in cooling water system. The aim of this study is to evaluate the appropriateness and effectiveness of reusing the reject as cooling water for semiconductor plant. A representative semiconductor plant was selected as a case study in this paper. Calculating the typical results of water samples analysis, it was found that the cycles of concentration of this cooling water system was only 1.5, and the water stabilization index were −0.11, 8.32 and 8.86 for Langelier Saturation Index (LSI), the Ryznar Stability Index (RSI) and the Practical Scale Index (PSI), respectively. This means that the current operational condition of the cooling water system had less tendency to scale formation. Consequently, further increasing the cycles of concentration (CC) and reducing the quantity of make-up in the cooling water system would be preferable. Furthermore, the related mass balance data of used water quantities in the whole plant indicated the reuse and recovery of used water could be appropriately carried out in the plant.

Mannich Base Derivatives - A Novel Class of Corrosion Inhibitors for Cooling Water Systems

Limited resources of good quality water and the stringent environmental regulations on disposal of water warrant the operation of the present day's cooling water treatment systems with the highest practically feasible cycle of concentration (COC). However, with increase in COC, all the inorganic and organic constituents of the recirculating water increase proportionally thereby augmenting the possibility of failure of the system due to corrosion, scaling and fouling. Environmental concerns on the use of heavy metal based corrosion inhibitors have called for an effective alternative approach that is environmentally safe as well as cost-effective. The present investigation is aimed at evaluating the suitability of some Mannich base derivatives, namely, 4-methyl-2-fonnyl-6-(piperidine-1-yl methyl) phenol (MFPP) and 4-methyl2-formyl-6-(molpholine-1-yl methyl) phenol (MFMP), synthesized in our laboratory, as corrosion inhibitors for cooling water treatment systems, under simulated laboratory conditions. Mild steel was used as the substrate material and the inhibition efficiency of MFPP and MFMP were assessed under varying conditions of temperature, pH and dissolved salts. Both compounds exhibit good inhibition towards the corrosion of mild steel under varying experimental conditions. The other interesting feature about these compounds is their ability to perform as a self-indicator in the cooling water system based on the existence of their chemical structure under acidic and alkaline conditions, respectively, exhibiting a colourless and fluorescent green colour. This inherent property of these compounds is very useful in continuous monitoring and control of cooing water systems. Besides it also helps in identifying critical conditions like tolerance level of the acid dosage, given to prevent scaling, which would otherwise cause excessive metal attack and ultimately lead to a premature failure of the system.