| Global shortage of freshwater resources has become an increasing concern, and reverse osmosis seawater desalination has become an important way to solve the global water resources crisis. Compared with tap water, reverse osmosis desalinated water has low content of mineral elements, pH, hardness and alkalinity, but research about disinfection and application of washing of reverse osmosis desalinated water is not reported at present. In this study, the water quality characteristics of reverse osmosis desalinated seawater is first characterized, followed by the comparison of disinfection methods for reverse osmosis desalination seawater and the discussion of factors affecting the cleaning ratio when the desalinated seawater is directly used for washing. The new idea of desalinated water remineralization to improve its cleaning efficiency is finally proposed. The main results obtained in this study are listed as following:(1) The three kinds of methods including calcium hypochlorite, chlorine dioxideand ultraviolet disinfection has their own advantages and disadvantages for the disinfection of RO desalinated seawater. The optimum adding amount of disinfectant is determined including 5 mg/L calcium hypochlorite,1 mg/L chlorine dioxide,5 mJ/cm2 UV. The pH, electrical conductivity, hardness and other water quality of RO desalinated seawater remain almost unchanged after the disinfection of calcium hypochlorite and calcium dioxide during the storage time of 28 days, while, the residual chlorine is reduced from 5 mg/L to 0.09 mg/L for 5 days when the disinfectant of calcium hypochlorite adding amount was 5 mg/L. Compared to calcium hypochlorite and chlorine dioxide disinfection, theUltraviolet is more suitable for pipe disinfection.(2) When the reverse osmosis desalination seawater is used for washing directly, the cleaning ratio of desalination seawater was lower than tap water. The comparison of effects of desalinated seawater and tap water on the pH, surfactant content and calcium magnesium chelating capacity of detergents show that pH and cleaning ratio of desalinated seawater is 5.9 and 12.89% respectively, while the pH of tap water is about 7.4, which is in closest scope of Lanyueliang detergent, and cleaning ratio is 13.18% in the washing process of Lanyueliang. The surface active matter content in desalinated seawater before and after washing is 0.69% and 0.23% respectively, and the cleaning ratio is 12.89%, while the surface active matter content in tap water is 0.58%and 0.31% respectively before and after washing and the cleaning ratio is 13.48%. So the surface active matter content consumption of desalinated seawater is less and the cleaning ratio is low. The nalcium magnesium chelating capacity of desalinated water is 2.47 mg/L and cleaning ratio is 12.99%, whereas the calcium and magnesium chelating capacity of tap water is 22.5 mg/L and the cleaning ratio is 13.58%. The cleaning ratio of Lanyueliang is significantly higher than Chaoneng and OMO detergent with same kind water.(3) The hardness and alkalinity can improve the cleaning ratio of the desalinated water. The cleaning ratio of reverse osmosis desalinated seawater is found increased firstly and then decreased slowly in a certain range of hardness(0 mg/L<hardness< 100 mg/L) and alkalinity(0 mg/L<alkalinity<100 mg/L). The cleaning ratio of compound 2#-7# (the concentration of Ca2+is 0.5-12 mg/L, the concentration of NaHCO3 is 2.5-60 mg/L, namely the hardness is 1.25-30 mg/L, alkalinity is 1.75-42 mg/L) is the highest when compared with other kinds of water. With the comparison of Chaoneng、Lanyueliang、OMO detergent in cleaning ratio, the cleaning ratio of Lanyueliang reached about 22.35%, while that of both Chaoneng and Aomiao is around 21%. |
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