Control Of Chemical Stability Of Remineralized Desalinated Water In The Existing Municipal Pipeline Network

As an effective solution of surface water shortage of coastal cities, desalinatedwater has been widely used by many countries in the world. However, when thedesalinated water enters the municipal network directly, it will appear “red water” or“yellow water” phenomenon because of the characteristics of desalinated water: lowhardness and alkalinity and lack of buffering capacity, which will influence the safetyof production and domestic water supply seriously. Nowadays, the main solution inChina is to mix the desalinated water with the surface water before delivery. But thevolatility of mixing water quality is high due to influence of season, and the securityof water quality can’t be guaranteed. So this study evaluates the chemical stability ofthe mixing water after regulating the water quality firstly, and then regulates thehardness and alkalinity through the remineralization method of dosing adjustment,and investigates the change of turbidity and iron release under different water qualitycondition systematically.Firstly, regulate the water quality using Ca（OH）₂, it can increase pH but has nosignificant influence on other water quality indexes. On that basis, this study takesLangelier Saturation Index as evaluation standard to judge the water quality stabilityof mixture of the source water and desalinated water in different seasons withdifferent mixing proportion after adjusting pH value. Through the above research, wefind that the mixing water of the same blending proportion is stable in some seasonsand is unstable in other seasons, so blending isn’t a reliable scheme of desalinatedwater utilization.Secondly, due to the limitation of the mixing water supply scheme, this papermakes further research on the secure transmission and distribution of desalinatedwater through the remineralization method of dosing adjustment. Though adjustingthe Ca²⁺concentration of desalinated water by CaCl₂, and research the change rules ofturbidity and iron release under different Ca²⁺concentration. It is found that in theprocess of secure transmission and distribution of desalinated water, when the Ca²⁺concentration is above28mg/L, all the water quality indexes reach the standard exceptthe pH.Thirdly, though the turbidity and iron can be controlled effectively through the adjustment of Ca²⁺concentration, the pH can’t be controlled effectively. So on thebasis of adjusting Ca²⁺concentration, adjust the alkalinity by NaHCO₃, and explorethe changes of water quality indexes. The study finds that when the Ca²⁺concentration is30mg/L and the alkalinity value is120mg/L, the turbidity, ironconcentration and pH can be controlled effectively.Finally, using the data of different experiment condition and selecting turbidityas controlling index, analyze the relation between turbidity and other water qualityindexes and establish the empirical statistic model, in order to direct the post-processing of mineralization process and provide necessary theoretical support for theremineralization of desalinated water. The prediction accuracy of total regression andstepwise regression is89.86%and91.76%respectively, so the model can meet theforecast requirements of turbidity in the water network.