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The sludge generated in the lime softening of recirculating cooling water has a large bulk volume and is difficult to dehydrate. The current study tested the effect of fly ash addition on the pollutant removal efficiency and the sludge properties improvement in the softening process. The hardness and alkalinity removal efficiency before and after the addition of fly ash were evaluated. The effects of fly ash addition on chemical sludge properties, such as the sludge water content, particle size, and microstructure, were also investigated. With a fly ash dosage of 270 mg/L, the removal rates of calcium hardness, total hardness, and total dissolved solids increased by 20.7, 11.5, and 6.1% compared with those obtained in the absence of fly ash. The addition of fly ash can improve the stability of treated water by reducing the scaling potential. Fly ash can improve the sludge properties. At a fly ash dosage of 200–250 mg/L, the median diameter of the flocs is four times bigger than the flocs produced ...

Lime softening is a well-established process for partially separating of hardness ions from water. Currently, the lime softening process is adjusted manually based on chemical titration tests aimed at maintaining the simple and total alkalinities in a certain range. Analysis of experimental data from bench and full-scale lime clarifier showed that the current control based on alkalinity is often not correct. It was found in this work that electrical conductivity (EC) can be used as a good indicator for evaluating the performance of lime clarifiers. Therefore, an eco-friendly and very cost effective alternative technique based on EC is introduced in this paper for successful control of lime softening process.

In the present article, the major treatment methods applied for uranium removal from groundwater, with specific applications in drinking water treatment, are reviewed. These include pump-and-treat technologies, such as membrane filtration methods, anion exchange, and the use of adsorbents, such as iron oxides, or titanium dioxide, as well as the application of coagulation processes with the addition of Fe/Al salts, or by lime softening. In all cases, uranium removal is mainly dependent on its speciation, which is greatly affected by the (usually coexisting) carbonate ions in the contaminated water. Under circumneutral pH values, uranium forms anionic complexes with carbonate of the type , or . In situ treatment technologies comprise mainly the use of permeable reactive barriers. These contain reactive materials, such as zero valent iron or hydroxyapatite, and uranium is usually removed by reduction to the respective insoluble products of U(IV); reducing bacteria, when present, can play a suppleme...

The City of Miramar, located in South Florida, has two water treatment plants which utilize two different water treatment processes. The East Water Treatment Plant (EWTP) uses lime softening, while the West Water Treatment Plant (WWTP) uses reverse osmosis treatment. Biscayne aquifer is used as the source water for both plants. Effectiveness of lime softening and reverse osmosis processes were evaluated in terms of trihalomethane (THM) levels in the distribution system with distance and at cul de sacs (dead end streets). The water treated by lime softening had significantly higher levels of THMs in comparison to the water treated by reverse osmosis. With the aging of reverse osmosis membranes (after 5 years), the THM levels exhibited similar levels in both distribution systems. The THM concentrations at the cul de sacs receiving water treated by lime softening were significantly higher in comparison to the system wide water quality. At the cul de sacs receiving water treated by reverse osmosis, T...

Chemical precipitation including lime softening, chlorination, clarification and filtration have been long recognized treatment for process water used in various industries because it provides consistent water quality, however these processes were rarely used in pre-treating feed to reverse osmosis desalination systems. The newly developed submerged spiral wound ultrafiltration membranes in conjunction with chemical precipitation or lime softening can be used to treat reverse osmosis feed. Previous studies have proven the feasibility of integrating immersed ultrafiltration (UF) membrane with chemical precipitation and lime softening. This paper describes the relationships of the operating parameters such as pH, membrane flux, trans-membrane pressure (TMP), membrane permeability; optimum dosage of coagulant; to be used as the basis for the design and construction of the full scale plant. A pilot unit consisting of chemical reactor and UF system was operated at various pH conditions, at membrane flux rates ...