Applications for reuse of lime sludge from water softening.

758653336Final report.PDFTech ReportTR-535SewerageSludge (Deposit)RecyclingWaste managementIowaIowa State UniversityBaker, Rob J.van Leeuwen, J (Hans)White, David J.Iowa State UniversityIowa. Highway DivisionIowa. Highway Research BoardNTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENTNTL-PLANNING AND POLICY-PLANNING AND POLICYNTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATIONNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsUS Transportation CollectionLime sludge, an inert material mostly composed of calcium carbonate, is the result ofsoftening hard water for distribution as drinking water. A large city such as Des Moines,Iowa, produces about 30,700 tons of lime sludge (dry weight basis) annually (Jones et al.,2005). Eight Iowa cities representing, according to the U.S. Census Bureau, 23% of thestate\ue2\u20ac\u2122s population of 3 million, were surveyed. They estimated that they collectively produce64,470 tons of lime sludge (dry weight basis) per year, and they currently have 371,800 tons(dry weight basis) stockpiled. Recently, the Iowa Department of Natural Resources directedthose cities using lime softening in drinking water treatment to stop digging new lagoons todispose of lime sludge. Five Iowa cities with stockpiles of lime sludge funded this research.The research goal was to find useful and economical alternatives for the use of lime sludge.Feasibility studies tested the efficacy of using lime sludge in cement production, power plantSOx treatment, dust control on gravel roads, wastewater neutralization, and in-fill materialsfor road construction. Applications using lime sludge in cement production, power plant SOxtreatment, and wastewater neutralization, and as a fill material for road construction showedpositive results, but the dust control application did not.Since the fill material application showed the most promise in accomplishing theproject\ue2\u20ac\u2122s goal within the time limits of this research project, it was chosen for furtherinvestigation. Lime sludge is classified as inorganic silt with low plasticity. Since it only hasan unconfined compressive strength of approximately 110 kPa, mixtures with fly ash andcement were developed to obtain higher strengths. When fly ash was added at a rate of 50%of the dry weight of the lime sludge, the unconfined strength increased to 1600 kPa. Further,friction angles and California Bearing Ratios were higher than those published for soils ofthe same classification. However, the mixtures do not perform well in durability tests. Themixtures tested did not survive 12 cycles of freezing and thawing and wetting and dryingwithout excessive mass and volume loss. Thus, these mixtures must be placed at depthsbelow the freezing line in the soil profile. The results demonstrated that chemicallystabilized lime sludge is able to contribute bulk volume to embankments in road constructionprojects