Powdered Ceramsite and Powdered Limestone Use in Aerobic Granular Sludge Technology

The effects of two powdered mineral materials (powdered ceramsite and powdered limestone) on aerobic granulation of sludge were evaluated. The experiment was conducted on a laboratory scale bioreactors treating wastewater for 89 days. Three granular sequencing batch reactors (GSBRs) were operated at the lowest optimal organic loading rate (OLR) of 2.55 g COD/(L∙d). In the control reactor (R1), the mean diameter (d) of the biomass ranged from 124.0 to 210.0 µm, and complete granulation was not achieved. However, complete granulation did occur in reactors to which either ceramsite (251.9 µm < d < 783.1 µm) or limestone (246.0 µm < d < 518.9 µm) was added. Both powdered materials served as a ballast for the sludge flocs making up the seed sludge. Ceramsite particles also acted as microcarriers of granule-forming biomass. The granules in the reactors with added powdered materials had nonfibrous and smoother surfaces. The reactor with ceramsite exhibited the highest average efficiencies for COD, total nitrogen, and total phosphorus removal (85.4 ± 5.4%, 56.6 ± 10.2%, and 56.8 ± 9.9%, respectively). By contrast, the average nitrification efficiency was 95.1 ± 12.8%.

Towards a low CO2 emission building material employing bacterial metabolism in a two-step process of limestone dissolution and recrystallization: The bacterial system and prototype production

The production of concrete for construction purposes is a major source of anthropogenic CO2 emissions. One promising avenue towards a more sustainable construction industry is to make use of naturally occurring mineral-microbe interactions, such as microbial-induced carbonate precipitation (MICP), to produce solid materials. In this paper, we present a new process where calcium carbonate in the form of powdered limestone is transformed to a binder material (termed BioZEment) through microbial dissolution and recrystallization. For the dissolution step, a suitable bacterial strain, closely related to Bacillus pumilus, was isolated from soil near a limestone quarry. We show that this strain produces organic acids from glucose, inducing the dissolution of calcium carbonate in an aqueous slurry of powdered limestone. In the second step, the dissolved limestone solution is used as the calcium source for MICP in sand packed syringe moulds. The amounts of acid produced and calcium carbonate dissolved are shown to depend on the amount of available oxygen as well as the degree of mixing. Precipitation is induced through the pH increase caused by the hydrolysis of urea, mediated by the enzyme urease, which is produced in situ by the bacterium Sporosarcina pasteurii DSM33. The degree of successful consolidation of sand by BioZEment was found to depend on both the amount of urea and the amount of glucose available in the dissolution reaction.

Preparation of β-belite using liquid alkali silicates

The aim of this study is the preparation of β-belite by a solid-state reaction using powdered limestone, amorphous silica and liquid alkali silicates. The raw materials were blended, the mixtures were agglomerated and then burnt. The resulting samples were characterized by X-ray diffraction analysis and scanning electron microscopy. Free lime content in the β-belite samples was also determined. The effects of CaO/SiO2 ratio (1.6–2.1), burning temperature (800–1400 °C), utilization of different raw materials (silica fume, synthetic silica, potassium silicate, sodium silicate, potassium hydroxide) and burning time (0.5–16 h) on free lime content and mineralogical composition were investigated. The purest ?-belite samples were prepared from a mixture of powdered limestone, silica fume and liquid potassium silicate with a ratio CaO/SiO2 = 2 by burning at temperatures between 1100 and 1300 °C for more than 2 h. Decreasing of the CaO/SiO2 ratio led to rankinite formation and lower a burning temperature led to the formation of wollastonite.

Egyptian blue: modern myths, ancient realities

Colours containing bright and saturated blue hues were popular for painterly effects in most of the Mediterranean cultures dating from the Bronze Age to the fall of the Roman Empire. Pigments providing the desired blue were produced from precious minerals such as azurite and lapis lazuli, but bright blue hues also came from pigments produced by merging other naturally occurring sources. This large group of synthetically-generated blue frits is referred to as Egyptian blue. Egyptian blue is a calcium copper tetrasilicate compound, a synthetic pigment made by heating a calcium compound (such as powdered limestone and sand rich in calcium carbonate) together with copper and quartz (fig. 1), although synthetic blue pigments based on cobalt are also known, so far mainly in Egypt (such as “Amarna-blue”). The hue of Egyptian blue pigments ranges from a saturated, almost black blue to light blue, bluish-green, and purple, each being dependent on the materials employed for its production and manufacturing process. Its material properties are crystal-like, resembling finely shattered glass. It ranges in saturation and brightness (which can be enhanced by secondary heating), and it has a relatively low covering power. It seems to have ceased being widely applied sometime after the fall of the empire, which added a certain mystery to it.

Integrated iron(II) oxidation and limestone neutralisation of acid mine water

Volumetric iron(II) oxidation rates exceeding 100 g/(l.d) were achieved by dosing powdered limestone to a bio-reactor treating artificial acid mine water. Neutralisation and partial sulphate removal were achieved as well. The rate is highly dependent on the surface area exposed to the liquid (RSA) and the OH−, oxygen, CaCO3, suspended solids and iron(II) concentrations, and less dependent on specific surface area (SSA) and pressure in the pH range 5 to 6. The chemical oxidation rate (pH greater than 6) is dependent on the OH−, oxygen, and iron(II) concentrations and the reactor surface area (RSA).

Chemistry of Lake Hovvatn, Norway, Following Liming and Reacidification

Hovvatn, a 1-km2, chronically acidified lake in southernmost Norway, was treated with 200 metric tons of powdered limestone in March 1981. An additional 40 metric tons was added to a 0.046-km2 pond (Pollen) draining into Hovvatn. At ice-out, pH rose from 4.4 to 6.3 (Hovvatn) and 7.5 (Pollen), Ca and alkalinity increased, and total Al decreased by about 120 μg/L. The amount of limestone dissolved, calculated from the lake Ca budgets, was 50% after 3.5 yr in Hovvatn and 25% in Pollen. A greater fraction dissolved at Hovvatn because the limestone lay in the active surf zone. In Pollen, limestone that was not dissolved at ice-out formed a layer on the sediment surface from which only minimal dissolution occurred. Hovvatn and Pollen reacidified to pH 4.9 and 5.5, respectively, 3 yr after liming. A simple flushing model describes the reacidification of Pollen. In Hovvatn, however, dissolution of additional limestone during the 3.5 yr since liming has considerably slowed reacidification.