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Bacterial “masons” at work with wastes for producing ECO-CEMENT

Industrial waste is now a global concern, causing environmental and economic harm. Industries are rapidly trying to find solutions, searching for optimal ways to manage waste and change the most common practices, as landfill or incineration. Industrial waste is a very heavy burden for the environment, where a significant proportion is attributable to construction and demolition waste. To mitigate these threats, a novel biomimetic technology for enzyme-based microbial carbonate precipitation was

Currently the production of one ton of cement commonly results in the release of 0.65 to 0.95 tons of CO2 depending on the efficiency of the process, fuels used, and specific type of cement product. Considering the scale of the worldwide cement production, even a slight decrease in the average global emissions per ton has a large CO2 reduction potential. Every 10% decrease in the cement CO2 intensity by 2050 could save around 0.4 Gt CO2, and substantially contribute to slow down climate change. Further abatement could originate from the more efficient use of cement and concrete. Additionally, innovative low CO2 cementitious materials are to be considered as a reduction measure. The use of waste materials in the cement industry, also referred to as co-processing, contributes towards achieving these objectives. An attempt to use treatments more in line with the nature of these materials has, in the past few decades, directed attention to biomaterials, generally carbonates, produced by living organisms, particularly bacteria. Microbial carbonate precipitation has gained interest in the past 20 years particularly with regard to the potential role marine systems may play as ”carbon sinks” for the increasing global production of CO2. The feasibility of microbial calcite precipitation is well established in literature, as a great number of researchers work on these type of processes, from one standpoint or another. The medium ingredients in biotechnology processes are a major cost factor, ranging between 10 to 60% of the total operating costs. The medium cost increases proportionally with the size of the scale up. Because of this, it is important to give consideration to optimization of the medium prior to scale up. Given that biocementation process does not require ease of removal of medium components or use of a defined medium, we are able to look at a range of more economical components to replace the existing expensive analytical grade chemicals. Reusing industrial by-products as a source of calcium, urea and nutrients for producing eco-cement is discussed in this paper. This alternative waste recycling has dual benefits as it contributes, not only to reduce the process costs, but to minimize environmental impacts associated to the disposal of such wastes. Biomineralization concept and waste recycling Biomineralization concept The mechanism of microbial induced calcium carbonate precipitation process (MICCP) involves the ureolytic bacteria that hydrolyze urea to produce carbonate ions (1), and in the presence of free calcium ions (2), the calcium carbonate will precipitate. (NH2)2CO + 2H2O → CO2−3 +2NH3 (1) Ca2++CO2−3 → CaCO3 (2) Urea is needed as primary reagent. If the saturation levels of the calcium carbonate produced are sufficiently high, it will precipitate forming bonds and consolidating its surroundings in the MICCP process. There are bacteria that produce urease in the cytoplasm of the cell for ATP generation. This enzyme hydrolyses the substrate urea. The urease enzyme is non-constitutive in nature, where its activity is independent of urea and ammonia, but varies with the presence of calcium, pH, temperature and calcium nitrate. Urease producing bacteria can be divided into two groups, according to their urease response to ammonium: (i) those, whose activities are repressed by high ammonium concentrations, such as Pseudomonas areuginosa, Alcaligenes eutrophas, Bacillus megaterium and Klebsiella aerogenes, and (ii) those whose activities are not repressed by ammonium, such as Sporosarcina pasteurii, Proteus mirabilis, Proteus vulgaris, Helicobacter pylori, Ureaplasma sp., but some of them are pathogens. Sporosarcina pasteurii was considered the most suitable for the biocementation process as it was the most resistant in alkaline conditions and do not present hazards to the human health. Its favorable growth condition is 30°C. In order to provide them with oxygen, it needs to be slightly shaken and it nee


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