Browsing by Author "Muriithi, Genson"

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    Bioremediation of mortar made from Ordinary Portland Cement degraded by Thiobacillus thioparus using Bacillus flexus
    (Heliyon, 2021-06) Ngari, Reginah Wangui; Thiong'o, Joseph K.; Wachira, Jackson M.; Muriithi, Genson; Mutitu, Daniel K.
    Cement is widely used as a construction material in the construction industry. However, there are challenges affecting its durability efficacy. Cement mortar/concrete is subject to degradation by aggressive ions such as sulphates and chlorides. Sulphates can be introduced into the concrete or mortar by Sulphur producing bacteria of the species Thiobacilli. Microbiologically induced CaCO3 precipitation (MICP) has found its application in bioremediating cement based materials. It has been found to be environmental friendly. However, no work has been reported on bioremediation of biodegraded cement based materials. This paper presents findings of possible bioremediation of mortars after undergoing biodegradation. Bacillus flexus, a beneficial bacterium was used. The control mortars were prepared using Ordinary Portland Cement (OPC). The test mortars were prepared and cured in a solution of Thiobacillus thioparus, a Sulphur oxidizing bacteria, deleterious bacterium for 14, 28, 56 and 90 days. Compressive strength analysis was conducted on the 14 day of curing. Results showed that the lowest compressive strength was recorded on the 90 th th th th ,28 ,56 and 90 day as 31.02 MPa. This was a 34.17 % loss in compressive strength. Another category of mortar cured in Thiobacillus thioparus for 28 days was bioremediated for 28 days using Bacillus flexus solution. Compressive strength and Scanning Electron Microscopy (SEM) analyses were then done. The results show a compressive strength of 45.83 MPa at the 56 th day. This represents a 99.91 % strength recovery from biodeterioration. The SEM analysis results revealed a denser material. This was due to massive precipitation of calcium carbonate in the mortar matrix and pores/voids for bioremediated mortars as opposed to the biodegraded mortars. The results further revealed reduced ettringite crystals on the bioremediated mortars. Bacillus flexus could perhaps be used in restoring lost compressive strength as well as in sealing voids in degraded concrete in sewer lines and other cement based materials. This could improve on its efficacy with minimal repair.
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    Evaluating the surface functional groups on banana leaf petioles and the resultant biochar for potential adsorbance
    (JMES, 2020) Ndung’u, Paul W.; Mwithiga, Gikuru; Onyari, Charles N.; Muriithi, Genson; Mukono, Simon T.
    The presence of surface functional groups is key to the performance of an adsorbent material. The aim of this study was to evaluate the presence of functional groups on banana leaf petiole and on biochar made from banana leaf petiole. These functional groups assist in determining the potential of the material as an adsorbent for pollutants and heavy metals in waste water. Banana leaf petioles were collected from a single plantation and analyzed using the Fourier transform infrared spectroscopy. The material was then pyrolyzed at pyrolytic temperatures of 300°C, 400°C and 500°C, and the resulting biochars were analyzed to identify the surface functional group. The results showed the presence of hydroxyl and carboxyl functional groups on the banana leaf petiole before pyrolysis. The biochars also showed presence of hydroxyl and carboxyl functional groups whose presence and abundance reduced with increase in pyrolytic temperature. The presence of hydroxyl and carboxyl functional groups in a material has been related to its ability to adsorb metals in waste water and thus the banana leaf petiole as well as its resulting biochar would be a promising adsorbent for waste water remediation
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    Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar
    (Elsevier, 2019-11) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Joseph Karanja; Munyao, Onesmus Mulwa; Muriithi, Genson
    Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 107 cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28th and 56th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28th day of curing respectively. Scanning electron microscope images taken after the 28th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.
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    Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar
    (Elsevier, 2019-11) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Joseph Karanja; Munyao, Onesmus Mulwa; Muriithi, Genson
    Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 107 cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28th and 56th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28th day of curing respectively. Scanning electron microscope images taken after the 28th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.