Articles: Department of Physical Sciences

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Energy recovery from biomethanation of vinasse and its potential application in ozonation post-treatment for removal of biorecalcitrant organic compounds
(ELSEVIER, 2020-10) Otieno, Benton; Apollo, Seth
Vinasse is characterized by a high chemical oxygen demand (COD) and dark brown colour, which requires abatement before disposal to prevent the pollution of receiving streams. Anaerobic digestion (AD) usually applied for vinasse treatment can only reduce the COD with the colour remaining unabated. This study investigated the feasibility of combining AD and ozonation for vinasse treatment. The AD process alone achieved high COD removal of 95 %, at a best organic loading rate of 15 kgCOD/m3/d. However, the anaerobic effluent still had an intense dark brown colour caused by a considerable amount of residual biorecalcitrant COD of 4.5 g/L. The ozonation post-treatment of the anaerobic effluent removed 80 % of the colour with up to 92 % ozone transfer at optimal parameters of pH 4, substrate dilution factor of 2, and 90 mg/L/min ozone dosage. Kinetic analysis showed that for a constant feed flow combined system, the ratio of the anaerobic reactor unit to the ozonation reactor unit is recommended to be 20:1. Also, from energy analysis, application of the bioenergy produced from AD to supplement the total energy requirement of the combined system could lead to 50 % savings on energy, and a carbon dioxide emission reduction of 122 kg CO2/m3 of vinasse treated. The combined system is thus a promising technology for vinasse treatment and can contribute to combating greenhouse gas emissions.
Malaria vector control strategies. What is appropriate towards sustainable global eradication?
(ELSEVIER, 2020-10) Ogunah, Joanne A; Lalah, Joseph O.; Schramm, Karl-Werner
Malaria a mosquito-borne disease caused by Plasmodium remains to be a main global burden despite concerted efforts to eliminate it. While diverse control strategies have been put in place for mosquito-borne diseases, vector control continues to be a critical component in infection prevention. Vector control majorly focuses on the eradication of mosquitoes using a variety of chemical insecticides that includes organochlorides, carbamates, organophosphates, and pyrethroids. The use of conventional insecticide-based as mosquito control strategies poses several challenges such as the widespread development of insecticide resistance, environmental damage concerns, and effects on non-target organisms. These challenges create a demand for the development and use of alternative pest control strategies that are sustainable, safer, and environmentally friendly to mosquito vector management. This review provides insight into alternative sustainable interventions for mosquito vector control in the form of biorational pesticides. Biorational pesticides are pesticides that have little or no effect on humans and environments and include entomopathogenic microorganisms, insect growth regulators, and endosymbiotic bacteria. It also puts into perspective their environmental impacts, benefits, and challenges. Further, countries like Sri Lanka, that are certified as malaria free by World Health Organization (WHO) incorporated the use of entomopathogenic bacteria, insect growth regulators and larvivorous fish in their national vector control programs leading to the successful elimination of malaria in 2016. We therefore highlight success stories of the countries that have implemented these interventions bringing out the lessons for countries that are battling malaria epidemics.
Effect of Bacillus cohnii on Some Physicomechanical and Microstructural Properties of Ordinary Portland Cement
(Hindawi, 2020-09) Ngari, Reginah Wangui; Thiong’o, Joseph K.; Wachira, Jackson M.
Cement-made materials face durability and sustainability challenges. (is is majorly caused by the presence of cracks. Cracking affects the mechanical strength of cement-based materials. Microbiologically induced calcite precipitation (MICP) has been found to enhance compressive strength, thus enhancing on the mechanical and durability properties of these materials. (is paper presents the findings of a study conducted to investigate the effect of Bacillus cohnii on compressive strength development of OPC mortar prisms and the effect of Bacillus cohnii on cement setting time and soundness. Microbial concentration of 1.0 ×107 cells·ml−1 was used. Compressive strength tests analyses were carried out for each category of mortar prisms. Compressive strength tests were carried out on the 2nd, 7th, 14th, 28th, 56th, and 90th day of curing in distilled water and microbial solutions. All microbial mortars exhibited a greater compressive strength compared to the control with the highest observed at 90 days. Highest percentage gain in compressive strength was observed at 90 days which is 28.3%. Microstructural analysis was carried out using a scanning electron microscope (SEM) after 28 days of curing. (e results indicated the presence of calcium carbonate and more calcium silicate hydrate (CSH) deposits on the bacterial mortars. (e bacteria did not have an effect on cement soundness. Setting time was significantly accelerated.
Crop residues used as lignocellulose materials for particleboards formulation
(Heliyon, 2020-09) Kariuki, Stephen W.; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson L.
Efforts to reduce pressure on use of wood in particleboard formulation have included the use of non-wood materials such as crop residues. Physical and mechanical properties are determined by the number of the hydroxyl (-OH) groups. Hydroxyl (-OH) groups attracts water molecules through hydrogen bonding affecting water absorption (WA) and thickness swelling (TS). WA and TS affect curing process of adhesive. Curing process of adhesives affects the mechanical characteristics of formulated particleboards. These challenges have been acted upon continuously through research. This review paper presents crop residues used as alternative lignocellulose material source in particleboard formulation and the various advances that have been made to improve on the properties of the resultant particleboards. Improvement over time of the non-wood material in composite materials focusses on increasing water resistance and compatibility between lignocellulose and binder. Crop residues-based are used in making medium and low density particleboards. These boards have shown good mechanical characteristics which include modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB). MOR, MOE and IB have over time been improved by enhancing chemical compatibility of lignocellulose material and the binders. Water absorption and thickness swelling remain challenge. This review paper further explored various methods of improving water absorption and thickness swelling of crop-residue based particleboards
A Review on Pyroprocessing Techniques for Selected Wastes Used for Blended Cement Production Applications
(Hindawi, 2020-08) Nalobile, Protus; Wachira, Jackson M.; Thiong’o, Joseph K.; Marangu, Joseph M.
Pyroprocessing is an important stage in cement manufacturing. In this process, materials are subjected to high temperatures so as to cause a chemical or physical change. Its control improves efficiency in energy utilization and hence enhances production for good quality assurance. Kilns used in cement manufacturing are complex in nature. *ey have longer time constants, and raw materials used have variable properties. *ey are therefore difficult to control. Additionally, the inclusion of various alternative fuels in burning makes the process more complex as the fuel characteristics remain inconsistent throughout the kiln operation. Fuel intensity standards for kilns using fuel oil are very high, ranging from 2.9 GJ to 7.5 GJ/ton of clinker produced. Grinding of clinker consumes power in the range of 2.5 kWh/ton of clinker produced. *ese and other pyroprocessing parameters make cement production costly. *e pyroprocessing process in kilns and the grinding technologies therefore have to be optimized for best processing. *is paper discusses the cement manufacturing and grinding processes. *e traditional kiln technologies and the current and emerging technologies together with general fuel and energy requirements of cement manufacturing have been discussed. From the discussion, it has been established that the cement manufacturing and grinding technologies are capitalintensive investments. *e kiln processes are advanced and use both electricity and natural fuels which are expensive and limited factors of production. *e raw materials used in cement manufacturing are also limited and sometimes rare. *e calcination of the raw materials requires external energy input which has contributed to the high cost of cement especially to low-income population in the developing countries. Self-calcining materials, in which the pozzolanic materials burn on their own, are potential pozzolanic materials with great potential to lower the cost of cement production. Such materials, as shown from the previous research study, are rice husks, broken bricks, spent bleaching earth, and lime sludge. *ere is a need, therefore, for research to look into ways of making cement using kiln processes that would use this property. *is will be cost-effective if successful. It can be done at microand small-scale enterprise.
Characterization of Local Nano-Heat Transfer Fluids for Solar Thermal Collection
(Hindawi, 2020-08) Kawira, Millien
Performance of organic oils in solar thermal collection is limited due to their low thermal conductivity when they are compared to molten salt solutions. Extraction of organic oils from plants can be locally achieved. 'e purpose of this study was to investigate the eﬀect of use of copper nanoparticles in some base local heat transfer ﬂuids (HTFs). Addition of volume fraction of 1.2% of the copper nanoparticles to oil-based heat transfer ﬂuids improved their thermal conductivity as deduced from the thermal heat they conducted from solar radiation. 'e oil-based copper nanoﬂuids were obtained by preparation of a colloidal solution of the nanoparticles. Impurities were added to increase the boiling point of the nano-heat transfer ﬂuids. Stabilizers were used to keep the particles suspended in the oil-based ﬂuids. 'e power output of the oil-based copper nano-heat transfer ﬂuids was in the range of 475.4 W to 1130 W. 'e heat capacity of the steam in the heat exchanger was 93.7% dry and had a thermal capacity of 5.71 × 10 3 to 89.1 Js kJ. 'e heat rate of ﬂow of the oil-based copper nano-heat transfer ﬂuids was an average of 72.7 Js −1 −1 ·kg −1 −1 . 'e thermal eﬃciency for the oil-based copper nano-heat transfer ﬂuids ranged from 0.85 to 0.91. 'e average solar thermal solar intensity was in the range 700 Wm ·kg . 'e heat exchanger used in this study was operating at 4.15 × 10 −2 −2 to 1180 Wm 3 kJ and a temperature of 500.0 ° C. 'e heat transfer ﬂuids entered the exchanger at an average temperature of 381 ° C and exited at 96.3 ° C. 'e average temperatures of operation ranged between 394.1 C and their heat coeﬃcient ranged between 290.1 Wm −2 ° −2 ° C and 254.1 Wm ° C and 219.7 ° C with respective temperature eﬃciencies ranging between 93.4% and 64.4%. It was established that utilization of copper nanoparticles to enhance heat transfer in oil-based local heat transfer ﬂuids can mitigate energy demand for meeting the world’s increasing energy uses, especially for areas inaccessible due to poor land terrain.
Characterization of composite material from the copolymerized polyphenolic matrix with treated cassava peels starch
(Heliyon, 2020-07) Kariuki, Stephen W.; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson L.; Marangu, Joseph M.
Conventional binders in the particleboards formulation involve use of formaldehyde resins. Epidemiologic studies show that formaldehyde is carcinogenic. Efforts to reduce formaldehyde emissions by use of scavengers has not been proven to reduce the emission. Molecular bonding of biobased adhesive molecules with lignocellulose materials provides an alternative way of producing composite material. In this study, maize stalk (MS), rice husks (RH) and sugarcane bagasse (SB) were used as sources of lignocellulose materials for particleboard formulation. SB, MS and RH were collected from their respective sites, sorted and dried. MS and RH were ground. Lignin content determination was done by drying lignocellulose material at 105 C. Lignocellulose materials were prepared by hydrolysis of dried lignocellulose material with sodium hydroxide. Oxidized starch was prepared by oxidation of cassava peel starch using alkaline hydrogen peroxide. Particleboards were formulated through starchlignocellulose polymerization at 60 C compressed with 6.5 Nmm 2 pressure. Characterization of raw materials and formulated particleboards was done using XRD for mineralogical analysis, FTIR and NMR for elucidation of functional groups transformation. The results showed that esteriﬁcation is the main process of chemical bonding in the particleboard formulation due to reaction between COOH from starch and and OH- from lignocellulose. Etheriﬁcation between hydroxyl groups from starch with hydroxyl groups from lignocellulose material. RH combined more through silication process with cassava peels starch than RH and SB showing materials containing high cellulose and hemicellulose content are more compatible. Composite materials formulated were used to produce medium density particleboards that can be used for making furniture and room partitioning.
Heavy metal concentrations in soil and vegetables irrigated with sewage eﬄuent: A case study of Embu sewage treatment plant, Kenya
(Elsevier, 2020-02) Sayo, Sussy; Kiratu, John M.; Nyamato, George S.
As a result of the increasing constraint in the availability of fresh water for irrigation, wastewater especially sewage eﬄuent is being used for irrigation of agriculture ﬁelds, par- ticularly in urban and peri–urban centers. However, there is increasing concern over the associated potential health risks due to the dietary intake of contaminated vegetables. This study was conducted to analyze the levels of copper, zinc, cadmium and lead in sewage ef- ﬂuent, and in the vegetables and soil irrigated using this sewage eﬄuent. Sewage eﬄuent, soil and plant samples were collected and subjected to acid digestion to extract the heavy metals from the samples. Thereafter, concentration levels of the heavy metals were de- termined using Atomic Absorption Spectrophotometer (AAS). The mean concentrations of 0.484–1.834 mg/L, 1.432–4.612 mg/L, 0.015–0.353 mg/L, 0.011–2.123 mg/L for copper, zinc, cadmium and lead, respectively, were obtained in the sewage eﬄuent which were above the WHO permissible levels in wastewater for irrigation. Due to continuous use of sewage eﬄuent for irrigation, gradual accumulation of heavy metals in the soil could occur which could eventually lead to increased uptake of the heavy metals by the growing vegetables. Therefore, to ensure food safety and the use of sewage eﬄuent for irrigation, we suggest that it is important to conduct continuous monitoring and pollution control.
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.
In vitro anti-cancer efﬁcacy and phyto-chemical screening of solvent extracts of Kigelia africana (Lam.) Benth
(Heliyon, 2020) Mukavi, Justus Wambua; Mayeku, Philip Wafula; Nyaga, Justin M.; Kituyi, Sarah N.
Background and objectives: Kigelia africana is a medicinal plant growing naturally in many parts of Africa. In Kenya, a water concoction of the plant is used to treat breast and prostate cancers. Laboratory data on its anti-cancer activity and active principles is limited, hence no scientiﬁc rationale for its medicinal use. This study reports on in-vitro toxic activities of dichloromethane and methanol extracts of the plant against human breast cancer cells and phytochemical screening of the two extracts. Methodology: Plant extracts were obtained by sequential solvent extraction of dry plant material (stem bark) using analytical grade dichloromethane: methanol (1:1) and methanol (Sigma Aldrich). In-vitro anti-cancer activities of the extracts were determined using the suphorhodamine (SRB) assay against a human breast cancer cell line (HCC 1937). Preliminary Thin layer chromatography of plant extracts was done using POLYGRAM® SIL G/UV254 plates (Merck) to establish presence of different classes of secondary metabolites. Results: In-vitro cytotoxic activities of the two extracts were signiﬁcantly different (P ¼ 0.05). The methanol extract exhibited higher activity (IC50 ¼ 55.01 μg/ml). Phyto-chemical screening of the two extracts revealed the presence of terpenoids, phenols, steroids 26.02 μg/ml) compared to that of dichloromethane: methanol (1:1) (IC50 ¼ and ﬂavonoids. Conclusion: The high in-vitro anti-cancer activities of solvent extracts of Kigelia africana justify its use in traditional medicine to manage breast cancer. Phytochemical analysis of the extracts reveal similar proﬁles hence the differences in their anti-cancer activities can be attributed to quantitative variations of various classes of secondary metabolites.
Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus sphaericus and Bacillus megaterium in Mortar Structures
(Hindawi, 2020-05) Mutitu, Daniel Karanja; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong’o, Joseph Karanja; Munyao, Onesmus Mulwa; Genson, Muriithi
The concrete/mortar durability performance depends mainly on the environmental conditions, the microstructures, and its chemistry. Cement structures are subject to deterioration by the ingress of aggressive media. This study focused on the effects of Bacillus megaterium and Lysinibacillus sphaericus on flexural strength and chloride ingress in mortar prisms. Microbial solutions with a concentration of 1.0 × 107 cells/ml were mixed with ordinary Portland cement (OPC 42.5 N) to make mortar prisms at a water/cement ratio of 0.5. Four mortar categories were obtained from each bacterium based on mix and curing solution. Mortar prisms of 160 mm × 40 mm × 40 mm were used in this study. Flexural strength across all mortar categories was determined at the 14th, 28th, and 56th day of curing. Mortars prepared and cured using bacterial solution across all curing ages exhibited the highest flexural strength as well as the highest percent flexural strength gain. Lysinibacillus sphaericus mortars across all mortar categories showed higher flexural strength and percent flexural strength gain than Bacillus megaterium mortars. The highest percent flexural strength gain of 33.3% and 37.0% was exhibited by the 28th and 56th day of curing, respectively. The mortars were subjected to laboratory prepared 3.5% by mass of sodium chloride solution under the accelerated ion migration test method for thirty-six hours using a 12 V Direct Current power source after their 28th day of curing. After subjecting the mortar cubes to Cl media, their core powder was analyzed for Cl content. From these results, the apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd Law using the error function. Bacillus megaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being 2.6456 × 10–10 while the highest value for Lysinibacillus sphaericus mortars was 2.8005 × 10–10. Both of the test bacteria lowered the ordinary Portland cement Cl-ingress but Bacillus megaterium was significantly more effective than Lysinibacillus sphaericus in inhibition.
Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars
(Hindawi, 2020-04) Munyao, Onesmus Mulwa; Thiong’o, Joseph K.; Wachira, Jackson M.; Mutitu, Daniel Karanja; Mwirichia, Romano K.
Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.
Formaldehyde Use and Alternative Biobased Binders for Particleboard Formulation: A Review
(Hindawi, 2019-10) Kariuki, Stephen Warui; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson Leonard
Characterization of Prototype Formulated Particleboards from Agroindustrial Lignocellulose Biomass Bonded with Chemically Modified Cassava Peel Starch
(Hindawi, 2019) Kariuki, Stephen Warui; Wachira, Jackson M.; Kawira, Millien; Murithi, Genson Leonard
Conventional methods of making particleboards utilize wood chips. +is has resulted in a decrease in the tree cover due to the increase in wood demand. +e effect has been climatic change. Wood is bound using phenol formaldehyde resin. Because of the decrease in the forest cover, alternative lignocellulose materials are required. In this study, lignocellulose materials used include sugarcane bagasse, maize stock, and rice husks. +e cassava-starch mix with borax was used as a binder in particleboard formulation. +e lignin content was determined, and its effect on properties of boards was investigated. +e resultant composite material was molded at a pressure of 6.5N/mm2 and at 30°C. +e resultant particleboards had mean densities ranging from 0.604 to 0.611 g/cm3. +e modulus of elasticity ranged from 2364.2N/mm2 to 3329.93N/mm2, modulus of rupture ranged from 13.55N/mm2 to 14.83 N/ mm2, and internal bonding ranged from 1.613N/mm2 to 2.370N/mm2. +e performance of the board was dependent on the lignocellulose material used. Fourier transform infrared spectroscopy analysis showed that main chemical bonding in the particleboard resulted from esterification of –COOHfrom lignocellulose and OH- from starch.+e particleboards formulated were found to be of low-density-fibre standard used in a similar manner to the conventional low-density particleboards
Thermal Resistivity of Chemically Activated Calcined Clays-Based Cements
(Springer, 2017-10) Mwiti, Marangu J.; Thiong’o, Joseph K.
The study investigated the effects of selected potential chemical activators on thermal resistivity of calcined clay based cement mortars. 0.5 M Na2SO4 and 0.5 M NaOH were used as activator solutions. The chemical composition of sampled clays was determined by use of X-Ray Florescence (XRF) technique. Clays were incinerated at a temperature of 800 °C for 4 h. The calcined clays obtained were blended with OPC at replacement level of 35 percent by mass of the OPC to make the test cement labeled PCC35. The PCC35 mortar prisms measuring 40 mmx40mmx160mm were cast with activator solutions and cured in water. Compressive strength was determined at the 28 th day of curing. As a control, OPC and PCC35 were similarly investigated without activator solutions. The 28 day cured mortars were exposed to a temperature of 700 °C for 2 h then cooled in water to room temperature and their compressive strengths determined. Chemically activated PCC35 and non-activated PCC35 exhibited lower loss in weight than OPC after exposure to the elevated temperatures. Chemically activated PCC35 and non-activated PCC35 exhibited higher residual compressive strength than OPC after exposure to the said temperatures. Na2SO4 activated mortars showed higher thermal resistance than NaOH activated mortars. Generally, chemically activated PCC35 exhibited the highest thermal resistance compared to non-activated PCC35 and commercial OPC mortars.
Survey on Nanotechnology
(2019-07) Wako, Ali Halake
Nanotechnology is a field where scientific knowledge and ideas emanating from the sub-atomic, atomic and molecular levels are applied in the manufacture of new and smart materials. Nanotechnology makes use of the novel properties exhibited by materials in the nanoscale. Nanocrystalline materials have microscopic grain sizes of up to 100 nm with remarkably distinct optical, electrical, chemical and mechanical properties different from those of the bulk material. Nanoparticles can be used to develop materials with unique properties since the number of atoms on the surface of a particle in the nanoscale is comparable to that inside the particle. Hence in order to meet the advanced technological demands in the areas such as electronics, catalysis, ceramics, magnetic data storage, structural components etc., it is important to make use of materials in the nanometer scale. Nanotechnology is a rapidly growing field of science which encompasses researchers and scientists from the areas of biology, chemistry, engineering, materials science and physics. This technology provides the basis for research and manufacture of materials in the 21st century. In addition, this interdisciplinary technology will provide a strong platform for the growth of pharmaceutical industry, medical diagnosis, materials industry and the overall economy of the country which will eventually enhance creation of job opportunities, food security, good health and affordable housing. It promises improved efficiency in ICT equipment used in computing, data storage (chips) and communications (fibre optics). It can be used to develop renewable energy sources such as solar cells and panels. It can also be utilized to synthesize filters that can be used to get rid of pollutants; contaminants, harmful salts and viruses in water and sewerage systems and for the diagnosis and treatment of diseases including cancer and to restore damaged human organs or tissues using engineered tissue.
Effects of biocementation on some properties of cement-based materials incorporating Bacillus Species bacteria – a review
(Taylor and Francis, 2019-11) Mutitu, Karanja Daniel; Munyao, Mulwa O.; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Karanja J.; Marangu, Mwiti J.
There is a growing need in the construction industry to improve transfer and durability aspects of Portland pozzolana cement. Ureolytic bacteria have recently emerged as potential micro-organisms well known for precipitation of calcium carbonate through microbiologically induced calcite precipitation (MICP) process. MICP process has emerged as a viable mechanism for improvement of the PPC performance. This paper presents an in-depth discussion on the effects of Bacillus pseudofirmus, Bacillus sphaericus, Sporosarcina pasteurii, Bacillus cereus, Bacillus megaterium and Bacillus subtilis on some selected physico-mechanical properties of cement-based materials. These properties include standard consistency, setting time, compressive strength, water absorptivity, porosity and chloride ingress. The influence of pH, temperature and various bacteria nutrient requirements on optimum MICP process is also presented. In conclusion, benefits and drawbacks on the use of MICP has been discussed. MICP as a potential technique for improvement of physico-mechanical properties as well as repair of cracked cement-based structures has been discussed.
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.
Effects of biocementation on some properties of cement-based materials incorporating Bacillus Species bacteria – a review
(Taylor and Francis, 2019-11) Mutitu, Karanja D.; Munyao, Mulwa O.; Wachira, Jackson M.; Mwirichia, Romano K.; Thiong'o, Karanja J.
There is a growing need in the construction industry to improve transfer and durability aspects of Portland pozzolana cement. Ureolytic bacteria have recently emerged as potential micro-organisms well known for precipitation of calcium carbonate through microbiologically induced calcite precipitation (MICP) process. MICP process has emerged as a viable mechanism for improvement of the PPC performance. This paper presents an in-depth discussion on the effects of Bacillus pseudofirmus, Bacillus sphaericus, Sporosarcina pasteurii, Bacillus cereus, Bacillus megaterium and Bacillus subtilis on some selected physico-mechanical properties of cement-based materials. These properties include standard consistency, setting time, compressive strength, water absorptivity, porosity and chloride ingress. The influence of pH, temperature and various bacteria nutrient requirements on optimum MICP process is also presented. In conclusion, benefits and drawbacks on the use of MICP has been discussed. MICP as a potential technique for improvement of physico-mechanical properties as well as repair of cracked cement-based structures has been discussed.
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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