Genson Murithi

Pathogenic microorganisms in wastewater pose serious health concerns. Several wastewater treatment facilities in parts of Africa discharge wastewater that has not been disinfected. In this regard, more effective approaches in wastewater disinfection are needed to tackle the problem of bacterial contamination. Various advanced oxidation processes (AOPs) have been successfully applied at laboratory and pilot scale. The aim of this study was to determine the efficacy of a single (UV photolysis and H ₂ O ₂ ) and hybrid (UV/H ₂ O ₂ , UV/TiO ₂ ‐zeolite, and UV/TiO ₂ ‐zeolite/H ₂ O ₂ ) AOPs on the removal of Escherichia coli from wastewater from the Embu Sewage Treatment Plant, Kenya. The solid‐phase catalyst TiO ₂ ‐zeolite was prepared by solid–solid dispersion immobilization and characterized by XRD, SEM, and BET. Analysis using SEM and BET showed a well‐formed TiO ₂ ‐zeolite catalyst, with zeolite corresponding to Type IV isotherm which is the characteristic of mesoporous materials. The UV photolysis achieved 81% E. coli , while H ₂ O ₂ achieved 86%. Hybrid systems, on the other hand, UV/H ₂ O ₂ , UV/TiO ₂ ‐zeolite, and UV/TiO ₂ ‐zeolite/H ₂ O ₂ achieved 89%, 91%, and 100% E. coli removal. Additionally, measurement of protein was conducted using the Kjeldahl method to monitor changes in concentration in the wastewater, and bacterial reactivation after 24 h in the dark was measured; no regrowth was observed after 60 min of UV/TiO ₂ ‐zeolite/H ₂ O ₂ , suggesting that this contact period was sufficient to kill cells. Therefore, the UV/TiO ₂ ‐zeolite/H ₂ O ₂ hybrid system has the potential to be used for disinfection purposes, enabling water generation that meets the requirements of regulated parameters in terms of water quality.

Fly ash is widely used as a supplementary cementitious material to reduce Portland cement consumption and enhance the long‐term performance of cementitious composites. However, meaningful comparison of fracture toughness and durability reported across published studies remains challenging because of differences in specimen geometry, testing methods, curing conditions, and reporting practices. This review critically evaluates recent advances in the fracture toughness and long‐term durability of fly ash–based cementitious composites through a structured synthesis of peer‐reviewed studies published between 2020 and 2025. A normalization‐based benchmarking framework was adopted to compare fracture and durability performance relative to corresponding control mixtures, thereby improving cross‐study comparability. The review examines key fracture parameters, including critical stress intensity factor and fracture energy, together with durability indicators such as chloride permeability, sulfate resistance, freeze–thaw resistance, and carbonation depth. The synthesized evidence indicates that moderate fly ash replacement levels of approximately 25%–35% consistently provide the most balanced improvements in fracture resistance and durability through pore refinement, interfacial transition zone densification, and enhanced crack path tortuosity. In contrast, replacement levels exceeding approximately 40% may increase carbonation susceptibility under inadequate curing despite continued improvements in transport resistance. This review further integrates fracture mechanics, durability behavior, and microstructural evolution within a unified interpretation framework and identifies current research gaps, including the need for standardized fracture testing protocols and long‐term field validation. The proposed benchmarking approach provides practical guidance for sustainable mix design and supports the development of more durable and resilient cementitious composites.

Microbial‐induced deterioration (MID) is a threat to the durability of cement‐based materials (CBMs) particularly in sewer and wastewater systems. Whereas blended cements incorporating supplementary cementitious materials (SCMs) offer environmental benefits such as reduced carbon (IV) oxide (CO ₂ ) emissions and enhanced mechanical performance, their long‐term resilience under microbial attack remains uncertain. The present systematic review synthesizes peer‐reviewed literature from 2019 to 2026, selected from Scopus, Web of Science, ScienceDirect, and Wiley Online Library using rigorously defined search terms and stringent inclusion and exclusion criteria. The subsequent analysis divides the results into microbial mechanisms, the performance of the materials, and mitigation strategies, which can help create a comparative analysis between SCMs‐rich systems and next‐generation binders, in particular limestone‐calcined clay cement (LC ³ ). Experimental evidence shows that the mechanical properties of cementitious building materials are significantly reduced by microbial exposure. For example, OPC mortars exposed to Thiobacillus thioparus showed a 34% decrease in compressive strength after 90 days, while exposure to Acidithiobacillus thiooxidans showed strength losses of 19.9% in PPC and 39.8% in OPC mortars. Moreover, compressive strength reductions of up to 96% and dimensional changes of 11% in OPC specimens have been observed after prolonged exposure of these materials to sulfur‐oxidizing bacterial cultures. Such findings highlight the importance of considering microbial activity in durability assessments of concrete structures. Incorporation of SCMs can reduce these adverse effects. Nanophase modified fly ash (FA) concretes, for instance, have negligible pH reduction and dimensional variation whereas calcium aluminate cement (CAC) mortars maintain a higher strength due to their inherent bacteriostatic properties. These observations suggest that SCMs not only alter the microstructure but also provide a degree of biochemical resilience against microbial attack. Though LC ³ show great potential for microbial attack resistance due its alumina‐rich hydrates and reduced portlandite content, there are still uncertainties about their buffering capacity and stability of carbonate phases in the presence of aggressive microbial environments. Mitigation strategies, such as coatings, biocidal additives and microbial‐induced mineralization (MIM) have been evaluated with varying levels of efficacy, but their long term mechanical, microstructural as well as environmental compatibility with the SCMs and LC ³ formulations are underexplored. This review identifies critical gaps in standardized microbial durability testing, LC ³ performance evaluation, and sustainability assessments of mitigation strategies. Addressing these gaps is essential for developing bio‐resilient, environmentally sustainable cementitious materials that support infrastructure resilience and align with the global sustainable development goals (SDGs).

Heavy metal contamination in wastewater remains a critical environmental challenge due to the persistence and toxicity of metal ions such as Pb ²⁺ , Cd ²⁺ , Cr ³⁺ /Cr ⁶⁺ , Cu ²⁺ , Ni ²⁺ , and Zn ²⁺ . Although conventional treatment technologies can achieve high removal efficiencies, their practical application is often limited by high operational costs, energy demand, and secondary pollution. This review critically examines the use of natural and synthetic zeolites as efficient and sustainable adsorbents for heavy metal removal from aqueous systems. Particular emphasis is placed on the fundamental adsorption mechanisms, including ion exchange, surface complexation, and electrostatic interactions, as well as the influence of key physicochemical parameters such as pH, competing ions, and zeolite framework composition. The role of structural modification strategies and zeolite‐based composites in enhancing adsorption performance is also discussed. In addition, the challenges associated with regeneration, stability, and large‐scale application are highlighted. By integrating recent advances with practical considerations, this review provides a comprehensive perspective on the potential and limitations of zeolite‐based materials in real wastewater treatment systems.

Rapid industrialization and urban growth have driven a rising demand for cement, yet ordinary Portland cement (OPC) production remains energy‐intensive and a major source of CO ₂ emissions. The partial substitution of OPC with supplementary cementitious materials (SCMs) offers a sustainable route to reduce environmental impact, production costs, and enhance performance. This study investigates the effects of replacing OPC with stone‐cutting dust (SD), natural pozzolana (NP), and limestone (L) individually and in ternary blends on the compressive strength and microstructure of cement mortars. OPC was partially substituted with SD and NP at 10%–40% and with L at 5%–20%. Ternary blends containing SD, NP, and L replaced OPC at 25%–40%. Compressive strength was measured at 2, 7, 28, and 56 days, and microstructural analysis was performed at 28 days using scanning electron microscopy (SEM). Commercial OPC and Portland pozzolana cement (PPC) served as control samples. Results showed that strength development increased with curing age for all mixes. Optimal performance was recorded at lower substitution levels particularly 10%–20% NP, 5%–15% L, and ≤25% SD achieving 28‐day strengths comparable to or exceeding OPC. High replacement levels (≥35%) reduced strength due to dilution of reactive clinker phases. Ternary blends demonstrated synergistic effects when reactive pozzolanic material and fine limestone were balanced, producing dense microstructures with refined pores and abundant calcium–silicate–hydrate (C–S–H) gel. SEM observations confirmed that improvements in compressive strength were associated with increased C–S–H formation, reduced calcium hydroxide (CH), and better particle packing in optimized mixes. These findings indicate that SD, NP, and L can be used effectively in partial substitution of OPC to produce environmentally friendly cement with satisfactory mechanical performance. Optimized blends can reduce OPC content by up to 25% without compromising strength, supporting sustainable construction practices while promoting the utilization of locally available industrial by‐products. PPC was only used as a microstructural reference to compare hydration morphology with blended OPC systems, while OPC was utilized as the mechanical control for compressive strength evaluation.

Ordinary Portland cement (OPC) remains the most common binder used in construction and accounts for nearly 7%‐8% of the world’s CO ₂ emissions due to calcination of limestone and high energy use during clinker production. Reducing OPC content using SCMs is one of the major strategies to achieve sustainable construction. Stone‐cutting dust, coming from quarrying activities and having a very fine particle size with oxide composition, has come out recently as a prospective SCM. Its chemical and mineralogical composition may vary widely depending on the type of parent rock: granite and basalt dusts, rich in silica and alumina, in contrast with marble and limestone dusts, which are mainly composed of crystalline calcium carbonate with low pozzolanic activity. This review aims to compile and discuss the published works concerning the use of SCD as a partial replacement of OPC, providing detailed information about its physicochemical, mechanical, and durability performance. Studies showed that 10%–25% replacement of OPC with SCD results in improvement in compressive strength (10%–20%), reduction of water absorption, and refinement of the pore structure due to the filler effect and limited pozzolanic reactivity. However, the obtained results are still inconsistent because of varying stone type, mix design, and curing conditions. Moreover, some reports show losses of strength or reduced workability when higher replacement levels were applied or in the case of using SCD enriched in carbonates. SEM, XRD, and FTIR studies demonstrated microstructural densification and secondary C–S–H in silica‐rich systems, while calorimetric and long‐term durability studies remain limited. Overall, SCD has the potential to be a promising sustainable supplementary cementitious material; however, its performance is strongly dependent on mineralogy and processing conditions. It is recommended that a standardized testing framework should be developed in order to allow better comparability between the various published studies and to guide safe and effective application in low‐carbon cementitious systems.

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 x 10(7) 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 x 40 mm x 40 mm were used in this study. Flexural strength across all mortar categories was determined at the 14(th), 28(th), and 56(th) 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 28(th) and 56(th) 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 28(th) 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, D-app, was approximated from solutions to Fick's 2(nd) Law using the error function. Bacillus megaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being 2.6456 x 10(-10) while the highest value for Lysinibacillus sphaericus mortars was 2.8005 x 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.

Conventional methods of making particleboards utilize wood chips. This has resulted in a decrease in the tree cover due to the increase in wood demand. The 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. The cassava-starch mix with borax was used as a binder in particleboard formulation. The lignin content was determined, and its effect on properties of boards was investigated. The resultant composite material was molded at a pressure of 6.5 N/mm2 and at 30°C. The resultant particleboards had mean densities ranging from 0.604 to 0.611 g/cm3. The modulus of elasticity ranged from 2364.2 N/mm2 to 3329.93 N/mm2, modulus of rupture ranged from 13.55 N/mm2 to 14.83 N/mm2, and internal bonding ranged from 1.613 N/mm2 to 2.370 N/mm2. The 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 –COOH from lignocellulose and OH- from starch. The particleboards formulated were found to be of low-density-fibre standard used in a similar manner to the conventional low-density particleboards.