Donald Chimobi Nwonu

High levels of heavy metal ions in wastewater pose significant challenges in the world, originating from both natural and anthropogenic sources. Among the effective techniques for removing heavy metal ions from various water sources, the adsorption process using natural and environmentally friendly materials stands out. In this work, a biocomposite obtained from the bio-treatment of geopolymer using chitosan was used for the effective removal of nickel and arsenic from a synthesised binary wastewater system using batch experiments. The adsorption process was significantly influenced by factors such as pH, adsorbent mass, adsorbent mass and metal ion concentrations. The maximum adsorption capacities for nickel and arsenic were determined to be 45.686 mg/g and 59.580 mg/g, respectively, which were achieved at a pH of 7.66, a contact time of 53 min, a metal ion concentration of 100 mg/l, an adsorbent dosage of 0.1 g and without biopolymer treatment. Four different isotherm models were used to evaluate the experimental data and it was found that the non-modified competitive Langmuir isotherm gave the best fit based on the Marquardt percentage standard deviation. Based on the reaction kinetics, the pseudo-second-order reaction model was the best for describing nickel adsorption process, while the pseudo-first-order model and the intraparticle diffusion model were the best for the arsenic adsorption process. Fourier transform infrared spectrometry and scanning electron microscopy analyses demonstrated the microstructural changes that undergirded the successful removal of nickel ion and arsenic ion using the novel material.

The arousal of environmental concerns due to spike in environmental degradation has necessitated proper waste management and disposal. Arsenic, a potentially toxic element in cassava wastewater, requires treatment prior to the wastewater disposal to minimize environmental pollution and associated health implications. The present study thus addressed the treatment of As⁵⁺ heavy metal in cassava wastewater using an efficient biosorbent from chemically pretreated unshelled Moringa oleifera seeds. The effect of various factors influencing the biosorption process for arsenate removal was studied including pH, contact time, biosorbent dosage, and biosorbent pretreatment concentration. The results of Fourier transform infrared spectroscopy clearly suggested that additional functional groups attributed to esters were formed in the pretreated biosorbent, which is responsible for improvement in biosorption. It was found that contact time, biosorbent dosage, and biosorbent pretreatment concentration had statistically significant effect (p values < 0.05) on arsenate removal. A maximum percentage removal of 99.9% was achieved in the synthetic solution at pH 4.0, contact time of 30 min, and dosage of 2 g for biosorbent pretreated with 1 M of chemical solution. Furthermore, through isotherm and kinetics studies, it was discovered that the biosorption process for untreated biosorbent is by ion exchange, while that for treated biosorbents indicated a multifarious adsorption mechanism. Moreover, the biosorption process was exothermic and spontaneous. Also, it is noted that the sorption capability of the biosorbent increases with pretreatment concentration. A statistical model has been developed with prediction R² of 0.898, which incorporates the effect of treatment concentration on the percentage removal of As⁵⁺ from cassava wastewater.

Highway pavement infrastructure projects which involve soil improvement should be executed, ensuring environmental sustainability. In the present study, guar gum (GG) and lime were assessed for the purpose of soft clay stabilization. The experimental program for the soil stabilization employed a two-stage process. The initial stage involves treatment of the soil with various percentages of lime (3, 5, 7, and 9%) and GG (0.6, 1.0, 1.4, and 1.8%), maintaining the same material acquisition cost and considering curing (0, 7, 14, and 28 days) for the unconfined compressive strength (UCS). In the second experimental stage, a complementary approach in which 3% lime was combined with GG at various percentages (0.1, 0.2, and 0.3%) was employed. The tests conducted include UCS, California bearing ratio (CBR), and strength loss resistance (SLR). Results show that the sole use of lime and GG resulted in significant improvement in the UCS, albeit lime was better. While UCS improved with curing time for the lime-stabilized soil, UCS gain for GG occurred only for up to 7 days curing because biodegradation of GG by microbes in the soil ensues on further curing. Lime-GG stabilization resulted in better UCS and CBR improvement with curing than lime stabilization; however, lime stabilization yielded better SLR. The optimum additive content for strength improvement was obtained at 3% lime + 0.3% GG. Microstructural analysis indicated cementation in the stabilized soil. Predictive models for the UCS were developed based on regression methods. Model evaluation revealed that Gaussian process model provided the best UCS prediction.

Industrialisation and urbanisation contribute greatly to the deposition of toxic waste and metalloids to the environment. Therefore, the use of efficient and eco-friendly materials such as geopolymers and biopolymers is essential for the adsorption of the toxic metals. The implementation of these low-cost sorbents has fascinated a great deal of interest owing to effectiveness, ease of operation, less environmental impact, etc. In this study, biocomposites were synthesised from bio-treatment of geopolymer (kaolin and palm oil fuel ash) using an anionic biopolymer. The biocomposites were utilised as biosorbent for removal of Cu, Fe and Zn in a multi-component system, with the process parameters optimised. FTIR and SEM/EDX outcomes clearly denoted the microporous framework of geopolymer structures and the presence of bio-molecules from the biopolymer. XRD and XRF techniques on the precursors described suitability for geopolymerisation due to the rich aluminate-silicate content. Based on response surface methodology, the adsorption capacities for Cu, Fe and Zn are 35.01 mg/g, 45.175 mg/g and 44.630 mg/g at optimal conditions of pH (7.5), time (40.5 min), metal ion concentration (80 mg/l), biosorbent dosage (0.2 g) and biopolymer concentration (0.75 g in 50 ml). The multi-component system was apt with the modified competitive Langmuir isotherm which described the homogeneity of the prominent sites of the biocomposites. Based on the adsorption kinetics, Cu was only dominated by the pseudo-first-order reaction (PFOR) while Fe and Zn were influenced by both PFOR and intra-particle diffusion processes. The result obtained from the synthesised biocomposites recommends application to actual wastewater systems.