Browsing by Author "Bakari, Omari"

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Conceptualizing the Fe0/H2O System: A Call for Collaboration to Mark the 30th Anniversary of the Fe0-Based Permeable Reactive Barrier Technology
(MDPI, 2022-10-03) Cao, Viet; Bakari, Omari; Tchidjo, Joseline; Bandjun, Nadège; Tchoupé, Arnaud; Gwenzi, Willis; Njau, Karoli; Noubactep, Chicgoua
Science denial relates to rejecting well-established views that are no longer questioned by scientists within a given community. This expression is frequently connected with climate change and evolution. In such cases, prevailing views are built on historical facts and consensus. For water remediation using metallic iron (Fe0), also known as the remediation Fe0/H2O system, a consensus on electro-chemical contaminant reduction was established during the 1990s and still prevails. Arguments against the reductive transformation concept have been regarded for more than a decade as ‘science denial’. However, is it the prevailing concept that denies the science of aqueous iron corrosion? This article retraces the path taken by our research group to question the reductive transformation concept. It is shown that the validity of the following has been questioned: (i) analytical applications of the arsenazo III method for the determination of uranium, (ii) molecular diffusion as sole relevant mass-transport process in the vicinity of the Fe0 surface in filtration systems, and (iii) the volumetric expansive nature of iron corrosion at pH > 4.5. Item (i) questions the capability of Fe0 to serve as an electron donor for UVI reduction under environmental conditions. Items (ii) and (iii) are inter-related, as the Fe0 surface is permanently shielded by a non-conductive oxide scale acting as a diffusion barrier to dissolved species and a barrier to electrons from Fe0. The net result is that no electron transfer from Fe0 to contaminants is possible under environmental conditions. This conclusion refutes the validity of the reductive transformation concept and calls for alternative theories.
Effects of zero-valent iron on sludge and methane production in anaerobic digestion of domestic wastewater
(Elsevier, 2023-12-08) Bakari, Omari; Njau, Karoli; Noubactep, Chicgoua
Iron metal (Fe0) materials enhance the performance of anaerobic digestion (AD) reactors to remove pollutants. Most research focused on the materials' mechanisms and effectiveness in enhancing AD. However, there is scant information on the biogas and sludge quality and quantity and the kinetics of generated methane (CH4) of biogas from the Fe0-aided AD of domestic wastewater (DW). The information is essential for AD reactors' management. This study characterizes the sludge and biogas from Fe0-aided AD of DW and predicts the CH4 yield using the Gompertz, Logistic, and Richard models to study the impact of Fe0 materials on the composition and generation of sludge and biogas. Bench-scale reactors containing DW were fed with Fe0 and operated for 53 days in a quiescent condition, at 24 ± 3 OC room temperature, at 7.3 initial pH value. Steel wool and iron scrap were used as Fe0 sources. A parallel experiment without Fe0 was performed as an operational reference. Results indicate that Fe0 significantly enriched most of the nutrients in sludges, produced well-settling sludge (sludge volume index ≤30), and enriched the CH4 of biogas by more than 12%. Furthermore, all the tested models exhibited good fitting (error <10%) in predicting CH4 production. Fe0-aided AD produced a sludge with the potential for application in agricultural land and increased the heating value of the biogas by enriching the CH4. More than 80% of particles generated from Fe0-aided AD of DW can be settled in sedimentation tanks designed at an overflow rate ≤40 m/d. Richard was the best model for predicting methane yield from Fe0-aided AD of DW (error <1.6%).
Fe0-Supported Anaerobic Digestion for Organics and Nutrients Removal from Domestic Sewage
(MDPI, 2022-08-15) Bakari, Omari; Njau, Karoli; Noubactep, Chicgoua
results from different research suggest that metallic iron (Fe0) materials enhance anaerobic digestion (AD) systems to remove organics (chemical oxygen demand (COD)), phosphorus and nitrogen from polluted water. However, the available results are difficult to compare because they are derived from different experimental conditions. This research characterises the effects of Fe0 type and dosage in AD systems to simultaneously remove COD and nutrients (orthophosphate (PO43−), ammonium (NH4+), and nitrate (NO3−)). Lab-scale reactors containing domestic sewage (DS) were fed with various Fe0 dosages (0 to 30 g/L). Batch AD experiments were operated at 37 ± 0.5 °C for 76 days; the initial pH value was 7.5. Scrap iron (SI) and steel wool (SW) were used as Fe0 sources. Results show that: (i) SW performed better than SI on COD and PO43− removal (ii) optimum dosage for the organics and nutrients removal was 10 g/L SI (iii) (NO3− + NH4+) was the least removed pollutant (iv) maximum observed COD, PO43− and NO3− + NH4+ removal efficiencies were 88.0%, 98.0% and 40.0% for 10 g/L SI, 88.2%, 99.9%, 25.1% for 10 g/L SW, and 68.9%, 7.3% and 0.7% for the reference system. Fe0-supported AD significantly removed the organics and nutrients from DS
Potential use of zero-valent iron in enhancing performance and resource recovery during the anaerobic digestion of domestic sewage
(NM-AIST, 2024-08) Bakari, Omari
Incorporating metallic iron (Fe 0 ) into anaerobic digesters can improve organics (chemical oxygen demand (COD)), phosphorus, and nitrogen from contaminated water. However, no study has systematically assessed Fe0 -supported anaerobic digestion (AD) systems for removing organic compounds and nutrients from domestic sewage (DS), limiting our understanding of their potential to replace tertiary treatment units. Besides, existing studies often focus on single contaminants at high concentrations, which may not reflect real-world effluents with multiple pollutants. Variations in experimental conditions and the type of wastewater effluent treated complicate comparisons across studies. Additionally, there is a lack of comprehensive evaluations of predictive models for methane (CH₄) yields in Fe0 -supported AD systems, hindering the identification of the most effective model and affecting future research and applications. Moreover, there is little information on sludge characteristics from Fe0 -aided AD systems and their potential applications. This research focused on three primary objectives: (i) assessing the impact of Fe0 type and dosage in AD systems for the simultaneous removal of COD and nutrients (orthophosphate (PO4 3- ), ammonium (NH4 + ), nitrate (NO3 - )), and (ii) characterizing the solids and biogas in Fe0 -supported AD of DS, and (iii) evaluating the Gompertz, Logistic, and Richard models for methane yield prediction. Two distinct experiments were conducted at various scales. In the first experiment, lab-scale reactors containing DS were subjected to varying dosages of Fe0 (0 to 30 g/L) over 32 experimental runs conducted for 76 days at a constant temperature of 37 ± 0.5℃. In the second experiment, bench-scale reactors with DS were fed with Fe0 and operated over 15 experimental runs for 53 days at 24 ± 3℃ temperature. Iron scraps (SI) and steel wool (SW) were used as the Fe0 sources. A control experiment was also conducted. It was found out that: (a) the optimal Fe0 dosage for organic and nutrient removal was 10 g/L SI, (b) NH4 + and NO3 - removal showed the lowest removal efficiency, and (c) maximum removal efficiencies for COD, PO4 3- , and NH4 + + NO3 - were 88.0%, 98.0%, and 40.0% for 10 g/L SI; 88.2%, 99.9%, and 25.1% for 10 g/L SW; and 68.9%, 7.3%, and 0.7% for the control system. Fe0 significantly enriched nutrients in the sludge, improved settling characteristics, and increased the percentage of methane content in biogas by over 12%. All tested methane prediction models showed good accuracy (error < 10%), with the Richard model demonstrating the highest level of fit (error < 1.6%). These findings confirm the effectiveness of Fe0 -supported AD in removing organics and nutrients from DS, producing agriculturally suitable sludge, and enhancing biogas methane content for potential energy recovery