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Abstract A nanosodalite (SOD) was synthesized utilizing Cameroonian kaolin and then used to prepare a nanocomposite (SOD‐GF) with graphene foam (GF). The as‐synthesized materials were characterized using X‐ray diffractometry (XRD), Fourier transform‐infrared (FT‐IR) spectroscopy, N2 adsorption‐desorption and scanning electron microscopy coupled with emission dispersive X‐ray (SEM/EDX). The results show a pure sodalite with high degree of crystallinity with crystallite size and BET surface area of 38.3 nm and 22 m2/g, respectively. The composite's characterization revealed a well‐integrated material in which the structural integrity of each material is maintained, its surface area being 4‐fold that of pristine SOD. Stable SOD and SOD‐GF modified glassy carbon electrode (GCE) were prepared by drop coating without a binder and utilized to study the electrochemistry of chlorpromazine (CPZ) in acidic, neutral and basic pHs. It appeared that (i) CPZ's electrochemical oxidation was a two‐step one‐electron process at SOD/GCE and a one‐step two‐electron process at SOD‐GF/GCE and (ii) the electrochemical reaction mechanism was an EEC mechanism at SOD/GCE while at SOD‐GF/GCE the mechanism was EEC at pH

Developing an efficient water electrolysis system is an important solution for on the development of highly active, cost-effective, and stable electrocatalysts. Carbon-based metal-free catalysts are one of the promising candidates for this purpose. Herein, we present a facile strategy to synthesize and characterize nitrogen and sulfur co-doped porous carbon (NS-PC) from spent sapelli wood sawdust and polyhydric alcohol (xylitol) for efficient hydrogen evolution reaction (HER) in alkaline electrolyte. The resultant NS-PC metal-free catalyst exhibits porous structure, high surface areas and enhanced HER performance with lowest Tafel slope of 68.1 mV dec−1. The enhanced performance is due to the high porosity of carbonaceous material and co-existence of active species (N in the forms of graphitic-N, pyridinic-N, pyrrolic-N, and S in the forms of C–S–C) induced by the maximum carbon-carbon bond polarization, charge re-distribution in the carbon matrices with a synergistically HER activity. In addition, this work provides a versatile and effective strategy for synthetizing excellent carbon-based metal free catalysts from the low cost biowaste for large-scale production of hydrogen through HER.

The specific contributions of the different bacterial flora during the biological treatment of slaughterhouse effluents remain unclear. The objective of this study is to identify the different microbial flora which mainly contribute to the efficiency of the biodegradation of the organic, nitrogenous and phosphate loads contained in the slaughterhouse effluent during its biological treatment. To achieve this, the effluent to be treated was sampled from three slaughterhouses in the city of Ngaoundéré (Cameroon). The various effluents underwent a physicochemical and microbiological characterization. The effluent was subjected to biological treatment. The biodegradation process (biological treatment) took place in two reactors, each operating in batch. One of the two reactors was supplied with oxygen (aeration). The effluent being treated underwent a physicochemical and microbiological characterization for 30 days. The results obtained show organic matter and ammonium contents >1,000 mgO2/L in each of the three effluents. Bacillus cereus (69 × 108 CFU/mL), Pseudomonas aeruginosa (201 × 107 colony forming unit (CFU)/mL) and Yeasts (101 × 106 CFU/mL) globally constitute the majority of microbial groups among the seven microorganisms identified in the effluents of the three slaughterhouses. There is no real oxygenation effect of the medium on the growth of the three microbial flora during the treatment. HIGHLIGHTS The presence of oxygen promotes the rate of elimination of the pollutant load without impacting microbial growth.; The quality of the pollutant favours microbial growth more than the concentration of the pollutant.; The concentration of the pollutant load is influenced by the microbial load during treatment.; The pollutant load varies from one microorganism to another.;

In a grid-connected photovoltaic system, the quality of energy injected by the photovoltaic system into the grid is directly linked to the topology of the inverter used and to the efficiency of its control technique. This paper addresses this problem for a two-level grid-connected photovoltaic inverter operating under low irradiance conditions. The aim is to reduce the harmonic distortion on the electrical network and therefore improve its power quality. To achieve this goal, a control strategy was set up considering the nonlinearity of the dynamic system, and the high dimension of the system model. Thus, a nonlinear controller designed using the backstepping technique is proposed. The effectiveness of this control strategy was evaluated by simulation in MATLAB/Simulink. Results show that the proposed control technique significantly improves the power quality of the grid-connected photovoltaic system by minimizing the current harmonic distortion rates in low irradiance conditions. The current harmonic distortion rates obtained for solar irradiance of 1000 W/m2, 750 W/m2, 500 W/m2, and 250 W/m2 are 0.48%, 0.78%, 1.22%, and 2.16%, respectively. The power factor is 0.988, and the DC bus voltage is maintained at its reference voltage of 600 V with a very low response time during the transient phases. A comparison of our simulation results with those found in the literature on other control techniques such as proportional-integral-derivative (PID) and synergetic controls shows the efficiency, superiority, and satisfactory performance of the proposed control scheme to minimize harmonic distortion under low irradiance conditions. The robustness and better dynamic performance of the proposed backstepping controller under varying irradiance conditions have also been shown.

The current work investigated the optimization of synthetic textile wastewater (STW) containing methyl orange, crystal violet, and neutral red reactive dye degradation on manganese dioxide coated on graphite electrode using the Box-Behnken design (BBD). Carbon coated by manganese oxide (C/ MnO2 ) electrode was prepared by the sol-gel method. Graphite substrates were obtained from spent lithium-ion batteries for recycling and reducing the price of the electrode material in electrochemical processes. C/MnO2 was used as anode and cathode in an electrochemical cell during experiments. In addition, BBD was applied to design the experiments and find the optimal conditions for the degradation of STW. From the proposed model, the rate of the removal efficiency of chemical oxygen demand (COD) reached 83.63% with the optimum conditions (6.989 hours, concentration of 1.5 g/L NaCl, and current density of 50 mA/cm2 ). Based on the obtained optimum values, the specific energy consumption was around 30.359 kWh (kg COD)-1. Furthermore, the C/MnO2 electrode was characterized by Raman spectroscopy, and MnO2 films were prepared from the sol-gel process and deposited on graphite. Thus, using graphite coated with manganese dioxide, indirect anodic oxidation (IAO) can be efficient for the removal of the organic matter from the real textile dye bath.

This article presents a method for the reduction of harmonics generated by photovoltaic generators in electrical networks. Very often, photovoltaic generators produce harmonics due to the nature of the direct current they generate. In order to eliminate these harmonics, parallel active filters are used. They are based on seven-level inverters. For the extraction of maximum power produced by the photovoltaic generators, the modified perturb and observe algorithm is used. Furthermore, to reduce the distortions due to the injected continuous quantities, the filtering of the harmonic quantities is done by four levels active filters using three switching cells per arm connected downstream of the seven-level inverters. The proposed algorithm and model of active filter are evaluated, by calculating of the total harmonic distortion of the current before and after filtering. The rate of 0.04 is obtained. Additionally, the simulation results show this rate is lower than that of the standard Institute of Electrical and Electronics Engineers norms. Besides, the voltage and current of the network after the energy injection are in phase.

This work concerns the treatment of Tenofovir (TEN) in aqueous medium by electro-persulfate (EPS) process. The influence of current intensity, persulfate concentration, solution pH and initial TEN concentration on the degradation of TEN and chemical oxygen demand (COD) removal were studied. The concentration of TEN and COD were analyzed by HPLC and spectrophotometrically method, respectively. The biodegradability was assessed by the measurement of biological oxygen demand (BOD5). The optimization of the COD removal was studied by the surface response methodology, following the Box Behnken design (BBD). The results showed 99.0% of degradation was attained at 30 min of electrolysis and 99.2% of COD abatement was achieved at 90 min at pH 3. The kinetic study of the degradation and COD removal showed that both follows the pseudo-first order law with maximum apparent kinetics constants equal to 0.129 and 0.041 min−1, respectively. The biodegradability of the initial solution was highly improved after 30 min of electrolysis. The model equation based on investigation of BBD shows a good adequacy and able to explain the COD removal during the electrochemical treatment of TEN. These findings contribute significantly to exhibit the potential of combination of electrochemistry with biological treatment for emerging pollutants removal from aqueous media.

Mycotoxins are naturally occurring toxins that contaminate different crops and foodstuffs under certain circumstances during harvesting, handling, storage, and processing. Neither the dietary intake of mycotoxins in Cameroon is well characterized, nor its health effects on the consumers. This review is intended to be the first milestone towards national risk management of mycotoxins. It is noteworthy that mycotoxins contaminate the main staple foods of Cameroonian communities, which are also often used as complementary foods for infants, young children, and people with compromised immune systems (e.g., HIV/AIDS), thus calling for urgent intervention in primary and secondary prevention. Very few data exist on mycotoxin contamination in Cameroonian agricultural commodities and food items. Only 25 studies from 14 different authors have been published in the last decade. On the basis of available data in Cameroon, the Estimated Daily Intake (EDI) of major mycotoxins in foods for Aflatoxins was 0.0018–14.2 µg/kgbw/day in maize, 0.027–2.36 µg/kgbw/day in cassava, and 0.023–0.1 µg/kgbw/day in groundnuts. The estimated daily intake of fumonisins was 0.12–60.6 µg/kgbw/day in maize and 0.056–0.82 µg/kgbw/day in beans. Based on the estimated distribution of human exposure levels by food, maize and cassava are the major sources of exposure and should be prioritized, followed by beans and spices. This estimate will be updated along with improvements on the national database on mycotoxin contamination of Cameroonian foods.

Treatment of wastewater originated from tannery in Cameroon by electro-Fenton (EF) and electro-persulfate (EP) processes using graphite as free-cost electrodes was investigated in this study. Graphite obtained from recycled spent lithium ion batteries and used as anode and cathode in an electrochemical device for degradation studies. Degradation study was evaluated based on the COD removal. Effect of current density, electrolysis time and the concentration of the electrolyte investigated, to evaluate the most suitable process and least energy consumption. Using the electro-Fenton process, the treatment reached a maximum reduction of 67.25% for COD removal under the following conditions: pH (3), I = 300mA, [Fe2+] = 0.1 mM, time = 6 h, meanwhile electro-persulfate process led to the removal of COD up to 95.62% under the following conditions: pH = 3, I = 300mA, [S2O82−] = 0.6mM and time 6 h. The energy consumption for high removal of COD showed that EF and EP have a cost of 8.357 and 6.867 kwh/gCOD respectively. EP was found to be the most efficient method for the degradation of tannery wastewater, since this technic has the lowest cost of operation. Thus, EP proved to be an appropriate technique for the removal of organic load from tannery wastewater.

Slaughterhouse effluent treatment processes require daily technological adjustments for better efficiency. With a view to combine adsorption to biological treatment, this work aims at evaluating the capacity of simultaneous elimination of nitrogen (NH4+, NO2−, NO3−), phosphates (PO43−) and organic (MO) charges contained in the slaughterhouse effluent, by adsorption on an adsorbent (carbon) made from sawdust Triplochyton scleroxylon (Ayous). To achieve this, the effluent to be treated was sampled in a cattle slaughterhouse in the town of Ngaoundéré. After physicochemical characterization, this effluent underwent various adsorption tests in two reactors operating in batch. Parameters such as the influence of the initial concentration and the initial pH of the effluent, the adsorption capacity of the pollutant load of the slaughterhouse effluent and the contact time were followed during these adsorption tests. The kinetics and absorption mechanisms of organic pollutants, nitrogen and phosphates were modelled. At the end of the manipulations carried out, the results obtained reveal that the average adsorption equilibrium time is 60 min with abatement rates varying between 31% and 52% for the three forms of nitrogen (NO3−, NO2−, NH4+), 40.7% and 52% for organic matter and phosphate respectively. The adsorption of MO, NO3−, NO2−, NH4+ and PO43− on the adsorbent based Ayous is globally optimal at pH 4, and is governed by the pseudo-second order kinetic model. This adsorption takes place both in monolayer and multilayer. The adsorbent made from Ayous sawdust, in combination with the biological treatment will significantly improve the efficiency of the treatment of slaughterhouse effluent.

Development of low-cost electrocatalyst for oxygen reduction reaction (ORR) is the main requirement for advanced chlor-alkali (ACA) cell. Herein, we report a simple and economical one-pot microwave assisted synthesis of nitrogen and phosphorus co-doped graphene (NPG) from graphene oxide in presence of ammonium dihydrogen phosphate. The optimized NPG showed well exfoliated graphene oxide with few layers of graphene and the XPS assured that about 6% of nitrogen and 4% of phosphorus co-doping into the graphene lattice through the various active forms of nitrogen and phosphorus. The large N and P content in the catalyst with all the active forms could facilitate faster ORR kinetics as well as it stability. The oxygen depolarized cathode containing electrocatalyst was fabricated and utilized in ACA cell. According to the result, the minimum cell voltage (2.01 V) was found under conditions: brine concentration 300 g/L, temperature 80 °C, pH 2 and current density 1.0 kA/m2.

Textile industries produce large quantity of toxic effluents, very loaded and hardly biodegradable. In this work, MnO2 was synthetized by sol-gel method and coated on graphite rods which were obtained from used batteries and tested as electrodes for the degradation of anionic dye. Physical and chemicals characteristics of the material were determined by Fourier transform infrared and X-ray diffraction spectroscopies. The electrochemical properties of the elaborated material were carried out using linear sweep voltammetry and electrochemical impedance spectroscopy. During this study, experiments were carried out an electrochemical cell where C/MnO2 electrode was employed as cathode and anode. Box-Behnken design was used to design the experiments and find the optimal conditions for the degradation of Methyl Orange (MO) synthetic solution. The results also show that indirect anodic oxidation of MO using sodium chloride as supporting electrolyte was effective for MO degradation. However, the optimum conditions were 25 ​mg/L of initial dye concentration, 5 ​g/L of NaCl concentration, 5.6 ​h of electrolysis time, and 108 ​mA/cm2 of current density, where 77.0% degradation would be achieved from proposed model. According to these results, indirect anodic oxidation using manganese dioxide electrode in an electrochemical cell is efficient in the degradation of MO synthetic solutions.

The treatment of slaughterhouse effluents still arouses particular interest today because of the complexity of the processes implemented with approximate yields. The objective of this work is to study the influence of time and oxygenation on the biodegradation of organic, nitrogen and phosphate loads in slaughterhouse effluent by biological treatment without the addition of bacterial flora. The effluent sampled in a slaughterhouse in the town of Ngaoundéré (Cameroon) underwent physicochemical characterization. It then underwent biological treatment in two stirred batch reactors, one in anoxia and the other in aeration. During the treatment, the organic, nitrogenous and phosphate pollutants were analysed on samples taken every three (3) days for nine (9) days, then every six (6) days for eighteen (18) days. The results obtained show that the effluent is generally basic in the two reactors during the treatment. The overall reduction rate of all pollutants (organic matter, NH4+, NO3-, NO2-, PO43- and SO42-) monitored, is higher in the reactor operating in anoxia (57 %) than in the one operating in aeration (44 %) at the end of the 27 days of treatment. However, biodegradation is more rapid during the first 9 days of treatment, during which the oxygenation of the medium was a real catalyst for accelerating the biodegradation of certain pollutants such as organic matter, NO2- and PO43-. So, the oxygenation of the environment has favoured the acceleration of the biodegradation of certain pollutants, without necessarily promoting the efficiency of their elimination in the effluent. Also, whether the reactor operating in anoxic or aerobic, there is an effective biodegradation time beyond which microbial activity is no longer effective.

The Egusi Okra soup is a traditional African meal that is considered of high nutritional value and protective against weight loss. We introduce the concept of âkitchen toxicologyâ to analyse the recipe of the Egusi Okra soup and highlight possible mitigation measures for toxic and/or antinutritional effects in the wide spectrum of health and nutritional needs of HIV+/AIDS subjects. In particular, we focus on toxicants (environmental contaminants, process contaminants, substances leaching from food contact materials) dysregulating the immune status, as well as on interactions between nutrients, contaminants, and/or antinutrients which may lead to secondary/conditioned nutritional deficiencies or imbalances; in their turn, these can modulate the ability to cope with toxicants, and increase nutritional requirements. Recommendations are given for practices preserving the Egusi Okra soup from such risk factors, identifying points of particular attention during meal preparation, from purchase of raw ingredients through to food handling, cooking, storage, and consumption. The Egusi Okra soup is discussed in the context of a diet that is asked to mitigate complications (weight loss, opportunistic infections) and support antiretroviral therapy in African countries with high HIV/AIDS prevalence. The paper discusses how nutritional interventions benefit of the integration of kitchen toxicology practices in everyday life. Toxicological risk assessment is crucial to understand the history and status of the person exposed to or affected by infectious diseases. Keywords: Traditional diet, Malnutrition, Food safety, Weight loss, Immune system, Dysmetabolic diseases, Clinical toxicology, Nutrition security

The aim of this work is to valorise wood waste in the discoloration of slaughterhouse effluent by the adsorption principle. To achieve this, two adsorbents were made from sawdust species Kaïcedra (Khaya senegalensis) and Pin (Pinus sp). A slaughterhouse effluent of cows was sampled in the town of Ngaoundéré and characterized. An experimental design was used to determine the minimum values of adsorbent mass and agitation time required for better turbidity reduction of the slaughterhouse effluent. The results obtained reveal that the two adsorbents produced are more microporous than macroporous with specific surface areas ranging from 39.40 m2/g to 79.65 m2/g for Kaïcedra and Pin, respectively. The effluent of the slaughterhouse to be treated is turbid, conductible and rich in sulphate. The discoloration tests of this effluent with the two adsorbents produced made it possible to reduce more than 75% of all the above-mentioned polluting loads. Under the optimum pair of factors (adsorbent mass - agitation time), it is possible on an industrial scale to use almost 200 g of Kaïcedra adsorbent or 550 g of Pin adsorbent to remove more than 90% of the turbidity of 100 L of slaughterhouse effluent stirred for 1 h. Keywords: Adsorption, Sawdust, Slaughterhouse effluent, Turbidity, Organic matter

We synthesized two series of androstane derivatives as inhibitors of type 3 and type 5 17β-hydroxysteroid dehydrogenases (17β-HSDs). In the first series, four monospiro derivatives at position C17 were prepared from androsterone (ADT) or epi-ADT. After the protection of the alcohol at C3, the C17-ketone was alkylated with the lithium acetylide of tetrahydro-2-(but-3-ynyl)-2-H-pyran, the triple bond was hydrogenated, the protecting groups hydrolysed and the alcohols oxidized to give the corresponding 3-keto-17-spiro-lactone derivative. The other three compounds were generated from this keto-lactone by reducing the ketone at C3, or by introducing one or two methyl groups. In the second series, two dispiro derivatives at C3 and C17 were prepared from epi-ADT. After introducing a spiro-δ-lactone at C17 and an oxirane at C3, an aminolysis of the oxirane with L-isoleucine methyl ester provided an amino alcohol, which was treated with triphosgene or sodium methylate to afford a carbamate- or a morpholinone-androstane derivative, respectively. These steroid derivatives inhibited 17β-HSD3 (14–88% at 1 μM; 46–94% at 10 μM) and 17β-HSD5 (54–73% at 0.3 μM; 91–92% at 3 μM). They did not produce any androgenic activity and did not bind steroid (androgen, estrogen, glucocorticoid and progestin) receptors, suggesting a good profile for prostate cancer therapy.

Chemical pesticides are widely used in Cameroon for agricultural production. In 2015, more than 600 pesticide products were approved for use in various foodstuffs. Much misuse of these chemicals by farmers has been documented in rural and urban settings. This pilot study aims to contribute to the improvement of the health of the population and the environmental preservation by identifying pesticide-poisoning cases, the most incriminated products and critical risk factors of exposure. Questionnaires were administered to pesticide vendors, farmers and health personnel, and observations made on farmers’ practices at their work places. From July to September 2016, 24 villages from five sites, representing the most important agricultural production areas of the five agro-ecological zones of Cameroon, were visited. In total, 519 people were interviewed: 412 farmers, 69 pesticide vendors and 38 health personnel. A total of 180 pesticide formulations out of 610 registered in 2015 were said to be used by farmers. In the 38 health centers visited, 56 cases of pesticide poisonings and intoxications were reported between 2011 and 2016. Paraquat-, glyphosate-, cypermethrin- and metalaxyl-formulated pesticides were the most incriminated. In total, 78% of poisoning cases were accidental, 12% suicide attempts, 4% criminal. Entry of pesticide products from neighboring countries needs to be better regulated, and the quality of pesticides sold on the market should be monitored periodically. Empty pesticide containers should be recuperated from smallholder farmers. Authorities should set up a harmonized pesticide-poisoning management procedure, and create a toxico-vigilance system for surveillance cases and preventive actions.

The Composite Centered Experimental Design (CCED) using the response surface methodology was used to optimize the synthesis of a hematite‐geopolymer composite, applied to the preparation of a Pb2+ electrochemical sensor. Two important experimental parameters in the formulation (curing time and hematite content) were considered in the optimization of the synthesis of the composite material. The electrochemical signal of Pb2+ at a carbon paste electrode modified by the synthesized composite was used as a response to identify the best formulation. After applying the generated experimental plan, the optimal composite material was obtained using 17.08% hematite and a curing time of 0.16 days. The characterization of the optimized composite material revealed the presence of a porous structure and a poly(phospho‐ferro‐siloxo) network, but with a fraction of well dispersed and unreacted hematite. Preliminary experiments confirmed that the sensor prepared with the composite showed high stability and reproducibility of the Pb (II) signal, justifying its application for accurate sensing of the metal cation in an aqueous solution. A Pb2+ calibration curve was obtained after optimizing the experimental detection parameters (composition of the carbon paste electrode, pH of the accumulation solution, accumulation time, and electrolysis potential). A detection limit of 0.2 nM (based on a signal‐to‐noise ratio of 3) was obtained for a studied concentration range between 0.04 and 0.48 nM. The designed sensor also showed remarkable selectivity and excellent performance in real media samples (spring, tap, rain, and well water). [ABSTRACT FROM AUTHOR]

A pure natural kaolinite (K) was modified by intercalation and grafting into the interlayer space of 1-(2-hydroxyethyl)piperazine (HEP). The resulting organo-inorganic hybrid material (referred as KHEP) was characterised using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and 29Si nuclear magnetic resonance (NMR) techniques. The electrochemical characterisation of K and KHEP materials was carried out by studying the electrochemical behaviour using cyclic voltammetry of [Fe(CN)6]3− ions on the surface of a glassy carbon electrode (GCE) modified with a film of each of these materials (GCE/K and GCE/KHEP). The GCE/KHEP organokaolinite film electrode was successfully applied for the simultaneous detection of Pb(II) and Cu(II) in contaminated media. The peak currents of Pb(II) and Cu(II) obtained under the same optimal conditions on GCE/KHEP were much more intense than those obtained on GCE/K and bare GCE. Under optimal conditions, the influence of the concentration of Cu2+ and Pb2+ ions on the peak currents was studied for several concentration ranges. The obtained linear calibration curves were then used to calculate the different limits of detection (LOD) on the basis of a signal-to-noise ratio of 3. Thus, in simultaneous detection and for the concentration range from 0.02 to 0.12 µmol L−1 (pH accumulation medium 5.0) and for each of the ions analysed, LODs of 1.942 nmol L−1 for Cu(II) and a LOD of 1.072 nmol L−1 for Pb(II) were obtained. The GCE/KHEP sensor developed in this work was successfully applied for the simultaneous detection of Pb(II) and Cu(II) in real samples. ASSWV signal corresponding to the simultaneous detection of Pb2+ and Cu2+ ions recorded on unmodified GCE (black curve), GCE/K; (red curve) and GCE/KHEP (blue curve) in 0.2 mol L−1 NaNO3 (with pH adjusted at 2.5) after 7 min of accumulation in aqueous medium (pH 5.0) of each ion at the concentration at 2.0 µmol L−1. Other experimental conditions are as follows: telec: 80 s, Eelec: − 0.90 V, Potential amplitude: 0.05 V, Step potential (V): 0.005 V and Frequency: 50 Hz. [ABSTRACT FROM AUTHOR]