Enhanced ex-situ bioremediation of soil contaminated with petroleum refinery waste effluents by biostimulation through electrokinetics and inorganic fertilizer

Ex situ bioremediation is an attractive and often cost-effective technology for the clean-up of organics-contaminated sites; however, it often requires extended treatment time under field conditions. Electrokinetic bioremediation is an emerging technology to remediate organic-contaminated soil. Thus, the objective of this study was to investigate the feasibility and effectiveness of using electrical biostimulation processes to enhance ex-situ bioremediation of soils contaminated with organic pollutants. The effect of different applied voltages (0.33 – 1.0 V/cm) as well as the effect of inorganic (NPK) fertilizer on the electrokinetic bioremediation of soil was evaluated. A bench-scale uniform electrokinetic system was developed for this purpose and tested by using a sandy loam soil spiked with petroleum refinery waste effluent having total organic compound (TOC) as model organic pollutant. The results demonstrated that the application of a low direct current (voltage) could be an effective strategy to accelerate the movement and ex situ biodegradation or removal of TOC in the soil. At the application of 0.33, 0.67 and 1.0 V/cm voltage, electricity biostimulation correspondingly and averagely remove 65.7%, 70% and 73.3% of TOC from soil in only 15 days without nutrient (NPK fertilizer) application; while with nutrient application, electricity biostimulation correspondingly and averagely removed 71.8%, 77.4% and 81.6% of TOC from soil. Thus, bioremediation of soil contaminated with petroleum refinery waste effluents can be enhanced by electrokinetics and the rate of TOC biodegradation or removal relatively increased with increased specific voltage application. The electrokinetic bioremediation of soil can further be enhanced or accelerated with the addition of nutrient in the form of nitrogen, phosphorus and potassium (NPK). Small changes in soil pH and/or moisture were induced by the applied electric field.Keywords: Bioremediation; Electrokinetics; NPK Fertilizer; Refinery Waste Effluents; TOC

Bioelectricity generation and treatment of petroleum refinery effluent by Bacillus cereus and Clostridium butyricum using microbial fuel cell technology

Microbial fuel cells (MFCs) being an emerging technology have been the research focus of increasing interest due to their sustainable capacity for wastewater treatment together with electricity generation. This study investigated the potential use of pure culture Bacillus cereus and Clostridium butyricum as inoculums in MFCs for simultaneous bioelectricity generation and treatment of petroleum refinery effluent. Double-chambered MFCs was used for the study and operated over four-batch cycles for 30 cumulative days but with different external resistances. The influent concentrations of chemical oxygen demand (COD) and total organic compound (TOC) in the petroleum refinery effluent was 970 mg/l (ppm) and 156 g/l, respectively. Experimental results indicated that the MFCs with the use of Bacillus cereus as biocatalyst achieved its maximum COD removal, TOC degradation and coulombic efficiencies of 70%, 88.7% and 19.21%, respectively; while with the use of Clostridium butyricum, it achieved the highest COD removal, TOC degradation and coulombic efficiencies of 54.2%, 68.7% and 17.84%, respectively. A maximum voltage of 450 mV and highest power density of 17066.67 mW/m2 with a maximum current density of 1.270 mA/m2 was obtained in regard to the external resistor of 1000 Ω using Bacillus cereus as biocatalyst. Similarly, using Clostridium butyricum as biocatalyst the maximum voltage of 370 mV and highest power density of 8816.17mW/m2 with a maximum current density of 0.913 mA/m2 was achieved. The study demonstrated that both Bacillus cereus and Clostridium butyricum has strong potentials to be used as inoculums for simultaneous bioelectricity generation and treatment of petroleum refinery effluent in MFCs.Keywords: Microbial fuel cell; Petroleum refinery effluent; Bacillus cereus; Clostridium butyricum; Bioelectricity; Biodegradatio

Removal of Phenol from Paint Wastewater by Adsorption onto Phosphoric Acid Activated Carbon Produced from Coconut Shell: Isothermal and Kinetic Modelling Studies

The feasibility of using phosphoric acid activated carbon produced from coconut shell to remove phenol from paint wastewater under batch mode was investigated. The results showed that adsorption of phenol was contact time, adsorbent particle size and adsorbent dosage dependent. The batch equilibrium adsorption data were analyzed by two-parameter adsorption isotherm models of Langmuir and Freundlich using the linear regression method. Both isotherm models fitted very well to the equilibrium adsorption data, however, the Freundlich isotherm equation provided the best model to describe the adsorption of phenol onto coconut shell activated carbon. Adsorption capacity of 2.01 mg/g and adsorption intensity of 1.07 was obtained for granular coconut shell activated carbon and corresponding 3.63 mg/g and 1.55 for powdered coconut shell activated carbon at 30 oC. The adsorption kinetic data were fitted to three adsorption kinetic models (pseudo first-order, pseudo second-order and intra-particle diffusion) using the linear regression method. The three kinetic models fitted well to the adsorption kinetic data; however, the pseudo second-order kinetic model gave the best fit and the adsorption mechanism was controlled by film diffusion. Thus, phosphoric acid activated carbon produced from coconut shell has the potential for application as an effective adsorbent for phenol removal from wastewater. Keywords: Activated carbon; Adsorption isotherms; Adsorption kinetics; coconut shell; paint wastewaters

Thin Layer Drying Kinetics and Modelling of Okra (Abelmoschus Esculentus (L.) Moench) Slices under Natural and Forced Convective Air Drying

The effect of sample thickness (10 and 20 mm), method of drying (open sun, solar and hot air drying) and drying air temperature (50, 60 and 70 oC) on the drying characteristics and kinetics of okra slices were investigated. The results showed that sample thickness, method of drying and drying air temperature significantly (P = 0.05) affected the drying rate and thus the drying time. It was observed that okra slices would dry perfectly within 216 – 240 h, 192 -216 h, and 12 – 19 h under open sun, solar and hot air drying, respectively. Irrespective of the drying method, all the samples dried in the falling rate period with no constant rate period. Four thin-layer semi-empirical mathematical drying models (Newton, Page, Henderson and Pabis, and Logarithmic models) were fitted to the experimental drying curves. The models were compared using the coefficient of determination ( ) and the root mean square error (RMSE). The logarithmic model has shown a better fit to the experimental data obtained from the open sun, solar and hot air drying respectively as relatively compared to other tested models. Correlation between the model parameters and the drying air temperature (under hot air drying) to calculate moisture ratio in relation to the drying time were also determined. The transport of water during drying was described by application of Fick’s diffusion model and the effective moisture diffusivity was estimated. The value ranges from 0.253 to 0.901 × 10-10 m2/s for open sun, 0.31 to 1.01 × 10-10 m2/s for solar drying and 3.29 to 14.7 × 10-10 m2/s for hot air drying, respectively. The Arrhenius-type relationship describes the temperature dependence of effective moisture diffusivity and was determined to be 16.74 kJ/mol and 10.39 kJ/mol for 10 and 20 mm sample sizes, respectively. Keywords: Okra; Open sun drying; Solar drying; Hot air drying; Mathematical modelling; Effective moisture diffusivity.

Mathematical Modelling and Simulation of the Mass and Heat Transfer of Batch Convective Air Drying of Tropical Fruits

In the present study, a mathematical model capable of predicting the instantaneous moisture and temperature distribution inside fruit and vegetable material undergoing shrinkage during drying process has been developed. The model takes into account moisture content and shrinkage of material as well as shrinkage dependent effective diffusivity. The mass transfer and heat equations were solved using a numerical technique. For evaluation and validation purposes, the model was applied to drying data obtained from the drying tests carried out on banana slices. An oven dryer was used to conduct the test. Banana slices of approximately 5 mm thickness and 30 mm diameter were dried over a temperature range of 50 oC and 70 oC for 6 hours. The predicted results compared favourably with the experimental results. Thus, the experimental results validated the model developed. In addition, empirical drying rate equations are developed. The model is therefore capable of predicting dynamic behaviour of drying of fruits undergoing shrinkage and, as such, it can be used as a design tool. Keywords: Drying; Mathematical modelling; Shrinkage; Simulation; Moisture diffusivit

Experimental and Kinetic Modelling Studies on the Acid-Hydrolysis of Banyan Wood Cellulose to Glucose

Bioconversion of agricultural waste products to produce value-added fuels and chemicals offers potential economical, environmental and strategic advantages over traditional fossil-based products. The kinetics of acid hydrolysis of cellulose isolated from banyan wood sawdust was studied at sulphuric acid concentration of 2 to 5 M (moles/dm3) and temperature ranging between 40 – 80 oC in a stirred conical flask which served as a batch reactor. The results showed that the rate of acid hydrolysis by virtue of glucose yield generally increased with increase in acid concentration and temperature used. The experimental data were fitted to integrated first order rate kinetics and the results obtained suggested a first order rate of glucose formation from banyan wood cellulose. The specific rate constant relatively increased with increase in acid concentration and temperature, respectively. The activation energy estimated from Arrhenius equation was found to be 6.75 kJ/mole. This value suggests the ease with which hydrolysis can occur between the four agricultural wastes cellulose. Keywords: Acid-hydrolysis; Arrhenius equation; First-order kinetics; Glucose; Wood cellulose

Modelling the Kinetics of Biogas Generation from Mesophilic Anaerobic Co-Digestion of Sewage Sludge with Municipal Organic Waste

This work investigated the effect of municipal organic waste as co-substrate in the anaerobic digestion of industrial sewage sludge for efficient and high biogas production. The biogas experiments were carried out in two different 30 L anaerobic digesters D1 and D2 which contained sewage sludge and mixture of sewage and municipal organic waste, respectively and were incubated for 25 days at ambient mesophilic temperatures (28 oC to 32 °C). The results showed that co-digestion of sewage sludge with municipal organic waste as co-substrate reduced start-up time for biogas generation and increased biogas yield by 132% as compared to sewage sludge alone. Peak biogas production was obtained for both digesters at pH of 6.85 and 7.85 as well as temperature of 30 and 31.5oC, respectively. Modelling study revealed that exponential plot simulated better than the linear plot, the biogas production rates in digester D1 (sewage sludge) and D2 (mixture of sewage sludge and municipal organic waste), respectively. Logistic growth model and modified Gompertz plot showed better correlation of cumulative biogas production than exponential rise to maximum plot. These results show that biogas production can be enhanced efficiently through co-digestion process. Keywords: Anaerobic digestion; Biogas; Municipal waste; Sewage sludge; Kinetic model

Bioadsorption of 2,6-Dichlorophenol from Aqueous Solution onto Plantain and Pineapple Peels Mixture Used as Adsorbent: Optimization Studies Based on Taguchi Method, Batch Equilibrium, and Kinetic Modelling

The feasibility of using pineapple/plantain peels mixture to remove 2, 6-dichlorophenol (2,6-DCP) from its aqueous solutions was investigated under batch mode. The effects of factors such as pH, initial 2, 6-DCP concentration, temperature and pineapple/plantain peels adsorbent ratio on the removal process were evaluated. Four factors and three levels according to Taguchi’s (L9) orthogonal array were used to assess and optimize the bioadsorption behaviour of pineapple/plantain peels mixture. Analysis of variance was applied to determine the significant factors that affect bioadsorption.  The levels of significant factors were optimized using Signal to Noise ratio. The results showed that bioadsorption of 2, 6-DCP was dependent on these factors. However, pH was the major factor that affects the percentage (%) removal of 2,6-DCP with its % contribution of 52.23. An optimum parameter combination for the maximum percentage removal of 2,6-DCP was obtained using the analysis of Signal to Noise (S/N) ratio. The best conditions for bioadsorption of 2,6-DCP were determined by the Taguchi method and desirability approach as pH = 7, initial 2,6-DCP concentration of 300 mg/l, temperature 50 °C, and pineapple/plantain adsorbent ratio of 2:1. The equilibrium bioadsorption data were analyzed by Langmuir and Freundlich isotherm models. The Freundlich isotherm model provided the best fit (R2 = 0.9980) to the experimental data. The maximum monolayer bioadsorption capacity ( ) was found to be 76.92 mg/g. The bioadsorption kinetics data of 2, 6-DCP were analyzed by pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The pseudo-second order kinetic model gave the best fit. Therefore, pineapple/plantain peel adsorbent mixture has potential for application as an effective bioadsorbent for 2, 6-DCP removal from aqueous solution. Keywords: Bioadsorption; Bioadsorption isotherms; Kinetics; Pineapple-Plantain peel mixture; 2, 6-Dichlorophenol; Taguchi method

Modelling the Kinetics of Biogas Production From Mesophilic Anaerobic Co-Digestion of Cow Dung with Plantain Peels

This work investigated the effect of plantain peels as co-substrate in the anaerobic digestion of cow dung for efficient and high biogas production. The biogas experiments were carried out in two different 5 L anaerobic digesters and incubated for 40 days at ambient mesophilic temperatures (28 oC to 34 °C). The results showed that co-digestion of cow dung with plantain peels as co-substrate reduced start-up time for biogas generation and increased biogas yield by 18% as compared to cow dung alone. Peak biogas production was obtained for both digesters at pH of 6.7 and 6.9 as well as temperature of 29 and 30oC, respectively. Modelling study revealed that exponential plot simulated better in both ascending and descending limb than the linear plot the biogas production rates in biogas production from cow dung co-digested with plantain peels and cow dung alone, respectively. Logistic growth model and modified Gompertz plot showed better correlation of cumulative biogas production than exponential rise to maximum plot. These results show that biogas production can be enhanced efficiently through co-digestion process

Biosorption Kinetics of vetiveria zizanioides Rhizobacter on Heavy Metals Contaminated Wastewater

The burden of heavy metals pollution in the environment has increased over the last century. Consequently, concerted efforts towards addressing this menace in the environment and subsequently on health has being on the increase. A number of plants and microorganisms are currently being experimented for their potential to uptake heavy metals from both soil and water. However, the kinetics of uptake of heavy metals in wastewater which are necessary for the design of the treatment system have been largely neglected, this paper therefore investigates the kinetics of biosorption of heavy metals in contaminated wastewater using two  microorganism isolated from rhizospheric soil of Vetiveria zizanioides (vetiver) plant.The result of bioaccumulation studies showed that Bacillus cereus showsthe maximum bioaccumulation capacity of 96.75% for Lead, 23% for Cadmium and 16.98% for Zinc while Bacillus subtilis accumulated 95.2% of the Lead, 41.3% of Cadmium and 32.2% of Zinc from solution.Also, the result of kinetic studies revealed that the kinetic data agrees with pseudo-second order kinetic model. Keywords: Biosorption, Heavy metals, Rhizospheric, Wastewater, Vetiveria zizanioides