Chiedu N. Owabor

Anaerobic bioremediation of marine sediment artificially contaminated with anthracene and naphthalene

The bioremediation of marine sediments contaminated with naphthalene and anthracene was studied under anaerobic conditions to investigate the enhancing effect of a biostimulating agent (Tween 80, silicone oil, pig dung and NPK fertilizer) on the rate of degradation. Sediment samples were amended with the biostimulating agent (alone or in combination). The results showed that all the tested agents, applied individually to the sediments, increased the rate of anthracene and naphthalene degradation, with the pig dung having the greatest effect. The biodegradation data were fitted to a pseudo‐first‐order kinetic model, from which the biodegradation rate constant, as a measure of the enhancement of degradation rate by the biostimulators, was estimated. The rate constant values were consistently higher for the sediments treated with individual stimulators, or a combination of them, than for the untreated sediment. The contaminated sediment treated with the combination of Tween 80 and pig dung exhibited the highest biodegradation rate. The results indicated that the effect of various biostimulating agents, in combination or alone, on enhancing the degradation rate of anthracene and naphthalene can be arranged in the following order: Tween 80 + pig dung > silicone oil + pig dung > Tween 80 + NPK fertilizer > silicone oil + NPK fertilizer > pig dung > NPK fertilizer > Tween 80 > silicone oil. The addition of biostimulators increased the biodegradation potential of the intrinsic microbial populations; thus, these results will contribute to the development of new strategies for in situ bioremediation of anoxic sediments contaminated with polycyclic aromatic hydrocarbons (PAHs).

Adsorption and Desorption Kinetics of Naphthalene, Anthracene, and Pyrene in Soil Matrix

Abstract The adsorption and desorption kinetics of naphthalene, anthracene, and pyrene in a soil slurry reactor at ambient conditions have been investigated to ascertain the mechanisms controlling the retention and release rates of these compounds in the soil matrix. A stirred-flow method was employed to perform the experiments. The extent of partitioning for the polycyclic aromatic hydrocarbons (PAHs) tested was found to be dependent on their solubility and diffusivity in the aqueous phase. Apparent adsorption and desorption rate coefficients were determined using the Langmuir and Freundlich isotherm models. Equilibrium adsorption and desorption at the external surface and in the internal pore of the soil particle obeyed the Freundlich isotherm equation. The pseudo-equilibrium condition established at the minimum contact time suggests that equilibrium adsorption attained for the contaminant PAHs was not instantaneous but rather time dependent.

Substrate Bioavailability on the Biodegradation of Recalcitrant Polycyclic Aromatic Hydrocarbons in Aqueous-Sediment Matrix: A Mini Review

The increased quest for technology and industrialization by a dynamic society, where the fuel requirements of the energy sector and the chemical and petrochemical needs of the chemical and allied industries are satisfied, is greatly dependent on the petroleum industry in which the downstream sector is a key player. These needs range from the feedstock requirements of the chemical industries, polymeric industrial sector, solvent sector, cosmetics industries, etc. The downstream environment has over time been subjected to a barrage of sustained and unmitigated pollution of its air, land, and sea by polycyclic aromatic hydrocarbons. The frequency of discharge of petroleum and petroleum products into the environment, particularly land, and their build-up, compromises the quality of the environment. Generally, the discharge of these groups of compounds into the environment, whether accidental or intentional, has adverse ecological effect in oil-producing areas of the world. These effects, apart from the degradation of the ecosystem, also results in commodity loss, loss to the communities that depend on such lands for their livelihood, and economic loss due to spill clean-up cost. The development of effective clean-up technology to reduce the levels of these hydrocarbon contaminants in order to meet environmental regulation standards is thus a continuing subject of research.

Linear and nonlinear kinetic modelling of the uptake rate of aromatic hydrocarbons in aqueous-sediment matrix

The time-dependent adsorption data of naphthalene, anthracene and pyrene onto sandy soil fraction conducted at a constant temperature of 25°C which represents environmental condition has been investigated using linear and nonlinear kinetic modelling approaches. Experimental data were analysed using four kinetic models; pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich model equations. In order to gain insights into the mechanism controlling the sorbate-sorbent system as well as to determine the best fitting model, the correlation coefficients, and standard error estimates were used for analysis. Results of the equilibrium rate constant, adsorption capacity and correlation coefficients obtained from the different kinetic models showed that the nonlinear approach had reasonably better fits to the experimental data. This was affirmed by the use of standard error estimates. Of all the nonlinear models used the pseudo-first order kinetics successfully predicted the adsorption of the contaminant solutes. Overall, the results demonstrate that linear modelling approach is not suitable for describing the uptake of these contaminant solutes onto sediment fractions being characterised by poor regression coefficients and high standard error measurements and hence not applicable to this study.

Evaluation of microbial systems for biotreatment of cassava mill waste water in Nigeria: biodegradation of cyanide

The capability of six isolated bacterial strains to utilise cyanide in cassava mill wastewater as a nitrogen source in a batch bioreactor was examined and evaluated. The results revealed that all the isolates were capable of degrading cyanide with percent degradation between 60 and 94% in 96 h. There was high positive correlation between cyanide biodegradation and microbial growth (0.90 ≤ R2 ≤ 0.97). The Monod kinetic model adequately described the dynamic behaviour of cyanide degradation by the different bacterial isolates. Thus, the study revealed the possibility of using the bacterial isolates in the biotreatment of cyanide waste effluents.

Growth kinetics of some subsurface microbial strains using naphthalene as a probe contaminant.

The focus of this study is the unravelling of the microbial dynamics of the biodegradation of naphthalene, a polycyclic aromatic hydrocarbon, in an aqueous–sediment matrix. The Pour plate procedure was adopted for the isolation of the microbial colonies, while the sub‐culturing of the isolates was based on their cultural (biochemical) and morphological characteristics. Investigations showed that the microbial colonies consisted of the bacterial and fungal strains. The logarithmic growth curve was characterized by an initial lag phase, a rapid and exponential increase in cell biomass, a stationary phase and finally a death phase. Both strains in the presence of naphthalene‐impacted basal salt medium demonstrated that the microbial growth results in an almost linear increase in biomass concentration – an indication that mass transfer from the solid phase to the liquid phase (lag phase) is limiting for growth. The kinetics of the utilization of naphthalene expressed as the growth and consumption rates indicated that all the microbial strains isolated from an indigenous soil used in this study exhibited a high metabolic affinity for naphthalene. Optimal performance was demonstrated by the bacterial strains that could use naphthalene as their sole carbon and energy source.