Biosorption of nickel(II) from aqueous solution by Aspergillus niger: Response surface methodology and isotherm study

In the present study, the effects of biosorbent Aspergillus niger dosage, initial solution pH and initial Ni(II) concentration on the uptake of Ni(II) by NaOH pretreated biomass of A. niger from aqueous solution were investigated. Batch experiments were carried out in order to model and optimize the biosorption process. The influence of three parameters on the uptake of Ni(II) was described using a response surface methodology (RSM) as well as Langmuir and Freundlich isotherm models. Optimum Ni(II) uptake of 4.82 mg Ni(II) g⁻¹ biomass (70.30%) was achieved at pH 6.25, biomass dosage of 2.98 g L⁻¹ and initial Ni(II) concentration of 30.00 mg L⁻¹ Ni(II). Langmuir and Freundlich were able to describe the biosorption isotherm fairly well. However, prediction of Ni(II) biosorption using Langmuir and Freundlich isotherms was relatively poor in comparison with RSM approaches. The biosorption mechanism was also investigated by using Fourier transfer infrared (FT-IR) analysis of untreated, NaOH pretreated, and Ni(II) loaded A. niger biomass.     

Response surface analysis of effects of hydraulic retention time and influent feed concentration on performance of an UASFF bioreactor

The interactive effects of hydraulic retention time (HRT) and influent chemical oxygen demand (COD_in) on the performance of an up-flow anaerobic sludge fixed film (UASFF) bioreactor treating palm oil mill effluent (POME) was studied. Anaerobic digestion of POME was modeled and analyzed with two variables i.e. HRT and COD_in. Experiments were conducted based on a general factorial design and analyzed using response surface methodology (RSM). The region of exploration for digestion of POME was taken as the area enclosed by HRT (1–6 days) and COD_in (5260–34,725 mg/l) boundaries. Eight dependent parameters were either directly measured or calculated as response. Increase in the variables resulted in decrease in COD removal efficiency, solid retention time (SRT) and sludge retention factor (SRF) and increase of COD removal rate, volatile fatty acid to alkalinity ratio (VFA/Alk), CO₂ percentage in biogas and methane production rate. The value of the maximum specific microbial growth rate (μ_m) determined through the equation that correlated organic loading rate (OLR) and μ (calculated by quadratic model for SRF) was found to be 0.153 d^?1. This value was close to that obtained using Chen and Hashimoto kinetic equation (0.207 d^?1) in a previous study. The present study provides valuable information about interrelations of quality and process parameters in POME digestion using a UASFF bioreactor.