Characteristics of Bacillus sp. PZ-1 and its biosorption to Pb(II)

During the long and cold winter season in northern area of China, wastewater treatment is often inefficient which causes the substandard discharge. In this study, a lead-resistant psychrotrophilic bacterium was isolated and used as an adsorbent to remove Pb(II) from aqueous solution at 15 °C. The strain was identified and designated as Bacillus sp. PZ-1 based on the morphology, physiological-biochemical experiments and 16S rDNA sequence analysis. The minimal inhibitory concentration and antibiotic experiments revealed that PZ-1 had high resistance to 1500 mg L(-1) of Zn(II), 800 mg L(-1) of Cu(II), 400 mg L(-1) of Ni(II), 15 µg mL(-1) of chloramphenicol and 50 µg mL(-1) of streptomycin, but susceptibility to 200 mg L(-1) of Co(II). Scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy analyses showed that biosorption of Bacillus sp. PZ-1 to Pb(II) involved surface adsorption, ion exchange and micro-precipitate. Fourier transform infrared spectroscopy analyses indicated that hydroxyl, carbonyl and carboxyl on cells may play vital roles in Pb(II) adsorption. Besides, siderophore secreted by PZ-1 had beneficial impacts on the Pb(II) removal. Biosorption experiments were carried out as a function of initial Pb(II) concentration (50-500 mg L(-1)), pH (3.0-7.0), biomass concentration (5-50 g L(-1)) and contact time (5-40 min). Biosorption rate of 93.01% with adsorption capacity of 9.30 mg g(-1) was obtained under the initial Pb(II) concentration of 400 mg (-1), pH of 5.0, contact time of 20 min, biomass concentration of 40 g L(-1) and the temperature of 15 °C. The equilibrium data were well fitted with Langmuir model, which indicated the adsorption process of Pb(II) is monolayer adsorption. Bacillus sp. PZ-1 appeared to be an efficient biosorbent for removing Pb(II) from wastewater at low temperature.