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

• Psychrotrophilic Bacillus sp. PZ-1 effectively removes Pb(II) from wastewater at 15 °C.
• Bacillus sp. PZ-1 expressed strong resistance to Pb(II), Zn(II), Cu(II), and Ni(II).
• Biosorption of Pb(II) involved surface adsorption, ion exchange and micro-precipitate.
• The equilibrium data was fitted well with Langmuir and Freundlich models.

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 L−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.