生物法制备聚合硫酸铁及其应用研究_英文_

Biological preparation and application of poly-ferric sulfate flocculant

WANG Hui-min, MIN Xiao-bo, CHAI Li-yuan, SHU Yu-de

School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China

Received 23 September 2010; accepted 5 January 2011

Abstract: A novel inorganic polymer flocculant, poly-ferric sulfate (BPFS) was prepared by oxidation of ferrous sulfate using domestic Thiobacillus ferrooxidans (T·f) under acid condition. The optimal conditions for the preparation were pH value of 1.5, (NH4)2SO4 dosage of 0.5 g/L, initial Fe2+ concentration of 45g/L, inoculum 10%, rotating speed of 120 r/min, reaction time of 5 6 d and reaction temperature of 30 °C. Under the optimal conditions, the BPFS product with pH value of 1.5 2.2, basicity of 17.5% 22.7% and total iron content of 43.87 45.24 g/L was obtained. The application of the BPFS to three wastewaters was carried out, and the removal efficiencies of COD, decolorization and Zn2+ by BPFS can be reached 70%, 90% and 99%, respectively. The result suggests that the BPFS is an excellent flocculant for water treatment. Key words: ferrite; poly-ferric sulfate; flocculant

1 Introduction

Flocculation sedimentation is one of the most widely used and lowest cost techniques for water treatment [1 2], and flocculant is the key in application of flocculation sedimentation technique. Recently, a novel inorganic polymer flocculant, poly-ferric sulfate(PFS) has received much attention because it has many advantages in comparison with conventional flocculant, such as low sample consumption, high efficiency, wide pH application range, low residual iron concentration, hydrolysate with high efficiently dehydration, non-toxicity, low-priced and fast settling rate [3 6].

At present, PFS is mostly prepared by direct oxidation of ferrous sulfate using strong oxidant such as H2O2, KClO3, NaClO, HNO3 or by catalytic oxidation of ferrous sulfate using NaNO2 or NaI as a catalyst in acid media. However, the methods mentioned above have many limitations such as extremely slow reaction, unstable product, low yield, large consumption of catalyst, high cost and emissions of nitrogen oxides causing environmental pollution, so it is difficult to be applied to the industrial production [7 10].

The objective of this study is to develop a new

preparation technique for PFS using the microbes and organic waste, and to gain the BPFS product with low cost, low energy consumption, high-quality and high stability [11 14]; the influencing factors in the preparation process of BPFS and its application in water treatment were also investigated.

2 Experimental

2.1 Microbial adaptation

9K culture medium containing 9 g/L Fe2+ was added into conical flask，then 10% (volume fraction) inoculum was innoculated and cultivated on a thermostatic waterbath at 30 °C with agitation of 120 r/min. The conversion rate of Fe2+ was determined at selected time until it reached 85%. After the reaction, the reaction mixture was used to initiate the next one, and the above-mentioned steps were replicated until the reaction time basically remained stable. With the repeated inoculation and cultivation, T·f bacteria gradually adapted to the new environment, and the reaction time gradually became stable. The T·f bacteria adaptation results are listed in Table 1.

As the T·f bacteria were in a new environment, their growth and oxidability were influenced to a certain extent. The reaction time to meet the oxidation rate

Foundation item: Project (2009ZX07212-001-01) supported by the Major Science and Technology Program for Water Pollution Control and Treatment,

China; Project (50925417) supported by the National Natural Science Foundation for Distinguished Young Scholars of China; Projects (50830301, 51074191) supported by the National Natural Science Foundation of China

Corresponding author: MIN Xiao-bo; Tel: +86-731-88830875; E-mail: mxb@ DOI: 10.1016/S1003-6326(11)61048-0