| Selenium nanoparticles (SeNPs) were considered to be a promising adsorbent due to the advantages of small size, large specific surface area and negative surface charge. Among various synthesizing methods, biological synthesis of SeNPs has attracted enormous attentions as an eco-friend, fast and economical process. With abundant bio-diversity, aerobic granular sludge system can mediate the biogensis of SeNPs via the reduction of selenium oxyanions. In this study, we cultivated the aerobic granular sludge in a SBR and the SeNPs were then reduced from sodium selenite. The SeNPs were characterized and the adsorption performance was investigated using Cd (Ⅱ) as an example. Moreover, we further evaluated the effects of BioSeNPs on the aerobic granular sludge system. Main contents and results are as follows:1. The aerobic granular sludge was successfully cultivated via increasing influent organic loading and aeration flux, along with added Ca2+as core plus shortening settling time step by step in a SBR. The obtained granule sludge was tawny with the characteristics of compact structure, well setting property and high biological activity. The content of EPS increased in the process of granulation and the main components of EPS were PN and PS, which play a key role in the aggregation of microorganism and may be attributed to the formation of aerobic granule. The size, SVI, maximum settling velocity of the granule sludge was between 1 and 5 mm,40 mL/g,56.6 m/h. The removal efficiency of COD and NH4+-N reached more than 97%.2. The red selenium nanoparticles were produced by aerobic granular sludge in a SBR and characterized by SEM, EDS, Raman, XRD, FTIR and XPS. In addition, adsorption property was investigated for the removal of Cd(Ⅱ) from aqueous solution. Batch experiments were carried out to investigate the effect of contact time, initial solution pH and adsorbent dosage on adsorption. The Langmuir model was more suitable to describe the adsorption process than the Freundlich model, with a monolayer maximum adsorption capacity of 59.7 mg/g for Cd(Ⅱ) adsorption by the BioSeNPs. The isotherm data were also well described by the Temkin model, which further supported that Cd(II) adsorption was a chemisorption process. The adsorption kinetics data were well described by the pseudo-second-order kinetic model with r2 values exceeding 0.999. The overall rate process was influenced by both external mass transfer and intraparticle diffusion, but was mainly controlled by intraparticle diffusion. The negative values of △G～0 and △H～0 indicated that the adsorption process was spontaneous and exothermic. FTIR and XPS analysis indicated that the removal of Cd(II) was a complicated process, in which electrostatic attraction and surface complex formation were involved. The results demonstrated that BioSeNPs could be used to remove cadmium from aqueous solution with high efficiency.3. The aerobic granule sludge outline is more clear due to the presence of trapped BioSeNPs. However, due to the blockage of pores by BioSeNPs, the transportion of nutrients was affected which reduced the bioactivity of microorganisms and the removal efficiency of COD and NH4+-N. Specific oxygen uptake rate (SOUR) tests showed a decrease of XBH activity and AOB activity due to the presence of trapped BioSeNPs. The existence of BioSeNPs also promoted the secretion of extracellular polymer content, but the increase is smaller. |
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