| Influence of Ca2+ on glucose-fed aerobic granule was investigated through sequencing batch reactor(SBR) and shaking flask experiments. Granules of two SBRs spiked with 30 mg/L and 100 mg/L of Ca2+ could be observed visually on day 20. In the first 50 days, the SBRⅡ had higher mixed liquor suspended solid(MLSS) and lower sludge volume index(SVI) than those of SBRⅠ. After 50 days, the difference of granule performance in two reactors gradually be reduced and little differences were found on day 80 or more, for example, MLSS of SBRⅠ,Ⅱ was 7.5 g/L and SVI arrived at 46-48 mL/g and 45-47 mL/g respectively. After 90 days, sludge Zeta potential of SBRⅠ,Ⅱreached -12.5--12.6 mV.Furthermore, with influent of 0-200 mg/L Ca2+,sludge Zeta potential of shaking flask reached -14.4-14 after 50 days. Ca2+ concentration of influent had little influence on Zeta potential of sludge during granulation process. Microbiological observations confirmed some appreciable changes in microorganism population and diversities with the increase of Ca2+ concentration of influent. The role of Ca2+ in bioflocculation of granule can be mainly attributed to its cation bridging instead of charge neutralization. The elemental analysis of seed sludge and aerobic granule by X-ray fluorescence (XRF) showed that the content of Ca,Mg,K, and Na in granule were less than seed sludge expect for Fe，increasing 4.42% and 7.82% respectively. Divalent metal ions such as Ca2+ and Fe2+ were probably constituent of biopolymer. It was possible that the binding of divalent metal ion with extracellular polymeric substances(EPS) enhanced the granulation of seed sludge. Consequently, the pollutant removal efficiency of SBRⅡ was higher than that of SBRⅠthroughtout the trial. Both NH+ 4-N and COD removal efficiencies reached 90% and both total N and total P removal efficiency were 65%-70% after day 70. |
