| Eutrophication becomes more and more serious with the continuous development of urban and industrial. And phosphorus (P) is the most important factor for causing eutrophication. Aiming at the condition of more strict control of effluent P concentration, the removal efficiency (RE) of P in wastewater needs to be improved. P removal in high salt containing phosphorus wastewater is a more difficult problem.An efficient phosphorus removal bacterium was screened from the deep-sea bacteria isolated from deep sea sediment of South China, identified as Alteromonas 522-1. The bacteria grew well under high salinity (NaCl 3% or so) and wide range of P concentration (5-80 mg/L). This deep-sea bacterium could decrease P concentration below 0.5 mg/L at initial P concentration below 20 mg/L independently. But biological phosphorus removal (Bio) was limited under higher P concentration. In this study, the removal of a wider P concentration range by biological phosphorus removal combined with iron (Bio-Fe), iron silicon (Bio-Fe-Si) and basic oxygen furnace slag (Bio-BOFS) (short for combined P removal) was studied to provide efficient phosphorus removal technology of high salt wider P concentration range and study their mechanisms.Results showed that the optimal P removal efficiency of iron enhanced biological treatment can reach to 98.5% for the initial P concentration of 25 mg/L in high salt synthetic wastewater with the molar ratio of Fe/P=1:1. Water pH after processing kept neutral and stable. Whereas the maximum phosphorus removal was 90% with molar ratio of Fe(III) and P ranging from 2 to 3 by independent iron treatment. Effluent pH reduced to 5.5 due to the hydrolysis of Fe(III). When the molar ratio of Fe and P was 1, P removal of iron enhanced biological treatment was kept at above 95% at pH of 6～9. The dynamic pseudo first order model could fit the biological phosphorus removal process well, and the pseudo second order model could well describe the iron enhanced biological phosphorus removal. Except the uptake of part of the phosphorus by bacterial growth and bio-sorption by extracellular polymeric substance, the hydroxyl phosphate iron complex compound and iron phosphorus precipitation induced by bacterium also contributed to the phosphorus removal.For iron and silicon enhanced biological treatment, the optimal P removal efficiency was 97.6% with the molar ratio of Fe/Si/P= 1:1.5:1 for initial P concentration of 30 mg/L. And RE of phosphorus removal was 96% for iron enhanced biological treatment. However, P removal by chemical treatment with singe iron and iron silicon were only 52.6% and 64%, respectively. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) found that the phosphorus precipitation induced by bacteria was also one of the main process, in addition to chemical phosphorus removal and biological phosphorus removal for P removal by Bio-Fe and Bio-Fe-Si. Compared with iron enhanced phosphorus removal, the addition of silicon can enhance the removal of P by forming more iron phosphorus flocs around the bacteria. And the main role of silicon in phosphorus removal was that P was combined closely with mineral and bacteria, avoiding the phenomenon of P release.Results showed Bio-BOFS could achieve improved performance at P concentration of 30 mg/L. The optimal RE can reach 97.3%, which was 21.83% and 15.43% higher than that of bacteria and BOFS alone, respectively. The stable P removal was kept in pH 4-9, P concentration lower than 40 mg/L and salinity range of 0.5～3.5% in Bio-BOFS treatment. There were crystals and organic metal phosphorus precipitation on bacterial surface of Bio-BOFS observed by SEM and Atomic Force Microscopy (AFM). And the crystals were confirmed as Ca2Mg(PO4)2·2H2O and SiO2 by X-ray diffraction analysis (XRD). Infrared spectrogram found functional groups on the bacterial surface of Bio-BOFS removed P by forming P-O-C. The effluent pH of 7.8～8 was reached due to pH buffer of bacteria in Bio-BOFS treatment. Whereas effluent pH was more than 9.5 for P removal by BOFS alone, which can’t meet the effluent standard. In the process of cultivation, the cementing of BOFS was relieved by this kind of bacterial encapsulation. Meanwhile, Ca2+ from BOFS in Bio-BOFS treatment could improve the settleability of sludge. The calculation found P removal by combined method could reduce the sludge amount generated per unit P removed compared with biological phosphorus removal.Compared to three methods of phosphorus removal, the removal efficiency of P was all improved, but phosphorus removal mechanism was different. For combined biological methods, in addition to chemical and biological phosphorus removal, P removal was mainly enhanced through the flocs formed around the bacteria for Bio-Fe and Bio-Fe-Si, and crystals and organic phosphorus metal precipitation were mainly formed around the bacteria for Bio-BOFS. In short, bacteria play an important role in phosphorus precipitation formation. The study showed that P removal by combined method can achieved the purpose of efficient phosphorus removal. P removal in high salt wastewater containing phosphorus have great application prospect. |
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