| Vivianite is a biological secondary ore,which is the most stable iron and phosphorus compound in thermodynamics,with low solubility,paramagnetic property,and easy separation,so it provides a new idea for the recovery of phosphate in sludge.In view of this,this subject will carry out research on the formation of vivianite in aerobic granular sludge(AGS)and draw the following conclusions:1.Comparing the anaerobic digestion reaction of aerobic granular sludge in the same period at room temperature(25?)and medium temperature(35?).At room temperature,the aerobic granular sludge has been in the stage of hydrolysis and acidification,the pH value is low and there is no CH4 output,the phosphorus release rate of the sludge is 36.6%,while at medium temperature,the phosphorus release rate of the aerobic granular sludge is high,It reaches 46.2%and the hydrolysis and acidification time is short,the optimal hydrolysis and acidification time period is 5-11 d.Therefore,the medium temperature(35?)was selected as the control condition for subsequent experiments.At medium temperature,anaerobic digestion reaction was carried out on granular and homogenized aerobic granular sludge.After adding FeOOH on the 8th day of the experiment,the experiment was continued to investigate the mode of adding iron after the hydrolysis and acidification stage of the two sludges.The result shows that the two systems of granular sludge and homogenized sludge are produced by vivianite after the addition of FeOOH and the phosphorus removal rate in the digestive juice is more than 99%.The introduction of iron is consistent with the changes of the two systems,and the result is weak,but it has a slightly greater effect on the granular sludge.2.Under the condition of medium temperature(35?),the effect of different Fe/P ratios on the formation of vivianite from granular aerobic granular sludge was studied,and the introduction of iron in the system with Fe/P ratios of 1.5,3,and 5 Can quickly remove TP in digestion,and the phosphorus removal rate is more than 99%,but the phosphorus release rate of granular sludge in the system is different,in order of 26.9%,39.6%and 21.6%.The average output of VFAs in the iron-added group was 42%higher than that of the iron-free group.There was no CH4 output in the iron-free group,while the iron-added group had the largest CH4 production when the Fe/P ratio was 3,which was 2.3 mL/g VS.It shows that vivianite is formed in the iron addition system,and the introduction of iron promotes the anaerobic process of aerobic granular sludge,and the best effect is promoted when the Fe/P ratio is 3.3.Under the condition of medium temperature(35?),investigate the effect of different Fe/P ratios on the formation of vivianite from homogenized aerobic granular sludge.The aerobic granular sludge is homogenized by a homogenizer,and the Fe/P ratio is set to 1.5,3,and 5.The results show that Phosphorus removal rate in the homogenized sludge digestion liquid of the iron-added group is above 99%and all the vivianite is formed in the system,but there are differences in the size and morphology of the vivianite particles.The addition of iron can effectively promote the anaerobic digestion reaction of homogenized sludge.The concentrations of NH4+-N and SCOD in the iron-added group are much higher than those in the iron-free group,and the average output of VFAs in the iron-added group is 24%higher than that in the iron-free group.The average output of acetic acid is 70%higher than that in the iron-free group,and the average output of CH4 is 5.7 times that of the group without iron.When Fe/P is 1.5,it has the best positive effect on the homogenized sludge anaerobic digestion system.4.Under the condition of medium temperature(35?),explore the effect of different Fe/P ratios on the formation of vivianite from aerobic granular sludge inoculated with anaerobic granular sludge.This process is to study granular aerobic granular sludge,hereinafter referred to as inoculated sludge,the Fe P ratio was also set to 1.5,3,and 5.Compared with the previous experiment without inoculated sludge,the optimal Fe/P ratio for inoculated sludge was 3.Under this condition,99%removal of TP in digestive juice,the phosphorus release rate of the sludge was 27.6%,the CH4 production was 34 mL/g VS,which was 12 times that of the non-inoculated sludge,and the total gas production was 115 mL/g VS,which was twice that of the non-inoculated sludge. |
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