Research On Facilitated Formation Technology And Activity Conservation Method Of Anaerobic Granules

In industrial application of wastewater biological treating, the granulating process of anaerobic sludge, inoculated in high efficiency anaerobic reactors, is running slowly, which results in the long lasting time( two or three months, even half a year ) for anaerobic reactors, like UASB and IC et al, from start-up to steady running. According to this problem in application, we ran the experiment in the following three respects.At first, we started the experiment from operating situation of reactors. The effect of sludge loading rate (SLR) on facilitating formation of anaerobic granules was studied, and then the range of SLR suitable for quick granulation of anaerobic sludge was determined. Furthermore, we ran the comparative experiment to study the facilitating granulation effect of GAC, CaCl₂, PAM and CHI, respectively, which is typical substance of three kinds of facilitating granulation matters—inert carrier particle, inorganic metal-ion and organic polymers, then determined the methanogenic toxicity and the level of acticity reviving. On the basis of the comparative experiment, we propounded a new technology for producting anaerobic granules quickly using anaerobic flocculent sludge outside of UASB. Lastly, the experiment was designed to study the effect of moisture percentage, temperature and dissolved oxygen on methanogenic activity of sludge, and also to study the method of conserving anaerobic granules according to the results of effect by factors. The conclusions of all experiments are as following:(1) Suitably higher SLR is helpful to enhance granulation of anaerobic sludge. There were large numbers of anaerobic granules emerging and forming when the SLR is among 0.29-0.51kgCOD/kgVSS·d, which is the optimal SLR range for forming anaerobic granules. At the end of the experiment, the percentage of granules with diameter of above 1mm in the R2, which was ran by suitably higher SLR, was 42.2%, while this rate in R2 with lower SLR was only 14%. Formated granules have a character of good sedimentation rate, and the sedimentation rate of granules with diameter of above 0.5mm is among 20-147m/h. Higher SLR also made guanules to character a higher rate of VSS/TSS.(2) Through analyzing the accumulative methane and granules diameter affected by facilitating granulation matters, we can make a conclusion that the effect of enhancing granulation by PAM is the most effective one, CHI and GAC play a less effective role than PAM, and the CaCl₂ takes the wakest effect. According to the results of toxicity experiment, we can get an order of amethangenic toxicity of four facilitating subsrance, the order is: GAC>CHI> CaCl₂ >PAM. The experiment of toxicity indicates that activity of granules harmed by GAC of 22ml/L can not revive when GAC is removed. Sludge amethangenic activity harmed by other added matters can come back, and the mechanism is a kind of inhibition of metabolizing toxin.(3) The main process of newly propounded technology of producing anaerobic granules is that: pretreating of flocculent anaerobic sludge—flocculating reaction of sludge adding PAM—flocculating dehydration by horizontal helix centrifuge—sifting particle—cultivating to maturation in reactor. SMA of sludge was not destroyed hadly during the process of production. And the SMA of produced mature granules increased by 18% compared to SMA of flocculent material sludge. After process of flocculating reaction and centrifugal dehydration, the percentage of granules with diameter of over 0.25mm is nearly 50%. And the sifting particle process result the percentage of granules with diameter of over 1mm to increase from 38% to 80%. And the final process of cultivating in reactors made anaerobic granules mature. Production rate is calculated as following: 37.7% of flocculent anaerobic sludge can be cultivated to anaerobic granules with dismeter of over 1mm, and 17.8% of flocculent sludge can be cultivated to anaerobic granules with diameter of over 4mm.(4) The SMA of granules is silightly destroyed, when the moisture percentage of hydrated granules is higher than 80% or granules are cultivated in aerobic wastewater for a short time. Temperature is a factor influencing the SMA of granules seriously. So the SMA was decreasing with the drop of temperature and the anaerobic sludge may become dormant at the temperature of 5℃. Through analyzing three evaluating indicator synthetically (SMA of granules stored, SMA of granules revived, integrity of granules), we can get an order of the effect by different methods of conservation (from good to bad): dehydrated conservation at 5℃(moisture percentage 90%) >not dehydrated conservation at 5℃> dehydrated conservation at room temperature >not dehydrated conservation at room temperature. The method of dehydrated conservation at 5℃and not dehydrated conservation at 5℃is the optimal way to conserve anaerobic granules with good avtivity in the industrical application. On the process of conservation, the existing of oxygen can destroy the SMA of granules. So protecting measure of eliminating oxygen is necessary, and we could take measures of suction or pumping in inert gas (like methane) to eliminate oxygen.