| Biogas slurry irrigation is the mainstream way of current biogas slurry’s disposal in our country, but because of biogas slurry’s storage and transport the service radius of traditional biogas slurry irrigation can’t be enough large,and is also restricted by season. In addition, Long-term large-capacity irrigation may lead to the risk of contamination of soil, surface water and ground water, coupled with that China has not yet issued a standard on biogas slurry irrigation. So research on high-value utilization of biogas slurry’s technology, expanding the radius of biogas slurry irrigation, and enhancing the efficiency of the value of biogas, is particularly important.This study aims to expanding the radius of biogas slurry irrigation and enhancing the efficiency of the value of biogas slurry, through the laboratory simulation test of vacuum evaporation concentration and nanofiltration concentrate, and providing a scientific basis for Chongqing’s high values technology of scale biogas slurry’s utilization.At first, this test performed vacuum concentration of biogas slurry, the test shows that concentrated in the same period, the volume of the condensate water increases with the vacuum’s degree increases, the concentration effect raises with the increase of the vacuum’s degree. When the vacuum is less than60%, the condensate water quality deteriorates with the increase of vacuum’s degree, when the vacuum is more than70%, the condensate water quality fluctuated with the increase of vacuum’s degree. And only when vacuum is90%, the condensate water quality can achieve "livestock industry wastewater discharge standard (GB18596-2001)". Considering low-power, good concentration effect and condensate water reaching the "GB18596", the vacuum’s degree90%is the suitable vacuum to the test.When the vacuum’s degree is90%, the test reveals that:viewing from the biogas slurry concentrated effect, concentrated effect of COD, TP is excellent, and concentrated effect of TN is not so good, but NH4+-N have not been concentrated. In actual operation, only when the ratio of concentration volume was bigger than3, TN can be concentrated, and NH4C1must be artificially added to biogas slurry after concentration that will meet the need of biogas slurry’s concentration.Then study on nanofiltration concentrating biogas slurry show that, with the increase of operating pressure, the concentrating velocity was increasing and the concentrating effect is also on the rise, but the upward trend gradually slowing down; With the decrease of biogas slurry’s pH, concentrating velocity slows down, and the concentrating effect is also going down. With the increase of operating temperature, the concentrating velocity goes up. The concentration effect goes up significantly from25℃to30℃, and fluctuates from30℃to40℃, but little changes.Multi-factor test found that:for concentrating velocity and concentrating effect, the operating pressure is the main factor, biogas slurry’s pH is a secondary factor, the operating temperature is a third factor. In case of considering the effect of concentrating and the transmitted water achieve "GB18596-2001", the optimal conditions of nanofiltration concentrating biogas slurry are determined as follows:operating pressure dosage of0.6MPa, pH dosage of5, operating temperature dosage of40℃.The permeating rate of nanofiltration concentrating biogas slurry decreased with biogas slurry’s concentration increasing, and the increasing trend slow down when biogas slurry’s concentration become enough high, the concentrating effect of nanofiltration concentrating become worse with the biogas slurry’s concentration increasing.Finally, the advantages and disadvantages of these two concentrate methods are as follows: nanofiltration concentrate does not be applied to high concentration of biogas slurry, but vacuum evaporation concentrate is applied to all kinds of concentration of biogas slurry. To nanofiltration concentrate, it’s better that biogas slurry is constantly added to original biogas slurry, while to vacuum evaporation concentrate, the biogas slurry only need be poured into concentrated tank at the beginning. When COD’s concentration is less than8170mg/L, that is to say volume concentration ratio is greater than approximately3.7, nanofiltration concentrate will save more energy than vacuum evaporation concentrtion, when COD is greater than8170mg/L, that is to say volume concentration ratio is less than approximately3.7, vacuum evaporation concentrtion will save more energy than nanofiltration concentrate. In actual application, nanofiltration concentrate can be use at first, when the biogas slurry’s concentration reach a concentration, vacuum evaporation concentrated slurry can be used, so that it is useful to save energy. |
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