Research On The Pretreatment Of Daqing Oilfield Sludge By Ultrasound Combined With Anerboic Methane Processing

The recycling treatment of the oily sludge is the main barrier to the sustainable development of oilfield, and its pollution is one of the major global environmental issues. There are millions of tons of oily sludge produced per year, most of which is stacked directly in the open air and only a small proportion of easy recovery is processed for recycling, which not only takes up a lot of land, but also causes serious secondary pollution. The oily sludge contains complex components, including a percentage of the crude oil, which is a kind of valuable energy. However, there has not been a satisfactory technique that has really realized the recycling of oily sludge so far. In fact, it is difficult for a single technique to achieve this goal, but the pretreatment by ultrasound combined with anaerobic methane treatment technology can not only achieve the separation of oil and sludge, but also recover the remaining petroleum hydrocarbon in the form of methane under anaerobic fermentation, so it has the incomparable advantages over others.The ultrasonic pretreatment can not only separate the oil and sludge, but also realize the conversion from the long hydrocarbon chains to short-chain ones by the high temperature and pressure of cavitation, which is conducive to the subsequent anaerobic fermentation. The anaerobic fermentation can degrade the complex and persistent substances to recover methane, so this subject adopted the pretreatment by ultrasound combined with anaerobic methane treatment technology to deal with oily sludge in Daqing, in order to explore a new way for sludge recycling.This subject included the following aspects: First, exploring the optimal pretreatment conditions for oilfield sludge. The pretreatment method, time, temperature, energy density and ratio of mud and water were selected as the major variable factors, with SCOD, p H, TN, TP as the evaluation parameters. The optimum conditions were determined as follows: the pretreatment method of ultrasound, time of 15 min, temperature of 35℃, the energy density of 2.50W/ml, ratio of mud and water of 1:3.Second, exploring the feasibility of ultrasonic pretreatment- anaerobic methane process for oily sludge in anaerobic reactors, with the anaerobic sludge from a refinery of Harbin as the inoculating sample. By determining the variations of COD, SCOD, VFA, and the volume and composition of the the gas produced, as well as the composition changes of petroleum hydrocarbon component, it could be known that ultrasonic pretreatment could dramatically improve the efficiency of methane production in anaerobic reactors, and the methane volume of ultrasonic treatment was 9 times more than that of control.Finally, studying the effect of ultrasonic pretreatment on microbial community structure in anaerobic reactors by the high throughput sequencing of Illumina. The results showed that the dominant Bacteriophyta in two reactors were Proteobacteria and Bacteroidetes, which produced volatile acids through hydrolytic acidification; For ultrasonic treatment, the proportion of Fervidobacterium sp., Caldisericum sp. and Bacteroidetes sp. were larger than that in the control. The dominant Phylum for Archaebacteria in the reactors was Euryarchaeota,including a lot of methanogenic bacteria, such as Methanospirillum sp. and Methanosaeta sp., and so on.