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Influential Factors in Fermentation of Refinery Oily Sludge Xiuxia Zhang,† Jicheng Wang,† Yunbo Zhang,‡ Qiyou Liu,‡ Chunxiang Geng,‡ and Jun Lu*,† School of Resource & EnVironmental Engineering, East China UniVersity of Science & Technology, Shanghai China 200237, and Department of EnVironmental Engineering, College of Chemistry and Chemical Engineering, China UniVersity of Petroleum, Dongying, Shandong China 257061
In an experiment of one-pass aerobic fermentation, sawdust was used as the amendment and straw was used as the bulking agent. The forced aeration was at the rate of 0.1 m3/h while the influence of nitrogen and microbe sources on the process was thus investigated. The oil degradation rate was up to 52.7% after fermentation under the conditions of poultry manure as the nitrogen source and HJ-1 strain as the microbe. Simultaneously, the color of oily sludge changed from black to brown, the stink from the manure disappeared, and the appearance of the sludge changed from a sticky state to loose particles. The analytical results indicated that the amount of saturated hydrocarbons in the refinery sludge was decreased remarkably after fermentation. 1. Introduction The components of oily sludge from refineries are extremely complicated, including water, oil emulsion, and impurities of suspended solids. Further, the oil in sludge exists in various agglomerative states such as dispersed oil, emulsified oil, and dissolved oil. The cost of discharging untreated oily sludge, as reported, is 1000 RMB per ton due to dehydrating operation.1,2 Mrayyan3 reported that an environmentally friendly treatment for oily contaminated sites by biodegradation through the use of microorganisms is cost-effective. In that study, laboratory experiments were conducted to establish the performance of bacterial isolates in the degradation of organic compounds contained in oily sludge from the Jordanian Oil Refinery plant. As a result of laboratory screening, three natural bacterial consortia capable of degrading total organic carbon (TOC) were prepared from isolates enriched from the oil sludge. Experiments were conducted in Erlenmeyer flasks under aerobic conditions, with TOC removal varying from 0.3% to 28% depending on consortium type and concentration. Consortia 7B and 13B exhibited the highest TOC removal percentage of 28% and 22%. The results concerning a laboratory screening of several natural bacterial consortia and laboratory tests to establish the performance in degradation of hydrocarbons contained in oily sludges from the Otesti oil field area were presented by Lazar et al.4 As a result of the laboratory screening, six natural bacterial consortia were selected (BCSI-I1 to BCSI-I6) for a high ability in degradation of hydrocarbons from paraffinic and nonparaffinic asphaltic oils. Kriipsalu5 investigated the aerobic biodegradation of oily sludge generated by a flotation-flocculation unit (FFU) of wastewater treatment at an oil refinery. The results show that some amendments result in increased amounts of total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) to be degraded in the mixture. Wei6 et al. reported a comparison of bioaugmentation and composting for remediation of oily sludge in the report of a field-scale study in China. The results showed that, after three biopreparation applications, the amount of total hydrocarbons (THC) decreased by 46-53% in the oily sludge and soil. Land farming7 * To whom correspondence should be addressed. Tel.: (+86)-2164253366. Fax: (+86)-21-64252737. E-mail:
[email protected]. † East China University of Science & Technology. ‡ China University of Petroleum.
is becoming one of the most preferred treatment technologies for oily sludge disposal in the Arabian Gulf region in general, and in the Kingdom of Saudi Arabia in particular. This technology is considered to be economical, energy efficient, and environmentally friendly with minimal residue disposal problems. Verma8 reported on oily sludge degradation by bacteria in Ankleshwar, India, in which three bacterial strains from contaminated soil were tested for their ability to degrade the complex mixture known as oily sludge containing petroleum hydrocarbons, sediments, heavy metals, and water. Gravimetric analysis showed that three strains degraded approximately 35-59% of the oily sludge in 5 days at 30 °C. Four different samples of polluted soils from Liaohe Oil Field were investigated by off-site bioremediation.9 Results from soil composting in a long stack showed that when the total amount of petroleum hydrocarbons (TPH) was within the range of 4.16-7.72 g/100 g of soil, the degradation rate of TPH could reach as high as 45.2-56.7% after 53 days of operation. As a reference, that was beneficial to the one-pass aerobic fermentation of oily sludge in this study. 2. Experimental Section 2.1. Experimental Equipment. The process of main aerobic fermentation treatment includes ventilation, temperature control, water control, turnover of compost pile, control of harmless release, and so on. A silo reactor of fermentation was used in this test, as shown in Figure 1. The flow sheet of this system includes a composting reactor, air compressor, gas flow meter, activated carbon absorber, and other accessories, such as pipes, tee-joint valve, thermometer, and insulating blanket. 2.2. Experimental Material. The raw material (Figure 2) in this study was obtained from a refinery in Shengli Oil Field in China. Due to high moisture and oil content, the oily sludge sample, before fermentation, must be prepared by an adding amendment and a bulking agent to adjust the moisture and porosity content. In this test sawdust and straw were used as the amendment and bulking agent (Figure 3), poultry manure, bean cake, or carbamide was used as a nitrogen source, and fermentation liquor which contained the efficient HJ-1 strain was used as the microbe source. The property data of oily sludge, sawdust, and straw are given in Table 1. The supple-
10.1021/ie061380l CCC: $37.00 © 2007 American Chemical Society Published on Web 07/25/2007
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Figure 1. Primary aerobic fermentation reaction system.
Figure 2. Oily sludge.
Figure 3. Straw.
mentation of dry-based sawdust and straw can be calculated from the moisture contents of sawdust, straw, and oily sludge (Table 2). 2.3. Analysis. The oil and moisture contents were measured by Soxhlet extractor-gravimetric method, and the contents of volatile organic substance were measured by incineration and a gravimeter. Through extraction analysis, organic carbon, total nitrogen, and pH could be measured. In order to analyze the changes of oil components in the sludge, four-component analyses (saturate, aromatics, resins, asphaltenes) were carried out before and after the fermentation process. 3. Results and Discussion 3.1. Effect of Microbe Source on the Fermentation. In the no. 2 fermentation system, 2 L of product from the no. 1 fermentation system circumfluence and 1.5 L of poultry manure were used as the microbe source and nitrogen source, respectively. Through comparing the no. 1 and no. 2 fermentation systems, the effects of microbe sources, either fermentation liquor or product circumfluence, on the one-pass aerobic fermentation of oily sludge were investigated. 3.1.1. Observed Characteristics. In both no. 1 and no. 2 fermentation systems, the stink decreased gradually during the fermentation, and the higher the degree of composting, the lighter the smell was. The odor disappeared, and the finished product had the smell of wet clay. The color of the oily sludge changed from black to brown, and it appeared as loose particles in the no. 2 fermentation system.
3.1.2. Temperature Profile. Figure 6 shows the temperature profiles of the no. 1 and no. 2 fermentation systems. Figure 6 indicates that the temperature rising rates for both processes remained almost parallel at the initial stage. However, after 2 days of composting, the fermentation liquor temperature of no. 1 remained nearly 2-5 °C higher than that of no. 2. Furthermore, the temperature rising rate, the length of retention time at high temperature, and the temperature limit reached in the no. 1 fermentation system were all higher than those in no. 2. Therefore, the microbe source from fermentation liquor was better than that from product circumfluence. 3.1.3. Oil Degradation. By the temperature comparison above, the effect of oil degradation in the no. 1 fermentation system was better than that in no. 2. The comparison of oil contents in the no. 1 and no. 2 fermentation systems is shown in Figure 7. Figure 7 shows that the oil content in the no. 1 fermentation system decreased from 18.8% to 8.9% and the oil degrading rate reached 52.7% while the oil content in the no. 2 fermentation system decreased from 18.8% to 9.7% and the oil degrading rate was 48.6%. Causes for the distinctions between no. 1 and no. 2 were as follows: the strain in the fermentation liquor was screened, which was especially effective for degrading oil hydrocarbons, this kind of strain was highly active and had fermentation efficiency, but the strain from the product circumfluence was mutated during fermentation, and after mutation, the capacity of degrading oil decreased. In conclusion, the effect of adding fermentation liquor was better than adding product circumfluence in the one-pass high-temperature aerobic fermentation for oily sludge experiment. 3.2. Effect of Nitrogen Source on Fermentation. The effect of the nitrogen source on fermentation was investigated using carbamide, bean cake, and poultry manure as inorganic, plant, and animal nitrogen sources, respectively. 3.2.1. Observed Characteristics. Poultry manure was added to the no. 1fermentation system; the stink decreased gradually during the fermentation, and the higher the degree the composting, the lighter the smell was. After composting, stink disappeared and the finished product had the smell of wet clay. The color of the oily sludge changed from black to brown, and it appeared as loose particles in the no. 1 fermentation system (see section 3.1.1). Bean cake was added to the no. 3 fermentation system. The odor decreased gradually to a certain degree during the fermentation, but the color was only reduced a little and remained black, and the sludge was still stiff. Carbamide was added to the no. 4 fermentation system. There was a strong ammoniacal smell produced during fermentation, the color was not changed, and the sludge was still stiff.
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Table 1. Properties of Oily Sludge, Sawdust, and Straw raw material
moisture content/%
volatile organic substance/%
oil content/%
C/N ratio
density/(g/mL)
sawdust and straw oily sludge
9-10 80-85
68-78 97-98
0 20-25
124:1 8333:1
0.057 1.04
Table 2. Experimental Designa,b IDno. 1 2 3 4
compositon of compost material for fermentation (volume)
moisture content/%
7.5 L of sludge, 8.5 L of sawdust and straw, 800 mL of fermentation liquor, 1.5 L of poultry manure 7.5 L of sludge, 8.5 L of sawdust and straw, 2 L of product circumfluence, 1.5 L of poultry manure 7.5 L of sludge, 8.5 L of sawdust and straw, 800 mL of fermentation liquor, 1.5 L of bean cake 7.5 L of sludge, 8.5 L of sawdust and straw, 800 mL of fermentation liquor, 250 g of carbamide
68.5
156:1
24
fermentation liquor of strain as microbe source
67.2
194:1
24
sludge fermented in the process of no. 1 as microbe source
69.3
179:1
22
bean cake as nitrogen source
67.3
104:1
10
carbamide as nitrogen source
C/N ratio
no. fermentation days
explanation
a The influences of the microbe source for the fermentation of oily sludge were investigated in processes nos. 1 and 2. b The influences of the nitrogen source for the primary aerobic fermentation of oily sludge were investigated in processes nos. 1, 3, and 4.
Figure 4. Characteristics of no. 1 fermentation system. Figure 6. Temperature comparison of nos. 1 and 2 fermentation systems.
Figure 5. Characteristics of no. 2 fermentation system.
3.2.2. Temperature Profile. The temperature profiles of fermentation systems no. 1, no. 3 and no. 4, in which poultry manure, bean cake and carbamide were added respectively, are illustrated in Figure 8. Figure 8 shows that the temperature of no. 3 fermentation system in which bean cake was added was not over 35 °C during the whole process. The temperature stayed between 30 °C and 35 °C for 18 days. Though the microbe was activated, the action was not intensive. The heat released from fermentation was only sufficient to keep the temperature below 40 °C. The microbe was inactive in the fermentation system no. 4 in which carbamide was added, for the temperature remained 25 °C during the whole process.
Figure 7. Oil content comparison of nos. 1 and 2 fermentation systems.
The data above showed when poultry manure was used as nitrogen source, microbe was most active and the temperature rose quickly and high-temperature could be retained several days. 3.2.3. Oil Degradation. The oil contents after the fermentation systems no. 1, no. 3, and no. 4 are indicated in Figure 9. From Figure 9, it can be seen that the oil content of no. 4 with carbamide added was almost unchanged before and after the fermentation; the oil content of no. 2 in which bean cake was added decreased from 17.2% to 12.1%, with the oil degrading rate up to 29.8%; and the oil content of no. 1 with poultry
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testify that these components were not degraded. Consequently, the saturates were degraded by the microbe source through the method of four components analysis. 4. Conclusion
Figure 8. Temperature comparison of nos. 1, 3, and 4 fermentation systems.
With the following experimental conditions, in the main aerobic fermentation used sawdust as the amendment, straw as the bulking agent. With forced aeration at 0.1 m3/h, the experiment results indicated that the oil degradation rate was up to 52.7% after fermentation in the feasible condition of poultry manure as the nitrogen source and fermentation liquor as the microbe source. The results of four components analysis indicated that the amount of saturates of oil degraded by strain HJ-1 in the refinery sludge was decreased remarkably after fermentation. Acknowledgment The authors thank the China National Petroleum Corporation (CNPC) Innovation Fundation for the financial support provided to carry out this work. The authors would like to acknowledge Chaocheng Zhao and Dongfeng Zhao for initiating an evaluation of this topic, and Chaocheng Zhao for providing valued input and guidance. We appreciate Weilin Wu sincerely for his support in this study. Literature Cited
Figure 9. Oil contents of nos. 1, 3, and 4 fermentation systems.
Table 3. Results of Four Components Analysis oil sample before treatment after treatment change between before and after treatment
saturates/% aromatics/% resin/% asphaltene/% 39.6 17.6 -22.0
36.2 43.1 6.9
24.8 39.2 14.4
0.9 1.5 0.6
manure added decreased from 18.8% to 8.9%, with the oil degrading rate up to 52.7%. Therefore, the effect of poultry manure as a nitrogen source for degrading oil was the best. Furthermore, it illustrates that microbes utilize animal nitrogen source more effectively and almost does not utilize the inorganic nitrogen source. 3.3. Analysis of Four Organic Components. In order to investigate what specific hydrocarbons were degraded by the strain, an analysis of four organic components was carried out for the oil samples extracted from the stockpile in no. 1 before and after fermentation. The results are listed in Table 3. Saturates decreased from 39.6% to 17.6% after treatment, namely, decreased by 22.0%. Because the method of the four components analysis determines only the relative content of each component in the oil sample, we can only conclude that the saturates content decreased significantly; namely, the saturates were degraded actually. Although from the table we can see that the contents of other components increased, we could not
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ReceiVed for reView October 26, 2006 ReVised manuscript receiVed April 13, 2007 Accepted June 19, 2007 IE061380L
