การปรับสภาพตะกอนลอยจากบ่อดักไขมันของอุตสาหกรรมทูน่ากระป๋องด้วยวิธีการทางชีวภาพเพื่อประยุกต์ใช้ในการผลิตแก๊สชีวภาพ

Abstract

This research studied the pretreatment of scum from oil trap tank of wastewater treatment system located at a tuna canning industry to be used as substrate in biogas production. The primary lipid hydrolysis with Bacillus subtilis AH73 only slightly improved methane production from scum likely due to its low enzyme activity. Therefore, lipase and protease in the isolation and selection of lipase and protease producing bacteria were isolated from wastewater treatment system and screened under aerobic and anaerobic conditions. The results revealed that 16 isolates presented the large clear zone of hydrolysis under aerobic condition and 2 isolates presented large clear zone under anaerobic condition. In the digestion of scum sludge under aerobic and anaerobic conditions, it was found that SNL1 had the highest lipase and protease activities of 177.45 U/L and 1,695 U/L, respectively. While INL11 gave highest soluble COD of 17.02 g/L. Later, SNL1 and INL11were identified as Bacillus cereus and Aeromonas caviae, respectively. The pretreatment of scum sludge by the biological method using isolated bacteria and the biochemical methane potential produced from the pretreated scum were studied at the flask level using in batch fermentation mode. It was found that the pretreatment with SNL1 under aerobic condition for 7 days resulted in the reduction of total solids from 112.9 g/l to 79.0 g/l, and the maximum methane yield was obtained at 34.3 mLCH4/gVS. In addition, the scum to wastewater ratio at 80:20 produced higher biogas production than at the ratio of 90:10 and 70:30. Moreover, the pretreatment of scum sludge by bioaugmentation using SNL1 and biostimulation with aeration (without microbial inoculation) was compared with unpretreatment of scum sludge in a 6.5 l fermentation tank using a batch fermentation mode. It was found that the experiment without pretreatment of scum sludge produce Methane lower than bioaugmentation by SNL1, which gave the maximum cumulative methane production of 14,759 ml at day 60. Due to SNL1 bacterial degradation and aeration, nutrients are readily available than untreated scum. Furthermore, the experiment was performed with the semi-continuous mode. The result showed that the bioaugmentation by SNL1 produced higher cumulative methane than the unpretreatment (1.96 times) and the biostimulation (1.21 times) with the methane yield of 259.8 mLCH4/gVS, since nutrients are transferred into and out of the system, microorganisms get new nutrients to use as a source for growth due to the addition of bacteria producing enzymes that can help decompose the preliminary sediment, causing the nutrients to be converted into usable structures easier than untreated scum. Pretreatment of scum sludge using the bioaugmentation by SNL1 and the biochemical methane potential from pretreated scum was investigated in a 200 L reactor using a batch fermentation mode. The results found that the pretreatment of scum sludge using bioaugmentation by SNL1 improved the methane production from 0.76 LCH4 (the experiment without sludge pretreatment) to 3.71 LCH4 with a maximum methane yield of 25.8 mLCH4/gVS and total solids removal efficiency of 38%. Finally, the methane production from SNL1 pretreated scum was scaled up to 1000 L reactor. It showed that the highest cumulative biogas and cumulative methane production were 6124.33 L and 1192.91 LCH4, respectively with the methane yield of 1893 mLCH4/gVS on day 81 of fermentation, the total solids removal efficiency of 83%, and the total COD removal efficiency of 87%. The methane content ranged from 50 to 73% throughout the period of fermentation.