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The research about remodeling and collecting gas from Imhoff tank at Dalat’s sewage treatment factory Lam Vinh Son Faculty of Environment and Biotechnology, Ho Chi Minh City University of Technology (HUTECH) Address: 475A Đien Bien Phu street, Binh Thanh district, Ho Chi Minh, Vietnam. Tel: 08 35120788 - 0903399800 (*) Email: lvson1610@gmail.com ABSTRACT The imhoff tank’s structure include the upper section is sedimentation compartment and the lower section known as the anaerobic digestion compartment. This tank is often used to process the sewage with high suspending oganic solids like domestic wastes. Anaerobic process in the lower section produce a kind of gas similarly biogas. The main purpose of this research is gas collection from anaerobic process of suspended solids in factory’s sewage. However, this collection must not effect to the processing ability of the model. With the inlet flow of model about 0,0217 - 0,0300 m 3 /h and the sludge retention time is 4 days, the processing ability of the model is: reducing 20 - 30 % SS, 40 - 50 % COD. When the Imhoff’s model get steady, it will be installed a gas collecting system. Gas store in model for 2 days has metan’s concentration about 5 . 10 5 – 7 . 10 5 ppm as percent volume of metan in gas compound about 50 - 70 %. The gas’s volume from Imhoff’s model is not steady, depend too much on the sludge retention time and the sewage’s temperature. However, this gas can realy use as a burning gas. Base on these data, the research make a plan to reform the Imhoff tank of Dalat’s sewage treatment factory for the collecting gas purpose. The reforming material is waterproof stuff HDPE Keyword : Imhoff, Dalat’s sewage, metan 1. INTRODUCTION The main purpose of this research is gas collection from anaerobic process of suspended solids in factory’s sewage. However, this collection must not effect to the processing ability of the model. 2. MATERIALS AND METHODS 2.1.The imhoff tank’s structure Imhoff one drawer deposition, the structure consists of an outside large tank with dimensions: 1m length, 3m width, 0.6m height. This is decomposed drawer of the model. At the bottom of the tank with two mirrors placed at an angle 30 o anh spaced 5cm. The purpose is to focused the amount of sewage sludge in the bottom of the tank. Above is a deposited drawer put in large tank. Deposited drawer consist of a rectangular part in the top and a triangle part in the lower (bottom of the deposited drawer). The rectangular part with dimensions: 1m length, 0.2m width, 0.15m height. The triangle (bottom of the deposited drawer) has specially constructed: one big bottom surface and one small bottom surface at an angle 50 o from horizontal plane. Two bottoms do not close, it has a 1.5cm gaping. With purpose is sludge from deposited drawer down to decomposed drawer. Besides, the width of big bottom surface loger than small bottom surface is 5cm. With purpose is to prevent the gas from anaerobic decomposition overflows to deposited drawer, affects the deposition. Figure 1: Imhoff tank model 2.2.Gas collection system Gas collection system is installed on the basis of sealed model’s two gas escape drain by two sheets of glass. One each glass is chased two holes to mount two gas collection pipes. According to the figure below: Figure 2: Gas collection system 2.3.The operating parameters Table 1.Imhoff model’s parameters Parameters values Units Outside large tank length 1 m width 0,3 m height 0,6 m Total volume 0,180 m 3 Working volume 0,150 m 3 Deposited drawer length 1 m width 0,2 m height 0,26 m Angle of bottom 50 o Gaping width of bottom 1,5 cm Width of big bottom surface 0,14 m Width of small bottom surface 0,18 m volume 0,0452 m 3 Decompo sed drawer Angle of bottom 30 o Width of bottom 0,15 m volume 0,1048 m 3 Sludge volumes max 0,07425 m 3 Sludge volumes min 0,05025 m 3 Gas escape drain Width of drain 0,05 m Length of drain 1 m Gas volume 7 l 2.4.The location of model and the method of operating The location of model: discharge – conditioning valve of Imhoff system tank’s input distributing hole in Da Lat waste water treatment factory. Model’s methods of waste water: method of gravity flowing. Model is placed negative down, so the water level in the distributing hole higher than model’s water level. From then, water flows from Φ 0.5cm pipes to model. Sludge from decomposed drawer will be drawn periodically out of model and poured into Imhoff tank’s escape gas drain. 2.5 The operational model Running model phase do not count the weight: the purpose of this phase is accumulated a part of sludge in decomposed drawer’s bottom in the running time model. Running model phase with count of determine weight: stabilize water discharge into model. Determination of water discharge into model and save sludge time. Running model phase with count of determine weight associated gas collection: started determining targets SS, COD in put, out put and installing gas collection system 3. RESULTS 3.1.The result analysis quality model’s water in put and out put (COD, SS) Table 2: Result analysis model’s COD, SS in put and out put Date test No. SS in (mg/l) SS out (mg/l) H- SS (%) COD in COD out 3/4 1 854 475 44,3 7 736 572 4/4 2 695 350 49,6 4 522 413 10/4 3 404 196 51,48 537 408 11/4 4 429 235 45,22 636 477 17/4 5 841 634 24,6 1 546 567 18/4 6 1000 600 40,0 0 1506 1546 21/4 7 759 305 46,58 722 456 24/4 8 570 324 43,1 373 286 6 25/4 9 1204 601 50,08 521 397 23,80 26/4 10 1665 927 44,3 2 672 560 16,67 28/4 11 913 486 46,7 7 696 496 28,74 2/5 12 1207 709 41,59 723 494 31,67 3/5 13 533 275 48,4 0 652 471 27,76 8/5 14 445 233 47,6 4 624 488 21,79 9/5 15 249 158 36,5 4 385 310 19,48 Remarks: - In general, the efficiency of the SS at about 40-50% COD removal efficiency of about 20-30%. With a pre-treatment process, the effectiveness of this treatment is unacceptable. 3.2. The results of analysis of methane concentration in the gas mixture generated from the model 3.2.1 Chromatograms 1st injection of the standard range Figure 3. 1st injection chromatograms 2nd injection of the standard range Figure 4. 2nd injection chromatograms Sample 1: Figure 5. Sample 1 chromatograms Sample 2: Figure 6. Sample 2 chromatograms 3.2.The results of analysis of methane concentration in the gas mixture generated from the model Table 3. The results of analysis of methane concentration in the gas mixture generated from the model spread (S) concentration (C) 1nd 2nd 3rd medium ppm Standard 941 950 - 945,5 15 Sample 1 5573 5574 5576 5574,0 707476 Sample 2 3960 3938 3943 3947,0 500941 The concentration of methane in the sample calculated by the formula: C sample = . 8000 (ppm) In which: S sample : spread of peak methane in the sample S standard : spread of peak methane in the standard sample C sample : methane concentration in the sample (ppm) C standard : methane concentration in the standard sample (ppm) 8000: sample coefficient of dilution Remarks: - Percentage of the volume of methane in the gas mixture is very high (50-70%). Fully capable of use as fuel. 3.3.The results of the volume determine gas produced per day from the model Table 3.3. Results of the volume determine gas produced per day from the model Gas volume Total volume of gas collected (ml/day) Time of gas accumulat ion (h) Total volume of gas collected (ml/day) 18/5 X - - - 19/8 4626 22,50 4934 20/5 6441 22,00 7026 4.I 21/5 8968 23,50 9159 22/5 X 9124 23,50 9318 23/5 6174 23,50 6305 24/5 9035 21,50 10084 25/5 10374 22.00 11317 26/5 X 11939 23,75 12065 27/5 7.I 4549 20,25 5391 28/5 6805 23,50 6950 29/5 8857 24,00 8857 30/5 9614 24,00 9614 31/5 9240 24,00 9240 1/6 8724 24,00 8724 2/6 X 7416 23,50 7416 3/6 7.II 4406 23,00 4597 4/6 6853 23,33 7050 5/6 8171 23,50 8345 6/6 8568 24,00 8568 7/6 7882 24,00 7882 8/6 6433 24,00 6433 9/6 X 5729 25,50 5392 10/6 4106 24,00 4106 11/6 5403 24,00 5403 12/6 5635 24,00 5635 13/6 6737 24,00 6737 In which: 4.I ; 4.II ; 4.III respectively 4-day sludge drawn period I; II; III. 7.I ; 7.II respectively 7-day sludge drawn period I ; II. The experiment measured the volume of gas produced within a day is caried out in parallel with sludge drawn period out of model. To explain the difference between gas collected and sludge drawn period: There are two factors that directly affect the amount of gas produced in the model: + Temperature of waste water: exert an influence on microbial activity in anaerobic decomposed drawer. In the time between the end of May, sunshine all over the country. Therefore, high waste water temperature, so anaerobic microbal is activities strongly, great amount of gas produced. From early June and after, the temperature in Da Lat lower due to appear drizzle rain all day. Therefore, waste water temperature is lower these days, reducing anaerobic microorganisms’s functional capability, collected less gas. Results of sludge drawn periods in May will be greater than the amount of gas collected in June. + Sludge drawn in decomposed drawer: non-homogeneous between periods.It is caused by the deposition of sludge at the decomposed drawer’s bottom. Because of this reason, unable to drawn completely sludge at the bottom of decomposed drawer. Causes each drawing sludge is not the same and inhomogeneous. That’s mixture of decomposed sludle and new sludge from decomposed drawer. This percentage is difference from withdrawal sludge. So it has change in gas collected volume between of sludge drawn periods. 4. DISCUSSION With 4-day sludge drawn periods, the amount of produced gas is directly proportional to sludge saved time. Gas produced is significantly reduced when drawn sludge out of model. With 7-day sludge drawn periods, the amount of gas produced increased to a certain level and then gradually decreases. For experiments measured the volume of produced gas from model in one day with 4-day sludge drawn period, and data from the first 4 days of 2 experiments measured the volume of produced gas from model in one day with 7-day sludge drawn period, derived the volume of gas produced relatively on average a day from model to 4-day sludge drawn period: V gas medium(mh) = 7,573 l/day. The ability to remove COD and SS of model is similar to factory’s Imhoff tank system, derived the volume of gas produced relatively per day of imhoff tank system is based on the correlation of the influent waste water discharge. Currently, the average of factory’s influent waste water discharge is Q medium(nm) = 4500m 3 /day. The average of model’s influent waste water discharge is Q medium(nm) = 0.62m 3 /day. So the volume of gas produced relatively per day from imhoff tank system with 4-day sludge drawn period: V gas medium(nm) = 54,965 m 3 /day. Thus, factory’s imhoff tank system can produce 19787.4 m 3 gas average per year. However, sludge retention time in the imhoff tank system usually 7 days and the sludge containing volume is large (two deposited drawer imhoff has sludge volume – decomposed drawer large) so the gas produced volume in reality will be greater than the above figures. Suggested gas collection prrocedure in Imhoff tank: References [1] Catherinem. Cooney - science advancing on methane’s behavior in carbon cycle – Insideclimate news [2] Tom Asmus (2005),The History of IMHOFF Technology -A Treatment Process for It's Time - www.wwoa.org. Imhoff tank for the purpose of improving gas Gas filter column system Gas bunker Making fuel gas Running generator . The research about remodeling and collecting gas from Imhoff tank at Dalat’s sewage treatment factory Lam Vinh Son Faculty of Environment and Biotechnology,. the Imhoff tank of Dalat’s sewage treatment factory for the collecting gas purpose. The reforming material is waterproof stuff HDPE Keyword : Imhoff, Dalat’s