Thesis - faculty.ait.ac.th - Asian Institute of Technology

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Dan, et al. (2002) conducted the high salinity wastewater with yeast membrane bioreactor. The COD removal efficiency obtained was from 60% to 85% with a volumetric loading rate of 3.4 to 16.3 kg COD/m 3 .d. It was found that yeast cell size, low operating pH, and poor adhesion capacity reduced membrane fouling. To reduce the problems of frequent membrane fouling, the application of yeast to treat wastewater is considered. 2.13 Rationale for the Study and Proposed Treatment Sequence 2.13.1 Leachate Characteristic The development of a treatment sequence incorporating biological and physicochemical processes is necessary for the treatment of medium-age or intermediate landfill leachate. In the proposed study, leachate obtained from a sanitary landfill in Pathumthani, Thailand which has been in operation for 5 years, together with leachate derived from compression of fresh domestic waste from a transfer station in Bangkok, Thailand were mixed to simulate a medium-age leachate. The leachate was simulated to mimic a low biodegradable, high ammonia leachate with BOD, COD and TKN ranging from 2,500±500, 8,000±1,000 and 1,900±100 mg/L, respectively. The decision to synthesize a leachate by combining the two leachate sources was to attain consistent characteristic was based on the continual variability of leachate obtained from a single source. Hence, little or no control of the leachate can be exercised in development of a treatment sequence making it more complicated. Since, it has been proposed by previous researchers that some degree of control should be maintained over the waste dumped and leachate generated, a synthetic leachate is justified. Further, Thailand’s tropical climate drastically affects the leachate quality. Therefore, over a longterm experimental investigation, it is deemed unfeasible to attempt to use a raw leachate source. 2.13.2 Need for Ammonia Stripping Due to the presence of elevated ammonia concentrations in the leachate, sludge properties are affected resulting in a fine floc which is difficult to settle. The high ammonium concentration also poses toxicity to the microorganisms, thus affecting the degradation process. Therefore, the effect of ammonia concentrations of 2,000 mg/L was investigated with yeast and bacterial cultures. Due to toxicity, removal of ammonia was therefore apparent for leachate treatment. Thus, ammonia stripping was evaluated. Ammonia removal by air stripping was selected as a pre-treatment for the reduction of ammonia from 2,000 to 200 mg/L. Ammonia stripping has the advantage of reducing refractory compounds and thereby reducing COD concentrations, by precipitation when pH is adjusted. This approach was adopted in the conventional biological nitrificationdenitrification process since nitrification-denitrification processes were subjected to many operation problems such as nitrification-denitrification inhibition. Further, for the leachate characteristic, treatment efficiency by nitrificationdenitrification is considered poor with BOD/TKN < 2.5, BOD/NH3 < 4 and COD/TKN < 5 (Grady, et al., 1999). In order to ensure successful removal of ammonia in the 52
nitrification-denitrification process, an external carbon source in the form of leachate, methanol etc. could be necessary. An external carbon source could further increase the operational costs. Chemical treatment by coagulation, flocculation and precipitation eliminates the increased chemical costs making this option realistic for ammonia removal. Thus, ammonia stripping seems to be the most viable option. While ammonia stripping can be conducted in packed towers with efficiencies up to 95 %, the intention of this study is to merely reduce leachate with total nitrogen content of 1,800-2,000 mg/L to a level below toxicity for further biological treatment, for which a conventional ammonia stripping would be sufficient. Thus, by maintaining an optimal operating condition by controlling, air flowrate and pH, an ideal condition based on ammonia removal, ammonia toxicity and mixing power efficiency could be obtained using a conventional stirred tank. One of the main disadvantages of ammonia stripping is the high cost associated with pH adjusters. The choice of pH adjuster is also crucial in design and rendering the process cost effective, a reduction in the amount of adjuster can be brought about by pre-aerating the leachate. The synthetic leachate used in this study has an average pH of 8.5 ±0.5. Since, this is already in the alkaline range; the amount of buffer added to raise pH for ammonia stripping is not significant. 2.13.3 Need for Membrane Bioreactors If the pre-treatment of ammonia stripping fails, this would lead to shock loading in the biological system, making it difficult for the floc to settle down. This problem can be solved by the adoption of a membrane process to replace the clarifier in a normal activated sludge process since the membranes can retain total solids until the sludge recovers from shock loading of ammonia. Purification of leachate by membrane processes aids in preventing further contamination of groundwater resources and surface water. However, in selecting a treatment option, or a combination of treatment operations, the economic feasibility and affordability of the technology should also be considered. In this regard, membrane filtration has proven to be a justifiable and economic solution in most cases, even when the overall costs for the purification are compared with other approaches for leachate treatment (Peters, 1997). By coupling of a membrane with the activated sludge reactor, a membrane bioreactor emerges as a logical treatment option. The reduced operational costs associated with immersed membrane bioreactors proves advantageous in its application and therefore preferred in the present study. The use of a MBR allows the HRT to be reduced from 1 to 10 days (Qasim and Chiang, 1994) to less than 24 h. This reduction is drastic and viable in terms of operation costs and effectiveness. Reduction in SRT from conventional activated sludge SRT of 15 to 60 d has the advantage of reducing air requirements in the MBR. Maintaining a lower MLSS is advantageous since lower the sludge produced, the greater is the effectiveness of aeration. This approach effectively reduces the aeration requirements and a smaller SRT and HRT reduces the required reactor volume and thus the capital cost. 53
Page 1 and 2:
APPLICATION OF MEMBRANE BIOREACTOR
Page 3 and 4:
Abstract Landfill leachate is a com
Page 5 and 6:
Table of Contents Chapter Title Pag
Page 7 and 8:
4.5.6 Cost Analysis for Operation 1
Page 9 and 10:
4.4 Effect of Free Ammonia Concentr
Page 11 and 12:
4.16 COD Concentration in the Influ
Page 13 and 14:
MWCO Molecular Weight Cut-off MWW M
Page 15 and 16: 1.1 Background Chapter 1 Introducti
Page 17 and 18: generally unsuccessful in removal o
Page 19 and 20: 2.1 Introduction Chapter 2 Literatu
Page 21 and 22: In the municipal solid waste landfi
Page 23 and 24: COD/TOC, VS/FS and VFA/TOC ratios o
Page 25 and 26: Table 2.3 presents the general leac
Page 27 and 28: Ground water 2.7.1 Seasonal Variati
Page 29 and 30: Table 2.5 Variation of COD, BOD & B
Page 31 and 32: entails the re-circulation of leach
Page 33 and 34: Table 2.8 Summary of Biokinetic Coe
Page 35 and 36: that extensive loss of nitrogen (up
Page 37 and 38: ammonia could only be achieved when
Page 39 and 40: Table 2.10 Treatment Efficiencies o
Page 41 and 42: Activated Carbon Adsorption Granula
Page 43 and 44: Colloidal material as well as metal
Page 45 and 46: iologically, physical-chemical proc
Page 47 and 48: Ammonia Stripping Air stripping of
Page 49 and 50: These systems are land intensive wh
Page 51 and 52: the biological treatment can be rep
Page 53 and 54: Table 2.16 Typical Leachate Composi
Page 55 and 56: influent reached 200 mg/L. For the
Page 57 and 58: Table 2.18 Advantages and Disadvant
Page 59 and 60: through the effluent. Different ope
Page 61 and 62: Mixed Liquor Suspended Solids and D
Page 63 and 64: 2.12 Yeasts 2.12.1 Introduction The
Page 65: Nishihara ESRC Ltd. (2001) studied
Page 69 and 70: Table 3.1 Composition of Simulated
Page 71 and 72: 3.4.1 Ammonia Toxicity The experime
Page 73 and 74: Figure 3.4 Experiments Conducted to
Page 75 and 76: Leachate Option Ammonia Stripping R
Page 77 and 78: MW larger than 50 kDa, (2) MW betwe
Page 79 and 80: Figure 3.7 Flowchart Showing Ammoni
Page 81 and 82: Chapter 4 Results and Discussion 4.
Page 83 and 84: COD Removal Effeciency (%) COD Remo
Page 85 and 86: MLSS (mg/L) 14000 12000 10000 8000
Page 87 and 88: Specific Growth Rate ( d -1 ) 0.50
Page 89 and 90: change in the predominant species w
Page 91 and 92: Table 4.4 Effect of Free Ammonia Co
Page 93 and 94: Table 4.5 Substrate Utilization by
Page 95 and 96: 4.3.1 Initial Membrane Resistance P
Page 97 and 98: when compared with the present stud
Page 99 and 100: COD Removal Efficiency (%) 90 80 70
Page 101 and 102: (2) TKN Removal Efficiency Prior to
Page 103 and 104: As there was no significant improve
Page 105 and 106: The probable reason for frequent fo
Page 107 and 108: Ammonia Concentration (mg/L) Ammoni
Page 109 and 110: concentration after treatment. Othe
Page 111 and 112: After the chemical cleaning of the
Page 113 and 114: emoval of 38%. A higher removal in
Page 115 and 116: Influent BOD (mg/L) Influent BOD (m
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(3) TKN Removal Efficiency The TKN
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Figure 4.34 gives the overall TKN r
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fraction and slowly biodegradable C
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BOD (mg/L) BOD (mg/L) 6000 5000 400
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Figure 4.39 Molecular Weight Cut-of
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COD (mg/L) 8000 6000 4000 2000 COD
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Though, the obtained COD removal ef
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cake used on the top of the membran
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Chapter 5 Conclusions and Recommend
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0.02, respectively. This can be con
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References Abeling, U., and Seyfrie
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Brown, M.J., and Lester, J.N., 1980
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Diamadopoulos, E., 1994. Characteri
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Grady, C.P.L., Daigger, G.T., and L
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Keenan, J.D., Steiner, R.L., and Fu
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Martin, G.M.A., Auzmenti, A.I., and
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Pohland, F.G., and Harper, S.R., 19
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Shin, H.S., An, H., Kang, S.T., Cho
Page 153 and 154:
Visvanathan, C., Ben Aim, R., and P
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Appendix A Pictures of Experiments
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Raw Leachate YMBR Effluent BMBR Eff
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Appendix B Leachate Characteristics
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Table B-2 Acclimation of Mixed Yeas
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Appendix C Experimental Data of Bio
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y: Where: OUR at line g: This is th
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Table C-3 Experimental Results for
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Appendix D Membrane Resistance Stud
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Table D-3 Experimental Data for Det
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Table D-4 Experimental Data for Det
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Pressure (kPa) Pressure (kPa) 25 20
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Appendix E MBR without Ammonia Stri
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Day HRT (h) pH COD (mg/L) Feed Reac
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Day HRT (h) pH COD (mg/L) Feed Reac
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Table E-3 Variation in TMP with Tim
Page 185 and 186:
Appendix F Ammonia Stripping Studie
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Table F-5 Pilot Scale Study on Ammo
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Table G-1 Feed, Reactor and Effluen
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Table G-3 Feed, Reactor and Effluen
Page 193 and 194:
Appendix H Other Studies 179
Page 195 and 196:
Table H-2 Membrane Resistance of th
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Table H-6 Chemical Cost for the Yea
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