analysis of a pilot-scale anaerobic baffled reactor treating domestic ...

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employed for a medium strength wastewater, with low alkalinity concentration if alkalinity supplementation is not employed, and if no additional sludge retention devices are included in the design. This gives a design upflow velocity of 0.28 m/h for a medium strength wastewater (COD = 680 mgCOD/ℓ) with an alkalinity concentration of approximately 300 mgCaCO3/ℓ. (In systems with higher alkalinity concentration, this value may be much higher). Number of compartments, reactor depth, and compartment upflow to downflow area ratio all define the peak upflow velocity within the reactor. Independently either increasing the number of compartments, the reactor depth or reducing the compartment upflow to downflow area ratio results in an increase in upflow velocity. Except in the case of the upflow to downflow area ratio, the increased liquid velocity is caused by the lengthening of the overall path that wastewater has to traverse through the reactor (working height of reactor x number of compartments x 2 [m]). 6.6.2.2 Secondary design parameters The number of compartments and the reactor width to length ratio are considered to be secondary design parameters. Intimate contact between sludge and wastewater ensures efficient use of treatment volume. This means that a greater number of passes through the sludge blanket, achieved by increasing the number of compartments will increase the overall contact time between wastewater and sludge, and therefore increase COD removal. Analysis of COD concentration in the overflow from each compartment however showed that, after a certain number of compartments, the added benefit in each additional compartment becomes progressively less (Section 4.4.2). The number of compartments should be selected to be equal to or greater than the number of zones within the reactor that can develop microbial consortia with significantly different characteristics. Boopathy (1998) showed that for 4 ABRs with 2, 3, 4 and 5 compartments respectively, and with all other dimensions identical, more compartments resulted in better solids retention and overall greater extent of treatment for a swine manure feed. This implies that repeated passes through the sludge bed has a greater beneficial effect in increasing extent of treatment than maintaining a low upflow velocity, although Boopathy’s findings were for constant flow-rate conditions. However the results from the pilot-scale ABR study reported here indicate that there must be a cross-over point where increasing the number of compartments will increase the upflow velocity to a point where washout of sludge occurs to the detriment of the biological processes, resulting in poorer COD removal performance than for a smaller number of compartments. It is proposed that a system should be designed with at least three, but up to 5 compartments, to ensure good contact between wastewater flow and sludge beds, and to provide for development of an acid zone in the first one or two compartments. The number of compartments may be increased to provide additional sludge storage volume to increase the desludging interval. However, if this is the purpose of the additional compartments, then the A-HRT should be increased accordingly, i.e. Design HRT = Reqd HRT ⋅ Reqd. no. of compartments Reqd. no. of compartments 158 + additionalstorage compartments Eq. 6-7
where the required HRT and number of compartments are those values that are understood to be necessary to achieve the required effluent specifications. Appropriate hydraulic design, particularly the length of each compartment (distance between successive standing baffles) is important to ensure that wastewater is not able to bypass large portions of the sludge bed. Reactor width to length ratio does not have a direct effect on the superficial upflow velocity. However, a compartment that is too long will experience channelling and by-passing effects; more liquid flow will pass up through the sludge blanket near to the hanging baffle than near the following standing baffle, effectively by-passing much of the sludge bed and under-utilising reactor space. 6.6.3 Example of design parameters Table 6.5 presents guidelines for selecting design parameters for an ABR using the findings of this study. Table 6.5: Example of design parameters for an ABR treating domestic wastewater Parameter Symbol Unit Recommended parameter range or equation Flow rate Q m 3 /d - Hydraulic Retention Time A-HRT h 12 1 to 20 but 40 to 60 during start-up Reactor working volume VW m 3 Q×HRT/24 Peak upflow velocity vp m/h 0.5 Design upflow velocity vd m/h vp/1.8 = 0.28 Number of compartments N - 4 to 6 Hanging baffle clearance dh m 0.15 to 0.20 Compartment upflow area AU m 2 Q/(vD×24) Upflow to downflow area ratio RU:D m 2 /m 2 2 to 3 Compartment width to length ratio CW:L m/m 3 to 4 Total compartment area AC m 2 AU × (1+RU:D)/RU:D Reactor depth rD m 1 to 3 (The reactor depth will largely be governed by the cost of excavation) Reactor width rW m V ⋅ C W W : L N ⋅ r Reactor length rL m N x rW / CW:L 1 See e.g. Lettinga (Lettinga, 2001) for justification of A-HRT values lower than attempted in this study 159 D
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ANALYSIS OF A PILOT-SCALE ANAEROBIC
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i DECLARATIONS I, Katherine Maria F
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My deepest thanks must be extended
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vii TABLE OF CONTENTS ANALYSIS OF A
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5.3 Feed characteristics and loadin
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xi LIST OF TABLES Table 1.1: List o
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xiii LIST OF FIGURES Figure 1.1: Gr
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Figure 5.1 Installation of the ABR
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Figure 6.8: WEST® representation o
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xix LIST OF ABBREVIATIONS A-HRT App
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1 1 INTRODUCTION The work presented
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obtained from anaerobic systems rel
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• Lalbahadur (MTech, 2005) perfor
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1.7 ORGANISATION OF THE THESIS This
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9 2 LITERATURE REVIEW A detailed re
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• Disintegration of composite par
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Homoacetogens are one of the most v
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Most of the control in anaerobic di
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therefore the sensitivity of the ov
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∆Gº (W) [kcal] -10 -8 -6 -4 -2 L
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For systems with low potential for
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design of the digester in which the
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2.2.2 Expanded granular sludge bed
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fact that for most non-ideal flow s
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hydrolysis steps to convert them to
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from the clarified zone between the
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Table 2.4: Typical pathogen surviva
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Table 2.5: Studies using anaerobic
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• There is no requirement for bio
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Kennedy and Barriault (2005) perfor
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methanogenic (Akunna and Clark, 200
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and 6 h with no significant differe
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2.5.1.12 Granule formation in ABRs
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• A baffled reactor is described
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2.5.3.4 Scanning electron microscop
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spacing on flow patterns in a singl
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Figure 3.5: Orthographic projection
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PLC calculated the fraction of that
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epresent buulk conditionns. Compart
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The rreactor was initially commmiss
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Phase I Phase II Phase III Phase IV
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Table 4.1: Characteristics of degri
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Table 4.2: Pilot-scale ABR approxim
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COD [mgCOD/ℓ] 2000 1800 1600 1400
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4.3.5 Phosphorus Figure 4.8 present
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Observation of sludge in compartmen
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Another interesting observation is
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4.4.3 pH pH measurements were perfo
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esult in low pH values. The reasons
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4.5 SUMMARY: PHASE I - OPERATION AT
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than the optimal range for methanog
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5 EXPERIMENTAL PHASES II-IV: KINGSB
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sludge on a number of occasions. Wh
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On days 99 and 100 of Phase III, a
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5.3.2 Analysis of variations in fee
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Table 5.2: Pilot-scale ABR average
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5.4.1.2 Phase III In Phase III, (Fi
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Phase II: Alkalinity [mgCaCO3/ℓ]
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Eq. 5-1 However, at a COD/SO4 2- ra
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wastewater was probably higher than
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5.5.2.2 Damping Figure 5.12 and Fig
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• The outflow COD values were not
Page 131 and 132: • Information about the volume of
Page 133 and 134: As with the total volume of sludge
Page 135 and 136: It is not clear why the rate of acc
Page 137 and 138: most compartments was exactly 6.5,
Page 139 and 140: Soluble COD [mg/ℓ] 600 500 400 30
Page 141 and 142: pathogens and parasites, which may
Page 143 and 144: % Probe of DAPI % Probe of DAPI % P
Page 145 and 146: later compartments at all. Furtherm
Page 147 and 148: and 4, with decreasing observations
Page 149 and 150: • The mechanism of sludge build-u
Page 151: Table 5.6: Inflow and outflow chara
Page 154 and 155: Behling et al. (1997) studied the p
Page 156 and 157: organisms in previous compartments.
Page 158 and 159: velocities. Unfortunately, these tw
Page 160 and 161: Thus for a fixed sludge load, at hi
Page 162 and 163: sampling was not possible since in
Page 164 and 165: Wentzel (2006) recommends a COD to
Page 166 and 167: 6.2.1.4 Calculation of CH4 producti
Page 168 and 169: organically bound N) or that N accu
Page 170 and 171: All VFA is consumed in the process,
Page 172 and 173: However, these assumptions are clea
Page 174 and 175: The calculated pH value is compared
Page 176 and 177: influent alkalinity will increase d
Page 178 and 179: The original objective to develop a
Page 180 and 181: • It was not possible to simulate
Page 184 and 185: 6.6.4 Alternative baffle design Thi
Page 186 and 187: 6.7.3 Monitoring requirements The m
Page 188 and 189: compartments (Section 6.1.1) pH val
Page 190 and 191: generally about anaerobic digestion
Page 192 and 193: 7.1.1.6 Effect of sludge age on bio
Page 194 and 195: 7.1.2.4 Critical design parameters
Page 196 and 197: 172
Page 198 and 199: Batstone D. J., Keller J., Angelida
Page 200 and 201: Gopala K. G. V. T. (2007). Treatmen
Page 202 and 203: MacLeod F. A., Guiot S. R. and Cost
Page 204 and 205: Sasse L. (1998). Decentralised wast
Page 206 and 207: Wanasen (2003). Upgrading conventio
Page 209 and 210: METTHODS OFF SAMPLINNG AND ANNALYSI
Page 211 and 212: 3.6 Enumeration of total coliforms
Page 213 and 214: that the means are the same, or con
Page 215 and 216: And the significance of the regress
Page 217 and 218: ADDITIONAL RESULTS 193 APPENDIX A3
Page 219 and 220: Table A3. 1 cont. Phase I Phase II
Page 221 and 222: each of the eight compartments were
Page 223 and 224: 3.2 Pathogen indicator organisms A
Page 225 and 226: APPLIED VS. APPARENT HYDRAULIC RETE
Page 227 and 228: 19 h apparent HRT 14 h apparent HRT
Page 229 and 230: 205 APPENDIX A5 CALCULATION OF SOLI
Page 231 and 232: i.e. the average SRT of an accumula
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X X = P Inert ⋅ where Xinert is t
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iodegradable organic material may b
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Substituting Eq. A6- 1 in Eq. A6- 7
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1.5 Implementation of steady-state
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X = 7⋅ Y = 7 Z = 7⋅ A = 7⋅ (
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Dama, P., Bell J., Naidoo, V., Foxo
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Lalbahadur T. (2004) Characterisati
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