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

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• It was not possible to simulate solids accumulation with any accuracy since the experimental data were extremely noisy, and the kinetic parameters were not well understood. • The composition of the feed in terms of alkalinity and ammonia generation potential (which can be inferred from a carbohydrate/ protein /lipid fractionation, or from elemental analysis of the feed) was required for accurate prediction of effluent characteristics. Some of these quantities were not available from the pilot-ABR experimental study (Foxon et al., 2004) • Representation of hydrolysable COD as a single component in the Siegrist model resulted in poor agreement between predicted and measured soluble COD concentrations (Foxon et al., 2004) 6.5.2.2 Recommendations for model development The following changes were proposed to the model structure: • It was concluded that a biochemical model with protolysis and deprotolysis of weak acids and bases is necessary to adequately describe soluble COD and pH value dynamics in the ABR treating domestic wastewater at low inflow alkalinity concentrations. (Foxon and Buckley, 2007) • One particulate biodegradable COD fraction is insufficient to represent decreasing average hydrolysis rates; a subdivision of particulate biodegradable COD is proposed. Both of these changes are implemented in the Anaerobic Digestion Model No. 1 (ADM1, Batstone et al., 2002), so it seems appropriate to adopt the ADM1 model structure in future modelling. The following additional data would improve the model’s predictive performance: • Model inputs • Particulate and soluble organic nitrogen in the feed • Particulate and soluble inert COD in the feed • Total gas production • Organic acid concentration in the feed and in compartments • Some measure of the biomass seeding rates, or indication of where the model is sensitive to the seeding rate • A sludge retention model that describes the relationship between upflow velocity and sludge carry-over for granular and dispersed sludge 6.6 DESIGN OF BAFFLED DIGESTERS FOR TREATING DOMESTIC WASTEWATER The analysis presented in this chapter has indicated that the principle parameters that must be fixed for design of an ABR treating domestic wastewater are upflow velocity in compartments and overall A- HRT. This is used as the basis for presenting a design methodology for a classic (hanging and standing baffle) ABR design. 156
6.6.1 Design objective In engineering terms, an ABR functions as a series of mixed reactors, in which the biological catalyst, the biomass in the sludge of each compartment is retained in that compartment when the liquid flow passes out of the compartment. The first one or two compartments have the added function of retaining solids originating from the feed. The design objective is to increase the amount of contact time between suspended or dissolved contaminants and the biomass and decrease the amount of sludge washout in the ABR effluent. This is achieved by finding a compromise between • increasing HRT (the treatment time); • increasing the number of passes through the sludge bed (i.e. number of compartments); • reducing the upflow velocity to reduce solids carry-over; and • reducing space requirements and capital cost. Low upflow velocity can be achieved by either selecting a reactor geometry that has a short flow path for a specified HRT (e.g. a low, wide reactor, or few compartments), or by reducing the flow to a specific reactor size, i.e. increasing HRT. In the analysis that follows, the parameters in the process design are described, indicating the effect on process performance of the choice of parameter value. 6.6.2 Design Parameters The classic ABR process design consists of a number of equally dimensioned compartments. For a specific wastewater flow, the design is fully specified by fixing the following 6 independent parameters: (i) design HRT, (ii) number of compartments, (iii) peak upflow velocity, (iv) compartment width to length ratio, (v) reactor depth and (vi) compartment upflow to downflow area ratio. The civil design of the reactor interior also requires values for hanging baffle clearance, headspace height, baffle construction and inlet and outlet construction. All other internal features such as length and width of individual compartments are dependent on the first six parameters. 6.6.2.1 Principle design parameters This thesis argues that the hydraulic retention time and the up-flow velocity are the most important parameters in the design of an ABR treating domestic wastewater. • Hydraulic retention time: The mean HRT affects the contact time in which wastewater treatment may occur, and indirectly, the upflow velocity, that controls solids/sludge retention. It is also the parameter that dictates the size of the reactor (working volume) and therefore has a significant effect on the capital cost of the system. Although not shown in this study, a design A-HRT of 20 h could be achieved if the upflow velocity is sufficiently low. • Peak upflow velocity is the maximum permitted upflow in the reactor that does not cause an unacceptable entrainment and washout of sludge (Section 6.1.2.1). The peak up-flow velocity is the design velocity increased by a peak flow factor. The latter is the ratio of the peak flow expected to the average daily feed flow rate. Studies on simplified sewerage (small bore sewer systems) in poor communities in Brazil found a peak flow factor of 1.8 to be adequate for design purposes (Mara et al., 2000). It is proposed that a peak upflow velocity of 0.5 m/h be 157
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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
Page 129 and 130: • 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 182 and 183: employed for a medium strength wast
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
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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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