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methanogenic (Akunna and Clark, 2000; Uyanik et al., 2001b; Baloch and Akunna, 2003; Sallis and Uyanik, 2003; She et al., 2006). Baloch and Akunna (2003) seeded an ABR with granular sludge and fed it with a synthetic glucosebased wastewater at OLRs from 1.25 to 20 kg COD/m 3 /d. They observed floating and breaking up of granular sludge in the early compartments of the reactor, while methanogenic sludge in later compartments retained their structure. These authors reported that a white sticky mass formed in the sludge of the early compartments. This proved to be bacteria of the Enterobacteriaceae genus that can use glucose as a sole carbon source and are tolerant to low levels of dissolved oxygen. Bell (2002) investigated microbial population characteristics through fluorescent in-situ hybridisation (FISH) analysis of samples drawn from different compartments of an 8-compartment ABR fed a soluble sucrose/ protein feed. Eubacteria were found to predominate in early compartments, while Archaea dominated in later compartments. There was also a distinct shift between H2, CO2 and formate utilising methanogenic Archaea in the early compartments and acetoclastic Archaea in the later compartments. Micro-organisms from the genus Methanosarcina were only occasionally observed in the first compartment. This genus is usually outcompeted by acetoclastic methanogens from the genus Methanosaeta and can only predominate at high acetate concentration (Speece, 1996). 2.5.1.5 Response to hydraulic and organic shock loads The ABR has exhibited superior resilience to hydraulic and organic shock loads compared to other reactor configurations (Barber and Stuckey, 1999). Grobicki (1989) simulated a hydraulic shock by decreasing the hydraulic retention time from 20 h to 1 h, for a period of 3 h in an ABR operating at an OLR of 4.8 kg COD/m³ on a soluble synthetic carbohydrate / sucrose / protein feed. The reactor returned to its previous COD removal efficiency of in excess of 95 % within 24 h of resuming normal operating conditions. Less than 15 % of the active biomass was lost. In a similar experiment, the OLR was increased to 20 kg COD/m³ and, under these conditions a COD removal efficiency of 72 % was still achieved. Nachaiyasit and Stuckey (1997b; c) investigated the effect of hydraulic and organic shock loads on a 10-ℓ 8 compartment ABR fed a synthetic sucrose/protein wastewater. Baseline conditions for these experiments were a hydraulic retention time of 20 h and an OLR of 4.8 kg COD/m 3 .d (Feed concentration = 4 g COD/ℓ). When the feed concentration was doubled to 8 g COD/ℓ at constant hydraulic retention time, increases in compartment VFA, dissolved H2 and COD concentrations and decreases in measured compartment pH values were observed in the early compartments, while no significant changes were observed in the last few compartments or outflow, and COD removal efficiency did not change. A further increase of feed concentration to 15 g COD/ℓ resulted in increases in VFA and COD concentration in all compartments and the outflow, but only saw significant increases in H2 concentrations in the early compartments. Measured pH values actually increased as a result of increased alkalinity production at the higher OLR, indicating that the reactor was not at risk of going sour. These results clearly showed that the compartmentalised design of the ABR resulted in the overall process anaerobic digestion of the feed COD being staged to allow development of an acidic zone (and higher dissolved H2 concentrations) in the early compartments and a neutral zone in later compartments. As a result, methanogenesis in later compartments was protected from high dissolved H2 and low pH incidents due to increased organic load, thereby enhancing the stability of the reactor (Nachaiyasit and Stuckey, 1997b). 42
Experiments to investigate the effects of hydraulic shock loads (increased flow at constant feed strength) were undertaken on the same system (Nachaiyasit and Stuckey, 1997c) and it was found that the COD removal rate decreased from 97 % at a hydraulic retention time of 20 h to 90 % and 52 % when the hydraulic retention time decreased to 10 h and 5 h respectively. However, the COD removal efficiency returned to its baseline level of 97 % after only 9 h after the baseline hydraulic retention time of 20 h was restored. Substantial biomass loss was observed during hydraulic shock loads, and tracer tests indicated that the dead space in the reactor increased substantially (from 18 % to 39 %) during shock hydraulic loads. The authors inferred that significant channelling of fluid flow occurs through the sludge beds during shock hydraulic loads and concluded that this effect helps to reduce the amount of biomass washed out of the reactor and therefore reduce the recovery time after the shock load. Channelling was also understood to result in reduced exposure of the biomass to substrate during these high load incidents, resulting in high outflow COD values, but reduced impact of organic overload on the sludge (Nachaiyasit and Stuckey, 1997c). Garuti et al. (2004) performed experiments on a 24.2 m 3 2-compartment hybrid ABR supported by laboratory-scale biomass transport experiments on a 9.4 ℓ UASB reactor. Both systems were fed with domestic wastewater at the Biancolina wastewater treatment facility near Bologna, Italy. Measurements of TSS concentrations at two heights on each of the ABR compartments and in the outflow of the UASB were obtained, and sludge bed height in the UASB was measured visually. A mathematical model of sludge bed expansion was developed by considering the sludge column to be divided into 6 height zones and modelling the TSS dynamics in each zone. Predictions of sludge bed height with upflow velocity dynamics were obtained, and it was concluded that short bursts of flow at high flow rates resulted in better overall sludge retention than longer periods of flow at a lower flow rate, (but overall equal average hydraulic load), since the maximum sludge bed expansion achieved during short bursts of flow was less than during sustained low flow periods. 2.5.1.6 Low-strength applications Several authors have treated low-strength wastewaters effectively in the ABR (Barber and Stuckey, 1999). Treatment of low-strength wastewaters necessarily occurs at low OLRs, except when very high hydraulic loading rates are applied. Thus, dilute wastewaters inherently provide a low mass transfer driving force between the biomass and substrate, reducing biomass activities according to Monod kinetics. As a result, treatment of low-strength wastewaters has been found to encourage the dominance of scavenging micro-organisms, such as Methanosaeta species (Polprasert et al., 1992). Speece (1996) cautions that for dilute wastewater, greater attention is required for biomass immobilisation since lower growth rates will be achieved at the same hydraulic loading than for more concentrated systems and thus the sludge washout rate would be equivalently higher. However, other authors (e.g. Barber and Stuckey, 1999) indicate that biomass retention may be good for low-strength treatment due to the low gas production rates and reduced agitation of the sludge bed, suggesting that low hydraulic retention times are feasible during low-strength treatment. Witthauer and Stuckey (1982) (cited in Barber and Stuckey, 1999) observed that biogas mixing was greatly reduced and this resulted in minimal biomass/substrate mass transfer. The authors suggested that when treating dilute wastewaters, baffled reactors should be started-up with relatively high biomass concentrations in order to obtain a sufficiently high sludge blanket and good gas mixing Langenhoff et al. (2000) studied the performance of the ABR on a dilute synthetic wastewater consisting of soluble and colloidal components (500 mgCOD/ℓ, milk, colloidal rice and dog food) at 35 ºC. High COD removal rates (>80%) were obtained at hydraulic retention times of between 80 h 43
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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
Page 15 and 16: xi LIST OF TABLES Table 1.1: List o
Page 17 and 18: xiii LIST OF FIGURES Figure 1.1: Gr
Page 19 and 20: Figure 5.1 Installation of the ABR
Page 21 and 22: Figure 6.8: WEST® representation o
Page 23 and 24: xix LIST OF ABBREVIATIONS A-HRT App
Page 25 and 26: 1 1 INTRODUCTION The work presented
Page 27 and 28: obtained from anaerobic systems rel
Page 29 and 30: • Lalbahadur (MTech, 2005) perfor
Page 31 and 32: 1.7 ORGANISATION OF THE THESIS This
Page 33 and 34: 9 2 LITERATURE REVIEW A detailed re
Page 35 and 36: • Disintegration of composite par
Page 37 and 38: Homoacetogens are one of the most v
Page 39 and 40: Most of the control in anaerobic di
Page 41 and 42: therefore the sensitivity of the ov
Page 43 and 44: ∆Gº (W) [kcal] -10 -8 -6 -4 -2 L
Page 45 and 46: For systems with low potential for
Page 47 and 48: design of the digester in which the
Page 49 and 50: 2.2.2 Expanded granular sludge bed
Page 51 and 52: fact that for most non-ideal flow s
Page 53 and 54: hydrolysis steps to convert them to
Page 55 and 56: from the clarified zone between the
Page 57 and 58: Table 2.4: Typical pathogen surviva
Page 59: Table 2.5: Studies using anaerobic
Page 62 and 63: • There is no requirement for bio
Page 64 and 65: Kennedy and Barriault (2005) perfor
Page 68 and 69: and 6 h with no significant differe
Page 70 and 71: 2.5.1.12 Granule formation in ABRs
Page 72 and 73: • A baffled reactor is described
Page 74 and 75: 2.5.3.4 Scanning electron microscop
Page 76 and 77: spacing on flow patterns in a singl
Page 78 and 79: Figure 3.5: Orthographic projection
Page 80 and 81: PLC calculated the fraction of that
Page 82 and 83: epresent buulk conditionns. Compart
Page 85 and 86: The rreactor was initially commmiss
Page 87 and 88: Phase I Phase II Phase III Phase IV
Page 89 and 90: Table 4.1: Characteristics of degri
Page 91 and 92: Table 4.2: Pilot-scale ABR approxim
Page 93 and 94: COD [mgCOD/ℓ] 2000 1800 1600 1400
Page 95 and 96: 4.3.5 Phosphorus Figure 4.8 present
Page 97 and 98: Observation of sludge in compartmen
Page 99 and 100: Another interesting observation is
Page 101 and 102: 4.4.3 pH pH measurements were perfo
Page 103 and 104: esult in low pH values. The reasons
Page 105 and 106: 4.5 SUMMARY: PHASE I - OPERATION AT
Page 107 and 108: than the optimal range for methanog
Page 109 and 110: 5 EXPERIMENTAL PHASES II-IV: KINGSB
Page 111 and 112: sludge on a number of occasions. Wh
Page 113 and 114: On days 99 and 100 of Phase III, a
Page 115 and 116: 5.3.2 Analysis of variations in fee
Page 117 and 118:
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
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• Information about the volume of
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As with the total volume of sludge
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It is not clear why the rate of acc
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most compartments was exactly 6.5,
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Soluble COD [mg/ℓ] 600 500 400 30
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pathogens and parasites, which may
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% Probe of DAPI % Probe of DAPI % P
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later compartments at all. Furtherm
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and 4, with decreasing observations
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• The mechanism of sludge build-u
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Table 5.6: Inflow and outflow chara
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Behling et al. (1997) studied the p
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organisms in previous compartments.
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velocities. Unfortunately, these tw
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Thus for a fixed sludge load, at hi
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sampling was not possible since in
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Wentzel (2006) recommends a COD to
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6.2.1.4 Calculation of CH4 producti
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organically bound N) or that N accu
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All VFA is consumed in the process,
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However, these assumptions are clea
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The calculated pH value is compared
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influent alkalinity will increase d
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The original objective to develop a
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• It was not possible to simulate
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employed for a medium strength wast
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6.6.4 Alternative baffle design Thi
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6.7.3 Monitoring requirements The m
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compartments (Section 6.1.1) pH val
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generally about anaerobic digestion
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7.1.1.6 Effect of sludge age on bio
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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
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METTHODS OFF SAMPLINNG AND ANNALYSI
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3.6 Enumeration of total coliforms
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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
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Table A3. 1 cont. Phase I Phase II
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each of the eight compartments were
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3.2 Pathogen indicator organisms A
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APPLIED VS. APPARENT HYDRAULIC RETE
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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
Page 238 and 239:
Substituting Eq. A6- 1 in Eq. A6- 7
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1.5 Implementation of steady-state
Page 242 and 243:
X = 7⋅ Y = 7 Z = 7⋅ A = 7⋅ (
Page 244 and 245:
Dama, P., Bell J., Naidoo, V., Foxo
Page 246:
Lalbahadur T. (2004) Characterisati
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