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4.2.2 Hydraulic and organic loading rates during Phase I The hydraulic retention time (HRT) of a system provides an indication of the amount of time that fluid flowing through a treatment system resides in the system. Hydraulic loading rates (HLR) report how much volume of flow is applied to a treatment system per unit volume of the treatment system, while organic loading rate (OLR) calculates how much organic material is applied to the system per unit volume of the system. 4.2.2.1 Interpreting HRT during Phase I operation It is impossible to calculate the hydraulic and OLRs accurately for Phase I operation due to lack of adequate flow data. Considering Figure 4.4, it appears that the project manager at the time calculated the HRT by first determining flow rates (blue data in Figure 4.4) for each measuring interval from cumulative volume of outflow data (red data in Figure 4.4) and then applying Eq. 4-1 to determine HRT: [] l Reactor Volume HRT = ⎛ ⎜ ∑calculated flow rates ⎝ number of measurements [ l ⎞ ] ⎟ h ⎠ 66 Eq. 4-1 Eq. 4-1 returns an HRT value of 30.8 h from the sample data presented in Figure 4.4, which is close to the target value of 32 h. However, the average applied HRT for this data is more accurately calculated from the cumulative volume of outflow data according to Eq. 4-2 and gives a HRT value of 29.6 h. HRT = Reactor Volume [] l Eq. 4-2 In addition it was observed that the average flow rate could change significantly with time depending on whether there were any objects (e.g. string) interfering with the pump inlet or not. The error in the calculation of HRT under-predicted the average loading on the ABR. Variation due to pump performance most probably resulted in lower flow rates than intended. The magnitude of the effects is not known, therefore it is not possible to say whether the hydraulic loading was greater or less than that reported. Thus for timer control of the ABR at Umbilo WWTP (day 0 to day 228, 2000- 2001) reported HRT values (and thus organic loading and solids retention) should only be regarded as a rough estimate of the true value. Similarly when the PLC was used to control the outlet flow rate to not exceed a fixed value (day 228 onwards) actual values are not known, but target or minimum possible HRT values, maximum possible OLR and minimum SRT values may be estimated. 4.2.2.2 Calculation of loading rates Table 4.2 presents the approximate OLR for each of the reported HRT values during operation at Umbilo WWTP under timer control and PLC control of outlet flow rate. Loading rates during start-up were low with a maximum loading of around 0.9 kg COD/m 3 .d. These numbers are well below the recommended start-up loading rates for anaerobic digesters (Section 2.5.1.1) [] l [] ⎟⎟ ⎛ Cumulative volume of effluent ⎞ ⎜ ⎝ time over which measurements were made h ⎠
Table 4.2: Pilot-scale ABR approximate organic loading rate [OLR] [kg COD/m 3 .d] under timer control and maximum possible OLR under PLC control in winter and summer during operation at Umbilo WWTP. Timer Control PLC control T-HRT [h] 60 32 20 20 OLR Winter[kg COD/m 3 .d] 0.30 - 0.91 - OLR Summer [kg COD/m 3 .d] 0.26 0.49 0.78 0.78 4.3 ABR OUTFLOW STREAM CHARACTERISTICS: PHASE I This section presents data relating to the characteristics of the flow exiting the pilot-scale ABR during operation at Umbilo WWTP during Phase I of experimentation. Outflow solids, COD, free and saline ammonia and phosphorus data are presented since these are the indicator determinands used to assess the quality of a wastewater or effluent. 4.3.1 Influence of feeding interruptions on reported results Samples of outflow were obtained from the outlet pipe as it discharged treated wastewater back into the WWTP. Samples and analyses were performed by staff at Umbilo WWTP. The data presented here are subject to substantial uncertainty since the project manager at the time reported that the pump was liable to trip and /or get blocked and that this would be remedied by the plant staff immediately before samples were taken. Thus the samples taken may not have been representative of normal conditions. Further, it was reported that for a few minutes after feeding was started, slugs of washed-out sludge were sometimes observed in the flow leaving the ABR. Thus it is expected that the frequently high solids concentrations measured in the outflow (occasionally above 50 g TS/ℓ) were a manifestation of transitory high sludge washout immediately after resumption of feeding. It is not possible to absolutely identify whether this was the case or not, however, the ABR outflow data for all determinands affected by solids content presented (e.g. total COD, total and volatile solids) may not be representative of the average outflow characteristics during Phase I. The data are presented nevertheless as certain trends observed therein have assisted in developing a theory of what occurs during start-up of an ABR treating domestic wastewater. 4.3.2 Total Solids Figure 4.5 shows measurements of total solids in the inflow and outflow of the pilot-scale ABR. For the 60 h and 32 h T-HRT, the outflow concentration of solids rarely exceeded 2 g TS/ℓ. In the 20 h T-HRT period, the outflow solids concentration showed dramatic increases, usually exceeding the corresponding inflow concentration. This was probably due to the fact that the reactor was often restarted just before sampling. However, this was also true for the lower flow operation and similar high values were not observed. The reason for this difference will become clear when compartment internal dynamics are presented, and may be attributed variously to the fact that the solids load in later compartments was substantially higher in the 20 h T-HRT time period due to the higher OLR and the fact that solids washout was facilitated by the higher flow rates employed in the 20 h T-HRT. 67
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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
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 66 and 67: methanogenic (Akunna and Clark, 200
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: Table 4.1: Characteristics of degri
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
Page 119 and 120: 5.4.1.2 Phase III In Phase III, (Fi
Page 121 and 122: Phase II: Alkalinity [mgCaCO3/ℓ]
Page 123 and 124: Eq. 5-1 However, at a COD/SO4 2- ra
Page 125 and 126: wastewater was probably higher than
Page 127 and 128: 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
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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
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172
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Batstone D. J., Keller J., Angelida
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Gopala K. G. V. T. (2007). Treatmen
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MacLeod F. A., Guiot S. R. and Cost
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Sasse L. (1998). Decentralised wast
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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
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And the significance of the regress
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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
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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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