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6.7.3 Monitoring requirements The monitoring requirements for any wastewater treatment system depend on the purpose for which the information is required. These may be divided into two categories: (i) compliance; and (ii) diagnosis. 6.7.3.1 Compliance monitoring Generally monitoring requirements for compliance purposes are specified in a licence or authorisation for the operation of a treatment system. These may include COD, suspended solids, nitrogen, phosphorus, pH, metals and pathogen indicator species. In South Africa, the major environmental contaminants of concern are nitrogen, phosphorus and pathogens, although other components are considered important in specific applications. 6.7.3.2 Diagnosis There are three main objectives in diagnostic monitoring; i.e. to determine (i) what the condition of digestion in the system is; (ii) what alkalinity supplementation could be recommended; and (iii) what the desludging requirements of the system are. Condition of digestion • The condition of digestion depends on the prevailing pH and alkalinity values and the presence of active anaerobic micro-organisms. Simple measurements of pH and alkalinity in feed and effluent will indicate whether the reactor pH is sufficiently high that methanogenesis is not inhibited by low pH. • Thereafter it is recommended that analyses of TKN, free and saline ammonia and COD are performed on the inflow and streams. COD provides the easiest measurement for identifying the fate of organic material in an anaerobic system; but the fate of COD is not easy to determine; it may leave the system in the outflow stream, as CH4 gas, or as accumulated sludge. Measurements of COD associated with accumulated sludge are difficult to obtain and imprecise, while measurements of CH4 production require that a gas seal is maintained on the ABR, and equipment for monitoring gas production and composition are available. Thus it is difficult to obtain an understanding of the relationship between accumulation and bioconversion of organic solids by looking at COD concentrations. Organically-bound nitrogen is associated with slowly biodegradable or particulate COD, and thus significant reductions in TKN between inflow and outflow stream indicate that significant quantities of particulate material are accumulating. However, if inflow and outflow TKN values are similar, and free and saline ammonia concentrations are significantly higher in the outflow than in the inflow, it may be inferred that particulate COD is being solubilised. Therefore, it is proposed that by monitoring the fate of both COD and nitrogen species in inflow and outflow streams, it is possible to understand what the predominant mechanism of COD removal is. Alkalinity supplementation • If it is desired that the ABR should achieve reasonable solids stabilisation rates and is operated at upflow velocities higher than 0.3 m/h, it is recommended that alkalinity supplementation be 162
employed to increase if the inflow stream alkalinity concentration to a value of 1 000 mgCaCO3/ℓ, if the concentration is substantially less than this value. Speece (1996) describes the relative merits of different types of alkalinity supplementation. Desludging requirements • In order to monitor the amount of sludge accumulated in an ABR, it is recommended that core samples of upflow section of each compartment be obtained and the fluidised and settled sludge bed heights be obtained. The fluidised bed heights provide an indication of how full the reactor is, i.e. how soon it will have to be desludged, while the settled sludge bed heights indicate how much sludge will have to be removed. 6.8 ADVANTAGES AND DISADVANTAGES OF ABR TECHNOLOGY The final objective of this study was to determine whether there was any advantage in the baffled design of the ABR over other anaerobic technologies used in the treatment of domestic wastewater (Section 1.4). This section presents a summary of the advantages and disadvantages identified and anticipated in the use of this technology. This study did not undertake a direct experimental comparison between different reactor designs; therefore the tabulated advantages and disadvantages are implied, rather than proven. 6.8.1 Advantages Besides all the well-documented advantages of anaerobic technology over aerobic technology (lower energy input, lower operation costs, lower sludge production, CH4 generation), the following specific advantages of the baffled design were identified: • Good solids retention can be achieved due to the baffled design. Specifically, the first compartment retained a significant portion of the inflow solids, initially through settling, and subsequently through the development of a thick sludge bed that acted as a filter for incoming solids. This is a significant benefit in suspended solids management; Aiyuk (2006) recommended that suspended solids be removed from domestic wastewater before treatment in a UASB to preserve integrity of sludge granules. However, the first compartment of the ABR filters out solids, creating an up-front sludge digester, thereby reducing the need for presettling and separate treatment of settleable solids. • The baffled design resulted in good contact between biomass and wastewater by forcing flow through sludge beds and sludge blankets (6.1.2.2 and 6.6.2.2). This advantage is amplified by the fact that flow is forced through a number of beds; multiple passes through beds decreases probability of that channelling and by-passing effects will result in slugs of fluid passing out of the reactor untreated. This is a significant benefit over the performance of most septic tanks, since most septic tank designs allow the bulk of the wastewater to pass from the inflow to the outflow without passing through a sludge bed (USEPA, 2002). • Partial phase separation may have resulted in the development of zones in the reactor that were separated from and therefore protected from transient low pH values exerted due to acidogenesis in the first compartment. Therefore, although low pH conditions prevailed in compartment 1 and at times, compartment 2, pH values were usually slightly higher in later 163
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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
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• Information about the volume of
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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 182 and 183: employed for a medium strength wast
Page 184 and 185: 6.6.4 Alternative baffle design Thi
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
Page 233: 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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