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

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different. However, the length of the residence time in either system can affect apparent biodegradability in terms of how much degrades while in the system. 2.4.2 Septic tank and soak-away systems There is little formal scientific literature relating to septic tank design and performance, but a large body of information on these subjects exists in the trade literature. Septic tanks are the most commonly used unit for pre-treatment of domestic wastewater in on-site applications. The United States Environmental Protection Agency (USEPA) has published an Onsite Wastewater Treatment Systems Manual (USEPA, 2002) which presents a thorough review and discussion of the subject of septic tank and soak-away design and performance. Unless otherwise stated, all further information presented in this section is taken from the USEPA document. A septic tank system consists of two units. The first unit is the septic tank itself, which pre-treats wastewater by solids and scum retention and partial anaerobic digestion. The second part of treatment occurs in a subsurface wastewater infiltration system, a french drain or evapo-transpiration area where septic tank effluent is infiltrated into the ground via a series of gravel-filled trenches. From here water percolates through the ground, or is removed by evapo-transpiration. Micro-organisms associated with the soil and plant roots, as well as specific plants are able to effect significant nutrient removal from the wastewater. Effluent from these systems is rarely collected for reuse. inlet baffle sludge inspection ports scum clarified zone manhole Figure 2.6: Example of septic tank construction showing internal baffle, inlet baffle, outlet tee piece, inspection ports and manhole (after USEPA, 2002) Figure 2.6 shows an example of a septic tank design. The tank is a covered, watertight rectangular, oval or cylindrical vessel that is usually buried. Dimensions vary, but the tank should be longer than it is wide or high. Primary treatment in the tank is due to wastewater retention under quiescent conditions. Solids and scum from the influent wastewater are separated in the tank by settling or floating. A population of anaerobic micro-organisms develops in the tank which partially digest solids and scum, and to a lesser extent, suspended organic material in the liquid phase. Digestion of scum and solids can result in reduction of up to 40% of retained material, however a slow accumulation of sludge is observed in the tank over a period of between 2 and 20 years, depending on loading. Anaerobic digestion in the tank generates CH4 and CO2 gases that are commonly vented. Wastewater inlet structures in the tank are designed to reduce short-circuiting of incoming wastewater across the tank to the outlet. Outlet structures are designed to retain sludge and scum layers by drawing effluent 30 baffle outlet
from the clarified zone between the sludge and scum layers. The outlet is usually fitted with an effluent screen and/or a tee-piece to retain larger solids that would otherwise be carried out in the effluent to the soak-away, contributing to clogging and eventual system failure. Inspection ports and manholes are provided in the tank cover to allow access for the periodic removal of tank contents, including the accumulated scum and sludge. Compartmentalised tanks such as that shown in Figure 2.6, or tanks placed in series are reported to provide better suspended solids removal than single-compartment tanks alone, although results from different studies vary. Septic tanks are reported to remove 60 to 80% of non-soluble material in domestic wastewater. Solid and colloidal material is hydrolysed and acidified, producing volatile fatty acids that are only partially converted to CH4, and exit in the effluent stream. Biological oxygen demand (BOD) removal is typically in the order of 30 to 50% for a septic tank operating at a 48 h retention time. Actual performance of the septic tank will depend on the ambient temperature, operating hydraulic retention time and presence of inert or micro-organism-inhibiting chemicals in the influent. Table 2.3 presents septic tank effluent characteristics from a number of systems, before secondary treatment in a soakaway or other system. Soak-away systems provide a degree of wastewater treatment and dispersal through soil purification processes and ground water recharge. The performance is dependent on the treatment efficiency of the septic tank, the method of wastewater distribution and loading to the soil infiltrative surface, and the properties of the vadose and saturated zones underlying the infiltrative surface. Considerable data on the treatment efficiency of soak-away systems are available in the trade literature (USEPA, 2002). High removal rates of BOD, suspended solids, faecal coliforms and surfactants have been observed within a few metres of unsaturated, aerobic soil. Phosphorus and metals are removed through adsorption, ion-exchange and precipitation reactions, although the retention capacity of the soil has a limit that depends on specific soil properties including soil mineralogy, organic content, pH, redox potential, and cation exchange capacity. Pathogen survival rates have been found to vary with a number of factors including initial pathogen load, temperature, humidity and solar radiation. Table 2.4 shows typical pathogen survival times in fresh water, sewage and unsaturated soil at 20 ºC to 30 ºC (Feachem et al., 1983). Bacterial and protozoan pathogens have relatively short survival times (less than a month), but viruses and helminth eggs (e.g. Ascaris spp.) can survive for considerably longer periods. 31
Page 1:
ANALYSIS OF A PILOT-SCALE ANAEROBIC
Page 5: i DECLARATIONS I, Katherine Maria F
Page 8 and 9: My deepest thanks must be extended
Page 11 and 12: vii TABLE OF CONTENTS ANALYSIS OF A
Page 13 and 14: 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: hydrolysis steps to convert them to
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 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
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
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 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
Page 233:
X X = P Inert ⋅ where Xinert is t
Page 236 and 237:
iodegradable organic material may b
Page 238 and 239:
Substituting Eq. A6- 1 in Eq. A6- 7
Page 240 and 241:
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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