Solids in Sewers

Richard M. Ashley; Jean-Luc Bertrand-Krajewski; T. Hvitved-Jacobsen; M. Verbanck

BOOK

Solids in Sewers

Richard M. Ashley | Jean-Luc Bertrand-Krajewski | T. Hvitved-Jacobsen | M. Verbanck

(2004)

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Book Details

ISBN: 978-1-78040-272-7
Edition: 1
Language: English
Pages: 362
Subjects: The environment
Environmental science, engineering & technology
Water supply & treatment

Abstract

This Report presents information on the current state of knowledge of the origins, occurrence, nature and effects of sewer solids for use by engineers, scientists, administrators and water quality planners for the planning, design and operation of sewerage systems. The report addresses both sewer maintenance requirements and environmental protection issues. Increasing environmental standards, coupled with public expectations, have led to stringent water quality standards. In response to this, it has been necessary to develop new methodologies and computer based analytical techniques to model and understand the performance of all aspects of waste water systems. Fundamental to these techniques is the understanding of the way in which sewer solids contribute to the poor performance of wastewater systems and consequential environmental damage. The information presented in this Report about the origins, nature, movement, hydraulic and polluting effects of solids in sewers has enabled strategies and rules to be developed for the management of sewerage systems to minimise the deleterious effects of these solids and associated pollutants. Scientific & Technical Report No. 14

Section Title	Page	Action	Price
Contents	6
Foreword	8
Executive summary	14
1.0 Introduction	18
References	23
2.0 Sewer solids - characteristics and processes	24
2.1\tORIGINS	24
2.1.1 Introduction	24
2.1.2 The atmosphere	24
2.1.3 Catchment surfaces	25
2.1.3.1 Roofs	26
2.1.3.2 Streets	27
2.1.3.2.1 Introduction	27
2.1.3.2.2 Solids location	28
2.1.3.2.3 Accumulation	29
2.1.3.2.4 Washoff by rainfall	33
2.1.3.2.5 Size distribution	36
2.1.3.2.6 Organic fraction	37
2.1.3.2.7 Concentrations and loads	37
2.1.3.2.8 Potential pollutants associated with the solids	38
2.1.3.3 Solids from gullies	40
2.1.3.3.1 Deposits	42
2.1.3.3.2 Outflow	43
2.1.3.3.3 Modelling of solids transfer through gully pots	45
2.1.3.4 Solids resulting from de-icing	49
2.1.4\tSolids from domestic wastewater	51
2.1.4.1 Sanitary solids	52
2.1.4.2 Gross solids and sanitary refuse	53
2.1.4.3 Kitchen waste inputs	58
2.1.5 Solids from infiltration and sewer decay or degradation and wrong connections	59
2.1.6 Sediment ingress from natural water bodies	60
2.1.7 Commercial, industrial and construction activities	61
2.1.8 Developing countries	63
2.1.9\tReferences	66
2.2 CHARACTERISTICS AND TRANSFORMATION PROCESSES	72
2.2.1\tProcesses in sewers – a general overview	72
2.2.1.1\tCharacteristics of sewer solids in suspension	74
2.2.1.1.1 Characterisation of suspended solids	74
2.2.1.1.2 Organic fractions in wastewater suspended solids	74
2.2.1.2\tCharacteristics of suspended solids in urban wet weather discharges	76
2.2.1.2.1 Introduction	76
2.2.1.2.2 Pollutants attached to suspended solids in urban wet weather discharges	76
2.2.1.2.3 Grain size, density and settling characteristics for suspended solids in urban wet weather discharges	77
2.2.2\tProcesses related to suspended solids and colloids	82
2.2.2.1\tSuspended solids and particle definitions – what is a solid?	82
2.2.2.2\tProcesses in the suspended water phase	82
2.2.2.3 Transformation of wastewater organic matter under aerobic conditions	83
2.2.2.4 Anaerobic processes	83
2.2.2.5 Process characteristics	84
2.2.2.6 Transformation of organic matter in resuspended sewer sediment	86
2.2.3 Characteristics of bed deposits	86
2.2.3.1 Introduction	86
2.2.3.2 Cohesive-like properties	87
2.2.3.3 Physical characteristics of sewer sediments	88
2.2.3.4 Chemical and biochemical properties	95
2.2.4 Processes related to bed deposits	99
2.2.4.1 Transformation processes	99
2.2.4.1.1 Introduction	99
2.2.4.1.2 Temporal fluctuations of deposit properties	100
2.2.4.1.3 ‘Ageing’ of deposits	101
2.2.4.1.4 Vertical variability of bed deposit characteristics	102
2.2.4.1.5 Sulphate reduction	102
2.2.4.1.6 Potential polluting properties	102
2.2.4.2 Settleable solids, heavy metals and organic micro pollutants	103
2.2.5 Biofilms	104
2.2.5.1 Characteristics	104
2.2.5.2 Processes related to biofilms	105
2.2.5.3 Biomass production in biofilms	105
2.2.5.3.1 Oxygen consumption	106
2.2.5.3.2 Nitrification	107
2.2.5.3.3 Denitrification	107
2.2.5.3.4 Sulphate reduction	107
2.2.5.4 Detachment	107
2.2.5.5 Adsorption of particles	108
2.2.6. Sediment analysis	108
2.2.6.1 Physical characterisation – sieving and settling	108
2.2.6.2 Chemical characterisation	110
2.2.6.3 Microbiological characterisation	113
2.2.7 Modelling of solids and pollutant transformation in sewers	114
2.2.7.1 A model concept for microbial wastewater transformations	115
2.2.8 Concluding remarks	118
2.2.9\tReferences	118
2.3 TRANSPORT, DEPOSITION AND EROSION	123
2.3.1 Introduction	123
2.3.2\tSewer flow hydraulics	123
2.3.2.1\tMean velocity, shear stress and turbulence distribution over the flow cross section	123
2.3.2.2\tComposite roughness and sidewall elimination procedures	125
2.3.2.3\tFlow resistance with sediment deposits	126
2.3.3\tTank, basin and CSO hydraulics	128
2.3.4 Solids movement in sewers	129
2.3.4.1\tSuspended solids movement in sewers	131
2.3.4.1.1 Suspended sediment concentration profiles	132
2.3.4.1.1\tSuspended sediment transport capacity in sewers	134
2.3.4.2\tNear bed solids	137
2.3.4.2.1\tNear bed (organic) solids	140
2.3.4.2.2 Dense undercurrent	142
2.3.4.3\tGross solids	144
2.3.4.4 Granular bed load	146
2.3.4.4.1 Transport rate/capacity relationships	146
2.3.4.4.2 Estimation of threshold of motion	150
2.3.5\tDeposits in combined sewer networks	151
2.3.5.1\tSediment deposition	152
2.3.5.2 Prediction of sedimentation in larger sewers	157
2.3.5.3 Bed deposit erosion	159
2.3.5.3.1 Prediction of bed erosion	163
2.3.6\tBiofilms	166
2.3.7\tSolids transport modelling in sewers	166
2.3.7.1\tAims of models	167
2.3.7.2\tComponents of models	167
2.3.7.3 Key factors affecting model performance	168
2.3.7.4\tGeneral assessment of contemporary models	169
2.3.8\tSolids movement in tanks, basins and CSO chambers	170
2.3.8.1 Solids occurrence – deposition problems	170
2.3.8.2 Solids movement – settling efficiency of tanks	171
2.3.9 References	174
3.0 The effects of sewer solids on the performance of wastewater systems	181
3.1\tOUTLINE OF THE EFFECTS OF SEWER SOLIDS	181
3.2 EFFECTS OF SOLIDS ON CONVEYANCE AND BLOCKAGE OF SEWERS	182
3.2.1 Hydraulic resistance changes caused by sewer solids	183
3.2.2\tSmall sewers	184
3.2.2.1\tBlockage formation	185
3.2.2.2\tBlockage frequency	185
3.2.3\tLarge sewers	186
3.2.3.1\tBlockage formation	186
3.2.3.2\tExtent of problems	186
3.3\tSULPHIDE FORMATION AND EFFECTS	188
3.3.1 Hydrogen sulphide formation	188
3.3.1.1\tPresence of sulphate	188
3.3.1.2\tQuantity and quality of biodegradable organic matter	189
3.3.1.3\tTemperature	189
3.3.1.4\tpH	189
3.3.1.5 Prediction of sulphide formation	189
3.3.1.6 Release of hydrogen sulphide gas from wastewater to the atmosphere	191
3.3.2 Corrosion	192
3.3.3 Particular problems in pumping mains and gravity sewers	193
3.4 CONTRIBUTIONS OF SOLIDS TO FLOW QUALITY AND CONCEPT OF FOUL FLUSH	194
3.4.1 Introduction	194
3.4.2\tRelative contributions	194
3.4.3. Concepts of flush	197
3.4.3.1 Origins of the first flush concept	197
3.4.3.2 Definition of the first flush	200
3.4.3.3 Modelling of first flushes	203
3.4.3.4 Role of sewer sediments and near bed solids	205
3.5\tEFFECTS OF SEWER SOLIDS ON PERFORMANCE OF ANCILLARIES AND TREATMENT PLANTS	211
3.5.1\tTanks and CSOs	211
3.5.1.1\tSuspended solids	212
3.5.1.2\tGross solids	212
3.5.1.3 Operation of CSOs	213
3.5.2 Pumping stations	214
3.5.3\tTreatment plants	215
3.5.3.1\tScreening	216
3.5.3.2\tDegritting	216
3.5.3.3\tPrimary clarification	217
3.5.3.4\tPollutant removal	217
3.5.3.5\tSludge treatment and dewatering	218
3.5.3.6\tSludge disposal	218
3.6\tOTHER EFFECTS	218
3.6.1\tFats and greases	218
3.6.2\tOdours	219
3.6.3\tExplosions and hazards to sewer workers	219
3.6.4\tMiscellaneous	219
References	220
4.0 Solids management for sewerage systems	225
4.1 SOLIDS CONTROL AT SOURCES AND AT INPUTS TO SEWERAGE SYSTEMS	227
4.1.1 Introduction	227
4.1.2\tPublic education	228
4.1.3 Alternative sanitary sewage collection and disposal methods and solids implications	229
4.1.4 Public works (utility) practices	233
4.1.4.1 Street cleaning	233
4.1.4.1.1 Introduction	233
4.1.4.1.2 Street cleaning efficiency related to particle size	234
4.1.4.1.3 Litter control	235
4.1.5 Storm drainage system inlet structures	237
4.1.5.1 Catchbasins and gully pots	240
4.1.5.2 Storm drain inlets with filters	243
4.1.5.3 Optimisation of storm drain inlet structures	246
4.1.6 Oil and grease (light liquid) separators	248
4.1.7. Sediment control by detention ponds and wetlands	250
4.1.7.1\tMaintenance of detention ponds and safety of disposal of removed sediments	251
4.1.7.2\tEnhancing pond performance during severe winter conditions	252
4.1.7.3\tDetention pond design guidelines for suspended solids reductions	253
4.1.8 Infiltration systems to control solids	253
4.1.8.1\tBenefits and problems associated with stormwater infiltration	253
4.1.8.2\tGrass swales	254
4.1.8.3\tPorous pavements	256
4.1.8.3.1 Efficiency of porous pavements	256
4.1.8.3.2 Maintenance of porous pavements	256
4.1.8.4\tProtection of groundwater quality during stormwater infiltration	259
4.1.9 Filtration and combination practices	259
4.1.10 Construction site erosion control	260
4.1.11 References	261
4.2 SEWERAGE DESIGN, OPERATION AND MAINTENANCE TO CONTROL SEDIMENT PROBLEMS	269
4.2.1 Design of sewer systems to control sediment	269
4.2.1.1 Design criteria – self-cleansing sewers	269
4.2.1.2 Transport capacity design approaches	271
Criterion I – Capacity to transport a minimum suspended sediment load	272
Criterion II – Bed load	273
Criterion III – Cohesion within in-sewer deposits	274
4.2.1.3 Alternative practical approach based on energy slope and geometrical considerations	274
4.2.2 Operation and maintenance to control sediments in sewers	276
4.2.2.1\tIntroduction	276
4.2.2.2\tCleaning	279
4.2.2.2.1 Cleaning techniques for small sewers	279
4.2.2.2.2 Cleaning requirements for man-entry combined sewers	282
4.2.2.3\tSewer flushing	283
4.2.2.4 Decantation basins	290
4.2.2.5 Sediment traps	290
4.2.2.5.1 Introduction	290
4.2.2.5.2. Types of traps	291
4.2.2.5.3 Use of traps	293
4.2.2.5.4 Operation of traps	296
4.2.2.5.5 Trap design and filling rates	297
4.2.2.6 Hydrogen sulphide control	301
4.2.3 Sewer solids treatment and disposal	301
4.2.3.1 Introduction	301
4.2.3.2 Sources of solids	301
4.2.3.3 Characteristics of silt trap solids	302
4.2.3.4\tSolids treatment processes	302
4.2.3.5\tReuse of materials recovered from sewer solids treatment	306
4.2.3.5.1 Screening refuse	307
4.2.3.5.2 Process water	307
4.2.3.5.3 Cleaned sand – usage	307
4.2.4\tReferences	309
4.3 CONTROL OF SEDIMENTS IN COMBINED SEWER OVERFLOWS AND TANKS	314
4.3.1 The function of CSOs	314
4.3.2 Sediment controls in CSOs	315
4.3.3 Screening technologies for the capture and retention of CSO solids	317
4.3.3.1 Sacks	318
4.3.3.2 Bar and mesh screens	318
4.3.3.3 Self-powered screens	319
4.3.4 Storage tanks	320
4.3.4.1 Volume of tank	321
4.3.4.2 Sediments in tanks	321
4.3.4.3 Design of tanks to control sediments	322
4.3.4.4 Management of deposited sediments	324
4.3.4.4.1 Tipping buckets/flushers	325
4.3.4.4.2 Hydroself flushing system	326
4.3.4.4.3 Prevention of deposition – agitators, etc.	327
4.3.4.4.4 Case study	328
4.3.4.4.5 Impact on sewer system downstream of tank	328
4.3.5 Lamella settling with chemicals	329
4.3.6 References	331
References	339
Appendix: Sewage settling velocity	341
A.1\tINTRODUCTION	341
A.2 STANDARDISATION OF TERMINOLOGY AND UNITS OF MEASUREMENT	342
A.3\tPRESENTATION OF RESULTS	342
A.4 STATEMENT OF METHODOLOGY	343
A.5 APPARATUS FOR DETERMINING SEWAGE PARTICULATE SETTLING VELOCITY GRADING CURVES	344
A.6 REFERENCES	348

Solids in Sewers

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