Sustainable Sewerage
Guidelines for community schemes
This handbook describes how conventional sewerage schemes can be modified to reduce the cost of construction and maintenance and suggests methods of prioritizing sewerage needs. Also surveys planning, selection, design, management and maintenance of community schemes as well as providing financial and technical guidance on cost-effective practice and procedures.
Published: 1995
Pages: 112
eBook: 9781780446080
Paperback: 9781853393051
| TABLES viii | |||
|---|---|---|---|
| FIGURES ix | |||
| PHOTOGRAPHS ix | |||
| ACKNOWLEDGEMENTS xi | |||
| INTRODUCTION xiii | |||
| 1 Background 1 | |||
| 1.1 Reasons for failure of on-site sanitation 3 | |||
| Insufficient plot area 3 | |||
| Ground infiltration failure 4 | |||
| Groundwater pollution 4 | |||
| Surface water pollution 6 | |||
| 1.2 Investing in sustainable sewerage 7 | |||
| 2 Prioritizing communities' need for sewerage 9 | |||
| 2.1 Need and viability assessment 9 | |||
| Projected total population 10 | |||
| Population density 10 | |||
| Failure of on-site sanitation systems 10 | |||
| Industrial pollution 11 | |||
| Cost 11 | |||
| Tourist impact 11 | |||
| Environmental impact 12 | |||
| Affordability 12 | |||
| Economy of scale 12 | |||
| Institutional capacity 13 | |||
| Health benefits 13 | |||
| 2.2 Numerical analysis of need and viability criteria 13 | |||
| Scoring for individual criteria 15 | |||
| Weighting 15 | |||
| Scoring and sensitivity analysis 17 | |||
| 3 Designing conventional sewer networks 19 | |||
| 3.1 Types of sewerage systems 20 | |||
| Separate systems 20 | |||
| Combined systems 20 | |||
| 3.2 The movement of solids in pipes 21 | |||
| Flow regimes 21 | |||
| Solids transport in the upper reaches 22 | |||
| Solids transport lower down the system 22 | |||
| 3.3 Pipe size 22 | |||
| Branch drains 22 | |||
| House sewers and the upper reaches of public networks 22 | |||
| Public sewers in the lower reaches of the network 23 | |||
| 3.4 Pipe gradient 23 | |||
| 3.5 Change point for sewer design 24 | |||
| Property drainage 24 | |||
| Communal sewer design 25 | |||
| Determining when a pipe is 'running full' 26 | |||
| 3.6 Sewer layout 26 | |||
| 3.7 Design procedure 26 | |||
| Minimizing capital costs 29 | |||
| 4.1 Sewerage components 29 | |||
| Sanitary fixtures 29 | |||
| Pipe materials 30 | |||
| Grease traps 30 | |||
| Interceptor tanks 33 | |||
| Small interceptor tanks 33 | |||
| Large interceptor tanks 33 | |||
| Access points 34 | |||
| 4.2 Sewerage design for low-cost systems 37 | |||
| By-laws and codes of practice 37 | |||
| Wastewater flow 37 | |||
| Pipe diameters 38 | |||
| Sewer slope 38 | |||
| Minimum pipe depth 42 | |||
| Number of connections before a sewer pipe runs full 42 | |||
| Sewer layout 46 | |||
| Pumping stations and trunk mains 48 | |||
| Sewage treatment 48 | |||
| 4.3 Construction project initiation 50 | |||
| Government agencies 50 | |||
| External organizations 50 | |||
| Recipient communities 51 | |||
| 4.4 Construction management 52 | |||
| Contracts and contractors 52 | |||
| Construction supervision 53 | |||
| Community mobilization 53 | |||
| 5 Maximizing uptake of sewerage facilities 54 | |||
| 5.1 Reducing connection costs 54 | |||
| Physical measures 54 | |||
| Providing subsidies 54 | |||
| 5.2 Increasing demand for sewerage 55 | |||
| Meetings 55 | |||
| Models 57 | |||
| General publicity 57 | |||
| Emphasizing positive impacts 57 | |||
| Confronting negative issues 58 | |||
| Offering user choice 58 | |||
| Linkage with other projects 59 | |||
| Choosing a name for a community project 59 | |||
| Campaign implementation 59 | |||
| 5.3 Legal issues 59 | |||
| Enforcement of connections 59 | |||
| Clarifying responsibility for connections 60 | |||
| Connections to rented accommodation 60 | |||
| 6 Achieving sustainable maintenance 61 | |||
| 6.1 Responsibility for operation and maintenance 61 | |||
| Property owners 61 | |||
| Institutions 61 | |||
| Community groups 62 | |||
| The private sector 62 | |||
| 6.2 Supervision of operation and maintenance 62 | |||
| 6.3 Minimizing maintenance: social issues 65 | |||
| Refuse collection and disposal 66 | |||
| Anal cleaning practices 66 | |||
| Utensil washing practices 66 | |||
| User abuse 66 | |||
| 6.4 Minimizing maintenance: system design 67 | |||
| Surface water drainage 67 | |||
| Topography 67 | |||
| Water supply 67 | |||
| Access points 67 | |||
| Trunk sewers and pumping stations 68 | |||
| Sewage treatment 68 | |||
| Interceptor tanks 68 | |||
| 6.5 Construction quality 69 | |||
| Supervision 69 | |||
| Construction components 69 | |||
| On-plot construction 69 | |||
| 7 Optimizing the return on investment in sewerage 71 | |||
| 7.1 Tariffs 71 | |||
| 7.2 Direct repayment of capital costs 72 | |||
| 7.3 Minimizing tariffs and maximizing returns 73 | |||
| 8 Non-conventional sewerage systems 75 | |||
| 8.1 Simplified sewerage 75 | |||
| 8.2 Condominial sewerage 76 | |||
| 8.3 Interceptor tank systems 78 | |||
| Appendix 1 Glossary of terms 85 | |||
| Appendix 2 The design of interceptor tanks 88 | |||
| REFERENCES 93 | |||
| FURTHER READING 94 | |||
| INDEX 96 |
R.A. Reed
Bob Reed is a Programme and Project Manager at the Water, Engineering and Development Centre, UK.
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