BOKU ‐ University of Natural Resources and Life Sciences, ViennaInstitute of Sanitary Engineering and Water Pollution Control

SPN7‐Sheffield, 28.08.‐30.08.2013

Innovative Sewer Inspectionas a Basis for an Optimised

Condition‐Based Maintenance Strategy

H. Plihal, F. Kretschmer, D. Schwarz and Th. Ertl

Overview

1. Introduction

2. Influence of deposits on sewer systems

3. Maintenance strategies

4. Sewer inspection by means of a manhole‐zoom camera (“electronic sewer mirror”)

5. Example of a selective cleaning strategy: City of Salzburg, Austria

6. Summary

Introduction

• approximately 100,000 km of public sewers in Austria

• sewer cleaning = main task of wastewater utilities

• sewer cleaning as financial burden for many cities andmunicipalities due to precarious financial situation

• Austrian technical guideline OEWAV RB 22 recommendsa forward‐looking sewer management strategyin order to: reduce costs and minimise enviromental impacts

Influence of deposits on sewer systems

1. Decrease of hydraulic capacity decrease of aviable cross sectional area of discharge increase of sewer pipe roughness change of surface curves in CSO‘s

2. Operational difficulties increase of sewer cleaning effort health risks for operational staff due to gas production under anaerobic 

conditions biochemical attack due to sulfuric acid

3. Enviromental impacts odour nuisance caused by the formation of hydrogen sulfide (H2S) increase of stormwater overflow discharge

Quantities of disposed waste in 2009(based on a survey preceding the OEWAV‐KAN convention)

pipe sections with blockages

pipe sections with hardly any deposits

Participant code BOKU Vienna – INNOKANIS Project

1. reactive strategy (“emergency strategy“)̶ sewer is not cleaned on a regular basis, only as required̶ “troubleshooting“ interventions

2. proactive strategy̶ inspection and maintenance based on predefined intervals̶ e.g. annual sewer cleaning cycle

3. selective strategy̶ cleaning occurs on a demand‐oriented basis̶ requires accurate knowledge of the sewer system

e.g. manhole‐zoom camera

Maintenance strategies

Sewer inspection by means of a manhole‐zoom camera

Figure: MesSen Nord GmbH;Photo: BOKU Vienna – INNOKANIS Project

Sewer inspection by means of a manhole‐zoom camera

• investigations based on 4 sewer catchment areasin Tyrol, Salzburg und Upper Austria

• pipe material (asbestos cement, clay, concrete, PVC)

• pipe dimension (DN 150 – oval 1,300 / 900)• 342 sewer sections (totalling 9.4 km) combined sewer systems: 242 sewer sections sanitary sewer systems: 100 sewer sections

• cleaning strategies: reactive / proactive

Sewer inspection by means of a manhole‐zoom camera ‐Assessing the degree of sediments

BOKU Vienna – INNOKANIS Project

Rates of deposited material in sewer systems

n = 242 n = 100

Combined Sewer Systems Sanitary Sewer Systems

BOKU Vienna – INNOKANIS Project

4%

Monitoring of the cleaning performance

BOKU Vienna – INNOKANIS Project

prior to cleaning

after cleaning

Monitoring of the cleaning performance

prior to cleaning after cleaning

BOKU Vienna – INNOKANIS Project

Example of a selective cleaning strategy: City of Salzburg, Austria

change proactive selective in 2010

Figure left: STADT:SALZBURG Magistrat, Kanal‐ und GewässeramtFigure right: http://www.bow‐modellhandel.de/

Data collection – Salzburg, 2010

STADT:SALZBURG Magistrat, Kanal‐ und Gewässeramt

Degree of pollution of pipe sections –City of Salzburg, 2010

BOKU Vienna – INNOKANIS Project

Quantities of disposed waste (t/km) –City of Salzburg

selective cleaning strategy

+cleaning due to upcoming CCTV inspection for sewer mapping

BOKU Vienna – INNOKANIS Project

Example of a selective cleaning strategy: City of Salzburg, Austria

Figure left: STADT:SALZBURG Magistrat, Kanal‐ und GewässeramtFigure right: http://www.bow‐modellhandel.de/

change proactive selective in 2010

Result of strategic change: sewer cleaning expenses 

decreased by 60 % within a year.

Summary• deposits cause decrease of hydraulic capacity and generate

operational difficulties and enviromental impacts

• degree of pollution in approx. 2/3 of all pipe sections ≤ 2,5 % (both sanitary and combined systems) 

• for majority of pipe sections self‐cleaning effect sufficient  no additional cleaning measures required

• manhole‐zoom camera = simple and quick tool to inspectthe sewer system, assess the amount of deposits and monitorthe cleaning performance

• due to strategic change (proactive  selective) the sewer cleaning expenses of the City of Salzburg decreased by 60 % within a year

Spülplan

Thank you for your attention !

Contact: University of Natural Resources and Life Sciences, ViennaInstitute of Sanitary Engineering and Water Pollution ControlDI Hanns Plihal; hanns.plihal@boku.ac.atTel.: +43 660 359 5371