During cleaning, the collected waste is to be checked as regularly as possible. A higher proportion of mineral solids and broken pipe bits indicates serious damage, e.g. pipe fracture or collapse. In such situations, the cleaning procedures have to be stopped immediately and protective measures have to be taken. If required, a less destructive cleaning method is to be chosen before cleaning is continued.

Disposal of the collected waste material.

Since June 1, 2005, the dumping of biodegradable waste - including the waste material from sewer cleaning procedures - without a prior thermal or appropriate mechanical-biological treatment is only permitted, insofar as the organic portion of the dry residue (measured as loss due to heating) does not exceed the values given:

• 3 % by weight: Geological barrier, Landfill class 0 and I

• 5 % by weight: Landfill class II

• 10 % by weight: Landfill class …

According to [Billm2002], a maximum of 40 – 50 % of the waste material from sewers, and a maximum of 15 – 25 % of the waste material from catch basins can be classified as recyclable substances. The re-utilisation potential of the waste material from the cleaning of sewers is limited to a fraction of the mineral solids.

The same applies to the waste material from catch basins. There is an additional re-utilisation potential for the ferrous and non-ferrous metals bound to particles [Billm2002].

Currently, the waste material from sewers and catch basins is, in most cases, dumped or thermally treated. Mineral solids are only recycled in exceptional circumstances and then re-utilised in the following fields:

• Landscape construction

• Road construction

• Sewer construction and earthworks

• Landfill construction

• Production of construction material

• Mining

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After the cleaning measures are completed, quality control is carried out in step 4.

• The cleaning performance and results are documented. This ensures that inadequately or insufficiently performed cleaning measures are immediately detected, and the service provider can be asked to undertake improvements

• Furthermore, the documented quality control information ensures a constant update to the much needed operational knowledge …

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According to EN 14654-1, the manner of inspection and approval of the cleaning measures should be specified and available before the start of the cleaning measures. This specification should include the following:

• A description of the required cleaning results

• General requirements regarding the documentation inclusive of a description of the achieved cleaning results and the circumstances under which these results were obtained

(Image: Permissible level of deposits) (Image: Mass of deposits) (Image: Volume of deposits)

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• The cleaning measures should be documented in the form of a comprehensive acceptance protocol. It has to be taken into account that a clearly structured reporting system will support both the operational processes and adherence to legal requirements.

• The acceptance protocol should be completed immediately after cleaning or after a clearly defined time interval.

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The acceptance protocol should contain:

• Place, date and time of the performed services

• Name of contractor, name of on-site inspector

• Assessment of the sewer line condition before cleaning

• The cleaning method and equipment used

• Type and amount of removed waste material. Estimation of the structural and hydraulic state of the sewer line after cleaning

(Table: Example for an acceptance protocol of a sewer cleaning modelled after […

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It is appropriate to amend the protocol by further fields to be able to document additional relevant operational data. These can for example include:

• The accessibility of the manholes

• Special characteristics (noise, development of odours)

• Cleaning objective and parameters

• Number of flushing cycles

• Time consumed for cleaning

• Water consumption

• Quantity or volume of waste material

• Time consumed for water refilling

• …

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• Time consumed to change over the cleaning vehicle

• Time consumed to dump the waste material

• Other efforts and expenses, etc.

• Inspection technology used to determine the cleaning result

• Deviations from the operational/flushing plan

This information is the basis for the update and constant optimisation of the demand- and state-oriented cleaning planning.

The assessment methods which are used to confirm the correlation between the specified (tender) and actual services should include:

• Optical inspection of the manhole and access shafts

• Optical inspection of the sewer line, via mirroring, video inspection via cart or drone

• Where appropriate, sewer measuring boat, culvert pressure unit, sonar measurement

The contract specifications should outline whether these tests are to be carried out at random…

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The following questions should already be considered with regard to quality control and documentation:

• Has the drainage capacity of the sewer been re-established?

• Have complaints due to odour nuisance decreased to the specified extent?

• Has the planned residual sedimentation height in the cleaned sections been undercut?

• Was a maximum deposit height achieved as a percentage of the sewer profile height?