Deposits have a number of negative consequences on the operation of drainage networks, all of which are also associated with economic disadvantages. They also contribute to water pollution. Impact of the deposits on the operation of the sewer systems are:

• Deposits lead to a reduction in the hydraulic performance of the sewer system by increasing the operational roughness reducing the flow area and the capacity of the sewer system. These circumstances …

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Drain and sewer may only be used in such a way that any avoidable impairment of groundwater and water bodies is eliminated. The solid’s physical properties and the sewer system’s hydraulic condition dictate whether they will reach the sewer treatment facilities or be deposited in the sewer line. The latter is the subject of this module.

After completing this module, you will have a sound knowledge of:

• the origin of solids and their transport characteristics;
• the consequences of solids discharge for the operation and maintenance of drain and sewer systems.

(Image: Picto Recht Standards Law )

The following is a summary of essential standards that apply to the planning and execution of cleaning measures:

Cleaning interval frequency depends on a large number of parameters such as:

• Type of drainage process,

• Gradient and discharge conditions,

• Type of deposit and agglomeration, …

(Image: Picto Proactive Reactive)

Cleaning measures can either be implemented proactively or reactively.

(Image: Picto Proactive)

Proactive cleaning as per DIN 14654-1 serves to mitigate problems before they occur by implementing the following principal objectives:

• Securing a defined status (safe and correct operation) of drains and sewers by eliminating debris, deposits, obstacles, etc.;

• Preventing the appearance of odours and gases caused by putrefaction processes as well as the formation of biogenic sulphuric acid corrosion in structures made of …

The following preventative cleaning measures differ depending on the stipulated objectives and requirements of the cleaning process:

• Cleaning prior to an inspection is a special cleaning method focusing on the entire cross section of the sewer in order to expose any visible structural damage so that it can be quantified.

• Cleaning prior to rehabilitation works is also a special cleaning method. The requirements to be met depend on the specifications of the planned rehabilitation project, and may extend from a basic cleaning up to a specialised treatment of the inner surface of …

The following section discusses cleaning objectives and strategies as well as the development of a cleaning plan.

In addition to the previously mentioned principal objectives, the development of the cleaning plan may include further objectives, as e.g.:

• Reduction of operating costs;

• Minimisation of public disturbance and citizen complaints;

• Compliance with technical and legal requirements;

• Improved quality control and documentation of cleaning works by the staff/service providers;

• Acquisition of information for future cleaning planning.

A specification of the principal objectives for individual network sections is realised through following performance requirements and measurable cleaning objectives outlined in [EN14654-1:2005] and [ASCE 2019]:

• Restoration of the flow capacity to the nominal design value;

• Removal of deposits and debris up to a prescribed level;

• Limitation of the build-up of sediments to prescribed levels;

• Limitation of the deposits to existing levels (maintaining …

The cleaning plan will be derived from the cleaning objectives and the chosen cleaning strategy.

(Image: Arrow Reactive preventive strategy)

Two cleaning strategies that are often applied, normally in combination, are:

• The reactive strategy and

• The preventive strategy

However, those two strategies are not contemporary anymore and should be substituted by

• The demand-oriented strategy and

• The demand- and condition-oriented-cleaning strategy.

In the following, all four strategies are introduced.

[Haußm98a]

(Image: Arrow Reactive strategy)