The chart shows the minimum slope, as per ATV-A 110 (1988), as a function of the circular pipes' diameter (inside diameter) d where the sediment transport ends (I_crit). In case of reoccurring low flow levels (h_t/d < 0,3) the planned minimum slope needs to be increased [ATVA110:2001].

(Image: Minimum slope requirement I crit for a deposit-free operation of circular channels) (Image: Minimum slope requirement I crit for a deposit-free operation of …

According to DIN EN 14654-1 deposits are "material deposited by gravity in the pipe invert or the bottom of a section of the drainage system" [DIN EN 14654-1]. According to [ASTM D4410-16], “deposits of sediment within a channel, partly or completely filling the channel. Such materials accumulate where the transporting capacity has been insufficient to remove it as rapidly as it has been delivered”.

The solids sink and form deposits only when the …

• Reduction of flow and thus the filling level through water conservation and stormwater management measures (e.g., water collection, evaporation and seepage basins) as well as the sealing of the sewer channels through rehabilitation [Stein98h].

• Reduction of the flow cross-section and/or increase of the surface roughness through construction or wear related defects (e.g. flow restrictions, pipe displacements, mechanical wear, internal corrosion, deformation, damaged pipe, etc.), as well as through foreign objects that have fallen into or were placed in the sewer [Stein98h].

The distribution of organic and mineral substances in the combined and storm sewers wastewater flow does not correspond to that of the already formed deposits [SteinR2005].

This is a result of the solids transport process in which the organic materials are further broken down and reduced, while the mineral deposits are able to maintain their shape and size throughout the entire flow path.

(Image: Deposit composition Image 1)The amount of organic and mineral matter in sewer deposits is determined by the dry weight of the sample after an ignition process.

The resulting loss on ignition revels the organic content, and the residue on ignition reveals the mineral content [DIN38409:1987].

Input and output (mass balance) of solids in sewers, and their composition (organic, mineral) using the example of the combined sewer system of the municipality of Entzheim (Germany) [Artie1988].

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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You have successfully finished this module.

Next you will have the opportunity to review the newly acquired knowledge with an interactive questionnaire.

You can of course still navigate back to any point in the modules if you wish to review a specific point or subject.

Stay curious!

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 is used to prevent problems from occurring and, in accordance with DIN EN 14654-3, includes the following fundamental or overarching objectives:

1. Ensuring performance, i.e. a defined operational state of the sewers and drains by removing deposits, obstructions, etc.

2. Limiting digestion processes and odour problems as well as the development of biogenic sulfuric acid corrosion in structures made of cement-…

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