Wastewater collection

Wastewater collection normally takes place by means of gravity from domestic households and the industry where the wastewater is led to pumping stations and pumped into the wastewater treatment plants.

There are two main systems for the wastewater collection: collection systems with combined sewers and collection systems with separated sewers for rainwater and wastewater. Combined sewers transport the wastewater from private households and companies as well as rainwater in the same pipe. Many new collection systems provide separate sewers for wastewater and rainwater.

Rainwater is collected in sewers and led either directly to the pumping stations or to rainwater storage tanks where it at a later stage is mixed with the wastewater. As the amount of rainwater is unpredictable it may be necessary to store the rainwater either in basins around the country side or in stormwater tanks inside the wastewater treatment plants. In this way it is easier to control the flow of the rainwater as it is mixed with the wastewater when the plant has the capacity to clean the rainwater.

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Wastewater treatment

At wastewater treatment plants the grease and sand is removed by means of a grease and sand trap to protect the equipment in the following processes from damage. There are many different technologies for cleaning wastewater but the far most common is a combination of mechanical treatment and biological treatment. The wastewater is cleaned in steps ending with a biological process or aeration of the wastewater in order to start the nitrification and denitrification processes.

Mechanical wastewater treatment is used to remove solid matter in the water. It involves two processes: filtration (or separation) and sedimentation. Filtration is carried out in various stages using various processes. These can remove coarse impurities such as paper or leaves using a rake or rotary screen. In the primary sedimentation tank the purification (reduction of organic material) takes place.

In the biological stage of the wastewater treatment process the main impurities, which are suspended in the water and not picked up by the mechanical process, are treated. The biological wastewater treatment process takes place when the wastewater is being treated in the sludge activation tank. Other processes (e.g. trickling filter, immersion filter) are used in isolated cases.

Sludge is produced as a waste product in the wastewater treatment process. Treatment and preparation of sludge give rise to its own equipment requirements, which may vary significantly depending on the plant. The most common way of disposing of wastewater sludge is still using it in agriculture. This is why some countries utilize wastewater sludge thermally. In some cases, the wastewater sludge is delivered to an external biogas plant.

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Wastewater outlet

Before cleansed wastewater is discharged into a stream, creek, river or the sea it must be ensured that local legislation is fulfilled with regards to the wastewater outlet specifications. In the EU countries, each wastewater treatment plant is obliged to take samples of the discharged wastewater up to 5 times per day in order to document the content of harmful substances. If the discharge values are exceeded, the wastewater utility is obliged to pay a fine. Of course, this increases the motivation to clean the wastewater effectively in order to meet the EU discharge requirements of wastewater outlets.

For wastewater outlet, AVK offers gate valves, butterfly valves, knife gate valves, penstocks, check valves, couplings, adaptors, fittings, and accessories.