Drainage of sludge is an important part of the drainage services Norva24 can offer. This applies to both conventional sludge drainage and mobile dewatering. Malvin Sandbakk is responsible for this service in Norva24, and he has also been an active contributor to the report on sludge disposal now published by Norsk Vann. Report 226/2017 “Drainage of sludge” has been prepared to increase knowledge about sludge dumping, and the report deals with both conventional sludge disposal and mobile dewatering. In the work of the report, the consequences of using mobile dewatering have been particularly focused, both in terms of effects on health and the aquatic environment, and considering the effects of downstream purification stages.

About half of Norway’s municipalities today use mobile dewatering technology, which had its introduction in Norway in the mid-1980s.

Useful for the municipalities
Sandbakk believes the report is particularly useful for municipal prosecutors in view of the preparation of a competition basis for sludge dumping and the follow-up of the emptying assignment. During the preparation of the report, there were a number of issues that were highlighted, and the expert group agreed on a number of key conclusions, says Sandbakk.

Effect of polymer on health and water environment
-Use of polymer for dewatering of sludge in central treatment plants is considered to not have adverse effects on the aquatic environment, with the possible exception for sensitive water-retardant recipients. – When sludge separators are associated with downstream purification stages, it is unlikely that the residues of residual polymer released to the recipient will be higher in mobile dewatering compared to central treatment plants. It is also unlikely that the use of polymer in mobile dewatering will lead to the addition of groundwater and surface water sources to concentrations of acrylamide which may cause health hazards.

Pollution Aspects
In less sensitive areas where direct emissions from sludge separators are concerned, it is unlikely that the supply of waste water from mobile dewatering could lead to negative pollution effects. In normal and sensitive areas where wastewater treatment in scattered buildings will mainly be carried out with minirense plants, infiltration plants, sand filters, etc., it is unlikely that reuse of waste water from mobile dewatering can lead to negative pollution effects.

Effects on downstream purification steps
The report concludes that it will not bother operating problems with recycling of waste water from mobile dewatering downstream purification stages as long as the sludge drainage is carried out according to appropriate procedures. However, if the sludge separator has malfunction or if the downstream purge stage is incorrectly sized or incorrectly executed, operational problems may arise that can be enhanced by rewashing water from mobile dewatering, even if the drainage is performed properly.

The professional group believes it is not likely that the nutrient burden due to the return of waste water from mobile dewatering will cause operational consequences for downstream purification steps, with the exception of a short-term nitrogen emissions, and possibly phosphorus, in the post-sludge period. This assessment applies to both infiltration plants, sand filters and minirense plants, explains Malvin Sandbakk.

Premises for sludge disposal
Slag massage is also a subject that needs to be learned, and Norva24 attaches great importance to solid internship training. The content of polymer in the scavenger can, to a large extent, depend on the operator’s expertise and routines related to dewatering of sludge and return of scrubbing water. To reduce the risk of elevated polymer values in the recycle water, we provide our operators with thorough training and knowledge about the actual dewatering process and the use of our modern equipment. We have clear procedures for work operations in connection with sludge dumping.

Economic and environmental benefits
It is important and reasonable to use mobile dewatering for sludge drainage in scattered buildings. It significantly reduces the amount of water transported with the sludge to central reception. By dewatering to 20 percent dry matter, the amount of water being transported will be reduced by about 90 percent compared to conventional sludge dumping.

Reduced transport needs involve reduced fuel consumption and thus reduced greenhouse gas emissions and NOx emissions. Mobile dewatering can therefore potentially give both economic and environmental benefits compared to conventional drainage. Mobile dewatering also causes lower load to the treatment plants that receive the sludge, which would be beneficial in places that have a limited capacity treatment plants. There will also be a significant reduction in the number of kilometers of transport.

Also in more central and densely populated areas, mobile dewatering will be beneficial. In case of traffic congestion and rush traffic, using this technology will significantly reduce the load on the road network into a central treatment plant.

Important report
Sandbakk recommends anyone who has sludge work as a work area, whether it is municipalities, intergovernmental companies, companies or actors in the industry to study the Norwegian Water Report. Among other things, it provides recommendations on what requirements should be made to the slumber contractor to ensure good quality performance of the drainage mission. Here are also recommendations on what information the municipality should provide in the tender documents, so that the provider must have sufficient information to provide resource efficient and environmentally friendly drainage services at the right price.

“For us in Norva24, it is important that the booking competency for the purchase of sludge services is also increased. Then we promise to be a safe and good partner with those who want a nationwide and serious player in this area. Experience and competence we can guarantee documenting finishes Sandbakk.

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