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Sludge treatment – great opportunities for improvement

Sludge dewatering can be a tricky operation due to varying sludge composition. A significant share of the operational costs of municipal wastewater treatment but also some industries is in sludge disposal. An investment into improved sludge treatment can bring significant cost-efficiencies.

Sludge treatment – great opportunities for improvement

The purpose of wastewater treatment is to separate undesirable substances from the water. This is done by making dissolved substances and small particles form larger solids that can be separated. When these larger solids clump together they form a sludge. Sludge is a mixture of particles and water. The sludge dryness can vary a lot, depending on the origin and its composition. By using inorganic coagulants in the wastewater treatment process, sludge properties are improved. Higher dryness, lower sludge volume and subsequently cost-savings can be reached on sludge disposal.

Sludge is processed in stages that comprise a sequence of operations such as thickening, stabilisation and dewatering. In almost all cases an organic polymer is used to support the settling and the water release performance of the sludge. Using inorganic coagulants in the wastewater treatment upstream creates an additional benefit in the final sludge dewatering as less organic polymer is needed and better dewatering results can be achieved. Composting, incineration, dumping or use as a soil improver are common methods for final disposal of sludge. Of the total costs of a wastewater treatment plant, around 40–60% go toward sludge treatment, despite the fact that the volume of sludge is only around 1% of that of the influent wastewater.

When looking for efficiencies in sludge treatment, application expertise is always an important piece of the puzzle. With an extensive global experience from a huge number of customer cases, we offer the expertise required for finding the right kind of technical approach overall. Combined with a unique portfolio of chemistries and smart technologies, it is the best available approach to optimize sludge treatment processes for our customers.

Of the total costs of a wastewater treatment plant, around 40–60% go toward sludge treatment, despite the fact that the volume of sludge is only around 1% of that of the influent wastewater.

Smarter sludge management in Copenhagen

By using a combination of sensor technology, Kemira chemistries and the digital KemConnect™ platform for smart process management, the BIOFOS Lynetten wastewater treatment plant in Copenhagen was able to optimize their sludge dewatering process, eliminate struvite-scale issues, and cut polymer consumption overall.

At Lynetten, sludge is digested to produce biogas, then dewatered in centrifuges, dried and incinerated.  Kemira introduced the KemConnect SD smart chemical solution where chemistry is adjusted in real-time depending on needs. With this solution, the sludge dewatering was improved so that less suspended solids and phosphorus was recycled to the wastewater treatment process with the reject water from the dewatering. Internal load at the plant was reduced dramatically. On top of this, it was possible to achieve much higher dryness in the sludge. Drier sludge requires less energy in the drying process, so energy could be saved as well.

The best results can be achieved when total cost of ownership and performance can be discussed with the customer, as was the case with Lynetten. In the future, the municipal tendering criteria is likely to also develop in this direction.

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