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Remmendalen Sewage Treatment Plant

Thursday, October 4, 2018

The Remmendalen Sewage Treatment Plant is a giant leap into the green future for Halden municipality. The 240 mill. NOK plant upgrade provides capacity for decades to come, as well as yielding both heat and electricity.

 

 

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The sewage treatment plant is located inside a protected natural area at Iddefjorden, a short walk from The King’s Pier in Halden city center. The newly renovated plant is built over previous facilities from 1979, and today satisfies the highest national requirements for wastewater effluent.

"We now have a state-of-the-art
facility that will contribute to a clean fjord. We have enough capacity in the plant to handle growth in the population for 50 years to come. The plant will also be self-sufficient with energy. This is a facility we can be proud of” ,
says operations manager Rune Løkkeberg.


The original plant had large basins with traditional chemical coagulation and sedimentation. In the rebuilding, the basins have been used to build a new sustainable treatment process. The investment amounts to a total of NOK 240 million.

 


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Just outside the plant lies Iddefjorden, a popular open-air area for the local residents

Sustainable
Since the plant is located in a protected natural area, there have been major challenges during the construction period, as heavy machinery could only be operated within the fence of the plant itself.
“It has been a demanding construction period with extra costs because we are so close to wild nature. The purpose of such an environmental investment is to reduce our impact on nature, so we feel that this has been well-spent. The area remains scenic and attractive for the population”, says Løkkeberg.
Most of the treatment plant is now situated under the floor of the old basin hall, which today has become an open workplace with good ventilation. In the choice of processes, solutions have been chosen that are in themselves resource-friendly and which make it possible to recycle energy.
"In the past, best possible treatment has been the theme. Today, we look for treatment methods that can also make use the resources in the wastewater“, emphasizes Løkkeberg.
The Remmendalen Sewage Treatment Plant is a giant leap into the green future for Halden municipality. The 240 mill. NOK plant upgrade provides capacity for decades to come, as well as yielding both heat and electricity.

Virgin sludge
After the standard grease and sand removal, the wastewater is distributed into three identical parallel runs, which are engaged after the amount of wastewater entering.
The first step of the treatment is a gentle filtering with band filters. Here, the soft particle fraction of the wastewater is taken out. This sludge from the filters is rich in energy, and goes directly to rotting tanks. In these, bacteria grow without access to air, producing methane gas that can be used for heating. The gas may also be used for the production of electricity, in gas turbines.
“Recycling of energy is an important measure in line with our sustainability concept. The virgin sludge from the filters contains organic substances that we can make use of. In the long run, the sludge treatment may provide a significant excess of heat to be used to heat municipal buildings, town hall, cinema and library. Provision for this future connection has been added to the plant”, explains Løkkeberg.

 

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The new process hall is neat and well lit

 

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The oxygen levels in bioreactors are monitored and automatically regulated

Bioreactors

After filtration, the wastewater goes to three parallel two-stage bioreactors. These hold plastic bio carriers that are kept in motion through aeration. The bioreactors stir and provide oxygen-rich water and carbon dioxide stripping.
The bio carriers have internal protected surfaces where natural bacteria colonies grow undistrurbed. The colonies consume the dissolved organic content in wastewater. As the bacteria build up in thick layers, these break off as particles in the water. The process is called CMFF (Complete Mix Fixed Film), as it uses only air and bio carriers to work.
“The bioreactors are the very heart of the new process and are dimensioned with some extra capacity. If we so wish, we can increase the amount of biocarriers as needed.
The plant is today designed to handle 29000 personal equivalents (p.e.), but can be increased to 42000 p.e, with modest investments”, explains Løkkeberg.

Coagulant
After the bioreactors, the effluent goes into “skimming” or floatation, a strong mixing with excess of air, besides coagulant and polymers. In the process, the coagulant causes the dissolved organic substances to congregate into flocs. The polymers make the flocs stick
together forming larger particles. The supersaturated water creates the air bubbles that bring the
particles to the surface. This generates surface foam which is scraped into a drain. There is also a scraper in the bottom that brings the bottom sludge to the same destination.
After the floatation the water is released into the fjord. However, 7% of the cleaned water is recycled back into the process and used in the the super-saturated water stream. The sludge from the floatation is pumped to rotting tanks and further thickening.

After the sludge has been centrifuged, it is analyzed and eventually used for agricultural purposes. The reject water from drained sludge enters the plant once again.
“The floatation is complex interaction of several factors. The fact that we make use of the purified water to make supersaturated water is a sustainable measure. At this point the operation is monitored daily with analyzes and adjustments, so that an optimum purification of phosphorus is obtained before the water is released", emphasizes Løkkeberg.


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Managing director Rune Løkkeberg at the operation center

Volumes

The planning of the plant started in 2013, after a demand for a reduction of organic content in the wastewater released into the Iddefjord. Previously, there was only a requirement for purification of phosphorus. Today the requirement is related to how much oxygen the waste water consumes (KOF / BOD) when released.
“Although the plant works well, it will for a while suffer from a large amount of rainwater entering the wastewater through our poor drainage system. During drought the amount of wastewater can be 7000 m3 / day. After a couple of days of high rainfall it may increase up to five times the volume. We have started an intensive cleanup of the drainage systems in the streets of Halden, with grants of the same size as this plant“, says Løkkeberg.
The sewage treatment process is delivered as a turn-key contract of Biowater Technology of Tønsberg.
The delivery includes intake filters, bioreactors and floatation plants. Biowater was also responsible for the water purification process and the cleaning results.
“We have had a robust and sustainable solution, that after a long planning and construction period, has come to a target at an affordable cost. In spite of demanding space conditions, the plant is realized without exceeding our estimates. Both engineering, construction management and cooperation has also worked very well", says Rune Løkkeberg, managing director at Remmendalen RA.

 

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The bio carriers have internal protected surfaces where
natural bacteria grow undisturbed.

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Band filters harvest sludge to be used for energy
production