Dream team of ‘cleaning bacteria’ surprises North Water
Something unusual is happening at North Water’s industrial salt wastewater purification plant in Delfzijl. After just five years in operation, the purification plant has developed ‘supersludge’. A scientific study to find out how this sludge is being created and how to make its technical application more robust is now under way.
North Water’s salt wastewater purification plant in Delfzijl purifies the wastewater of chemical companies that operate in the Oosterhorn industrial estate. The wastewater produced by around thirty companies is being purified by the joint venture between Waterbedrijf Groningen and Evides Industriewater. This is being done in a conventional aerobic water purification plant (40,000 pollution units) with an equalisation tank, a bio-reactor and a clarifier.
Nothing special, you might think. However, the sludge’s ability to settle has increased significantly since the plant went into operation in 2008. The sludge volume index (SVI) is now more than a factor of four smaller than the index for normally active sludge. From flocculated sludge, the biomass has transformed into granular sludge with good and fast settlement as a result. In a wastewater purification country such as the Netherlands, granular sludge is highly praised. That is because this type of sludge produces an efficient and compact water purification process, exactly the type of process for a plant that covers a small space. The process shows some resemblance to RoyalHaskoningDHV’s Nereda water purification technology.
How this dream team of ‘cleaning sludge’ came about in a continuous system and under salt conditions is still a bit of a mystery. The process does not involve a high sludge load or typical hydraulic selection pressure, for example. But the scientists do have strong suspicions, says adviser and business developer Perry van der Marel of drinking water laboratory WLN, who advises North Water. Granule-forming bacteria called GAOs – glycogen accumulating organisms – that thrive in the North Water plant have been detected in the sludge. “These micro-organisms are usually displaced by other competing, fast-growing bacteria. In our plant, they’re given every chance to reproduce. That’s all down to the specific operational and process conditions in our water purification process, which apparently boost the selection process.” There is still no definitive explanation of which factors this involves. One of the factors may be the balance between the anaerobic and aerobic zones in the process. According to Van der Marel, a good deal of scientific research still needs to be carried out. In that research, North Water is being supported by the University of Groningen, Paques and Delft University of Technology.
“The outlook is really promising,” says Van der Marel. “When sludge has a robust ability to settle, you can increase the amount of sludge in the plant and therefore the plant’s purification capacity without having to adapt the plant itself. That gives you a high degree of flexibility and may even reduce the amount of investment required.”
“There’s a huge demand for robust salt wastewater purification techniques,” say Van der Marel. “Especially in the oil and gas and chemical industries, which operate globally with a regularly changing production capacity. This is also the reason why one of the studies in the recently launched WaterNexus programme is focusing on salt wastewater treatment with granular sludge technology. WLN is taking part in this study, as are Shell and Dow. “With the experience we’ve gained at North Water’s purification plant, we’re delighted that we can help expand the industry’s knowledge of this area.”
Author: Pieter van den Brand
North Water is a reliable and expert partner in the supply of industrial water and the processing of wastewater using custom-designed purification plants. North Water is a joint venture of Evides Industriewater and Waterbedrijf Groningen. These two companies have combined their expertise and experience in the field of water to help optimise the industry.
Evides Industriewater, inventive.