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 Industrial Water. 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 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 Industrial Water and Waterbedrijf Groningen. These two companies have combined their expertise and experience in the field of water to help optimise the industry. WLN advises both North Water and Waterbedrijf Groningen in the field of water treatment and quality.
Since 2012 WLN has a MALDI-TOF MS biotyper at its disposal with which suspicious bacteria can be identified by means of chemotaxonomy. The great advantage of this technique is its speed: within a matter of minutes we know with certainty whether a sample has been contaminated.
If suspicious bacteria are encountered in a growth, their nature must be confirmed. This confirmation used to be executed by means of the classical growth method or, until recently, a DNA analysis. The MALDI-TOF MS offers an extremely fast alternative. The suspicious bacterium, for example a Coliform, Enterococcus or Legionella, is brought onto a small steel plate. By adding a chemical substance the cell wall of the bacterium is destroyed. The released proteins are shot into a tube by a laser. The small proteins will reach the detection gate sooner than the large ones. This results in a unique spectrum for a bacterium (‘fingerprint’ ) which is characteristic for that specific bacterium. By comparing this spectrum with a vast database we can identify the bacterium. If desired we can even name the genus and the type. Thus the MALDI-TOF MS enables us to inform you even quicker and more complete.