Sewage water is regarded as waste, but according to professor Jules van Lier it should be viewed as a valuable source of energy and fertilizers.
Western countries are proud of their sewer systems, and for good reason: infectious waters are effectively removed from residential areas and the effluent water from treatment installations is of reasonably good quality. But recently appointed professor, Jules van Lier (wastewater treatment and environmental engineering), believes that the way we deal with our water and waste streams is questionable.
By flushing the toilet and mixing that water with all other household waters, prof. Van Lier says: “We dilute our sludge with a factor of hundred.” Subsequently, we aerate the sewage water in treatment installations, in order for aerobic (oxygen consuming) bacteria to break down the organic compounds. But this aeration – pumping air inside the basins – costs lots of energy.
Instead, sewage treatment could produce energy. “For this we have to concentrate the sludge and use an anaerobic waste treatment technique that produces methane”, Van Lier says. “And what’s more, by doing so we can also recuperate nitrates and phosphates that we can use as fertilizers.”
The professor explains that in the agro food business, waste streams are already widely being treated through fermentation by methane bacteria in so called biogas plants. “These methane producing bacteria thrive well in waste streams because the temperature is relatively high”, he says. “The optimum temperature for these microorganisms is 38°C. Sewage water is generally much cooler than that. Heating the low-concentrated, large quantities of sewage is out of the question, however, because of the energy requirement. This is why the waste must be concentrated prior to anaerobic treatment.”
One way of doing this is through the use of vacuum toilets. Experiments with separate collections for faeces and urine are currently being conducted in the Frisian town of Sneek.
Van Lier, and a PhD student from Wageningen University, are working on a technique to treat the highly concentrated waste streams deriving from these kind of toilets. They are using a high pressure fermentation tank, and their goal is not simply to produce methane, but also to produce high quality green gas, which is a gas consisting of almost pure methane. Because of this high pressure, the carbon dioxide, which is normally part of the biogas, largely remains dissolved in the sludge.
“We found that these methane bacteria can survive a pressure of ninety atmosphere”, Van Lier says, “and that’s more than enough. We already obtain high quality gas with ten atmosphere.”
The trick now is to make this fermentation process suitable for the black waters that are collected via vacuum sewers. Instead of batch digestion processes, a continuous flow process that can be operated in a decentralized mode is needed. With the support of a TU Delft PhD student, the professor will now try to build a user friendly, continuous flow fermentation tank.
Because most sewer systems in the Netherlands date from just after the Second World War, large sections of these aging systems must be replaced in the coming years. According to Van Lier, now is the time for a paradigm shift. Decentralised sanitation, coupled with resource recovery, might be a better solution, he believes.
The advantages of this technique are even more obvious for developing countries. Since such countries cannot afford to build sewer systems like we have in the west, why waste the energy that’s locked inside the waste?
Net als vorig jaar neemt het aantal studenten dat aan de TU Delft wil studeren fors toe. Deze week is er in totaal al elf procent meer studenten dat zich heeft aangemeld voor een studie bij de TU dan vorig jaar rond deze tijd.
Voor bouwkunde hebben zich nu al 602 studenten aangemeld, terwijl dat aantal vorig jaar rond deze tijd op 468 lag. Dat is een stijging van 29 procent. Het daadwerkelijke aantal eerstejaars bij bouwkunde bedroeg in december vorig jaar 502. Op dit moment zijn er dus al precies honderd belangstellenden meer.
Het college maakt zich zorgen over de gevolgen die dat heeft voor de onderwijskwaliteit en de belasting van docenten. De term numerus fixus bleef deze week dan ook niet onbesproken tijdens een vergadering met de ondernemingsraad.
Het aanvragen van een zogeheten instellingsfixus moet de TU echter vóór 1 december doen. Het komende collegejaar kan er dus geen sprake zijn van een maximum aantal studenten dat mag komen studeren.
Volgens collegevoorzitter Dirk Jan van den Berg wordt binnen de TU wel met enige huiver gekeken naar het instellen van een numerus fixus. “In Leiden is dat niet zo goed gelopen. Die universiteit groeide niet meer, want studenten liepen weg en de numerus fixus werd niet gehaald.”
Vorig jaar kwam het onderwerp ‘numerus fixus’ ook al aan de orde, zegt Van den Berg. “Toen hadden we de indruk dat we het nog konden redden. Je wilt je deuren niet sluiten.”
Bouwkunde maakte vorig jaar na de brand ook al een opmerkelijke sprong in het aantal vooraanmeldingen. “Ik denk dat de universiteit zeer geloofwaardig overkwam met hoe het daarna gegaan is”, zegt Van den Berg. “Het gebouw aan de Julianalaan is heel aantrekkelijk om te zien.”
De decaan van de faculteit was vanwege een congres in het buitenland niet bereikbaar voor commentaar. Van den Berg meldt dat gekeken wordt of er extra ruimte bij de faculteit te vinden is. “Daar komen we wel uit, maar het vraagt creativiteit.”
Niet alleen Bouwkunde loopt tegen capaciteitsproblemen op. Zo kan Industrieel Ontwerpen volgens Van den Berg ‘maar net’ de hoeveelheid studenten aan die ze nu heeft. Het aantal vooraanmeldingen voor deze faculteit ligt met 331 belangstellenden slechts twee procent lager dan vorig jaar rond deze tijd.
Luchtvaart- en Ruimtevaarttechniek zit nu al krap en ziet nu exact evenveel belangstellenden op zich af komen als vorig jaar: 318. Voor deze faculteit moet het nieuwe, naastgelegen ‘onderwijsgebouw zuid’ lucht brengen. Dit demontabele gebouw wordt in september in gebruik genomen.
Ook moeten de collegezalen van de faculteit Werktuigbouw, Maritieme Techniek en Materiaalwetenschappen (3mE) dit jaar echt een opknapbeurt krijgen, stelt Van den Berg. Het aantal aanmeldingen stijgt hier van 374 naar 427. Civiele Techniek trekt 11 procent en Technische Natuurwetenschappen 17 procent meer vooraanmelders.
Western countries are proud of their sewer systems, and for good reason: infectious waters are effectively removed from residential areas and the effluent water from treatment installations is of reasonably good quality. But recently appointed professor, Jules van Lier (wastewater treatment and environmental engineering), believes that the way we deal with our water and waste streams is questionable.
By flushing the toilet and mixing that water with all other household waters, prof. Van Lier says: “We dilute our sludge with a factor of hundred.” Subsequently, we aerate the sewage water in treatment installations, in order for aerobic (oxygen consuming) bacteria to break down the organic compounds. But this aeration – pumping air inside the basins – costs lots of energy.
Instead, sewage treatment could produce energy. “For this we have to concentrate the sludge and use an anaerobic waste treatment technique that produces methane”, Van Lier says. “And what’s more, by doing so we can also recuperate nitrates and phosphates that we can use as fertilizers.”
The professor explains that in the agro food business, waste streams are already widely being treated through fermentation by methane bacteria in so called biogas plants. “These methane producing bacteria thrive well in waste streams because the temperature is relatively high”, he says. “The optimum temperature for these microorganisms is 38°C. Sewage water is generally much cooler than that. Heating the low-concentrated, large quantities of sewage is out of the question, however, because of the energy requirement. This is why the waste must be concentrated prior to anaerobic treatment.”
One way of doing this is through the use of vacuum toilets. Experiments with separate collections for faeces and urine are currently being conducted in the Frisian town of Sneek.
Van Lier, and a PhD student from Wageningen University, are working on a technique to treat the highly concentrated waste streams deriving from these kind of toilets. They are using a high pressure fermentation tank, and their goal is not simply to produce methane, but also to produce high quality green gas, which is a gas consisting of almost pure methane. Because of this high pressure, the carbon dioxide, which is normally part of the biogas, largely remains dissolved in the sludge.
“We found that these methane bacteria can survive a pressure of ninety atmosphere”, Van Lier says, “and that’s more than enough. We already obtain high quality gas with ten atmosphere.”
The trick now is to make this fermentation process suitable for the black waters that are collected via vacuum sewers. Instead of batch digestion processes, a continuous flow process that can be operated in a decentralized mode is needed. With the support of a TU Delft PhD student, the
professor
will further research the possibility to build a user friendly,
continuous flow
fermentation tank. Commercialization of the process will be performed by a company called Bareau, that is currently working on innovative technologies to use the pressure
as an
additional energy source for reactor equipment.
Because most sewer systems in the Netherlands date from just after the Second World War, large sections of these aging systems must be replaced in the coming years. According to Van Lier, now is the time for a paradigm shift. Decentralised sanitation, coupled with resource recovery, might be a better solution, he believes.
The advantages of this technique are even more obvious for developing countries. Since such countries cannot afford to build sewer systems like we have in the west, why waste the energy that’s locked inside the waste?
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