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Alternative Uses for Sewage Sludge |
The Ocean Dumping Ban signed into law in 1988 outlawed the dumping of sewage sludge into the ocean after December 31, 1991. At the same time that municipalities had to come up with alternative methods to dispose of the highly concentrated waste product solids that remain after water extraction, many of them were also confronted with growing populations helping to create increasing amounts of it to dispose of. Landfilling, incineration, and land application became the most common disposal methods, but with increasing concerns over the safety of those methods, researchers around the world have been exploring other ways to manage sludge. In this section, you’ll find samples of that research. Some of the most promising has looked at sludge as a renewable energy source. The renewable part comes as no surprise, but the fact that sludge can be used in a variety of ways to generate energy and fuel may. As exciting a prospect as that may be at a time when we feel an increasing urgency to find alternative energy sources, it’s important to note that this is an emerging technology and that many of the concerning heavy metals, pathogens, and other pollutants found in sludge still need to be addressed. It’s also fair to say that there will be no “one size fits all” solution; no one method will work for every municipality. Finally, it’s critically important to approach the management of sludge in a deliberate, thoughtful manner, as in the following example from Sweden. |
Sweden’s Sustainable Waste Management System |
The Swedish system of Sustainable Waste Management is highly regarded around the globe. As the Swedes put it, “Waste and refuse are resources in the wrong place,” and so they’ve spent decades finding ways to make the most of sewage sludge. According to Stephen J. Salter, an engineer from Victoria, British Columbia, who has written extensively about his travels in Sweden to study their methods, sewage sludge is used to fuel vehicles and heat homes. But it’s not just that the Swedes have turned sludge into energy that makes their system so special. It’s that they’ve developed an integrated approach to dealing with waste that sets them apart from so many other nations, including the United States. In “Powered by the People: Victoria Engineer Discovers Swedes View Sewage as a Valuable Resource” from Victoria’s Times Colonist newspaper, Salter says, “I went [to Sweden] expecting to see really cutting-edge technology, and instead what I found was a lot of common sense applied to community planning,” he said. “Instead of just looking at liquid waste separately, they look at liquid waste, solid waste, energy, transportation and environment. They look at all of those five areas as one plan.” |
For more information on Sweden’s Sustainable Waste Management System, please refer to the following sources as well as those listed in the endnotes of the Alternative Uses Chart: (see link at top and bottom of page) |
Stephen J. Salter – Treating Waste as a Resource: Inspiration from Sweden (video and pdf versions + related article from Georgia Strait Alliance site) |
Waste Not
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Survey Sewage Sludge Research The avenues of research into alternative uses of sewage sludge are as diverse as the locations of the research facilities themselves. It would be impossible to provide a comprehensive list of studies, so here is a sampling. The accompanying chart provides a more orderly look at some of the more interesting uses being investigated. |
General: This is a more general list, but contains several great examples specific to sewage sludge. It was compiled by Stephen Salter, who was cited in the discussion on Sweden. Worldwide: The SUSAN Project is a consortium created by the EU to find safe ways of recovering nutrients, primarily phosphorous, from sludge by using a two-part process of mono-incineration followed by a thermochemical treatment. Members of the consortium are listed in this document. USA: Schmack BioEnergy is the partner of Germany’s Schmack Biogas AG. They are located in Ohio and claim that the equivalent of 20,000,000 gallons of gasoline could be produced annually by making Biogas from sludge. This document also contains some info about their German counterpart. According to the authors, the CWT Thermal Process can be applied to any type of waste, including sewage sludge. There is apparently a 7-ton-per-day pilot plant unit in Philadelphia where the final scale-up information for the first commercial plant in Carthage, Mo was obtained. Additional US companies making biofuel: European Union: Final report for the European Commission Germany: Hosted by Hans Huber AG, a German company that supplies sewage treatment equipment and operates a sludge division. There are many case studies on the site of applications of their technology. “IWEtec (Innovative Water and Environmental Technologies, Germany) and Dirk European Holdings, Ltd. (United Kingdom) have developed the "DIRK Power Ultrasound" treatment. Full-scale application of this treatment in Germany has shown that the use of this patented split-flow disintegration by means of high-powered ultrasound offers a reliable and cost-effective means to treat wastewater treatment sludge. The treatment results in a decrease in sludge quantity (volume and mass) and increases the biogas yield. It also results in a higher dry solids output and a lower requirement for polymer/additives in the dewatering process.” Greece: Explores use of dried sewage sludge as an additive in construction materials. Japan: Japan has been using ash or slag resulting from the incineration of sludge as backfill for civil engineering projects, raw material for brick and tiles, etc., but supply has exceeded demand, so this paper discusses methods of supplying sludge to Portland Cement plants. Netherlands: Scotland: The specific page in the link contains pdf files for each of Scotland’s Waste Recovery Technologies. They provide nice overviews of the technologies. United Kingdom: Anaerobic digestion refers to a process that takes place in the absence of oxygen. It is a bacterial process that occurs during the fermentation of the sludge and leads to methane production. |
Additional Articles: M. Pogrzeba, R. Kucharski, A.Sas-Nowosielska, E. Malkowski, K. Krynski, J. M. A. Ito, K. Takahashi, J. Aizawa and T. Umita, Enhanced heavy metals removal without phosphorus loss from
W.C. Leung, M-F. Wong, H. Chua, W. Lo, P.H.F. Yu, and C.K. Leung, Removal and recovery of
Parliamentary Office of Science and Technology, Energy and Sewage, 2007
Hajime Takahashi, STUDY ON SEWAGE SLUDGE GASIFICATION, 2008
Veronica Arthurson, Proper hygienization of sewage sludge – a critical issue 1 for a sustainable society, 2008
Charothon Jindarom, Vissanu Meeyoo, Thirasak Rirksomboon,
E. Levlin and B. Hultman, PHOSPHORUS RECOVERY FROM SEWAGE SLUDGE – IDEAS FOR FURTHER
Shireen Meher Kotaya, Debabrata Das, Feasibility of biohydrogen production from sewage sludge using
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Updated 04/2009
