Abstract
The anaerobic treatment of organic rich pollutants has a very long history within the water industry. Two major applications have been used: Treating sludge streams from midsized and large wastewater treatment plants and for industrial wastewater streams containing high concentrations of organic carbon. This paper presents the status of anaerobic digestion of sludge streams in municipal wastewater. The paper highlights both the potentials and limitations of the technology. Further the alternative or complementing HTC-technology is presented and analyzed. The constraints, limitations and options for the reuse of processed municipal sludge is accordingly pointed out. Our usage of water is found more and more complex, along with the addition of a number of synthetic agents, such as pharmaceuticals and other complex polluting agents we find that the traditionally acknowledged sludge treatment stabilization methods are not sufficient. The paper points out that the anaerobic digestion may be combined with for instance the HTC-process. In a longer perspective the HTC may even replace the current anaerobic digestion. However, the HTC-technology will raise further interesting questions: The important points that need further investigations are inter alia: 1) To further clarify the quality of reject water from the hydrochar, with respect to rest pollutants. 2) To evaluate to what extent the HTC process may become a feasible way to disintegrate pharmaceutical remains found in municipal sludge. 3) How to further enhance the ways to recover raw materials from the hydrochar, such as phosphorus and carbon. Nethertheless, the process may allow for some very promising pathways within the future municipal sludge management.
Highlights
The anaerobic digestion of municipal sludge is by convention based on natural processes found in nature
Results obtained in this study suggest that phosphorus recovery from sewage sludge processed via hydrothermal carbonization could pose as a promising sewage sludge nutrient recycling method
The current knowledge on municipal sludge as both a potential resource for carbon and phosphorus recovery is contributing to an increased interest to develop and refine technologies for the capture and reuse of these resources
Summary
The anaerobic digestion of municipal sludge is by convention based on natural processes found in nature. Wastewater management has been developed to a very high extent based on the conviction that a sustainable path for wastewater and sludge treatment is to mimic the processes found around us. The anaerobic digestion is in this respect a typical example. Examples of anaerobic digestion are found especially within European countries, either as decentralized small “septic tanks”, anaerobic ponds or as separate sludge reactors at larger plants. Typical large anaerobic digesters were built during the 1930s for instance in Stockholm, the capital of Stockholm. The updated and modernized plants are to a large extent still based on the early technological concept. The initial reasons for the use of sludge treatment with anaerobic digestion maybe summarized as follows:.
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