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I have read about the application of sewage sludge incinerators1 but they do not have a net-positive power-generation. enter image description here Is there a way to generate net-power from sewage sludge? What are the processes to do so?


1: German: www.berlin-klimaschutz.de/...

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  • $\begingroup$ If the sewage does not burn on its own then it is not going to generate power. Cannot change that with a process. $\endgroup$
    – paparazzo
    Jan 23, 2018 at 23:02
  • $\begingroup$ Check on Cook Co. , IL ( Chicago) : they have been incinerating wet garbage for decades . $\endgroup$ Jan 23, 2018 at 23:37
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    $\begingroup$ @blacksmith37 Is Cook Co. generating power? $\endgroup$
    – paparazzo
    Jan 24, 2018 at 0:55
  • $\begingroup$ @Paparazzi I am under the impression, that you could dry it with the heat of the process. $\endgroup$
    – rul30
    Jan 24, 2018 at 5:26
  • $\begingroup$ Possible duplicate, see : engineering.stackexchange.com/q/13040/10902 $\endgroup$
    – Solar Mike
    Jan 24, 2018 at 7:13

2 Answers 2

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In order to make use of it as a fuel, you could consider these options:
- Processing the stuff with micro-organisms like bacteria that can create methane from it, or other usable fuels.
- Drying it and using it directly as a combustible fuel. The dryer you can get it, the more efficient your combustion will be.(less energy will be wasted to vapourising the water it's containing)
- You can gassify it after it's been dryed, like they do with wood. This gets you a more versatile/dense/clean end product.

But all this will waste a lot of other usable components within the sludge. Granted that the sludge isn't contaminated, I suppose it would be best to use it as fertiliser. Almost all of the components will be put to use then.

You could also extract usable compounds that are present abundantly enough, like ammonia. You can sell that to fuel manufacturers to make ad blue from. That way, our pee/poo will contribute to a cleaner environment.

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In order to generate net-positive power from sewage-sludge the chemical energy contained in the the sludge needs to be big enough in order to:

  1. Dry the sludge to an acceptable level
  2. Overcome all process inefficiencies

In a study from Dieter O. Reimann1 the necessary energy content to maintain incineration of different wast types was calculated. enter image description here Reimann concludes:

To achieve self-propagating incineration, a minimum calorific value in the sewage sludge app. 2,500 kJ/kg above the energy required for drying should therefore be aimed at.

An overview of the properties of sewage-sludge shows that even in dried form sewage-sludge is under the minimum value of 2,500 kJ/kg. enter image description here

A energy-content of 20MJ/kg for dried sewage-sludge is reported by Gerhardt et al.2: enter image description here

This means there exist the possibility to produce electrical-power using sewage-sludge if the water-content is low enough. Which could be achieved by a solar-thermic-process3.

enter image description here

[1]: Problems about sewage sludge incineration, founded by the European Union
[2]: Fuel Characteristics Of Sewage Sludge...
[3]: Universität Hannover - ISAH

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