The situation that you ...

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The situation that you describe is a very normal practice in municipal waste water treatment plants in The Netherlands and Belgium. I worked with rotating belt filters (from the German company Bellmer) and used liquid polymer emulsions from Kemira and Ashland (Praestol). The result was a 5 - 9 % DS slurry. This could be pumped with mono pumps into a sludge digester on site or transported with a vacuum truck to a central sludge digester somewhere else. This process is technically called; thickening with a belt thickener. Dewatering to 19 25 % DS comes after full digestion. 

If you don't trust the precedence of chlorine then you should feed the Polymer Preparation Units with normal tap water. A well designed sludge handling line should be able to switch between final effluent and fresh tap water. 

Furthermore: Polymer products for this purpose are in most cases PolyAcrylAmides. They are not easy biodegradable but the will surely decompose into fish smelling rotting products due to the amino groups. 

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Very Interesting. SO does the presence of Poly not lower your Biogas yield based on what you designed for. We do not want to use potable water. Here in SA we work hard to reuse our treated water produced by the plant, so the municipality avoids using potable as much as possible. The remedy would be to replace chlorine dosing with UV treatment.

But I would like to know how the biogas deviates with poly compare to conditions when not using with poly. I am thinking at initial design stage when sizing the Anaerobic digesters you did not take the the Poly affect into account and only found that out afterwards??

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I've never heard that Polymers used in wastewater treatment can affect the production of biogas. Not in a positive way, neither in a negative way. 

 

What the Dutch water authorities did in recent years is switching from digestion of sludge that was thickened by gravity (1% DS) to digestion of sludge is thickened by rotating belt filters (5 - 7 % DS). In this way they were able to handle much more sludge in their existing digesters or extending the residence time of the sludge in the reactor. In many cases they collected the sludge from different locations via vacuum transport trucks to one central digester. The rotating belt filters were operated unmanned and in most cases the whole wwtp was operated unmanned. 

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