These days I am working with a paper on recycling of sewage. There are problems, unwanted metals and organic agents of different kinds.

How important is recycling of waste from sewage works? On a closer look I was surprised. It is not as crucial as I had thought.

Sweden does not produce its own food demands. Yes, we could, but there is the market.

But we eat well. Export industrial products and buy food as well as export some. There is an exchange as it should be. And we produce waste for the sewage works.

The best technology can do is to take care of all nutrients going to the sewage work and use them in agriculture. Impossible, but let us look at this unattainable potential. If we recycle everything only 20% of the plant nutrient demand would be covered.

Phosphorus is special. The reserves are limited and it is an active element in the environment. So P recovery seems essential. But other elements should not complicate this development. Nitrogen is an energy issue and potassium reserves are not critical.

Organic matter? Well, it is important for the soil as such, but sludge is a small post in this context.

A primitive energy consideration: We have 1 kg sludge, dry matter. We can use it in energy production and get 10 MJ. For 10 MJ we can produce 0,25 kg N. W use that in a good agricultural production and get 10 kg organic matter, to use for food, feed or soil improvement.

Yes, there are considerations of energy quality. But there are also margins. And varying technologies to use.



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