Recycling. Phosphorus should have priority.

The food we eat contains nitrogen and phosphorus, important elements for everything living. It ends up as toilet waste. After treatment in sewage works most of the phosphorus and some of the nitrogen end up in sewage sludge. This contains also some heavy metals, bacteria, hormones, medicins and various chemicals.  Sludge (biosolids) is a kind of fertilizer containing especially phosphorus but some nitrogen and above-mentioned impurities. To apply it on food-producing soils , is that right?

There are processes where the sludge is burnt, pure phosphorus compounds are extracted and a clean phosphorus fertilizer is produced. Then we miss the nitrogen. Is that right?

Systems can be developed where the toilet waste is collected, hygienized and used more directly as fertilizer. Then we take care of both phosphorus , nitrogen as well as potassium and other nutrients. Unfortunately hormones , drugs and chemicals are included.  Physically it is a thin sludge to transport and distribute. Is that right?

We need some guidelines to choose.

Phosphorus is special for two reasons:

1. It is a limited resource. We know about mineral deposits for 10-20 generations, but then ?

2. All we take out from mineral deposits ends up in our environment, in fields, gardens, waste dumps, waters.  It is active and causes eutrophication. And we never get rid of it. It might move, but is still active.

These are two, as I see it, overriding reasons to give phosphorus priority, to keep down extraction from mineral deposits by recycling as much as possible.

Nitrogen is different.

1. We have unlimited resources,  80% of the air is nitrogen. But we need energy to make it active, and all kinds of energy can be used. The present oil and gas can be replaced by hydro- or solar energy or even bioenergy.

2. An important process, denitrification, removes active nitrogen from the biosphere and gives it back to the air. There is no unavoidable  accumulation.

3. Active nitrogen (ammonia, nitrate, nitrogen oxides) are environmenal pollutants. Research has suggested that we already exceed the limits of the globe in this respect.

The main priority for nitrogen is to avoid losses of active nitrogen. To handle the farm nutrients as efficiently as possible. (Organic nitrogen in for instance sludge is in fact a disadvantage in this respect). Environmental analysis should guide the development

Conclusion: Extract pure phosphorus when possible. The loss of nitrogen is no great disadvantage (provided there is no nitrogen pollution from that process)

There are local needs for more smallscale processes.

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