Can We Recycle the Phosphate?

Readers of this column will have noted that two weeks ago I wrote about the pending worldwide scarcity of phosphate. Last week I wrote about the pollution caused by phosphate. This week I deal with some ways of addressing both problems.

As we have noted, all animals ingest phosphate. It is a necessary component of the food they eat. Their bodies use a very small portion of the phosphate they ingest. The remainder is expelled in the urine and feces. That phosphate can have one of two destinies, but only two: it can recycle and again become a plant nutrient; or it does not recycle, and becomes a pollutant.

So there is an incentive for us to find ways of recycling the phosphate.

Were phosphate the only component of interest in excrement, we would probably be recycling the phosphate now. However, we have been much more interested in the pathogens found in excrement. We have become singularly adept at dealing with those pathogens. We are all familiar with the tragic part of the Walkerton story, but we should also note the other part of that narrative – the Walkerton story is unusual, a commentary on the effectiveness of our common treatment technologies in dealing with these pathogens. Unfortunately, as we deal with the pathogens, we more or less disregard the phosphate.

It need not be so. There is technology that will deal with human excrement in a way that will kill pathogens and allow the recycling of the plant nutrient component. The most familiar technology is composting toilets. These come in many designs, but all ultimately convert the excrement into compost in a way that will kill any pathogens. Unfortunately, managing a composting toilet is not as easy as pressing a leaver to generate a five-gallon flush. Any composting toilet requires committed management if it is to work well.

There are also technologies that allow for the safe application of municipal sewage onto cropland in a way that conserves the plant nutrients. Nevertheless, because of the way the sewage has been treated before it gets to the application stage, this is problematic. Firstly, our households dilute any organic effluent with prodigious amounts of water. This water needs to be dealt with if the organic matter is to be applied to cropland. Secondly, so much of what we flush plants do not like, things like cleaning agents, paints, and petroleum derivatives.

The best way of dealing with the phosphate and other potential plant foods generated in our households is to separate them from other waste at source. This way we would not dilute it with perfectly clean water or contaminate it with other waste. This could be done quite easily at the municipal level, but requires a cultural commitment to work.

At this time, we are probably not ready to change the way we treat human effluent, but as phosphate for food production becomes harder to get, and the impact of the pollution of our waterways with phosphates becomes more evident, we will have little choice but to become more resourceful in what and how we recycle.

Eric Rempel