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Recovery of crop nutrients from wastewater

  • Recovery of crop nutrients from wastewater

It is possible that some of the vegetables we have eaten have been grown using wastewater. This does pose numerous problems such as exposure to toxic metals, bacteria and dissolved substances. However, this seems to be a practice that is rife especially in the low-class urban neighborhoods. Communities strained by unemployment and lack of basic resources such as water attempt to make ends meet by growing crops along industrial effluent and sewage lines. This reality is grim if we consider the risks wastewater avails to us. But it is loaded with opportunities if we choose to see this same wastewater as holding very vital resources for agriculture.

Agricultural nutrients

These essential substances are not only lost through fertilizer runoff after a downpour. They are present in human waste, livestock droppings, industrial effluents to name but a few. Since these waste materials somewhat find their way into our wastewater it is essential to find ways of isolating them in order to ‘repackage’ them for reuse as soil amendments.

Several strategies are essential for removal of agricultural nutrients from wastewater.

Here we shall consider a few:

  • Algae: These plant-like organisms easily accumulate nutrients such as nitrates and phosphates bringing a whole baggage of inconvenience in water bodies. The proliferation of algae in wastewater contaminated water bodies creates a myriad of environmental and health challenges such as eutrophication and the release of cyanotoxinsEutrophication renders freshwater bodies ‘dead’. This means that over time, no life thrives there due to the uptake of oxygen by the breakdown of excessive algae. But that’s not all. Blue-green algae also release toxic chemicals called ‘cyanotoxins’ which are categorized as liver toxins. This is the vicious cycle agricultural nutrients create when they are in the wrong place. But what if we harvest these algae and reuse them in our soils? What if we dessicate it and spread it over our crops? Over time, the algae will break down releasing the ‘locked’ nutrients easily converting them into a sort of controlled-release fertilizer. But this possibility doesn’t just work with algae.
  • Charcoal: The same ol’ charcoal we use to cook food (assuming that you’ve grown up in Sub-Saharan Africa) possesses qualities that allow it ‘suck up’ dissolved substances around it. Ask yourself why activated charcoal has been used over time as a water treatment medium. Its purely because of its insatiable appetite for dissolved substances around it. The same script works when charcoal is thrown into a wastewater body loaded with agricultural nutrients. However, a point to note is that charcoal is indiscriminate. If there are other pollutants, it will also end up sucking them up in a process called ‘adsorption’.

So how can we engineer charcoal to specifically target agricultural nutrients?

One of the ways is to react it with substances that improve its affinity for nutrients. Its high internal surface area could be the perfect scaffold to anchor materials such as layered double hydroxides and modified silicates for efficient removal of nutrients.

In conclusion

Recovery of agricultural nutrients from wastewater should be a subject of priority in order to create a cyclic and suatainable economy.

Not only can agricultural nutrients be recovered. Excessive phosphate minining will be discouraged (because it is recovered from wastewater). The cost of fertilizer will be checked due to recovery of already existing nutrients from wastewater. Treated wastewater could be rechanneled to irrigation and industry. Employment opportunities will be created.

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