3.5 Use and/or Disposal – Agricultural Use as Fertilizer and Soil Conditioner


Hi, and nice to see you again! We now arrive
at the last functional group which describes the technologies
for use or disposal of the sanitation end products. The use and disposal technologies
are split in two modules. Now I will discuss the use of products
as fertilizers and soil conditioners. In the following lecture,
we will be looking at what can be done with effluent
and other products. In this module, I will show you
how products can be used as fertilizer and/or soil conditioner
in agriculture, and I will explain
what the difference is between the two. In order for the agricultural
use to be safe, it’s important that measures
are in place to control the exposure and manage the health risks. I will give you a brief introduction
of the so-calledmulti-barrierconcept. When a single pit fills up,
it is often abandoned and its content, left to degrade.Fill and coverdescribes the way
of disposing of the pit content by leaving it where it is. A so-called “arborloo”is the simplest way
of upgrading this solution and making use of the nutrients
contained in a pit. After moving the toilet superstructure
to a new site, the full pit is covered
with a layer of earth and a tree is planted on top of it. The photo on the left shows a banana tree that grows vigorously on the nutrients
of an abandoned pit in Malawi. Papaya is the one from Zimbabwe
on the right side and guava have also
proven to be successful. Compared to the arborloo, there are more targeted
and more effective ways to use the nutrients
contained in human excreta. Urine, for example, is nutrient-rich
and normally sterile, and can therefore be used
as a liquid fertilizer when diluted. Its nitrogen to phosphorus
to potassium ratio is similar to that
of conventional fertilizers. Dehydrated feces, pit humus and compost typically contain
lower levels of nutrients, but are rich in organic matter and/or
decomposed organic matter. They have good
soil conditioning properties, meaning that they enhance the water
and nutrient retaining properties of soil. We therefore call these products “soil conditioners”,
rather than “fertilizers”. As you know from the previous lectures, the properties of sludge
can vary greatly. Sludge may be seen
as a both fertilizer or soil conditioner depending on its form
and characteristics. Before applying excreta-derived
products in agriculture, we should be sure it is safe,
and put in place adequate health protection measures. The World Health Organization
published guidelines for the safe use of wastewater, excreta and greywater with detailed recommendations
for different products and conditions. You can find those guidelines
on our Course Webpage. The guidelines promote
a multi-barrier approach for managing the health risks
related to the use of excreta. In other words, WHO recommends
to put in place several barriers if needed in order to reduce the health risk
to an acceptable minimum. The figure shows different barriers
between toilet and food consumption for the case of urine use. For example,
treatment mechanisms like storage can decrease the number
of pathogens in urine and the use of protective equipment
reduces contact. Maintaining those barriers
helps to control exposure and to keep the health risks low. I have taken this figure
from the very useful publication called,“Practical Guidance on the Use
of Urine in Crop Production” which can also be downloaded
from the course page. In these pictures you can see
the fertilization with stored urine and its effect on plant growth. Urine that has been diluted
with water can be applied to plants either manually or using trucks. A three to one mix of water and urine is an effective dilution for vegetables although the correct amount depends
on the soil and the type of vegetables. In the pictures at the bottom,
you can see impressive trials with maize and spinach, with and without urine fertilization. The photos here show how
the content of a dehydration vault is brought to a field
to be used as a soil conditioner. As you can see, ash was used
as a cover material Hence the grayish color of the material. If the end user is hesitant about using
the dehydrated feces on his or her fields, the possibility could be
to further store and compost the material before application as shown
on this picture here. Those two pictures here
show the excavation of humus fromfosa alternapits, after one year or more of storage. In this photo you can see human excreta
after thermophilic composting. Both humus and compost can be used
as soil amendments in gardening. For example, when planting a new tree. In the case of sludge
we have to distinguish between the application
of liquid and solid sludge. Liquid sludge can be, for example, the digestate from biogas reactors
as shown in this photo from Morocco. Solid sludge can originate
from unplanted drying beds, for instance. The characteristics of the sludge
and how it has been treated determine the necessary health precautions
and application strategies. As we have seen from the examples
presented in the last few minutes, improved soil quality and higher yields
are two clear benefits from the agricultural use
of excreta-derived fertilizers and soil conditioners. Besides that, the controlled application
can contribute to reducing the environmental degradation
through uncontrolled discharge and to closing the nutrient loop. Ideally, resource recovery
should be the economic driver of the sanitation chain,
but the market value of the different products
is quite low. Research is currently going on
in order to develop higher market value end products. WHO’s multi-barrier approach
helps to control exposure to pathogens and to minimize health risks
associated with the use of end products of a sanitation system. WHO guidelines should be consulted
for specific guidance. In the following module I will talk
about the use and disposal of treated effluent
and a few more products.

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