Using the Aqueous Byproduct of the Hydrothermal Carbonization of Cow Manure As a Fertilizer

Cow manure is often used as a fertilizer for plants; however, recently cow manure is being
looked into as an energy source. The hydrothermal carbonization (HTC) of cow manure is a
thermochemical process that converts organic matter into hydrocarbon fuels. The products of
this process include hydrochar, a carbon-rich solid fuel, and a hydrothermal aqueous product
(HAP). Converting the manure to an energy source leaves farmers without an important
fertilizing source, but HAP retains many of the necessary nutrients needed for fertilization.

These experiments looked into the effectiveness of HAP as a fertilizer for wheat and barley.
Twelve wheat plants were grown in soil. Four of each plant were treated with 5% concentrated
HAP, four other plants were treated with a fertilizer called Miracle Gro at a concentration to
match the nitrogen levels in the 5% HAP solution, and the last four plants were treated with
water. Five days a week the plants were given their treatment and the height of the longest stem
of each plant was measured and recorded. The same experiment was carried out while growing
the twelve wheat and twelve barley plants in sand rather than soil to remove any extra nutrients
that were not a part of the treatment. A third experiment was conducted similarly to the second
one, but a culture of Chlorella vulgaris was grown in and later removed from a solution of 5%
HAP to create a Chlorella vulgaris effluent that plants were treated with instead of directly 5%
HAP. When grown in dirt, the wheat plants grew the highest in water. When grown in sand, the
wheat and barley plants grew the highest in the Miracle Gro solution, but the 5% HAP and
Chlorella vulgaris were still an effective fertilizer compared to the water treatment. The HTC of
manure does not completely eliminate a source of fertilizer from farmers as HAP has potential to
be fertilizer for crops.