🚾 Solar energy can recover ammonia from wastewater and reduce climate emissions

• Researchers have developed a cheap method for recovering ammonia from wastewater using solar energy.
• The system can both purify wastewater and provide farmers with cheaper fertilizer.
• The economic analysis shows that the system can pay for itself in 3.5 years.

Large need for ammonia

About 240 million tons of ammonia are produced every year. Most of it is used to manufacture synthetic fertilizer that is necessary to feed the world's population. The production requires high temperatures and fossil fuels to convert nitrogen from the air into a form that crops can absorb.

When farmers use fertilizers, the excess often ends up in wastewater. This leads to the growth of toxic algae blooms. Existing treatment plants can recover ammonia, but the process is expensive and energy-intensive.

Simple solution with solar power

The researchers created a plastic sponge coated with a thin layer of titanium carbide, a black material that absorbs heat. On the sponge's surface, they attached alkaline compounds called amino groups.

The sponge floats in the wastewater inside a solar distillation plant. The amino groups remove hydrogen ions from ammonium ions in the water and convert them to ammonia. Heat from the sun evaporates both ammonia and water, which then condense and are collected.

Also produces hydrochloric acid

When the sponge becomes saturated with hydrogen ions, the researchers can focus sunlight on it to heat it up further. This triggers a reaction between the hydrogen ions and chloride ions in the wastewater. The reaction produces hydrochloric acid, another valuable chemical.

The process also resets the sponge so it can be used again to make ammonia.

Profitable system

An economic analysis shows that sales of the collected ammonia and hydrochloric acid can pay for the system's costs in just 3.5 years. The system requires no exotic materials to function.

So far, the method has only been tested at laboratory scale. The researchers see no major obstacles to scaling up the system to industrial level.

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