The Emerald Option

The Emerald Option

Ammonia, an Abundant Natural Element

Within the solar system, there is an abundance of ammonia spread throughout the planets. Astrogeologists estimate there are approximately 220 million km2 of sub-surface ammonia-water oceans on 14 solar system moons as well as the planet Pluto. One ocean on Titan, the largest moon of Saturn, is estimated to have a surface area of 80 million km2. On Earth, oceans cover 361 million km2, but none are composed of ammonia.

Sources of Ammonia on Earth

On Earth, there are no ammonia oceans, but copious quantities are produced each year. It is estimated that the total non-manufactured production of ammonia is some 290 million tonnes per year (tpy). Of this total, approximately 130 tpy derive from humans and livestock. Non-industrial ammonia production is augmented by the Haber-Bosch process which is the source of a further 200 million tpy.

One of the primary naturally occurring sources of ammonia originates from the decay of organic matter. Ammonia forms during the degradation of amino acids within acidogenesis. It also forms part of the excreta cycle of humans and animals as the kidneys secrete ammonia to neutralize excess acid. Consequently, it is a commonly encountered water pollutant.

To many wastewater engineers, ammonia in water represents a problem that costs money to fix. If a carbon source is required to treat the ammonia, as food for anoxic bacteria, annual costs can run into the millions.

Ammonia is also recognized as being toxic to fish. Lethal concentrations range from 2.5 to 25 mg/I. Further, as ammonia is biologically oxidized to nitrate, it exerts an oxygen demand on the receiving water. This can reduce the oxygen in the water to a point where aquatic life forms cannot survive. Ammonia also acts as a fertilizer causing the profuse growth of stringy bacteria and/or fungi and generally disrupting the natural environment.

In this article, Dr. Robert Eden discusses the latest innovations in the technology for the separation of ammonia from wastewater and landfill leachate.

Ammonia from Wastewater

Ammonia from Wastewater

Wastewater management can be complicated. A principal reason is that excessive ammonia concentration in wastewater can cause issues with odor and the ability to clean and reuse the water. If it is not removed before release to the environment, it is highly toxic for aquatic life.

Ammonia is increasingly recognized as a compound that, whilst being highly polluting if released to the environment untreated, can also be recovered and thus represent a viable commercial resource. Using waste heat as the basis for ammonia removal and recovery meets the combined objectives of ensuring a long-term sustainable two-pronged solution to the challenges of ammonia pollution and the recycling of waste material; this latter is one of the defining tenets of the circular economy.

The principle of using heat to separate ammonia from landfill leachate is being successfully applied in Hong Kong. On this large landfill site, leachate is highly ammoniated, containing up to 8000 mg/l. As the site produces so much landfill gas, this is used to heat the leachate before separation in the stripping towers. From there, the ammonia concentration is reduced to <150mg/l and is treated by the adjacent sequence batch reactors before release outside the boundary of the landfill site. The site produces up to 9 tons of ammonia a day.