Thermal Ammonia Stripping

Questions and Answers

Organics has developed specialised equipment for removing and recovery ammonia from different wastewater streams. Ammonia is not only a harmful environmental agent, but it is also a highly useful element that can be used in a variety of industrial situations, including to produce energy. Its recovery from wastewater therefore, is highly attractive not only from the point of view of pollution control, it can also contribute significantly towards offsetting operational costs; important factors in the drive towards the construction of a durable and self-sustaining circular economy.

The equipment has been developed and successfully operated over more than twenty years with several key criteria in mind that should significantly enhance wastewater treatment and management from a wide range of industrial processes. The focus has been the delivery of a high removal efficiency, low cost, low maintenance wastewater treatment solution that can be implemented for a variety of wastewater compositions ranging from landfill leachate to highly ammoniate urban wastewater.

The technology has been tried and tested under the most demanding of industrial situations and has proven to be effective across a broad spectrum of wastewaters with variable ammonia concentrations. 16 thermal ammonia recovery installations have been built and installed over a 20-year period and have amply proven the effectiveness of the technology. The first plant was built in 1998 and, after having been added to on several occasions, is still fully operational today. The smallest plant has a flow rate of 450m3 / day, while the largest installation is processing nearly 4,000m3 / day of highly ammoniated leachate from one of the world’s largest landfill sites. Removal efficiency rate is typically over 98%; this from wastewater with 6,700 mg/l influent and produces an effluent of <100mg/l. This is the norm for all plants currently in operation. Significant improvements in efficiency have enabled a dramatic reduction of the energy required to run the process and avoid the need for using fossil fuel.

The ammonia that is recovered from the process can be used to provide profitable secondary revenue streams such as ammonium salts, liquified ammonia gas and ammonium hydroxide, and there are currently studies underway to use recovered ammonia either directly as a fuel or as a vector for facilitating transport and ease of storage for hydrogen production.

Q&A – thermal ammonia removal and recovery

What methods have been used to treat ammonia in wastewater?
Commonly employed methods include the lowering of pH and temperature or to dilute it with water. It is also possible to add lignocellulosic biomass with a high C:N ratio to increase the C:N ratio of the substrate. Where, for various reasons, these approaches cannot be employed, there are also several technology variants that operators can deploy to control ammonia, including biological treatment, membranes, pH-driven processes and thermally driven air stripping; the latter being the system currently being developed.

What is thermal ammonia stripping? Thermal ammonia stripping uses heated air to drive the ammonium ion in water from the liquid phase to the gas phase. Through this process, high ammonia concentrations (10,000 mg/l or higher) can be reduced to levels below 100/mg/l in a single pass through the system.

We have strict discharge requirements for ammonia in wastewater (20mg/l or lower). What are the options to further treat effluent after thermal ammonia treatment? Sequencing Batch Reactors (SBR’s) can bring ammonia levels down to single digits in order to meet final discharge requirements.

Why should thermal ammonia stripping be considered over other traditional methods?
There are several benefits attributable to thermal stripping which indicate situations of optimum deployment:
• high removal rates may be achieved in a relatively small footprint;
• the process is particularly suited to high-strength ammoniated wastewater;
• no costs are incurred for chemical additions;
• greenhouse gas production is mitigated by avoiding nitrous oxide formation (N2O);
• compared to biological processes, relatively rapid startup can be achieved (1 or 2 hours);
• there is no risk of biology failure;
• substantial savings may be available from avoidance of carbon-source costs;
• there is no sludge formation; and
• the system is relatively easy to operate compared to biological processes.

There are many methods of ammonia treatment. How and why was this particular technology developed by Organics?
In 1997 Organics worked in cooperation with Suez in Hong Kong to develop a method of ammonia removal that was more cost-effective than their previous method of pH driven air stripping. Chemical dosing proved very costly at ammonia concentrations of 6,500 mg/l. Until recently, landfills in Hong Kong had excessive amounts of available landfill gas due to the fact that electricity production to the grid was not allowed at the time. This excess gas provided a valuable resource to provide the heat for the thermal ammonia stripper. Ammoniated air from the process is driven to a thermal oxidizer for the destruction of ammonia.

Since 1998 16 ammonia strippers have been built for our clients, including Suez, Veolia and other companies whose industrial focus is waste, as well as wastewater management. Over time the efficiency has improved significantly and has provided options for using other sources of heat (cogeneration, steam) for providing process energy.

Ammonia recovery from wastewater has been gaining impetus as a profitable and viable option for augmenting a sustainable, circular economy within the waste sector. Current developments of using green ammonia as a source of power generation, either directly as a power source or for producing hydrogen, are also gaining attention.

What are the optimum ammonia concentrations for implementing this system? The system becomes an attractive option for implementation at 1,000 mg/l. As the ammonia concentration rises it becomes an increasingly cost-effective treatment method. Ammonia levels of 10,000 mg/l or higher can effectively be treated down to <100 mg/l.

What inputs are needed to power the system? A primary fuel source such as biogas is an ideal fuel to power the system. Other alternative heat sources that can be used to power the system are steam or heat recovered from gas engines.

Can the system handle a high solids content? The system ideally operates with total suspended solids (TSS) content under 500 mg/l (0.05%), although factors such as calcium, magnesium, iron and manganese concentrations also need to be considered to accurately predict efficiency. Generally, 1% TSS can be dealt with by adding a pretreatment system such as a settling tank before entry of the influent to the system.

What is the range of sizes offered? The system can cope with a widely variable flow rate, from 100 – 4,500 m3/day. As it is modular, additions to the system can be made to accommodate most flow rates.

If a utility is recovering and selling their biogas, what other alternatives are there for heating the system? Other alternative heat sources include heat recovered from gas engines and excess heat from site load such as steam.

How would process upsets affect their ammonia concentrations? For example, if a utility was relying on this process to meet their ammonia concentration limits, is there any redundancy in this process or would process failure result in a permit violation? A duty-standby configuration can be provided to avoid interruption in the treatment process. Generally, the lowest achievable level is 100 mg/l for our system. A further process, such as an SBR, may be needed to reach discharge limits below 100 mg/l, depending on local regulations.

Can ammonia be recovered and what are the uses of ammonia? Ammonia can be recovered in 3 forms:

  • Ammonium hydroxide. Ammonium hydroxide is used as a cleaning agent and sanitizer in many household and industrial cleaners. Ammonium hydroxide is also used in the manufacture of products such as fertilizer, plastic, rayon and rubber.
  • Anhydrous ammonia. Anhydrous ammonia can be used to produce site power with a fuel cell.
  • Ammonium salt (typically ammonium sulphate). The primary use of ammonium sulphate is as a fertilizer for alkaline soils. Ammonium ions are released in the soil, thus lowering the pH balance and contributing essential nitrogen for plant growth.

Why hasn’t this technology been implemented outside of Hong Kong? Given the original heat requirement of the system and the abnormally high ammonia levels in leachate in Hong Kong, this was an ideal system for this location. Due to improvements in efficiency over the years, it has become an attractive option outside of Hong Kong. Ammonia levels in leachate throughout the world have become noticeably higher in some regions. This has led to an interest in expanding implementation to new areas. Additionally, resource recovery and the circular economy has become a hot topic throughout the world in recent years. This has generated a need to explore cost-effective ways of recovering these resources. Thermal ammonia stripping presents an attractive case for this type of resource recovery.

Explain Green Ammonia and its possible future in power production. It has been estimated that the combined global emissions of ammonia are to the order of 800,000 tonnes per day. This includes from humans, crops, natural sources, biomass burning, livestock and fertilisers. Of this total around 350,000 tonnes per day comes from human activity and livestock. If this ammonia could be harnessed and used as a fuel for a direct ammonia fuel cell, it would be possible to produce 39 Gigawatts of electricity, some 1.3 times the power requirement of Australia.

Clearly, it would not be possible to collect all of this ammonia in one place. A direct ammonia fuel cell power plant of this capacity is also unachievable at present. However, the figures do demonstrate that ammonia can produce meaningful quantities of energy where it can be found at concentration. One site in Hong Kong, for example, removes and disposes of 17 tonnes per day of ammonia, which would be enough to produce 1.8 MW of electricity

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