AMMONIUM RECOVERY AND PLANT-BASED WATER PURIFICATION FROM NITROGEN-RICH WASTEWATER
The processing of nitrogen-rich wastewater with activated sludge water treatment is characterized by high energy and chemical needs, production of nitrous oxide (a.k.a. laughing gas, a strong greenhouse gas) and sludge.
AMREWAS alternatively demonstrates the stripper-scrubber combination for ammonia recovery followed by an aerated reed bed as further purification.
During the project, the ammoniacal nitrogen was recovered in the form of an ammonium nitrate solution (25%), which can be used by fertilizer factories or applied locally by farmers.
Using an aerated reed bed as post-treatment greatly reduces operational costs and sludge production. Energy consumption, follow-up efforts and maintenance of this system are also significantly lower.
The main project goal was the demonstration of the treatment of a nitrogen-rich wastewater, i.e. thin fraction of manure and/or digestate, where ammonia is recovered and a plant-based purification is applied. The project aimed at and achieved to:
• Reduce the operational and investment costs associated with the current state of the art of constructed wetlands, by first stripping out the ammoniacal nitrogen
• Research the possibilities with the effluent for water reuse in agriculture because of the remaining potassium salts
• Establish a purification technology to treat other types of wastewater with high ammoniacal nitrogen concentration, such as landfill leachate or black water from residential areas, based on a "nature-based solution"
Although the ammonium content of the stream to be treated varied, the stripping/scrubbing ammonium removal efficiency was fairly constant at around 30%. This efficiency was achieved without additional energy for heating or chemical dosing at an operating temperature of 20°C to minimise ecological and financial impact. It is estimated that the efficiency can be greatly increased, up to 95%, by adding chemicals and heat.
The aerated reed bed achieved good removals for total nitrogen and chemical oxygen demand.
• Removal efficiencies were greater than 90% for suspended solids, biodegradable contamination, ammonium nitrogen and phosphorus
• Nitrate concentrations increase with higher loads, indicating that an optimum must be sought between adding extra energy during stripping or taking up more surface area for the aerated reed beds
• Recirculation over the reed bed could help to lower the nitrate concentrations in the effluent to be able to meet the discharge criteria with smaller downstream flow fields