Excessive nitrogen discharge into natural water bodies due to rapid industrial and agricultural development has led to widespread eutrophication, posing severe threats to both human and ecological health. The leaching of nitrate-nitrogen (NO3−–N) is considered the most essential nitrogen loss pathway [4,5]. Nitrate fertilizers have been extensively used in agriculture since nitrogen is primarily absorbed in the form of nitrate ions, which can migrate to the surface and groundwater, thereby contaminating water resources. This situation could be worse owing to the inappropriate treatment of wastewater. For example, the concentration of nitrate in the groundwater of Yantai, China, was 17.80 mg·L−1, surpassing the World Health Organization’s (WHO) drinking water limit of 10 mg·L−1. Therefore, the removal of NO3−–N has become a critical concern in water treatment strategies.

NO3−–N removal is a challenging task as nitrate ions exhibit strong stability and high solubility in water. Currently, various methods are employed for removing nitrate ions from water, including physiochemical methods, biological technologies, membrane separation, and adsorption methods. Among these, the adsorption method stands out as one of the most widely used methods because of its remarkable efficiency, cost-effectiveness, and high capacity. In this context, biochar, produced through biomass pyrolysis, has received considerable attention as an effective adsorbent for treating pollutants, including nitrates. Its appeal lies in its straightforward production and operation, renewable nature, sustainability, affordability, eco-friendliness, high removal efficiency, and the abundance of surface functional groups that facilitate easy functionalization. Moreover, biochar can be derived from a variety of materials, such as agricultural waste, garden waste, and animal waste sources. Garden waste, a biodegradable byproduct resulting from the natural withering and artificial pruning of garden plants, such as grass clippings, leaves, branches, wood debris, and residual flowers, has become one of the main components of solid waste in cities. In fact, the dry weight of garden waste in Beijing, China, reaches an impressive 3 million tons per year [20], providing ample raw material for biochar production. Utilizing garden waste for biochar production not only mitigates the drawbacks associated with traditional disposal methods like incineration, landfill, and biodegradation but also offers advantages, such as minimal environmental pollution, swift reaction rates, and versatile applications. Additionally, garden waste exhibits low levels of harmful components, primarily comprising elements like C, O, P, N, K, H, Na, Mg, and Ca. Therefore, the application of garden waste biochar in NO3−–N adsorption holds significant promise for both wastewater treatment and garden waste management.

The application potential of biochar in contaminant removal is governed by its physical and chemical characteristics, including porosity, specific surface area, and volume, as well as the abundance of functional groups on its surface. These traits are highly influenced by factors such as feedstock, pyrolysis temperature, residence time, and heating rate [15,23,24,25]. Among these factors, pyrolysis temperature has a particularly significant influence on the yield and properties of biochar. Studies have shown that high-temperature biochars can effectively remove cations from aqueous solutions and water.

Osama Bahnas , Thanks for your answer, but my question is whether its recommended to use biomass pyrolysed under a nitrogen atmosphere for the removal of nitrate from wastewater?

Dear Ababo Workineh ,

There is no need to add organic carbon such as pyrolysed biomass (which contains recalcitrants pollutants) to remove nitrate from wastewater.

Since 30 years we remove up to 99% of all nitrogen (organic, ammonia, nitrite and nitrate) from wastewater using our advanced activated sludge process which includes simultaneous ammonia and nitrite/nitrate (NOx) removal as shown on https://modelengineering.eu/circulate_water .