Summary of the Advantages and Disadvantages of Various Ammonia Removal and Denitrification Processes!

In the past 20 years, considerable research has been conducted on the treatment of ammonia nitrogen in wastewater. The research covers various treatment processes using biological and physicochemical methods. Currently, the most practical and widely used domestic technologies for ammonia nitrogen treatment are: conventional biological denitrification, ammonia stripping, breakpoint chlorination, chemical precipitation, ion exchange, membrane methods, and so on.

One. Various Nitrogen Removal Processes

1. Traditional Biological Nitrogen

RemovalTraditional biological nitrogen removal technology achieves nitrogen removal through ammonification, nitrification, denitrification, and assimilation. The process is mature and achieves good nitrogen removal performance. However, it has drawbacks such as long process flow, large footprint, often requiring external carbon sources, high energy consumption, and high costs.

2. Ammonia Stripping

This includes steam stripping and air stripping. Its mechanism involves adjusting the wastewater to a basic pH and then passing air or steam through a stripping tower, where free ammonia in the wastewater is volatilized through gas-liquid contact. This method has a simple process, stable effect, strong applicability, and relatively low investment. However, it consumes a lot of energy and produces secondary pollution.

NH4+ OH-= NH3   +H2O

OH- is generally provided by NaOH. The molecular weight of NaOH is 40; without considering other factors, theoretically, the amount of NaOH needed to remove 1 kg of NH4 is 2.86 kg. Based on industrial-grade NaOH at 2.0 yuan/kg, the chemical cost to remove 1 kg of NH4 is 5.72 yuan (assuming the ammonia gas is not absorbed). The energy consumption for stripping is about 4 kWh per ton.

3. Ion ExchangeIon

The ion exchange method actually utilizes the exchangeable ions on insoluble ionic compounds (ion exchangers) to react with other similar ions (NH4) in the solution, thereby firmly adsorbing NH4 in the wastewater onto the surface of the ion exchanger, achieving the purpose of removing ammonia nitrogen. Although the ion exchange method has achieved certain results in removing ammonia nitrogen from wastewater, it requires a large amount of resin and is difficult to regenerate, leading to high operating costs and secondary pollution.

4. Membrane Filtration

This method removes ammonia nitrogen by utilizing the selective permeability of membranes. This method is easy to operate, achieves a high recovery rate of ammonia nitrogen, and causes no secondary pollution. However, it requires a high investment cost and places high demands on the water quality of the wastewater, especially salinity.

5. Breakpoint Chlorination Method

The breakpoint chlorination method is a chemical denitrification process in which an excess of chlorine or sodium hypochlorite is added to oxidize ammonia nitrogen in wastewater into nitrogen gas. This method can achieve a treatment efficiency of 90% to 100%, with stable results that are not affected by water temperature. However, it has high operating costs, and by-products such as chloramines and chlorinated organic compounds can cause secondary pollution.

6. Magnesium ammonium phosphate precipitation method (struvite method)

Adding Mg²⁺ and PO₄³⁻ to ammonia-containing wastewater results in the formation of MgNH₄PO₄·6H₂O (abbreviated as MAP) precipitate through their reaction. This method features a simple process, easy operation, fast reaction, few influencing factors, and can efficiently recover ammonia for wastewater resource utilization. The main limitation of this method is the relatively large amount of precipitating agents required, which leads to higher treatment costs, and the applications of the MAP precipitate still need further development and promotion.

Mg₂₊+ PO4_3-+ NH₄₊= MgNH₄PO₄

Mg_²⁺ is generally provided by MgCl₂, with a molecular weight of 95; PO₄³⁻ is generally provided by NaH₂PO₄, with a molecular weight of 145. Without considering other factors, theoretically, to remove 1 kg of NH₄⁺, 7.6 kg of MgCl₂ and 10.36 kg of NaH₂PO₄ are required. Based on industrial-grade MgCl₂ priced at 2.5 yuan/kg and industrial-grade NaH₂PO₄ at 3.0 yuan/kg, the reagent cost for removing 1 kg of NH₄⁺ is 50 yuan. This produces 18 kg of magnesium ammonium phosphate precipitate (without considering crystal water).

Two. Advantages and Disadvantages of Various Ammonia Removal Processes