One. A review of ammonia nitrogen wastewater treatment
Ammonia nitrogen has a high oxygen consumption, it is toxic to aquatic organisms, and can stimulate its entropy change. The water body contains a large amount of ammonia nitrogen, which makes the water body produce eutrophication effects, stimulate and accelerate the growth of aquatic plants, such as a large number of seaweeds and aquatic plants, which leads to the imbalance of the water body ’s ecological balance and the deterioration of water quality. The state ’s control of ammonia nitrogen emission indicators is extremely Strict, so it also poses higher challenges for the application of ammonia nitrogen treatment technology.
At present, the ammonia nitrogen treatment method is divided into two categories: one is the physicochemical method, including the stripping method, the MAP precipitation method, the membrane method, the inflection point chlorine method and the ion exchange method; the second type is the biological nitrogen removal method, including nitrification and nitrosation / Denitrification process. For high-concentration ammonia nitrogen wastewater, air stripping method, steam stripping method, and MAP precipitation method can be generally used for pretreatment to recover ammonia products to compensate operating costs; for low-concentration ammonia nitrogen wastewater, it is difficult to recover ammonia products to compensate Operating costs generally include biological denitrification, ion exchange and advanced oxidation.
The composition of ammonia nitrogen wastewater is complex. The salt, COD, and various heavy metals in different wastewaters are cross-combined, and contain high, medium, and low concentrations of COD and various heavy metals. Most of the ammonia nitrogen in wastewater is composed of compound molecular ammonia (such as ammonia chloride). It exists in a state of maintaining equilibrium with ammonia ions (NH4 +) and free ammonia (NH3). In the above-mentioned several methods, it is technically necessary to convert the combined ammonia into free ammonia before disposal. The key is to mix high-, medium-, and low-concentration salts, COD, and various heavy metals from the source of ammonia nitrogen wastewater. The sequence of the salt, COD, and heavy metals used in the treatment process and the combination of technology modules become complicated. In order to make the program designed in terms of operational reliability, process investment, and operating costs for processing 1 kg of ammonia nitrogen, the high investment and operating costs also make it difficult to achieve a stable discharge of ammonia nitrogen wastewater. Therefore, the treatment of mixed ammonia nitrogen wastewater has become a problem.
Yilin introduced Japanese technology and successfully developed a three-dimensional electrolytic treatment of ammonia nitrogen wastewater equipment (hereinafter referred to as "ammonia nitrogen treatment equipment"), which has a significant effect on high, medium and low concentration ammonia nitrogen wastewater treatment.
two. Discussion on the principle of ammonia nitrogen treatment equipment for treating ammonia nitrogen wastewater
The three-dimensional electrode method is a technological improvement in the application of the original electrochemical treatment method. The three-dimensional electrode is also called a ternary electrode. It is a new type of electrochemical reactor. It is a method of filling granular electrode materials between traditional two-dimensional electrolytic cell electrodes and An electrochemical reaction occurs on the surface of the material. Under the action of the electric field, the granular electrode material generates a microelectrode pool, which shortens the mass transfer distance between the reactants and the electrode. The granular electrode provides a larger specific surface area and active sites for pollutants and active radicals.
The ammonia nitrogen removal equipment combines the two mechanisms of direct oxidation and indirect oxidation in the electrochemical method to achieve the purpose of reducing ammonia nitrogen in wastewater.
Direct oxidation: ammonia nitrogen is adsorbed on the anode surface and is directly oxidized to generate nitrogen. At the same time, the oxygen evolution reaction of the anode generates oxygen, and the reaction on the surface of the granular electrode generates • OH radicals, ammonia nitrogen oxides and organic substances.
Indirect oxidation: • OH radicals are reduced to H2O2 after cathodic reduction. According to the theory of inflection point chlorine addition, in the presence of high-concentration chloride ions in the system, • OH radicals react with chlorides in the solution to form active chlorine, which strengthens indirect oxidation. Electrochemical reaction of chloride ions generates strong oxidant hypochlorous acid (oxygen acid of chlorine element, chemical formula is HClO). After hypochlorous acid completely reacts with ammonia, it will generate an equal amount of chloride ions. In this reaction, chloride ions can be regarded In the catalyst, ammonia nitrogen undergoes indirect oxidation. The higher the chloride ion concentration, the higher the active chlorine generation rate and the faster the ammonia nitrogen degradation rate.