# The Use of Chalcogenite as a Biosorption Bed in the Treatment of Groundwater
## 4 Discussion of Results  
The research study mainly focused on the removal of ammonium nitrogen in the nitrification process in the presence of iron and manganese. Therefore, iron and manganese sorption isotherms were not determined and the sorption capacity of the chalcogenite deposits was not calculated. The research enabled the observation of the effect of activation of the deposit with potassium manganese (VII) on the effectiveness of biotransformation of ammonium nitrogen and the activity of nitrifying bacteria. The activity of microorganisms was assessed by ammonium nitrogen removal efficiency. Chemical activation was necessary because non-activated chalcogenite removes iron but does not remove manganese. The creation of a catalytic MnO\({}_{2}\) coating enabled the simultaneous removal of iron, manganese, and ammonium nitrogen. The creation of a catalytic MnO\({}_{2}\) coating and can be carried out with 2 methods: self-activation of chalcogenite by filtration of water containing manganese (this is a 2-3 month long process), or by chemical activation continuously or periodically with potassium manganese (VII). The creation of a catalytic MnO\({}_{2}\) coating enabled the simultaneous removal of iron, manganese, and ammonium nitrogen. The manganese (II) dissolved in water is adsorbed on the surface of manganese dioxide, where in sequence according to theoretical reactions (1) or (2) it undergoes the oxidation of Mn (II) to Mn (III). \[\mathrm{Mn(OH)_{2}+MnO(OH)_{2}}\  
+++ ==WARNING: Truncated because of repetitions==
\[\mathrm{Mn_{3}O_{4}(OH)_{2}+1/2O_{2}+H_{2}O\ \ \ \ \ >\ \ 3 MnO(OH)_{2}} \tag{4}\]  
This results in the renewal of manganese dioxide on the surface of the material and the restoration of its initial state. In the described mechanism, manganese dioxide acts as an adsorbent and redox catalyst. According to the described mechanism, removal of iron from water occurs by oxidizing Fe (II) to Fe (III). Conventional methods of underground water conditioning, i.e., aeration and filtration through sand beds, appear to be ineffective in the case of high concentration of iron and manganese, accompanied by high levels of ammonia nitrogen and hydrogen sulfide [26]. Studies [29] have shown that groundwater with an excessive iron (\(>6.0\) g/m\({}^{3}\)), manganese, and ammonium nitrogen content should be treated with two-stage filtration. Quartz sand should be used in the first stage as it effectively stops the iron compounds present in the water. However, in order to remove manganese and ammonium nitrogen, chemically active masses should be used--Greensand obtains the best results. Compared to Greensand, clinoptilolite beds are characterized by comparable efficiency in removing iron compounds but obtain worse results in reducing the content of manganese and ammonium nitrogen. The Crystal-Right 100 zeolite mass met the high requirements for the removal of iron, manganese, and ammonium nitrogen; however, impurities were removed in the adsorption and ion exchange processes, resulting in frequent regenerations of the bed and shorter working cycles compared to chalcogenite [29]. On the other hand, the removal of ammonium ions is possible only in the nitrification process involving the biofilm produced on the surface of the mineral. The high concentration of nitrite nitrogen in the water after the biofilration process is a negative phenomenon due to the inhibition of the development of nitrifying bacteria on the biofilter filling [19]. In order to maintain the high activity of nitrifying microorganisms, commencing the second phase of nitrification as soon as possible and eliminating excessive accumulation of nitrite ions are both extremely important [33]. In the analyzed cases, the commencement of the second stage of nitrification occurred on days 51 (water I), 24 (water II), and 21 (water III) of the filter's operation, but higher increases in nitrate nitrogen were observed in the system without chemical activation (water III).