# The Use of Chalcogenite as a Biosorption Bed in the Treatment of Groundwater
## 1 Introduction  
Groundwaters are the main source of drinking water around the world [1; 2]. In many cases, groundwater is characterized by an increased content of iron, manganese, and ammonium nitrogen compounds and their presence may contribute to deterioration of the organoleptic quality of the water and discoloration of sanitary facilities, as well as the formation of deposits in the water pipes [1; 3; 4; 5; 6]. Although iron and manganese are necessary for the proper functioning of the human body, their consumption in excessive amounts, in particular manganese, may be the cause of chronic food poisoning, pulmonary embolism, bronchitis, impotence, nerve damage, or Parkinson's disease [7; 8]. In addition, the presence of ammonia increases the consumption of chlorine and hence the numbers of chloramines formed [9]. Groundwater quality mainly depends on natural factors, including aquifer lithology, the quality of water recharge, and groundwater rock interactions, as well as anthropogenic factors, e.g., agriculture, industry, the exploitation of water resources, and urban development [10]. In water intended for consumption, maximum concentrations of iron, manganese, and ammonium nitrogen should not exceed 0.2, 0.05, and 0.5 g/m3, respectively [11]. However, over 50% of users of groundwater intakes are exposed to an excessive content of iron and manganese compounds. It is rare that underground water is suitable for direct use for water supply purposes, yet many treatment stations face the need to intensify the water treatment process and modernize their equipment [12; 13; 14]. Groundwater treatment and purification technologies based on biological methods are popular in European countries and most often include combined removal of iron and manganese, and sometimes also nitrification of ammonium nitrogen by natural or synthetic filtration deposits [10; 15; 16]. In classic iron removal, the abiotic process dominates the biological one [17]. It consists of water aeration, homogeneous oxidation of divalent iron with oxygen dissolved in water, and mechanical separation of precipitated iron (III) hydroxide, which can be assisted by heterogeneous oxidation by catalytic interaction of a ferric coating deposited on grains of filtration material [16]. The biological oxidation plays a role in iron removal mainly in conditions that are unfavorable to the physical and chemical process when they have low pH and redox potential and very low oxygen content in water [18]. Manganese removal is a result of a chemical process of heterogeneous catalysis, which involves fluid-formed deposits of manganese dioxide, and biological oxidation [15]. The operation of biologically active filters consists of using the metabolic activity of microorganisms for strictly defined transformations, giving the assumed technological effect. An integral element of underground water purification treatment technology, based on biological processes, is the carrier, which plays an important role in them. Depending on the structure and properties of the carrier, it may additionally be adsorbed or ion exchanged, but it may also supply nutrients and buffer the biochemical reaction environment, and the remaining parameters related to the type of carrier that translate into colonization with microorganisms are granulation, surface area, porosity, and ability to produce stable connections between the surface of the carrier and microflora [19; 20; 21]. In biosorption beds the carrier--the biofilter filler--plays a special role. Depending on its characteristics, it may serve as an adsorbent, molecular sieve, ion exchanger, and substance for nutrition and buffering of the biochemical reaction environment. The role of microorganisms that cover the bed is also double:  
1. Performance of biodecomposition of chemical compounds [20];
2. Cause for biodecomposition of the support material [22].