# A Preliminary Study on the Use of Xylit as Filter Material for Domestic Wastewater Treatment
## 1 Introduction  
Individual wastewater systems are common in many regions of Europe and some parts of the world (USA), due to lack of economic justification or sewerage systems; its building needs will develop. Septic tanks are in general devices used for preliminary wastewater treatment; however, they are prone to periodically increased concentrations of suspended solids in effluent, which may accelerate clogging processes. Clogging, it should be noted, can occur even after a few years [1]. In view of the disadvantages of septic tanks and aiming to prevent outflow from small wastewater treatment facilities from instability and exceeding recommended or required limits, there is a need to look for systems of better treatment, including nutrients, which can ensure longer life of existing soil infiltration systems. Some interesting and promising solutions are referred to in the literature. They utilise, e.g., a geotextile fabric filter [2], a modified up-flow septic tank, followed by an anaerobic baffled reactor [3] and a gradual chamber using a gravel bed as an effluent filter [4]. The authors are therefore of the opinion that there is a need to look for trickling filter filling materials that are cheap, highly effective in removing contaminants, and where possible, ones that have a low (negative) impact on the environment (carbon footprint). Such systems should be as cheap and simple as possible, especially in less developed or developing countries. The traditional trickling filter technology preceded by a septic tank or preliminary settled still seems to be a promising solution because of its simplicity and resistance to load and hydraulic overloading. In contrast, plastic carriers being used for trickling filter filling are relatively expensive and are often associated with negative side effects on the environment during their production, such as energy consumption and carbon footprint. Xylit (usually referred to as xyloid lignite) is a waste material (by-product) obtained from the mining of lignite (brown coal). Xylit is a type of lignite, sometimes referred to as fossil wood. The use of the term is justifiable because xylit frequently has an appearance similar to wood; some properties (and visual or physical features) of \"wood\" are altered [5]. The structure of carbonised wood fibres can be observed in this material of density around 400 kg/m\({}^{3}\). It is not used as fuel for heat generation due to very low heat content (even in a dried state) and due to the obstruction of the technological process of construction ceramics production [6]. Xylit is not well recognised as a filtering material for wastewater or greywater treatment and only a few studies have been carried out on this usage [5;7]; however, it is used as a biocarrier in some decentralised wastewater systems [8]. One of the most detailed research was conducted by [PERSON] [9]. This author highlighted several interesting and important features of xylit that can prove useful in polluted water treatment, such as (1) particle size of 20 mm, (2) solvent-accessible area (surface area approx. 2.5 m\({}^{2}\)/g), (3) pore volume of 0.01 cm\({}^{3}\)/g, (4) average pore size of about 16-17 nm, (5) overall negatively charged surfaces and molecular weight, and (6) positively correlated removal of micropollutants by xylit (with both apolar and polar surface area ratio, and pH value favouring bacteria growth). These all can be considered as features also useful for dissolved organic compound removal. For the purposes of the research experiment, xylit was crushed and sieved to obtain the relevant particle size of 2-4 mm [10]. Xylit proved to be a highly effective DOC removal material, it removed 52% DOC during the screening experiment and 89% DOC in the long-term experiment [9]. In that study, only granular activated carbon was better in DOC removal efficiency (average removal efficiency above 95%).