# A Preliminary Study on the Use of Xylit as Filter Material for Domestic Wastewater Treatment
## 4 Conclusions  
It should be noted that due to periodic leaching of biomass, it is recommended to use secondary settling tanks for biological deposits.  
The use of xylit for domestic wastewater (raw or pre-treated in a septic tank) treatment can be a promising solution taking into account both macro- and micropollutant removal. This material can be packed much more densely than was used in this study, which should increase its efficiency in the removal of wastewater quality indicators. Although the experiment (all stages) lasted 15 months and no xylit material clogging problems were observed, there is a need to verify the clogging process intensity (e.g., under technical conditions).  
Based on the results obtained, the following conclusions and recommendations can be proposed:  
* The average efficiencies of COD removal were over 70, 80, and 85% for preliminary stage, stage I, and stage II, respectively;
* The effectiveness of TSS removal was strongly differentiated in the preliminary stage and stage I: 42% and 70% during the preliminary stage and 88, 91, and 65% during stage I;
* The efficiency of ammonium nitrogen (NNH4) removal was very high at stage I: 97-99%, but relatively low at stage II: 36-49%;
* Average total phosphorus removal efficiencies were practically equal at stages I and II: 51-54% and 52-56%, respectively;
* The removal efficiency of wastewater quality indicators using both types of materials did not differ significantly;
* The investigated hydraulic load of filters enables their use in filed scale a relatively compact treatment system (less than 1.0 m\({}^{2}\) of surface area in plain view) for one homesetead (four-person family);
* The study demonstrated that xylit was a material highly effective in the removal of wastewater quality indicators, even during the initial period of its use (preliminary stage);
* Using xylit as a trickling filter material it is recommended to take care about uniform distribution of wastewater on the filter surface.  
There is a need for further research on xylit material under technical conditions (field scale) to determine basic applicable conditions, e.g., hydraulic and organic load or packing density.  
**Author Contributions:** Conceptualisation, M.S. and R.M.; methodology, M.S. and R.M.; validation M.S. and R.M.; formal analysis, M.S.; investigation, M.S. and R.M.; resources, M.S.; data curation, M.S. and T.N.; writing--original draft preparation, M.S. and T.N.; writing--review and editing, M.S. and R.M.; visualisation, M.S. and T.N; supervision, M.S.; project administration, M.S.; funding acquisition, M.S. and R.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received external funding: Project No. 005/RID/2018/19 under \"Wienkopolska Regional Initiative of Excellence in the area of life sciences of the Poznan University of Life Sciences\". The project was financed under the program of the Minister of Science and Education in 2019-2022.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data available on request.  
**Acknowledgments:** The authors thank [PERSON] and EKOTECH Company for the delivery of research material (xjlit) and the information related to it. The authors also thank [PERSON]--a laboratory technician at the Department of Water and Sanitary Engineering--for her help in laboratory measurements and the Amica S. A. company, for renting a washing machine.  
**Conflicts of Interest:** The authors declare no conflict of interest.