Efficiency analysis of two sequential biofiltration systems in Poland and Ethiopia - the pilot study

The study presents the results of comparative analysis of sequential biofiltration systems (SBS) efficiency in Poland (SSBS) and Ethiopia (ASBS) constructed in order to purify urban storm- and waste water and mixed agricultural water, and treated sewage from a Water Treatment Plant, respectively.The efficiency of SSBS (Poland) has been tested in different hydrological conditions prevailing during three storm events. The obtained results showed that the SSBS reduction efficiency reaches 95% for MM, 86% for TP and OM and 81% for TN. The results also demonstrated the enhanced reduction of analysed compounds in the diluted stage of storm events. The obtained data showed also that the SSBS purification rate is increasing with the flow up to 0.04 m3 s-1. Above this value the efficiency decreased and SSBS appears as the source of the analysed pollutants. For comparison, the effectiveness of ASBS (Ethiopia) which was examined when the sedimentation chamber was filled with sediments, showed the reduction of 8%, 78% and 65% for TP, OM and MM, respectively. Whereas TN was released from the system with a higher concentration in the ASBS outlet. The increased reduction in all the analysed compounds, amounted to 93% for TP, 73% for TN, 67% for MM and 36% for OM, was observed for samples collected after the sediment removal during proper maintenance of the system. The obtained results for both SBSs demonstrated the crucial role of monitoring and quantification of hydrological processes, especially transport of MM, OM and nutrients, for enhancement of the studied SBS efficiency.