Ala Kirjanova, Mindaugas Rimeika, Regimantas Dauknys

Pilot-scale trials of stone wool substrate media filters as a potential technology for tertiary domestic wastewater treatment

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Abstract

The aim of the present study was to investigate the application of trickling filters with stone wool medium for the tertiary on-site wastewater treatment. The experiment with three filters (0.5 m in diameter and with 1.0 m, 1.5 m and 2.0 m medium height) feeding three different flow rates (0.25 m3/d, 0.5 m3/d and 0.75 m3/d) of treated wastewater was carried out over a period of 430 days and at influent wastewater temperature of 1.9–23.2 ºC. Depending on a filter height and a flow rate, mean 7-day biochemical oxygen demand (BOD7) and mean suspended solids (SS) removal efficiencies fluctuated from 60 to 85 % and from 50 to 70 % respectively. The removal efficiencies increased when increasing SS and BOD7 influent concentrations, however no dependence on volumetric loading (up to 242 g SS/m3 /d and 228 g BOD7/m3 /d) was observed. The main nitrogen transformation/removal processes were nitrification and the removal of organic nitrogen (N-org). Due to low temperature, full nitrification was first achieved on day 177 and from that point was dependent on volumetric ammonium loading, but did not depend on volumetric organic loading in the range of 5–228 g BOD7/m3/d and wastewater temperature in the range of 5.6–23.2 °C. Mean N-org removal efficiency ranged from approximately 30 to 70 % and was positively dependent on N-org influent concentration. Total phosphorus removal was unstable in all the filters with its mean values of – 18–13 % depending on a filter height and a flow rate.

Keywords:Trickling filter; tertiary treatment; filter medium; stone wool; wastewater.