Phosphorus removal from agricultural runoff by enhanced denitrifying woodchip bioreactors

Phosphorus removal from agricultural runoff by enhanced denitrifying woodchip bioreactors

en

The water pollution caused by nutrients has become a problem, especially in agricultural areas. Nitrogen (N) and phosphorus (P) can cause the eutrophication of surface waters, and problems with their use as drinking water sources. One of the possible solutions is to employ denitrifying bioreactors, which are used for the reduction of high nitrate concentrations in shallow groundwaters. Our research was focused on the enhancement of these bioreactors with steel byproducts. These materials release Fe, which causes the precipitation and adsorption of P. The contribution presents the results of laboratory tests with 4 denitrifying columns. The columns were filled with the same material (poplar woodchips) and two of them were enhanced by the addition of steel turnings upstream of the wood medium. Inlet concentrations were approx. 20 mg/L of NO3-N and 1 mg/L of TP (total phosphorus). The bioreactors were operated for 9 weeks and the physicochemical parameters at the inlet and outlet were determined weekly – temperature, pH, oxidation-reduction potential (ORP), NO3-N, TP, and Fe. According to the results, the addition of steel has no noticeable impact on the pH, ORP and NO3-N at the outlet: there was no significant difference between the standard columns and the columns enhanced by steel turnings. The NO3-N removal initially increased with the time of column operation, stabilizing after 3 weeks of operation. In the 9th week, the outlet NO3-N concentration decreased to 1.3 mg/L; NO3-N removal efficiency was 94 % on average. In the first 5 weeks, the outlet TP concentrations increased due to woodchip leaching. The enhanced columns achieved higher P removal with a TP removal efficiency in the 9th week of 58 %. In the case of the columns with woodchips only, no TP removal was observed. The concentrations of Fe leached from the columns enhanced with steel turnings had a decreasing tendency, dropping from 2.4 to 0.4 mg/L.

The water pollution caused by nutrients has become a problem, especially in agricultural areas. Nitrogen (N) and phosphorus (P) can cause the eutrophication of surface waters, and problems with their use as drinking water sources. One of the possible solutions is to employ denitrifying bioreactors, which are used for the reduction of high nitrate concentrations in shallow groundwaters. Our research was focused on the enhancement of these bioreactors with steel byproducts. These materials release Fe, which causes the precipitation and adsorption of P. The contribution presents the results of laboratory tests with 4 denitrifying columns. The columns were filled with the same material (poplar woodchips) and two of them were enhanced by the addition of steel turnings upstream of the wood medium. Inlet concentrations were approx. 20 mg/L of NO3-N and 1 mg/L of TP (total phosphorus). The bioreactors were operated for 9 weeks and the physicochemical parameters at the inlet and outlet were determined weekly – temperature, pH, oxidation-reduction potential (ORP), NO3-N, TP, and Fe. According to the results, the addition of steel has no noticeable impact on the pH, ORP and NO3-N at the outlet: there was no significant difference between the standard columns and the columns enhanced by steel turnings. The NO3-N removal initially increased with the time of column operation, stabilizing after 3 weeks of operation. In the 9th week, the outlet NO3-N concentration decreased to 1.3 mg/L; NO3-N removal efficiency was 94 % on average. In the first 5 weeks, the outlet TP concentrations increased due to woodchip leaching. The enhanced columns achieved higher P removal with a TP removal efficiency in the 9th week of 58 %. In the case of the columns with woodchips only, no TP removal was observed. The concentrations of Fe leached from the columns enhanced with steel turnings had a decreasing tendency, dropping from 2.4 to 0.4 mg/L.