Denitrification of groundwater using a biodegradable polymer as a carbon source: long-term performance and microbial diversity

Abstract

Nitrate pollution in groundwater is a worldwide problem. This paper reports on the denitrifying performance of using the biodegradable polymer polybutylene succinate (PBS) as a biofilm medium and carbon source to remove nitrate from groundwater via a packed bed bioreactor which was operated continuously for nearly 2 years. Results showed that the effluent nitrate concentration reached 3.3–8.8 mg L⁻¹ and 88–97% of nitrate removal was achieved. The denitrification rate range was 0.25–0.35 g N per L per d at 20–29 °C and decreased to 0.12 g N per L per d at 10–18 °C. According to microelectrode analysis, the nitrate consumption rate (1069 ± 103 μmol cm⁻¹ h⁻¹) was much higher than the ammonium production rate (74 ± 7 μmol cm⁻¹ h⁻¹), which proved that denitrification plays the major role in the system. A low level of DOC (1.7 ± 0.6 mg L⁻¹) and ammonium (0.5 ± 0.3 mg L⁻¹) was observed in the effluent, which was beneficial for practical application. The consumption rate of PBS was 2.75 ± 0.72 g PBS/g NO₃–N_removed. In the attached biofilm, Proteobacteria, Betaproteobacteria, Burkholderiales and Comamonadaceae were the major phyla (75.6%), classes (59.8%), orders (42.3%) and families (42.2%) in each level. In the top 20 genera accounting for 25% of total sequences, 9 genera including Simplicispira, Comamonadaceae, Hydrogenophaga and Rhodocyclaceae were affiliated with denitrifying groups with an abundance of 16%, whereas the bacteria belonging to the other 11 genera including Veillonellaceae, Propionivibrio and Bdellovibrio were reported to have the function of degradation and acidification of organic substance and might serve for degrading PBS in the system. The PBS solid-phase denitrification is promising for removing nitrate from groundwater.