Denitrification of groundwater using PHBV blends in packed bed reactors and the microbial diversity

• The bioreactors packed with biodegradable polymers were used to remove nitrate.
• PHBV, PHBV blend with starch and bamboo powder served as carbon source and carrier.
• PHBV/BP blend is economically attractive carbon source with good denitrification.
• Proteobacteria and Firmicus are dominant phyla in all biofilm samples.
• Clostridium was the most dominant genus for degrading biopolymers.

In the present study, three kinds of biopolymers, PHBV, PHBV/starch and PHBV/bamboo powder (BP) blends were used as carbon source and biofilm carriers for denitrification in packed bed reactors to remove nitrate from groundwater. Results showed that a fast start-up was obtained in bioreactors filled with both PHBV/Starch and PHBV/BP blends without external inocula and it took more than 3 month for PHBV reactor to reach the same loading rate. The PHBV/BP packed reactor exhibited a better nitrate removal efficiency (87.4 ± 7.0%) and less adverse effects in nitrite accumulation and DOC release (below 0.5 mg NO2N L−1 and 10.5 mg DOC L−1 in the effluent) during stable operation. Pyrosequencing analysis demonstrated that bacteria belonging to genus Clostridium in phylum Firmicus, which play the primary role in degrading the biopolymers, are the most dominant (33–15% of the sequences). The predominant species in all samples is related to Clostridium crotonatovorans. All the identified 11 genera of denitrifying bacteria affiliated with phylum Proteobacteria and constituted 30–55% in the representative sequences. The PHBV/BP blend is economically attractive carbon source with good denitrification performance.