Deep abatement of low nitrate in oligotrophic surface water based on a sustained-release carbon source and aerobic denitrifying agent

Abstract

Oligotrophic surface water is characterized by low nitrogen content (mainly in nitrate-N form), low carbon content, and high levels of dissolved oxygen compared to mesotrophic and eutrophic surface water. Such waters are also slightly polluted and at risk of abnormal algae proliferation resulting from the low nitrogen levels. Thus, abatement of low nitrate-N levels ( ∼ 1.5 mg/L) is urgent, but also a massive challenge, especially when organic carbon is typically limited. In this study, a novel strategy for deep abatement of low nitrate in oligotrophic surface waters was proposed, mainly based on the use of an aerobic denitrifying agent. The aerobic denitrifying agent, termed PHB(AOB-7), was developed using an aerobic denitrifying bacterial strain, Pseudomonas sp. AOB-7, which attaches and grows on polyhydroxy butyrate (PHB) granules serving as a sustained-release carbon source. Two oligotrophic surface water samples, from the South-to-North Water Diversion Project and the urban stormwater storage project, were treated with PHB(AOB-7) in the laboratory. The results indicated that this aerobic denitrifying agent was fairly efficient in abatement of nitrate-N (<1.5 mg/L) in both South-to-North water and stormwater, in both conical flask and bioreactor experiments. Nitrate-N was reduced from ∼ 1.5 to ∼ 0.3 mg/L. Meanwhile, ammonia and nitrite were maintained at very low levels. All N-contents satisfy level II of the Environmental Quality Standards for Surface Water. This study shows the great potential of the addition of low-N-abatement technology based on aerobic denitrification and a sustained-release carbon source to surface water. • A novel strategy for deep abatement of low nitrate in surface water was proposed. • It was based on aerobic denitrifying strain and sustained-release C-source. • Oligotrophic surface water samples were treated efficiently with this strategy. • NO 3 - -N was reduced from ∼ 1.5 to ∼ 0.3 mg/L, accompanied by lower NH 4 + -N and NO 2 - -N.