Recovery of partial nitrification in a down-flow hanging sponge reactor by salt shock loading

ABSTRACT

Partial nitrification of ammonium-containing artificial wastewater was achieved using a down-flow hanging sponge (DHS) reactor with a hydraulic retention time (HRT) of 2 h by adjusting the influent salinity to 25 g Cl L⁻¹ with NaCl. The effect of HRT on partial nitrification was examined by varying HRT from 1 to 4 h. Extending HRT from 2 to 4 h had the effect of decreasing nitrite production and increasing nitrates. Since partial nitrification was not completely recovered after returning the HRT to 2 h, we examined the effect of salt shock loading on the recovery of partial nitrification. Salt shock loading with 150 gCl L⁻¹ for 72 h resulted in the fraction of NO₂-N to total inorganic nitrogen in the effluent reaching 83.0% as much as 83 days after returning the salinity to the original level. Thus, despite the time required for the restoration of partial nitrification, the effectiveness of salt shock loading to achieve this aim was verified.

KEYWORDS:

• DHS
• partial nitrification
• recovery
• salinity
• salt shock loading

Funding

This study was supported in part by research grants from the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Japan Society for the Promotion of Science (JSPS) and the Science and Technology Research Partnership for Sustainable Development (SATREPS).