Factors Influencing Removal of Sewage Nitrogen Through Denitrification in Mangrove Soils

Abstract

Mangrove forests as a coastal ecosystem can remove N in sewage effluent through the denitrification in mangrove soils. This research was designed to evaluate effects of temperature, salinity, nitrate, and organic carbon (OC) on denitrification enzyme activity (DEA). The test was conducted using an acetylene inhibition method in controlled laboratory conditions. Results showed potential DEA was lowest in soil collected from the site with lowest amount of soil OC and total nitrogen. With increased soil temperature (15–25 °C), the DEA was enhanced by 2.5–5 times. Soil potential DEA was negatively correlated to salinity (0–60 psu). The potential DEA at the highest experimental salinity (60 psu) was still 3 times higher than the field DEA, implying that salinity has less effect on soil denitrification in the field. The potential DEA was stimulated by labile OC such as glucose and sucrose, but it was not affected by the addition of lactose, acetate and mannitol. Overall, this study showed that mangrove forest soils can reach maximum rate of treating NO3 − from sewage effluent if the inflow NO3 − concentration is < 3 mM. The treatment efficiency of NO3 − appears to vary, depending on availability of labile OC, soil redox, and temperature.