Nitrogen removal via nitrite from seawater contained sewage

Under the control of both pH and the concentration of free ammonia (FA), the nitrification-denitrification via nitrite pathway was accomplished in SBR to achieve enhanced biological nitrogen removal from seawater contained wastewater, which is used to flush toilet, under relatively high salinity. Several parameters including salinity, temperature, pH, and NH₄ ⁺-N loading rate were studied to evaluate their effects. The results indicate that at different salinity the nitrogen removal efficiency is relative to ammonia-nitrogen loading rate. The nitrogen removal efficiency reaches above 90% when the NH₄⁺-N loading does not exceed 0.15 kg NH₄⁺-N/kgMLSS d. With the salinity increasing, the ammonia-nitrogen loading rate should be lowered to obtain high removal efficiency. The evaluation of temperature effect shows that nitrogen removal efficiency is promoted twice when reaction temperature is elevated from 20 to 30°C. Moderately high pH in the range of 7.5-8.5 has advantage to achieve effective nitrification-denitrification via nitrite, the process of which is caused by the selective inhibition of free ammonia (FA).