Assessment of low concentration wastewater treatment operations with dewatered alum sludge-based sequencing batch constructed wetland system.

Competition of volatile fatty acids between anoxic denitrification and anaerobic phosphorus release is prominent. Therefore, low concentration wastewater has restricted effects on nitrogen and phosphorus removal. The purpose of this study is to treat dormitory sewage with a biochemical oxygen demand (BOD) ranging from 50 to 150 mg/L using dewatered alum sludge-based sequencing batch constructed wetland system. Vegetation in the wetland system was chosen to be Phragmites australis. Three parallel cases were carried out to assess impacts due to different hydraulic retention time (HRT) and artificial aeration. The results showed that this system is effective in removing total nitrogen (TN), ammonia nitrogen (NH3-N) and total phosphorus (TP) under different HRT. However, nitrous oxide (N2O) emission poses to be the greatest challenge in the high HRT cases. Artificial aeration could reduce N2O emission but is associated with high operational cost. Results indicate that dewatered alum sludge-based sequencing batch constructed wetland system is a promising bio-measure in the treatment of low concentration wastewater.