Application of SS-VF Bed for the Treatment of High Concentrated Reject Water from Autothermal Termophilic Aerobic Sewage Sludge Digestion

The autothermal termophilic aerobic digestion (ATAD) technology is used in the municipal and industrial wastewater treatment plants (WWTPs) with personal equivalent up to 30.000. The process provides a high level of sewage sludge stabilization and its hygienization. The main operation problems are caused by the high concentration of nitrogen and phosphorus in the reject water from sewage sludge treatment and air purification (odor removal). Reject water usually is returned to the main sewage treatment, which has a negative impact, especially on the sewage treatment systems based on the sequence batch reactors (SBR). Applying high-performance and expensive separate reject water treatment methods such as SHARON, Anammox or CANON in small facilities is not justified economically. The article presents the research results concerning the effectiveness of applying subsurface vertical flow constructed wetlands (SS VF) for reject water treatment from the ATAD process. An innovative type of bed filling was used, which was produced from waste (ash from a heat and power plant). The efficiency of reject water treatment during the research period was on average at 45.6% for ammonia nitrogen, 32.3% for total phosphorus and 85.1% for BOD5. Applying SS VF beds for separate reject water treatment might ensure a stable and effective functioning of municipal WWTPs by decreasing the load of biological part of a WWTP.