The return flows of reject water from sewage sludge dewatering alter the activated sludge process in a conventional WWTP and increase TN concentration in the final effluent from WWTP. The objective of the investigation carried out was to consider the application of multistage treatment wetland (MTW) for the treatment of reject water from sewage sludge dewatering in a centrifuge (RWC). This paper aims to present the design and performance of each stage of the treatment as well as the efficiency of total MTW. The full scale pilot plant for RWC, consisting of two vertical flow beds (SS VF) working in series, followed by an horizontal flow bed (SS HF), was built in 2008. The applied configuration ensured a very high removal efficiency of principal pollutant (COD – 76.0% and NH4+-N – 93.6%). In the investigated facilities, the SS VF beds ensured an effective removal of nitrogen compounds, especially NH4+-N, whereas the decomposition of hardly degradable Org-N and COD took place in SS HF. This research illustrates that the MTW could be successfully applied for the treatment of RWC.
Keywords: reject water from sewage sludge dewatering, role of SS VF and SS HF beds, treatment wetlands