Post-treatment of anaerobic effluents in constructed wetland systems

Abstract

This papers describes the behaviour of wetlands as a post-treatment unit for anaerobically treated sewage for the removal of organic matter, suspended solids, nutrients (nitrogen and phosphorus) and faecal coliforms. Raw sewage was treated in a UASB reactor with a retention time of 5 h and the effluent was used in four units of wetlands with coarse sand as the medium and operated with different hydraulic loads. Three of the units had emerging macrophytes (Juncus sp), whereas the fourth one was operated as a control unit without plants. During the 12 months of operation, the organic material removal efficiency (measured as COD) was in the range of 79 to 85%, whereas suspended solids removal varied from 48 to 71%. Faecal coliform removal was very high (99,99%); phosphorus was also efficiently removed (average efficiency of 90% for the lowest hydraulic load), but nitrogen removal was only partial (45 to 70% for ammonia and 47 to 70% for TKN). The experimental results clearly show the technical feasibility of using wetlands for treatment of municipal sewage after a pre-treatment in the UASB reactor.

Post-Treatment Options for the Anaerobic Treatment of Domestic Wastewater

“…Results of the 1-year research developed by Sousa et al (2001), with a UASB/constructed wetland system, showed average COD removal efficiencies in the range of 79-85%, suspended solids in the range of 48-71% and faecal coliforms around 4 log-units. Phosphorus was also efficiently removed (average of 90% for the lowest hydraulic load) but nitrogen removal was only partial (45-70% for ammonia and 47-70% for TKN).…”

The effects of flow regime and temperature on the wastewater purification efficiency of a pilot hybrid constructed wetland

“…Purification efficiencies of BOD 7 , N tot and NH 4 -N responded negatively to the increases in hydraulic loading rates, and positively to the enhancing of recirculation rate, whereas the purification efficiency of P tot only showed a positive response to enhanced recirculation rate in the LWA system, and was not affected by the changes in the hydraulic loading rates.…”

“…The number of water samples per operational regime (1-6) varied in the following order: 1 st -4 samples, 2 nd -11 samples, 3 rd , 4 th and 5 th -9 samples each, and 6 th -11 samples. In the laboratory of the AS Tartu Veevärk, water samples were analyzed for BOD 7 , TSS, COD, N tot , NH 4 -N, NO 2 -N, NO 3 -N, P tot using Standard Methods for the Examination of Water and Wastewater [47]. * summarized recirculation rates from outflow and interim well were used in correlation analysis.…”

“…The growth of the removal efficiency of BOD 7 (Fig. 2) in the 3 rd operational regime compared to the 2 nd operational regime could be caused by the enhanced recirculation rate, decreasing rates of wastewater inflow to the CW, and also by increasing water temperature due to seasonal changes.…”

“…Excessively high hydraulic load has been reported as a main limiting factor of purification processes in both subsurface flow wetland systems [7,8] and free water surface wetlands (FWSW [9,10]). The recirculation of treated effluent from CWs as a procedure enhancing aeration and purification processes has been used in various laboratory experiments and pilot-and full-scale CW systems [11].…”