title: Effect of by-pass and effluent recirculation on nitrogen removal in hybrid constructed wetlands for domestic and industrial wastewater treatment.
abstract: Hybrid constructed wetlands (CWs) including subsurface horizontal flow (HF) and vertical flow (VF) steps look for effective nitrification and denitrification through the combination of anaerobic/anoxic and aerobic conditions. Several CW configurations including several configurations of single pass systems (HF + HF, VF + VF, VF + HF), the Bp(VF + HF) arrangement (with feeding by-pass) and the R(HF + VF) system (with effluent recirculation) were tested treating synthetic domestic wastewater. Two HF/VF area ratios (AR) were tested for the VF + HF and Bp(VF + HF) systems. In addition, a R(VF + VF) system was tested for the treatment of a high strength industrial wastewater. The percentage removal of TSS, COD and BOD5 was usually higher than 95% in all systems. The single pass systems showed TN removal below the threshold of 50% and low removal rates (0.6-1.2 g TN/m(2) d), except the VF + VF system which reached 63% and 3.5 g TN/m(2) d removal but only at high loading rates. Bp(VF + HF) systems required by-pass ratios of 40-50% and increased TN removal rates to approximately 50-60% in a sustainable manner. Removal rates depended on the AR value, increasing from 1.6 (AR 2.0) to 5.2 g TN/m(2) d (AR 0.5), both working with synthetic domestic wastewater. On real domestic wastewater the Bp (VF + HF) (AR 0.5 and 30% by-pass) reached 2.5 g TN/m(2) d removal rate. Effluent recirculation significantly improved the TN removal efficiency and rate. The R(HF + VF) system showed stable TN removals of approximately 80% at loading rates ranging from 2 to 8 g TN/m(2) d. High TN removal rates (up to 73% TN and 8.4 g TN/m(2) d) were also obtained for the R(VF + VF) system treating industrial wastewater.
authors.affiliation: Department of Physical Chemistry and Chemical Engineering I, University of A Coruña, Rúa da Fraga 10, A Coruña 15008, Galiza, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Torrijos
authors.affiliation: Department of Physical Chemistry and Chemical Engineering I, University of A Coruña, Rúa da Fraga 10, A Coruña 15008, Galiza, Spain.
authors.forename: O G
authors.initials: OG
authors.lastname: Gonzalo
authors.affiliation: Department of Physical Chemistry and Chemical Engineering I, University of A Coruña, Rúa da Fraga 10, A Coruña 15008, Galiza, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Trueba-Santiso
authors.affiliation: Department of Physical Chemistry and Chemical Engineering I, University of A Coruña, Rúa da Fraga 10, A Coruña 15008, Galiza, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Ruiz
authors.affiliation: Department of Physical Chemistry and Chemical Engineering I, University of A Coruña, Rúa da Fraga 10, A Coruña 15008, Galiza, Spain. Electronic address: m.soto@udc.es.
authors.forename: M
authors.initials: M
authors.lastname: Soto
mesh_terms: D058440:Denitrification; D058465:Nitrification; D009584:Nitrogen; D014865:Waste Disposal, Fluid; D062065:Wastewater; D053833:Wetlands
chemical_list: D009584:Nitrogen; D062065:Wastewater
keywords: Domestic and industrial wastewater; Effluent recirculation; Hybrid constructed wetlands; Nitrogen removal rate; Step feeding