Nitrogen removal in an aerobic gravel filtration-sedimentation pond-constructed wetland-overland flow system treating polluted stream waters: Effects of operation parameters.

Nitrogen pollution in streams can be controlled by serially constructing natural wastewater treatment (NWT) systems inside streams. Therefore, a pilot-scale hybrid NWT system consisting of gravel filtration (GF), sedimentation pond (SP), gravel filtration-free water surface constructed wetland (GF-FWSCW), and gravel filtration-overland flow (GF-OF) was installed in order to prevent contamination in a stream (Nigde stream) that feeds and pollutes surface water source (Akkaya lake). The pilot-scale system was installed on a new 60 m-long channel which was located off the stream. Changes in ammonium (NH4+-N), organic nitrogen (Norg.), total nitrogen (TN), and biochemical oxygen demand (BOD) concentrations was routinely monitored in influent and effluent of all stages of the hybrid NWT system and the bottom sediment of the SP over a one-year operation period. According to the study results, while NH4+-N plus Norg. was reduced by an average of 75% (from 49,1 mg L-1 to 7,1 mg L-1), TN was reduced by an average of 85% (from 50,2 mg L-1 to 12,4 mg L-1). Colder seasons and higher hydraulic loading rates (HLRs) negatively affected nitrogen removal efficiency of the pilot-system. The use of vegetation and filter medium had a positive effect on the average removal efficiencies. The results showed that nitrogen pollution in polluted streams could be greatly reduced by establishing a NWT system in series within them.

Performance of a pilot-scale, three-stage constructed wetland system for domestic wastewater treatment.

This study investigates the effects of season, organic matter loadings, hydraulic conditions, recycling, and rapid drainage on water quality in a pilot-scale, three-stage subsurface flow constructed wetland (SSF CW) system. The pilot CW system consisted of a vertical flow-gravel filtration (v-GF) wetland in the first stage, a horizontal-subsurface flow (h-SSF) bed planted with Iris in the second stage, and a vertical-subsurface flow (v-SSF) bed vegetated with Phragmites in the third stage. The objective of this study was to evaluate the potential of these CW systems to remove organic matter from domestic wastewater on a pilot-scale three-stage SSF CW system. Comparisons of average influent and effluent concentrations showed that the multistage system could effectively reduce total suspended solids (TSS), biological oxygen demand (BOD) and chemical oxygen demand (COD) levels in effluent by as much as 98% and total organic carbon (TOC) by as much as 79%. Contributions of the first, second and third stages to the overall treatment were approximately 10%, 45% and 45%, respectively. The average TSS, COD, and TOC concentrations were reduced in the entire CW system by 70%, 80% and 90%, respectively. The BOD and TOC removal efficiencies displayed seasonal variations with average removals generally increasing in warmer seasons. Our results also demonstrate that there were strong correlations between removal efficiencies and loading rates. Average removals decreased with an increase in the hydraulic retention time (HRT). The rapid drainage and recycling operation increased the efficiency of BOD removal only.

Removal of nutrient and bacteria in pilot-scale constructed wetlands.

Three pilot-scale horizontal-subsurface flow (H-SSF), surface flow (SF), and free water surface flow (FWS) constructed wetland system designs were installed and evaluated to determine the effectiveness of constructed wetlands to treat tertiary effluent wastewater generated from Pasaköy Advanced Biological Wastewater Treatment Plant (PABWWTP). The average ammonia-nitrogen (NH(+)(4)) removal efficiencies of % 49 to 52% were observed in all three system designs. Average NO(-)(3) removal efficiency was approximately 58% in the SF system design, suggesting that this design had the highest denitrification rate. Total phosphorus (TP) removal efficiency was the highest (approximately 60%) in the h-SSF system, possibly due to substrate (gravel). Systems were capable of removing approximately 94% of fecal coliform (FC) bacteria. Removal rate coefficients (k(20), 1/day) in the H-SSF, the FWS and the SF systems were estimated for NH(+)(4), NO(-)(3), TP and FC. The average nutrient removal efficiencies were found higher in the summer periods except for the FC. The results of statistical analyses indicated that nutrient removals were affected by temperature, hydraulic residence time (HRT), and nitrogen loading rate (NLR).