Pilot-scale Free Water Surface Research Articles

Phosphorus removal in a pilot scale free water surface constructed wetland: hydraulic retention time, seasonality and standing stock evaluation

Constructed wetlands (CWs) are decentralized wastewater treatment systems considered to be green and low cost. They have the potential to effectively remove pollutants and recycle nutrients with plant composting. However, they need large areas to implement them due to the usual high Hydraulic Retention Times (HRT), reaching up to 50 days. The main objective of the present study was to evaluate the influence of HRT (HRT = 3, 7, and 10 days), and seasonality on Total Phosphorus (TP) removal, and standing stock in a pilot scale free water surface CW (FWS CW). Unplanted and planted (Eichhornia crassipes) tanks were evaluated in wet and dry seasons. The FWS CW was set up as a complementary treatment to a secondary level wastewater treatment plant. The system was monitored weekly for ten months, totalizing 29 replicate samplings (n = 58). Planted tanks were harvested every week to keep free space for plant reproduction (∼40%). The mean removal efficiency of TP ranged between 82% and 95% without a significant difference between HRT (pvalue > 0.05). However, when the effects of the sedimentation of the unplanted tanks were disregarded, the lowest HRT (3 days) tank presented the highest standing stock of TP. The wet season presented a significant difference in TP removal results (pvalue < 0.05), associated with higher macrophyte growth rate due to more intense solar irradiation and incorporation of TP by E. crassipes. The results point out advances in P removal and recycling by a low-cost ecological engineering system.

BTEX removal in a modified free water surface wetland

A pilot scale free water surface (FWS) wetland with provision of additional intermediate berms composed of gravel material was tested for assessing its potential to remediate hydrocarbons present in produced water from a gas field. The average influent BTEX values were as follows: benzene (1.57mg/L), toluene (0.14mg/L), ethyl benzene (0.29mg/L), m and p-xylene (2.01mg/L) and o-xylene (0.13mg/L). The FWS wetland removed all monitored hydrocarbons with very good removal efficiencies during the monitoring period: benzene (92.6%), toluene (93.4%), ethyl benzene (98.3%), m and p-xylene (91.3%) and o-xylene (87.4%). Biodegradation was considered to be the main pathway for benzene removal in the studied system. Reaction kinetics were studied and the first-order area based rate coefficient for benzene was 0.13m/d while for BTEX it was 0.12m/d. Metagenomic analysis of bacterial community retrieved from the wetland showed majority of sequences were related to phylum proteobacteria.

A model for organic matter removal in free water surface constructed wetlands

This study was conducted to determine performance of free water surface (FWS) constructed wetlands located in the tropics in the removal of organic matter and to assess the importance of biofilm bacteria in the overall kinetics of organic matter (or chemical oxygen demand, COD) removal. Because constructed wetlands normally contain both biofilm and suspended bacteria, a kinetic model incorporating the activities of these two bacteria groups, dispersion number and hydraulic retention time, was employed. The model parameters essential for the calculation of COD removal in FWS constructed wetlands were determined from the experiments and some from the literature. The model was found satisfactory in predicting COD removal efficiencies in a pilot-scale FWS constructed wetland unit treating a domestic wastewater.

A model for organic matter removal in free water surface constructed wetlands

This study was conducted to determine performance of free water surface (FWS) constructed wetlands located in the tropics in the removal of organic matter and to assess the importance of biofilm bacteria in the overall kinetics of organic matter (or chemical oxygen demand, COD) removal. Because constructed wetlands normally contain both biofilm and suspended bacteria, a kinetic model incorporating the activities of these two bacteria groups, dispersion number and hydraulic retention time, was employed. The model parameters essential for the calculation of COD removal in FWS constructed wetlands were determined from the experiments and some from the literature. The model was found satisfactory in predicting COD removal efficiencies in a pilot-scale FWS constructed wetland unit treating a domestic wastewater.