Conventional on-site wastewater treatment systems are no longer able to fully meet the needs of coping with the impacts of the variegated pollutants with which they are confronted. Without proper nitrification and denitrification, this implies a large fraction of nutrient loads such as nitrogen and phosphorus will flow into groundwater aquifers adversely affecting the water quality and public health. Constructed wetland, a cost-effective small-scale wastewater treatment system with low energy, maintenance requirements and operational costs may well fill the current gaps. In Phase I of this study, a subsurface constructed wetland system designed as an integral part of a performance-based passive on-site wastewater treatment system was proved effective after receiving septic wastewater flow. Using a suite of selected plant species, it is configured to handle 189 liters per day (50 GPD) of influent for a wastewater treatment and reuse study using green sorption media (recycled and natural materials) at a test center located at the University of Central Florida (UCF). During the three-month test run, the system achieved a removal efficiency of 75.4% in total nitrogen (TN) and 94.9% in total phosphorus (TP). Overall, the removal efficiency of TN and TP in an integrated septic tank and constructed wetland (ST/CW) system became as high as 81.3% and 95.8%, respectively.

Constructed wetlands have been popular in ecological engineering regime; yet, modeling the physical, chemical, and biological processes within these wetlands is a long-standing challenge in the past decades. In concert with our field-scale pilot testing of a new-generation subsurface upflow wetland (SUW) system, this article highlights an advancement of modeling the SUW system with a layer-structured compartmental simulation model. This is the first wetland model of its kind to address the complexity between plant nutrient uptake and medium sorption. Such a system dynamics model using STELLA Ò as a means for a graphical formulation was applied to illustrate the essential mechanism of the nitrification and denitrification processes within a sorption mediumbased SUW system, which can be recognized as one of the major passive on-site wastewater treatment technologies in this decade. Model calibration and validation received fairly good R-squared values of 0.9998 and 0.9644, respectively. Such good agreement with the measured data confirms that the developed system dynamics model may provide a reliable tool for designing this particular type of constructed wetland. This work also entails the significant movement of linking green building with green infrastructure as part of the urbanization for nature.

On-site sewage treatment and disposal systems, commonly referred to as a septic systems, consist basically of a septic tank and soil adsorption field or drainfield. It may represent a large fraction of nutrient loads and pathogen impacts in vadose zone and groundwater systems. It includes not only nitrogen (N) and phosphorus (P), but also pathogen indicators such as fecal coliform and Escherichia coli, which indicate the presence of other disease-causing bacteria flowing into the aquatic system and potentially adversely affecting public health. Constructed wetlands, an effective small-scale wastewater treatment system with low energy and maintenance requirements and operational costs, will cover current needs for nutrient and pathogen removal. In our study, a next-generation subsurface upflow wetland system that is filled with green sorption media (e.g., mixes of recycled and natural materials) along with selected plant species was tested as a substitute for the conventional drainfield in septic tank systems. Four parallel subsurface upflow wetlands (i.e., three planted versus one unplanted) were built to handle 454 L/day (120 gallons/day) of septic wastewater flow. It proved effective in removing both nutrients and pathogens. During the test run in 2009, the planted wetlands achieved a removal efficiency of 84.2%, 97.3%, 98.93%, and 99.92% in total nitrogen, total phosphorus, fecal coli, and E. coli, respectively. A stress test conducted in winter 2010 successfully verified the reliability of this treatment process. Denitrification and precipitation were shown to be the dominant pathways for removing N and P, as evidenced by mass balance and real-time polymerase chain reaction analyses.

Groundwater contamination due to the failure of septic tank systems is a vital concern in environmental health. Active on-site wastewater treatment counts on the use of pumps to sustain the aerobic condition in the process and promote the nitrification which might not be sustainable in terms of energy saving. In current practice, passive on-site wastewater treatment processing is deemed a cost-effective option to improve the nutrient removal. The recirculation filtration tank (RFT) is an intermediate process installed to trigger or promote the proper nitrification/denitrification process between the septic tank and the drain field. However quantification of the nitrification remains difficult. To explore the structure and function of the microbiological community in the RFT, two types of sands-fine and coarsewere used in two consecutive phases for elucidating the nitrification and denitrification effects. With the aid of realtime PCR, the growth of nitrifiers and denitrifiers in sand was monitored in the RFT without adding any external carbon source to the sand. Further, phosphorus removal from the wastewater and the ability of limestone for phosphorus removal were also confirmed in the RFT. Fine sand with limestone mixture performed better in nutrient removal if clogging was overcome by using a grinder pump for dosing. On average, removal efficiencies of 60.54% ammonium, 49.48% total Kjeldahl nitrogen (TKN), 42.57% total nitrogen (TN), 92.06% soluble reactive phosphorus (SRP) and 87.16% total phosphorus (TP) were achieved by the RFT with fine sand. The E. Coli removal efficiency by the RFT was 99.9% in both phases.

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