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A next generation septic tank media filter to replace or enhance the current on-site wastewater treatment drainfields was proposed in this study. Unit operation with known treatment efficiencies, flow pattern identification, and system dynamics modeling was cohesively concatenated in order to prove the concept of a newly developed media filter. A multicompartmental model addressing system dynamics and feedbacks based on our assumed microbiological processes accounting for aerobic, anoxic, and anaerobic conditions in the media filter was constructed and calibrated with the aid of in situ measurements and the understanding of the flow patterns. Such a calibrated system dynamics model was then applied for a sensitivity analysis under changing inflow conditions based on the rates of nitrification and denitrification characterized through the field-scale testing. This advancement may contribute to design such a drainfield media filter in household septic tank systems in the future.

In this study, a new-generation subsurface upflow wetland (SUW) system packed with the unique sorption media was introduced for nutrient removal. To explore the interface between hydraulic and environmental performance, a tracer study was carried out in concert with a transport model to collectively provide hydraulic retention time (7.1 days) and compelling evidence of pollutant fate and transport processes. Research findings indicate that our pollution-control media demonstrate smooth nutrient removal efficiencies across different sampling port locations given the appropriate size distribution conversant with the anticipated hydraulic patterns and layered structure among the sorption media components. The sizable capacity for nutrient removal in this bioprocess confirms that SUW is a promising substitute for an extension of traditional on-site wastewater treatment systems.

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 coarse—were used in two consecutive phases for elucidating the nitrification and denitrification effects. With the aid of real-time 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.

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.