Geothermal Paving Systems for Urban Runoff Treatment and Renewable Energy Efficiency
Water and energy are two of the most precious and essential resources which are inseparably connected; vital for the survival and well-being of humanity. Sustainable water resources and energy management emphasizes the requirement for a holistic approach in meeting the needs of the present and future generations. In order to indentify the needs and obstacles relating to water reuse and renewable energy initiatives, Hanson Formpave in partnership with The University of Edinburgh implement a five-year pilot project between May 2005 and June 2010. The research project addressed the use of sustainable urban drainage systems (SUDS) such as permeable pavements systems (PPS) and integration of renewable energy tools such as geothermal heat pumps (GHPs). The research uses the novel and timely urban drainage system and focuses on water quality assessment when incorporated with GHPs. Twelve-tanked laboratory scaled experimental PPS were evaluated at The King’s Building campus (The University of Edinburgh, Scotland) using different compositions. Variations in designs included the presence of geotextiles layers and geothermal heating/cooling applications. The experimental rigs were examined for a two year period (March 2008 to April 2010). Two types of urban stormwater were used in the analysis; (i) gully pot liquor and (ii) gully pot liquor spiked with Canis lupus familiaris (dog) faeces. This urban wastewater represented the extreme worstcase scenario from a storm event, which can occur on a permeable pavement parking lot. The pavement systems operated in batch-flow to mimic weekly storm events and reduce pumping costs. Six PPS were located indoor in a controlled environment and six corresponding PPS were placed outdoors to allow for a direct comparison of controlled and uncontrolled environmental conditions. The outdoor rig simulated natural weather conditions whilst the indoor rig operated under controlled environmental conditions such as regulated temperature, humidity and light. The project assessed the performance of these pavement rigs with the integration of ground-source heating and cooling, standalone PPS and the abilities for water quality treatment from a physical, chemical and microbiological perspective. The performance efficiency of the GHP was measured by the energy efficiency ration (EER) for steady state cooling efficiency and the coefficient of performance (COP) for the heating cycle efficiency. Findings from the combined PPS and GHP system and standalone systems were able to significantly lower levels for all physiochemical and microbial water quality parameters in the range of (70-99.99%) respectively. Outflow concentrations for all pavement systems met the European Commission Environment Urban Wastewater Treatment Directive (91/271/EEC). The presence of geotextiles resulted in a significant reduction of contaminants when compared to PPS systems without (p <0.05). Photocatalytic disinfection with titanium dioxide (TIO2) was applied to the effluent from PPS for further treatment and polishing of the stormwater. After the photocatalytic disinfection, the water met the requirements for the United States Environmental Protection Agency (US EPA) water recycling guidelines and the World Health Organisation (WHO) guidelines for potable water consumption with regards to microbial contamination. An Energy and temperature balance was developed for two PPS using a 4th order Runge-Kutta numerical method to model the heat fluxes and energy balance within the pavement system. Machine learning techniques such as artificial neural networks (backpropagatioin feed forward neural networks) and self-organising maps (SOM) were applied and successfully predicted the effluent concentrations of nutrients, biochemical oxygen demand (BOD) and microbial pollutants. The overall outcome of this research is a significant contribution to the development of a new generable of sustainable and eco-friendly pavements. The research project proves scientifically that PPS is one of the most appropriate systems for GHP installation and does not affect its efficiency for water pollutant removal.