Cementitious permeable pavement (CPP) has the potential to provide in situ particulate, chemistry, and hydrologic control for storm water. The specific aspects of this control that have been the subject of significant interest and discussion are filtration, hydrologic control, and the potential for clogging. This study investigated the behavior of CPP subject to particle loadings for a constant particle size gradation, a sandy silt gradation. Recovered from an 1-75 Cincinnati, Ohio, site subject to runoff loadings, these CPP specimens had similar pore size distributions and effective porosities. The total mass removal efficiencies for the particles were significant, ranging from nearly total removal for medium and coarse sands to greater than 60% removal for fine silt-size particles. With an engineered surface matrix, total phosphorus reductions exceeded 80%. The commensurate turbidity reductions were significant, and the turbidity of the effluent was generally reduced from 50% to 90% of the influent values. In situ hydrologic restoration was significant, generating peak flow reductions and storage within the pore space that represented approximately 25% of the CPP volume, and the temporal aspects of the influent hydrograph were attenuated compared with that for conventional impervious pavement. The initial hydraulic conductivity was in the range of 10(-2) cm/s and followed a first-order exponential decline, and restoration of this hydraulic conductivity required some form of pavement cleaning approximately once every 6-month period. Cleaning by pavement vacuuming restored more than 95% of the initial hydraulic conductivity
Constructed wetland technique for waste water treatment has many advantages, including high treatment efficiency, low investment and energy cost, and easy operation and maintenance. However, the inhibitive effect of low temperature on treatment efficiency remains a serious problem in cold weather for many small size wetlands. In this study, the application of cold-tolerating bacteria in maintaining the nitrogen waste treatment efficiency of small size constructed wetland during cold weather was investigated in Hebei province, northern China. Three strains of cold-resistant bacteria were purified, and their physiological characteristics in terms of growth rate and generation time under different growth conditions were tested. The effects of various environmental factors on the growth of these strains were also investigated, including ambient temperature, dissolved oxygen, carbon concentration, bio-retention time and pH. These strains of purified bacteria were then applied to constructed wetland systems, and their effects on nitrogen removal in cold temperatures were measured. It was found that these bacteria strains significantly improved the nitrogen removal efficiency of the constructed wetlands, suggesting a promising role that these microorganisms play in improving the efficiency of small size constructed wetlands in waste water treatment in cold weather.
A certain level of alkalinity acts as a buffer and maintains the pH value in a stable range in water bodies. With rapid urban development, more and more acidic pollutants flow to watersheds with runoff and drop alkalinity to a very low level and ultimately degrade the water environment. Cementitious porous pavement is an effective tool for stormwater acidic neutralization. When stormwater infiltrates cement porous pavement (CPP) materials, alkalinity and pH will be elevated due to the basic characteristics of cement concrete. The elevated alkalinity will neutralize acids in water bodies and maintain the pH in a stable level as a buffer. It is expected that CPP materials still have a certain capability of alkalinity elevation after years of service, which is important for CPP as an effective tool for stormwater management. However, few previous studies have reported on how CPP structures would elevate runoff alkalinity and pH after being exposed to rainfall-runoff for years. In this study, three groups of CPP specimens, all exposed to rainfall-runoff for 3 years, were used to test the pH and alkalinity elevation properties. It was found that runoff pH values were elevated from 7.4 to the range of 7.8-8.6 after infiltrating through the uncoated specimens, and from 7.4 to 8.5-10.7 after infiltrating through aluminum-coated specimens. Runoff alkalinity elevation efficiencies are 11.5-14.5% for uncoated specimens and 42.2% for coated specimens. The study shows that CPP is an effective passive unit operation for stormwater acid neutralization in our built environment.
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