A passive sink-zeolite permeable reactive barrier to control NH4+-N pollution plume within groundwater: Conceptual design and numerical modeling

Performance investigation of cutoff wall and permeable reactive barriers at a landfill: Multiscale experiments and numerical analyses

Environmental issues from waste management require reliable remediation techniques to prevent groundwater and soil pollution. Cut-off walls and permeable reactive barriers (PRBs) have been widely used for the control and remediation of groundwater pollution. However, the performance of the newly modified barrier materials and site remediation was not well explored. Therefore, in-depth and comparative analyses of 2 % carboxymethyl cellulose (CMC)-modified bentonite and 2 % unmodified sodium bentonite used in vertical barriers are required. Curtain and high-pressure jet grouting composed of CMC-modified bentonite were investigated in a field scale. Additionally, laboratory experiments were conducted to examine the permeability and adsorption properties of the PRB comprised of natural zeolite. The performances of vertical barriers and the PRB were compared by a three-dimensional numerical simulation based on the hydrogeological characteristics of a municipal solid waste landfill (MSWL) in southeastern China. The hydraulic conductivities of CMC-modified bentonite barriers could range from 21.9 %-50.5 % of those of unmodified sodium bentonite barriers, and could be as low as 1.02 × 10-8 cm/s. Contaminant fluxes through the cut-off wall and PRB were 38.67 % and 44.97 % of that without protection after 10 years in the polluted stratum. It was indicated that the removal rate of NH3-N can be 52.30 % at the 10th year by using PRBs. These results demonstrated the long-term performance of CMC-modified bentonite vertical barriers combined with PRBs is quite good at landfills or contaminated sites.

A critical review of the mechanisms, factors, and performance of pervious concrete to remove contaminants from stormwater runoff

Stormwater can carry pollutants accumulated on impervious surfaces in urban areas into natural water bodies in absence of stormwater quality improvement devices. Pervious concrete (PC) pavement is one of the low-impact development practices introduced for urban flooding prevention and stormwater pollution reduction. PC removes various types of water contaminants. Mechanisms contributing to the water pollution removal capacity of PC can be categorized into three groups: physical, chemical, and biological. Properties of PC such as permeability, porosity, thickness, and adsorption capacity influence removal of all contaminants, although their impact might differ depending on the pollutant properties. Chemical mechanisms include precipitation, co-precipitation, ion and ligand exchange, complexation, diffusion, and sorption. Bulk organics and nutrients are removed primarily by biodegradation. Physical filtration is the primary mechanism to retain suspended solids, although biological activities may have a minor contribution. Release of calcium (Ca2+) and hydroxide (OH-) from hardened cement elevates the effluent pH, which is an environmental concern. However, the pH elevation is also the prime contributor to heavy metals and nutrients removal through precipitation. Specific cementitious materials (e.g., Pozzolans and nanoparticles) and carbonation curing approach are recommended to control effluent pH elevation. Complexation, diffusion, ion solubility, and stability constants are other mechanisms and parameters that influence heavy metal removal. Organic matter availability, electrostatic attraction, temperature, pH, contact time, specific surface area, and roughness of PC pores contribute to the pathogen removal process. Although PC has been found promising in removing various water pollutants, limited salinity removal can be achieved due to the inherent release of Ca2+and OH- from PC.