Comprehensive benefits assessment of using recycled concrete aggregates as the substrate in constructed wetland polishing effluent from wastewater treatment plant

Large-scale horizontal subsurface flow constructed wetland is widely used to polish the effluent from wastewater treatment plant in China. Though it is effective in improving the urban water quality, the great consumption of natural sandstone arouses growing concern. Using recycled concrete aggregate instead of gravel as the substrate of constructed wetland may solve this problem. Recycling of waste concrete can reduce the adverse effect of inertial material disposal. This study aims to investigate the comprehensive superiority of this practice. For this purpose, a traditional gravel-based horizontal subsurface flow constructed wetland (system 1) and a horizontal subsurface flow constructed wetland filled with recycled concrete aggregate (system 2) were studied. Life cycle assessment combined with life cycle cost analysis was carried out to reveal the systems' environmental burden and economic effectiveness. Grey water footprint reduction was calculated to represent the systems' wastewater polish performance. Finally, a new index was initiated to facilitate the comparison between system 1 and 2. Results have demonstrated that substrate makes great contribution to the life-cycle environmental burden (25.2%) and total costs (55.1%) of constructed wetland and using recycled concrete aggregate as the substrate can lower them. LCEB is reduced by 36.6% while LCC is reduced by 23.2%. Due to better phosphorus removal capacity, horizontal subsurface flow constructed wetland filled with recycled concrete aggregate is superior to traditional gravel-based horizontal subsurface flow constructed wetland concerned with wastewater polish performance. Grey water footprint reduction of system 2 is on average 4.5 times as large as that of system 1. The comprehensive benefits assessment result indicates that using recycled concrete aggregate instead of gravel has an absolute superiority and the superiority is more evident when polishing secondary effluent. (C) 2020 Elsevier Ltd. All rights reserved.