Construction of hybrid constructed wetlands for phosphorus chemical industry tailwater treatment in the middle Yangtze river basin: Responses of plant growth and root-associated microbial communities

Abstract

Constructed wetlands are commonly utilized to treat industrial wastewater due to their effectiveness, affordability, and environmental benefits. Many phosphorus chemical enterprises in the middle Yangtze River basin are facing high pollution load challenges and efforts are needed to improve removal efficiency of pollutants. This work was the first to use constructed wetlands for phosphorus chemical industry tailwater (PCITW) treatment. The new hybrid constructed wetlands (CWs) proposed were the aeration horizontal subsurface flow constructed wetland (AHSCW) and the integrated vertical flow constructed wetland (IVCW), which were constructed on a pilot scale. Here, the effectiveness of pollutant removal along hybrid CWs, wetland plant growth, and root-associated microbial community responses to the PCITW were investigated. The results showed that there was spatial variation in removal of carbon, nitrogen, and phosphorus in the hybrid CWs, and that the AHSCW and the IVCW played synergistic roles in the removal of pollutants. Compared with influent, the toxic effect of effluent to embryos of a rare minnow (Gobiocypris rarus) was alleviated. Exposure to the effluent resulted in no malformation or death for embryos. Plants and microorganisms in the wetland system of the phosphate chemical tailwater were then compared with the control system of municipal tailwater. Plants in the former system had lower root density, and higher average root diameter, root shoot ratio, specific root length, and specific surface area. Plant roots also had decreased NH₄⁺ uptake ability but increased Ca²⁺ uptake to adapt to the high load and complex pollution stress. Unlike the control system, stochastic mechanisms had a more important role than deterministic processes in shaping the microbial community assembly associated with the PCITW. Meanwhile, analysis of microbial network-level topological characteristics demonstrated substantial reduction in network interactions complexity and microbiome stability in the treatment system. Findings from this study suggest wetlands will be helpful for efficient purification of phosphorus chemical industry wastewater in the Yangtze River basin.