Performance of constructed wetlands and associated mechanisms of PAHs removal with mussels

Jian Zhang,Tingting Cheng,Huu Hao Ngo,Zizhang Guo,Huijun Xie,Yan Kang,Wenshan Guo,Shuang Liang,Liwei Zhang,Qiang Kong,Bo Li,Jie Liu

doi:10.1016/j.cej.2018.09.152

Abstract

The role of mussels in laboratory-scale constructed wetlands (CWs) where wastewater was contaminated with five typical polycyclic aromatic hydrocarbons (PAHs) (three 3-ring PAHs and two 4-ring PAHs) was investigated in this study. The CWs performance and PAHs removal mechanisms were well studied. Results indicated that these five PAHs improved removal efficiencies of NO3-N but in the case of NH4-N accumulation occurred. Of the five added PAHs, the 4-ring PAHs were more refractory with higher concentrations in effluent than 3-ring PAHs. By monitoring the five PAHs concentration in water, mussels had excellent removal efficiency of the five PAHs (97%). According to the mass balance calculation, mussels promoted plant uptake of five PAHs, contributing 15.2% of five PAHs removal in CWs. The PAHs could also accumulate in mussels through ingested substrate. Thus, mussels presented a positive correlation with five PAHs purification at a depth of 0–10 cm in substrate, which was 34.7 μg/kg lower than the control group. Due to the purification and enhanced aerated degradation, mussels performed better in removing 3-ring PAHs in substrate, decreasing 8.3% for 3-ring PAHs compared to the control. A positive correlation between five PAHs addition and nirS, nrfA genes was observed. However, PAHs showed negative impact on nitrifying bacteria (amoA). The significant correlations between mussels and five PAHs made it possible to improve CWs for PAHs treatment with aquatic faunas.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are important organic contaminants and they are widespread with hyper toxicity, and carcinogenic properties [1]
Two possibilities can account for these: firstly, the organic matter stimulated soil microbiological activity due to the additional source of carbon, which was highly beneficial for denitrification and NO3-N degradation [10]; and secondly, the dissimilatory N reduction to ammonium (DNRA) process was the dominant pathway of NO3-N removal and NH4-N accumulation with rich electron donors, such as organic carbon [34]
The potential of mussels to influence the removal of five typical PAHs in constructed wetlands (CWs) and the effect of PAHs on CWs performance were studied

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are important organic contaminants and they are widespread with hyper toxicity, and carcinogenic properties [1]. PAHs accumulate in the aquatic environment and are difficult to be biodegraded Due to their low solubility and high hydrophobicity, PAHs contaminants in the aquatic ecosystem are adsorbed onto suspended particles and accumulate in sediments instead of dissolving in water [3]. To mitigate the risks to ecological health induced by PAHs contamination, several current research projects have attempted to increase the bioavailability of PAHs through surfactants and co-substrates addition This increases the costs and causes secondary pollution [9]. The bioremediation technologies consist of bioaugmentation and biostimulation [11] It occurs through microbial degradation of PAHs in aerobic or anaerobic conditions [12, 13]. Exerts a minimal environmental impact and releases no other pollutants

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