Characterizing the Variation of Dissolvable PAHs in Receiving Water in a Reclaimed Water Irrigation Region

Yajun Wang,Xianfang Song,Lihu Yang,Ying Ma,Binghua Li

doi:10.3390/w12102766

Abstract

Long-term wastewater and reclaimed water irrigation systems constitute the major processes in local water circulation, which concomitantly introduce plenty of undesirable substances that can threaten water quality, ecosystem functions and human health. At the Southeast Reclaimed Water Irrigation Region (SRWIR) of Beijing, wastewater irrigation was adopted from 1969 to 2002, and second-treated effluents (reclaimed water) has been used thereafter. Polycyclic aromatic hydrocarbons (PAHs) were the most ubiquitously detected contaminant in wastewater and reclaimed water and are reported to be carcinogenic. Hence, we measured the concentrations of dissolved sixteen United States Environmental Protection Agency (USEPA) priority PAHs in surface water and groundwater at the SRWIR to characterize their spatial and temporal variations, and to clarify the role of reclaimed water to natural water. The concentration of 16 individual PAHs in reclaimed water, rivers and groundwater varied from 339.4 to 636.2 ng/L, 359.1 to 3,435.0 ng/L and 216.5 to 488,205.2 ng/L, respectively. The lower aromatic rings of PAHs prevailed in aquatic environments rather than the higher ones. Thereinto, naphthalene was the predominant isomer within the highest concentration reached to 486,600 µg/L. The groundwater samples had higher PAHs concentrations at Tongzhou district which attributed to the higher vulnerability of aquifer. Additionally, strong correlations between PAHs and total nitrogen, nitrate, dissolved oxygen and electrical conductivity suggested those potential factors affecting the photo degradation and/or biodegradation of PAHs. The relationship identified between PAHs concentrations and physical and chemical indices would help us to enhance the understanding migration and transformation of PAHs spatially and temporally, enable us to assess the potential risks of the environmental pollutants to aquatic organisms and human water supplies.

Highlights

Water quality impairment has been received increased attentions globally over last decades, in particular for these long-standing wastewater and reclaimed water irrigation regions [1,2,3].In northern China, several cities (e.g., Beijing, Tianjin and Shijiazhuang) have the experience of using reclaimed water for agriculture irrigation and have made great efforts on its potential effects of contaminants in reclaimed water applications [4]
55–70% polycyclic aromatic hydrocarbons (PAHs) can be removed through particle absorption, precipitation, biological degradation and/or volatilization in wastewater treatment plants (WWTPs) [14,15], but dissolved PAHs concentrations in the range of 339.4 to 636.2 ng/L with an average value of 475.7 ng/L still could be detected in WWTPs effluents in our study
During two collection campaigns at Southeast Reclaimed Water Irrigation Region (SRWIR), the dissolved PAHs concentrations in reclaimed water, rivers and groundwater increased by one order of magnitude in the range of 339.4 to 636.2 ng/L, 359.1 to

Summary

Introduction

Water quality impairment has been received increased attentions globally over last decades, in particular for these long-standing wastewater and reclaimed water irrigation regions [1,2,3].In northern China, several cities (e.g., Beijing, Tianjin and Shijiazhuang) have the experience of using reclaimed water for agriculture irrigation and have made great efforts on its potential effects of contaminants in reclaimed water applications [4]. Water quality impairment has been received increased attentions globally over last decades, in particular for these long-standing wastewater and reclaimed water irrigation regions [1,2,3]. Organic contaminants such as persistent organic pollutants (POPs) in the reclaimed water have caused focused attention. Over 10 million organic compounds have been discovered or synthesized [5], and polycyclic aromatic hydrocarbons (PAHs) are recognized as the. Water 2020, 12, 2766 most ubiquitously detected POPs in the natural aquatic environment owing to their propensity for persistence, semi-volatility and long-range transport [6,7,8,9]. Qiao et al 2014 calculated that 68.5% of PAHs in receiving rivers were contributed from wastewater treatment plants. In order to prioritize regulation of organic contaminants in the aqueous environment, information on distribution and magnitude of PAHs contamination is needed [9]

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