Abstract
As one of the major sources of pollutions in the environments, effluents from municipal wastewater recently became a hot topic. This study quantified monthly county-level releases of five heavy metals, i.e., lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg), from municipal wastewater into the environment in the Heilongjiang Province of China, based on sampling, measurement, and modeling tools. Wastewater samples were collected from 27 municipal wastewater treatment plants (MWTPs) in 15 county-level cities of Heilongjiang every month from 2015 to 2017. The concentrations of five heavy metals were analyzed in both influents (Pb: 160 ± 100 μg/L; Cd: 15 ± 9.0 μg/L; Cr: 170 ± 64 μg/L; Hg: 0.67 ± 1.5 μg/L; As: 6.2 ± 4.8 μg/L) and effluents (Pb: 45 ± 15 μg/L; Cd: 5.2 ± 5.1 μg/L; Cr: 57 ± 13 μg/L; Hg: 0.28 ± 0.12 μg/L; As: 2.6 ± 1.4 μg/L). The removal ratios of the five heavy metals ranged from 50% to 67%. Inflow fluxes of Pb, Cr, and Cd displayed increasing trends first then decreased after reaching a maximum value, whereas those of Hg and Pb remained stable. Material flow analysis reveals that constructions of MWTPs are conducive to significantly reduce the releases of heavy metals from urban areas into the aquatic environment in the study area. Additionally, municipal wastewater sludge (used as fertilizer or spread on the land) could be a significant source of heavy metals in the land.
Highlights
Excessive heavy metals accumulation perturbs the environment and causes serious adverse health effects to organisms, including humans [1]
An exact estimation of the amounts of heavy metals released into environmental systems and their fate is crucial for health risk assessment and policymaking
Cd, and Cr were detected in all the raw influent wastewater samples analyzed, with concentrations ranging from 44 μg/L to 940 μg/L, from 7.0 μg/L to
Summary
Excessive heavy metals accumulation perturbs the environment and causes serious adverse health effects to organisms, including humans [1]. Human activities (industrial, domestic, agricultural, medical, etc.) significantly accelerate release of the naturally existing heavy metals into the environment [9]. Human activities directly emitted 2500 tons/year of Hg into the atmosphere in recent years, accounting for 31% of the total emissions (including natural background and legacy sources) [10]. A total of 28,600 tons of As is emitted into the atmosphere annually, 14-times greater than emissions from natural sources [11]. Contamination by heavy metals has spread globally, including to all environment matrixes, such as the atmosphere, soil, sediment, fresh water, sea water, etc. An exact estimation of the amounts of heavy metals released into environmental systems and their fate is crucial for health risk assessment and policymaking
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