Determining Discharge Characteristics and Limits of Heavy Metals and Metalloids for Wastewater Treatment Plants (WWTPs) in China Based on Statistical Methods

Abstract

Industrial wastewater and sewage are both important sources of heavy metals and metalloids in urban wastewater treatment plants (WWTPs). China has made great efforts to control heavy metal and metalloid pollution by setting discharge limits for WWTPs. There is, however, limited discharge data and no systematic methodology for the derivation of discharge limits. In this study, 14 heavy metals and metalloids (Hg, alkyl mercury, As, Cd, Cr, Cr6+, Pb, Ni, Be, Ag, Cu, Zn, Mn, Se) that are listed in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) were selected for the analysis of discharge characteristics while using the supervised monitoring data from more than 800 WWTPs located in nine provinces in China. Of the 14 heavy metals and metalloids, all but alkyl mercury were detected in the discharge water. There was a high rate of detection of As, Cu, Mn, Se, and there were some samples that exceeded the standard concentrations of Cr, Cr6+, Pb, and Ni. Removal rates of Hg, As, Cd, Cr, Cr6+, Pb, Ni, Cu, Zn, Mn, and Se were higher than 40%, comparable to values from other countries. Hg and As were selected to analyze the influencing factors of effluent and derive discharge limits of WWTPs using a statistical method, because these two metals had more detected data than other metals. The study used supervised monitoring data from Zhejiang WWTPs with 99 for Hg and 112 for As. Based on the delta-lognormal distribution, the results showed that geographic location was significantly closely correlated with Hg (P = 0.027 < 0.05) and As (P ≈ 0 < 0.05) discharge concentrations, while size (for Hg P = 0.695 > 0.05, for As P = 0.088 > 0.05) and influent concentration (R2 < 0.5) were not. Derived Hg and As discharge limits suggest that it is necessary to establish stricter discharge limits for WWTPs, which is more consistent with the real-world situation in China. The study here comprehensively researches the discharge characteristics of heavy metals and metalloids in effluent of WWTPs in China, and developed for the first time in China heavy metals and metalloids discharge limits based on statistical methods. The results may inform special discharge limit settings for WWTPs in China.

Heavy Metals in Wastewater and Sewage Sludge from Selected Municipal Treatment Plants in Eastern Cape Province, South Africa

“…Overall, the heavy metal dominance in the aqueous media of the study sites follows this order: Fe > Cd > Cu. The concentrations of Cu in the effluents in this study are comparable to those reported by Okonkwo and Mothiba [84] (2 × 10 −3 -3 × 10 −3 mg L −1 ), [36] (6.99 × 10 −3 to 0.305 mg L −1 ), Nyamukamba et al [37] (0.054 to 0.152 mg L −1 ), Wilderer and Kolb [85] in Munich, Germany (0.2 mg L −1 ), and Zhou et al [42] (0.01-0.36 mg L −1 ) in China. For Cd, Fatoki et al [86] and Awofolu et al [87] had results similar to those obtained in the present study from the Umtata and Tyume Rivers in the same province, respectively.…”

“…A number of studies in South Africa [35][36][37] and other regions of the world, including Kenya [38], Iran [39], Tunisia [40], Poland [8], China [41], and the United States [42], among others, have documented heavy metal contaminations in soil and aquatic environments. For instance, Shamuyarira and Gumbo [35] reported the occurrence of high levels of Cd, Pb, Zn and Cu, above the recommended guidelines, in sludge samples collected from five different locations in the Limpopo area of South Africa.…”

Evaluation of Fecal Coliform Prevalence and Physicochemical Indicators in the Effluent from a Wastewater Treatment Plant in the North-West Province, South Africa

“…Similar findings were observed in this study with lead complying 100% to both general and special limits. A study in China indicated cases of lead above the Chinese standard and such occurrence was mostly observed from WWTPs receiving wastewater from electroplate plants [ 66 ].…”

Comparison of Heavy Metals Removal from Aqueous Solution by Moringa oleifera Leaves and Seeds

“…Equation (1) gives the amount of metallic ions sorbed per gram of adsorbent at each contact time t, q t (mg/g) by L-MO and S-MO:…”

“…Beyond even a low concentration, their presence in aquatic and soil matrixes can cause undesirable effects on human and animal health. Therefore, the United States Environmental Protection Agency (US EPA) established that the maximum concentration of the aforementioned heavy metal ions in wastewater must be 1.7 µg/L for Co(II), 5 µg/L for Cd(II), 15 µg/L for Pb(II), and 20 µg/L for Ni(II) [1,2]. However, concentration values up to 200 µg/L, 20 µg/L, 900 µg/L, and 670 µg/L of Pb(II), Cd(II), Co(II), and Ni(II), respectively, were reported in different effluents due to the uncontrolled discharge of these pollutants in the wastewater [1,2].…”