Biological Alteration of Zinc Complexation Characteristics of Dissolved Organic Matter in Domestic Wastewater Treatment Plant Effluent under River Water Environment

Abstract

Naturally occurring processes such as biological reaction might modify the properties of dissolved organic matter (DOM) for binding with heavy metals. Complexation of heavy metals with DOM determines their environmental and ecological impacts. In this study, biodegradation experiments were carried out separately for river water and river water spiked with DOM in wastewater treatment plant (WWTP) effluent to evaluate the biological alteration of zinc complexation characteristics of DOM under river water environment. Zinc complexation parameters, conditional stability constant and binding site concentrations were determined using anodic stripping voltammetry with Scatchard linearization. Total ambient zinc binding site concentration of river water DOM was reduced from 410 nM to 74 nM (82% decline) during two weeks of incubation. Compared to the river water DOM, 1-month incubation of DOM in WWTP effluent under the river water environment, showed only 22% decline in total ambient Zn binding sites. On the other hand, conditional stability constants, for Zn binding sites of DOM from WWTP effluent, did not vary during 1 month of incubation. The result suggests that metal (Zn) binding sites of DOM from WWTP effluents are biologically persistent in the urban river water environment.

Metal (Zn, Cu, Cd and Ni) Complexation by Dissolved Organic Matter (DOM) in Wastewater Treatment Plant Effluent

“…The conditional stability constant for Zn with DOM in WWTP effluents determined in this study was consistent with the values (log K 1 ' = 6.9 and log K 1 ' = 7.2) reported by Cheng (2005) and Chaminda et al(2010b), respectively. The conditional stability constant (log K 1 ' = 12.9) for Cu with DOM in WWTP effluents reported by Sarathy …”

“…According to Scatchard linearization technique, Zn and Cu titration data showed distinctively separate two linear regions within a set of plots, that indicate two ligand classes (Chaminda et al, 2010b) for WWTP effluents (see Table 1). In contrast to Zn and Cu, Cd was best modeled as one-ligand system (only one linear region in the plot) with Scatchard linearization, indicating that only one type of ligand for Cd was available in the effluent of WWTP.…”

“…Metal titration against DOM in water samples were conducted by the addition of known increments of metals (Zn, Cu and Cd, from CertiPUR) followed by the measurement of electrochemical labile metals (Zn, Cu and Cd) after a certain equilibrium period (titration condition: DOC = 3.5 mg C/L; pH ≈ 7; ionic strength = 0.02 M; temperature = 25°C). The titration data were then linearly transformed using the Scatchard equation, which was derived from appropriate mass balance and conditional stability constant (K') relationship, as explained in Chaminda et al (2010a and2010b).…”