<p class="first" id="d13504947e96">Reclaimed water has recently become an important
water source for urban use, but the
composition of dissolved organic matter (DOM) in reclaimed water has rarely been characterized
at the compound level because of its complexity. In this study, the transformation
and changes in composition of low molecular weight DOM in water reclamation processes,
where secondary effluent of the municipal wastewater treatment plant was further treated
by biofiltration, ozonation and chlorination, were investigated by "unknown" screening
analysis using Orbitrap mass spectrometry (Orbitrap MS). The intense ions were detected
over an m/z range from 100 to 450. In total, 2412 formulae with various heteroatoms
were assigned, and formulae with carbon (C), hydrogen (H) and oxygen (O) only and
C, H, O and sulfur (S) were the most abundant species. During biofiltration, CHO-only
compounds with relatively high hydrogen to carbon (H/C) ratio or with saturated structure
were preferentially removed, while CHOS compounds were mostly removed. Ozonation induced
the greatest changes in DOM composition. CHOS compounds were mostly decreased after
ozonation while ozone selectively removed CHO compounds with relatively unsaturated
structure and produced compounds that were more saturated and with a higher degree
of oxidation. After chlorination, 168 chlorine-containing formulae, chlorinated disinfection
by-products (DBPs), were additionally detected. Candidate DBP precursors were determined
by tracking chlorinated DBPs formed via electrophilic substitution, half of which
were generated during the ozonation.
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