On-site classification of humic-rich hydrocolloids and their metal species by means of online multistage ultrafiltration.

Humic-rich hydrocolloids and their metal species (e.g., Al, Fe, Ca, Cu, Fe, Mg, Mn, Pb, Zn) in selected bogwaters of German origin (Black Forest (HO), Muensterland (VM), Arnsberger Wald (AW)) were size classified in the subparticulate and macromolecular range by on-site multistage ultrafiltration (MST-UF). For this purpose two MST-UF cascades, equipped with up to eight conventional flat membranes (0.45, 0.22, 0.1 micron (Millipore); 100, 50, 10, 5, 3, and/or 1 kDa (Gelman PallFiltron OMEGA), were coupled and used for an online fractionation of hydrocolloidal matter immediately after water sample collection. Quantification of dissolved organic carbon (DOC) and metals was carried out off-site by conventional laboratory methods (carbon analyzer, atomic spectrometry). The size distribution of some humic-rich hydrocolloids (e.g. in HO) was exhibited to be surprisingly stable even over storage periods of 1-4 weeks. On the other side, their size distribution (e.g. in VM) considerably varied during the collection period. The natural metal loadings (e.g. Al, Fe, Mn, Zn) of hydrocolloids showed characteristic size distributions and, mostly, strong metal enrichment in subparticulate and macromolecular fractions. Further results of on-site classification of hydrocolloids, obtained by parallel single-stage ultrafiltration (P-UF) with the same membranes, were only comparable to those of MST-UF in the case of low DOC concentration.