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The Yangtze Estuary is heavily influenced by coast-continent geochemical processes and anthropogenic activity; thus, the source and distribution of chromophoric dissolved organic matter (CDOM) in the estuary are strongly impacted by these processes. Here, a series of samples were collected from across the Yangtze Estuary to investigate the source and spatial dynamics of CDOM and its components throughout the system. Three indices (a(355), spectral slope, and fluorescence) were then calculated and interpreted. The results indicated that the distribution of CDOM was dominated by allochthonous input, conservative mixing, and phase transfer. The contribution of biogenic CDOM to total CDOM increased with salinity, and three individual CDOM components were identified upon fluorescence excitation emission matrix spectroscopy and parallel factor analysis of the water samples: C1, corresponding to humic substance-like CDOM, C2, corresponding to tryptophan-like CDOM, and C3, corresponding to tyrosine-like CDOM. C1 primarily originated from a terrestrial source, C2 had widespread origins, none of which played a dominant role, and C3 mainly originated from allochthonous input in the medium salinity area. Unexpectedly, no marine humic-like component was found in the surface water of the Yangtze Estuary, possibly because turbidity decreased the depth of sunlight penetration, limiting production of this component.

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Three PAC-DMBRs were developed for wastewater treatment under different PAC dosages with biomass concentrations averaged at 2.5, 3.5 and 5.0g/L. The DMBRs could be continuously operated at 40-100L/mh, while higher fluxes were obtained within the PAC-DMBRs with hydraulic retention times varying in 4-10h. A dose of 1g/L PAC brought about obvious improvement in the sludge particle size distribution, settling, flocculating and dewatering properties due to the formation of biological PAC, and the sludge properties were further improved at a higher PAC dose (3g/L). The addition of PAC notably shortened the DM formation time after air backwashing and enhanced pollutant removal. Moreover, under a long solid retention time (approximately 150d), the concentrations of both soluble and bound extracellular polymeric substances (EPS) decreased substantially because of the adsorption and biodegradation effects of the biological PAC. No obvious impact on biomass activity was observed with PAC addition.

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Highlights  Fiber-like substances served as the skeleton of larger size aggregates.  A fractionation method was proposed for cake sludge characterization.  Cake sludge had higher cake layer fouling potential but prevented pore blocking.  Accumulation of organics (mainly polysaccharides) and inorganics was detected.  Refractory organics accumulation enhanced their microbial metabolic diversity.

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