Carbon quantum dots (CQDs) were synthesized via a hydrothermal method, in which extracellular polymeric substance (EPS) from anaerobic ammonium oxidation (anammox) granular sludge was used as a carbon precursor, while citric acid and ethylenediamine were applied as auxiliary carbon source and passivation agent, respectively. The synthesized CQDs, with orderly spherical shape and mean size of 7.15 nm, emitted blue fluorescent light under UV radiation of 365 nm. The CQDs had a high fluorescence yield (40.84%), with good water solubility and excellent spectroscopic properties. In addition, the CQDs exhibited selective, sensitive and distinctive fluorescence quenching behaviors for Cr(VI) and Mn(VII) in a PBS buffer solution (NaH₂PO₄–Na₂HPO₄) of pH 7, with a detection limit of 5.8 nM for Cr(VI) and 2.3 nM for Mn(VII). Owing to the nitrogen components from the EPS of anammox granules, the CQDs were well nitrogen-doped, promoting electron-transfer and leading to reduction between the CQDs and Mn(VII)/Cr(VI). These results indicate that CQD-based chemical sensing is a simple and efficient means for the fluorescence detection of Mn(VII) and Cr(VI).

Immobilized sulfate-reducing bacteria (SRB) in polyvinyl alcohol (PVA)-sodium alginate matrix were applied as biosorbents to remove cadmium (Cd) from aqueous solutions. Multiple characterization techniques including scanning electron microscope (SEM)-energy dispersive spectrometer (EDS), and Fourier transform infrared (FT-IR) spectra indicate that immobilized beads provided a suitable microenvironment for SRB. Performance tests show that Cd removal was highly affected by pH value and temperature, with optimum temperature at 35ºC and pH value of 8.0. A pseudo second-order model was applied to describe the adsorption kinetic. FT-IR and x-ray photoelectron spectroscopy (XPS) analyses imply that biosorption, sulfide, and hydroxide precipitation are the main mechanisms for removing Cd. The immobilized SRB beads have great potential for remediating Cd-containing wastewater.