Toc vcph instrument

During the experiment, the hydraulic conductivity and the chemical compositions of sampled leachate from the influent, middle, and effluent of each column were tested regularly to study the clogging development in the gravel and nonwoven geotextile layers. At the end of the experiment, the precipitate properties were detected to analyze the clogging mechanism.
When testing the hydraulic conductivity, two methods of falling head and constant head were duly adopted according to the filtration velocity [20 (link)]. For the liquid samples, the pH value was measured by a Fe20 pH electrode (Mettle, Switzerland); the total organic carbon (TOC) and TIC were tested using a TOC-VCPH instrument (Shimadzu, Japan); the VFAs were obtained by gas chromatography (GC, Shimadzu, Japan) with flame ionization detectors, and the Ca²⁺ and Mg²⁺ concentrations were analyzed by inductively coupled plasma-atomic emission spectrometry (ICP-AES, Perkin Elmer, USA).
For the solid samples, the ratio of organic to inorganic substances was measured by weighing after being dried at 105 and 550 °C; the elemental composition and crystal structure of the inorganic part were studied by X-ray fluorescence spectrometer (XRF, Thermo Fisher, USA) and X-ray diffraction (XRD, PAN alytical X’Pert, The Netherlands), respectively.

Samples for quantification of DOC were collected from the 0.2-µm-filtered seawater. Each sampling day, four replicate samples of 10 mL were acidified to pH 2 (HCl, p.a.) in pre-combusted glass vials (400 °C, 4 h) and stored in the dark at 4 °C until analysis. DOC was analysed on a Shimadzu TOC-VCPH instrument via high temperature catalytic oxidation. Analytical accuracy and precision were tested with deep-sea reference material (D. Hansell, University of Miami, USA) and were better than 5%. Standard deviation for replicates was on average 2.8 ± 1.6%. DOC analysis of the 0.5 L HMWDOM samples was also performed. Based on the DOC concentrations of the DOM (0.2-µm-filtered seawater) and HMWDOM samples, we determined that by TFF we recovered on average 5.5% of the DOM.