Biodegradation of Carbon Sources in Seawater

Add 40 grams of each carbon source into a 1,000 mL wide mouth bottle, and mixed with 800 ml natural seawater (salinity 31 ± 1 ‰, pH 7.72 ± 0.15, DO 5.56 ± 0.41, COD 2.32 ± 1.17). The bottle was then sealed with a plastic cap to prevent evaporation and contamination. The experimental temperature was 25°C and the experimental period was 30 days. The water in the bottle was collected every 2 days for determination of COD, TOC, and, DOC. Analysis of CODs was done according to the method described in the Standard Method for Examination of Water and Wastewater GB 17378.7-1998 (1999) . TOC and DOC were measured using a TOC analyzer (Shimadzu, TOC-L) with an automatic sampler (Shimadzu, ASI-V). At the end of this experiment, the contents of short-chain fatty acids (SCFAs) in water were measured. SCFAs, including acetic acid (AC), propionic acid (PA), butyric acid (BA), and other types (isobutyric acid, valeric acid, isovaleric acid, and hexanoic acid) were measured by ion chromatography-mass spectrometry (Shimadzu GCMS QP2010-ULTRA, Japan). After each sampling, an equal amount of sterilized seawater was added to the mouth-wide mouth bottle to keep the volume constant. Before and after the experiment, the carbon source samples were analyzed by Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. The carbon sources were crushed and randomly sampled to observed using SEM (ZEISS Gemini SEM 300, Germany), and the carbon distribution on the surface of the solid carbon source was analyzed using SEM-energy dispersive X-ray spectroscopy (EDS) (ZEISS Gemini SEM 300, Germany). The functional group information of carbon sources was identified by FTIR using a FTIR spectrometer (Thermo Scientific Nicolet iS20, USA). The physical properties of the three repeated tests are shown in Table 1.