Toc l tnm l

Activated sludge samples were collected from seven full-scale wastewater treatment processes (WWTPs) treating fermentation wastewater (sites A1, A2, B1, B2, and C1), chemical wastewater (site D1), and municipal wastewater (site E1) in Japan. All wastewaters did not contain specific organic carbon or nitrogen species and/or toxic chemicals. After centrifugation (8,500 × g, 10 min), the precipitated sludge and supernatant were collected separately. The supernatant samples were filtered with a 0.22 µm pore-sized membrane filter (Millex-GV Syringe Filter Unit, 0.22 µm, PVDF, 33 mm, Merck, Rahway, NJ, USA). The samples were stored in an −80 °C freezer before use for DNA extraction and chemical analyses. In this study, due to technical limitations, we have measured only TC and TN concentrations, which are hypothetically considered to affect wastewater treatment performance. TC and TN concentrations were analyzed using a TOC-TN analyzer (TOC-L/TNM-L; Shimadzu, Kyoto, Japan) (Inaba et al., 2018 ).

Total organic carbon (TOC) was determined in the form of non-purgeable organic carbon (NPOC). An organic carbon analyzer TOC-L/TNM-L with TOC-Control L software (Shimadzu, Japan) was used for the TOC determination. The liquid sample before (blank samples) and after the photocatalytic process was acidified to pH < 3.0 with 1.0 M HCl and blown with air at a flow of 200 mL min⁻¹. Next, the sample was burned with a platinum catalyst at 720 °C with a continuous carrier gas flow. Air was used as the carrier gas at a flow rate of 150 mL min⁻¹ and a pressure of 285 ± 5.0 kPa. Carbon dioxide produced by catalytic combustion of the sample was directed to a non-dispersive infrared sensor (NDIR). The analysis was performed at the temperature of 65 ± 1 °C, and the concentration of CO₂ obtained as a result of combustion of the sample was proportional to the TOC content in the sample. Each of the samples was analyzed in triplicate. The degree of sample mineralization was determined from the formula: $$MR=\frac{TO{C}_i-TOC}{TO{C}_i}·100\%$$
where MR is Mineralization rate (%); TOC_i is the TOC value before photocatalytic process, initial concentration of TOC in the sample (mg L⁻¹); TOC is TOC value after the photocatalytic process (mg L⁻¹).

The mixed liquor suspended solid, temperature, DO, and pH in all three compartments of the MBR as well as the TMP of the membrane module were monitored throughout the operation. The liquid and solid phases of the activated sludges sampled from the first and second compartments were separated by centrifugation (15,300×g, 15 min, 4 °C) and the supernatants were filtered using a cellulose acetate membrane (ø0.20 μm, ADVANTEC, Tokyo, Japan). The TOC and total nitrogen (TN) concentrations in the supernatants and treated effluent were analyzed using a TOC-TN analyzer (TOC-L/TNM-L; Shimadzu, Kyoto, Japan). The COD value was measured with a COD analyzer (DR2800 and DRB200; Hach, CO, USA) and an appropriate kit (TNT820 or TNT821; Hach).