Toc 5

The model xenobiotic was supplied by Fluka Chemical Corp. Amaranth concentration was determined spectrophotometrically (Utrospec3000, PharmaciaBiotech), λ = 520 nm.[2 ] The COD in water was analysed according to a standard procedure.[13 ] Total organic carbon (TOC) was measured with a TOC/TN analyser (TOC-V, SHIMADZU CORP., Japan).
Efficiency of Amaranth removal was calculated according to the following formula:
where Ct is the concentration of Amaranth in the moment t.
Rate of biodegradation was calculated according to the following formula:
where Ct is the concentration of Amaranth in the moment t.

Shimadzu TOC-V (Japan) was used to determine the SOC and SIC. The TOC (total organic carbon) instrument uses combustion oxidation-non-dispersive infrared absorption method for total organic carbon. Using high purity air (N₂ + O₂) as carrier gas, quantitative soil samples were added to the total carbon (TC) and IC (inorganic carbon) reaction chamber, respectively. The TC and IC were measured under their respective working conditions, and the TOC was calculated (TOC = TC—IC). Test conditions: carrier gas (high purity oxygen) pressure: 300 kPa; flow rate: 500 ml/min. TC condition: temperature 900 °C, cobalt oxide platinum catalyst. IC condition: temperature 200 °C, 25% phosphoric acid (superior purity) is reactive acid. Glucose (superior purity) and anhydrous sodium carbonate (Reference Reagent) are used as standard samples of TC and IC respectively.

DOC samples were analysed on a Shimadzu TOC-V (Sweden) or TOC-L (UK) analyser (Shimadzu, Japan) and quantified as non-purgeable organic carbon (NPOC). Measurements were made in triplicate. For Swedish samples, pure water (Milli-Q) blanks and an ethylenediaminetetraacetic acid (EDTA, 8 mg C per L) standard were included throughout the analysis run. For UK samples, deionised (DI) water blanks and a 10 mg C per L potassium hydrogen phthalate standard were used throughout for QA/QC. For both studies, the measured values were within 5% of the expected values.
Before sampling, we also determined the concentration of water required to rinse the cellulose acetate filters used in the UK so that they did not release any DOC. Briefly, we flushed DI water in increments of 10 mL from 0 to 50 mL through a cellulose acetate syringe filter. Then, we passed an additional 25 mL of DI water through the filter and collected the filtrate. We measured DOC concentration in the filtrate and in the DI water. Passing 20 mL of DI water through the filter was enough to reduce the DOC to the original concentration of the DI water (mean ± standard error: filtered DI = −0.003 ± 0.052 mg C per L; original DI = 0.008 ± 0.031 mg C per L, N = 3).

MWCO of the membranes was determined by the molecular weight of the neutral solute, in which 90% of the solute was retained by the membrane. The MWCO values of the pristine and Fenton-modified membranes were obtained using the previously reported method [30 (link),31 (link),32 (link)]. Filtration tests were conducted using the feed solutions of 50 ppm polyethylene glycol (PEG) with molecular weights of 400, 600, 1000, and 2000 Da as a model solute at 25 °C and a flow rate of 2.5 L/min. The concentrations of PEGs in the feed and permeate were measured using a total organic carbon analyzer (TOC-V, Shimadzu, Japan). Because the molecular weight (M_w, Da) of the solute, PEG, is related to the Stokes–Einstein radius (R, cm), the average pore size of the membrane can be estimated [33 (link)] using
$$R=\left(16.73\times {10}^{-10}\right)M_w^{0.557}$$

Water samples were filtered through a pre-combusted (500°C for 6 h) filter (GF/F Whatman^™), and stored frozen until analysis for nutrient concentrations at the University of Hawai‘i at Hilo Analytical Laboratory. Nutrients were analyzed on a Pulse Technicon^™ II autoanalyzer using standard methods (NO₃^- + NO₂^- [Detection Limit (DL) 0.07 μmol/L, USEPA 353.4], total dissolved phosphorus (TDP) [DL 0.5 μmol/L, USGS I-4650-03], H4SiO4 [DL 1 μmol/L, USEPA 366]), and reference materials (NIST; HACH 307–49, 153–49, 14242–32, 194–49). Total dissolved nitrogen (TDN) was analyzed by high-temperature combustion, followed by chemiluminescent detection of nitric oxide (DL 5 μmol/L, ASTM D5176, Shimadzu TOC-V, TNM-1) [58 ]. Salinity, pH, and temperature were measured at the time of water collection using a YSI Pro 2030 multi-parameter probe.

The experiment of BPA degradation was carried out over MxOy–Bi₂O₃ (M: Ca, Mg, Sr) binary oxide in a cylindrical quartz micro-photoreactor. Fifty mL of a 25 mg/L aqueous BPA solution was prepared and then 100 mg of catalyst was added in this mixture to initiate the reaction. Before exposure illumination, the solution was stirred in the dark for 1 h to establish an the adsorption-desorption equilibrium between the catalyst and the liquid. All reactions were conducted at ambient temperature under constant magnetic stirring and natural pH conditions. The photocatalytic activity of catalyst were compared using different light sources (UV-B, sunlight, and visible light irradiation). During the irradiation, sample was taken at regular intervals from the solution and filtered through a PTFE filter (pore size 0.45 mm for use total organic content (TOC) measurement (TOC-V, Shimadzu, city, country) and HPLC analysis. The analysis of BPA was performed by a HPLC (Thermo Scientific) using a C18 column. The mobile phase consists of a mixture of water and acetonitrile (40:60, v/v).