Toc vcsn

Extracellular algal organic (EOM) matter released by the microalgae during its growth was analyzed for its total organic carbon (TOC), humic acid, and pigment contents. Analysis was conducted using a TOC analyzer ( TOC-V_CSN, Shimadzu) and UV–vis spectrophotometer (UV-2600i, Shimadzu). The growth medium was recycled three times without any pretreatment. After the third cycle, water was treated with commercial granular activated carbon (Sigma Aldrich) to remove the EOM and pigments by measuring the absorbance at 254 and 440 nm, respectively (Mejia-da-Silva et al., 2018 (link)). All the macro- and micronutrients were added before each recycle.

The residual concentration of glucose was measured with a dinitrosalicylic acid (DNS) reagent [16 (link)]. The residual IC was analyzed by a total organic carbon analyzer (TOC-VCSN, Shimadzu Corp., Kyoto, Japan). To analyze chlorophyll-a, 10 mL of algal suspension was collected from the reactor and filtered through a 0.45 μm glass microfiber filter/Circles (GF/C). The filtrate was mixed with 90% acetone and stored at 4 °C in the dark for 24 h. The filtrate was then centrifuged at 3000 rpm for 20 min. The OD of the supernatant was measured at wavelengths of 664, 647 and 630 nm with a spectrophotometer (Optizen POP, Mecasys Co., Ltd., Daejeon, Korea). The concentration of chlorophyll-a in the extract was calculated using Equation (4).

where C_a was the concentration of chlorophyll˗a in the extract and OD₆₆₄, OD₆₄₇ and OD₆₃₀ were the corrected optical densities at the respective wavelengths.
The amount of pigment per unit volume was calculated as follows (Equation (5)): $\mathrm{Chlorophyll}¯\mathrm{a}\left({\mathrm{mg}\mathrm{m}}^{-3}\right)=\frac{{\mathrm{C}}_{\mathrm{a}}\times \mathrm{extracted}\mathrm{volume}\left(\mathrm{L}\right)}{\mathrm{volume}\mathrm{of}\mathrm{sample}\left({\mathrm{m}}^3\right)}.$

The different samples collected from the investigated processes were analyzed for electrical conductivity (EC), total dissolved solids (TDS), Ca²⁺, Mg²⁺, Na⁺, TOC, and pH.
The removal efficiency for each component was expressed in terms of rejection (R) according to the following equation: $R=1-\left(\frac{C_p}{C_f}\right)·100$
where C_f and C_p are the concentrations of a specific component in the feed and permeate, respectively.
EC and TDS were measured using a digital conductivity meter (HI 2300 Microprocessor Conductivity, Hanna Instruments, Woonsocket, RI, USA).
Ca²⁺, Mg²⁺, and Na⁺ concentrations were determined by using a high-resolution continuum source atomic absorption spectrometer (HR-CSAAS, ContrAA700, Analytik Jena AG, Jena, Germany), with a high intensity Xe short arc lamp as a continuum source. Samples and standards were appropriately diluted (300 times for Mg and Ca, 3000 times for Na). Subsequently, they were acidified with 1% HCl and the absorbance measurements were performed using the spectral lines at 422.67 nm, 588.99 nm, and 285.21 nm for Ca²⁺, Na⁺, and Mg²⁺, respectively.
pH was measured by an Orion Expandable ion analyzer EA 920 pH meter (Allometrics, Inc., Baton Rouge, LA, USA) with automatic temperature compensation.
Total organic carbon (TOC) was analyzed by a TOC analyzer (TOC-V CSN, Shimadzu, Kyoto, Japan).

To determine BOD₅, treated wastewater was sampled from the aeration tank once per a day. BOD₅ was measured at 20 °C via a respirometric method by using a BODTrack^TM apparatus equipped with a pressure sensor (Hach, Düsseldorf, Germany), in the presence of a nitrification inhibitor for 5 days. Concentrations of NH₄-N, NO₂-N, and NO₃-N were determined using an ion chromatograph, IC-2010 (Tosoh, Tokyo, Japan). Total nitrogen was analysed with a total carbon and nitrogen analyser, TOC-V CSN (Shimadzu, Kyoto, Japan).

For geochemical analysis of snow, 50 ml of melted snow samples were filtered using a 0.22 μm syringe filter and stored at -20°C. DOC was analyzed using a Shimadzu TOC-V/CSN with three replicates of 100 μl injection volume as described previously (Fujii et al., 2012 (link)). Total ammonia was measured using the Sigma ammonia assay kit (AA0100, detection limit of 11 μM) and total phosphate was measured using the Abcam colorimetric phosphate assay kit (ab65622, detection limit of 1 μM). A Dionex ICS-1500 ion chromatograph was used to measure chloride, nitrate, and sulfate.

Water for dissolved organic carbon (DOC) analysis was collected at 1 m depth, filtered through a Whatman® 25 mm GF/F (0.7 μm porosity) which was pre-combusted in a drying oven at 500°C for at least four hours, and stored in pre-rinsed 40 mL vials (VWR®TraceClean®). The samples were preserved with 250 μL trace metal grade hydrochloric acid and analyzed with a Shimadzu® TOC-V CSN at Scripps Institution of Oceanography.