Phs 25

SEM images were acquired by using a field emission SEM (JSM-7500F, JEOL), and the samples needed to be coated with a gold film (a thickness of ~3–5 nm) beforehand. The optical microscopy images were obtained using a Motic BA400 microscope equipped with a charge coupled device camera. The pH of the solutions was calibrated by using a precision pH meter PHS-25 (INESA) with a resolution of 0.01. The Young’s modulus of the SU-8 microstructures was measured by using an Agilent Nano Indenter G200 equipped with an XP-style actuator, and the continuous stiffness measurement method was adopted. The measurement was carried out using a Berkovich diamond tip at 30 °C with a relative humidity of 20%.

A distillation machine prepared the distilled water (Shenzhen Yiliyuan Water Treatment Equipment Co., LTD., Shenzhen, China). The main components of acid rain are NH⁴⁺, Ca⁺, Na⁺, K⁺, Mg⁺, H⁺, SO₄²⁻, HSO₄²⁻, NO₃⁻, HCO₃⁻, Cl⁻, etc. The concentration of ${\mathrm{SO}}_4^{2-}$ in acid rain is 5–10 times higher than that of ${\mathrm{NO}}_3^{-}$ . In this paper, the acid solution was prepared by analytically pure sulfuric acid and nitric acid and distilled water, according to ${\mathrm{SO}}_4^{2-}:{\mathrm{NO}}_3^{-}$ = 9:1 and PH = 3 [28 (link),29 (link)], which is measured by PH-meter (PHS-25, Shanghai INESA Scientific Instrument Co., Ltd., Shanghai, China). Sodium chloride crystals and distilled water at a concentration of 7% prepared the salt solution. Figure 1 shows the distilled water and two solutions.

Water content, total organic carbon (TOC, dissolved), total nitrogen (TN), total sulfur (TS), total organic sulfur (TOS), and pH of the samples were determined. Briefly, the samples were dried at 105°C to determine the moisture. Any animal and plant residues, and stones were removed after drying. The samples were ground and passed through a 2-mm sieve. Then, the samples were mixed with DI water at a sample-to-water ratio of 1:5 (w/v) with continuous mixing for 4 h, and filtered with membrane filters (0.45 μm, F513132, Sangon Biotech Co. Ltd) prior to TOC and TN analyses (TOC-L TNM-L CSN, Shimadzu, Japan) (Jones and Willett, 2006 (link); Li et al., 2017 (link)). TS and TOS were measured using an automatic sulfur meter (CTS3000, Xuzhou Terui Instrument and Equipment Co., Ltd., Xuzhou, China) (Lange and Brumsack, 1977 (link); Bohn et al., 2002 ). Sample pH was determined with a soil-to-water ratio of 1:2.5 (w/v) using a pH meter (PHS-25, Shanghai INESA Scientific Instrument Co., Ltd., Shanghai, China) (Liang et al., 2017 (link)).

The initial and final pH readings of the lignin media, and the initial and final pH of the chemically pretreated lignin solution with H₂O₂ were conducted with a pH meter (INESA, PHS-25, China) with a precision of 0.01. Intermediate readings were made with litmus paper. For litmus paper readings, a pH band of ±0.50 was added throughout the readings.

The pH, reducing sugar, nitrite, and salinity of both NF and BMF samples after 10, 30, 60, and 90 days of fermentation were determined. Reducing sugar and nitrite were measured according to Chinese national standards (GB 5009.7-2016 and GB 5009.33-2016). pH of the samples was measured on a pH meter (PHS25, INESA, Shanghai, China), and their salinity was determined by a salinity meter (ES-421, ATAGO, Tokyo, Japan).