Ph meter

To evaluate the soil characteristics after the materials addition, a mixed sample from three points per plot of 0–30 cm-soil layer were taken from soil samplers (φ5 cm) along the diagonal line, on June 2021. Soil samples were air-dried, crushed, sieved (0.149 mm mesh) and stored in sealed plastic bags [29 ]. Soil cores were also collected (using a 200 cm³ cylinder) from each plot, for determination of BD and maximum water-holding capacity [30 ]. SOM was determined by the potassium dichromate oxidation-heating method [31 ]. Hydrolysable nitrogen was determined by the alkaline-hydrolysis diffusion method [32 ]. Cation exchange capacity was determined by the ammonium chloride–ammonium acetate exchange method [33 ]. Soil pH and electrical conductivity were determined using a pH meter (Hach, Loveland, CO, USA) with a measuring range of −2.00 to 14.00, and an electrical conductivity instrument (Leici Company, Shanghai China) with a measuring range of 0.0 to 10.0 ec in the supernatant of 2:5 and 1:5 soil and water mixtures, respectively [34 ,35 ]. Water-soluble Cu was measured using inductively coupled plasma-mass spectrometry (ICP-MS) on the supernatant of 1:12.5 soil-to-water ratio. The suspension reacted on a reciprocal shaker for 2 h, was centrifuged (1400× g) for 10 min, filtered with a nylon membrane (0.45 mm), and stored in 0.2% trace metal grade HNO₃ [36 (link)].

Prior to chemical analysis, the samples were freeze-dried (−80°C), thoroughly ground, and sieved (<0.075 mm). Soil pH was determined using a pH meter (HACH, Loveland, United States) after mixing 10 g of soil with 25 ml of MQ water in a 50 ml conical flask. The total nitrogen (TN) and total organic carbon (TOC) contents were measured using an elemental analyzer (Vario MACRO cube, Elementar, Hanau, Germany). The sieved samples were then completely digested using concentrated hydrofluoric acid and nitric acid (1:5, v/v) before elemental analysis (Xiao et al., 2021b (link)). After digestion, the contents of Cd were measured using inductively coupled plasma mass spectrometry (ICP-MS, Agilent, 7700x, California, United States; Liu et al., 2020 (link); Wang et al., 2021 (link)). To improve the reliability of ICP-MS, certified references (SLRS-5 and GBW07310) were used during the measurements following our previous studies (Xiao et al., 2021b (link)).

The composite samples were retrieved from the serum bottles at predetermined intervals and subsequently centrifuged at 10,000 rpm for 5 min. The supernatant was filtered through a 0.45-μm membrane for the subsequent analysis of soluble chemical oxygen demand (sCOD) and filtered through a 0.22-μm membrane for the analysis of VFAs.
The COD, TS, and volatile solids (VS) were determined with standard methods (APHA, 2005 ). Acetate, propionate, butyrate, valerate, and caproate were measured by high-performance liquid chromatography (HPLC) (Bio-Rad, Hercules, California) using 5 mM H₂SO₄ as the mobile phase (Huang et al., 2022 (link)). The cumulative VFAs, calculated as acetate (g/L), were the sum of acetate, propionate, isobutyrate, and n-butyrate during fermentation. pH was measured with a pH meter (HACH, United States). The gas volume collected in a 1-L sampling bag was measured using an air pump every 1–3 days, and then, the gas was transferred back into the bag. The hydrogen content in both the gaseous samples in the sampling bag and the headspace was measured using gas chromatography apparatus equipped with a thermal conductivity detector (TCD) (Tianmei, GC7900, China). In addition, the decomposition of garden waste was assessed by Fourier-transform infrared (FT-IR) spectroscopy (Bruker; VERTEX 70; Germany) through a full scan across the wavenumber range of 400–4,000 cm⁻¹.

Physicochemical analyses were conducted according to the Association of Official Agricultural Chemists [23 ]. They were performed for each production on days 0, 15, 30, and 60 for batches A, B, C, and D, by taking the homogenized cheese used for microbial analyses. The samples were homogenized in ultrapure water to be measured with a pH meter (Hach Lange Spain S.L.U., Barcelona, Spain) previously calibrated with standard solutions (Scharlau Chemie S.A.). The a_w was measured with a Novasina Lab Master Water activity meter model a_w SPRINT-TH 300 (Novasina AG, Lachen, Switzerland). Moisture content was calculated through the dehydration of samples at 105 °C with the addition of previously dehydrated washed sea sand (Scharlau Chemie S.A.).