Hach2100n

All the oenological tannins were analyzed using the gelatin precipitation method [59 ]. Briefly, 4 mL of oenological tannin solutions were placed in two centrifuge tubes. Tube A (sample) received an addition of 0.4 mL of aqueous BSA solution (7% w/v). Tube B (control) was prepared similarly, but the added BSA solution was replaced with water. After 24 h at room temperature, the two tubes were centrifuged, and the supernatants were diluted 1:100 with water and read at 280 nm in a 1 cm quartz cuvette, obtaining the absorbance values (A₀ for tube B diluted solution, A for tube A diluted solution). The gelatin index was calculated according to the following formula:
This index gives information concerning the reactivity of the tannin: the higher the value, the higher the reactivity of the extract towards proteins.
The turbidity of Tube A was also measured before and after the addition of BSA solution and monitored for approximately 20 min, until turbidity stabilization, using a HACH2100N turbidimeter.

The pH was quantified with a Hannah pH–meter (HI98130, Hanna Instruments, Woonsocket, RI, USA). A HACH 2100N turbidity meter (Hach Company, Colorado, CO, USA) HACH DR 3900 within the wavelength of 455–635 nm (Hach Company, Colorado, CO, USA) was used for the COD and TKN measurements. The sludge samples were characterized using scanning electron microscopy and energy dispersive X-ray (SEM/EDX, FEI Nova NanoSEM 450 coupled with EDT and TLD detector) equipment based at the University of Cape Town, South Africa. The biogas composition analysis was carried out with a Geotech Biogas 5000 Portable Biogas Analyser (ISO17025) supplied by Keison Products, (Chelmsford Essex, UK).

In this study, synthetic wastewater was simulated with the chemical compositions shown in Table 1. All the chemicals were of analytical grade and were evenly dissolved in 25 L of deionized water (ELGA PURELAB Option-Q water deionizer, UK) at room temperature [37 ]. Immediately after preparation, the initial sample concentrations were characterized in terms of turbidity (13.8 ± 0.94 NTU), color (47 ± 1.74 PtCo), and total suspended solids (TSS; 19 ± 0.24 mg/L). Turbidity was measured using a Hach 2100N turbidimeter, whereas color and TSS were analyzed by a spectrophotometer (HACH DR 3900, Germany). All the procedures used for analysis conformed to the standard methods of water and wastewater treatment [38 ].