Technical Yearbook 2024

FIGURE 1. Results of biochemical methane potential tests using primary winery wastewater sludges from the crush and post-crush periods. 2 The results from the first study at ambient temperatures are shown on the left of the vertical black line, while those from a second study comparing results from ambient and mesophilic temperatures (37°C) are shown on the right of the line. ISR = inoculum to substrate ratio; N = nutrients (Co, Zn, Cu).

TABLE 1. Estimated amount of energy from primary winery wastewater sludge for different-sized wineries. 3 Units of measurement

Size of the winery: tons of grapes crushed per annum 1 000 5 000 10 000 20 000

Wastewater

m 3 .year -1 kg.year -1

2 633 5 953

11 654 26 349

22 116 50 004

41 971 94 896 12 266 25 760

Primary wastewater sludge

Methane

ML CH 4 .year

769

3 406 7 152

6 464

-1

Energy

kW.year -1

1 616

13 574

ML = megalitres; CH 4 = methane.

season and skewed the results. Nonetheless, the results were promising, especially because high yields were also obtained at ambient temperatures. This suggests that PWWS could be easily digested without heating, particularly during the warmer grape harvesting and crushing months. The composition of the residual matter (digestate) after AD indicated that it may be suitable as an agricultural fertiliser, with high concentrations of N (21.5 to 27.7 g/kg dry weight) and C (229 to 277 g/kg dry weight), as well as the presence of all essential micronutrients. The composition was compared favourably with commercial agricultural organic fertilisers based on supplemented chicken manure. The volumes of wastewater and PWWS generated from wineries crushing from 1 000 to 2000 tons of grapes per

year were estimated. The AD experimental data was applied to the latter to extrapolate the potential volumes of methane and the amount of methane-derived energy that could be generated from AD of PWWS (Table 1). Overall, the results indicated that it might be feasible for larger wineries that generate significant volumes of PWWS/SWWS to utilise AD as a means of (1) generating utilisable biogas for energy, (2) producing fertiliser, and (3) limiting the economic and environmental burden associated with disposal of PWWS/SWWS to landfill. The next steps are: (1) to pilot AD of PWWS at a medium-large winery, and (2) to conduct pot growth experiments to compare the performance of PWWS digestate with organic commercial fertilisers on plant growth and soil health.

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TECHNICAL YEARBOOK 2024