The waste samples were sourced from:

1. Pulp & Paper Industry (Heinzelpaper):
Residues from various processes, including de-inking (DIP), recycled fiber processing (RCF), chemical pulp production (POELS), and wastewater treatment (ARA). The characterization analyzed parameters such as total solids (TS), volatile solids (VS), pH, chemical oxygen demand (COD), soluble COD (sCOD), total Kjeldahl nitrogen (TKN), and biomethane potential.

• DIP and ARA samples showed low methane yield.

• RCF10-04 had a relatively high methane yield but contained a large amount of inorganic sand, which poses challenges in reactors.

• The most promising samples for acidification were RCF10-03, RCF10-05, RCF10-06, and POELS-03, selected for further analysis and pre-treatment.

2. Organic Waste (Green Generation):
Includes slaughterhouse waste (rumen content), wastewater treatment sludge from the dairy industry (Glanbia Ballitore WWTP Sludge, Rosderra Edenderry WWTP Sludge), and bioprocess waste (glycerine from biodiesel production).

Samples from the pulp and paper industry were inspected for impurities such as plastics, polystyrene, stickies, and metals.

• RCF10-03, RCF10-05 and RCF10-06 were almost free of impurities, only small styrofoam pieces remained in RCF10-03.

• POELS-03 sample contained no impurities.

• Therefore, no additional impurity removal was required for these selected samples.

Pre-treatment trials were then carried out to enhance VFA yields. Four methods were tested:

• Heat treatment at 125 °C (most effective, increasing solubilised organic matter up to +40%).

• High-shear mixing (limited effect in some cases).

• Acid addition (pH 4–5).

• Base addition (pH 9–11), which strongly improved organic matter availability.

Overall, alkaline conditions proved most favourable for subsequent acidification.

Fermentation trials were conducted in glass bioreactors (1–2 L) under acidic (pH 5.5) and alkaline (pH 10) conditions.

• Alkaline pH produced the highest VFA concentrations.

• Glycerine reached 1928 mg/L, sludge 1657 mg/L, and bellygrass 1652 mg/L.

• VFA yields: 0.33 g/g VS (glycerine), 0.47 g/g VS (sludge), 0.27 g/g VS (bellygrass).

• The main acids formed were acetic, propionic, and butyric acids.

These results demonstrate that selected industrial wastes can be effectively transformed into VFAs, which are essential precursors for producing PHBV bioplastics.