Effective Bio-Waste Recycling: Minimizing the Risk of Heavy Metal Emission

The concepts of circular economy increase the need to recycle bio-waste. Effective implementation requires knowledge about associated risks and environmental concerns. This study examines the composition and heavy metal content of bio-waste from municipal waste in western Poland, considering waste type, location, and season. Food waste constituted 36.7% to 47.6% of the total bio-waste, while garden waste accounted for 35.8% to 52.8%, with a strong seasonal dependency. Impurities such as plastics and glass were significant issues for urban and multi-family houses (16.6%), whereas rural and single-family home bio-waste had much lower impurity levels (10.0%). Heavy metals were identified in bio-waste, with the highest concentrations found in inedible food and garden waste. The ecological risk and cumulative effects of heavy metals were assessed using the contamination factor (CF), pollution index (PI), Nemerow Pollution Index (NPI), potential ecological risk index (Ef), and potential toxicity response index (RI). Urban bio-waste exhibited slightly higher levels of heavy metals and impurities compared to rural bio-waste. Zinc was the most abundant heavy metal, while cadmium had the lowest concentration. A seasonal pattern was observed, with winter bio-waste showing the lowest heavy metal concentrations. The results indicate that, despite localized elevated ecological risks, bio-waste recycling can be considered a conditionally safe waste management strategy, although localized and fraction-specific ecological risks, particularly related to cadmium and chromium, were identified.