Treatment of concrete waste from construction and demolition activities: Application of organic acids from continuous dark fermentation in moving bed biofilm reactors

Concrete construction and demolition waste (CDW) treatment and disposal is often complicated and expensive. The recourse to bioleaching processes, able to weaken the concrete CDW leading to a decrease in its weight and volume could play a key role to increase the effectiveness of the treatment, making possible the recovery of valuable substances, such as aggregates and calcium-based compounds. This paper presents the result of an experimental study aimed at testing concrete CDW bioleaching, using volatile fatty acids (VAFs) generated by a continuous dark fermentation (DF) processe, conducted in a moving bed biofilm reactor (MBBR) under different operating conditions. Bioleaching tests are conducted on ∼25 g concrete blocks with VFA mixtures obtained operating the reactor varying the pH value from 6.0 to 4.0. Best results, in terms of concrete dissolution, are obtained at pH 5.5 (weight loss 30 % and bio-hydrogen production 0.90 L/d) and 5.0 (weight loss 32 % and bio-hydrogen production 0.58 L/d). The main objective of the study include the evaluation, as performance indicators, of concrete waste debris weight and volume reduction, and bio-hydrogen and VFAs production. Further development of this technique will enable testing its applicability on a pilot scale and enhance understanding of its environmental impact, establishing the groundwork for more sustainable and efficient CDW management. This innovative approach aims to mitigate the environmental impact of CDW and offers a new pathway for resource recovery.