Permeable reactive barrier rejuvenation by alkaline wastewater

Abstract

Chemical armouring of recycled concrete in a permeable reactive barrier (PRB) used for the neutralisation of acidic groundwater in acid sulfate soil terrain significantly decreases its acid neutralising capacity (ANC) by approximately 50% compared with its theoretical ANC. A long-term column test was conducted under simulated field groundwater conditions to assess the re-conditioning of armoured recycled concrete aggregates with alkaline wastewater, with the aim to restore and enhance the ANC and longevity of the PRB. The benefits of alkaline wastewater injection included sharp but short enhancement of the recycled concretes' ANC, as indicated by an increase in effluent pH (pH 3 to 7·7) and alkalinity (0 to 21·6 mM CaCO3) and a reduction in oxidation reduction potential (ORP,. While the results showed that the alkaline wastewater did not significantly reduce chemical armouring, it aided in the liberation of lodged mineral precipitates between concrete aggregates, reducing the severity of chemical and physical clogging. Batch tests demonstrated that, when exposed to acidic water, the ANC of recycled concrete pre-conditioned with alkaline wastewater was enhanced as indicated by higher pH, lower ORP and greater release of calcium (Ca2+) and alkalinity, compared to non-pre-conditioned concrete.

Chemical clogging of granular media under acidic groundwater conditions

“…This intense clogging raised the need of treating or replacing the granular fill. For instance, rejuvenation of affected material with alkaline irrigation water from an agricultural farm has been successfully demonstrated by Banasiak et. al.…”

Editorial

“…The sixth paper, authored by Banasiak et al (2015), deals with the utilisation of recycled concrete as reactive media of the permeable reactive barrier (PRB) for remediating acid-contaminated soils, which pose a major concern for coastal floodplains and estuaries in Australia. The utilisation of this material facilitates 100% removal of aluminium(3+) and total iron, and alkaline effluent waste water for replenishment, arrested reconditioning of the recycled concrete aggregates, thereby enhancing the acid-neutralising capacity.…”