Integrating reverse osmosis to a conventional river water treatment plant as a strategy to produce drinking water after mining dam rupture events: a case study.

Incidents of mining dam failure have compromised the water quality, threatening the water supply. Different strategies are sought to restore the impacted area and to guarantee the water supply. One example is water treatment plants that treat high-polluted waters within the required limits for their multiple usages. The current study assesses the integration of reverse osmosis (RO) to a river water treatment plant (RWTP) installed in Brumadinho (Minas Gerais, Brazil) to treat the water from the Ferro-Carvão stream impacted by the B1 dam rupture in 2019. The RWTP started eleven months after the mining dam rupture and is equipped with eight coagulation-flocculation tanks followed by eight pressurised filters. A pilot RO plant was installed to polish the water treated by the RWTP. Water samples were collected at different points of the water treatment plant and were characterised by their physical, chemical, and biological parameters (160 in total). The results were compared with the historical data (1997-2022) to reveal the alterations in the water quality after the rupture event. The compliance with both parameters was only achieved after the RO treatment, which acted as an additional barrier to 30 contaminants. The water quality indexes (WQI) suggested that the raw surface water, even eleven months after the incident, was unfit for consumption (WQI: 133.9) whereas the reverse osmosis permeate was ranked as excellent in the rating grid (WQI: 23.7).

Integration of two-stage nanofiltration with arsenic and calcium intermediate chemical precipitation for gold mining effluent treatment.

The aim of this study was to evaluate an innovative treatment route for gold-mining effluents rich in calcium, arsenic, and sulfate. This treatment route comprised two nanofiltration (NF) stages and a two-step intermediate precipitation. Arsenic and iron coprecipitation (first step) and calcium carbonate precipitation (second step) were assessed aiming to treat the first-stage NF concentrate and increase the permeate recovery rate in a second-stage NF. The pH, the molar ratio of Fe/As (first step), and the molar ratio of CO3/Ca (second step) were optimized by using rotational central composite design. Under optimal conditions, the arsenic removal was 99.8% (at pH = 7.0 and Fe/As = 4.0), and the calcium removal was 99.5% (at pH 11.5 and CO3/Ca = 3.5). The supernatant of Ca precipitation had very basic pH and had to be acidified before the second-stage NF. The pH 8.5 proved to be the best one regarding retention efficiency and flux. The flux decay of the second-stage NF was attributed to both osmotic pressure increase and reversible fouling resistance. It was concluded that the proposed treatment system is efficient for the treatment of gold-mining wastewater, ensuring higher production of treated effluent and an easy disposable of the final concentrate.