Voicu Oncu’s scientific contributions

Mine water as a result of meteoric and/or underground water’s contact with tailings and underground workings could have an elevated content of metals associated with sulfate, often acidic, due to the bio-oxidation of sulfides. When entering aquatic ecosystems, the mine water can cause significant changes in the species’ trophic levels, therefore a treatment is required to adjust the alkalinity and to remove the heavy metals and metalloids. The conventional mine water treatment removes metals, but in many cases it does not reduce the sulfate content. This paper aimed to predict the impact of conventionally treated mine water on the receiving river by assessing the genotoxic activity on an engineered Escherichia coli and by evaluating the toxic effects generated on two Gram-negative bacterial strains, Pseudomonas aeruginosa and Escherichia coli. Although the main chemical impact is the severe increases of calcium and sulfate concentrations, no significant genotoxic characteristics were detected on the Escherichia coli strain and on the cell-viability with a positive survival rate higher than 80%. Pseudomonas aeruginosa was more resistant than Escherichia coli in the presence of 1890 mg SO42−/L. This paper reveals different sensitivities and adaptabilities of pathogenic bacteria to high concentrations of sulfates in mine waters.

The present paper aims to evaluate the toxic effects generated by conventional treated mine water as well as freshwater samples (Macris river) on primary producers (green algae, Selenastrum capricornutum) and primary consumers (planktonic crustaceans, Daphnia magna). Those organisms could be very realiable biological models to assess the toxic effect of mine waters on the environment. The green algae growth inhibition test (performed according to OECD201) and the acute immobilization test of freshwater crustaceans (Daphnia magna) (performed according to OECD 202) showed no growth inhibition or Daphnia magna immobilization / mortality during 72h and 48h incubation in presence of surface water samples from Macris river. The aqueous system with 1.89 g/L sulphate ion (SO42-) concentration, containing treated mine water mixed with freshwater sample (ratio 2.4:1), generated 100% toxic effect on crustaceans (Daphnia magna) after 48h incubation.

Mine water treatment scope is to produce an effluent which satisfies the discharge limits according to permits. However, the production of metal-rich sludge is a consequence of the mine water treatment and its disposal as a waste raises the cost of the whole operation, so ways to convert the sludge into marketable products are desirable. For example, mine water treatment sludge can be used for adsorbents or pigments production or some of the sludge components can be extracted and utilized as coagulants. Coagulants were obtained from mine water after partial precipitation of metal species or after conventional treatment, by leaching the sludge with acid. The effectiveness of coagulants considering phosphate, chemical oxygen demand and turbidity is presented in this paper, alongside with some of the drawbacks as observed.