Change in the microbial community of saline geothermal fluids amended with a scaling inhibitor: effects of heat extraction and nitrate dosage

Green inhibitors reduce unwanted calcium carbonate precipitation: Implications for technical settings

Mineral scale deposits in water drainage and supply systems are a common and challenging issue, especially by clogging the water flow. The removal of such unwanted deposits is cost intensive arguing for case-specific and sustainable prevention strategies. In the present study, a novel on-site approach to prevent calcium carbonate (CaCO₃) scale formation was assessed in two road tunnel drainages: Application of the eco-friendly green inhibitor polyaspartate (PASP) caused (i) a significant inhibition of CaCO₃ precipitation, (ii) a more porous or even unconsolidated consistence of the deposits, and (iii) a shift from calcite to the metastable aragonite and vaterite polymorphs. Even relatively low PASP concentrations (1-33 mg/l) can significantly decrease CaCO₃ scale deposition, removing up to ∼7 t CaCO₃/year at an efficiency up to 84%. Application of PASP for water conditioning should also consider case-specific microbial activity effects, where consumption of PASP, e.g. by Leptothrix ochracea, can limit inhibition effects.

Sulphur-based autotrophic denitrification of wastewater obtained following graphite production: Long-term performance, microbial communities involved, and functional gene analysis

Sulphur-based autotrophic denitrification is an energy-efficient NO3--N removal process; it does not require carbon and may potentially replace traditional denitrification processes. This process was used to treat graphite production-derived wastewater and achieved almost complete removal of NO3--N (concentration in effluent: 5.2 mg/L; concentration in influent: 606 mg/L) at a salinity of 15 g/L with a 30 h hydraulic retention time. A unique microbial community was established, in which the abundance of Thiobacillus increased with the increase of the NO3--N concentration and salinity. Metagenomic analysis revealed that the denitrification metabolic pathway in the bioreactor was active. It also revealed the increased activation of nhaH, a gene encoding Na+/H+ antiporters; proA, proB, and proC, genes encoding proline; and Trk and Kdp systems during the treatment of graphite production-derived wastewater to maintain cell function, providing valuable information about utilizing the sulphur-based autotrophic denitrification process to treat graphite production-derived wastewater.