Simultaneous removal of Cd2+, NO3-N and hardness by the bacterium Acinetobacter sp. CN86 in aerobic conditions

Effects of Cd(II) on nitrogen removal by a heterotrophic nitrification aerobic denitrification bacterium Pseudomonas sp. XF-4

Simultaneous heterotrophic nitrification and aerobic denitrification (SND) is gaining tremendous attention due to its high efficiency and low cost in water treatment. However, SND on an industrial scale is still immature since effects of coexisting pollutants, for example, heavy metals, on nitrogen removal remains largely unresolved. In this study, a HNAD bacterium (Pseudomonas sp. XF-4) was isolated. It could almost completely remove ammonium and nitrate at pH 5-9 and temperature 20 ℃-35 ℃ within 10 h, and also showed excellently simultaneous nitrification and denitrification efficiency under the coexistence of any two of inorganic nitrogen sources with no intermediate accumulation. XF-4 could rapidly grow again after ammonium vanish when nitrite or nitrate existed. There was no significant effects on nitrification and denitrification when Cd(II) was lower than 10 mg/L, and 95 % of Cd(II) was removed by XF-4. However, electron carrier and electron transport system activity was inhibited, especially at high concentration of Cd(II). Overall, this study reported a novel strain capable of simultaneous nitrification and denitrification coupled with Cd(II) removal efficiently. The results provided new insights into treatment of groundwater or wastewater contaminated by heavy metals and nitrogen.

Isolation of urease-producing bacteria from cocoa farms soils in Santander, Colombia, for cadmium remediation

Cadmium (Cd) is a toxic heavy metal that causes serious health problems and is present in agriculturally important soils in Colombia, such as the ones used for cocoa farming. Recently, the use of ureolytic bacteria by the Microbiologically Induced Carbonate Precipitation (MICP) activity has been proposed as an alternative to mitigate the availability of Cd in contaminated soils. In this study, 12 urease-positive bacteria able to grow in the presence of Cd(II) were isolated and identified. Three were selected based on urease activity, precipitates formation and growth, with two belonging to the genus Serratia (codes 4.1a and 5b) and one to Acinetobacter (code 6a). These isolates exhibited low urease activity levels (3.09, 1.34 and 0.31 μmol mL-1 h-1, respectively), but could raise the pH to values close to 9.0 and to produce carbonate precipitates. It was shown that the presence of Cd affects the growth of the selected isolates. However, urease activity was not negatively influenced. In addition, the three isolates were observed to efficiently remove Cd from solution. The two Serratia isolates presented maximum removals of 99.70% and 99.62%, with initial 0.05 mM Cd(II) in the culture medium (supplemented with urea and Ca(II)) at 30 °C and 144 h of incubation. For the Acinetobacter isolate, the maximum removal was 91.23% at the same conditions. Thus, this study evidences the potential use of these bacteria for bioremediation treatments in samples contaminated with Cd, and it is one of the few reports that shows the high cadmium removal capacity of bacteria from the genus Serratia.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03495-1.

Microbial-induced calcium carbonate precipitation: Influencing factors, nucleation pathways, and application in waste water remediation

Microbial-induced calcium carbonate precipitation (MICP) is a technique that uses the metabolic action of microorganisms to produce CO₃^2- which combines with free Ca²⁺ to form CaCO₃ precipitation. It has gained widespread attention in water treatment, aimed with the advantages of simultaneous removal of multiple pollutants, environmental protection, and ecological sustainability. This article reviewed the mechanism of MICP at both intra- and extra-cellular levels. It summarized the parameters affecting the MICP process in terms of bacterial concentration, ambient temperature, etc. The current status of MICP application in practical engineering is discussed. Based on this, the current technical difficulties faced in the use of MICP technology were outlined, and future research directions for MICP technology were highlighted. This review helps to improve the design of existing water treatment facilities for the simultaneous removal of multiple pollutants using the MICP and provides theoretical reference and innovative thinking for related research.

A mechanistic review on aerobic denitrification for nitrogen removal in water treatment

The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N₂ for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.