The imbalance of C, N, and P caused by the spilled oil could be regulated by the addition of nitrogen and phosphorous. Moreover, different kinds of N and P sources were used in order to stimulate oil biodegradation under laboratory and field conditions, but the results were conflicting. To evaluate the effectiveness of nutrient supplementation, N sources (NO3‐N and NH4‐N) and P sources (PO4‐P) were applied to the simulated diesel‐polluted seawater in the N/P ratio of 10:1 and 20:1, respectively. The results showed that the addition of nutrients increased the oil biodegradation rate and the counts of petroleum degrading bacteria (PDB) and heterotrophic bacteria (HB). A strongly positive correlation existed (the interrelated coefficient was nearly 0.9) between the percentage ratio of PDB/HB and the oil biodegradation rates, and therefore the percentage ratio of PDB/HB could be used as a good indicator to predict oil biodegradation. Among the four samples treated with nutrients, the biodegradation efficiency of the group amended with NO3‐N and PO4‐P in the ratio of 10:1 (10NO3‐P group) was as much as 75.8 %, while in the 10NH4‐P, 20NO3‐P and 20NH4‐P groups this value was 61.3 %, 52.4 % and 40.5, respectively. It would take natural degradation without nutrient supplementation about 78 days to achieve the result obtained within 14 days with 10NO3‐P amendment. Chemical and microbiological analyses confirmed that the addition of nutrients in the same N/P ratio remarkably enhanced the biodegradation rate and the counts of microorganisms in the NO3‐N treated groups, indicating that the microorganisms tend to utilize NO3‐N rather than NH4‐N as their growth N source. When the same kind of N source was added to the system, the promoted efficiency in the 10:1 (N/P ratio) groups was notable compared to the 20:1 groups, i.e., adding nutrients in the ratio of 10:1 is superior in the stimulation of oil biodegradation to the ratio of 20:1.
Single-atom
catalysts (SACs) have attracted great attention due
to their high atom-utilization and catalytic efficiency. However,
a universal synthetic route is still lacking, which restricts the
SAC-related investigation and application. Here, we report a simple
and cost-effective method to fabricate transition metal SACs through
ion exchange and annealing procedures. Benefiting from the “egg-box”
structure property of alginate, the metal ion can be effectively anchored
into the organic center. Using CuCl2 as a representative
transition metal ion, the Cu SAC structure was synthesized and identified
by aberration-corrected high-angle annular dark-field scanning transmission
electron microscopy and X-ray absorption fine structure spectroscopy.
Through optimizing CuCl2 concentration, the obtained Cu
SAC exhibited a good oxygen reduction reaction activity, whose onset
potential, half wave potential, and limiting current density are all
comparable to those of 20 wt % Pt/C. Cu–N4 was identified
as the responsible catalytic site. More importantly, other transition
metal SACs can be easily synthesized via altering
metallic solution, which proves the universality of our proposed method.
This work may be valuable for the cost-effective and universal SAC
synthetic method development.
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