Q2. How should the authors improve the denitrification of aquifers?
Future experiments using sediments from nitrate-contaminated aquifers should address 496 denitrification enhancement by addition of pyrite to stimulate indigenous denitrifying bacteria.
Q3. how much nitrate was produced in the inoculated experiments?
In fact, the excess of sulfate 325 produced in the inoculated experiments (assuming that the reaction occurs via eq. 3) ranged from 0.2 326 to 5.0 mM in agreement with sulfate produced in the blank experiments (between 0.2 and 4.9 mM).
Q4. Why was nitrate removal efficiency lower in the flow-through experiments?
Under non-sterilized, non-279 inoculated conditions, nitrate removal efficiency was lower, probably because of changes in the 280 microbial population.
Q5. How many nitrate removal experiments were performed at low nitrate loading rate?
in three 48125experiments performed at low nitrate loading rate, almost 100% of nitrate removal was attained at the 482 end (375 d).
Q6. Why did the pyrite-driven denitrification experiment produce high concentrations?
High concentrations at the start of the experiments were probably due to 296 dissolution of an outer layer of the reacting mineral or to dissolution of microparticles (Lasaga, 1998).
Q7. How much nitrate did 15NNO3 and 18ONO?
In the experiment with 25-50 µm 418 pyrite, after 16 d, δ15NNO3 and δ18ONO3 increased to +2.6‰ and +29.2‰, respectively, with 18% 419 reduction of initial nitrate.
Q8. how much nitrate is consumed to sulfate?
If nitrate reduction was coupled to pyrite dissolution via eq. (3), the measured molar ratio of nitrate 308 consumed to sulfate produced should be close to the stoichiometric ratio of this reaction, which is 1.5.
Q9. How was the accuracy of the measurements of mg, 191 Ca, Na, Cl?
The accuracy on the measurement of Mg, 191 Ca, Na, Cl, P and K was estimated to be around 3%, whereas the accuracy on the measurement of Fe 192 and S was estimated to be 25%, with detection limits of 0.36 and 3.12 µmol L-1, respectively.
Q10. What is the reason for the low S concentration in the inoculated experiments?
This suggests that part of the S released in the inoculated 291 experiments could be attributed to pyrite oxidation by traces of dissolved oxygen as observed in the 292 blank experiments.
Q11. What is the nitrate removal efficiency in the pyrite-amended batch?
In most of the pyrite-amended batch experiments nitrite reduction took place rapidly and the final 255 products were N-gaseous compounds (i.e. NO, N2O or N2).
Q12. What could be attributed to the changes in the composition of the dominant microbial community?
These behaviors could be attributed to shifts over the course of the runs in the composition of 238 the dominant microbial community or in the enzyme regulation of the denitrifying organisms, 239 probably as a result of changes in the experimental conditions that control the activity and growth of 240 bacteria (such as oxygen concentration or nutrient availability).
Q13. What is the drawback of using pyrite as the electron donor?
a drawback of 490 using the pyrite-driven denitrification process as a remediation strategy is at some extent the release 491 of trace metals (e.g. As, Ni) and sulfate as a result of pyrite oxidation.
Q14. What was the pH of the modified medium used in the batch experiments?
The modified medium used in the batch experiments was the 141 T. denitrificans nutrient medium without thiosulfate and iron, replacing sulfate salts by chloride salts 142 and adding the desired nitrate concentration: NH4Cl (18.7 mM), KH2PO4 (14.7 mM), NaHCO3 (30 143 mM), MgCl2·6H2O (3.25 mM) and CaCl2·2H2O (0.05 mM) and the desired NO3- concentration as KNO3.
Q15. What pH was the nitrate reduction in the flow-through experiments?
At pH 4.5 (NON-1), nitrate reduction 241 was less effective than that observed in experiments carried out at pH 6.5-8, confirming the marked 242 decrease in microbial activity due to acid pH (Table 4).
Q16. What is the effect of pyrite on the denitrifying activity?
On the one hand, as pyrite powder and solutions were not previously autoclaved, a mixture of both 338 autotrophic and heterotrophic denitrifying bacteria could have enhanced the denitrifying activity not 339 linked to pyrite oxidation.
Q17. What is the role of pyrite in the oxidation of nitrate?
In these studies, the role of pyrite as electron 52 donor has been questioned and only in Jorgensen et al. (2009), has been denitrification coupled to 53 pyrite oxidation satisfactorily accomplished.
Q18. how many nitrates were released after time 0?
In the inoculated pyrite-amended batch experiments, the nitrate/sulfate ratio was calculated using 320 sulfate released after time 0 given that nitrate reduction started after this time.
Q19. What was the nitrate reduction rate in the pyrite-amended batch?
In pyrite-amended batch experiments, nitrate reduction rates were computed assuming zero-order 368 kinetics and using linear regression to fit the remaining nitrate concentrations vs. time (Fig. 1).
Q20. what is the effect of granular iron on nitrate transformation rates in sediments?
The effects of electron donor and granular iron on nitrate 550 transformation rates in sediments from a municipal water supply aquifer.
Q21. What is the reason for the nitrate reduction in batch and flow-through experiments?
the results of both batch and flow-through experiments show that nitrate reduction 299 occurred concurrently with the release of sulfate in the sterilized pyrite-amended experiments 300 inoculated with T. denitrificans and in the non-inoculated experiments with non-sterilized pyrite, 301 which showed inherent activity of indigenous bacteria.