The impact of gravel, polymer film and aeration of the reduced nitrogen forms in surface
waters was studied in a previous paper [1]. Authors [1] found that gravel, polymer film and
aeration caused the acceleration of decreasing ammonia content in water. Gravel and polymeric
film speeded up the oxidation process of ammonia, while the aeration diminished its amount. In
this paper, the ammonium ion oxidation in the water samples, in the presence and absence of
mineral substrates, has been investigated. The presence of granite and expanded clays speeds the
oxidation of ammonium ion by 12 days in the case of downstream of the South Racovat River.
The time of oxidation of ammonium ion in the presence of these substrates is 7 days, while in
their absence is 20 days. The ammonium ion oxidation for samples with granite has an
insignificant delay in comparison with expanded clays, while the formation and decrease of the
nitrite ion concentration is favored for clays by 3-4 days with the maximum difference in the
concentration of 1 mg/L. The water models from the Isnovat River, in which the impact of
granite, ceramsite, calcium carbonate and their combination have been investigated, demonstrate
that separate granite and ceramsite as well as their combination have a significant influence on
the dynamics of nitrification. The addition of calcium carbonate slows down the oxidation of
reduced forms of nitrogen. The adding up of CaCO3 causes a larger effect on more polluted
water samples in the Ungheni section after WWTP than on less polluted ones in the Sculeni
section. On the other hand, the largest effect is registered for the highly polluted by cationic
detergents waters in the Varancau section of the Nistru River downstream of the Soroca city. In
the water samples without substrates, both the NH4
+ oxidation and the NO3
- reduction to the
NO2
- ions take place to their greater extent of nitrite formation (4-5 mg/L). The ammonium
oxidation is practically blocked by adding CaCO3 to the water samples. For the samples taken
from the Nistru River near to the Bursuc village the effect of calcium carbonate is smaller, but
still noticeable. In the case of the Cunicea village vicinity, where the river water is not polluted
by detergents, the nitrification dynamic of ammonia and nitrite ions with and without CaCO3 is
more or less similar.
As a result, granite and expanded clay substrates as well as their combination have a
comparable effect in supporting the oxidation of nitrogen reduced forms in natural surface
waters. Concomitantly, CaCO3 blocks abovementioned process, essentially for highly polluted
waters. Our research proves again that the organic pollutants, especially the cationic ones,
produce a noticeable impact on the ammonia oxidation process dynamics in natural waters.
References:
[1] Sandu, M.; Spataru, P.; Arapu, T.; Lupascu, T. Biochemical oxidation – a pathway for
ammonia removal from aquatic systems. In: „Methods and Techniques for Cleaning-up
Contaminated Sites”, Springer, 2008, 137-143.