Investigating the effects of physical properties of sulphur-based carriers on autotrophic denitrification

In this study, four sulphur-based carriers (C1-C4) which have different mass ratio of sodium silicate to carrier from 30% to 50% (C1-C3) and the existence of water (C4) were prepared in order to evaluate the effect of the different physical properties on denitrification in sulphur-based autotrophic processes. While the apparent density and the compressive strength decreased as the proportion of sodium silicate increased and water was added in the carriers, the average pore size and the porosity increased from 0.43 to 3.13 µm and from 38% to 67%, respectively. The treatment system using the carrier C4 with the highest surface area was stabilized most rapidly and achieved the highest nitrogen removal efficiency of 85.6 ± 5.0% during a relatively short HRT of 3 h. The efficiency of nitrate removal was enhanced by 36.9% due to the increase of the ratio of sodium silicate in the carriers from C1 to C3, and more 4.8% point of removal rate increased in the carrier C4 by adding water to the carrier C3. The sum of Thiobacillus and Sulfurimonas was obtained up to 65.90% among the microbial community in the carrier C4 which has the highest distribution (38.35%) of pore size above 20 µm considered to be favourable for retaining autotrophic denitrifiers. From the above results, it is obvious that the physical properties of the sulphur-based carrier and its ability of denitrification can be influenced significantly by the composition of the carrier.