Introducing PHBV and controlling the pyrite sizes achieved the pyrite-based mixotrophic denitrification under natural aerobic conditions: Low sulfate production and functional microbe interaction

Effect of pyrite particle size on the denitrification performance of autotrophic or split‐mixotrophic bioreactors supported by pyrite/polycaprolactone

“…The upper PHD system could not completely remove the SO 4 2− produced in the lower PAD system, which resulted in a higher SO 4 2− eff than the influent for some time (40–52 days). Similarly, Zhou et al (2022) reported that in the FeS 2 /PHBV system, the SO 4 2− eff decreased with the operation of the reactor, and finer‐grained FeS 2 (<150 μm) generated greater initial SO 4 2− . According to previous studies, in the PPMD system, sulfur oxidation and SO 4 2− reduction mainly occurred in the FeS 2 and PCL layers, respectively (Yuan et al, 2023).…”

“…According to the above discussion, when the SO 4 2À eff of R1 or R3 PAD was stable, the SO 4 2À was mainly produced from the PAD process and subsequently reduced in the upper PCL layer. In addition, the reduction of 1-mg NO 3 À -N by the PAD process theoretically produces 4.57 mg of SO 4 2À (Zhou et al, 2022). To further explore the respective proportions of PAD and PHD in R3 PAD + PHD at different FeS 2 grain sizes, the SO 4 2À eff of R3 PAD during the stable period in phases I-III (8-18, 28-38, and 52-62 days, respectively) was selected for the calculations, which were based on the following Equations ( 4)-( 7) (Jin et al, 2019;Yuan et al, 2022):…”

“…In addition, the pH eff of R1 in phases I-III reduced gradually with the decrease of FeS 2 particle size. This might be because the reduction of particle size increased the extent of the PAD process and the associated pyrite chemical oxidation (Zhou et al, 2022). R2 was a PHD system, where heterotrophic denitrification generated alkalinity resulting in a normal increase in pH.…”

“…Among them, pyrite (FeS 2 )-based autotrophic denitrification (PAD) uses FeS 2 as a source of electron donor to reduce NO 3 À -N, and the reaction can be expressed by Equation (1) (Tong et al, 2017). However, the PAD normally has drawbacks including poor treatment effectiveness, slow microbial growth, long start-up period, and massive sulfate (SO 4 2À ) generation, which severely limit its practical application (Zhou et al, 2022).…”

“…Among them, pyrite (FeS 2 )‐based autotrophic denitrification (PAD) uses FeS 2 as a source of electron donor to reduce NO 3 − ‐N, and the reaction can be expressed by Equation () (Tong et al, 2017). However, the PAD normally has drawbacks including poor treatment effectiveness, slow microbial growth, long start‐up period, and massive sulfate (SO 4 2− ) generation, which severely limit its practical application (Zhou et al, 2022). $$$$ {\displaystyle \begin{array}{c}0.364\mathrm{Fe}{\mathrm{S}}_2+\mathrm{N}{\mathrm{O}}_3^{-}+0.116\mathrm{C}{\mathrm{O}}_2+0.023\mathrm{N}{\mathrm{H}}_4^{+}+0.821{\mathrm{H}}_2\mathrm{O}\to \\ {}0.364\mathrm{Fe}{\left(\mathrm{OH}\right)}_3+0.729\mathrm{S}{\mathrm{O}}_4^{2-}+0.5{\mathrm{N}}_2+0.023{\mathrm{C}}_5{\mathrm{H}}_7{\mathrm{O}}_2\mathrm{N}+0.480{\mathrm{H}}^{+}\end{array}}.$$…”