Effect of pistachio shell as a carbon source to regulate C/N on simultaneous removal of nitrogen and phosphorus from wastewater

Enhancing manganese redox-driven nitrogen removal by integrating manganese ore with microelectrolysis into constructed wetlands

Microelectrolysis-integrated constructed wetlands (e-CWs) typically exhibit limited total phosphorus (TP) removal performance, while manganese ore-amended CWs (MOCWs) encounter challenges associated with the interplay between Mn redox cycling and nitrogen transformation. To overcome these limitations, this study introduced MO around the cathode or anode regions in e-CWs, designated as e-CMOCW and e-AMOCW, respectively. Results demonstrated that manganese oxides accelerated NH4+-N removal. Additionally, microelectrolysis enhanced the reductive dissolution of MO, increasing Mn2+ production. This process significantly enriched diverse denitrifying bacteria within e-CMOCW and e-AMOCW, promoting Mn redox cycling and nitrogen transformation, thereby achieving higher NO3--N and total nitrogen removal efficiencies. Moreover, elevated Mn2+ concentrations facilitated TP removal by forming Mn-P precipitates. Canna indica L. mitigated oxidative stress induced by MO and microelectrolysis through increased activity of superoxide dismutase (SOD) and catalase (CAT), ensuring its growth remained unaffected. This study proposes a novel optimization strategy to enhance pollutant removal efficiency in CWs.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in anaerobic/anoxic/oxic + nitrification system

A two-sludge anaerobic/anoxic/oxic + nitrification system with simultaneous nitrogen and phosphorus removal was studied for enhanced low-strength wastewater treatment. After 158 days of operation, excellent NH4+-N, chemical oxygen demand (COD) and PO43--P removal (99.0 %, 90.0 % and 92.0 %, respectively) were attained under a low carbon/nitrogen ratio of 5, resulting in effluent NH4+-N, COD and PO43--P concentrations of 0.3, 30.0 and 0.5 mg/L, respectively. The results demonstrate that the anaerobic/anoxic/oxic sequencing batch reactor (A2-SBR) and nitrification sequencing batch reactor (N-SBR) had favorable denitrifying phosphorus removal and nitrification performance, respectively. High-throughput sequencing results indicate that the phosphate-accumulating organisms Dechloromonas (1.1 %) and Tetrasphaera (1.2 %) were enriched in the A2-SBR, while the ammonia-oxidizing bacteria Nitrosomonas (7.8 %) and the nitrite-oxidizing bacteria Nitrospira (18.1 %) showed excellent accumulation in the N-SBR. Further analysis via functional prediction revealed that denitrification is the primary pathway of nitrogen metabolism throughout the system. Overall, the system achieved low carbon and high efficiency nutrient removal.

Effects of released organic components of solid carbon sources on denitrification performance and the related mechanism

Here, a hybrid scaffold of polyvinyl alcohol/sodium alginate (PVA/SA) was used to prepare solid carbon sources (SCSs) for treating low carbon/nitrogen wastewater. The four SCSs were divided into two groups, biodegradable polymers group (including polyvinyl alcohol-sodium alginate (PS) and PS-PHBV (PP), and blended SCSs (PS-PHBV-wood chips (PPW) and PS-PHBV-wheat straw (PPS)). After the leaching experiments, no changes occurred in elemental composition and functional groups of the SCSs, and the released dissolved organic matter showed a lower degree of humification and higher content of labile molecules in the blended SCSs groups using EEM and FT-ICR-MS. The denitrification performance of the blended SCSs was higher, with nitrate removal efficiency over 84%. High-throughput sequencing confirmed PPW had the highest alpha-diversity, and the microbial community structure significantly varied among SCSs. Results of functional enzymes and genes show the released carbon components directly affect the NADH level and electron transfer efficiency, ultimately influencing denitrification performance.