Improved sulfur autotrophic denitrification using supplementary bovine serum albumin

Effect of dissolved oxygen on sulfur autotrophic denitrification and how to address it: An experimental and modelling work

Sulfur autotrophic denitrification (SAD) using elemental sulfur as the electron donor has aroused increasing interest of its application in treating secondary effluent from wastewater treatment plants (WWTPs). However, high influent dissolved oxygen (DO) in secondary effluent would limit the SAD process. This study examined the effect of different DO concentrations on SAD. Results revealed that both low (0-0.5 mg/L) and moderate (2.5-3.5 mg/L) DO concentrations would not harm the nitrate removal rate (NRR) (p > 0.05). However, high DO concentration (5.5-6.5 mg/L) significantly decreased the NRR (p < 0.05) through strong competition over the nitrate for electrons and cutting the relative abundance of sulfur-oxidizing bacteria (SOB). Both modeling and experimental results showed that applying internal reflux could serve as a strategy to mitigate the negative effect of high DO concentration, while keeping an appropriate ratio was crucial. When treating real membrane bioreactor (MBR) effluent with high DO concentration (5.5-6.5 mg/L), an internal reflux ratio of 0.5 boosted the NRR by 1.5 times. This study provided potential reference and strategy for dealing with high DO concentration wastewater by applying SAD technology.

Amorphous Fe substrate enhances nitrogen and phosphorus removal in sulfur autotrophic process

The autotrophic denitrification of coupled sulfur and natural iron ore can remove nitrogen and phosphorus from wastewater with low C/N ratios. However, the low solubility of crystalline Fe limits its bioavailability and P absorption capacity. This study investigated the effects of amorphous Fe in drinking water treatment residue (DWTR) and crystalline Fe in red mud (RM) on nitrogen and phosphorus removal during sulfur autotrophic processes. Two types of S-Fe cross-linked filler particles with three-dimensional mesh structures were obtained by combining sulfur with the DWTR/RM using the hydrogel encapsulation method. Two fixed-bed reactors, sulfur-DWTR autotrophic denitrification (SDAD) and sulfur-RM autotrophic denitrification (SRAD), were constructed and stably operated for 236 d Under a 5-8-h hydraulic retention time, the average NO3--N, TN, and phosphate removal rates of SDAD and SRAD were 99.04 %, 96.29 %, 94.03 % (SDAD) and 97.33 %, 69.97 %, 82.26 % (SRAD), respectively. It is important to note that fermentative iron-reducing bacteria, specifically Clostridium_sensu_stricto_1, were present in SDAD at an abundance of 58.17 %, but were absent from SRAD. The presence of these bacteria facilitated the reduction of Fe (III) to Fe (II), which led to the complete denitrification of the S-Fe (II) co-electron donor to produce Fe (III), completing the iron cycle in the system. This study proposes an enhancement method for sulfur autotrophic denitrification using an amorphous Fe substrate, providing a new option for the efficient treatment of low-C/N wastewater.

The performance, mechanism and greenhouse gas emission potential of nitrogen removal technology for low carbon source wastewater

Excessive nitrogen can lead to eutrophication of water bodies. However, the removal of nitrogen from low carbon source wastewater has always been challenging due to the limited availability of carbon sources as electron donors. Biological nitrogen removal technology can be classified into three categories: heterotrophic biological technology (HBT) that utilizes organic matter as electron donors, autotrophic biological technology (ABT) that relies on inorganic electrons as electron donors, and heterotrophic-autotrophic coupling technology (CBT) that combines multiple electron donors. This work reviews the research progress, microbial mechanism, greenhouse gas emission potential, and challenges of the three technologies. In summary, compared to HBT and ABT, CBT shows greater application potential, although pilot-scale implementation is yet to be achieved. The composition of nitrogen removal microorganisms is different, mainly driven by electron donors. ABT and CBT exhibit the lowest potential for greenhouse gas emissions compared to HBT. N2O, CH4, and CO2 emissions can be controlled by optimizing conditions and adding constructed wetlands. Furthermore, these technologies need further improvement to meet increasingly stringent emission standards and address emerging pollutants. Common measures include bioaugmentation in HBT, the development of novel materials to promote mass transfer efficiency of ABT, and the construction of BES-enhanced multi-electron donor systems to achieve pollutant prevention and removal. This work serves as a valuable reference for the development of clean and sustainable low carbon source wastewater treatment technology, as well as for addressing the challenges posed by global warming.

High-rate iron sulfide and sulfur-coupled autotrophic denitrification system: Nutrients removal performance and microbial characterization

Iron sulfides-based autotrophic denitrification (IAD) is a promising technology for nitrate and phosphate removal from low C:N ratio wastewater due to its cost-effectiveness and low sludge production. However, the slow kinetics of IAD, compared to other sulfur-based autotrophic denitrification (SAD) processes, limits its engineering application. This study constructed a co-electron-donor (FeS and S⁰ with a volume ratio of 2:1) iron sulfur autotrophic denitrification (ISAD) biofilter and operated at as short as 1 hr hydraulic retention time (HRT). Long-term operation results showed that the superior total nitrogen and phosphate removals of the ISAD biofilter were 90-100% at 1-12 h HRT, with the highest denitrification rate up to 960 mg/L/d. Considering low sulfate production, HRT of 3 h could be the optimal condition. Such superior performance in the ISAD biofilter was achieved due to the interactions between FeS and S⁰, which accelerated the denitrification process and maintained the acidity-alkalinity balance. Metagenomic analysis found that the enriched nitrate-dependent iron-oxidizing (NDFO) bacteria (Acinetobacter and Acidovorax), sulfur-oxidizing bacteria (SOB), and dissimilatory nitrate reduction to ammonia (DNRA) bacteria likely supported stable nitrate reduction. The metabolic pathway analysis showed that completely denitrification and DNRA, coupled with sulfur oxidation, disproportionation, iron oxidation and phosphate precipitation with FeS and S⁰ as co-electron donors, were responsible for the high-rate nitrate and phosphate removal. This study provides the potential of ISAD as a highly efficient post-denitrification technology and sheds light on the balanced microbial S-N-Fe transformation.