Effects of salinity, C/S ratio, S/N ratio on the BESI process, and treatment of nanofiltration concentrate

Autotrophic denitrification by sulfur-based immobilized electron donor for enhanced nitrogen removal: Denitrification performance, microbial interspecific interaction and functional traits

Sulfur-driven autotrophic denitrification (SdAD) is a promising nitrogen removing process, but its applications were generally constrained by conventional electron donors (i.e., thiosulfate (Na2S2O3)) with high valence and limited bioavailability. Herein, an immobilized electron donor by loading elemental sulfur on the surface of polyurethane foam (PFSF) was developed, and its feasibility for SdAD was investigated. The denitrification efficiency of PFSF was 97.3%, higher than that of Na2S2O3 (91.1%). Functional microorganisms (i.e., Thiobacillus and Sulfurimonas) and their metabolic activities (i.e., nir and nor) were substantially enhanced by PFSF. PFSF resulted in the enrichment of sulfate-reducing bacteria, which can reduce sulfate (SO42-). It attenuated the inhibitory effect of SO42-, whereas the generated product (hydrogen sulfide) also served as an electron donor for SdAD. According to the economic evaluation, PFSF exhibited strong market potential. This study proposes an efficient and low-cost immobilized electron donor for SdAD and provides theoretical support to its practical applications.

Removal of Cr (VI) and microbial community analysis in PCB wastewater treatment based on the BESI® process

The treatment efficiency of Chromium (Cr)-containing Printed Circuit Board (PCB) wastewater is significantly hampered by the limited physiological activity of microorganisms when activated sludge is applied. In this study, the biodegradation and electron transfer based on sulfur metabolism in the integrated (BESI®) process use sulfur as the electron acceptor to achieve sulfate reduction and sulfide oxidation, leading to efficient removal of Cr. The concentrations of total Cr and Cr(VI) in the effluent were reduced to 0.5 mg/L and 0.1 mg/L, respectively, from an initial range of 25-32 mg/L in the influent. The removal of Cr (ΔC(Cr(VI))) mainly occurred in the Sulfate Reduction (SR) reactor, which was significantly correlated with the generation of sulphide ([Formula: see text]) (R2 = 0.9987). Meantime, analysis of the microbial community showed that Cr (VI) stress increased the diversity of the bacterial community in sludge. The presence of Clostridium (52.54% and 47.78%) in SR & Sulfide Oxidation (SO) reactor, along with the Synergistaceae (31.90%) and Trichococcus (26.59%) in aerobic reactor, might contribute to the gradient degradation of COD, resulting in a removal efficiency exceeding 80% when treating an influent with a concentration of 1000 mg/L. In addition, the main precipitation components in the SR reactor were identified by scanning electron microscope, indicating that Cr has been removed from wastewater as Cr(OH)3 precipitation. This study sheds light on the potential of using the BESI® process for the real PCB wastewater treatment.

Integration of the sulfate reduction and anammox processes for enhancing sustainable nitrogen removal in granular sludge reactors

The Anammox and Sulfate Reduction Ammonium Oxidation processes were compared in two granular sequencing batch reactors operated for 160 days under anammox conditions. It was hypothesized that increasing the concentration of SO₄^2- may positively influence the rate of N removal under anaerobic conditions and it was tested whether SO₄^2- reduction and anammox occur independently or are related to each other. The cooperation of N-S cycles by increasing the concentration of influent SO₄^2- to 952 mg S/L in the second reactor, a higher ammonium utilization rate and sulfate utilization rate was achieved compared to the first reactor, i.e., 2.1-fold and 15-fold, respectively. Nitrosomonas played the dominant role in the N metabolism, while Thauera - in the S metabolism. This study highlights the benefits of linking the N-S cycles as an effective approach for the treatment of NH₄⁺ and SO₄^2- - rich wastewater, including lower substrate removal cost and reduced energy consumption.

Recent advances in dissimilatory sulfate reduction: From metabolic study to application

Sulfate-reducing bacteria (SRB) are a group of diverse anaerobic microorganisms omnipresent in natural habitats and engineered environments that use sulfur compounds as the electron acceptor for energy metabolism. Dissimilatory sulfate reduction (DSR)-based techniques mediated by SRB have been utilized in many sulfate-containing wastewater treatment systems worldwide, particularly for acid mine drainage, groundwater, sewage and industrial wastewater remediation. However, DSR processes are often operated suboptimally and disturbances are common in practical application. To improve the efficiency and robustness of SRB-based processes, it is necessary to study SRB metabolism and operational conditions. In this review, the mechanisms of DSR processes are reviewed and discussed focusing on intracellular and extracellular electron transfer with different electron donors (hydrogen, organics, methane and electrodes). Based on the understanding of the metabolism of SRB, responses of SRB to environmental stress (pH-, temperature-, and salinity-related stress) are summarized at the species and community levels. Application in these stressed conditions is discussed and future research is proposed. The feasibility of recovering energy and resources such as biohydrogen, hydrocarbons, polyhydroxyalkanoates, magnetite and metal sulfides through the use of SRB were investigated but some long-standing questions remain unanswered. Linking the existing scientific understanding and observations to practical application is the challenge as always for promotion of SRB-based techniques.