Effect of Low-Density Static Magnetic Field on the Oxidation of Ammonium by Nitrosomonas europaea and by Activated Sludge in Municipal Wastewater

Bioaugmentation and vermicompost facilitated the hydrocarbon bioremediation: scaling up from lab to field for petroleum-contaminated soils

The biodegradation of total petroleum hydrocarbon (TPH) in soil is very challenging due to the complex recalcitrant nature of hydrocarbon, hydrophobicity, indigenous microbial adaptation and competition, and harsh environmental conditions. This work further confirmed that limited natural attenuation of petroleum hydrocarbons (TPHs) (15% removal) necessitates efficient bioremediation strategies. Hence, a scaling-up experiment for testing and optimizing the use of biopiles for bioremediation of TPH polluted soils was conducted with three 500-kg pilots of polluted soil, and respective treatments were implemented: including control soil (CT), bioaugmentation and vermicompost treatment (BAVC), and a combined application of BAVC along with bioelectrochemical snorkels (BESBAVC), all maintained at 40% field capacity. This study identified that at pilot scale level, a successful application of BAVC treatment can achieve 90.3% TPH removal after 90 days. BAVC's effectiveness stemmed from synergistic mechanisms. Introduced microbial consortia were capable of TPH degradation, while vermicompost provided essential nutrients, enhanced aeration, and, potentially, acted as a biosorbent. Hence, it can be concluded that the combined application of BAVC significantly enhances TPH removal compared to natural attenuation. While the combined application of a bioelectrochemical snorkel (BES) with BAVC also showed a significant TPH removal, it did not differ statistically from the individual application of BAVC, under applied conditions. Further research is needed to optimize BES integration with BAVC for broader applicability. This study demonstrates BAVC as a scalable and mechanistically sound approach for TPH bioremediation in soil.

Enhanced chlorobenzene removal by internal magnetic field through initial cell adhesion and biofilm formation

Magnetic fields (MF) have been proven efficient in bioaugmentation, and the internal MFs have become competitive because they require no configuration, despite their application in waste gas treatment remaining largely unexplored. In this study, we firstly developed an intensity-regulable bioaugmentation with internal MF for gaseous chlorobenzene (CB) treatment with modified packing in batch bioreactors, and the elimination capacity increased by up to 26%, surpassing that of the external MF. Additionally, the microbial affinity to CB and the packing surface was enhanced, which was correlated with the ninefold increased secreted ratio of proteins/polysaccharides, 43% promoted cell surface hydrophobicity, and half reduced zeta potential. Furthermore, the dehydrogenase content was promoted over 3 times, and CB removal steadily increased with the rising intensity indicating enhanced biofilm activity and reduced CB bioimpedance; this was further supported by kinetic analysis, which resulted in improved cell adhesive ability and biological utilisation of CB. The results introduced a novel concept of adjustable magnetic bioaugmentation and provided technical support for industrial waste gas treatments. KEY POINTS: • Regulable magnetic bioaugmentation was developed to promote 26% chlorobenzene removal • Chlorobenzene mineralisation was enhanced under the magnetic field • Microbial adhesion was promoted through weakening repulsive forces.

Novel magnetic coupling constructed wetland for nitrogen removal: Enhancing performance and responses of plants and microbial communities

Vertical flow constructed wetlands (VFCWs) have been widely applied worldwide due to their small footprint and large hydraulic load, however, its sustainable operation and application is still challenging because of the unsatisfactory nitrogen removal. This study developed a novel CW coupled with a magnetic field for treating simulated wastewater, and investigated the effects of magnetic field on enhancing treatment performance and responses of wetland plants and microbial community. The results showed that the magnetic field (average 110 mT) had a significantly intensifying effect on organics and nitrogen removal. The removal efficiencies of NH₄⁺-N and TN in CW exposed to magnetic field (MF-CW) were 10.14% and 9.16% higher than those in control CW (C-CW), and an increased COD removal was also found in MF-CW. Biochemical characteristics of plants indicated that the MF did not cause a severe stress for wetland plants, while MF application shifted significantly the microbial community in CWs. Relative abundances of nitrifying bacteria such as Nitrospira (2.36%), Dokdonella (0.27%) and Nitrosomonas (0.17%) had been significantly promoted due to MF exposure, and nitrification-related microbial enzyme (AMO) activity was also increased by 63%. It can be concluded that introducing MF into CWs could intensify organics and nitrogen removal via the biological process, which would contribute to a better understanding of magnetic coupling mechanism.

Application of magnetic fields to wastewater treatment and its mechanisms: A review

Magnetic field (MF) has been applied widely and successfully as an efficient, low-cost and easy-to-use technique to enhance wastewater treatment (WWT) performance. Although the effects of MF on WWT were revealed and summarized by some works, they are still mysterious and complex. This review summarizes the application of MF in magnetic adsorption-separation of heavy metals and dyes, treatment of domestic wastewater and photo-magnetic coupling technology. Furthermore, the mechanisms of MF-enhanced WWT are critically elaborated from the perspective of magnetic physicochemical and biological effects, such as magnetoresistance, Lorentz force, and intracellular radical pair mechanism. At last, the challenges and opportunities for MF application in WWT are discussed. For overcoming the limitations and taking advantages of MFs in WWT, fundamental research of the mechanisms of the application of MFs should be carried out in the future.

Treatment of low-strength ammonia wastewater by single-stage partial nitritation and anammox using upflow dual-bed gel-carrier reactor (UDGR)

This study investigated the single-stage partial nitritation and anammox (S-PNA) treatment of low-strength ammonia wastewater (≤140 mg NH₄⁺-N/L). Upflow dual-bed gel-carrier reactor (UDGR) with polyvinyl alcohol cryogel biocarriers, developed in this study, was employed for the anammox biomass enrichment from conventional activated sludge and subsequent S-PNA experiments. Anammox biomass was successfully enriched from conventional activated sludge. The enriched anammox carriers were inoculated together with gel carriers containing nitrifying sludge into the S-PNA reactors. S-PNA activity developed rapidly, and the nitrogen removal efficiency and rate reached up to 90.1% (with complete ammonia removal) and 0.15 kg N/m³⋅d, respectively, under low nitrogen loading conditions (0.10-0.17 kg N/m³⋅d). The microbial community structure changed significantly while adapting to anammox and S-PNA conditions. Anammox was likely driven solely by a Candidatus Jettenia population accounting for ≤49.4% of bacterial 16S rRNA genes. The results demonstrate that the UDGR-based S-PNA is suitable for treating low-strength wastewater.

Response of nitrite accumulation and microbial characteristics to low-intensity static magnetic field during partial nitrification

Static magnetic field (SMF) with the intensity of 15 mT was applied during partial nitrification (PN) process to evaluate the impacts on nitrogen transformation and microbial characteristics. Results showed that the startup period of PN process at ambient temperature was markedly shortened by SMF, and the nitrite accumulation increased by 18% due to SMF exposure. The ammonia oxidizing bacteria (AOB) amoA gene copy numbers in the reactor with SMF exposure were 40% higher than that without SMF exposure, indicating the AOB abundance was enriched by SMF exposure. The characteristics of extracellular polymeric substances (EPS) changed accordingly. The extracellular protein increased by 30% due to SMF exposure, and it favored the aggregation of sludge flocs. The activated sludge with SMF exposure had a more compact structure, which was in favor of partial nitrification.

Nitrification in Activated Sludge Exposed to Static Magnetic Field

The study investigated wastewater treatment in an aerobic reactor with activated sludge exposed to static magnetic field (SMF) with mean induction of 8.1 mT. The efficiency of chemical oxygen demand removal was about 90% in a control reactor and an SMF-exposed reactor. Although the nitrification efficiency was higher than 95% in both reactors, the activity of ammonia-oxidizing bacteria was higher in the SMF-exposed reactor. This resulted in shortening of nitrification time to 4 h compared to 8 h in the control reactor. Higher number of ammonia-oxidizing bacteria in the SMF-exposed reactor might result from increased oxygen penetration into the liquid exposed to SMF, which favored growth of these bacteria. The results indicate that SMF enhanced nitrification, the most sensitive process from the biological nitrogen transformations. SMF influenced the overall biomass content that was 14% higher in the SMF-exposed reactor than in the control reactor.