Inhibition and recovery in a fixed microbial film leachate treatment system subject to shock loading of copper and zinc

Exposure to zinc and dialkyldimethyl ammonium compound alters bacterial community structure and resistance gene levels in partial sulfur autotrophic denitrification coupled with the Anammox process

Dialkyldimethyl ammonium compound (DADMAC) is widely used in daily life as a typical disinfectant and often co-exists with the heavy metal zinc in sewage environments. This study investigated the effects of co-exposure to zinc (1 mg/L) and DADMAC (0.2-5 mg/L) on the performance, bacterial community, and resistance genes (RGs) in a partial sulfur autotrophic denitrification coupled with anaerobic ammonium oxidation (PSAD-Anammox) system in a sequencing batch moving bed biofilm reactor for 150 days. Co-exposure to zinc and low concentration (0.2 mg/L) DADMAC did not affect the nitrogen removal ability of the PASD-Anammox system, but increased the abundance and transmission risk of free RGs in water. Co-exposure to zinc and medium-to-high (2-5 mg/L) DADMAC led to fluctuations in and inhibition of nitrogen removal, which might be related to the enrichment of heterotrophic denitrifying bacteria dominated by Denitratisoma. Co-exposure to zinc and high concentration DADMAC (5 mg/L) stimulated the secretion of extracellular polymeric substances and increased the proliferation risk of intracellular RGs in sludge. This study provided insights into the application of PSAD-Anammox system and the ecological risks of wastewater containing zinc and DADMAC.

A review of heavy metals inhibitory effects in the process of anaerobic ammonium oxidation

Anaerobic ammonium oxidation (anammox) is a promising biological technology for treating ammonium-rich wastewaters. However, due to the high sensitivity of anammox bacteria, many external factors have inhibitory effects on this process. As one of the commonly found toxic substances in wastewater, heavy metals (HMs) are possible to cause inhibition on anammox sludge, which then results in a declined treatment performance. Getting insights into the response mechanism of anammox sludge to HMs is meaningful for its application in treating this kind of wastewater. This review summarized the effect of different HMs on treatment performance of anammox bioreactor. In addition, the mechanism of toxication raised by HMs was discussed. Also, the potential mitigation strategies were summarized and the future prospects were outlooked. This review might provide useful information for both scientific research on and engineering application of anammox process for treating HMs containing wastewater.

How anammox responds to the emerging contaminants: Status and mechanisms

Numerous researches have been carried out to study the effects of emerging contaminants in wastewater, such as antibiotics, nanomaterials, heavy metals, and microplastics, on the anammox process. However, they are fragmented and difficult to provide a comprehensive understanding of their effects on reactor performance and the metabolic mechanisms in anammox bacteria. Therefore, this paper overviews the effects on anammox processes by the introduced emerging contaminants in the past years to fulfill such knowledge gaps that affect our perception of the inhibitory mechanisms and limit the optimization of the anammox process. In detail, their effects on anammox processes from the aspects of reactor performance, microbial community, antibiotic resistance genes (ARGs), and functional genes related to anammox and nitrogen transformation in anammox consortia are summarized. Furthermore, the metabolic mechanisms causing the cell death of anammox bacteria, such as induction of reactive oxygen species, limitation of substrates diffusion, and membrane binding are proposed. By offering this review, the remaining research gaps are identified, and the potential metabolic mechanisms in anammox consortia are highlighted.

Ca(II) and Mg(II) significantly enhanced the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II)

This study investigated the impacts of alkaline-earth metals [Ca(II), Mg(II)] and heavy metals [Zn(II), Ni(II)] on the nitrogen removal capacity of Arthrobacter arilaitensis Y-10. StrainY-10 was able to tolerate 20 mg/L Ca(II) and its ammonium removal efficiency was 100%. 0.5 mg/L Ca(II) effectively promoted total nitrogen removal from wastewater containing nitrite. Mg(II) supplementation substantially enhanced the bacterial growth and nitrogen reduction. As Mg(II) concentrations increased from 0 to 2 mg/L, the ammonium, nitrate and nitrite removal efficiencies increased by 40.62%, 69.91% and 64.68%, respectively. Although the nitrogen removal ability of strain Y-10 was sharply hindered by Zn(II) and Ni(II), it occurred continuously even when the Zn(II) concentration reached 30 mg/L. However, the ammonium and total nitrogen removal almost stopped at 8 mg/L Ni(II), and the denitrification capacity was lost when the Ni(II) concentration exceeded 1 mg/L. The results demonstrate that Ca(II) and especially Mg(II) could significantly enhance the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II).

Impacts of the heavy metals Cu (II), Zn (II) and Fe (II) on an Anammox system treating synthetic wastewater in low ammonia nitrogen and low temperature: Fe (II) makes a difference

In this study, the impacts of heavy metals (1 mg L^-1) on the nitrogen removal, bioactivity of anaerobic ammonia-oxidizing bacteria (AAOB) and the microbial community of anaerobic ammonium oxidation (Anammox) process were investigated. It was observed that short-term exposure in Cu (II) and Zn (II) both improved AAOB bioactivity, while long-term exposure significantly lowered the nitrogen removal to 0.218 and 0.302 kg m^-3 d^-1, when treated the wastewater with 100 mg L^-1 nitrogen under 14-16 °C. Fe(II) had slight impact on Anammox in short-term experiment but deeply enhanced nitrogen removal during the long-term contact, and finally increased the that to 0.58 kg m^-3 d^-1. The impact on Anammox was Cu(II) > Zn(II) > Fe(II). Cu(II) and Zn(II) lowered the share of Candidatus Kuenenia to 3.32% and 3.80%, while Fe(II) improved that to 11.30% from 7.99%. Extracellular polymeric substance in biofilm had prominent iron adsorption capacity, which was the key factor that help AAOB resist Fe(II).

Enhancement of the adaptability of anammox granules to zinc shock by appropriate organic carbon treatment

Heavy metals, which are commonly present in high ammonia-containing wastewater, can cause inhibitory effects to anammox reaction. This study proposes a novel approach to enhance the adaptability of anammox granules to heavy metal [Zn(II)] shock by organic carbon (sodium acetate, NaAc) treatment, paying special attention to optimization of the treatment dosage and duration. For granules treated with 200 mg chemical oxygen demand (COD)/L NaAc for 2 d, the activity recovery (six cycles) efficiency after Zn(II) (40 mg/L) shock reached 127.4%. The extracellular polymeric substance (EPS) production increased by 168% and heterotrophic bacteria mildly proliferated (increased by 14%) in such granules compared with the control. The dramatic recovery capacity was likely due to the entrapment and barrier function of EPS and the outer-layer proliferated heterotrophic bacteria. This finding offers a useful process to enable maximum adaptability of anammox granules from heavy metals shocks, allowing anammox technology to be more widely applied.

Inhibitory effects of heavy metals and antibiotics on nitrifying bacterial activities in mature partial nitritation

To facilitate the use of partial nitritation (PN) in nitrogen removal processes for livestock wastewater, this work investigated the inhibitory effects of heavy metals and antibiotics on the nitrifying bacterial activities of the PN processes. Biomass was collected from a continuous-flow internal-loop airlift reactor and cultured with fixed ammonium concentrations of 921 mg N L^-1. Batch activity tests were conducted to determine the specific oxygen uptake rate. The individual and interactive inhibitory effects of Zn²⁺, Cu²⁺, oxytetracycline (OTC) and sulfamethazine (SMZ) were evaluated using an orthogonal test. The results showed that the half maximal inhibitory concentration (IC₅₀) values of Zn²⁺, Cu²⁺, OTC and SMZ on PN sludge were 50.1, 35.4, 447 and 1890 mg L^-1, respectively. The joint toxicities of heavy metals (Zn²⁺ and Cu²⁺) and antibiotics (OTC and SMZ) in the PN mixed culture were generally synergistic, except for between Zn²⁺ and Cu²⁺, which was antagonistic. In joint toxicity tests, the significance of the inhibitory effect of Zn²⁺ (15.3-164.3 mg L^-1), Cu²⁺ (13.8-90.9 mg L^-1), OTC (27.0-866.5 mg L^-1) and SMZ (290-3490 mg L^-1) on the nitrifying bacterial activity can be ranked in the following order: SMZ > Cu²⁺ > Zn²⁺ > OTC. Additionally, different exposure times (1 h, 3 h and 24 h) with or without aeration were also comparatively studied. These results show that a greater PN sludge activity loss than when exposure without aeration.

Influence of elevated Zn (II) on Anammox system: Microbial variation and zinc tolerance

Nitrogen removal by anaerobic ammonium oxidation (Anammox) has attracted increasing attention in nowadays. An Anammox biofilter was subjected to a continuous loading of elevated Zn (II). The influence of Zn (II) on the nitrogen removal, microbial community and biofilm property was investigated in the condition of 23-26 °C and 3.5 h HRT. The nitrogen removal greatly decreased to 0.054 from the initial 0.502 kg m^-3 d^-1, with the Zn (II) addition. Anaerobic ammonia-oxidizing bacteria (AAOB) had self-adaption to Zn (II) in 1-10 mg L^-1 and was significantly enhanced after long-term acclimatization, while the suppression threshold was 20 mg L^-1. Soluble microbial products (SMP) increased correspondingly with Zn (II), while extracellular polymeric substance (EPS) climbed up initially and then decreased. Anammox biofilm performed the highest zinc adsorption as 158.27 mg g^-1 SS in biofilm. High Zn (II) improved the microbial diversity and lowered the Candidatus Kuenenia abuandance to 1.38% from 20.89%.

Short-term and long-term effects of Zn (II) on the microbial activity and sludge property of partial nitrification process

Autotrophic nitrogen removal was an innovative and economical nitrogen removal technology with less oxygen and no organics consumption, in which partial nitrification (PN) is the key component. It is necessary to clear the impact of metal ions on PN since the development of industry increased their opportunity for entering into wastewater. In this study, PN process was successfully started-up in an SBR, the short-term and long-term effects of Zn (II) on microbial bioactivity and the sludge adsorption ability for Zn (II) were investigated. Results suggested that low Zn (II) were favorable for AOB bioactivity, while the long-term effect also induced NOB bioactivity. The suppression threshold of Zn (II) on AOB in short-term effect was 10mgL^-1, which rose to 50mgL^-1 in the long-term effect due to the self-adaption. The PN sludge presented prominent absorbability for zinc and performed a quadratic relation with the Zn (II) concentration.

Inhibition of the partial nitritation by roxithromycin and Cu(II)

To facilitate the application of partial nitritation (PN) - anaerobic ammonium oxidation process in nitrogen removal from livestock wastewater, the inhibition of roxithromycin (ROX) and Cu(II) on the PN sludge was examined using a respirometric method. The results showed that the IC50 of ROX and Cu(II) on PN sludge were 346 and 74.3mgL(-1), respectively. The relative specific respiration rate (SRR) of ammonia-oxidizing bacteria (AOB) decreased from 87.4% to 17.7% with the ROX concentration increased from 0 to 500mgL(-1). When the concentration of Cu(II) increased from 0 to 160mgL(-1), the SRRs of AOB and nitrite-oxidizing bacteria decreased by 85.5% and 11.2%, respectively. According to the isobole plots analysis, combined suppression by ROX and Cu(II) was synergistic. Fourier transform infrared spectroscopy analyses showed that ROX exposure altered the positions of CO bonds, and the intensity of the absorption peak at 2100cm(-1) changed under Cu(II) exposure.

Assessing the treatment of acetaminophen-contaminated brewery wastewater by an anaerobic packed-bed reactor

The treatment of high-strength organic brewery wastewater with added acetaminophen (AAP) by an anaerobic digester was investigated. An anaerobic packed-bed reactor (APBR) was operated as a continuous process with an organic loading rate of 1.5-g COD per litre per day and a hydraulic retention time of three days. The results of steady-state analysis showed that the greatest APBR performances for removing COD and TOC were as high as 98 and 93%, respectively, even though the anaerobic digestibility after adding the different AAP concentrations of 5, 10 and 15 mg L(-1) into brewery wastewater can affect the efficiency of organic matter removal. The average CH4 production decreased from 81 to 72% is counterbalanced by the increased CO2 production from 11 to 20% before and after the injection of AAP, respectively. The empirical kinetic models for substrate utilisation and CH4 production were used to predict that, under unfavourable conditions, the performance of the APBR treatment process is able to remove COD with an efficiency of only 6.8%.

Improvement of landfill leachate biodegradability with ultrasonic process

Landfills leachates are known to contain recalcitrant and/or non-biodegradable organic substances and biological processes are not efficient in these cases. A promising alternative to complete oxidation of biorecalcitrant leachate is the use of ultrasonic process as pre-treatment to convert initially biorecalcitrant compounds to more readily biodegradable intermediates. The objectives of this study are to investigate the effect of ultrasonic process on biodegradability improvement. After the optimization by factorial design, the ultrasonic were applied in the treatment of raw leachates using a batch wise mode. For this, different scenarios were tested with regard to power intensities of 70 and 110 W, frequencies of 30, 45 and 60 KHz, reaction times of 30, 60, 90 and 120 minutes and pH of 3, 7 and 10. For determining the effects of catalysts on sonication efficiencies, 5 mg/l of TiO₂ and ZnO have been also used. Results showed that when applied as relatively brief pre-treatment systems, the sonocatalysis processes induce several modifications of the matrix, which results in significant enhancement of its biodegradability. For this reason, the integrated chemical–biological systems proposed here represent a suitable solution for the treatment of landfill leachate samples.

Treating landfill leachate using passive aeration trickling filters; effects of leachate characteristics and temperature on rates and process dynamics

Biological ammoniacal-nitrogen (NH(4)(+)-N) and organic carbon (TOC) treatment was investigated in replicated mesoscale attached microbial film trickling filters, treating strong and weak strength landfill leachates in batch mode at temperatures of 3, 10, 15 and 30 degrees C. Comparing leachates, rates of NH(4)(+)-N reduction (0.126-0.159 g m(-2) d(-1)) were predominantly unaffected by leachate characteristics; there were significant differences in TOC rates (0.072-0.194 g m(-2) d(-1)) but no trend relating to leachate strength. Rates of total oxidised nitrogen (TON) accumulation (0.012-0.144 g m(-2) d(-1)) were slower for strong leachates. Comparing temperatures, treatment rates varied between 0.029-0.319 g NH(4)(+)-N m(-2) d(-1) and 0.033-0.251 g C m(-2) d(-1) generally increasing with rising temperatures; rates at 3 degrees C were 9 and 13% of those at 30 degrees C for NH(4)(+)-N and TOC respectively. For the weak leachates (NH(4)(+)-N<140 mg l(-1)) complete oxidation of NH(4)(+)-N was achieved. For the strong leachates (NH(4)(+)-N 883-1150 mg l(-1)) a biphasic treatment response resulted in NH(4)(+)-N removal efficiencies of between 68 and 88% and for one leachate no direct transformation of NH(4)(+)-N to TON in bulk leachate. The temporal decoupling of NH(4)(+)-N oxidation and TON accumulation in this leachate could not be fully explained by denitrification, volatilisation or anammox, suggesting temporary storage of N within the treatment system. This study demonstrates that passive aeration trickling filters can treat well-buffered high NH(4)(+)-N strength landfill leachates under a range of temperatures and that leachate strength has no effect on initial NH(4)(+)-N treatment rates. Whether this approach is a practicable option depends on a range of site specific factors.