Long-term impact of nano zero-valent iron on methanogenic activity, microbial community structure, and transcription activity in anaerobic wastewater treatment system.

Nano zero-valent iron (NZVI) is commonly used in industrial wastewater treatment. However, its long-term impact mechanisms of metabolization in anaerobic systems are not well understood. This study investigated the effects of long-term and continuous addition of NZVI on methanogenic activity, microbial community, and transcription activity. The results demonstrated that low levels of NZVI (1000 mg/L) induced inhibition of methanogenesis after 80 days, while high levels of NZVI (5000 mg/L) immediately led to a sharp decrease of cumulative methane production and chemical oxygen demand removal, which arrived at a steady state (14.4 % of control and 17 %) after 30 days. NZVI adversely affected cell viability, adenosine triphosphate production, and fatty acid evolution of cell membranes played a crucial role in resisting chronic NZVI toxicity. Moreover, high NZVI levels hindered the transcription of key enzymes CoM and mcrA, while low NZVI levels maintained its high CoM and mcrA activity, but down-regulated the transcription of cdh and hdr. Besides, amino-utilizing bacteria was reduced under the high NZVI concentration, while low NZVI changed dominant genus with potential protein hydrolysis function from Candidatus Cloacamonas to Sedimentibacter. These results provide a guideline for proper NZVI utilization in wastewater treatment.

How anaerobic sludge microbiome respond to different concentrations of nitrite, nitrate, and ammonium ions: a comparative analysis.

High concentrations of ammonium, nitrite, and nitrate always induce inhibition in anaerobic wastewater treatment. Due to the complexity and vulnerability of the microbial community (especially methanogens) in anaerobic sludge, little is understood about its underlying microbial mechanism under such inhibition. In this study, the shifts of microbial communities in anaerobic sludge under increasing levels of nitrite, nitrate, and ammonium ions were compared. Results show that although half maximal inhibitory concentrations (methanogenesis) were different for nitrite, nitrate, and ammonium ions with EC50 values of 12, 30, and 3000 mg N/L, respectively, bacteria genera Kosmotoga and Brooklawnia dominated in all of the three high-stress inhibitory systems. Network analysis and redundancy analysis (RDA) of the microbial community showed the treatments with nitrate and nitrite ions decreased the modularity of anaerobic microorganisms. RDA showed that specific methanogenic activity was positively related to coenzyme F420 under nitrite inhibition (rp = 0.833, p < 0.05) and closely correlated with viability under nitrate inhibition. Gram-positive and nonmotile Brooklawnia genus showed a negative correlation with physiological characteristics in the ammonia treatments, suggesting its high resistance to ammonia.

[Impact of Nano Zero-Valent Iron (NZVI) on Methanogenic Activity, Physiological Traits, and Microbial Community Structure in Anaerobic Digestion].

Effects of short-term nano zero-valent iron (NZVI) and zero-valent iron (ZVI) exposure on methanogenic activity of anaerobic sludge, physiological traits, composition of phospholipid fatty acids (PLFA), and microbial community structure were investigated. Results show that accumulated methane production decreased with an increase of NZVI concentration; yet, methane production only changed slightly with the same concentration of ZVI. In the NZVI (100-5000 mg·L-1) sets, dissolved iron (DFe) concentrations were 1.6-7.4 times that of the control value at 5 d, whereas DFe was only slightly above the control in the ZVI set (5000 mg·L-1). The concentration of extracellular polymeric substances and cell viability decreased to 21.1% and 79.7%, respectively, of the control in the 5000 mg·L-1 NZVI treatments. Coenzyme F420 and coenzyme M decreased to 40.2% and 61.1%, respectively, of the control in the 5000 mg·L-1 NZVI treatments, which were significantly increased to 1.3 times that of the control value in the 100 mg·L-1 NZVI and 5000 mg·L-1 ZVI treatments. The order of unsaturation and branch PLFA content was ZVI-5000 (21.18%) > control (19.37%) > NZVI-1000 (16.69%) > NZVI-5000 (15.94%) > NZVI-100 (12.08%). High NZVI concentration (5000 mg·L-1) resulted in an increase of DFe and a decrease of cell membrane fluidity and key coenzyme activity of methanogenesis, which led to the inhibition of methane production. Principle component analysis and redundancy analysis indicated that differences in the microbial community existed among these treatments and that Nakamurella, Bacillus, Trichococcus, and Petrimonas showed tolerance to NZVI.

Weighted species sensitivity distribution method to derive site-specific quality criteria for copper in Tai Lake, China.

Tai Lake (Ch: Taihu), which is the largest lake in Jiangsu province, China, has been affected by human activities. As part of a concerted effort to improve water quality to protect the integrity of the Tai Lake ecosystem, a water quality criterion (WQC) was developed for copper (Cu) II. The acute WQC was based on 440 values for acute toxicity of Cu to 24 species from 6 phyla, 16 families, and 20 genera. In addition, 255 values for chronic toxicity of Cu to 10 species from 5 phyla, 8 families, and 9 genera were used to derive chronic WQC. Instead of using a traditional approach based species sensitivity distributions (SSD), a weighted species sensitivity distribution (WSSD) approach was used to calculate the cumulative probability based on endemic species to Tai Lake. Acute and chronic WQC developed by use of the WSSD were 5.3 and 3.7 µg Cu/L, respectively. While the WQC values were comparable to those of other countries, there were slight differences due to variability in species composition of different regions. The site-specific criteria indicated that the current standard set for surface water by the Chinese government might not be protective of aquatic organisms in Tai Lake.