Chunguang He

Assessing nitrogen transformation processes in a trickling filter under hydraulic loading rate constraints using nitrogen functional gene abundances.

A study was conducted of treatment performance and nitrogen transformation processes in a trickling filter (TF) used to treat micro-polluted source water under variable hydraulic loading rates (HLRs), ranging from 1.0 to 3.0 m(3)/m(2) d. The TF achieved high and stable COD (97.7-99.3%) and NH4(+)-N (67.3-92.7%) removal efficiencies. Nitrification and anaerobic ammonium oxidation were the dominant nitrogen removal processes in the TF. Path analysis indicated that amoA/anammox and amoA/(narG+napA) were the two key functional gene groups driving the major processes for NH4(+)-N and NO2(-)-N, respectively. The analysis also revealed that anammox/amoA and nxrA/(nirK+nirS) were the two key functional gene groups affecting processes associated with the NO3(-)-N transformation rate. The direct and indirect effect of functional gene groups further confirmed that nitrogen transformation processes are coupled at the molecular level, resulting in a mutual contribution to nitrogen removal in the TF.

Fate of free chlorine in drinking water during distribution in premise plumbing.

Free chlorine is a potent oxidizing agent and has been used extensively as a disinfectant in processes including water treatment. The presence of free chlorine residual is essential for the prevention of microbial regrowth in water distribution systems. However, excessive levels of free chlorine can cause adverse health effects. It is a major challenge to maintain appropriate levels of free chlorine residual in premise plumbing. As the first effort to assessing the fate of chlorine in premise plumbing using actual premise plumbing pipe sections, three piping materials frequently used in premise plumbing, i.e. copper, galvanized iron, and polyvinyl chloride (PVC), were investigated for their performance in maintaining free chlorine residual. Free chlorine decay was shown to follow first-order kinetics for all three pipe materials tested. The most rapid chlorine decay was observed in copper pipes, suggesting the need for higher chlorine dosage to maintain appropriate levels of free chlorine residual if copper piping is used. PVC pipes exhibited the least reactivity with free chlorine, indicative of the advantage of PVC as a premise plumbing material for maintaining free chlorine residual. The reactivity of copper piping with free chlorine was significantly hindered by the accumulation of pipe deposits. In contrast, the impact on chlorine decay by pipe deposits was not significant in galvanized iron and PVC pipes. Findings in this study are of great importance for the development of effective strategies for the control of free chlorine residual and prevention of microbiological contamination in premise plumbing.

Response to Comment on "Enhanced Long-Term Nitrogen Removal and Its Quantitative Molecular Mechanism in Tidal Flow Constructed Wetlands".

and Its Quantitative Molecular Mechanism in Tidal Flow Constructed Wetlands” W wish to thank Yi Chen and Jan Vymazal for their constructive comments. We would like to take this opportunity to clarify our research objective and methodology. Whether RNA-based techniques are more suitable than DNAbased techniques in studying the role of microbial communities in environmental systems depends on the specific application, the characteristics of the bioreactor system, and the trade-off between the cost and the amount of information provided by each method. It is generally true that the analysis of mRNA, which is synthesized in response to changing environmental conditions, is useful for identifying active microbes and assessing in situ metabolic activity. However, this mRNAbased approach must be used with caution because the assessment of the gene expression level is likely to underestimate the total functioning of a microbial community. This underestimation is partly due to the presence of dormant and deceased cells, which are unaccounted for in the gene expression analysis but may contribute to ecosystem functioning. Dormant cells are a significant repository for system functioning and have the potential to restart once they adapt to the environment. Deceased cells provide a source of nutrients for other living microorganisms that drive ecosystem processes. Another technical problem with mRNA-based techniques is that high-quality environmental mRNA is difficult to extract in sufficient quantities and degrades rapidly. DNAbased quantification, which accounts for all active, dormant, and deceased cells, is a robust alternative for measuring the total microbial activity for the given environmental conditions. In addition, it is often necessary to consider the scales at which microbes interact with their surrounding environment. The highly variable and short-lived mRNA is useful mainly for identifying functionally active microbes by quantifying the gene expression dynamic before and after the application of a specific stimulus and on a time scale of hours. This short exposure time is often essential to minimize shifts in the community structure and to maintain the genetic background. To date, mRNA-based quantification has been used mainly to investigate the transcriptional activity of amoA genes in response to shortterm perturbations such as nutrient amendments, loading rate changes, and operation alteration. In this study, we chose to investigate long-term nitrogen removal in a large-scale bioreactor (80 L) over a broader scope rather than focus on the transcriptional activity in one specific process (e.g., ammonia oxidation) on the molecular scale. Thus, the complete chain of nitrogen removal processes was investigated in specifically designed constructed wetlands (CWs) with the following characteristics: (1) the systems were operated with set procedures for 245 days at a constant feeding rate to achieve a stable environment for the succession of microbial community structures and to minimize fluctuations in the microbial activity level and (2) a relatively longer hydraulic cycle was employed to support an approximately steady-state gene expression level. We are thus comfortable stating that using DNA-based quantification to assess the succession of the community structure is preferable because this method provides a broader perspective on the macroscale mechanisms affecting long-term nitrogen removal. As the comments suggested, the N isotope and gas measurements are valuable tools for distinguishing anammox from denitrification; however, the partitioning of the nitrogen loss were beyond the scope of this study and are thus not addressed in this response. At the molecular level, the oxidation of ammonia to nitrite is catalyzed by ammonia monooxygenase (AMO), which is specifically regulated by the amoA gene. However, the complexity increases with system scaling-up and the oxidation of ammonia to nitrite is affected both by internal controls (e.g., the amoA gene) and environmental factors (e.g., inhibitors) in a large-scale system. As mentioned in the study by Zhi et al., the negative correlation between the ammonia transformation rate and amoA/(nxrA + anammox) is due to the inhibitory effect of accumulated nitrite. This result indicates that nitrogen transformation processes are closely interwoven in complex environmental settings, and a broader perspective is essential for revealing their coupled effects on nitrogen removal rates on a large scale. Although abiotic processes may contribute to nitrogen removal, our previous work showed that ammonia adsorption is a transient process that occurs mainly at the initial stage (in the first 35 days) and contributes little to long-term nitrogen removal. Although vegetation is considered an important component in CW systems favoring microbial immobilization and enrichment, the plants in our study had no direct effect on ammonia and nitrate removal, as demonstrated by our two unplanted control systems (unpublished data). This result was likely due to the low planting density and the shallow rooting depth. Thus, the microbial process was the dominant mechanism for long-term nitrogen removal. In fact, 89−96% of nitrogen removal in wetland systems has been attributed to microbial reactions. This evidence and established correlations can be used to identify the direct roles of functional genes in governing long-term nitrogen removal. We understand the concern regarding sampling. Unfortunately, sampling remains a challenge because it is nearly impossible to quantify the representativeness of a sample unless the entire population is analyzed, which is typically costprohibitive and impractical. Therefore, it is difficult to reach definitive conclusions for questions such as the degree of representativity and the number microbial samples required for a heterogeneous biosystem. In practice, the sampling problem is normally addressed based on the research objective (the scale and the resolution) and previous experience. In this study, the microbial sampling was designed to provide temporal data for Correspondence/Rebuttal

The Spatial Distribution of Nitrogen Removal Functional Genes in Multimedia Constructed Wetlands for Wastewater Treatment.

The real-time polymerase chain reaction was used to quantitatively evaluate distribution patterns and nitrogen removal pathways of the amoA, nxrA, narG, napA, nirK, qnorB, nosZ, nas, and nifH genes and 16S rRNA in anaerobic ammonia oxidation bacteria in four multimedia constructed wetlands for rural wastewater treatment. The results indicated that the abundance of functional genes for nitrogen removal in the rhizosphere layer (0 to 30 cm), water distribution layer (30 to 50 cm), multime filler layer (50 to 130 cm), and catchment layer (130 to 170 cm) of the constructed wetlands were closely related. The rhizosphere layer was conducive to the absolute enrichment of dominant genes. The other three layers were favorable to the relative enrichment of rare genes.

Characteristics of Cadmium Sorption by Heat-Activated Red Mud in Aqueous Solution

Red mud as a waste material is produced in large quantities by the aluminum industry. Heat activation has been used to enhance sorption capacity of red mud for its beneficial reuse as an effective sorbent. In this study, heat-activated red mud (HARM) was investigated for its Cd(II) sorption capacity under various process conditions (Cd concentration, pH and contact time) using response surface methodology (RSM). Analysis with RSM identified pH as the most important process parameter. The positive correlation between higher pH and greater Cd(II) sorption was likely due to: (i) decreased proton competition with Cd(II) for sorption sites at higher pH; (ii) enhanced sorption via ion exchange by monovalent Cd species from hydrolysis at higher pH; and (iii) improved thermodynamics of sorption at higher pH as protons are being released as products. Further analysis indicated the sorption process was thermodynamically favorable with a negative change in Gibbs free energy. Additionally, the sorption process exhibited a positive change in enthalpy, indicative of endothermic nature of sorption; this is consistent with sorption increase at higher temperature. These findings provide needed insight into the mechanisms underlying Cd(II) sorption by HARM for more effective applications of heat-activated red mud as sorbents for Cd(II) removal.

Effect of planting and fertilization on lead partitioning in dredged sediment

Dredging has been practiced to remove sediment impacted by persistent contaminants, such as heavy metals. Of these metals, lead (Pb) is of particular concern due to its toxicity. Therefore, dredged sediment containing Pb requires further mitigation. One method for Pb mitigation is phytoremediation of dredged sediment. In this study, the partitioning of Pb in sediment during phytoremediation by willow (Salix integra) was assessed. The results showed that, in general, the bioavailable forms of Pb declined with increased application of the standard Hoagland nutrient solution, which appeared to enhance the Fe–Mn oxide fraction and residual inert fraction. In contrast, the addition of excess phosphorus decreased the bioavailable fractions of Pb. However, the bioavailable fractions of Pb increased with additional potassium addition. Planting Salix integra was shown to promote the stabilization of Pb in sediment and led to a transformation from bioavailable forms to non-bioavailable forms. The results suggest that planting Salix integra can remediate Pb-contaminated dredged sediment via Pb immobilization by the roots. During this process, the application of Hoagland nutrient solution and the application of nutrient solutions with excess phosphorus not only promote root growth of Salix integra which would reduce Pb bioavailability, but also further enhance the immobilization of Pb in contaminated sediment, likely through the formation of Pb-containing compounds with low bioavailability.

Using 13 C isotopes to explore denitrification-dependent anaerobic methane oxidation in a paddy-peatland

Peatlands are organic-matter-rich but nitrogen-limited natural systems, the carbon/nitrogen (C/N) status of which are subject to increasing exposure from long-term nitrate (NO3−) fertilizer inputs and atmospheric nitrogen (N) deposits. To manage and protect these unique environments, an improved understanding of denitrification-dependent anaerobic oxidation of methane (DAMO) in peatlands is needed. In this study, we used stable isotope measurements and incubation with NO3− additions to facilitate an investigation and comparison of the potential DAMO rates in a paddy-peatland that has been influenced by N fertilizer over 40 years and an undisturbed peatland in northeast China. Monitoring of 13CO2 production confimed DAMO did occur in both the paddy-peatland and the undisturbed peatland, the rates of which increased with NO3− additions, but decreased logarithmically with time. When NO3− was added, there were no significant differences between the CH4 oxidation in the paddy-peatland and peatland samples after 36 hours of incubation (97.08 vs. 143.69 nmol g−1 dry peat) and the potential DAMO rate after incubation for 1 hour (92.53 vs. 69.99 nmol g−1 h−1). These results indicate that the occurrence of DAMO in peatlands might be controlled by the amount of NO3− applied and the depth to which it penetrates into the anoxic layer.