Guibing Zhu

Biological nitrogen removal with nitrification and denitrification via nitrite pathway

Presently, the wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. To meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when wastewater with high ammonium concentrations or low C/N ratios is treated. For successful implementation of the technology, the critical point is how to maintain partial nitrification of ammonium to nitrite. Partial nitrification can be obtained by selectively inhibiting nitrite oxidizing bacteria through appropriate regulation of the system’s DO concentration, microbial SRT, pH, temperature, substrate concentration and load, operational and aeration pattern, and inhibitor. The review addressed the microbiology, its consequences for their application, the current status regarding application, and the future developments.

A review on removing pharmaceutical contaminants from wastewater by constructed wetlands: Design, performance and mechanism

This paper presents a comprehensive review of the current state of research activities on the application of constructed wetlands for removing pharmaceutical contaminants from wastewater. The focus of the review was placed on the application of constructed wetlands as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system. The design parameters of the reported constructed wetlands including the physical configuration, hydraulic mode, vegetation species, and targeting pharmaceuticals were summarized. The removal efficiencies of pharmaceuticals under different conditions in the wetlands were evaluated at the macroscopic level. In addition, the importance of the three main components of constructed wetlands (substrate, plants and microbes) for pharmaceutical removal was analyzed to elucidate the possible removal mechanisms involved. There is a general consensus among many researchers that constructed wetlands hold great potential of being used as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system for the removal of pharmaceuticals, but relevant reported studies are scarce and are not conclusive in their findings. Current knowledge is limited on the removal efficiencies of pharmaceuticals in constructed wetlands, the removal mechanisms involved, the toxicity to constructed wetlands caused by pharmaceuticals, and the influences of certain important parameters (configuration design, hydraulic mode, temperature and seasonality, pH, oxygen and redox potential, etc.). This review promotes further research on these issues to provide more and better convincing evidences for the function and performance of larger laboratory-scale, pilot-scale or full-scale constructed wetlands.

Biological removal of nitrogen from wastewater

This comprehensive review discusses diverse conventional and novel technologies for nitrogen removal from wastewater. Novel technologies have distinct advantages in terms of saving configuration, aeration, and carbon sources. Each novel technology possesses promising features and potential problems. For instance, SND and OLAND processes can achieve 100% total nitrogen removal, but the low oxygen concentration required by these two processes substantially reduces the nitrification rate, which limits their application. On the other hand, denitrification can still be carried out by aerobic denitrifiers at high DO levels in activated sludge process, but it is difficult to cultivate this type of bacteria. The SHARON process is most commonly used for shortcut nitrification and denitrification because of its low requirements for retention time, oxygen concentration, and carbon source. However, its high operational temperature (about 35 degrees C) limits the application. Several real-time control strategies (DO, pH, and ORP) have been developed to achieve a stable nitrite accumulation in SHARON. The ANAMMOX process can sustain at high total-N loadings and has been employed in full-scale treatment plants, but the problem of nitrite supply has not been solved, and the treated wastewater still contains nitrate. In addition, the inoculation and enrichment of ANAMMOX bacteria (i.e., anaerobic AOB) is difficult. The problem of nitrite supply has been solved by combining partial nitrification with ANAMMOX, which provides abundant nitrite for anaerobic AOB. ANAMMOX is currently used for treating sludge digestion supernatant. Aerobic dammonitrification is a process combining partial nitrification and ANAMMOX at different layers of biofilm. Although the technology has been tested in pilot- and full-scale experiments, the mechanism is still unclear. CANON and OLAND are one-step ammonium removal processes that possess distinct advantages of saving carbon sources and aeration costs. The major challenge is the enrichment of anaerobic microorganisms capable of oxidizing ammonia with nitrite as the electron acceptor. Molecular biology and environmental biotechnology can help identify functional microorganisms, characterize microbial communities, and develop new nitrogen removal processes. Extensive research should be conducted to apply and optimize these novel processes in wastewater treatment plants. More effort should be invested to combine these novel processes (e.g., partial nitrification, ANAMMOX) to enhance nitrogen removal efficiency.

Anaerobic ammonia oxidation in a fertilized paddy soil

Evidence for anaerobic ammonium oxidation in a paddy field was obtained in Southern China using an isotope-pairing technique, quantitative PCR assays and 16S rRNA gene clone libraries, along with nutrient profiles of soil cores. A paddy field with a high load of slurry manure as fertilizer was selected for this study and was shown to contain a high amount of ammonium (6.2–178.8 mg kg−1). The anaerobic oxidation of ammonium (anammox) rates in this paddy soil ranged between 0.5 and 2.9 nmolN per gram of soil per hour in different depths of the soil core, and the specific cellular anammox activity observed in batch tests ranged from 2.9 to 21 fmol per cell per day. Anammox contributed 4–37% to soil N2 production, the remainder being due to denitrification. The 16S rRNA gene sequences of surface soil were closely related to the anammox bacteria ‘Kuenenia’, ‘Anammoxoglobus’ and ‘Jettenia’. Most of the anammox 16S rRNA genes retrieved from the deeper soil were affiliated to ‘Brocadia’. The retrieval of mainly bacterial amoA sequences in the upper part of the paddy soil indicated that nitrifying bacteria may be the major source of nitrite for anammox bacteria in the cultivated horizon. In the deeper oxygen-limited parts, only archaeal amoA sequences were found, indicating that archaea may produce nitrite in this part of the soil. It is estimated that a total loss of 76 g N m−2 per year is linked to anammox in the paddy field.

Potential roles of anaerobic ammonium and methane oxidation in the nitrogen cycle of wetland ecosystems

Anaerobic ammonium oxidation (anammox) and anaerobic methane oxidation (ANME coupled to denitrification) with nitrite as electron acceptor are two of the most recent discoveries in the microbial nitrogen cycle. Currently the anammox process has been relatively well investigated in a number of natural and man-made ecosystems, while ANME coupled to denitrification has only been observed in a limited number of freshwater ecosystems. The ubiquitous presence of anammox bacteria in marine ecosystems has changed our knowledge of the global nitrogen cycle. Up to 50% of N2 production in marine sediments and oxygen-depleted zones may be attributed to anammox bacteria. However, there are only few indications of anammox in natural and constructed freshwater wetlands. In this paper, the potential role of anammox and denitrifying methanotrophic bacteria in natural and artificial wetlands is discussed in relation to global warming. The focus of the review is to explore and analyze if suitable environmental conditions exist for anammox and denitrifying methanotrophic bacteria in nitrogen-rich freshwater wetlands.

Performance of anammox UASB reactor treating low strength wastewater under moderate and low temperatures

An integrated approach to enhance and maintain high anammox activity and abundance in an upflow anaerobic sludge blanket (UASB) treating low strength wastewater under moderate and low temperatures was developed. A quantitative PCR assay showed the abandance of anammox bacteria to be 1.68±0.08×10(9) copies/ml in mixed liquor when the temperature was 30 °C and was maintained at the level of 1.93±0.41×10(9) copies/ml in mixed liquor at 16 °C. A nitrogen removal rate (NRR) of up to 5.72 kg N/m3/d was achieved with a hydraulic retention time (HRT) of 0.12 h at 30 °C, while nitrite and ammonium removal efficiencies were 94.35% and 92.81%, respectively. NRR decreased with a decrease in temperature and was maintained at 2.28 kg N/m3/d with an HRT of 0.28 h when at 16 °C, while nitrite and ammonium removal efficiencies were 92.31% and 78.45%, respectively. The emission rate of the greenhouse gas N2O was below 0.006% of the NRR in the anammox UASB reactor treating low strength wastewater.

Quantitative analyses of ammonia-oxidizing Archaea and bacteria in the sediments of four nitrogen-rich wetlands in China

With the rapid development of ammonia-synthesizing industry, the ammonia-nitrogen pollution in wetlands acting as the sink of point and diffuse pollution has been increased dramatically. Most of ammonia-nitrogen is oxidized at least once by ammonia-oxidizing prokaryotes to complete the nitrogen cycle. Current research findings have expanded the known ammonia-oxidizing prokaryotes from the domain Bacteria to Archaea. However, in the complex wetlands environment, it remains unclear whether ammonia oxidation is exclusively or predominantly linked to Archaea or Bacteria as implied by specific high abundance. In this research, the abundance and composition of Archaea and Bacteria in sediments of four kinds of wetlands with different nitrogen concentration were investigated by using quantitative real-time polymerase chain reaction, cloning, and sequencing approaches based on amoA genes. The results indicated that AOA distributed widely in wetland sediments, and the phylogenetic tree revealed that archaeal amoA functional gene sequences from wetlands sediments cluster as two major evolutionary branches: soil/sediment and sediment/water. The bacteria functionally dominated microbial ammonia oxidation in different wetlands sediments on the basis of molecule analysis, potential nitrification rate, and soil chemistry. Moreover, the factors influencing AOA and AOB abundances with environmental indicator were also analyzed, and the results addressed the copy numbers of archaeal and bacterial amoA functional gene having the higher correlation with pH and ammonia concentration. The pH had relatively great negative impact on the abundance of AOA and AOB, while ammonia concentration showed positive impact on AOB abundance only. These findings could be fundamental to improve understanding of the importance of AOB and AOA in nitrogen and other nutrients cycle in wetland ecosystems.

Potential Contribution of Anammox to Nitrogen Loss from Paddy Soils in Southern China

ABSTRACT The anaerobic oxidation of ammonium (anammox) process has been observed in diverse terrestrial ecosystems, while the contribution of anammox to N2 production in paddy soils is not well documented. In this study, the anammox activity and the abundance and diversity of anammox bacteria were investigated to assess the anammox potential of 12 typical paddy soils collected in southern China. Anammox bacteria related to “Candidatus Brocadia” and “Candidatus Kuenenia” and two novel unidentified clusters were detected, with “Candidatus Brocadia” comprising 50% of the anammox population. The prevalence of the anammox was confirmed by the quantitative PCR results based on hydrazine synthase (hzsB) genes, which showed that the abundance ranged from 1.16 × 104 to 9.65 × 104 copies per gram of dry weight. The anammox rates measured by the isotope-pairing technique ranged from 0.27 to 5.25 nmol N per gram of soil per hour in these paddy soils, which contributed 0.6 to 15% to soil N2 production. It is estimated that a total loss of 2.50 × 106 Mg N per year is linked to anammox in the paddy fields in southern China, which implied that ca. 10% of the applied ammonia fertilizers is lost via the anammox process. Anammox activity was significantly correlated with the abundance of hzsB genes, soil nitrate concentration, and C/N ratio. Additionally, ammonia concentration and pH were found to be significantly correlated with the anammox bacterial structure.

Nitrogen loss by anaerobic oxidation of ammonium in rice rhizosphere

Anaerobic oxidation of ammonium (anammox) is recognized as an important process for nitrogen (N) cycling, yet its role in agricultural ecosystems, which are intensively fertilized, remains unclear. In this study, we investigated the presence, activity, functional gene abundance and role of anammox bacteria in rhizosphere and non-rhizosphere paddy soils using catalyzed reporter deposition–fluorescence in situ hybridization, isotope-tracing technique, quantitative PCR assay and 16S rRNA gene clone libraries. Results showed that rhizosphere anammox contributed to 31–41% N2 production with activities of 0.33–0.64 nmol N2 g−1 soil h−1, whereas the non-rhizosphere anammox bacteria contributed to only 2–3% N2 production with lower activities of 0.08–0.26 nmol N2 g−1 soil h−1. Higher anammox bacterial cells were observed (0.75–1.4 × 107 copies g−1 soil) in the rhizosphere, which were twofold higher compared with the non-rhizosphere soil (3.7–5.9 × 106 copies g−1 soil). Phylogenetic analysis of the anammox bacterial 16S rRNA genes indicated that two genera of ‘Candidatus Kuenenia’ and ‘Candidatus Brocadia’ and the family of Planctomycetaceae were identified. We suggest the rhizosphere provides a favorable niche for anammox bacteria, which are important to N cycling, but were previously largely overlooked.

Suppressing nitrite-oxidizing bacteria growth to achieve nitrogen removal from domestic wastewater via anammox using intermittent aeration with low dissolved oxygen

Achieving nitrogen removal from domestic wastewater using anaerobic ammonium oxidation (anammox) has the potential to make wastewater treatment energy-neutral or even energy-positive. The challenge is to suppress the growth of nitrite-oxidizing bacteria (NOB). This study presents a promising method based on intermittent aeration with low dissolved oxygen to limit NOB growth, thereby providing an advantage to anammox bacteria to form a partnership with the ammonium-oxidizing bacteria (AOB). The results showed that NOB was successfully suppressed using that method, with the relative abundance of NOB maintained between 2.0–2.6%, based on Fluorescent in-situ Hybridization. Nitrogen could be effectively removed from domestic wastewater with anammox at a temperature above 20 °C, with an effluent total nitrogen (TN) concentration of 6.6 ± 2.7 mg/L, while the influent TN and soluble chemical oxygen demand were 62.6 ± 3.1 mg/L and 88.0 ± 8.1 mg/L, respectively.