Total Nitrogen Removal Rate Research Articles

Comprehensive metagenomic analysis reveals the effects of silver nanoparticles on nitrogen transformation in constructed wetlands

The extensive use of silver nanoparticles (Ag NPs) inevitably leads to their release into aquatic ecosystems through sewage discharge. Currently, the impact of Ag NPs on activated sludge has been widely reported, however little is known about how Ag NPs influence nitrogen transformation and metabolic pathways in biofilm systems. In this study, the effects of Ag NPs on nitrogen transformation in constructed wetlands (CWs) were studied using metagenomic analysis. Results showed that total nitrogen and ammonia-nitrogen removal rates were significantly lowered after short-term exposure (5 d) to 1 and 50 mg/L Ag NPs, and long-term exposure (60 d) to Ag NPs caused cumulatively inhibitory effects on nitrogen removal. In addition, the majority of Ag NPs were captured by the CW substrate, with minor amounts reaching plant tissues and effluent. Scanning electron microscopy images and lactate dehydrogenase release assays suggested that a large number of NPs were adsorbed onto the biofilms covering the gravel, which significantly inhibited microbial viability. Furthermore, metagenomic analysis revealed that, bacterial community structures were significantly altered by the presence of Ag NPs, especially those of nitrogen-transforming microorganisms. Clusters of Orthologous Groups annotation demonstrated that Ag NPs impacted metabolic functional potentials, especially for amino acid transport and metabolism. Kyoto Encyclopedia of Genes and Genomes annotation indicated that Ag NPs changed the nitrogen metabolic pathways. Overall, Ag NPs resulted in a decline in the nitrogen removal rate in CWs, which is likely to cause eutrophication of receiving waters.

Diversity and distribution of bacteria in a multistage surface flow constructed wetland to treat swine wastewater in sediments

Managing waste produced from swine farming operations is a significant agricultural and environmental challenge. Confined animal feeding operations continually generate large amounts of animal waste, which necessitates adequate waste management systems. This study examines the use of multistage surface flow constructed wetlands (SFCWs) to treat pig farm sewage. The wastewater removal rate, sediment deposits, physicochemical properties, and microbial community compositions of each segment of a SFCW were examined. The results indicated that removal rates of chemical oxygen demand (COD), total nitrogen (TN), NH4+, NO3-, and total phosphorus (TP) were 89.8%, 97.9%, 98.2%, 87.6%, and 96.4%, respectively, in the multistage SFCW. The general trend showed increase in the dissolved oxygen (DO) concentrations and oxidation reduction potential (Eh) from the beginning of the SFCW to its end. Sediment concentrations of N and P in each segment of the SFCW generally decreased, suggesting their accumulation in each segment. High-throughput sequencing indicated that the bacterial diversity increased over time. Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes were dominant in multistage SFCW bacterial communities at the phylum level. Results further indicate that DO and Eh are major environmental factors that influence the bacterial community distribution. Overall, our findings suggest that multistage SFCWs not only improve contaminant removal but also change the bacterial community composition and promote bacterial community diversity.

Assessment of the treatment of domestic sewage by a vertical-flow artificial wetland at different operating water levels

Artificial wetlands are a sewage treatment technology that operate via the optimization of the physical, chemical, and biological effects of wetland natural ecosystems. The operating conditions and treatment efficiencies of artificial wetlands are researched based on the parameters of domestic sewage, while a vertical-flow artificial wetland is used to simulate domestic sewage as the inlet water of artificial wetlands. The results show that the oxygen-nitrogen removal rate is highest when the water level is 3 cm, while the ammonia nitrogen removal rate increases as the height of the operating water level decreases. When the water level exceeds 35 cm, the nitrate-nitrogen removal rate by the artificial wetland is maintained at a high level, while the nitrate-nitrogen removal rate is highest during operation at the full water level. More nitrite accumulates during operation at a low water level. Considering the total nitrogen removal rate, the vertical-flow artificial wetland reactors M1, M2, and M3 achieved better total nitrogen removal efficiencies. When the water level is 35 cm, the total nitrogen removal rate of the three reactors is the highest. Different operating water level heights do not affect the total phosphorus removal. The Chemical Oxygen Demand（COD） removal efficiency of reactors is higher when the operating water level of the artificial wetland is reduced; that is, the four reactors reached the highest COD removal rate during operation at a low water level.

Intermittent operating characteristics of an ecological soil system with two-stage water distribution for wastewater treatment

Ecological soil systems (ESSs) are usually used to remove nitrogen from wastewater. Due to the poor denitrification performance of traditional ecological soil systems (ESSs), this study proposes a two-stage water distribution system to improve the nitrogen removal. The effects of different distribution ratios on the system treatment effect were studied in an intermittent operation mode. After determining the optimal distribution ratio and intermittent operation conditions, the dynamics of system inflow, outflow, and nitrogen removal were monitored. Theoretical analysis of the denitrification mechanism was carried out. The results showed that the optimum water distribution ratio was 2: 1, and a mean total nitrogen removal rate of 60.42% was achieved, which is 23.09% greater than that is typically achieved by the single-section ecological system. Under optimum distribution ratio conditions, the system also demonstrated effective removal of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+-N), allowing the effluent to satisfy China's urban sewage treatment plant level B emission standards.

Temperature sensitivity of nitrogen-containing compounds decomposition during supercritical water oxidation (SCWO)

Abstract Supercritical water oxidation (SCWO) has sprung up as a promising technique to eliminate refractory compounds, which are difficult to be removed by conventional wastewater treatment processes. However, data is still sparse on SCWO of a series of N-containing compounds, such as TN removal, N-containing species distribution and molecular characteristics. In this work, decomposition of 44 nitrogen-containing compounds was investigated under temperature of 350–550 °C, resulted in total nitrogen (TN) removal from 55 to 94%. The N-containing products were primary N2, nitrate and ammonium. The primary products were NO3− and NH4+ from nitro- and amino-group compounds, respectively. As for diazo and N-heterocyclic ones, NO3− and NH4+ were the main nitrogen containing products, respectively. Interestingly, in terms of aniline and its derivatives, the amount of N2 followed the order: aniline > N-methylaniline (N-MA) > N,N-dimethylaniline (N,N-DMA). These experimental results were in agreement with the results of Fukui function. The correlationship between the temperature at TN removal rate of 50% (TN50) and 17 molecular characteristics has been calculated, which resulted EHOMO and Fukui indices could largely influence temperature behavior of TN removal.

C:N ratio shaped both taxonomic and functional structure of microbial communities in livestock and poultry breeding wastewater treatment reactor

C:N ratios play critical roles in determining the stability and performance of the wastewater treatment reactor. Here, we investigated bacterial and archaeal community composition, diversity, association networks, and functional profiles in livestock and poultry breeding wastewater (LPBW) with C:N gradients from 7.8 to 18.9 using 16S rRNA gene amplicon sequencing. Highest total nitrogen (TN) and total phosphorous (TP) removal rates were detected in the wastewater with high C:N ratios, while bacterial and archaeal communities in the wastewater varied across the four C:N ratios. Proteobacteria, Acidobacteria, and Bacteroides were generally the dominant phyla in the wastewater across treatments, with Candidatus Saccharibacteria being more enriched in the wastewater with high C:N ratios. Association network analysis showed that specific bacterial and archaeal taxa likely have similar metabolic activities allowing them to respond similarly to different C:N ratios. Bacteroidetes, Actinobacteria, Verrucomicrobia, Candidatus Saccharibacteria, and Proteobacteria were the keystone species found in the networks. Most dominant bacterial functions in the wastewater were chemoheterotrophy and aerobic chemoheterotrophy. Nitrite respiration, nitrous oxide denitrification, nitrate denitrification and nitrite denitrification were up-regulated with increased C:N ratios. Our findings provide new insights into our understanding of the compositions, potential associations, and predicted functional profiles of the microbial community in LPBW treated with different C:N ratios.

Microbial aerobic denitrification dominates nitrogen losses from reservoir ecosystem in the spring of Zhoucun reservoir

The mechanism and factors influencing nitrogen loss in the Zhoucun reservoir were explored during the spring. The results showed that the nitrate and total nitrogen concentration decreased from 1.84 ± 0.01 mg/L and 2.34 ± 0.06 mg/L to 0.06 ± 0.01 mg/L and 0.48 ± 0.09 mg/L, respectively. Meanwhile, the nitrate and total nitrogen removal rate reached 97.02% ± 0.25 and 79.38% ± 3.32, respectively. Moreover, the abundance of nirS gene and aerobic denitrification bacteria increased from 1.04–3.38 × 103 copies/mL and 0.71 ± 0.22 × 102 cfu/mL to 5.36–5.81 × 103 copies/mL and 8.64 ± 2.08 × 103 cfu/mL, respectively. The low MW fractions of DOM (<5 kDa) increased from 0.94 ± 0.02 mg/L in February to 1.51 ± 0.09 mg/L in April. E3/E4 and absorption spectral slope ratio (SR) showed that fulvic acid accounted for the main proportion with autochthonous characteristics. These findings were consistent with the fluorescence components and fluorescence characteristic indices based on EEM-PARAFAC. Meanwhile, the microbial metabolism activity increased significantly from February to April, which contributed to the cycle of nutrients within the reservoir water system. Moreover, the abundance of the bacterial species involved in denitrification (Exiguobacterium, Brevundimonas, Deinococcus, Paracoccus, and Pseudomonas) increased significantly. The relative abundance of KOs related to nitrogen metabolism, were initially increased and then decreased. Specifically, K02567 (napA) represented the main proportion of KOs related to denitrification. The abundance of napA-type denitrifying bacteria (Dechloromonas, Pseudomonas, Azospira, Rhodopseudomonas, Aeromonas, Zobellella, Sulfuritalea, Bradyrhizobium, Achromobacter, Enterobacter, Thauera, and Magnetospirillum) increased significantly during the period of nitrogen loss. Furthermore, the levels of nitrate, T, DO, and AWCD were the most important factors affecting the N-functional bacteria composition. The systematic investigation of the nitrogen loss would provide a theoretical foundation for the remediation of the water reservoir via aerobic denitrification in the future.

Effect of Temperature and pH on Nitrogen Conversion in Feammox Process

In recent years, the oxidation of NH4+ using Fe(Ⅲ) as an electron acceptor under anaerobic conditions (Feammox) has received significant research attention. In this study, the effect of pH and temperature on nitrogen conversion during the Feammox process was studied through activity recovery of Feammox sludge acclimated by anaerobic ammonium oxidation (ANAMMOX) sludge. Results showed that after 40 d operation, activity of Feammox sludge was recovered. There was evident ammonia nitrogen conversion and total nitrogen removal from the environment, and the products were mainly nitrate and nitrogen. The concentration of nitrite remained below 2 mg·L-1. pH value and temperature significantly influenced nitrogen transformation during the Feammox process. With pH value of 7 and temperature of 30℃ during the Feammox process, the removal rate of total nitrogen was relatively high (>50%). When the pH value was 6.5, the conversion rate of ammonia nitrogen was 80.2%. During the Feammox reaction process, precipitation of iron ion compounds and coating on the sludge surface were the main interference factors leading to continuous operation of the reactor and exploration of the reaction mechanism.

Effect of HRT on Nitrogen Removal Using ANAMMOX and Heterotrophic Denitrification

Real domestic sewage was first treated in SBR and partial nitrification was achieved. When average concentrations of NH4+-N, NO2--N, and COD were 37.27, 39.97, and 120 mg·L-1, respectively, the effluent was delivered as influent of an anaerobic ammonia oxidation reactor (ASBR). The effect of different HRTs (36 h, 33 h, 30 h, 27 h) on nitrogen removal of ANAMMOX and heterotrophic denitrification were investigated under conditions of temperature of 24℃ and pH of 7.2±0.2. Results showed that 1 nitrogen removal efficiency was optimum with HRT of 33 h. The average total nitrogen load rate(TNLR)and total nitrogen removal rate(TNRR)were 0.056 kg·(m3·d)-1and 0.050 kg·(m3·d)-1, respectively. The average effluent concentrations of NH4+-N, NO2--N, and COD were 1.36, 0.47, and 49.79 mg·L-1, and removal rates were 96.30%, 98.83%, and 56.17%, respectively. △NO2--N/△NH4+-N and △NO3--N/△NH4+-N were 1.17 and 0.15, 0.15 and 0.11 less than theoretical ANAMMOX values (1.32, 0.26) due to heterotrophic denitrification. 2 The contribution of ANAMMOX to nitrogen removal decreased; however, the contribution of heterotrophic denitrification to nitrogen removal gradually increased with decreasing HRT. This provides a point of reference for ANAMMOX in engineering applications.

Nitrogen Removal and N₂O Emission in Biochar-Sludge Subsurface Wastewater Infiltration Systems.

Nitrogen removal and N2O emission of biochar-sludge amended subsurface wastewater infiltration systems (SWISs) with/without intermittent aeration under different organic surface loading rates (OSLRs) were investigated. Under OSLR, between 8.5 and 54.6 g COD/(m2 d), average chemical oxygen demand (COD), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm01.gif"/>, and total nitrogen (TN) removal rates decreased with OSLR increasing in non-aerated SWISs amended with/without biochar-sludge; increasing OSLR hardly affected COD and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm12.gif"/> removal in biochar-sludge amended SWIS with intermittent aeration; N2O emission rate decreased with influent OSLR increasing in the SWISs. Biochar-sludge amended SWIS with intermittent aeration obtained higher removal rates for COD (94.9 to 95.5%), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm23.gif"/> (90.5 to 93.7%), TN (86.5 to 89.9%) and lower N2O emission rates [13.4 to 14.7 mg/(m2 d)] under high influent OSLR of 36.2 and 54.6 g COD/(m2 d) were compared with non-aerated SWISs with/without biochar-sludge. Furthermore, the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ genes involved in nitrogen removal were enhanced under high influent OSLR in biochar-sludge amended SWIS with intermittent aeration.

Denitrification Characteristics and Functional Genes of Denitrifying Bacteria Under Aerobic or Anaerobic Conditions

An efficient aerobic denitrifying bacterium was isolated from the sediments of the Jin Pen Reservoir in Xi'an. The strain was identified by morphological features and 16S rDNA sequences as Pseudomonas stutzeri and named it KK99. The denitrification characteristics of the strain and the expression level of the functional genes narG, nirS, and nosZ in aerobic/anaerobic conditions were investigated. The results showed that the strain can carry out both anaerobic and aerobic denitrification and has a high efficiency of denitrification, which occurs under both aerobic and anaerobic conditions; after 24 h, the removal rates of total nitrogen (TN) were 85.08% and 89.05%, respectively. Under both the conditions, the expression levels of the functional genes nosZ and nirS are high. nosZ plays a vital role in denitrification in the aerobic pathway, nirS plays a vital role in denitrification in the anaerobic pathway, and narG expression is low under both the conditions. At the same time, simultaneous nitrification and denitrification (SND) capacity of the strain was observed when nitrate and ammonium salts were the nitrogen sources, with the total nitrogen removal rate being 76% within 24 h in aerobic conditions. The P. stutzeri KK99 strain can be used for controlling eutrophication of micro-polluted water, and the application of total nitrogen reduction engineering.

In Situ Water Quality Improvement Mechanism (Nitrogen Removal) by Water-Lifting Aerators in a Drinking Water Reservoir

A field scale experiment was performed to explore the nitrogen removal performance of the water and surface sediment in a deep canyon-shaped drinking water reservoir by operating WLAs (water-lifting aerators). Nitrogen removal performance was achieved by increasing the densities and N-removal genes (nirK and nirS) of indigenous aerobic denitrifiers. After the operation of WLAs, the total nitrogen removal rate reached 29.1 ± 0.8% in the enhanced area. Ammonia and nitrate concentrations were reduced by 72.5 ± 2.5% and 40.5 ± 2.1%, respectively. No nitrite accumulation was observed. Biolog results showed improvement of carbon metabolism and carbon source utilization of microbes in the enhanced area. Miseq high-throughput sequencing indicated that the denitrifying bacteria percentage was also higher in the enhanced area than that in the control area. Microbial communities had changed between the enhanced and control areas. Thus, nitrogen removal through enhanced indigenous aerobic denitrifiers by the operation of WLAs was feasible and successful at the field scale.

Effects of gibberellin on the activity of anammox bacteria

The enhancement of gibberellin (GA) on the activity of anaerobic ammonium oxidation(anammox) bacteria in short-term batch experiments(500 mL serum bottle) was studied in this paper. To make sure the accuracy of the data, each experiment group was conducted some statistical analysis. The results showed that GA played an important role in improving anammox activity when the GA dosage ranged from 0.1 to 1.5 mg L−1, and the total nitrogen removal rate (NRR) was increased by 34% when the GA dosage was 1 mg L−1. The monitoring results of extracellular polymeric substances (EPS) and biomass of anammox bacteria indicated that GA addition improved the secretion of EPS and the biomass increasing, whose amount achieved maximum under the GA dose of 1 mg L−1. Compared to the control test, the maximum improvement ratio of the EPS and biomass was 28.6% and 34%, respectively. In addition, the cloning results also indicated that the anammox bacterial community structure shifted in species level of Candidatus Brocadia genus during the experiment, and the most dominant anammox bacteria were Candidatus Brocadia fulgid.

Nitrogen removal from water of recirculating aquaculture system by a microbial fuel cell

Maintaining low concentrations of nitrogen compounds in aquaculture water is a key requirement for a recirculating aquaculture system (RAS), due to the potential detrimental effects of ammonia or nitrate on fish growth and metabolic activities. Herein, a microbial fuel cell (MFC) was investigated to accomplish the removal of either nitrate or ammonia from real RAS water (with simulated daily nitrate/ammonium accumulation) while generating electricity, via aerobic nitrification in the cathode, electricity/concentration driven transport across anion exchange membrane, and subsequent heterotrophic denitrification in the anode chamber. The experiment went through two stages, nitrate removal (Stage I) and ammonia removal (Stage II). In Stage I when daily nitrate addition was performed to mimic nitrate accumulation (0.050 kg NO3−-N m−3 NCC d−1, NCC: net cathodic chamber volume) in the MFC cathode, a stable current density of 12.48 A m−3 could be achieved with a 73.3% nitrate removal and 91.3% COD removal at the end of day 15. To better mimic ammonium accumulation in the RAS effluent without a biofilter, daily ammonium addition (0.050 kg NH4+-N m−3 NCC d−1) was performed in the cathode in Stage II. The MFC system achieved a total inorganic nitrogen removal rate of 0.051 kg N m−3 NCC d−1, and a COD removal efficiency of 91.8% with a current density of 74.00 A m−3. A preliminary analysis of energy balance indicated that the proposed MFC could potentially achieve energy-positive RAS water treatment with a net energy production of 7.50 × 10−3 kWh m−3 treated RAS water or 0.145 ± 0.031 kWh kg−1 removed nitrogen. The results of this study indicate that MFCs have a potential to treat RAS water with simultaneous energy recovery.

Purification efficiency of zeolite and two planted grasses on sewage and relationship with carbon-nitrogen-phosphorus ratios in simulated constructed wetland system.

For achieving the economical and efficient configuration of constructed wetlands (CWs), a simulated device of vertical flow CWs was used to investigate the effects of different volume ratios of substrates to two cold-resistant plants on pollutant concentrations as well as their ratios in effluent under different inflow domestic sewage concentrations. The average removal rates (ARRs) of ammonia nitrogen, total nitrogen (TN) and total phosphorus were 82.7%, 84.9% and 80.6% respectively in the treatments with zeolite but no plants, which increased by 22.6%, 20.8% and 14.9% compared with those without zeolite and plants. However, in the treatments with zeolite and planted grasses, the ARRs of the three pollutants were over 90%, and those of chemical oxygen demand were lower. The removal rates of ammonia nitrogen, TN and total phosphorus had negative correlations with C:N and N:P ratios and positive correlations with the C:P ratios. Increasing the ratio of zeolite to soil from 1:1 to 2:1 had no significant effects in the removal efficiency. It was suggested that planting Lolium perenne or Poa annua on the substrate with a zeolite to soil volume ratio of 1:1 could be considered as the optimum combination to purify the domestic sewage in north rural areas of China.

Black water collected from the septic tank treated with a living machine system: HRT effect and microbial community structure

In this study, the performance of a living machine (LM) system was evaluated for use in the treatment of black water collected from septic tanks with hydraulic retention times (HRTs) of 6, 5, and 4 days. We found that the HRT had little effect on the removal efficiency of chemical oxygen demand (COD). However, the removal rates of total nitrogen (TN) and ammonium nitrogen (NH4+-N) decreased with the reduction of HRT, whereas the removal efficiency of total phosphate (TP) was consistently low because of the long sludge retention time. The working conditions of #1 achieved the highest removal efficiency of COD (85%), NH4+-N (75%), and TN (47%), although the removal efficiency of TP (11%) was slightly lower than that of #2 (12%). The microbial communities in each tank of the LM system were characterized by high-throughput sequencing, which showed that the LM system successfully created more favorable conditions for fermentative bacteria than traditional systems, with relative abundances of 13% (#1), 13% (#2), and 15% (#3) compared to that of the anaerobic/anoxic/oxic (A2O) system (<3%). Smithella was the dominant fermentative bacteria, accounting for 9% (#1), 7% (#2), and 10% (#3) of total bacteria in the LM system. The relative abundances of ammonia oxidizing bacteria (AOB) (12%) and anaerobic ammonium oxidizing bacteria (AnAOB) (7%) in the LM system were much higher than that in the A2O system. Overall, the LM system offered a more sustainable and economical solution for treating black water.

Does influent COD/N ratio affect nitrogen removal and N2O emission in a novel biochar-sludge amended soil wastewater infiltration system (SWIS)?

Nitrogen removal and N2O emission of a biochar-sludge amended soil wastewater infiltration system (SWIS) with/without intermittent aeration under different influent COD/N ratios was investigated. Nitrogen removal and N2O emission were affected by influent COD/N ratio. Under a COD/N ratio between 1:1 and 15:1, average chemical oxygen demand (COD), NH4 +-N and total nitrogen (TN) removal rates decreased with COD/N ratio increase in non-aerated SWISs amended with/without biochar-sludge; an increasing COD/N ratio hardly affected COD and NH4 +-N removal in a biochar-sludge amended SWIS with intermittent aeration; the N2O emission rate decreased with COD/N ratio increase in the studied SWISs. The biochar-sludge amended SWIS with intermittent aeration achieved high COD (92.2%), NH4 +-N (96.8%), and TN (92.7%) removal rates and a low N2O emission rate (10.6 mg/(m2 d)) under a COD/N ratio of 15:1, which was higher than those in non-aerated SWISs amended with/without biochar-sludge. Combining the biochar-sludge amended SWIS with intermittent aeration enhanced the number of nitrifying bacteria, denitrifying bacteria, nitrate reductase activities, nitrite reductase activities, and improved the abundance of nitrogen removal functional genes under a high influent COD/N ratio. The results suggested that the joint use of intermittent aeration and biochar-sludge in a SWIS could be an effective and appropriate strategy for improving nitrogen removal and reducing N2O emissions in treating high COD/N ratio wastewater.

Stability of Nitritation Combined with Limited Filamentous Bulking Under Intermittent Aeration

Limited filamentous bulking (LFB) combined with nitritation under low dissolved oxygen (DO) is a new technology for enhancing nitrogen removal and reducing aeration requirements. In order to investigate the feasibility and sustainability of this technology, two sequence batch reactors (SBRs) were operated under different regimes to stimulate different aeration modes under low DO (0.3-0.8 mg·L-1). Sludge settleability, nitrite accumulation ratio (NAR), total nitrogen (TN) removal rate, dynamic variation of dominant filaments, and nitrifying bacterial communities were investigated. The results indicated that short-cut nitrification combined with LFB could be achieved under intermittent aeration, and the ratio of anoxic/aerobic was 15 min/30 min, the value of sludge volume index (SVI) was maintained from 170 mL·g-1 to 200 mL·g-1. An NAR above 95% was achieved under real-time continuous aeration. Meanwhile, LFB was induced when nitrite started to accumulate, and the dominant filament was Type 0092. However, the limited bulking was not maintained for the long term. After a transfer from continuous aeration to intermittent aeration, LFB reappeared in 60 days and the value of SVI remained between 170 mL·g-1 and 200 mL·g-1. The process of nitritation combined with LFB was maintained stably for the next two months, and the TN removal rate was above 66%. FISH analysis indicated that the identical dominant filaments were M. parvicella and Type 0092 for maintaining limited bulking in the two reactors. qPCR results showed that proportion of AOB in the total bacteria increased from the previous 0.53% to 2.19% in the end, whereas that of NOB decreased from 17.5% to 3.2% in SBR A. Moreover, the proportion of AOB increased from 0.51% to 1.53%, whereas that of NOB decreased from 18.05% to 11.01% in SBR B.

Effect of Biochar on Root Morphological Characteristics of Wetland Plants and Purification Capacity of Constructed Wetland

A constructed wetland with Acorus calamus L. was built. Straw biochar, reed biochar, and sawdust biochar was added into the constructed wetland individually to study the effect of different biochars on the root morphology, dissolved oxygen, and purification ability of the constructed wetland. The results show that the total root length, total projection area, total volume, total surface area, root number, branch number, and root dry weight of Acorus calamus L. significantly increased when all three kinds of biochar were added into the constructed wetland (P<0.05). Similarly, adding the biochars into the constructed wetland also significantly increased dissolved oxygen content in the wetland (P<0.05). Addition of sawdust biochar into the constructed wetland increased the root length, projection area, surface area, total volume, number of root tips, number of branches, and root dry weight of Acorus calamus L. by 96.1%, 106.2%, 185.6%, 172.5%, 75.3%, 121.6%, and 84.9%, respectively. After adding biochars into the constructed wetland, the root morphology of Acorus calamus L. and dissolved oxygen content was significantly correlated with removal rate of TN, TP, and COD, respectively. Addition of sawdust biochar into the constructed wetland significantly increased the removal rates of total nitrogen, total phosphorus, and COD when the hydraulic load was 0.022 m3·(m2·d)-1 (P<0.05). These results suggested that the addition of sawdust biochar to the constructed wetland increased the root growth of Acorus calamus L. and enhanced dissolved oxygen content, resulting in purification capacity of the constructed wetland.

Fast start-up of the cold-anammox process with different inoculums at low temperature (13 °C) in innovative reactor

Three innovative reactors (CAMBR) through optimally combining with the Anaerobic Baffled reactor and Membrane bioreactor were applied to start up the cold-anammox process at low temperature (13 °C) through inoculating flocculent nitrification sludge (R1), anaerobic granular sludge (R2) and flocculent denitrification sludge (R3), respectively. Results showed that anammox process was started successfully with over 90% total nitrogen removal rate in R1, R2 and R3 after 75d, 45d, and 90d, respectively. Microbial community revealed that Ca. Brocadia and Ca. Jettenia were the dominant anammox bacteria in R1, R2 and R3, accounting for an abundance of 0.08%, 12.18%; 3.17%, 0 and 0.08%, 0.38%, respectively. Three anammox species, Ca. Brocadia caroliniensis, Ca. Brocadia sinica and Ca. Jettenia asiatica were annotated based on the phylogenetic tree, suggesting the anammox species with larger maximum growth rate contributed to the rapid start-up of the cold-anammox process. This study reinforces the potential application of mainstream anammox.