Tracing the impacts of ecological water replenishment on the sources and transformation of groundwater nitrate through isotope and microbial analysis.

Ecological water replenishment (EWR) changes the recharge conditions, flow fields, and physicochemical properties of regional groundwater. However, the resulting impacts on mechanisms regulating the sources and transformation of groundwater nitrate remain unclear. This study investigated how EWR influences the sources and transformation processes of groundwater nitrate using an integrated approach of Water chemistry analysis and stable isotopes (δ15N-NO3- and δ18O-NO3-) along with microbial techniques. The results showed that groundwater NO3-N decreased from 12.98 ± 7.39 mg/L to 7.04 ± 8.52 mg/L after EWR. Water chemistry and isotopic characterization suggested that groundwater nitrate mainly originated from sewage and manure. The Bayesian isotope mixing model (MixSIAR) indicated that EWR increased the average contribution of sewage and manure sources to groundwater nitrate from 46 % to 61 %, whereas that of sources of chemical fertilizer decreased from 43 % to 21 %. Microbial community analysis revealed that EWR resulted in a substantial decrease in the relative abundance of Pseudomonas spp denitrificans, from 13.7 % to 0.6 %. Both water chemistry and microbial analysis indicated that EWR weakened denitrification and enhanced nitrification in groundwater. EWR increases the contribution of nitrate to groundwater by promoting the release of sewage and feces in the unsaturated zone. However, the dilution effect caused by EWR was stronger than the contribution of sewage and fecal sources to groundwater nitrate. As a result, EWR helped to reduce groundwater nitrate concentrations. This study showed the effectiveness of integrated isotope and microbial techniques for delineating the sources and transformations of groundwater nitrate influenced by EWR.

Treatment of aniline-containing wastewater by electrochemical oxidation using Ti/RuO2 anode: the influence of process parameters and reaction mechanism.

Aniline detected in many industrial wastewater is a refractive organic pollutant with strong biological toxicity to aquatic organisms and humans. In this research, electrochemical oxidation process with Ti/RuO2 as the anode has been used to degrade aniline-containing wastewater on a laboratory scale. The influence of anode materials, electrolyte, NaCl concentration, current density, and aniline initial concentration on COD removal, ICE, and Ep were studied. The results showed that Cl- addition in the electrolyte is essential to promote aniline degradation efficiency and avoid the anode being passivated. Furthermore, decreasing the current density, increasing Cl- concentration, and initial aniline concentration are beneficial to increase current efficiency and reduce energy consumption. Although the addition of SO42- has a restriction on the active chlorine evolution process, the conductivity increased, which resulted in the reduction of energy consumption. At last, the aniline degradation mechanism in the presence of chloride ions was summed up and proposed based on the literature.

Research on the electrochemical treatment of nitrobenzene wastewater: The effects of process parameters and the mechanism of distinct degradation pathways.

Nitrobenzene is a typical organic pollutant of petroleum pollutant, which is a synthetic chemical not found naturally in the environment. Nitrobenzene in environment can cause toxic liver disease and respiratory failure in humans. Electrochemical technology provides an effective and efficient method for degrading nitrobenzene. This study, the effects of process parameter (e.g., electrolyte solution type, electrolyte concentration, current density and pH) and distinct reaction pathways for electrochemical treatment of nitrobenzene were investigated. As a result, available chlorine dominates the electrochemical oxidation process compared with hydroxyl radical, thus the electrolyte of NaCl is more suitable for the degradation of nitrobenzene than that of Na2SO4. The concentration and the existence form of available chlorine were mainly controlled by electrolyte concentration, current density and pH, which directly affect the removal of nitrobenzene. Cyclic voltammetry and mass spectrometric analyses suggested that electrochemical degradation of nitrobenzene included two important ways. Firstly, single oxidation: nitrobenzene → other forms of aromatic compounds→ NO-x + organic acids + mineralization products. Secondly, coordination of reduction and oxidation: nitrobenzene → aniline→ N2 + NO-x + organic acid + mineralization products. The results of this study will encourage us to further understand the electrochemical degradation mechanism of nitrobenzene and develop the efficient processes for nitrobenzene treatment.

Environmental risk of tailings pond leachate pollution: Traceable strategy for leakage channel and influence range of leachate.

Identifying the leakage channel and the influencing range is essential for controlling the environmental risks of leachate from the tailings pond. The investigation of leachate pollution in tailings pond has the defect of focusing only on the scope of tailings pond in recent studies. This study innovatively built a comprehensive investigation and accurate verification system for leachate leakage of tailings pond integrated with the aeromagnetic survey, ground penetrating radar, hydrochemistry and isotope coupling methods. Geophysical exploration found that among the four fault zones, and the F1 was the channel for leachate to recharge the groundwater 2.53 km away from the tailings pond. The fissures inside the tailings pond were connected with the natural fissures outside, forming a leachate migration channel. The hydrochemistry and isotope characteristics showed that the groundwater far away from the tailings pond were polluted by arsenic containing leachate, which verified the geophysical exploration results. The significant correlation between arsenic and SO2-4 concentration indicated that arsenic in leachate originated from the oxidation release of sulfide minerals (i.e., arsenopyrite). This study sheds light on the comprehensive investigation of leachate leakage in the tailings pond. This development method also provides guidance for environmental risk identification of other contaminated sites.

Cost-effectiveness of recombinant tissue-type plasminogen activator for acute ischaemic stroke with unknown time of onset: a Markov modelling analysis from the Chinese and US perspectives.

OBJECTIVE: The effectiveness of MRI-guided intravenous recombinant tissue-type plasminogen activator (r-tPA) for acute ischaemic stroke (AIS) with an unknown time of onset has been demonstrated by the WAKE-UP Trial. We aim to evaluate its long-term cost-effectiveness from the perspective of Chinese and US healthcare payers. METHODS: A combination of decision tree and Markov model was built to project lifetime costs and quality-adjusted life-years (QALYs) associated with intravenous r-tPA or placebo treatment. Model inputs including the transition probabilities, costs and utilities were derived from the WAKE-UP Trial, similar cost-effectiveness studies and other published sources. To compare intravenous r-tPA to placebo, we calculated incremental costs, incremental QALYs and incremental cost-effectiveness ratio (ICER). One-way sensitivity, probabilistic sensitivity and subgroup analyses were performed to evaluate uncertainty in the results. RESULTS: In China, intravenous r-tPA gained an additional lifetime QALY of 0.293 with an additional cost of the Chinese Yuan (¥) of 7871 when compared with placebo, resulting in an ICER of ¥26 870 (US$3894)/QALY. In the USA, intravenous r-tPA yielded a higher QALY (difference: 0.430) and lower cost (difference: ¥-4563) when compared with placebo. In probabilistic sensitivity analyses, intravenous r-tPA had a 97.8% and 99.8% probability of being cost-effective or cost-saving in China and the USA, respectively. These findings remained robust under one-way sensitivity and subgroup analysis except for patients with a National Institute of Health Stroke Scale Score of less than 4, between 11 and 16, and over 16. CONCLUSIONS: MRI-guided intravenous r-tPA for patients with AIS with an unknown time of onset is cost-effective in China and cost-saving in the USA.

Hybrid zeolite-based ion-exchange and sulfur oxidizing denitrification for advanced slaughterhouse wastewater treatment.

The discharge of slaughterhouse wastewater (SWW) is increasing and its wastewater has to be treated thoroughly to avoid the eutrophication. The hybrid zeolite-based ion-exchange and sulfur autotrophic denitrification (IX-AD) process was developed to advanced treat SWW after traditional secondary biological process. Compared with traditional sulfur oxidizing denitrification (SOD), this study found that IX-AD column showed: (1) stronger ability to resist NO3- pollution load, (2) lower SO42- productivity, and (3) higher microbial diversity and richness. Liaoning zeolites addition guaranteed not only the standard discharge of NH4+-N, but also the denitrification performance and effluent TN. Especially, when the ahead secondary biological treatment process run at the ultra-high load, NO3--N removal efficiency for IX-AD column was still ~100%, whereas only 64.2% for control SOD column. The corresponding average effluent TN concentrations for IX-AD and SOD columns were 5.89 and 65.55 mg/L, respectively. Therefore, IX-AD is a promising technology for advanced SWW treatment and should be widely researched and popularized.

Performance and mechanism of a novel woodchip embedded biofilm electrochemical reactor (WBER) for nitrate-contaminated wastewater treatment.

In this study, a woodchip biofilm electrode reactor (WBER) with woodchips embedded anode and cathode was developed, and its denitrification mechanism was analyzed by investigating the denitrification performance, organic matter change, redox environment and microbial community. The results show that the WBER with a carbon rod as anode (C-WBER) had a higher denitrification efficiency (2.58 mg NO- 3-N/(L·h)) and lower energy consumption (0.012 kWh/g NO- 3-N) at 350 mA/m2. By reducing the hydroxyl radical and dissolved oxygen concentrations, anode embedding technology effectively decreased the inhibition on microorganisms. Lignin decomposition, nitrification and aerobic denitrification were carried out in anode. Additionally, hydrogen autotrophic denitrification and heterotrophic denitrification were occurred in cathode. The WBER effectively removed nitrate and reduced the cost, providing a theoretical basis and direction for further develop BERs.

Antegrade or Retrograde Approach for the Management of Tandem Occlusions in Acute Ischemic Stroke: A Systematic Review and Meta-Analysis.

Background: Acute ischemic stroke (AIS) caused by tandem intracranial and extracranial occlusions is not rare. However, optimal strategy between antegrade (extracranial first) or retrograde (intracranial first) approaches still remains elusive. This systematic review and meta-analysis aim to compare the two approaches to provide updated clinical evidence of strategy selection. Methods: PubMed, Ovid, Web of Science, and the Cochrane Library were searched for literature comparing antegrade and retrograde approaches for patients with AIS with concomitant tandem occlusions. Outcomes including successful reperfusion [Throbolysis in Cerebral Infarction (TICI) 2b-3] and 90-day favorable outcome [modified Rankin Scale (mRS) 0-2], any intracerebral hemorrhage, symptomatic intracerebral hemorrhage, procedural complications, and mortality were evaluated. The risk of bias was assessed using the Newcastle-Ottawa Scale and illustrated in the Funnel plot. Heterogeneity was assessed by I 2 statistic. Subgroup and sensitivity analyses were also performed. Results: A total of 11 studies accounting 1,517 patients were included. 831 (55%) patients were treated with an antegrade approach and 686 (45%) patients were treated with the retrograde approach. A higher successful reperfusion rate was achieved in retrograde group than that of antegrade group [83.8 vs. 78.0%; odds ratio (OR): 0.63, 95% CI: 0.40-0.99, p = 0.04]. 90-day favorable outcome (mRS 0-2 at 90 days) also showed significantly higher in retrograde group compared with antegrade group (47.3 vs. 40.2%; OR: 0.72, 95% CI: 0.58-0.89, p = 0.002). The incidence of any intracranial hemorrhage (ICH), symptomatic intracranial hemorrhage, 90-day mortality, and other complications did not differ between two groups. Conclusion: In AIS with tandem occlusions, the retrograde approach might achieve a higher successful reperfusion rate and better functional outcome with a comparable safety profile when compared with an antegrade approach. Further prospective controlled studies with more meticulous design and a higher level of evidence are needed to confirm these results. Systematic Review Registration: "PROSPERO" database (CRD 42020199093), https://www.crd.york.ac.uk/PROSPERO/.

Electrochemical oxidation of aniline using Ti/RuO2-SnO2 and Ti/RuO2-IrO2 as anode.

Electrocatalytic properties of anode and the electrolyte composition are important parameters influence the degradation efficiency for aniline wastewater. Ti/RuO2-SnO2 and Ti/RuO2-IrO2 have been fabricated using thermal decomposition method and experiments in electrolyte containing 0.05 M Na2SO4, 0.05 M NaCl and 0.05 M Na2SO4+0.005 M FeSO4 at different current density were conducted to study the influence on aniline degradation. Linear sweep voltammetry (LSV) showed that Ti/RuO2-SnO2 had higher oxygen evolution potential and degrade aniline through electrochemical transformation and electrochemical combustion while Ti/RuO2-IrO2 degrade aniline mainly through electrochemical transformation. The study showed that Ti/RuO2-SnO2 had higher electrocatalytic activity towards the degradation of aniline than Ti/RuO2-IrO2 anode in 0.05 M Na2SO4 and in 0.05 M NaCl electrolyte. The maximum TOC removal efficiency for Ti/RuO2-SnO2 was 64.2% at 40 mA cm-2 in Na2SO4 electrolyte while the average MCE was 1.6% and the average ECTOC was 1.51 kWh (g TOC)-1. On the contrary, the maximum TOC removal efficiency for Ti/RuO2-IrO2 was 63.1% at 40 mA cm-2 in NaCl electrolyte while the average MCE was 1.6% and the average ECTOC was 1.95 kWh (g TOC)-1. The presence of Fe2+ in Na2SO4 electrolyte would decrease the TOC removal efficiency except at low current density (20 mA cm-2) for Ti/RuO2-SnO2. These results indicated that Ti/RuO2-SnO2 and Ti/RuO2-IrO2 anode were suitable in Na2SO4 and NaCl electrolyte, respectively, while the presence of Fe2+ would inhibit aniline degradation.

Review on electrochemical system for landfill leachate treatment: Performance, mechanism, application, shortcoming, and improvement scheme.

Landfill leachate is a type of complex organic wastewater, which can easily cause serious negative impacts on the human health and ecological environment if disposed improperly. Electrochemical technology provides an efficient approach to effectively reduce the pollutants in landfill leachate. In this review, the electrochemical standalone processes (electrochemical oxidation, electrochemical reduction, electro-coagulation, electro-Fenton process, three-dimensional electrode process, and ion exchange membrane electrochemical process) and the electrochemical integrated processes (electrochemical-advanced oxidation process (AOP) and biological electrochemical process) for landfill leachate treatment are summarized, which include the performance, mechanism, application, existing problems, and improvement schemes such as cost-effectiveness. The main objective of this review is to help researchers understand the characteristics of electrochemical treatment of landfill leachate and to provide a useful reference for the design of the process and reactor for the harmless treatment of landfill leachate.

Performance and mechanism of synchronous nitrate and phosphorus removal in constructed pyrite-based mixotrophic denitrification system from secondary effluent.

The performance and process of the constructed pyrite-based mixotrophic denitrification (POMD) system using pyrite and residual organic matters as the co-electron donors were investigated for simultaneous removal of N and P from secondary effluent. After the batch experiments, 61.80 ± 3.26% of phosphate and 99.99 ± 0.01% of nitrate were removed, and the obtained nitrate removal rate constant can reach 2.09 days-1 in POMD system, which was significantly superior to that reported (0.95 day-1) in pyrite-based autotrophic denitrification (PAD) system. PO43--P removal was mainly achieved via chemical precipitation as FePO4 with iron, and it was irrelevant with the initial nitrate and ammonium concentrations. High-throughput 16S rRNA gene sequencing analysis showed the coexistence of heterotrophic and autotrophic denitrifiers in the mixotrophic environment. The denitrification process could be divided into two stages according to the carbon balance and calculation of sulfate accumulation: (a) nitrate was mainly reduced heterotrophically during 12-36 h and (b) nitrate was reduced autotrophically after 36 h. The calculated proportion of heterotrophic denitrification was 58.17 ± 3.78%, which was promoted by a higher ammonium concentration. These findings are likely to be useful in understanding the mixotrophic denitrification process and developing a cost-effective technology to simultaneously remove N and P from secondary effluent. Graphical abstract.

Abscisic acid-enhanced starch accumulation of bioenergy crop duckweed (Spirodela polyrrhiza).

To meet the increasing energy consumption around the world and fight global climate change, there is an urgent need to explore renewable energy crops to replace the traditional energy sources. Duckweed (Spirodela polyrrhiza) is widely distributed in the world and has high starch and low lignin contents, which is perhaps an ideal feedstock for bioenergy production. To investigate the effects of abscisic acid (ABA) on duckweed biomass and starch accumulation, Spirodela polyrrhiza was cultivated at different ABA concentrations. The results showed that the highest starch content in duckweed (21.8% dry weight) was achieved in 1.0 × 10-2 mg L-1 ABA medium, 70.3% higher than that of the control medium without ABA. The number of starch granules in 1.0 × 10-2 mg L-1 ABA medium was far more than that in the control medium. The highest adenosine diphosphate (ADP)-glucose pyrophosphorylase (AGPase) activity was observed in the 1.0 × 10-2 mg L-1 ABA medium, which was caused by the up-regulation expression of ADP-glucose pyrophosphorylase 2 (APL2). Further investigations on cell ultra-structures and stomatal property of the duckweed indicated that ABA increased the number and size of starch granules and stomatal size in duckweed cells. These enhancements lead to a greatly improved energy flow in the aquatic plant from photosynthesis to carbon storage, making duckweed a potential renewable bioenergy crop.

Research on complexation ability, aromaticity, mobility and cytotoxicity of humic-like substances during degradation process by electrochemical oxidation.

The humic-like substances were the main organic components in most wastewater (e.g. domestic sewage, toilet wastewater and landfill leachate). Two types of actual humic-like substances (fulvic acid (FA) and biologically treated landfill leachate (BTLL)) were selected to describe the changes in the properties of humic-like substances (complexation ability, aromaticity and mobility) during electrochemical oxidation. Meanwhile, the acute cytotoxicity of FA and BTLL was also tested by acute toxicological test of luminescent bacteria. The results showed that the consumption of coordinating groups such as phenolic groups and hydrogen bonds reduced the complexation ability of FA and BTLL. The functional groups were degraded with the removal order of quinone group, phenolic group and aromatic group, and finally realized the molecular saturation and aromaticity decrease for humic-like substances. The mobility of FA and BTLL was decreased because of the enhancement of hydrophobicity during electrolysis process. Furthermore, the available chlorine produced during electrochemical oxidation was the main acute cytotoxicity substance, therefore, it is necessary to remove it before discharge in order to reduce ecological risks. This study provides a basis for understanding and evaluating the electrochemical degradation process of humic-like substances in detail.

Degradation of nitrogen-containing refractory organic wastewater using a novel alternating-anode electrochemical system.

This study presented a novel alternating-anode electrochemical system (AAES) based on single electrolytic cell for the treatment of nitrogen-containing refractory organic wastewater (NOW). The core of AAES lies in the alternating working of iron anode and DSA anode to integrate different electrochemical processes. The biologically treated landfill leachate (BTLL) was selected as a practical NOW for assessing the performance of AAES. The results indicated that after 140 min of electrolytic reaction, the removal efficiency of chemical oxygen demand and total nitrogen (TN) using AAES was found to be 76.9 and 98.9%, respectively. The main component of dissolved organic matter (DOM) in BTLL included humic-like substances, which could be degraded into small-molecule DOM, such as fulvic-like substances and protein-like substances, by available chlorine and hydroxyl radicals present in AAES. Cathode reduction (NOx--N → NH4+-N and N2) under iron anode and indirect oxidation (NH4+-N → N2) under DSA anode were the main pathways to remove TN from NOW. Owing to the redox conditions created by the alternating anodes, the main stable crystalline forms of precipitates obtained from AAES were Fe3O4 and γ-Fe2O3, which could be separated by using the external magnetic field. The findings of this study may provide a feasible solution for the advanced electrochemical treatment of NOW in a single electrolytic cell as well as rapid separation of precipitates.

Research on the treatment of biologically treated landfill leachate by joint electrochemical system.

Biologically treated landfill leachate (BTLL) is typically characterized by significantly high amount of total nitrogen (TN) and chemical oxygen demand (COD), and it has low biodegradability. In this study, a joint electrochemical system (JES) composed of iron anode reactor (IAR) and Ti/RuO2 anode reactor (TAR) was constructed to remove both TN and COD from BTLL and improve its biodegradability. The IAR and TAR with the same structure but using different anodes. As a result, JES could simultaneously remove COD and TN by 90.9 ±â€¯0.3% and 90.2 ±â€¯1.0%, respectively. Reduction of nitrite-N by Cu/Zn cathode in IAR and oxidation of ammonium-N by active chlorine in TAR were the major pathways for TN removal, while the COD could be removed by coagulation of iron flocs and oxidation by hydroxyl radicals and active chlorine. Fluorescence spectrum and parallel factor analysis showed that the main components of organics in BTLL were humic-like substances, fulvic-like substances, and soluble microbial degradation products. Humic-like substances were particularly removed by JES, and the remaining organics after electrolysis were some alkanes (e.g., heptane and nonane). Furthermore, decrease in molecular weight and aromaticity and increase in biodegradable substances indicated that the biodegradability of BTLL was effectively improved by the JES. The developed JES is a promising approach for application in the BTLL treatment.

Design and applications of Ti nano-electrode for denitrification of groundwater.

In the present study, a Ti-nano-electrode was fabricated for electrochemical denitrification. Response surface methodology (RSM) was utilized for the optimization of the factors that influence the production of Ti nano-electrodes. Box-Behnken design was applied to develop mathematical models for predicting the best electrochemical nitrate removal geometry. Parameters interacting together can be identified in this typical electrochemical removal process. A correlation coefficient R2 > 0.90 for the mathematical model was predicted to be a high correlation between observed and predicted values. The optimal NH4F concentration, oxidation time and oxidation voltage for preparation of Ti nano-electrode in the present experiment are 0.03 wt%, 34.61 min and 6.31 V, respectively. In this case, the increase in the nitrate reduction efficiency was more d (105%) than that from an untreated electrode, and energy consumption was 4.45 × 10-4 kWh.

Kinetic studies of nitrate removal from aqueous solution using granular chitosan-Fe(III) complex.

In the present study, a granular chitosan-Fe(III) complex was prepared as a feasible adsorbent for the removal of nitrate from an aqueous solution. There was no significant change in terms of nitrate removal efficiency over a wide pH range of 3-11. Nitrate adsorption on the chitosan-Fe(III) complex followed the Langmuir-Freundlich isotherm model. In order to more accurately reflect adsorption and desorption behaviors at the solid/solution interface, kinetic model I and kinetic model II were proposed to simulate the interfacial process in a batch system. Nitrate adsorption on the chitosan-Fe(III) complex followed the pseudo-first-order kinetic model and kinetic model I. The proposed half-time could provide useful information for optimizing process design. Adsorption and desorption rate constants obtained from kinetic model I and kinetic model II were beneficial to understanding the interfacial process and the extent of adsorption reaction. Kinetic model I and kinetic model II implied that nitrate uptake exponentially approaches a limiting value.

Investigation on the adsorption of phosphorus by Fe-loaded ceramic adsorbent.

This aim of this study was to remove phosphorus from aqueous solution using a Fe-loaded ceramic (Fe-LC) adsorbent prepared by mixing dolomite, montmorillonite, FeSO4·7H2O and starch. Simplex-centroid mixture design method was used to determine the optimum mixture proportions by evaluating both phosphorus adsorption efficiency and adsorbent hardness. The study found that the optimum adsorption capacity and the strength can be achieved with the composition of 3.87g dolomite, 3.00g starch, 2.13g montmorillonite and 1.00g FeSO4·7H2O (10g in total). The optimized Fe-LC was evaluated in the batch and the fixed bed experiments. The point of zero charge, pHpzc was found to be 6.0. The adsorption kinetic and isotherm data well agreed with the pseudo-second-order kinetic and the Langmuir isotherm models, respectively. The breakthrough time increased with increasing in the bed depth, whereas inverse relationship was observed with the initial phosphorus concentration in the fixed bed studies. The co-existing anions (SO4(2-), NO3(-) and Cl(-)) had negligible influence on phosphorus removal. The BDST and Thomas model explained the breakthrough behavior for phosphorus removal with a high degree of correlation.

Optimization of enhanced bioelectrical reactor with electricity from microbial fuel cells for groundwater nitrate removal.

Factors influencing the performance of a continual-flow bioelectrical reactor (BER) intensified by microbial fuel cells for groundwater nitrate removal, including nitrate load, carbon source and hydraulic retention time (HRT), were investigated and optimized by response surface methodology (RSM). With the target of maximum nitrate removal and minimum intermediates accumulation, nitrate load (for nitrogen) of 60.70 mg/L, chemical oxygen demand (COD) of 849.55 mg/L and HRT of 3.92 h for the BER were performed. COD was the dominant factor influencing performance of the system. Experimental results indicated the undistorted simulation and reliable optimized values. These demonstrate that RSM is an effective method to evaluate and optimize the nitrate-reducing performance of the present system and can guide mathematical models development to further promote its practical applications.

Woodchip-sulfur based heterotrophic and autotrophic denitrification (WSHAD) process for nitrate contaminated water remediation.

Nitrate contaminated water can be effectively treated by simultaneous heterotrophic and autotrophic denitrification (HAD). In the present study, woodchips and elemental sulfur were used as co-electron donors for HAD. It was found that ammonium salts could enhance the denitrifying activity of the Thiobacillus bacteria, which utilize the ammonium that is produced by the dissimilatory nitrate reduction to ammonium (DNRA) in the woodchip-sulfur based heterotrophic and autotrophic denitrification (WSHAD) process. The denitrification performance of the WSHAD process (reaction constants range from 0.05485 h(-1) to 0.06637 h(-1)) is better than that of sulfur-based autotrophic denitrification (reaction constants range from 0.01029 h(-1) to 0.01379 h(-1)), and the optimized ratio of woodchips to sulfur is 1:1 (w/w). No sulfate accumulation is observed in the WSHAD process and the alkalinity generated in the heterotrophic denitrification can compensate for alkalinity consumption by the sulfur-based autotrophic denitrification. The symbiotic relationship between the autotrophic and the heterotrophic denitrification processes play a vital role in the mixotrophic environment.