Start-up of the SHARON and ANAMMOX process in landfill bioreactors using aerobic and anaerobic ammonium oxidising biomass

Chitosan-stabilized iron-copper nanoparticles for efficient removal of nitrate

Chitosan-stabilized iron-copper nanomaterials (CS-nZVI/Cu) were successfully prepared and applied to the nitrate removal. Batch experiments were conducted to examine the effects of experimental parameters on nitrate removal, including Cu loading, CS-nZVI/Cu dosages, initial nitrate concentrations, and initial pHs. From the experimental date, it was concluded that CS-nZVI/Cu has a high nitrate removal efficiency, which can be more than 97%, respectively, at Cu loading = 5%, dosages of CS-nZVI/Cu = 3 g/L, initial nitrate concentrations of 30~120 mg/L, and initial pH values = 2~9. Additionally, the kinetic data for CS-nZVI/Cu were found to fit well with the first-order kinetic model with a rate constant of 0.15 (mg∙L)1-n/min, where n=1. The Langmuir model showed a good fit for NO3- removal, indicating that monolayer chemisorption occurred. The SEM and TEM analyses showed that the addition of chitosan resulted in improved dispersion of the CS-nZVI/Cu. The CS-nZVI/Cu nanomaterials have a more complete elliptical shape and are between 50 and 100 nm in size. The XRD analysis showed that the chitosan encapsulation reduced the oxidation of the iron component and the main product was Fe3O4. The FT-IR analysis showed that the immobilization of chitosan and the iron was accomplished by the ligand interaction. The nitrogen adsorption-desorption isotherm results showed that the CS-nZVI/Cu specific surface area and pore volume decreased significantly after the reaction. Adsorption, oxidation, and reduction are possible mechanisms for nitrate removal by CS-nZVI/Cu. The XPS analysis investigated the contribution of nZVI and Cu in the removal mechanism. Adding copper accelerates the reaction time and rate. In addition, nZVI played a vital role in reducing nitrate to N2. Based on these results, it looks like CS-nZVI/Cu could be a satisfactory material for nitrate removal.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55 days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103 days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4 kg N·(m³·d)^-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%. The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105 days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 10¹² copies/g sludge and 28.39 × 10¹² copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.

Aerobic biocathodes with potential regulation for ammonia oxidation with concomitant cathodic oxygen reduction and their microbial communities

Aerobic biocathodes are effective construct for the simultaneous nitrification and denitrification, but the disturbance of cathodic oxygen reduction on ammonia oxidation and denitrification remains unclear. In this study, we revealed the oxygen reduction peak at -0.4 V (versus silver/silver chloride) by cyclic voltammetry analysis at a cathode without a biofilm. The reduction peak, however, showed a right shift from -0.4 to -0.3 V for the biocathode, indicating that the aerobic biocathode could simultaneously perform traditional nitrification and cathode oxygen reduction. Therefore, different electrode potentials ranging from -0.5 to -0.1 V were designed for regulating the ammonia oxidation rate, and the results showed that the highest oxidation rate reached 3.08 mg/h/L at a potential of -0.2 V under a low-aeration rate of 5 mL/min. High-throughput sequencing showed that Nitrosomonas and Rhodococcus were the dominant nitrogen removal genera in the biocathode, and the abundance of Devosia was related to the interactions between the aeration rate and the electrode potential. Furthermore, the amoC and hao genes responded to aeration and electrode potential regulation, and -0.2 V was more suitable for promoting the denitrification process under low-aeration conditions. Therefore, these findings provided new insights on cathodic potential control for ammonia oxidation and nitrogen removal as well as for the regulation of microbial communities.

Realization of nitrite accumulation in a sulfide-driven autotrophic denitrification process: Simultaneous nitrate and sulfur removal

The study was based on the removal of nitrate and sulfide, and aimed to nitrite accumulation. The process of autotrophic denitrification driven by sulfide as an electron donor was investigated in a sequencing batch reactor. The research showed that autotrophic denitrification successfully started on day 22, and the removal rates of NO₃^--N and S^2--S were 95.8% and 100%, respectively, when the S/N molar ratio was 1.45. When the S/N ratio was reduced to 0.94, the phenomenon of NO₂^--N accumulation was observed. NO₂^--N continuously accumulated, and the maximum accumulation rate was 55.3% when the S/N ratio was 0.8. In the batch test, the study showed that NO₂^--N accumulation was optimal when the S/N ratio was 0.8, and the NO₂^--N concentration increased with increasing NO₃^--N concentration at the same S/N ratio. Microbial communities also changed based on the high-throughput analysis, and Proteobacteria (59.5%-84%) was the main phylum. Arenimonas (11.4%-28.2%) and uncultured_f_ Chromatiaceae (5.7%-27.5%) were the dominant bacteria, which complete denitrification and desulfurization throughout the operating system. Therefore, this study provided a theoretical basis for the simultaneous removal of NO₃^--N and S^2--S, as well as the accumulation of nitrite, and provided material support for anaerobic ammonia oxidation technology.

Decolorization of molasses alcohol wastewater by thermophilic hydrolase with practical application value

The aim of this work was to explore the ability of cutinase in the decolorization of molasses wastewater. Thermophilic cutinase from Thermobifida alba eliminated 76.1-78.2% of colorants and exhibited the highest decolorization efficiency amongst all of the cutinases tested. Cutinase from Thermobifida alba was immobilized on an affordable and efficient modified chitosan carrier and achieved a decolorization yield of 79.3-81.2%. This cutinase removed 66.3-71.1% of pigments and lasted continuously for 5 days. Importantly, it was also shown to continuously and effectively remove COD and BOD₅. Compared to other enzymes, the immobilized cutinase from Thermobifida alba had the advantage of being low-cost and had a high expression level and activity. The results confirmed the decolorization occurred by destroying the conjugated system of melanoidins via an addition reaction by cutinase from Thermobifida alba. Thus, this study contributes a more practical and efficient approach to enzymatic decolorization of molasses wastewater.

Start-Up of Anammox SBR from Non-Specific Inoculum and Process Acceleration Methods by Hydrazine

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH4Cl, NaNO2, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl−/L), high (18.2 g of Cl−/L), or optimum salinity (0.5–2 g of Cl−/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m3/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N2H4/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers’ activity was diminished by all hydrazine additions compared to the control; 5 mg of N2H4/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N2H4/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment.

In situ elimination of nitrite inhibition on AnAOB by acetate dosing in an up-flow granular anammox reactor

The inhibition of over-accumulated nitrite on anaerobic ammonium oxidation (anammox) activity has been widely reported and intensively studied. Surprisingly, there are limited researches on the strategy to deal with nitrite inhibition. In this work, to eliminate nitrite inhibition in an up-flow granular anammox reactor, acetate dosing (600 mg COD L^-1) and simultaneous acetate and denitrifying sludge dosing (600 mg COD L^-1 and 1.4 g dry weight L^-1) were implemented to temporarily activate microbial denitrification to reduce nitrite, respectively. In two strategies, reactor nitrogen removal and extracellular ATP were resumed to initial levels, while the recovery ratios of intracellular ATP and nitrite removal rate (67.1% and 15.6 mg N h^-1) of the former were higher than those (52.5% and 11.2 mg N h^-1) of the latter, indicating acetate dosing was more qualified to nitrite removal. Meanwhile, although a decrease of the dominated Ca. Brocadia from 30.7 to 25.8% was not reversed through high-throughput sequencing, acetate dosing did not cause denitrifiers proliferation. As easily implemented acetate dosing was as effective as direct discharge of inhibitory nitrite as the control strategy, it was recommended when nitrite inhibition happened. Additionally, an irregular behavior of nitrate overproduction via nitrite oxidation and the drastic increase of extracellular ATP were detected and proposed as the response of AnAOB to nitrite inhibition.

Enhanced nitrate adsorption by using cetyltrimethylammonium chloride pre-loaded activated carbon

This paper used cetyltrimethylammonium chloride (CTAC) pre-loaded activated carbon (AC) to research nitrate adsorption. Effects of various parameters such as AC types, AC dosage as well as initial pH were studied. The results indicated that the ACs modified by CTAC can get higher nitrate removal. Even pH is neutral and basic, an accepted removal about 2.5 mg/g can be observed. The more CTAC pre-loaded on the AC surface, the higher nitrate adsorption capacity can be obtained. pH is regarded as a key factor affecting interactions between adsorbent and adsorbate, and the results confirmed that the nitrate adsorption on modified AC decreases gradually with the growth of initial pH. Besides, the acidic pH condition is much favoured for adsorption while the results gained a nitrate adsorption about 4.28 mg/g at pH = 3 condition. Sorption mechanism of nitrate on CTAC modified AC was investigated through two kinetic modellings including pseudo-second-order and Weber and Morris intra-particle diffusion model. The results imply that the generalized kinetic models tally well with experimental data. Additionally, interference of co-existing anions is examined, and the results showed that higher co-anions concentration would bring a heavier depression of the nitrate uptake due to its competing for adsorption sites.

Chemical removal and selectivity reduction of nitrate from water by (nano) zero-valent iron/activated carbon micro-electrolysis

The processes of (n)ZVI/AC（（nano）zero valent iron/activated carbon）micro-electrolysis were applied for nitrate removal from groundwater, aiming to reduce nitrate to N₂, an environmentally friendly end product. (n)ZVI was utilized and combined with selected commercial AC to form the micro-electrolysis. Effect of different operational parameters, including reductant dosage, (n)ZVI/AC ratios, and reaction pH, on nitrate and TN removal were cleared. The results showed that nZVI presents higher reaction activities than ZVI in micro-electrolysis. With the increase of the (n)ZVI/AC mass ration from 1:2 to 2:1, the TN removal increased from 16.8% to 38.9%, then declined with the further increase of the ratio. The nitrate removal was negatively correlated with the initial pH of the solution. Compared to ZVI particles, even with a lower dosage, nZVI presented 100% nitrate removal at acidic and neutral pH conditions, and TN removal could maintain higher than 35% with pH lower than 9.0. A kinetic model was also established to explain the pathways of nitrate removal, and the results indicated that AC not only enriched nitrate as an adsorbent but also present highly potential in catalytic converting nitrate to N₂. The technique presented great potentials in removing nitrate from water and a promising application prospect.

Highly efficient of nitrogen removal from mature landfill leachate using a combined DN-PN-Anammox process with a dual recycling system

An efficient and stable combined denitrification-partial nitrification-Anammox process with a dual recycling system was used to remove nitrogen from mature landfill leachate. After 155 d of operation, the NO₃^- as the PN-Anammox byproduct was almost treated with biodegradable organic carbon in raw wastewater in a pre-denitrification reactor by external recycling system. When raw landfill leachate with NH₄⁺-N concentration of 1900 mg/L was treated, an integrated reactor with airlift recycling was combined with the PN and Anammox reactions to efficiently remove NH₄⁺ from the inflow. The total nitrogen concentration of effluent stabilized at 20 mg/L and total nitrogen removal efficiency was 99%. The maximum NO₂^- production rate in the aerobic zone was 2.2 kg/(m³·d) and the maximum nitrogen removal rate in the anaerobic zone was 21.4 kg/(m³·d). The most common phyla among the nitrification and the Anammox functional bacteria were Nitrosomonas, Candidatus Kuenenia, and Candidatus Brocadia after landfill leachate treatment.

Bio-hythane production from microalgae biomass: Key challenges and potential opportunities for algal bio-refineries

The interest in microalgae for wastewater treatment and liquid bio-fuels production (i.e. biodiesel and bioethanol) is steadily increasing due to the energy demand of the ultra-modern technological world. The associated biomass and by-product residues generated from these processes can be utilized as a feedstock in anaerobic fermentation for the production of gaseous bio-fuels. In this context, dark fermentation coupled with anaerobic digestion can be a potential technology for the production of hydrogen and methane from these residual algal biomasses. The mixture of these gaseous bio-fuels, known as hythane, has superior characteristics and is increasingly regarded as an alternative to fossil fuels. This review provides the current developments achieved in the conversion of algal biomass to bio-hythane (H₂+CH₄).

Biological denitrification process based on the Fe(0)-carbon micro-electrolysis for simultaneous ammonia and nitrate removal from low organic carbon water under a microaerobic condition

A combined process between micro-electrolysis and biological denitrification (MEBD) using iron scraps and an activated carbon-based micro-electrolysis carrier was developed for nitrogen removal under a microaerobic condition. The process provided NH4(+)-N and total nitrogen (TN) removal efficiencies of 92.6% and 95.3%, respectively, and TN removal rate of 0.373±0.11kgN/(m(3)d) at corresponding DO of 1.0±0.1mg/L and HRT of 3h, and the optimal pH of 7.6-8.4. High-throughput sequencing analysis verified that dominant classes belonged to β-, α-, and γ-Proteobacteria, and Nitrospira. The dominant genera Hydrogenophaga and Sphaerotilus significantly increased during the operation, covering 13.2% and 6.1% in biofilms attached to the carrier in the middle of the reactor, respectively. Autotrophic denitrification contributed to >80% of the TN removal. The developed MEBD achieved efficient simultaneous nitrification and autotrophic denitrification, presenting significant potential for application in practical low organic carbon water treatment.

Impact of methionine on a partial-nitritation biofilter

It has been demonstrated that an anaerobic digestion process cannot attain an efficient removal of several amino acids, with methionine being one of the most persistent of these. Thus, the effect that methionine amino acid has over the partial-nitritation process with fixed-biofilm configuration in terms of performance and bacterial community dynamics has been investigated. With respect to the performance with no addition, 100 mg/L methionine loading decreased ammonium oxidation efficiency in 60% and 100% at concentrations of 300 and 500 mg/L methionine, respectively. Bacterial biomass sharply increased by 30, 65, and 230% with the addition of 100, 300, and 500 mg/L methionine, respectively. Bacterial community analysis showed that methionine addition supported the proliferation of a diversity of heterotrophic genera, such as Lysobacter and Micavibrio, and reduced the relative abundance of ammonium oxidizing genus Nitrosomonas. This research shows that the addition of methionine affects the performance of the partial-nitritation process. In this sense, amino acids can pose a threat for the of partial-nitritation process treating anaerobic digester supernatant at full-scale implementation.

Process of nitrogen transformation and microbial community structure in the Fe(0)-carbon-based bio-carrier filled in biological aerated filter

Nitrogen pollutants in low-organic carbon wastewater are difficult to biodegrade. Therefore, the Fe(0)-carbon-based bio-carrier (FCBC) was firstly used as hydrogen producer in a biological-aerated filter (BAF) to make up for the lack of organic carbon in biological nitrogen removal. Physical and chemical properties of FCBC were detected and compared in this study. The nitrogen removal rate for low COD/TN ratio wastewater, nitrogen transformation process, and microbial communities in the FCBC filled in BAF were investigated. Results showed that the nitrogen removal rates was 0.38-0.41 kg N m(-3) day(-1) in the FCBC filled BAF and reached 0.62 kg N m(-3) day(-1) within the filter depth of 60-80 cm, under the conditions of the dissolved oxygen 3.5 ± 0.2 mg L(-1) and the inlet pH 7.2 ± 0.1. Hydrogenophaga (using hydrogen as electron donor), Sphaerotilus (absorbing [Fe(3+)]), Nitrospira (nitrificaion), and Nitrosomonas (ammonia oxidation) were found to be the predominant genera in the reactor. The reaction schemes in the FCBC filled in BAF was calculated: hydrogen and [Fe(3+)] were produced by Fe(0)-C galvanic cells in the FCBC, ammonia was oxidized into nitrate by Nitrosomonas and Nitrospira genera, hydrogen was used as electron donors by Hydrogenophaga genus to reduce nitrate into N2, and [Fe(3+)] was partly absorbed by Sphaerotilus and diverted via sludge discharging.

Advanced low carbon-to-nitrogen ratio wastewater treatment by electrochemical and biological coupling process

Nitrogen pollution in ground and surface water significantly affects the environment and its organisms, thereby leading to an increasingly serious environmental problem. Such pollution is difficult to degrade because of the lack of carbon sources. Therefore, an electrochemical and biological coupling process (EBCP) was developed with a composite catalytic biological carrier (CCBC) and applied in a pilot-scale cylindrical reactor to treat wastewater with a carbon-to-nitrogen (C/N) ratio of 2. The startup process, coupling principle, and dynamic feature of the EBCP were examined along with the effects of hydraulic retention time (HRT), dissolved oxygen (DO), and initial pH on nitrogen removal. A stable coupling system was obtained after 51 days when plenty of biofilms were cultivated on the CCBC without inoculation sludge. Autotrophic denitrification, with [Fe(2+)] and [H] produced by iron-carbon galvanic cells in CCBC as electron donors, was confirmed by equity calculation of CODCr and nitrogen removal. Nitrogen removal efficiency was significantly influenced by HRT, DO, and initial pH with optimal values of 3.5 h, 3.5 ± 0.1 mg L(-1), and 7.5 ± 0.1, respectively. The ammonia, nitrate, and total nitrogen (TN) removal efficiencies of 90.1 to 95.3 %, 90.5 to 99.0 %, and 90.3 to 96.5 % were maintained with corresponding initial concentrations of 40 ± 2 mg L(-1) (NH3-N load of 0.27 ± 0.01 kg NH3-N m(-3) d(-1)), 20 ± 1 mg L(-1), and 60 ± 2 mg L(-1) (TN load of 0.41 ± 0.02 kg TN m(-3) d(-1)). Based on the Eckenfelder model, the kinetics equation of the nitrogen transformation along the reactor was N e  = N 0 exp (-0.04368 h/L(1.8438)). Hence, EBCP is a viable method for advanced low C/N ratio wastewater treatment.

Determine the operational boundary of a pilot-scale single-stage partial nitritation/anammox system with granular sludge

The partial nitritation/anammox (PN/A) process has been applied to ammonium-rich wastewater treatment, but the operational boundary has not been well determined for long-term stability. This pilot-scale study was targeted at a single-stage PN/A process using a sequencing batch reactor (SBR) (volume: 53 m(3)) and granulated activated sludge. The maximum nitrogen removal rate reached 0.83 kg N/(m(3)·d). Microbial analysis suggested that ammonium oxidizing bacteria were mainly present in small sludge flocs while anammox bacteria were prone to grow in large sludge granules. The PN/A performance was enhanced when dissolved oxygen (DO) was increased from 0.25 to 0.76 mg/L, and deteriorated at DO higher than 1.15 mg/L. The PN/A was inhibited at free ammonia (FA) over 77.0 mg/L. High DO or FA concentrations inhibited anammox activity and further induced high and inhibitory nitrite concentrations. Therefore, appropriate DO and FA concentrations should be controlled to achieve single-stage PN/A in SBRs.

Current state of sewage treatment in China

The study reported and analyzed the current state of wastewater treatment plants (WWTPs) in urban China from the aspects of scale, treatment processes, sludge handling, geographical distribution, and discharge standards. By 2012, there were 3340 WWTPs in operation in China with a capacity of 1.42 × 10(8) m(3)/d. The number of medium-scale WWTPs (1-10 × 10(4) m(3)/d) counted for 75% of total WWTPs. On average, the chemical oxygen demand (COD) removal efficiencies of small-scale, medium-scale, large-scale and super-large-scale WWTPs were 81, 85.5, 87.5 and 86.5%, respectively. Generally speaking, the nutrients removal instead of COD removal was of concern. As to the different processes, oxidation ditch, anaerobic-anoxic-oxic (A(2)/O) and sequencing batch reactor (SBR) were the mainstream technologies in China. These technologies had minor difference in terms of overall COD removal efficiency. The sludge treatment in WWTPs was basically "thickening-coagulation-mechanical dehydration" and the major disposal method was sanitary landfill in China. The distributions of WWTPs and their utilization showed significant regional characteristics. The sewage treatment capacity of China concentrated on the coastal areas and middle reaches of Yangtze River, which were the economically developed zones. Besides, most WWTPs enforced the Class 1 or Class 2 discharge standards, but few realized wastewater reuse. Finally, existing problems were discussed, including low removal efficiency of nitrogen and phosphorus, emerging contaminants, low reuse of reclaimed water, poor sludge treatment and disposal, low execution standard of effluent, and emissions of greenhouse gas from WWTPs. Suggestions regarding potential technical and administrative measures were given.

Start-up and bacterial communities of single-stage nitrogen removal using anammox and partial nitritation (SNAP) for treatment of high strength ammonia wastewater

In this study, a lab-scale sequencing batch biofilm reactor (SBBR) was used to start up the single-stage nitrogen removal system using anammox and partial nitritation (SNAP) process seeding from surplus activated sludge. The volumetric nitrogen loading rate (vNLR) was firstly 0.075 kg N m(-3) d(-1) and then gradually increased to 0.60 kg N m(-3) d(-1). A maximal total nitrogen (TN) removal rate of 0.54 kg N m(-3) d(-1) was achieved by the SNAP process after 132 days operation with NH4(+)-N and TN removal efficiency of 99.4% and 90.5%, respectively. This reactor may have applications for the SNAP process treating high strength ammonia wastewater. And dewatered surplus activated sludge was recommended as the seed sludge for engineering applications. The dominant bacterial strains were Xanthomonas campestris, Nitrosomonas europaea and Ignavibacterium album, corresponding to the percentage of 24%, 22% and 20%, respectively, based on the 16S rDNA amplicon pyrosequencing of the SNAP sludge.