Autotrophic Heterotrophic Denitrification Research Articles

Simultaneous heterotrophic and FeS2-based ferrous autotrophic denitrification process for low-C/N ratio wastewater treatment: Nitrate removal performance and microbial community analysis

Heterotrophic-autotrophic denitrification reduces the cost of wastewater treatment and the risk of excess chemical oxygen demanded (COD) in the effluent. A mixotrophic denitrification system involving mixed heterotrophic and ferrous autotrophic bacteria was investigated to treat low-C/N ratio (C/N, defined as chemical oxygen demand (COD)/total nitrogen (TN)) wastewater with pyrite and organic carbon as electron donors. The system yielded effluent total nitrogen (TN) of 0.38 mg/L in 48 h due to a synergistic effect when the C/N ratio was 0.5 and influent nitrate nitrogen (NO3−-N) was 20 mg/L; this TN value was significantly lower than those of the heterotrophic system (14.08 mg/L) and ferrous autotrophic system (12.00 mg/L). The highest abundance of the narG gene was observed in the mixotrophic denitrification system, along with more abundant microbial species. The dominant denitrification bacteria in each system included Thaurea, Ferritrophicum, Pseudomonas, and Thiobacillus, which varied with the initial inoculum source and the environment. Nevertheless, the abundance of the heterotrophic bacteria Thaurea decreased with prolonged operation of the systems. Together, these results implied that the simultaneous heterotrophic and FeS2-based ferrous autotrophic denitrification process can be an alternative approach for the treatment of low-C/N ratio wastewater.

Wood and sulfur-based cyclic denitrification filters for treatment of saline wastewaters

This study investigated the performance and microbiome of cyclic denitrification filters (CDFs) for wood and sulfur heterotrophic-autotrophic denitrification (WSHAD) of saline wastewater. Wood-sulfur CDFs integrated into two pilot-scale marine recirculating aquaculture systems achieved high denitrification rates (103 ± 8.5 g N/(m3·d)). The combined use of pine wood and sulfur resulted in lower SO42− accumulation compared with prior saline wastewater denitrification studies with sulfur alone. Although fish tank water quality parameters, including ammonia, nitrite, nitrate and sulfide, were below the inhibitory levels for marine fish production, lower survival rates of Poecilia sphenops were observed compared with prior studies. Heterotrophic denitrification was the dominant removal mechanism during the early operational stages, while sulfur autotrophic denitrification increased as readily biodegradable organic carbon released from wood chips decreased over time. 16S rRNA-based analysis of the CDF microbiome revealed that Sulfurimonas, Thioalbus, Defluviimonas, and Ornatilinea as notable genera that contributed to denitrification performance.

Simultaneous removal of sulfamethoxazole and enhanced denitrification process from simulated municipal wastewater by a novel 3D-BER system

In this study, at an electric current intensity at 60mA, more than 90.50 ± 4.76% of Sulfamethoxazole (SMX) was degraded. The strengthening of bacterial metabolisms and the sustainment of electrical stimulation contributed to the rapid removal of SMX and nitrates from simulated wastewater by a novel 3D-BER system. From the literature, very few studies have been performed to investigate the high risk of nitrates and antibiotics SMX found in wastewater treatment. The highest antibiotic SMX and nitrogen removal efficiency was 96.45 ± 2.4% (nitrate-N), 99.5 ± 1.5% (nitrite-N), 88.45 ± 1.4% (ammonia-N), 78.6 ± 1.0% (total nitrogen), and SMX (90.50 ± 4.76%), respectively. These results were significantly higher as compared to control system (p< 0.05). The highest denitrification efficiency was achieved at the pH level of 7.0 ± 0.20 - 7.5 ± 0.31. Lower or higher pH value can effect on an approach of heterotrophic-autotrophic denitrification. Moreover, low current intensity did not show any significant effect on the degradation, however, enhanced the removal rate of nitrate or nitrite as well as antibiotic SMX. Based on the results of HPLC and LC-MS/MS analysis, the intermediate products were proposed after efficient biodegradation of SMX. Finally, these results is expected to provide some new insights towards the high electric currents, changes the bacterial community structure, and the activated sludge which played an important role in the biodegradation of SMX and nitrates removal more efficiently.

Biostimulation of heterotrophic-autotrophic denitrification in a microbial electrochemical system using alternating electrical current

In this study, a novel integrated anoxic bioreactor with an electrochemical system was developed for heterotrophic-autotrophic denitrification using alternating current. The obtained results were revealed that sinusoidal and triangular waveforms were more effective than the square wave for enhancing the heterotrophic-autotrophic denitrification process efficiency. The nitrate removal efficiency was significantly decreased by increasing frequency ranges from 10 to 50 Hz. The system performance had an optimum response at 4 peak-to-peak voltage (Vpp). Nitrate reduction occurred at longer reaction times in higher voltage values (6, 8, and 10 Vpp). It was demonstrated that both heterotrophic and autotrophic bacteria coexist in the heterotrophic-autotrophic denitrification bio-electroreactor induced by the alternating current. The most probable numbers were determined 5.2 × 106 and 5.2 × 104 for heterotrophic and autotrophic denitrification bacteria, respectively. Pseudomonas spp., Nesterenkonia spp., Bacillus spp., and Brevibacillus spp. were determined using 16S rRNA, as the most abundant denitrifiers present in the system. Accordingly, it is concluded that heterotrophic-autotrophic denitrification supplied with low-frequency low-voltage alternating current could be a promising technique for water treatment contaminated with nitrate.

Biological denitrification in marine aquaculture systems: A multiple electron donor microcosm study

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S0) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m3·d)), followed by FW (4.5 g N/(m3·d)), S0 (3.5 g N/(m3·d)), eucalyptus mulch (2.6 g N/(m3·d)), and eucalyptus mulch with sulfur (2.2 g N/(m3·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2–11.9 g N/(m3·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.

Nitrate Removal from Groundwater by Heterotrophic/Autotrophic Denitrification Using Easily Degradable Organics and Nano-Zero Valent Iron as Co-Electron Donors

Heterotrophic/autotrophic denitrification (HAD) is an effective approach to remove nitrate from contaminated groundwater. To improve its performance, easily degradable organics (methanol, ethanol, oxalic acid, and sodium acetate) and nano-zero valent iron (nZVI) were selected as co-electron donors for HAD, and their effectiveness in enhancing HAD to remove nitrate from simulated groundwater was evaluated. It was found that the removal efficiency of HAD to nitrate was significantly affected by the species of easily degradable organics as their different biological availability. Among the tested organics, ethanol-supported HAD system exhibited a better removal efficiency, and after 10 days reaction, it could achieve a high nitrate removal rate to 85.6% with an initial concentration of 90.94 mg/l, and at the end of the test (27 days), nitrate was almost completely removed in the interaction of heterotrophic denitrification (HD) and autotrophic denitrification (AD), and there was no nitrite and ammonium accumulation (< 0.1 and 1.0 mg/l). Moreover, the initial C/N ratios (0.2, 0.5, 1.0, 2.0, and 4.0) of simulated groundwater had a significant influence on nitrate removal by HAD. Increasing the C/N from 0.2 to 2.0 could markedly enhance nitrate removal efficiency, but continuously increased to 4.0 the removal rate just decreased; nevertheless, the accumulation of nitrite and ammonium were closely related to both the C/N ratios and species of organics. The synergistic effect between HD and AD process plays a vital role in the mixotrophic environment. Therefore, this research provides an effective method for nitrate removal from contaminated water with low organic carbon.

Effect of citric acid on the efficiency of the removal of nitrogen and phosphorus compounds during simultaneous heterotrophic-autotrophic denitrification (HAD) and electrocoagulation

The paper discusses the effect of electric current density and the C/N ratio on the efficiency of the removal of oxygenated nitrogen forms and total phosphorus in a bio-electrochemical sequencing batch biofilm reactor. The study was performed under anaerobic conditions, at the electric current densities of 53, 105, 158 and 201mAm−2, the C/N ratios of 0.5, 1.0 and 1.5 and pH=7.5. For a particular electric current density, a higher efficiency of the removal of nitrogen (from 46.92(±1.20)% to 94.13(±1.50)%) and phosphorus (from 84.54(±1.90)% to 99.91(±1.60)%) compounds was achieved in the reactor fed with wastewater containing citric acid (R1) than in the control reactor without citric acid supplementation (R0). The efficiency depended on the electric current density and the dose of organic substrate.An increase in the C/N ratio of wastewater eliminated the need to apply higher electric current densities. Carbon dioxide produced during heterotrophic denitrification constituted an additional source of inorganic carbon for autotrophic bacteria. The higher total phosphorus removal efficiency in reactor R1 was caused by simultaneous electrocoagulation and higher phosphorus assimilation by the increasingly thicker biofilm.

Autotrophic denitrification with sulfide as electron donor: Effect of zeolite, organic matter and temperature in batch and continuous UASB reactors

The effect of zeolite and temperature on the autotrophic denitrification process for hydrogen sulfide removal in the presence of organic matter was evaluated. Four batch reactors (1 l) at 35 °C were used to study the effect of zeolite on denitrification, without the presence of organic matter. Two continuous UASB reactors (6 l) were used for the autotrophic denitrification with addition of natural zeolites at mesophilic controlled temperature (35 °C) and room temperature (13–20 °C). In continuous assays, COD/N ratios between 1.4 and 10 were used. It was found that zeolites have a positive effect on the autotrophic denitrification startup process (batch and continuous modes), decreasing by up to 50% the time required to achieve stabilization conditions of the process. Autotrophic denitrification with zeolite as amendment in a continuous UASB in the presence of organic matter could be carried out at uncontrolled room temperatures (13 °C – 20 °C), although processes at a controlled mesophilic temperature of 35 °C were more efficient than the room temperature process. The proposed system allows the simultaneous heterotrophic-autotrophic denitrification, with removal percentages better than 95% for nitrogen and COD, while sulfide had removal percentages better than 75%.

Remediation of nitrate–nitrogen contaminated groundwater using a pilot-scale two-layer heterotrophic–autotrophic denitrification permeable reactive barrier with spongy iron/pine bark

A novel two-layer heterotrophic–autotrophic denitrification (HAD) permeable reactive barrier (PRB) was proposed for remediating nitrate–nitrogen contaminated groundwater in an oxygen rich environment, which has a packing structure of an upstream pine bark layer and a downstream spongy iron and river sand mixture layer. The HAD PRB involves biological deoxygenation, heterotrophic denitrification, hydrogenotrophic denitrification, and anaerobic Fe corrosion. Column and batch experiments were performed to: (1) investigate the NO3−–N removal and inorganic geochemistry; (2) explore the nitrogen transformation and removal mechanisms; (3) identify the hydrogenotrophic denitrification capacity; and (4) evaluate the HAD performance by comparison with other approaches. The results showed that the HAD PRB could maintain constant high NO3−–N removal efficiency (>91%) before 38 pore volumes (PVs) of operation (corresponding to 504d), form little or even negative NO2−–N during the 45 PVs, and produce low NH4+–N after 10 PVs. Aerobic heterotrophic bacteria played a dominant role in oxygen depletion via aerobic respiration, providing more CO2 for hydrogenotrophic denitrification. The HAD PRB significantly relied on heterotrophic denitrification. Hydrogenotrophic denitrification removed 10–20% of the initial NO3−–N. Effluent total organic carbon decreased from 403.44mgL−1 at PV 1 to 9.34mgL−1 at PV 45. Packing structure had a noticeable effect on its denitrification.

The heterotrophic-combined-with-autotrophic denitrification process: performance and interaction mechanisms.

In this work, the interaction mechanisms between an autotrophic denitrification (AD) and heterotrophic denitrification (HD) process in a heterotrophic-autotrophic denitrification (HAD) system were investigated, and the performance of the HAD system under different S/Ac(-) molar ratios was also evaluated. The results demonstrated that the heterotrophic-combined-with-autotrophic denitrification process is a promising technology which can remove chemical oxygen demand (COD), sulfide and nitrate simultaneously. The reduction rate of NO(3)(-) to NO(2)(-) by the HD process was much faster than that of reducing NO(2)(-) to N₂, while the reduction rate of NO(3)(-) to NO(2)(-) by the AD process was slower than that of NO(2)(-) to N₂. Therefore, the AD process could use the surplus NO(2)(-) produced by the HD process. This could alleviate the NO(2)(-)-N accumulation and increase the denitrification rate. In addition, the inhibition effects of acetate on AD bacteria and sulfide on HD were observed, and the inhibition was compensated by the promotion effects on NO(2)(-). Therefore, the processes of AD and HD seem to react in parallel, without disturbing each other, in our HAD system.

Remediation of Nitrate-Nitrogen Contaminated Groundwater by a Heterotrophic-Autotrophic Denitrification Approach in an Aerobic Environment

A novel heterotrophic-autotrophic denitrification (HAD) approach supported by mixing granulated spongy iron, methanol, and mixed bacteria was proposed for the remediation of nitrate-nitrogen (NO3-N) contaminated groundwater in a dissolved oxygen (DO)-rich environment. The HAD process involves biological deoxygenation, chemical reduction (CR) of NO3-N and DO, heterotrophic denitrification (HD), and autotrophic denitrification (AD). Batch experiments were performed to: (1) investigate deoxygenation capacities of HAD; (2) determine the contributions of AD, HD, and CR to the overall NO3-N removal in the HAD; and (3) evaluate the effects of environmental parameters on the HAD. There were 174, 205, and 2,437 min needed to completely reduce DO by the HAD, spongy iron-based CR, and by the mixed bacteria, respectively. The HAD depended on abiotic and biotic effects to remove DO. CR played a dominant role in deoxygenation in the HAD. After 5 days, approximately 100, 63.0, 20.1, and 9.7 % of the initial NO3-N was removed in the HAD, HD, AD + CR, and CR incubations, respectively. CR, HD, and AD all contributed to the overall NO3-N removal in the HAD. HD was the most important NO3-N degradation mechanism in the HAD. There existed symbiotic, synergistic, and promotive effects of CR, HD, and AD within the HAD. The decrease in NO3-N and the production of nitrite-nitrogen (NO2-N) and ammonium-nitrogen (NH4-N) in the HAD were closely related to the C to N weight ratio. The C to N ratio of 3.75:1 was optimal for complete denitrification. Denitrification rate at 27.5°C was 1.36 times higher than at 15.0°C.

Heterotrophic/autotrophic denitrification (HAD) of drinking water: prospective use for permeable reactive barrier

This work aims to explore the use of an innovative denitrification process developed by our group for groundwater remediation. This process is coupling heterotrophic-autotrophic denitrification processes (HAD) supported by cotton and zero-valent iron (ZVI). In the experimental part, the effect of two amounts of ZVI (150 and 300 g), two nitrate (100 and 220 mg/l) and phosphate (3 and 6 mg/l) inlet concentrations on nitrate removal performance is investigated in two parallel continuous fed plug-flow reactors. The possible in-situ application of the proposed system in permeable reactive barriers (PRB) is further discussed. The HAD showed higher volumetric nitrate removal ratio (VNR) than the cotton supported heterotrophic denitrification one, and VNR increased with the amount of ZVI packed in the reactors. Ammonium production by the reductive action of iron was kept on acceptable level adjusting the contact time between water and ZVI. Iron release from ZVI decreased with time to negligible value (<0.5 mg/l) thanks to the formation of iron green rust compounds (GR). The HAD seems to be adequate for PRB systems, because both cellulose-based material and ZVI have been used in reactive trench for site remediation. Moreover, the proposed process could have the function for removal of nitrate and priority pollutants, such as chlorinated ethenes, simultaneously.

An heterotrophic/autotrophic denitrification (HAD) approach for nitrate removal from drinking water

An heterotrophic/autotrophic denitrification (HAD) approach supported by cotton and zero valent iron (ZVI) was proposed for nitrate removal from drinking water. Preliminary batch tests were performed to investigate the behaviour of ZVI and nitrate rich water system. Afterwards the HAD process was tested in continuous pilot-scale column reactors containing 380 g of cotton and 150–300 g of ZVI (R2–R4) and a blank reactor (R1) filled only with 380 g of cotton (cotton supported denitrification, CSD). The performance of the reactors was evaluated according to volumetric nitrate removal, stability with time and by-products formation. The HAD reactors, in particular, the HAD with 300 g of ZVI (R4), showed higher volumetric nitrate removal efficiencies (from 0.235 to 0.275 kg N m −3 day −1) than the CSD reactor (0.190 kg N m −3 day −1). Furthermore, released by-products such as soluble iron and ammonium were limited to very low levels (<0.095 and <1.25 mg l −1, respectively). The promising high performance obtained by the HAD shall be evaluated for in situ application as further study.