Chunbo Hao

Denitrification of nitrate contaminated groundwater with a fiber-based biofilm reactor

A fiber-based biofilm reactor was developed using a laboratory-scale apparatus for treatment of nitrate-contaminated groundwater. Denitrification bacteria were inoculated by anaerobic sludge from a wastewater treatment plant. Nitrate removal efficiency, nitrite accumulation, COD and pH in the treated water were investigated under various conditions set by several parameters including hydraulic retention times (HRTs) (24, 20, 16, 12, 8, 4 and 2h), influent nitrate loading (around 50, 100 and 150 NO(3)(-)-N mg L(-1)), pH (5, 6, 7, 8, and 9) and ratios of carbon to nitrogen (C/N=3.00, 2.00, 1.50 1.25 and 1.00). The experimental results demonstrated that the optimum reaction parameters were pH 7-7.5,C/N=1.25 and HRT=8h, under which over 99% of NO(3)(-)-N was removed, almost no NO(2)(-)-N accumulated and COD was nearly zero in treated water when the concentration of NO(3)(-)-N was around 100.00 mg L(-1) in influent.

Characteristics of heterotrophic/biofilm-electrode autotrophic denitrification for nitrate removal from groundwater.

A heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER) was developed to improve denitrification efficiency and reduce the consumption of organic carbon source. Maximum nitrate removal efficiency of 99.9% was gained under the optimum current density of 200 mA/m(2). The number of heterotrophic denitrification bacteria (HDB) 2.0 × 10(5) and hydrogen autotrophic denitrification bacteria (ADB) 2.0 × 10(3) in per milliliter biofilm solution were observed by the most probable number (MPN) culture, demonstrating that HDB and ADB coexist in the HAD-BER. The inorganic carbon source for autotrophic denitrification was supplied by the dissolved carbon dioxide (CO2) evolved from the heterotrophic denitrification process, indicating that there was synergistic interaction between the HDB and ADB, i.e., the organic carbon source used for denitrification could be decreased in the HAD-BER. Therefore, the developed HAD-BER would be a promising approach for nitrate removal from groundwater.

Inhibition of the growth of two blue-green algae species (Microsystis aruginosa and Anabaena spiroides) by acidification treatments using carbon dioxide

The effect of pH adjusted by aeration with carbon dioxide (CO(2)) on the growth of two species of blue-green algae, Microcystis aeruginosa and Anabaena spiroides, was investigated. Three conditions (pH 5.5, 6.0 and 6.5) were found to have significant inhibitory effects on the growth of the two algae species when acidification treatment was conducted during the logarithmic phase. Differences in the inhibition effect of acidification existed between the two species algae. The tolerance of M. aeruginosa to these conditions was also investigated. The results indicated that M. aeruginosa was inhibited significantly, but not dead at pH 6.5, whereas death occurred at pH 5.5 and 6.0. The greatest inhibitory effect of acidification treatment conducted during the stable breeding phase of M. aeruginosa occurred at pH 5.5, while no inhibitory effect was found at pH 6.5.

Pyrite-based autotrophic denitrification for remediation of nitrate contaminated groundwater

In this study, pyrite-based denitrification using untreated pyrite (UP) and acid-pretreated pyrite (AP) was evaluated as an alternative to elemental sulfur based denitrification. Pyrite-based denitrification resulted in a favorable nitrate removal rate constant (0.95 d(-1)), sulfate production of 388.00 mg/L, and a stable pH. The pretreatment of pyrite with acid led to a further increase in the nitrate removal rate constant (1.03 d(-1)) and reduction in initial sulfate concentration (224.25±7.50 mg/L). By analyzing the microbial community structure using Denaturing Gradient Gel Electrophoresis, it was confirmed that Sulfurimonas denitrificans (S. denitrificans) could utilize pyrite as an electron donor. A stable pH was observed over the entire experimental period, indicating that the use of a pH buffer reagent would not be necessary for pyrite-based denitrification. Therefore, pyrite could effectively replace elemental sulfur as an electron donor in autotrophic denitrification for nitrate-contaminated groundwater remediation.

A soil infiltration system incorporated with sulfur-utilizing autotrophic denitrification (SISSAD) for domestic wastewater treatment.

To enhance the denitrification performance of soil infiltration, a soil infiltration system incorporated with sulfur-utilizing autotrophic denitrification (SISSAD) for domestic wastewater treatment was developed, and the SISSAD performance was evaluated using synthetic domestic wastewater in this study. The aerobic respiration and nitrification were mainly taken place in the upper aerobic stage (AES), removed 88.44% COD and 89.99% NH4(+)-N. Moreover, autotrophic denitrification occurred in the bottom anaerobic stage (ANS), using the CO2 produced from AES as inorganic carbon source. Results demonstrated that the SISSAD showed a remarkable performance on COD removal efficiency of 95.09%, 84.86% for NO3(-)-N, 95.25% for NH4(+)-N and 93.15% for TP. This research revealed the developed system exhibits a promising application prospect for domestic wastewater in the future.

Optimization of C/N and current density in a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER).

In this study, central composite design (CCD) and response surface methodology (RSM) were applied to optimize the C/N and current density in a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER). Results showed that nitrate could be effectively reduced over a wide range of C/Ns (0.84-1.3535) and current densities (96.8-370.0 mA/m(2)); however, an optimum C/N of 1.13 and optimum current density of 239.6 mA/m(2) were obtained by RSM. Moreover, the HAD-BER performance under the optimum conditions resulted in almost 100% nitrate-N removal efficiency and low nitrite-N and ammonia-N accumulation. Furthermore, under the optimum conditions, H2 generated from water electrolysis matched the CO2 produced by heterotrophic denitrification by stoichiometric calculation. Therefore, CCD and RSM could be used to acquire optimum operational conditions and improve the nitrate removal efficiency and energy consumption in the HAD-BER.

The feasibility of an up-flow partially aerated biological filter (U-PABF) for nitrogen and COD removal from domestic wastewater

An up-flow partially aerated biological filter (U-PABF) was developed to study the removal of nitrogen and chemical oxygen demand (COD) from synthetic domestic wastewater. The removal of NH4(+)-N was primarily attributed to adsorption in the zeolite U-PABF and to bioprocesses in the ceramic U-PABF. When the hydraulic retention time (HRT) was 5.2h, the ceramic U-PABF achieved a good performance and the NH4(+)-N, total nitrogen (TN), and COD removal efficiency reached 99.08±8.79%, 72.83±0.68%, and 89.38±1.04%, respectively. The analysis of NH4(+)-N, NO3(-)-N, NO2(-)-N, and TN at different depths revealed the simultaneous existence of nitrification-denitrification, and anaerobic ammonium oxidation (anammox) in ceramic U-PABF. Illumina pyrosequencing confirmed the existence of Planctomycetes, which are responsible for anammox. The results indicated that the nitrification-denitrification and anammox all contributed to the high removal of NH4(+)-N, TN, and COD in the U-PABF.

Sulfur-based autotrophic denitrification with eggshell for nitrate-contaminated synthetic groundwater treatment

ABSTRACT Eggshell is considered to be a waste and a significant quantity of eggshell waste is generated from food processing, baking and hatching industries. In this study, the effect of different sulfur/eggshell (w/w) ratios and temperatures was investigated to evaluate the feasibility of the sulfur-based autotrophic denitrification with eggshell (SADE) process for nitrate removal. The results showed eggshell can maintain a neutral condition in a range of pH 7.05–7.74 in the SADE process, and remove 97% of nitrate in synthetic groundwater. Compared with oyster shell and limestone, eggshell was found to be a desirable alkaline material for sulfur-based autotrophic denitrification (SAD) with no nitrite accumulation and insignificant sulfate production. Denitrification reaction was found to follow the first-order kinetic models (R2 > .9) having nitrate removal rate constants of 0.85 and 0.93 d−1 for raw eggshell and boiled eggshell, respectively. Sulfur/eggshell ratio of 2:3 provided the best efficiency on nitrate removal. Nitrate was removed completely by the SADE process at a low temperature of 15°C. Eggshell could be used for the SAD process due to its good effect for nitrate removal from groundwater. GRAPHICAL ABSTRACT

Bioremediation of nitrate and Fe(II) combined contamination in groundwater by heterotrophic denitrifying bacteria and microbial community analysis

Species of denitrifying bacteria are capable of nitrate reducing and Fe(II) oxidizing. The optimal temperature, pH and C/N ratio for denitrification coupled with Fe(II) oxidation in circumneutral anaerobic groundwater was investigated by a Box–Behnken design and response surface methodology. The microbial diversities were analyzed by high-throughput sequencing. The results showed that the optimal condition was achieved at a temperature of 24.93 °C, pH of 7.23 and C/N ratio of 1.43, at which almost 100% of nitrate-N and Fe(II) was removed with little byproduct accumulation. Within the temperature range 15–25 °C, pH 7–8.25 and C/N ratio 1.23–1.47, both nitrate and Fe(II) concentration could be removed effectively. The distributions of the microbial taxonomy composition (e.g., phylum, genus) differed under different temperatures, pH values and C/N ratios. Betaproteobacteria and Bacteroidetes dominated the bacterial phyla, and Methyloversatilis was the predominant bacterial genus in the enrichment cultures. Complex species of bacteria were attributed to the sophisticated reaction system. Though heterotrophic denitrification and Fe(II) oxidation dominated the system, autotrophic denitrification, H2 and acetate production may, somehow, have contributed to the entire reaction system. Denitrifiers (e.g., Azonexus), bacteria capable of nitrate dependent Fe(II) oxidation (NDFO) (e.g., Dechloromonas) and bacteria which could produce acetate as co-substrates for NDFO (e.g., Acetobacterium) were unevenly distributed. These findings provide support for nitrate and Fe(II) contaminated groundwater bioremediation, and a better understanding of the microbial ecosystem of the enriched heterotrophic denitrifiers.

Effect of phosphate rock on denitrification in a nitrate-polluted groundwater remediation system

AbstractThis study was conducted to evaluate the performance of phosphate rock for the promotion of denitrification in groundwater remediation. The results showed that phosphate rock can release phosphorus in the leaching experiment and thus has potential to provide phosphorus for denitrifying bacteria growth. In column experiments, the nitrate removal efficiency of columns containing 1,500 and 750 g of phosphate rock was over 97% at 20 ± 2°C, and the nitrite concentrations were lower than 0.5 mg NO2-N/L. However, the nitrate removal efficiency in columns containing 500 and 0 g of phosphate rock was lower than 90%, and nitrite accumulation was observed. Additionally, the nitrate concentration in effluent increased evidently when the influent flow rate was increased from 2.6 to 3.6 mL/min. Nevertheless, nitrate removal efficiency of columns containing 1,500 and 750 g of phosphate rock was higher than that of columns containing 500 and 0 g of phosphate rock. These findings indicated that phosphate rock was ...