Weili Zhou

Autotrophic denitrification for nitrate and nitrite removal using sulfur-limestone.

Sulfur-limestone was used in the autotrophic denitrification process to remove the nitrate and nitrite in a lab scale upflow biofilter. Synthetic water with four levels of nitrate and nitrite concentrations of 10, 40, 70 and 100 mg N/L was tested. When treating the low concentration of nitrate- or nitrite-contaminated water (10, 40 mg N/L), a high removal rate of about 90% was achieved at the hydraulic retention time (HRT) of 3 hr and temperature of 20-25 degrees C. At the same HRT, 50% of the nitrate or nitrite could be removed even at the low temperature of 5-10 degrees C. For the higher concentration nitrate and nitrite (70, 100 mg N/L), longer HRT was required. The batch test indicated that influent concentration, HRT and temperature are important factors affecting the denitrification efficiency. Molecular analysis implied that nitrate and nitrite were denitrified into nitrogen by the same microorganisms. The sequential two-step-reactions from nitrate to nitrite and from nitrite to the next-step product might have taken place in the same cell during the autotrophic denitrification process.

Investigation of soluble microbial products in a full-scale UASB reactor running at low organic loading rate

Investigation on a full-scale UASB treating industrial wastewater at a low organic loading rate (OLR) was conducted. Excellent treatment performance was achieved when treating the evaporator condensate of distillery wastewater at the OLR of less than 1 kg COD/m(3)d. Anaerobic effluent could be discharged without further treatment, which saved energy and running cost considerably. GC-MS analysis showed that the soluble microbial products (SMPs) were decreased to a low level at the low OLR. The main SMP in the anaerobic effluent were long chain carbohydrates and esters, accounting for 55-65% of the total organic matters. Anaerobic SMP was more complex than the aerobic ones. Soluble COD, protein and polysaccharide showed an obvious decrease at the sludge layer from 10 to 15m despite the low MLSS/MLVSS content. Methanogens were found to be predominant in this layer, which indicated that the methanogens might be the main consumers of the SMP in anaerobic reactors. Economic comparison confirmed that the anaerobic treatment at low OLR could be a good option.

Comparison of microbial communities in different sulfur-based autotrophic denitrification reactors

Sulfur-based autotrophic denitrification is a useful approach for the eutrophication control in lakes and rivers, yet the microorganisms in this process are still not clearly known. In order to reveal the bacterial composition in these denitrification reactors, high-throughput sequencing was performed over the sludge samples. And the results indicated that when using thiosulfate, elemental sulfur, and sulfide as electron donors, the microbial communities were clearly different. Besides the well-known Thiobacillus, many other genera of denitrifiers were identified. Chlorobaculum, Dechloromonas, and Acinetobacter were the most predominant genera in thiosulfate, elemental sulfur, and sulfide systems, respectively, while Janthinobacterium accounted for the most in the heterotrophic reactor with ethanol as electron donor. Thiobacillus existed abundantly in every system, even in the heterotrophic one. PCA comparison revealed that the microbial communities in the denitrification systems may vary greatly according to the electron donor, the running condition, sampling position, and other factors.

Nitrogen removal by the enhanced floating treatment wetlands from the secondary effluent

Three novel floating treatment wetlands, including autotrophic enhanced floating treatment wetland (AEFTW), heterotrophic enhanced floating treatment wetland (HEFTW) and enhanced floating treatment wetland (EFTW) were developed to remove nitrogen from the secondary effluent. Results showed that the analogously excellent nitrogen removal performance was achieved in AEFTW and HEFTW. About 89.4% of the total nitrogen (TN) was removed from AEFTW at a low S/N of 0.9 and 88.5% from HEFTW at a low C/N of 3.5 when the hydraulic retention time (HRT) was 1d in summer. Higher nitrification and denitrification performance were achieved in AEFTW. Addition of electron donors effectively reduced the N2O emission, especially in summer and autumn. High-throughput sequencing analysis revealed that the electron donors distinctly induced the microbial shifts. Dechloromonas, Thiobacillus and Nitrospira became the most predominant genus in HEFTW, AEFTW and EFTW. And autotrophic and heterotrophic denitrification could simultaneously occur in HEFTW and AEFTW.

Sulfur-based autotrophic denitrification from the micro-polluted water

Eutrophication caused by high concentrations of nutrients is a huge problem for many natural lakes and reservoirs. Removing the nitrogen contamination from the low C/N water body has become an urgent need. Autotrophic denitrification with the sulfur compound as electron donor was investigated in the biofilter reactors. Through the lab-scale experiment, it was found that different sulfur compounds and different carriers caused very different treatment performances. Thiosulfate was selected to be the best electron donor and ceramsite was chosen as the suitable carrier due to the good denitrification efficiency, low cost and the good resistibility against the high hydraulic loads. Later the optimum running parameters of the process were determined. Then the pilot-scale experiment was carried out with the real micro-polluted water from the West Lake, China. The results indicated that the autotrophic denitrification with thiosulfate as electron donor was feasible and applicable for the micro-polluted lake water.

Comparison of heterotrophic and autotrophic denitrification processes for treating nitrate-contaminated surface water

The goal of this study was to compare the nitrogen removal rate, effluent algal growth potential (AGP), nitrous oxide (N2O) emissions and global warming potential (GWP) between two laboratory-scale bioreactors: the autotrophic denitrification biofilter (ADBF) and heterotrophic denitrification biofilter (HDBF) for treating nitrate-contaminated surface water. The comparative study of nitrogen removal rate between ADBF and HDBF was conducted by a long-term experiment, and the comparative study of the effluent AGP, N2O emissions and GWP between ADBF and HDBF were carried out by the corresponding batch tests. The results show that the heterotrophic and autotrophic denitrification rates were close to each other. Besides, the AGP of the ADBF effluent was 2.08 times lower than that of the HDBF effluent, while the N2O concentration in off-gas emitted from HDBF was 6-8 times higher than that from ADBF. The higher N2O-N emission rate of HDBF was mainly responsible for the higher GWP of HDBF than that of ADBF. Furthermore, with a novel light-weight filtration media (NLWFM) for filtration, the autotrophic denitrification (ADN) process combined with biofilter process would be the optimal denitrification process for nitrogen removal from nitrate-contaminated surface water. The study also provided a systematic method for evaluation of biological nitrogen removal (BNR) process.

Removal of anaerobic soluble microbial products in a biological activated carbon reactor.

The soluble microbial products (SMP) in the biological treatment effluent are generally of great amount and are poorly biodegradable. Focusing on the biodegradation of anaerobic SMP, the biological activated carbon (BAC) was introduced into the anaerobic system. The experiments were conducted in two identical lab-scale up-flow anaerobic sludge blanket (UASB) reactors. The high strength organics were degraded in the first UASB reactor (UASB1) and the second UASB (UASB2, i.e., BAC) functioned as a polishing step to remove SMP produced in UASB1. The results showed that 90% of the SMP could be removed before granular activated carbon was saturated. After the saturation, the SMP removal decreased to 60% on the average. Analysis of granular activated carbon adsorption revealed that the main role of SMP removal in BAC reactor was biodegradation. A strain of SMP-degrading bacteria, which was found highly similar to Klebsiella sp., was isolated, enriched and inoculated back to the BAC reactor. When the influent chemical oxygen demand (COD) was 10,000 mg/L and the organic loading rate achieved 10 kg COD/(m3 x day), the effluent from the BAC reactor could meet the discharge standard without further treatment. Anaerobic BAC reactor inoculated with the isolated Klebsiella was proved to be an effective, cheap and easy technical treatment approach for the removal of SMP in the treatment of easily-degradable wastewater with COD lower than 10,000 mg/L.

Decomposition of Emergent Aquatic Plant (Cattail) Litter Under Different Conditions and the Influence on Water Quality

Decomposition of aquatic plant might generate a significant influence on the receiving water body. In this study, decomposition of emergent aquatic plant (cattail) litter was investigated under different conditions to determine the influencing level of the decomposition process on the water quality. Different litter addition rates (0.1, 0.5, 1.0xa0gxa0L−1), temperature changes, sediment additions, and kinestates (static and dynamic conditions) were selected as the influencing factors for the decomposition process. The results suggested that the decomposition process could be all accelerated when conducted at a higher litter addition rate, under a cold condition, with sediment addition or on dynamic condition, respectively. Additionally, the maximum ratio of releasing carbon to nitrogen (C/N) was increased when the decomposition process was conducted with a higher litter addition rate, under a cold condition (31.0), with sediment addition (24.6) and on a dynamic condition (28.0), respectively, and the C/N ratios were all higher than that with only 0.5xa0gxa0L−1 litter addition (24.5), suggesting that lowering of water temperature, sediment addition, and increasing of oxygen might also enhance the C/N. The high C/N released during the decomposition process implied that the cattail litter might be utilized as the potential organic carbon source for nitrogen removal in the CW system.

Decomposition characteristics of three different kinds of aquatic macrophytes and their potential application as carbon resource in constructed wetland

Decomposition of aquatic macrophytes usually generates significant influence on aquatic environment. Study on the aquatic macrophytes decomposition may help reusing the aquatic macrophytes litters, as well as controlling the water pollution caused by the decomposition process. This study verified that the decomposition processes of three different kinds of aquatic macrophytes (water hyacinth, hydrilla and cattail) could exert significant influences on water quality of the receiving water, including the change extent of pH, dissolved oxygen (DO), the contents of carbon, nitrogen and phosphorus, etc. The influence of decomposition on water quality and the concentrations of the released chemical materials both followed the order of water hyacinthxa0>xa0hydrillaxa0>xa0cattail. Greater influence was obtained with higher dosage of plant litter addition. The influence also varied with sediment addition. Moreover, nitrogen released from the decomposition of water hyacinth and hydrilla were mainly NH3-N and organic nitrogen while those from cattail litter included organic nitrogen and NO3--N. After the decomposition, the average carbon to nitrogen ratio (C/N) in the receiving water was about 2.6 (water hyacinth), 5.3 (hydrilla) and 20.3 (cattail). Therefore, cattail litter might be a potential plant carbon source for denitrification in ecological system of a constructed wetland.

Effects of hydraulic retention time and ratio on thiosulfate-driven autotrophic denitrification for nitrate removal from micro-polluted surface water

ABSTRACT This study was carried out to investigate the possibility of a thiosulfate-driven autotrophic denitrification for nitrate-N removal from micro-polluted surface water. The aim was to study the effects of ratio (S/N molar ratio) and hydraulic retention time (HRT) on the autotrophic denitrification performance. Besides, utilization efficiencies of along the biofilter and the restart-up of the bioreactor were also investigated. Autotrophic denitrification using thiosulfate as an electron donor for treating micro-polluted surface water without the addition of external alkalinity proved to be feasible and the biofilter could be readied in two weeks. Average nitrate-N removal efficiencies at HRTs of 0.5, 1 and 2u2005h were 78.7%, 87.8% and 97.4%, respectively, and corresponding removal rates were 186.24, 103.92 and 58.56u2005g , respectively. When water temperature was in the range of 8–12°C and HRT was 1u2005h, average nitrate-N removal efficiencies of 41.9%, 97.1% and 97.0%, nitrite accumulation concentrations of 1.45, 0.46 and 0.22u2005mg/L and thiosulfate utilization efficiencies of 100%, 98.8% and 92.1% were obtained at S/N ratios of 1.0, 1.2 and 1.5, respectively. Besides, the autotrophic denitrification rate in the filtration media layer was the highest along the biofilter at an S/N ratio of 1.5. Finally, after a one-month period of starvation, the biofilter could be restarted successfully in three weeks without inoculation of seed sludge.