Baihang Zhao

The nitritation performance of biofilm reactor for treating domestic wastewater under high dissolved oxygen.

The objective of this study was to investigate the nitritation performance in a biofilm reactor for treating domestic wastewater. The reactor was operated in continuous feed mode from phases 1 to 3. The dissolved oxygen (DO) was controlled at 3.5-7 mg/L throughout the experiment. The biofilm reactor showed excellent nitritation performance after the inoculation of nitrifying sludge, with the hydraulic retention time being reduced from 24 to 7 hr. Above 90% nitrite accumulation ratio (NAR) was maintained in phase 1. Afterwards, nitratation occurred with the low NH4(+)-N concentration in the reactor. The improvement of NH4(+)-N concentration to 20-35 mg/L had a limited effect on the recovery of nitritation. However, nitritation recovered rapidly when sequencing batch feed mode was adopted in phase 4, with the effluent NH4(+)-N concentration above 7 mg/L. The improvement of ammonia oxidizing bacteria (AOB) activity and the combined inhibition effect of free ammonia (FA) and free nitrous acid (FNA) on the nitrite oxidizing bacteria (NOB) were two key factors for the rapid recovery of nitritation. Sludge activity was obtained in batch tests. The results of batch tests had a good relationship with the long term operation performance of the biofilm reactor.

Effects of carbon sources, COD/NO2−-N ratios and temperature on the nitrogen removal performance of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm

The aim of the present work was to evaluate the effects of carbon sources and chemical oxygen demand (COD)/NO2--N ratios on the anammox-denitrification coupling process of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm. Also, the anammox activities of the SNAD biofilm were investigated under different temperature. Kaldnes rings taken from the SNAD biofilm reactor were operated in batch tests to determine the nitrogen removal rates. As a result, with the carbon source of sodium acetate, the appropriate COD/NO2--N ratios for the anammox-denitrification coupling process were 1 and 2. With the COD/NO2--N ratios of 1, 2, 3, 4 and 5, the corresponding NO2--N consumption via anammox was 87.1%, 52.2%, 29.3%, 23.7% and 16.3%, respectively. However, with the carbon source of sodium propionate and glucose, the anammox bacteria was found to perform higher nitrite competitive ability than denitrifiers at the COD/NO2--N ratio of 5. Also, the SNAD biofilm could perform anammox activity at 15 °C with the nitrogen removal rate of 0.071 kg total inorganic nitrogen per kg volatile suspended solids per day. These results indicated that the SNAD biofilm process might be feasible for the treatment of municipal wastewater at normal temperature.

A coupled system of half-nitritation and ANAMMOX for mature landfill leachate nitrogen removal

ABSTRACT A coupled system of membrane bioreactor-nitritation (MBR-nitritation) and up-flow anaerobic sludge blanket-anaerobic ammonium oxidation (UASB-ANAMMOX) was employed to treat mature landfill leachate containing high ammonia nitrogen and low C/N. MBR-nitritation was successfully realized for undiluted mature landfill leachate with initial concentrations of 900–1500 mg/L and 2000–4000 mg/L chemical oxygen demand. The effluent concentration and the accumulation efficiency were 889 mg/L and 97% at 125 d, respectively. Half-nitritation was quickly realized by adjustment of hydraulic retention time and dissolved oxygen (DO), and a low DO control strategy could allow long-term stable operation. The UASB-ANAMMOX system showed high effective nitrogen removal at a low concentration of mature landfill leachate. The nitrogen removal efficiency was inhibited at excessive influent substrate concentration and the nitrogen removal efficiency of the system decreased as the concentration of mature landfill leachate increased. The MBR-nitritation and UASB-ANAMMOX processes were coupled for mature landfill leachate treatment and together resulted in high effective nitrogen removal. The effluent average total nitrogen concentration and removal efficiency values were 176 mg/L and 83%, respectively. However, the average nitrogen removal load decreased from 2.16 to 0.77 g/(L d) at higher concentrations of mature landfill leachate.

Adsorptive removal of naphthalene induced by structurally different Gemini surfactants in a soil-water system.

A new generation of surfactant, Gemini surfactants, have been synthesized and have attracted the attention of various industrial and academic research groups. This study focused on the use of symmetric and dissymmetric quaternary ammonium Gemini surfactants to immobilize naphthalene onto soil particles, and is used as an example of an innovative application to remove HOC in situ using the surfactant-enhanced sorption zone. The sorption capacity of modified soils by Gemini surfactant and natural soils was compared and the naphthalene sorption efficiency, in the absence and presence of Gemini surfactants with different alkyl chain lengths, was investigated in the soil-water system. The results have shown that the increased added Gemini surfactant formed admicelles at the interface of soil/water having superior capability to retard contaminant. Symmetric and dissymmetric Gemini surfactants have opposite effect on the aspect of removing of PAH attributing to their solubilization and sorption behavior in soil-water system. Compared with the natural soil, sorption of naphthalene by Gemini-modified soil is noticeably enhanced following the order of C12-2-16 < C12-2-12 < C12-2-8. However, the symmetric Gemini surfactant C12-2-12 is the optimized one for in situ barrier remediation, which is not only has relative high retention ability but also low dosage.

Inhibition factors and Kinetic model for ammonium inhibition on the anammox process of the SNAD biofilm

The aim of the present work was to evaluate the anaerobic ammonium oxidation (anammox) activity of simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm with different substrate concentrations and pH values. Kaldnes rings taken from the SNAD biofilm reactor were incubated in batch tests to determine the anammox activity. Haldane model was applied to investigate the ammonium inhibition on anammox process. As for nitrite inhibition, the NH4+-N removal rate of anammox process remained 87.4% of the maximum rate with the NO2--N concentration of 100mg/L. Based on the results of Haldane model, no obvious difference in kinetic coefficients was observed under high or low free ammonia (FA) conditions, indicating that ammonium rather than FA was the true inhibitor for anammox process of SNAD biofilm. With the pH value of 7.0, the rmax, Ks and KI of ammonium were 0.209kg NO2--N/kg VSS/day, 9.5mg/L and 422mg/L, respectively. The suitable pH ranges for anammox process were 5.0 to 9.0. These results indicate that the SNAD biofilm performs excellent tolerance to adverse conditions.

Influence, equilibrium, thermodynamic and kinetic investigations on adsorption of 17 beta-estradiol by anaerobic granule sludge

The effects of adsorbate concentration, adsorbent concentration, temperature, pH, and ion strength on the 17beta-estradiol (E2) adsorption process by anaerobic granular sludge (AnGS) were investigated in this study. The adsorption process was analyzed according to adsorption isotherm, adsorption thermodynamics and adsorption kinetics. It was found that E2 was quickly and effectively adsorbed by AnGS. The adsorption capacity and adsorption removal efficiency of E2 increased as E2 concentration increased, and decreased as AnGS concentration increased. Low temperature, low pH, and low ionic strength promoted E2 adsorption by AnGS. The Freundlich absorption isotherm accurately described the E2 adsorption equilibrium process by AnGS and the pseudo-second-order model accurately described the adsorption kinetics. The overall adsorption process of E2 by AnGS was a physical adsorption process of spontaneous heat release controlled both by film diffusion and intraparticle diffusion.

Collaborative effect of secondary chlorination and organic matter content on biological safety in secondary water supply system

Biofilm in secondary water supply system (SWSS) may reduce the biological safety of tap water. This study focused on the collaborative effect of secondary chlorination and organic matter content on the regrowth of biofilm bacteria and the diversity of microbial community in lab scale SWSS. Several biofilms cultivated in the same condition were used for secondary chlorination under different organic matter content and chlorination dose conditions. Bacteria regrowth yield under the highest organic matter content and the lowest free residual chlorine (FRC) condition was 2.84–3.11 times of that under the lowest organic matter content and the highest FRC condition. The collaborative effect ratio of organic matter content increase (per 1.00 mg/L) and secondary chlorination decrease (per 0.10 mg/L as Cl2) was 0.99. Metagenomic sequencing was used to analyze the biofilm microbial community diversity in this experiment. Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes were the four major phyla of biofilm microbial communities. Proteobacteria presented significant increase after secondary chlorination in both high and low organic matter contents. The phylum Bacteroidetes was found to be dominant in beakers with high organic matter content while Actinobacteria was the most in beakers with low organic matter content. Firmicutes could almost be controlled by secondary chlorination with the dose more than 0.10 mg/L as Cl2.