Yanzhuo Zhang

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.

Achieving nitritation in a continuous moving bed biofilm reactor at different temperatures through ratio control.

A ratio control strategy was implemented in a continuous moving bed biofilm reactor (MBBR) to investigate the response to different temperatures. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and total ammonia nitrogen (TAN) concentrations. The results revealed that a stable nitritation in a biofilm reactor could be achieved via ratio control, which compensated the negative influence of low temperatures by stronger oxygen-limiting conditions. Even with a temperature as low as 6°C, stable nitritation could be achieved when the controlling ratio did not exceed 0.17. Oxygen-limiting conditions in the biofilm reactor were determined by the DO/TAN concentrations ratio, instead of the mere DO concentration. This ratio control strategy allowed the achievement of stable nitritation without complete wash-out of NOB from the reactor. Through the ratio control strategy full nitritation of sidestream wastewater was allowed; however, for mainstream wastewater, only partial nitritation was recommended.

Effect of particle size on removal of sunset yellow from aqueous solution by chitosan modified diatomite in a fixed bed column

This study investigated how the particle size of the modified adsorbent diatomite earth & chitosan (DE&C) affects the removal of sunset yellow (SY) from water using a fixed bed column. Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the amino group (–NH2) played an important role during the adsorption of SY. The calculated surface area of the DE&C absorbent was found to be 69.68 m2 g−1 and SEM images showed that DE&C is a superior porous adsorbent. Four dimensions of DE&C were measured in a fixed bed column. The breakthrough time of SY increased as the size of DE&C decreased and the effluent concentration showed a trend of first increasing and then decreasing. It was also found that the nature of the variation in the effluent concentration with time was parabolic and that the adsorption data fitted the parabolic equation at Ct/C0 = 0–0.1. Due to the different combination ability with hydrogen bonding, the phenomenon of parabolic variation is quite disparate from other adsorbents. But, compared with the breakthrough time, the saturation time was close to other particle sizes, except for 2.86–3.35 mm in size. pH is an important parameter for the adsorption of SY and the main mechanism is adsorption with each other between positive and negative charges. The Thomas model shows lower correlation with the smaller sizes and R2 with an average of 0.9413. The Thomas model indicated that the maximum value of q0 was 97.06 mg g−1 and with an increase in the initial SY concentration, the bed height and the values of q0 decreased as kt increased. The Yoon–Nelson model describing the theoretical required time was close to the experimental values and kYN increased as C0 increased.

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.

Efficient removal of crystal violet by diatomite and carbon in the fixed bed column: influence of different glucose/diatomite

This study investigated the way in which the modified adsorbent diatomite earth and glucose (DE & C) content affects the removal of crystal violet (CV) from water using a fixed bed column during hydrothermal carbonization. Fourier transform infrared spectroscopy results demonstrated the importance of functional groups (carbonyl and amino) during CV adsorption. The calculations showed the particle strength of DE & C was excellent. Scanning electron microscope images, energy dispersive spectrometry, Brunauer–Emmett–Teller analysis and Barrett–Joyner–Halenda analysis showed where the carbon species and pore structure provided highly favorable adsorption conditions. These characteristics indicated that DE & C is an excellent porous adsorbent. Five different levels of glucose content in the DE & C were tested in the fixed bed column. Because of differences in adsorption capacity, as the breakthrough time increased, the trend line changed from a straight line to an arc at Ct/C0 = 0–0.1. The best adsorption capacity was reflected by the related breakthrough time, but there was little change between different saturation times. Based on the calculated data, the optimal glucose/diatomite ratio was found to be 6/5, where the excessive carbon molecules blocked adsorbent bind sites in the sample. The Thomas model was used to determine the kinetics of CV column adsorption. When the CV concentration was 200 mg L−1, the flow rate was 7.5 mL min−1, the height was 5 cm, and the Thomas model showed that the maximum adsorption capacity (q0) was 87.05 mg g−1. Disparities in the slopes of the bed depth service time (BDST) models showed that the initial adsorption efficiency was better than the later adsorption on the DE & C. The column packing was viable for five adsorption–elution cycles.