Adsorption removal of tetracycline from aqueous solution by anaerobic granular sludge: equilibrium and kinetic studies.

High concentration animal wastewater is often contaminated by tetracycline and an upflow anaerobic sludge bioreactor (UASB) with granular sludge is often used to treat the wastewater. The investigation of the adsorption process of tetracycline on anaerobic granular sludge during anaerobic digestion of animal wastewater will increase the understanding of antibiotics behavior in the UASB reactor. In this study, the effects of initial pH, humic acid concentration, and temperature on the removal of tetracycline by anaerobic granular sludge from aqueous solution were investigated using the batch adsorption technique in 100 mL flasks with 75 mL of work volume. The results show that the highest removal efficiency of 93.0% was achieved around pH 3.0 and the removal efficiency at the neutral pH range (pH 6.0-8.0) is about 91.5%. The thermodynamic analysis indicates that the adsorption is a spontaneous and endothermic process. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms analysis indicates that the Langmuir model is better than the Freundlich model for the description of the adsorption process and confirms the result of thermodynamics analysis. The maximum adsorption capacities were 2.984, 4.108 and 4.618 mg/g at 25, 35 and 45 °C, respectively. These results provide useful information for understanding the fate and transformation of tetracycline in a UASB digestion system and improving the management of tetracycline contaminated animal wastewater.

[Effect of substrate concentration on pathogen indicators inactivation during thermophilic anaerobic digestion].

Because excess sludge contains high density of pathogens, it has to be treated to reduce pathogens before being disposed for land application. In this study, the effect of substrate concentration on pathogen inactivation during thermophilic anaerobic digestion was investigated. The results show that, with the increase of substrate concentration, VFAs and cumulative methane production increased. The density of total coliforms in the suspension liquid has a 2.0-3.0 orders of magnitude decline and fecal coliforms has 1.8-3.3 orders of magnitude decline after 28 days thermophilic anaerobic digestion at substrate concentration of 28-84 g x L(-1) and temperature of 55 degrees C. More than 99% of total coliforms and fecal coliforms have been killed after 28 days digestion. Salmonella spp. was not detected in the suspension and solid after anaerobic digestion. When substrate concentration was higher than 45 g x L(-1), the inactivation of total coliforms and fecal coliforms declined.

Adsorption of roxarsone from aqueous solution by multi-walled carbon nanotubes.

Roxarsone, an organoarsenic compound serving as a common feeding additive in poultry industry, brings about potential risk of the toxic inorganic arsenate contamination in ambient environment. Current understanding in the dynamics of roxarsone removal and the determining environmental processes remains unclear, thus restricts the progress in roxarsone-contaminated wastewater treatment. In this study, the adsorption of roxarsone on multi-walled carbon nanotubes (MWCNTs) was investigated. The adsorption of roxarsone on MWCNTs decreased dramatically with increasing pH from 2.0 to 11.7 and decreased significantly with increasing ionic strength from 0 to 1.0 mol/L KCl. It was found that the sorption isotherms of roxarsone on MWCNTs were nonlinear, which can be well described according to the Freundlich and Polanyi-Manes models. Thermodynamic analysis indicates that the adsorption of roxarsone on MWCNTs is an exothermic and spontaneous process. Sorption site energy analysis reveals a distribution of sorption energy and the heterogeneous adsorption sites of roxarsone on MWCNTs. The dynamic adsorption with column shows the potential of the practical application for the roxarsone-contaminated wastewater treatment by MWCNTs. The FTIR analysis indicates that EDA interaction and electrostatic repulsion might be the dominant mechanisms for the adsorption of roxarsone on MWCNTs.

[Anaerobic digestion of animal manure contaminated by tetracyclines].

Anaerobic digestion of pig manure spiked with tetracycline (TC) and chlortetracycline (CTC) and the degradation of the two antibiotics during the anaerobic digestion at 35 degrees C were investigated. The results indicate that propionate was the main volatile fatty acid produced during the anaerobic digestion followed by acetate. Compared with the CTC addition, TC + CTC addition showed obvious inhibitory effect on the hydrolysis and acidification of easily digestible organic components of pig manure. The cumulative methane production of TC, CTC, TC + CTC and CK2 during anaerobic digestion was 386.4 mL, 406.0 mL, 412.1 mL and 464.6 mL, respectively. Degradation of TC and CTC followed the first-order kinetic equation. The half-life of TC and CTC was 14-18 days and 10 days, respectively. After the treatment of 45-day anaerobic digestion, the degradation efficiency of TC was 88.6%-91.6% with 97.7%-98.2% of CTC. Therefore, anaerobic digestion shows the benefit on the management of animal manures contaminated by tetracyclines.