Artificial Sweetener Enhances the Spread of Antibiotic Resistance Genes During Anaerobic Digestion.

Artificial sweeteners have been frequently detected in the feedstocks of anaerobic digestion. As these sweeteners can lead to the shift of anaerobic microbiota in the gut similar to that caused by antibiotics, we hypothesize that they may have an antibiotic-like impact on antibiotic resistance genes (ARGs) in anaerobic digestion. However, current understanding on this topic is scarce. This investigation aimed to examine the potential impact of acesulfame, a typical artificial sweetener, on ARGs in anaerobic digestion by using metagenomics sequencing and qPCR. It was found that acesulfame increased the number of detected ARG classes and the abundance of ARGs during anaerobic digestion. The abundance of typical mobile genetic elements (MGEs) and the number of potential hosts of ARGs also increased under acesulfame exposure, suggesting the enhanced potential of horizontal gene transfer of ARGs, which was further confirmed by the correlation analysis between absolute abundances of the targeted ARGs and MGEs. The increased horizontal dissemination of ARGs may be associated with the SOS response induced by the increased ROS production, and the increased cellular membrane permeability. These findings indicate that artificial sweeteners may accelerate ARG spread through digestate disposal, thus corresponding strategies should be considered to prevent potential risks in practice.

UV-C irradiation for harmful algal blooms control: A literature review on effectiveness, mechanisms, influencing factors and facilities.

UV-C irradiation has drawn much attention in recent years as a candidate for controlling harmful algal blooms (HABs). In this review, we have collated the recent knowledge about the UV-C irradiation technique for suppressing HABs, including the effectiveness, mechanisms, influencing factors, growth recovery pattern, and UV-C irradiation facilities. Most microalgal species have been proved to be effectively suppressed by UV-C irradiation and the suppression effects had positive correlation with UV-C dose. However, the effectiveness on difference algal species varied dramatically. The understanding for growth suppression mechanisms upon UV-C irradiation has been significantly deepened beyond pyrimidine dimers. The suppression effects on algal cell density were the results of UV-induced damage on nucleic acid, light harvesting and electron transfer and transportation, nitrogen fixation and assimilation, toxin synthesis, settle ability, antioxidative capacity and cellular membrane integrity. While several influencing factors, such as algal sensitivities, UV transmittance (UVT), salinity, pH, and microalgal growth recovery should be paid attention to in practical application. UV-C facilities with high maturity, especially flow-through reactors, make it possible to develop ship-born UV-C facilities and put UV-C irradiation technique into real practice on controlling HABs.

Electron donating capacity reduction of dissolved organic matter by solar irradiation reduces the cytotoxicity formation potential during wastewater chlorination.

After treated wastewater is discharged into surface water for unplanned indirect potable reuse, solar irradiation transforms the dissolved organic matter (DOM), which would alter the formation of disinfection byproducts (DBPs) and change the cytotoxicity formation potential (CtFP) during post-chlorination in drinking water treatment plants. This study investigated the effects of solar irradiation on the CtFP and total organic halogen formation potential (TOXFP) of wastewater during post-chlorination. Exposure to natural sunlight decreased the formation potential of cytotoxicity to Chinese Hamster Ovary cells. Under 24 h simulated solar irradiation, CtFP and TOXFP decreased by more than 40%. X-ray photoelectron spectra and Fourier transformation infrared spectra suggested solar irradiation destroyed the key DBP precursors containing phenolic hydroxyl moieties (Ph-OH). The destruction of Ph-OH under solar irradiation was reflected by a decrease in the electron donating capacity (EDC) of DOM and the post-chlorination decreased the EDC further. Increasing the irradiation-consumed EDC abated the chlorine-consumed EDC, while the chlorine-consumed EDC was positively correlated to the CtFP and TOXFP by means of the electrophilic substitution-aromatic ring cleavage. Solar irradiation thus reduced the CtFP and TOXFP in wastewater during post-chlorination. This study revealed that solar irradiation decreased the risks of treated wastewater for unplanned indirect potable reuse and provided a strategy of controlling CtFP and TOXFP via reducing EDC of DOM in pretreatments.

[Stability of Short-cut Nitrification Nitrogen Removal in Digested Piggery Wastewater with an Intermittently Aerated Sequencing Batch Reactor].

Stability of short-cut nitrification nitrogen removal performance was studied in a step-feeding, intermittently aerated sequencing batch reactor (IASBR) at 30°C to treat digested piggery wastewater. Results showed that the nitrogen removal was greatly influenced by the ratio of chemical oxygen demand (COD) to total nitrogen (TN) in the influent. Nitrite nitrogen kept accumulating up to 800 mg · L⁻1 when the influent COD/TN ratio was 0.8 ± 0.2, and the removal rates of TN, ammonium nitrogen and total organic carbon (TOC) were only 18.3% ± 12.2%, 84.2% ± 10.3% and 60.7% ± 10.7%, respectively. By contrast, as the influent COD/ TN ratio was increased to 2.4 ± 0.5, the accumulated concentration of nitrite nitrogen sharply decreased from 800 mg · L⁻¹ to below 10 mg-L⁻¹, and the removal rates of TN, ammonium nitrogen and TOC were increased to over 90%, 95% and 85%, respectively. Gradually shortened hydraulic retention time ( HRT) reveales that the ammonia load is a restricting factor for nitrogen removal. The ammonia load should be controlled at no more than 0.30 kg · (m³ · d) ⁻¹, or else, the removal rates of TN, ammonium and TOC would be greatly decreased. The nitrite accumulation rate over the whole run was 74.6%-97.8% and the TN removal rate in the stable phase was over 90%. With efficient and stable short-cut nitrification-denitrification in a low COD/TN, moreover, and unnecessary for addition of alkaline, IASBR shows great advantage for treating wastewater with high concentration of ammonia while low COD/TN ratio.

Biofilm growth and characteristics in an alternating pumped sequencing batch biofilm reactor (APSBBR).

A novel biofilm reactor-alternating pumped sequencing batch biofilm reactor (APSBBR)-was developed to treat synthetic dairy wastewater at a volumetric chemical oxygen demand (COD) loading rate of 487 g COD m(-3) d(-1) and an areal loading rate of 5.4 g COD m(-2) d(-1). This biofilm reactor comprised two tanks, Tanks 1 and 2, with two identical plastic biofilm modules in each tank. The maximum volume of bulk fluid in the two-tank reactor was the volume of one tank. The APSBBR was operated as a sequencing batch biofilm reactor with five operational phases-fill (25 min), anoxic (9 h), aerobic (9 h), settle (6 h) and draw (5 min). The fill, anoxic, settle and draw phases occurred in Tank 1. In the aerobic phase, the wastewater was circulated between the two tanks with centrifugal pumps and aeration was mainly achieved through oxygen absorption by micro-organisms in the biofilms when they were exposed to the air. In this paper, the biofilm growth and characteristics in the APSBBR were studied in a 98-day laboratory-scale experiment. During the course of the study, it was found that the biofilm thickness (delta) in Tank 1 ranged from 1.2 to 7.2 mm and that in Tank 2 from 0.5 to 2.2 mm; the biofilm growth against time (t) can be simulated as delta=0.07t0.99 (R2 = 0.97, P = 0.002) in Tank 1 and delta = 0.08t0.66 (R2 = 0.81, P = 0.04) in Tank 2. The biomass yield coefficient, Y, was 0.18 g volatile solids (VS) g(-1) COD removal. The biofilm density in both tanks, X, decreased as the biofilm thickness increased and can be correlated to the biofilm thickness, delta .

Effect of salinity variations on the performance of activated sludge system.

OBJECTIVE: To investigate the influence of salinity variations on the performance of activated sludge systems, treating domestic wastewater. METHODS: The completely mixed reactor was used and operated in a batch-wise mode. The activated sludge taken from the Gaobeidian Wastewater Treatment Plant was used as a seeding sludge. Total organic carbon (TOC), oxygen uptake rate (OUR) and suspended solids (SS) were used as parameters to characterize the performance of the treatment systems. TOC was measured using a TOC-analyzer (TOC-5000, Japan). The OUR value was measured with a dissolved oxygen meter (YSI model-58). SS was measured gravimetrically. RESULTS: The TOC removal efficiency and the OUR value of activated sludge were not deteriorated when the NaCl shock concentration was less than 0.5 g/L. However, when the NaCl shock concentrations were up to 10g/L and 20 g/L, the OUR of activated sludge was reduced by 35% and TOC removal efficiency was dropped by 30%, compared with the control experiment without NaCl shock loading. CONCLUSION: The effect of NaCl shock loading on the activated sludge wastewater treatment system is dependant upon the NaCl concentrations and the degree of influence can be inferred through the change of substrate utilization rate at different shock NaCl loadings.

Mixing characteristics and whey wastewater treatment of a novel moving anaerobic biofilm reactor.

A novel moving anaerobic biofilm reactor was used to treat whey wastewater. In this process, biofilm was grown on a plastic biofilm media module, which was vertically moved up and down in the bulk fluid. The objectives of the study were to investigate the mixing and performance characteristics of the new process in treating whey wastewater. The mixing efficiency was indicated by a dispersion number, D(L)/uL. D(L)/uL was up to 1.34, showing that the anaerobic reactor can be taken as a completely mixed reactor. At mesophilic conditions (35+/-2 degrees C), the admissible volumetric COD loading rate up to 11.6kg COD m(-3) day(-1) was achieved with the COD removal efficiency of 89% and the hydraulic retention time (HRT) of 1 day. When the HRT was 0.6 days, the volumetric COD loading rate was 15.2 kg COD m(-3) day(-1), but COD removal efficiency decreased to 81%. The percentage of methane (CH4) in the biogas was 63% on average and the yield of methane was 333.4 L CH4 kg(-1) COD removal at ambient conditions.

Biological nitrogen removal using a vertically moving biofilm system.

In this study, a biological nitrogen removal process using a vertically moving biofilm system was used to treat synthetic wastewater. The process consisted of two pre-denitrification units, one combined carbonaceous removal/nitrification unit and three nitrification units. Each unit employed biofilm growth on a plastic module. In the anoxic units, the modules were vertically moved, while always submerged, in the bulk fluid; in the aerobic units, they were moved vertically up into the air and down into the wastewater. Three small-scale experiments, having different recirculation ratios and influent loadings, were conducted at a controlled temperature of 11 degrees C. In this system, the carbonaceous removal efficiency was in the range of 94-96% and the total nitrogen removal efficiency was 77-82%. In the anoxic units, the denitrification efficiency was 94-98% and the areal denitrification rates, based on the surface area of the biofilm modules, were 2.9-3.8 g NO3-N/(m2 x d). The nitrification efficiency occurring in the aerobic tanks was up to 95% and the maximum areal ammonium removal rates were 1.3-1.8 g NH4-N/(m2 x d).

Ammonium removal using a vertically moving biofilm system.

Ammonium-nitrogen (NH4-N) removal using a vertically moving biofilm system was investigated at a temperature of 11 degrees C. The biofilms in this process were grown on biofilm modules, consisting of high surface area plastic media, which were vertically and repeatedly moved up into the air and down into the wastewater. The maximum NH4-N removal efficiency was up to 98.8% and the areal NH4-N removal rates, based on the surface area of the biofilm modules, were within the range of 0.68-1.94 g NH4-N m(-)2 day(-1). The kinetics of ammonium removal occurring after carbonaceous oxidation was completed can be simulated by using a zero-order empirical model. The ammonium removal rate was found to be proportional to the square root of the mass of biofilms on the modules. Monitoring DO concentrations in the bulk fluid showed that the vertically moving biofilm system possessed good aeration efficiency.

Mechanism of lead adsorption from aqueous solutions using an adsorbent synthesized from natural condensed tannin.

Adsorption is a method for removing lead from wastewater. The adsorption of lead on a new adsorbent synthesized from natural condensed tannin has been investigated using a series of batch adsorption experiments. The study on the adsorption mechanism indicates that the adsorbent performed in aqueous solutions as an ionic exchanger whose end group was sodium ion (Na(+)). One lead (II) ion (Pb(2+)) was adsorbed onto the adsorbent by taking the place of two Na(+) ions. The maximum exchangeable Na(+) present on the adsorbent was measured with the proton titration experiments and it was up to 1.0 mmol x Na(+)g(-1) dry adsorbent. To a significant extent, pH influenced the extraction of lead from aqueous solutions. The lead removal efficiency was up to 71%, 87% and 91% with initial solution pH at 3.0, 3.6 and 4.2, respectively. The Langmuir equation fitted the adsorption isotherm data well. The maximum adsorption capacity of lead calculated was 57.5, 76.9 and 114.9 mg lead g(-1) dry adsorbent at initial solution pH of 3.0, 3.6 and 4.2, respectively. Therefore, the adsorbent does offer favorable characteristics in lead removal from acidic wastewater.

Removal of lead from aqueous solutions by condensed tannin gel adsorbent.

Lead has caused serious environmental pollution due to its toxicity, accumulation in food chains and persistence in nature. In this paper, lead removal from aqueous solutions was investigated using condensed tannin gel adsorbent synthesized from a natural tannin compound. It is found that the adsorption is strongly affected by pH values of aqueous solutions. Within pH range of 3.5-6, when initial lead concentration is 100 mg/L, removal efficiency is more than 90%. Adsorption equilibrium is reached within 150 minutes. The adsorption isotherm fits well with the Langmuir equation, by which the saturated adsorption uptake of 190 mg Pri2+ /g dry tannin gel adsorbent is obtained. By means of thermodynanamics analysis, it is revealed that the process is exothermic and the adsorption heat is up to 38.4 kJ/mol. With respect to high efficiency, moderate pH requirement and minimized second pollution, the tannin gel adsorbent exhibits a promising potential in the removal of lead from wastewater.