Degradation characteristics of refractory organic matter in naproxen pharmaceutical secondary effluent using vacuum ultraviolet-ozone treatment.

Vacuum ultraviolet-ozone (VUV-O3) treatment was found to be superior to ultraviolet-ozone (UV-O3) treatment in terms of ozone utilization and hydroxyl radicals (·OH) generation when used to treat the secondary effluent (SE) from a naproxen pharmaceutical plant. VUV-O3 treatment was beneficial in terms of decolorization (100%), chemical oxygen demand removal (43.29%), and total organic carbon removal (54.81%). The VUV-O3 process was applicable over a wide pH range, and the presence of various anions had no significant influence on the oxidation efficiency. After treatment, the genotoxicity, unsaturation degree, and polarity of the SE decreased. In addition, the oxidation sensitivities of the fluorescent organic compounds were ranked as follows: humic acid-like > tyrosine-like > fulvic acid-like > tryptophan-like Moreover, the VUV-O3 process effectively converted refractory organic matter (molecular weights, MW > 2000 Da) into short-chain molecules with low MWs. The removal efficiency of dissolved organic matter (DOM) was 63.27%, and 77.27% of the DOM was found to be reactive to VUV-O3 oxidation. The unsaturation, polarity, and compositional complexity of the DOM decreased after VUV-O3 treatment. Finally, it was deduced that the direct O3 oxidation,·OH, O2·- and 1O2 played a role in the VUV-O3 oxidation process.

Enhanced dewaterability of lake dredged sediments by electrochemical oxidation of peroxydisulfate on BDD anode.

Dredged sediments, as a product of mitigating endogenous pollution of rivers and lakes, cause severe environmental pollution without suitable disposal. To reduce dredged sediments, the electrochemical oxidation (EO) of peroxydisulfate (PS) on a boron-doped diamond (BDD) anode (EO/BDD-PS) was utilized to enhance the dewaterability of the dredged sediments. The soluble chemical oxygen demand increased in the EO/BDD-PS system, and more than 70.0% of the specific resistance to filtration was reduced by EO/BDD-PS within 20 min. The optimal conditions were determined to be as follows: current density, 30 mA cm-2; PS dosage 4 g L-1; and initial pH, 6.96. After treatment with EO/BDD-PS, the electronegativity of the sludge flocs was alleviated and the particle size increased from 7.61 to 10.64 µm. Furthermore, proteins and polysaccharides were degraded, and tightly bound extracellular polymeric substances (TB-EPS) and loosely bound EPS (LB-EPS) were effectively transported to soluble EPS (S-EPS). Furthermore, humification of organic matter occurred in S-EPS and LB-EPS when the dredged sediment was treated with EO/BDD-PS. Dominant hydroxyl radicals (•OH) and sulfate radicals (SO4•-) were generated in the EO/BDD-PS system. Moreover, the efficiency of the filtrate as an electrolyte decreased slightly after recycling five times. Therefore, this method may be economical for enhancing the dewaterability of dredged sediments.

Enhancing nitrate removal efficiency of micro-sized zero-valent iron by chitosan gel balls encapsulating.

The activity of micro-sized zero-valent iron (MZVI) material for nitrate removal in neutral pH and low C/N ratios water needs to be improved. In this study, micro-sized zero-valent iron@chitosan (MZVI@CS) material was synthesized through embedding MZVI particles into chitosan (CS) gel by sol-gel method, and was used for deep removal of NO3--N in the absence of organic carbon sources and neutral pH. The NO3--N removal rate of MZVI@CS was 0.37 mg-N·L-1·d-1 (dosage of 1%, initial pH = 7, 25 °C, initial nitrate concentration = 15 mg-N·L-1), which was 11.33 times higher than that of MZVI. The apparent activation energy (Ea) of MZVI@CS with nitrate was 38.23 kJ·mol-1. MZVI@CS can remove nitrate effectively at a low concentration (15 mg-N·L-1). A stable denitration rate (0.37-2.28 mg-N·L-1·d-1) could be maintained under weak acidic, neutral and alkaline conditions (pH = 5-9). More than 80% of reduced nitrate was converted to N2, and only a small amount was converted to NH4+ or NO2-. The gel structure of MZVI@CS eliminated the agglomeration between MZVI particles while the forming of Fe-CS chelates reduced the formation of iron oxide and solved the problems of passivation, hence successfully strengthened the NO3--N removal efficiency of MZVI. Therefore MZVI@CS has great application potential in NO3--N deep removal of water bodies with neutral pH and low C/N ratios.

Metagenomic analysis reveals that activated carbon aids anaerobic digestion of raw incineration leachate by promoting direct interspecies electron transfer.

The raw fresh leachate from municipal solid waste (MSW) incineration plants contains high concentrations of volatile fatty acids (VFAs), ammonia and metals, all compounds that severely limit anaerobic digestion treatment efficiencies. These inhibitory compounds make reactor systems unstable, causing reactor start-up periods to take more than 100 days, even when the leachate is diluted significantly. In this study, granular activated carbon (GAC) was incorporated into a bioreactor fed with raw incineration leachate. Addition of GAC allowed direct treatment of raw incineration leachate without any start-up acclimation period, while the non-amended control reactor soured immediately and collapsed within 17 days. When hydraulic retention time (HRT) of the GAC-amended reactor was stepwise decreased to increase organic loading rates (OLR) to 25.0 kgCOD/(m3·d), COD removal efficiencies remained stable at >90%. Metagenomic analysis of the GAC-amended reactor revealed that Geobacter and Methanosarcina, species known to participate in direct interspecies electron transfer (DIET), were more abundant in the GAC-amended reactor than the seed sludge. In addition, the abundance of genes coding for proteins thought to be involved in DIET such as electrically conductive pili and the outer membrane c-type cytochrome, OmcS, increased significantly, while genes involved in fermentation, and nitrate (narG) and sulfate (dsrA) reduction dropped significantly as the experiment progressed. These results are significant because this is the first detailed investigation into the metabolic capabilities of microbial communities involved in efficient treatment of raw incineration leachate within biomethanogenic reactors that did not require a long start-up period.