[Removal of Humic Acid from Water Using Pt/biochar Electrode Reactor].

A Pt/biochar electrode reactor was developed to remove humic acid in water. The removal efficiency and characteristics of the reactor were investigated. Experimental results showed that Pt/biochar electrode reactor obtained 74.58% removal rate after 300 min reaction under current density of 20 mA·cm-2. The removal rate was increased by 58.3% comparing with 47.10% removal rate achieved by Pt/graphite electrode reactor. Electrochemical oxidation and air floating played the main roles in removal of humic acid from water. The improved removal efficiency of humic acid in Pt/biochar electrode reactor was attributed to the fact that the biochar cathode could produce more H2O2 than graphite cathode. Three-dimensional excitation emission matrix fluorescence spectroscopy and Gel permeation chromatography measurement revealed that Pt/biochar electrode reactor had strong oxidation capability to mineralize the low molecular weight humic acid directly. It suggests that biochar could be use as an innovative cathode material of electrode reactor for organic pollutants treatment in water.

[Studies of Dynamic Adsorption Behavior of VOCs on Biochar Modified by Ultraviolet Irradiation].

Coconut shell based biochar was modified by ultraviolet irradiation with UV light at a wavelength of 365 nm in order to enhance the adsorption capacity for volatile organic compounds (VOCs). The breakthrough curves of biochars for adsorbing two typical VOCs (benzene and toluene) were examined. The results showed that the adsorption capacity of modified biochar was greatly increased. The saturation adsorption capacity of modified biochar for benzene and toluene was increased to 122.80 mg·g-1 and 236.36 mg·g-1, comparing to that of the pristine biochar (7.27 mg·g-1 and 7.98 mg·g-1, respectively). The breakthrough time of modified biochar for benzene and toluene (390 min and 620 min) was also drastically prolonged as compared to the raw biochar (1 min and 2 min). The characterization analysis of biochars suggested that the carboxylic groups and external surface area were largely enriched, which might be the main factor responsible for the enhanced adsorption of the two VOCs on the modified biochar. The processes of adsorbing benzene and toluene at different concentrations on modified biochar were fitted by Yoon-Nelson, Thomas and BDST models. The result demonstrated that these three models could provide good fitting and the correlation coefficients were all above 0.992. The TG-DTG result proved that ultraviolet irradiation had little effect on the thermal stability of biochar. The modified biochar after adsorption saturation could be reused after thermal regeneration and the regenerated char also had high adsorption capacity after five times of repeated utilization.

Effect of the mixing ratio during co-treatment of landfill leachate and sewage with a combined stripping and reversed A²/O process.

In this study, pilot-scale tests were conducted to evaluate the effect of volumetric mixing ratio of landfill leachate to sewage on the performance of the combined ammonia stripping and reversed anaerobic/anoxic/oxic (A(2)/O) process for co-treatment of landfill leachate and municipal sewage. Stripping, as pre-treatment, could significantly remove ammonia nitrogen (NH3-N) and total nitrogen (TN) by 55% and 52%, respectively. Moreover, chemical oxygen demand (COD) was slightly reduced by 6.8%, and little total phosphorus (TP) was removed. The subsequent reversed A(2)/O process appeared to be highly influenced by the volumetric mixing ratio of leachate to sewage. Typically, the effluent COD, NH3-N, TN and TP increased with the increasing ratio from 1:30 to 1:15, namely, the increasing fraction of leachate. Over the all tested mixing ratio range, the effluent COD and NH3-N were satisfied with the primary B standards of Chinese Discharge Standard of Pollutants for municipal waste water treatment plant (GB18918-2002). The standards different from the primary A standards for water reuse are used for discharge into the most surface water bodies in China. However, TN and TP would exceed the primary B standard levels at a mixing ratio of 1:15 or greater. These findings suggest that an appropriate volumetric mixing ratio should be carefully selected to ensure the performance of the reversed A(2)/O process.

[Spectra analysis of dissolved organic matter in pretreatment process of leachate treated by reverse osmosis].

In order to examine the removal of organic matter in the leachate which results in reverse osmosis (RO) membrane fouling, and to provides a reference to select appropriate pretreatment processes of RO, synchronous-scan fluorescence, three-dimensional excitation emission matrix fluorescence spectroscopic and UV-Vis spectrum of the dissolved organic matter (DOM) in different molecular weight range in effluent from each leachate process of "biochemical (UASB+A/O)and UF" pretreatment in some incineration plant were examined. The results of synchronous fluorescence spectra analysis showed that DOM in the wavelength range of 250-320 nm with all the molecular weight and in the wavelength>320 nm with molecular weight>1 KDa was removed obviously by the pretreatment processes. The results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the pretreatment processes removed low-excitation wavelength tyrosinelike, low-excitation wavelength tryptophan-like and high-excitation wavelength tryptophan-like with all the molecular weight off, and fulvic-like matter and high-excitation wave length tyrosine-like with molecular weight>1 KDa effectively. The results of UV-Vis spectra analysis showed that the pretreatment processes removed DOM of molecular weight>1 KDa with pi-pi transition and DOM of all molecular weight with conjugated system of the benzene ring structure. It was concluded that the removal of both fulvic-like matter and high-excitation wave length tyrosine-like with the wavelength>320 nm, molecular weight<1 KDa and with pi-pi transition should be strengthened for controlling (RO) membrane fouling, when leachate was treated by RO with the pretreatment processes of "biochemical(UASB+A/O)and UF".

[Mechanism of Cr( VI) removal from aqueous solution using biochar promoted by humic acid].

Biochar derived from excess sludge was used for hexavalent chromium [Cr( VI)] removal from water as a sorbent, and impacts of co-existing humic acid on performance of Cr( VI) sorption onto biochar were studied. The experimental results indicated that humic acid facilitated biochar adsorption of Cr(VI), which enhanced capacity of Cr sorption and shortened reaction time reaching equilibrium remarkably. The sorption kinetic process could be described with the pseudo second order model. On the condition of initial pH 4.0, biochar concentration 20 g x L(-1), initial concentration of Cr(VI) in the range of 50-800 mg x L(-1), the Langmuir model fitted adsorption isotherm better than the Freudlich model. The Langmuir Q0 values of biochar with and without existing humic acid were 10.10 mg x g(-1) and 5.56 mg x g(-1), respectively. In the pH range of 2.0-8.0, sorption capacity of all sorbents decreased with increasing initial pH value. Ascending concentration of humic acid in solution promoted sorption capacity of biochar. Fourier transform infrared spectroscopy (FTIR) analysis showed that hydroxyl, carboxyl, ester, aromatic C-H stretch and ring C=C on the biochar were responsible for Cr(VI) sorption. Combined with X-ray photoelectron spectroscopy (XPS) analysis, mechanism of promoting Cr( VI) sorption onto biochar was speculated that humic acid enhanced concentration of Cr( VI) ions aggregating on the surface of biochar and benefited Cr(VI) adsorption coupled with subsequent reduction by biochar functional groups. Meanwhile, humic acid also increased amount of Cr(VI) and Cr(II) removal from aqueous solution.

[Fluorescence of early stage leachates DOM using RO membrane as tertiary treatment].

In the present study, fluorescence spectra of the dissolved organic matter (DOM) extracted from early stage leachate samples obtained from biologically pretreated leachate fed to RO tertiary treatment, the permeated, the concentrate, and liquids collected after cleaning the membrane with acid and then with base were determined. The results of synchronous fluorescence spectra analysis showed the RO membrane effectively removed the high content of organic matter corresponding to short wavelengths of 280, 340, and 370 nm of the feed. Liquids collected after cleaning membrane with acid and base showed obvious influence on the organic pollutant matters in the range of 300-420 nm. The results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed three protein-like peaks, namely low-excitation wavelength, tyrosine-like high-excitation wavelength, tyrosine-like high-excitation wavelength, tryptophan-like and two fulvic-like peaks, visible and ultra visible fulvic-like were found in the feed. The permeated contains two peaks with higher intensity than the feed, low-excitation wavelength tyrosine-like and high excitation wavelength tyrosine-like, while the other three peaks were shown in the concentrate. The acid and the base cleaning had great influence on the molecule chemical structure of the organic pollutants on the RO membrane and caused obvious location shifts. It can be concluded that the RO mainly separated the fulvic matter in the early stage leachate and the fouling consisted of fulvic-like matter together with the protein-like, and low-excitation wavelength tyrosine-like.

[Various effects on the activity of activated sludge by low intensity ultrasonic treatments with different parameter combinations].

Aerobic activated sludge was used as experimental material. Specific oxygen uptake rate (SOUR), mixed liquor suspended solids (MLSS), COD ratio and lambda (deltaMLSS/deltaCOD) were taken as experimental indexes to indicate the changes of sludge activity and metabolism. The influences on activated sludge induced by ultrasonic treatments with different parameter combinations were studied by equal-distribution experiments about frequency, ultrasound intensity and irradiation time. The results indicated that the best parameter combination (28 kHz, 20 W/L, 2 min) leaded to an evident enhancement of sludge activity and reduced the sludge production at the same time. MLSS, as a vital factor which influences the ultrasonic treatment, was concerned in this study. To the sludge used in these experiments, the results of multilevel experiments showed that the MLSS of 3 000 mg/L induced to a relative highest performance after ultrasonic treatment with the best parameter combination. This article also hypothetically presented the mechanism of sludge activity enhancement stimulated by low intensity ultrasound.