Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives.

Diesel removal of contaminated soil by washing/flushing was enhanced with micro-bubbles and selected surfactants based on their solubilization properties and decontamination capacities. The influencing factors were studied to aim for increasing washing/flushing efficacy. The mixture solution of saponin and cyclodextrin increased the removal efficiency significantly compared to the single-agent solution flushing with an increasing range of 20%-31%. Meanwhile, micro-bubble enhancement increased over 20% of the diesel removal for the sandy soil flushing. As the flushing process may cause soil eroded, the TDS and soil solute in flushing solution were measured to evaluate the circulation time. The 90 min flushing time ensured the cleaning goal and reserved the soil solute by circulation flushing. The soil solute, especially the electron acceptor (NO3-) , was remained in the soil, which was highly demanded for residual diesel biodegradation of loam soil. It is concluded that mixed agents, circulation of flushing solution, and micro-bubbles increased the diesel removal, and the circulation flushing could be very promising in practical applications.

Electrochemical removal of RRX-3B in residual dyeing liquid with typical engineered carbonaceous cathodes.

Electro-catalytic activities of carbonaceous cathodes including graphite plate, graphite felt, carbon felt, activated carbon felt (ACF) and carbon fiber felt (CFF) for degradation of Reactive Red X-3B (RRX-3B) in residual dyeing liquid were compared. The best electrochemical performance was obtained using dimensional stable anode (DSA) and CFF cathode due to the higher capacity for electro-generation of H2O2 by selective two-electron oxygen reduction. The CFF/DSA electrolysis system realized 78.2% COD removal and complete decolorization over a wide pH range. The efficacy of RRX-3B degradation was found to be dependent on the nature of carbonaceous materials. Electrochemical measurements showed that CFF possessed higher electrochemical surface area and hydrogen evolution reaction over-potential. Furthermore, the intrinsic graphitic N in CFF was proved to be catalytic active site by DFT calculations. Reactive Red X-3B degradation intermediates with benzene structures and carboxylic acids via hydroxylation in RRX-3B oxidation were identified by GC-MS. It was found that S/Cl/N-containing groups in RRX-3B molecule were mineralized to SO42-, NO3- and Cl- ions in the electrolysis.

Simultaneously enhanced surfactant flushing of diesel contaminated soil column and qualified emission of effluent.

Seven surfactants were selected as candidate agents for in situ soil column flushing. Column flushing lacks the interaction between surfactants and contaminants, so efficiency is not easy to improve. Microbubbles generated in situ may adhere to the contaminant diesel. Thereafter, the bubbles were mobilized to lift the multi-system oil to the top layer. This process must be attributed to the increased column flushing efficiency of diesel removal. Compared with a single solution, using randomly methylated beta-cyclodextrin (RAMEB) and microbubble enhancement, the diesel removal of column flushing increased by 30.7%. Compared with the existing conditions (5.25 × 10-4 cm s-1), the hydraulic conductivity of loam soil (3.74 × 10-3 cm s-1) increased by 7.1 times after the continued operation of the two processes. The oil layer was collected for further reuse. After three treatments, the effluent for the RAMEB was more than 85%. The collected effluent was treated with a synthetic absorbent and then qualifiedly discharged with a TOC value of only 2.6 mg L-1. By combining surfactant flushing with microbubbles and other equipment, not only can the reaction time be effectively saved, but organic pollutants could be concentrated and reused in the soil, so no additional treatment was required.

Electrocatalytically active and charged natural chalcopyrite for nitrate-contaminated wastewater purification extended to energy storage Zn-NO3- battery.

Charged natural chalcopyrite (CuFeS2, Ncpy) was developed for a three-dimensional electrochemical nitrate reduction (3D ENO3-RR) system with carbon fiber cloth cathode and Ti/IrO2 anode and Zn-NO3- battery. The 3D ENO3-RR system with Ncpy particle electrodes (PEs) possessed superior nitrate removal of 95.6 % and N2 selectivity of 76 % with excellent reusability under a broad pH range of 2-13 involving heterogeneous and homogeneous radical mechanisms. The Zn-NO3- battery with Ncpy cathode delivered an open-circuit voltage of 1.03 V and a cycling stability over 210 h. It was found that Ncpy PEs functioned through self-oxidation, surface dynamic reconstruction (Cu1.02Fe1.0S1.72O1.66 to Cu0.61Fe1.0S0.27O2.98), intrinsic micro-electric field (CuI, S2- anodic and FeIII cathodic poles), and reactive species (•OH, SO4•-, 1O2, •O2- and •H) generation. Computational analyses reveal that CuFeS2(112) surface with the lowest surface energy preferentially exposes Fe and Cu atoms. Cu site is beneficial for reducing NO3- to NO2-, Fe and Fe-Cu dual sites are conducive to N2 selectivity, lowering the overall reaction barriers. It paves the way for selective NO3- reduction in wastewater treatment and can be further extended to energy storage devices by utilizing low-cost Ncpy.

Insight into Cu (II) adsorption on pyrochar and hydrochar resultant from Acacia Senegal waste for wastewater decontamination.

Acacia Senegal waste (ASW) is remaining biomass following gum Arabic harvesting and has no use mentioned in the literature as of yet. This study aims to convert ASW into valuable biochar via two comparative thermal and hydrothermal techniques, which include pyrochar ASW at 300 °C (PC ASW300) and hydrochar ASW at 180 °C (HC ASW180), respectively, for Cu (II) adsorption from aqueous solutions. SEM-EDS, FTIR, XRD, and XPS were used to characterize the biochar. Adsorption performance was studied as a function of pH, contact time, and adsorbent concentration. Adsorption kinetics were best fit for a pseudo-second-order model. And thermodynamics studies revealed that Cu (II) on biochar was endothermic, spontaneous, and best fitted to the Langmuir isotherm model. Pyrochar adsorption capacity (31.93 mg g-1) was seven times that of hydrochar (5.45 mg g-1). ASW treated with phosphorus (PC H3PO4 and HC H3PO4) prior to the carbonization altered the pore structure and surface functional groups as well (O-P-O, P-CH3, and P-OH) of biochar. It was found that treating with phosphorous acid increased adsorption capacity to 141.7 mg g-1 and 22.24 mg g-1 for PC H3PO4 and HC H3PO4, respectively. The surface functional groups of biochar resulted from lignin, alkaloids, and polysaccharides combined with Cu (II) during the adsorption process via surface complexation accompanied by π-electron interaction and Cu (II) reduction. These findings shed light on the ASW biochar potential as a new green cost-effective adsorbent and drew an insightful understanding of Cu (II) adsorption performance and mechanism. It is concluded that ASW-derived biochar is highly effective and a promising alternative for Cu (II) decontamination from wastewater.

Decreased transport of nano- and micro-plastics in the presence of low-molecular-weight organic acids in saturated quartz sand.

Low-molecular-weight organic acids (LMWOAs) and nano- and micro-plastics (NPs and MPs) are both widely distributed in terrestrial systems. To better understand the influence of LMWOAs on the transport of NPs and MPs, the effects of 0.5 mM citric- (CA), malic- (MA), and tartaric- (TA) acid on the transport of nano- (0.51 µm, PS NPs) and micro- (1.1 µm, PS MPs) polystyrene particles (2 mg L-1) in saturated quartz sand were investigated. All three LMWOAs decreased the transport of PS NPs and MPs, regardless of ionic composition or strength (0.1-10 mM NaCl and 0.1-1 mM CaCl2). Further investigation revealed that the interfacial interactions between PS-quartz sand surfaces and PS-PS were altered by LMWOAs. LMWOAs adsorbed to quartz sand surfaces could serve as new deposition sites, as evidenced by the decreased transport of PS NPs and MPs in quartz sand that was subjected to pre-equilibration with selected MA, the low inhibition of PS transport with low concentrations of LMWOAs (0.1 mM), and also the adsorption of LMWOAs onto quartz sand surfaces by batch experiments. Meanwhile, the adsorption of LMWOAs on PS, hydrodynamic measurement and visual TEM observation together clarified the slight aggregation of PS NPs and MPs in suspensions, inducing the subsequent decrease in transport. Among them, the adsorption of LMWOAs onto quartz sand surfaces was found to be the main factor dominating the decreased transport of both PS NPs and MPs in saturated quartz sand.

Catalytic activity and mechanism of typical iron-based catalysts for Fenton-like oxidation.

Heterogeneous Fenton-like systems were exploited for the degradation of Reactive Red X-3B (RR X-3B) using iron-carbon composite, sponge iron, chalcopyrite and pyrite as catalysts. The effect of operational variables on the catalytic activity and metal leaching behavior of catalysts was evaluated and the catalytic mechanism was discussed. The experimental results showed that under the optimum conditions, chemical oxygen demand (COD) removals by Fenton-like systems could reach 89.91%, 86.84%, 80.11% and 60.02% with iron-carbon composite, sponge iron, chalcopyrite and pyrite, respectively. Micro-electrolysis of iron-carbon composite and sponge iron resulted in higher COD removal at acid pH range. Electron Paramagnetic Resonance (EPR) analysis and quenching tests showed that •OH was the main reactive oxygen species responsible for the degradation of RR X-3B. A large amount of Fe2+ leached from iron-carbon composite and sponge iron, which served as a homogeneous Fenton catalyst during the degradation of RR X-3B. In contrast, much lower amount of Fe2+ was leached from chalcopyrite and pyrite, and surface catalysis of the minerals played more important role in the generation of •OH. Surface characterization and density functional theory (DFT) calculation results illustrated that ≡Fe(II) was the primary surface catalytic site during the reaction. The reduction of ≡Fe(III) and ≡Cu(II) can be facilitated by sulfides on the mineral surface. The Fenton-like systems catalyzed by iron-based materials exhibited higher H2O2 utilization and COD removal than classical Fenton system. With the lower metal leaching concentration and stable surface property, chalcopyrite and pyrite may be more practical applicable from a long-term catalytic activity point of view.

Enhancement of peroxymonosulfate activation for 2,4-dichlorophenoxyacetic acid removal by MoSe2 induced Fe redox cycles.

The limited regeneration of Fe2+ in the Fe-catalyzed advanced oxidation processes (AOPs) constrained its application for the removal of organic pollutants. Herein, MoSe2 was introduced to promote the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the Fe2+/PMS system. Compared with Fe2+/PMS processes, the 2,4-D degradation efficiency and PMS decomposition rate respectively increased by 73.8% and 84.2% in the MoSe2/Fe2+/PMS system. DFT simulation results suggested that Se atoms acted smoothly as the bridge supporting the charge transfer from Mo to adjacent Fe atoms, which led to the reduction of Fe3+. The rapid regeneration of Fe2+ boosted the activation of PMS and the degradation of pollutants. Additionally, the electron paramagnetic resonance (EPR) and quenching experiments results indicated that SO4∙-, ∙OH, and 1O2 accounted for 2,4-D degradation, and SO4∙- and 1O2 predominated the reaction. The Mo based co-catalysts showed better co-catalytic effect than the W counterparts, and the moderate adsorption for PMS and lower electron transfer electron transfer resistance accounted for the more excellent co-catalytic performance of MoSe2 than that of WSe2. In addition, the degradation efficiency of 2,4-D was up to 95.5% after five cycles of MoSe2 in the co-catalytic system. The coexistent humic acid (HA) and Cl- showed ignorant negative effect on the degradation, while HCO3- would depress the oxidation reaction. The acidic etching wastewater can be applied as the Fe ions source in this co-catalytic process to remove 2,4-D effectively.

Complexation modelling and oxidation mechanism of organic pollutants in cotton pulp black liquor during iron salt precipitation and electrochemical treatment.

Removal behavior of organic pollutants such as lignin in cotton pulp black liquor (CPBL) was investigated in precipitation followed by electrochemical oxidation (EO) using FeCl3, Fe2(SO4)3, FeCl2 and FeSO4 as precipitants, electrolyte and catalysts. Based on comparison of precipitation efficacy of iron salts, spectroscopic techniques, thermodynamic equilibrium calculations and molecular dynamics (MD) simulations were used to provide insight into the interaction between iron cations and lignin. The results showed that FeCl3 achieved the highest removal of chemical oxygen demand (COD, 76.05%), UV254 (69.21%) and lignin (78.28%). Iron cationic complexation with lignin was identified as the key mechanism in precipitation. Fe3+ was more active in binding to organic ligands mainly due to charge effect compared to Fe2+. The strong Fe-sulphate coordination affected the complexation with lignin. MD simulations showed the formation of inner sphere complexes of iron cations with deprotonated carboxyl and hydroxyl groups via bidentate and monodentate coordination. The removal efficiency of electrochemical oxidation (EO) as a post-treatment of the precipitation was dependent on iron salts. Removals of COD, UV254 and color can achieve 98.88%, 98.9% and 99.97% by FeCl3 precipitation and EO processes. The effluent reached the primary discharge standard specified in Integrated Wastewater Discharge Standard of China (GB8978-1996). FeCl3 demonstrated significant advantages in the removal of organic pollutants from cotton pulp black liquor in the combined process of precipitation and electrochemical treatment and may have practical application potential.

Catalytic activity comparison of natural ferrous minerals in photo-Fenton oxidation for tertiary treatment of dyeing wastewater.

Natural ferrous minerals are readily available and recyclable catalysts in photo-Fenton-like oxidation for wastewater treatment. In this work, typical ferrous oxide and sulfide minerals including magnetite, chalcopyrite, and pyrrhotite were exploited as catalysts in heterogeneous photo-Fenton oxidation for purification of biological effluent of dyeing wastewater. In a wide initial pH range (3.0~7.5), ferrous mineral-based heterogeneous photo-Fenton-like reactions were proven to be effective on the oxidation of recalcitrant pollutants. COD removals achieved 60.57%, 58.83%, and 57.41% using pyrrhotite, chalcopyrite, and magnetite, respectively, as catalyst under ultraviolet irradiation of 220~275 nm at H2O2 concentration of 9.8 mM. The corresponding COD removals were 51.75% and 34.09% with or without ferrous sulfate additions in UV/H2O2 systems. Minerals exhibited excellent stability and reusability with photo-catalytic activity reduction of less than 10% in the reuse of 5 cycles. Dissolved iron concentrations were determined to be 1.86 mg L-1, 4.62 mg L-1, and 7.53 mg L-1 for magnetite, chalcopyrite, and pyrrhotite, respectively, at pH 3 and decreased to zero in neutral pH environment, which were much lower than those required for homogenous Fenton reaction. It was deduced that oxidation of recalcitrant pollutants was mainly catalyzed by Fe(II) on the mineral surface. The more reactive oxygen species such as hydroxyl radicals were resulted from the reaction of surface Fe (II) with H2O2, H2O2 photolysis, and charge separation of minerals under UV irradiation.

Cu2+/Cu+ cycle promoted PMS decomposition with the assistance of Mo for the degradation of organic pollutant.

The limited production of Cu+ in the Cu2+/PMS processes constrained its large-scan application for the elimination of organic pollutants. In this study, molybdenum powder (Mo) was applied as the co-catalyst to improve the degradation of 2,4-dichlorophenol (2,4-DCP) in Cu2+/PMS system at pH 5.6. By the assistance of Mo, Cu2+ was rapidly reduced to Cu+ which exhibited super activity for the peroxymonosulfate (PMS) activation. Compared with Cu2+/PMS processes, the PMS decomposition rate and 2,4-DCP degradation efficiency respectively increased by 62.1% and 83.6% in the Mo co-catalytic Cu2+/PMS system after reaction for 20 min. The degradation of 2,4-DCP was completed via both the free radical and non-radical pathways and the free radicals rather than Cu3+ contributed most to the reaction. In contrast to fresh Mo, the ratio of Mo4+ increased and Mo6+ decreased in the used Mo powder, due to the oxidation of Mo0 by Cu2+ and/or ∙OH and the reduction of Mo6+ by O2∙-. Additionally, the coexistence of Cl- and humic acid with low concentrations showed little effects on the Mo/Cu2+/PMS system while HCO3- presented an obvious depression for 2,4-DCP degradation. During five cycling runs, all the degradation rates were higher than 92.8%, indicating the good stability of Mo/Cu2+/PMS system.

WS2 as highly active co-catalyst for the regeneration of Fe(II) in the advanced oxidation processes.

The greatest constraint in the advanced oxidation processes involved Fe(II)/PMS was the low utilization of Fe(II) and PMS. In the present study, the co-catalytic effect of WS2 on the Fe(II)/PMS system for the degradation of organics was investigated. In the presence of WS2, Fe(III) was reduced to Fe(II) during the reaction and resulted in improved decomposition of PMS as well as the degradation of 4-chloriphenol (4-CP). The decomposition rate of PMS and degradation efficiency of 4-CP were 10% and 25% in the Fe(II)/PMS process, while the efficiencies respectively increased to 99% and 100% in the WS2 assisted Fe(II)/PMS system. The degradation of 4-CP was completed via the free radical pathway and SO4•- played a more important role than other active species. Low concentration of inorganic ions such as Cl- and HCO3- exhibited irrelevant effect while humic acid showed significant suppression on the WS2/Fe(II)/PMS system. Additionally, characterization and recycle results implied that WS2 maintained a good stability during the co-catalytic processes.

Optimization of aeration enhanced surfactant soil washing for remediation of diesel-contaminated soils using response surface methodology.

Surfactant-enhanced soil washing has been used for remediation of organic pollutants for an extended period, but its effectiveness and wide application was limited by the high concentration of surfactants utilized. In this work, the efficiency of conventional soil washing performance was enhanced by 12-25% through the incorporation of air bubbles into the low concentration surfactant soil washing system. Surfactant selection pre-experiment using aerated and conventional soil washing reveals Brij 35 > TX100 > Tween 80 > Saponin in diesel oil removal. Optimization of the effect of time, surfactant concentration, pH, agitation speed, and airflow rate in five levels were undertaken using Response Surface Methodology and Central composite design. The optimum degree of variables achieved was 90 min of washing time, 370 mg/l of concentration, washing pH of 10,535 rpm of agitation speed and 7.2 l/min of airflow rate with 79.5% diesel removal. The high predicted R 2 value of 0.9517 showed that the model could efficiently be used to predict diesel removal efficiency. The variation in efficiency of aeration assisted and conventional soil washing was variable depending on the type of surfactant, organic matter content of the soil, particle size distribution and level of pollutant weathering. The difference in removal efficiency of the two methods increases when the level of organic matter increases and when the particle size and age of contamination decreases.

[Treatment of Wastewater Containing Naphthalene Sulfonic Acid by Persulfate Oxidation].

Naphthalene sulfonic acid is widely used in the industry. In this study, H acid (1-amino-8-naphthol-3,6-disulfonic acid) was selected as the characteristic pollutant, and the alkali-activated, thermally-activated, and alkali-heat-complex activated persulfate (PS) degradation of H acid was analyzed. The effects of other factors on complex activation were discussed. The experimental results showed that with the addition of calcium oxide from 0 to 1250 mg ·L-1, the H acid removal rate increased from 42.5% to 82.8% after 100 min of reaction. The removal rate of H acid in thermal activation is positively correlated with temperature. The removal rate of H acid at 65℃ is 77.5%, and the apparent activation energy is 37.85 kJ ·mol-1. Although composite activation speeds up the reaction rate, rapid degradation of PS at high temperatures caused the degradation of H acid to be worse than single thermal activation. The change in PS concentration did not significantly improve the removal rate of H acid, and the inorganic anion CO32- was not conducive to the removal of H acid. Compound activation is not ideal for the mineralization of H acid, and the removal rate of TOC is only 16%. GC-MS identified the degradation product of H acid as terephthalic acid, indicating that phthalic anhydride may be formed after the naphthalene ring is opened.

Enhancement of auxiliary agent for washing efficiency of diesel contaminated soil with surfactants.

We used five types of surfactants assisted with sodium salts, including sodium tartrate (ST), sodium chloride (SC), and humic acid sodium (HAS) as auxiliary agents for soil washing to remove diesel from contaminated soil. Decontamination enhancement of diesel polluted soil washing with biosurfactant and H2O2 was examined, which showed higher effectiveness for newly contaminated soil. An increase in temperature and sodium salt addition exhibited a profound enhancement in diesel removal from aged contaminated soils. Compared to ST and SC, HAS exhibited a higher removal efficiency with saponin washing for aged diesel contaminated soil by lowering surface tension, shifting zeta potential, and increasing the number of micelles. Phytotoxicity experiments showed no significant inhibition of germination of lettuce, arugula, and cucumber with 0.2 g L-1 saponin incubation. Conversely, there was a promotion on the root extension of lettuce and cucumber except for arugula. Similarly, the addition of 2% HAS (wight of saponin) improved on root growth of lettuce, arugula, and cucumber, increasing by 25%, 5%, and 22% at the period of 14 d, respectively. Because of excellent removal efficiency and non-toxicity, enhanced wash with saponin and HAS might be considered in the future design of full-scale remediation processes of diesel contaminated soil.

Precipitation of heavy metals from wastewater using simulated flue gas: sequent additions of fly ash, lime and carbon dioxide.

Lime is a preferred precipitant for the removal of heavy metals from industrial wastewater due to its relatively low cost. To reduce heavy metal concentration to an acceptable level for discharge, in this work, fly ash was added as a seed material to enhance lime precipitation and the suspension was exposed to CO2 gas. The fly ash-lime-carbonation treatment increased the particle size of the precipitate and significantly improved sedimentation of sludge and the efficiency of heavy metal removal. The residual concentrations of chromium, copper, lead and zinc in effluents can be reduced to (mg L(-1)) 0.08, 0.14, 0.03 and 0.45, respectively. Examination of the precipitates by XRD and thermal analysis techniques showed that calcium-heavy metal double hydroxides and carbonates were present. The precipitate agglomerated and hardened naturally, facilitating disposal without the need for additional solidification/stabilization measures prior to landfill. It is suggested that fly ash, lime and CO2, captured directly from flue gas, may have potential as a method for wastewater treatment. This method could allow the ex-situ sequestration of CO2, particularly where flue-gas derived CO2 is available near wastewater treatment facilities.

Characterization of carbonated tricalcium silicate and its sorption capacity for heavy metals: a micron-scale composite adsorbent of active silicate gel and calcite.

Adsorption-based processes are widely used in the treatment of dilute metal-bearing wastewaters. The development of versatile, low-cost adsorbents is the subject of continuing interest. This paper examines the preparation, characterization and performance of a micro-scale composite adsorbent composed of silica gel (15.9 w/w%), calcium silicate hydrate gel (8.2 w/w%) and calcite (75.9 w/w%), produced by the accelerated carbonation of tricalcium silicate (C(3)S, Ca(3)SiO(5)). The Ca/Si ratio of calcium silicate hydrate gel (C-S-H) was determined at 0.12 (DTA/TG), 0.17 ((29)Si solid-state MAS/NMR) and 0.18 (SEM/EDS). The metals-retention capacity for selected Cu(II), Pb(II), Zn(II) and Cr(III) was determined by batch and column sorption experiments utilizing nitrate solutions. The effects of metal ion concentration, pH and contact time on binding ability was investigated by kinetic and equilibrium adsorption isotherm studies. The adsorption capacity for Pb(II), Cr(III), Zn(II) and Cu(II) was found to be 94.4 mg/g, 83.0 mg/g, 52.1 mg/g and 31.4 mg/g, respectively. It is concluded that the composite adsorbent has considerable potential for the treatment of industrial wastewater containing heavy metals.

[Strengthening Effects of Sodium Salts on Washing Kerosene Contaminated Soil with Surfactants].

The impact of sodium salt on kerosene contaminated soil washing with surfactants was investigated. The results indicated that sodium silicate greatly enhanced the washing efficiency of SDS. Sodium tartrate can largely enhance the washing efficiency of SDBS and Brij35. Sodium salts can enhance the washing efficiency on kerosene contaminated with TX-100. No significant differences were observed between different sodium salts. Sodium salt of humic acid and sodium silicate had similar enhancement on kerosene contaminated soil washing with saponin. Sodium humate can be a better choice since its application can also improve soil quality. The enhancement of sodium silicate on kerosene contaminated soil washing with Tw-80 increased with the increase of Tw-80 dosage. However, the impact of sodium chloride and sodium tartrate was opposite to sodium silicate. Sodium salts can reduce surface tension and critical micelle concentration of ionic surfactants to enhance the washing. Sodium salts can also reduce re-adsorption of oil to soil with nonionic surfactants to enhance the washing. Kerosene contamination can increase the contact angle of soil, which indicated the increase of hydrophilicity of soil. Washing with surfactants can reduce the hydrophilicitiy of soil according to contact angle measurement, which indicated that kerosene contaminated soil remediation with surfactant can also benefit nutrient and water transportation in the contaminated soil.

Stabilization of heavy metals in MSWI fly ash using silica fume.

The objective of this work was to investigate the feasibility and effectiveness of silica fume on stabilizing heavy metals in municipal solid waste incineration (MSWI) fly ash. In addition to compressive strength measurements, hydrated pastes were characterized by X-ray diffraction (XRD), thermal-analyses (DTA/TG), and MAS NMR ((27)Al and (29)Si) techniques. It was found that silica fume additions could effectively reduce the leaching of toxic heavy metals. At the addition of 20% silica fume, leaching concentrations for Cu, Pb and Zn of the hydrated paste cured for 7 days decreased from 0.32 mg/L to 0.05 mg/L, 40.99 mg/L to 4.40 mg/L, and 6.96 mg/L to 0.21 mg/L compared with the MSWI fly ash. After curing for 135 days, Cd and Pb in the leachates were not detected, while Cu and Zn concentrations decreased to 0.02 mg/L and 0.03 mg/L. The speciation of Pb and Cd by the modified version of the European Community Bureau of Reference (BCR) extractions showed that these metals converted into more stable state in hydrated pastes of MSWI fly ash in the presence of silica fume. Although exchangeable and weak-acid soluble fractions of Cu and Zn increased with hydration time, silica fume addition of 10% can satisfy the requirement of detoxification for heavy metals investigated in terms of the identification standard of hazardous waste of China.

Influence of Fenton's reagent doses on the degradation and mineralization of H-acid.

The recalcitrant H-acid (1-amino-8-naphthol-3,6-disulfonic acid) in aqueous solution was oxidized by Fenton process, focusing on the relation of Fenton's reagent doses and degradation products. The experimental results showed that COD and TOC removals and biodegradability (BOD/COD ratio) of the solution increased with increasing Fenton's reagent doses. Over 80% COD can be removed and the biodegradability was improved significantly. It was found that major SO3H and NH2 groups in H-acid molecules were mineralized to SO4(2-) and NH4(+) ions during Fenton oxidation processes. H-acid degradation intermediates with benzene structures substituted by hydroxyl and/or carboxyl groups were identified by GC-MS. It was also found that short-chain fatty acids primarily oxalic acid were degradation products of H-acid by Fenton oxidation. Oxalic acid accumulated could account for approximately 60% of the residual TOC. The degradation pathway of H-acid was proposed based on above analyses in this work.