Effect of Oxygen on the Adsorption of Pentachlorophenol by Peat from Water

Pentachlorophenol (PCP), a versatile biocide has been extensively used in industry and agriculture. PCP has been designated as a priority organic pollutant by the United States Environmental Protection Agency (USEPA) and its use in consumer products has been banned since 1984. Extensive use of PCP as a wood preservative has led to soil, surface water and groundwater pollution. Batch adsorption studies using peat at various dissolved oxygen (DO) levels in water showed that higher PCP removals can be attained at elevated DO levels. This effect can be quantified by a comparison of the adsorption capacities of peat from linearized Freundlich isotherms developed for different oxygen levels. An increase of approximately 300% in adsorption was observed for an increase in the DO level from 2 to 26 mg L^-1. Thus, molecular oxygen was found to significantly impact the removals of PCP by peat. The increase in adsorptive capacity of peat was not very significant for an increase in DO level from 2 mg L^-1 to 10 mg L^-1.However a rapid increase in adsorptive capacity was observed for an increase in DO level from 10 to 26 mg L^-1.     

The Effect of Organic Structures on Pentachlorophenol Adsorption on Soil

The adsorption of pentachlorophenol (PCP) on a soil was studied by equilibrating the soil (with and without its indigenous organic matter) with PCP in the presence and the absence of added natural organic species (benzoic acid, lactic acid, glucuronic acid and catechol). Both the added organic species and the indigenous organic matter were found to enhance PCP adsorption, the enhancement being greater with benzoic acid than with the less hydrophobic lactic acid. Adsorption of these organic species was also enhanced by PCP, suggesting the existence of a co-operative adsorption mechanism.     

Adsorptive Removal of Pentachlorophenol by Anthracophyllum discolor in a Fixed-Bed Column Reactor

This study investigates pentachlorophenol (PCP) adsorption by the white-rot fungus Anthracophyllum discolor in a fixed-bed column reactor. PCP adsorption at different concentrations (20, 30, and 50?mg?L^?1) and pH values (5.0, 5.5, and 6.0) was determined and modeled using the Thomas model. Fourier transform infrared spectroscopy (FTIR) was used to identify functional groups of biomass that may participate in the interaction of PCP. The biosorption capacity of A. discolor was pH-dependent, and the PCP adsorbed increased with the decrease in the pH solution. Acid pH values of the influent gave an increase in saturation time in all PCP concentrations. By contrast, the increase in PCP concentration caused that the binding sites were filled quickly, resulting in a decrease in saturation time. The Thomas model was found suitable for describing the entire dynamic of the column with respect to the PCP concentration and pH of the solution. FTIR results showed that amines, carboxylates, alkanes, and C?CO groups might participate in the PCP adsorption on the biomass surface. It was concluded that A. discolor biomass was a good adsorbent for PCP removal from influent with mainly acidic pH.     

Removal of Phosphate from Waste Waters by Adsorption

In this study, the adsorption of phosphate on gas concrete from aqueous solutions has been studied as functions of temperature, mixing rates and suspension pH. Over 99% of phosphate removal was found. The chemical composition of the gas concrete has been defined by X-ray analysis. Experimental data was fitted to the Langmuir equation in order to Langmuir coefficients. After calculating Langmuir coefficients, adsorption free energy (Δ G ⁰ _ads.) has been determined. In order to gather information about adsorption mechanism, electrophoretic mobilites of particles were measured at various pHs by using Zeta meter 3.0+. It has been found that the adsorption is driven by the interactions between the ionizations of CaO and Al₂O₃ and the formation of AlPO₄. According to the BET (N₂) measurements, the specific surface area of gas concrete was found as 22 m²g^-1. The surface area after adsorption has been found as 17 m²g^-1. The surface area covered by adsorbate has been found as 5.23 m²g^-1 by usinga_s = n^s _m. a_m. N_A. These two areas determined by BET and Langmuir model were close to each other (BET: 22 m²g^-1–17 m²g^-1).     

Kinetic and Removal Mechanisms of Ethylbenzene from Contaminated Solutions by Chitin and Chitosan

In this study, the efficiency of chitin and chitosan toward the removal of ethylbenzene from aqueous solutions was investigated. Batch adsorption experiments of ethylbenzene-contaminated waters (5?C200 mg/L) were carried out to evaluate the removal performance. Ethylbenzene uptake was determined from the changes in concentration, as the residual concentration was measured by gas chromatography with mass spectroscopy. The results indicated that the adsorption of ethylbenzene by chitin and chitosan were in agreement with the Langmuir isotherm, for two parameters model, and Redlich?CPeterson isotherm, for three parameters model. A maximum removal percentage of 65% of ethylbenzene can be achieved using chitosan as adsorbent material. The adsorption capacity of ethylbenzene followed the order chitosan?>?chitin. The pseudo-second order rate model described best the adsorption kinetics of ethylbenzene for the two selected adsorbents. The kinetic studies also revealed that the pore diffusion is not the only rate controlling step in the removal of ethylbenzene. Overall, the study demonstrated that chitosan is a potential adsorbent for the removal of ethylbenzene at concentrations as high as 200 mg/L.     

Study of Phosphorus Removal by Using Sponge Iron Adsorption

Phosphorus is one of the key elements causing lake eutrophication. This paper deals with phosphate removal by Sponge iron in batch and fixed-bed operation. Isotherm and kinetic studies are conducted. The isotherm data is described by the Freundlich and Langmuir model, while the kinetic data of adsorption is fitted by the pseudo-second-order kinetic model. The saturated adsorption capacity of Langmuir isothermal equation is about 3.25 mg/g. The concomitant anions have adverse effect on phosphate adsorption and the effects follow the order: NO₃^??>?Cl^??>?SO₄^2?. The phosphate adsorption capacities of SI were improved significantly under the acidic condition. The results of the fixed-bed operation show that, with the increase of the influent phosphate concentrations, the breakthrough curve becomes steeper while the break point time decrease. According to the Adams–Bohart model, the critical height of the column decrease from 0.135 to 0.105 m when the contact time increased from 10 to 30 min with the influent concentration of 1.0 mg/L. According to BDST model, the critical bed depth is 0.15 m when the influent concentration of phosphate is 1.0 mg/L and the contact time (h) is 20 min.     

Removal of Tartrazine from Aqueous Solution by Adsorption on Activated Red Mud

In this study, activated red mud was used to develop an effective adsorbent in order to remove a toxic azo dye (tartrazine E102) from aqueous solutions. To increase the adsorption capacity, the red mud was activated by acid-heat treatment using 20 wt.% HCl (RM-HCl). To establish the optimum operating parameters, the influence of pH, adsorbent dose, contact time, initial dye concentration, and stirring rate was investigated. The adsorption equilibrium was studied using Langmuir, Freundlich, Dubinin-Radushkevich, Temkin isotherm models, and the characteristic parameters for each adsorption isotherm were determined. The kinetics of the adsorption process was analyzed by means of pseudo-first-order and pseudo-second-order models. The maximum removal efficiency obtained under optimum conditions was 84.72%. These results were in accordance with the isotherm and kinetic data. The results suggested that tartrazine adsorption process follows the pseudo-second-order kinetic model and also that fits Langmuir isotherm model. The maximum monolayer adsorption capacity was 136.98 mg/g.     

Removal of Fluoride from Water by Adsorption onto Lanthanum Oxide

Rare earth mineral based adsorbent viz. lanthanum oxide was investigated for potential application in defluoridation of drinking water for isolated and rural communities. Results of batch experiments indicated about 90% removal in 30 min from a 4 mg L⁻¹ synthetic fluoride solution. The effects of various parameters like contact time, pH, initial concentration, and sorbent dose on sorption efficiency were investigated. Adsorption efficiency was dependent on initial fluoride concentration and the sorption process followed BET model. Variation of pH up to 9.5 has insignificant effect on sorption and beyond a pH of 9.5, the effect was drastic. Among anions investigated, carbonates exhibited high detrimental effect on fluoride adsorption while anions like bicarbonates, chlorides, and sulfates did not seriously affect the process. Adsorbent showed negligible desorption of fluoride in distilled water. Alum was more effective regenerant than HCl and NaOH. Results of cyclic regeneration with alum indicated that the sorbent could be regenerated for ten cycles without significant loss of sorption capacity. Studies with upflow fixed-bed continuous flow columns indicated the usefulness of sorbent for fluoride removal in continuous flow process.     

The Removal of Dye Colours from Aqueous Solutions by Adsorption on Low-cost Materials

The ability of five low cost adsorbents – rice husk, cotton, bark, hair and coal – to adsorb two basic dyes, namely, Safranine and Methylene Blue, has been studied. Equilibrium isotherms have been determined and analysed using the Langmuir equations. The monolayer saturation capacities for Safranine are 1119, 838, 875, 190 and 120 mg g^-1adsorbent and for Methylene Blue are 914, 312, 277, 158 and 250 mg g^-1adsorbent for bark, rice husk, cotton waste, hair and coal respectively. A limited number of fixed bed column studies have been performed and the bed depth service time for each dye-adsorbent system has been determined.     

Removal of Residual Oils from Palm Oil Mill Effluent by Adsorption on Natural Zeolite

The adsorption of residue oil from palm oil mill effluent using natural zeolite was investigated in this study. The adsorption was performed in batch mode, and the effect of different operational parameters such as pH, dose of adsorbent, stirring rate, contact time and initial oil concentration were explored. It was found that the pH plays a major role in the adsorption process. Isotherm data best fitted with the Freundlich model, and kinetic data followed the pseudo-second-order kinetic model. The results obtained demonstrated that the oil removal efficiencies by natural zeolite were up to 70?% at a pH of 3.0 and 50?min of contact time. The adsorbent material also has been characterised by X-ray diffraction, X-ray fluorescence and scanning electron microscopy.     

Effects of Various Parameters on Removal of NO2 Gases in Fixed Beds by Adsorption on Sepiolite

Removal of NO₂ gases in fixed beds was investigatedby using brownish, whitish and regenerated whitish sepioliteand perlite as adsorbents. For this purpose, NO₂ wasproduced by reaction of copper with nitric acid. The producedgas was mixed with air and the mixture was sent through a fixedbed. Studies were conducted using various gas flow rates,NO₂ concentrations, packing sizes and heights of bed.Remaining NO₂ within the gas mixture leaving the column,unadsorbed on packing, was further absorbed by passing itthrough a series of washing bottles, filled by a solution ofNaOH. At the end of the study, it was observed that theadsorption capacity of sepiolites, especially whitishsepiolite, was much higher than that of perlite. Additionally,it was seen that its adsorption capacity increased withincreasing bed height, particle size, NO₂ concentrationand decreasing gas flow rate.     

Degradation of Pentachlorophenol by Ozone Generated by a Pulsed Power Corona Discharge

Ozone, generated by a pulsed power corona discharge, was usedto degrade pentachlorophenol (PCP). The degradation of PCP wasdriven by ozone and superoxide radical (SOR). The coronadischarge reactor was made without glass dielectric material,not only to reduce the power consumption but also to enhancethe formation of the SOR. In addition, the corona dischargedevice was operated with pin-plate or pin-ring typeelectrodes, which had a normal and parallel oxygen flow,respectively. The ozone generated in the corona dischargereactor was in the range of 0-0.39 mg min^-1. To confirm the generation of SOR, the hydrogen peroxide was measuredunder acidic conditions without ozone effects. PCP at 10 ppm wascompletely degraded in 10 min in both electrode types withnegative high DC voltage. The degradation rate of PCP was muchgreater at a high frequency (1 kHz). Oxalic, malonic andglyoxylic acids were generated as final products of the reaction.     

秸秆碳和硫酸铝对富营养化水体中氮磷的吸收去除效应及其影响因素

为解决中国水体富营养化问题,将秸秆碳与硫酸铝作为一种有效吸附水体中总氮、总磷的吸附剂,通过室内模拟试验,采用平衡吸附法,考察了秸秆碳和硫酸铝投加量、pH值、振荡时间、温度、扰动、秸秆碳粒径等不同环境因素条件下对吸附效果的影响。结果表明:在秸秆碳和硫酸铝投加量为0.2 mg/L、振荡时间为120 min的条件下,吸附效果最好,去除率可达80%以上。通过对各因素与秸秆碳、硫酸铝对总氮和总磷的吸附效果分析得知,加入适量的秸秆碳和硫酸铝,可以降低水体中总氮、总磷的含量,吸附效果对温度、振荡时间、pH值变化敏感,这也为解决水体富营养化问题提供了基础依据。     

Electrokinetic Remediation of Pentachlorophenol Contaminated Clay Soil

This paper presents a bench-scale experimental study performed to investigate the remediation of low permeable soil contaminated with pentachlorophenol (PCP) using the electrokinetic technique. A total of six electrokinetic tests were performed using kaolin soil spiked with 100 mg/kg of PCP. The first three tests were performed with an applied voltage gradient of 1 VDC/cm, where each test employed one of the three different flushing solutions: deionized water, electrolyte, or buffered electrolyte. The other three tests were performed using the same electrolyte solution, but each employed voltage gradient of 2 VDC/cm under constant and periodic application modes and constant voltage gradient with electrode liquid recirculation. The results of this study showed that PCP can be degraded in an electrokinetic system due to the direct electrochemical reduction process at the electrodes. The degradation of PCP ranged from 52% to about 78% depending on the conditions present. As the applied voltage gradient across the PCP-contaminated soil increased, the electroosmotic flow and PCP migration toward the cathode increased, resulting in higher PCP degradation by the direct reduction process. In the tests with electrolyte flushing solution, PCP degradation was about 58% and 65% under the applied voltage gradients of 1 and 2 VDC/cm, respectively. The mode of application of voltage potential across the PCP-contaminated soil showed noticeable effect on the system pH and electroosmotic flow and hence the PCP degradation. The highest PCP degradation (i.e., 78%) was in the test with constant 2 VDC/cm voltage gradient and recirculation application. Overall, this study demonstrated that electrokinetic technology has the potential to remediate PCP-contaminated clay soils by the direct reductive process. The electroosmatic flow as well as degree of PCP degradation during electrokinetics depend on the applied potential gradient and properties of the aqueous phase such as pH, ionic strength, and presence of carbonates.     

Adsorption of polyphosphates by allophane

Although many investigations have been carried out on the reaction of phosphates with allophane as well as with crystalline clays, they have been almost with the orthophosphates (2, 13, 19, 21). Recent investigations have revealed that certain condensed phosphates (polyphosphates) have a considerable promise as a long-term, slow-release source of phosphorus for plants (3, 7, 9, 10. 14, 17. 18, 20. 25). Relatively little information is available, however, on the reaction of those substances with soil clay minerals (8. 15).     

Adsorption of pentachlorophenol by soils

The adsorption studies using soils various in the species of clay minerals and organic matter content indicate:

1) That apparent adsorption occurs to the greatest extent on the strong acid soil system compared to the moderate acid soil system, regardless of the species of clay mineral and organic matter content. And there is no adsorption on the slightly acid or neutral soil system.

2) The apparent adsorption involves adsorption of molecules and/or anions and precipitation of molecules in the micell and the external liquid phase.

3) The magnitude of adsorption occurs in the decreasing order of humus-allophanic, allophanic, montmorillonitic, and halloysitic soils.

4) The major factor governing the magnitude of apparent adsorption is pH.