The BAC-process for treatment of waste water containing non-ionogenic synthetic surfactants

In this paper experimental results on the biological-activated carbon (BAC)-process for biological degradation and adsorption of non-ionogenic surfactants (NISS) in the waste water treatment are discussed. It is shown that the mechanism of the BAC-process is not the simple addition but the synergetic combination of biodegradation and carbon adsorption. The major aspects of such synergism are the biological regeneration (bioregeneration) of the adsorbent and the reduction of the toxic effect of waste water contaminants on microorganisms. It is shown that the basis of the bioregeneration process is the desorption of substances previously adsorbed on the activated carbon. The desorption from micropores takes place because of the reverse concentration gradient, due to the microbial degradation of waste water contaminants in the liquid phase. The desorption from mesopores is also supported by the activity of microorganisms exoenzymes. Thus, the process of bioregeneration is featured by two non-contradictory hypotheses.     

Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-II. Kinetics

The kinetics of pentachlorophenol (PCP) adsorption/desorption with Calgon F300 granular activated carbon (GAC) was studied. A previously-developed model of GAC adsorption/desorption kinetics was applied to the case of PCP for both batch and continuous plug-flow liquid conditions. The model predictions were found to be in good agreement with the experimental observations.     

Solvent regeneration of activated carbon

Nineteen solvents were evaluated in batch tests involving the desorption of a representative organic adsorbate (phenol) from activated carbon. Three of the better solvents which also possess complete miscibility with water (acetone, dimethylformamide, methanol) were tested further in fixed-bed runs. The effects of solvent temperature and solvent flow rate on phenol desorption were evaluated. In addition, the recovery of phenol adsorption capacity by an activated carbon bed operated cyclically using a sequence of phenol adsorption, desorption with methanol, and rinsing with water was determined. It was found that solvent temperature and flow rate are not critical variables. Solvent volume and type were the most important factors in phenol desorption. A modest volume of methanol restored 88% of the fixed-bed adsorption capacity for phenol after 1 regeneration, and the capacity essentially leveled off after 5 regenerations at a value of 81% of the capacity of fresh carbon. Methanol regeneration is effective, easy to perform and offers convenient solvent recovery. Thus, it is an attractive alternative to thermal regeneration methods.     

Microwave-assisted regeneration of activated carbons loaded with pharmaceuticals

The purpose of this work was to explore the application of microwaves for the regeneration of activated carbons spent with salicylic acid, a metabolite of a common analgesic frequently found in wastewater from the pharmaceutical industry. The exhausted carbon was treated in a quartz reactor by microwave irradiation at 2450 MHz at different temperatures and atmospheres, the regeneration efficiency being highly dependent on the operating conditions. Quantitative desorption of the pollutant was achieved at high temperature and oxidizing atmosphere, with regeneration efficiencies as high as 99% after six cycles. The stripping efficiency was superior to 95% at high temperatures and decreased at 450 degrees C. The incomplete desorption of the adsorbate at low temperature was further confirmed by the changes in the porosity observed by N2 and CO2 adsorption isotherms. Hence, micropores remain blocked which results in a reduction in loading capacities in successive cycles.     

Studies on the efficiency of a local fertilizer waste as a low cost adsorbent

Waste slurry, generated in local fertilizer plants, is converted into activated carbon in air, steam and nitrogen atmospheres. Products so obtained have been characterized and utilized for the removal of phenols, especially 2,4-dinitrophenol. Investigations include the effect of pH, kinetics of adsorption and the effect of salts on the uptake of DNP. Carbon prepared in air exhibits good sorption capacity for DNP and the adsorption data follows both Langmuir and Freundlich models. Some experiments have also been performed with a view to recover phenols and have in situ regeneration of spent carbon column. It is observed that 5% NaOH removes almost 96% of phenol loaded on the carbon column and a treatment with 1 M HNO₃ reactivates the adsorbent particles which can be used for 6–10 cycles at a stretch.     

Solar regeneration of powdered activated carbon impregnated with visible-light responsive photocatalyst: factors affecting performances and predictive model

This study demonstrated a green technique to regenerate spent powdered activated carbon (AC) using solar photocatalysis. The AC was impregnated with a photocatalyst photoexcitable under visible-light irradiation to yield a solar regenerable composite, namely nitrogen-doped titanium dioxide (N-TiO₂/AC). This composite exhibited bifunctional adsorptive-photocatalytic characteristics. Contaminants of emerging environmental concern, i.e. bisphenol-A (BPA), sulfamethazine (SMZ) and clofibric acid (CFA) which exhibited varying affinities for AC were chosen as target pollutants. The adsorption of BPA and SMZ by the N-TiO₂/AC was significantly higher than that of CFA. The performance of solar photocatalytic regeneration (SPR) of the spent N-TiO₂/AC composite generally increased with light intensity, N-TiO₂ loading and temperature. The regeneration efficiency (RE) for CFA-loaded spent composite was the highest compared to the other pollutant-loaded spent composites, achieving 77% within 8 h of solar irradiation (765 W m⁻²). The rate-limiting process was pollutant desorption from the interior AC sorption sites. A kinetic model was developed to predict the transient concentration of the sorbate remaining in the spent composite during SPR. Comparison studies using solvent extraction technique indicated a different order of RE for the three pollutants, attributable to their varying solubilities in the aqueous and organic solvents.     

Treatment of naphthalene-2-sulfonic acid from tannery wastewater by a granular activated carbon fixed bed inoculated with bacterial isolates Arthrobacter globiformis and Comamonas testosteroni

The kinetics of naphthalene-2-sulfonic acid (2-NSA) adsorption by granular activated carbon (GAC) were measured and the relationships between adsorption, desorption, bioavailability and biodegradation assessed. The conventional Langmuir model fitted the experimental sorption isotherm data and introduced 2-NSA degrading bacteria, established on the surface of the GAC, did not interfere with adsorption. The potential value of GAC as a microbial support in the aerobic degradation of 2-NSA by Arthrobacter globiformis and Comamonas testosteroni was investigated. Using both virgin and microbially colonised GAC, adsorption removed 2-NSA from the liquid phase up to its saturation capacity of 140 mg/g GAC within 48 h. However, between 83.2% and 93.3% of the adsorbed 2-NSA was bioavailable to both bacterial species as a source of carbon for growth. In comparison to the non-inoculated GAC, the combination of rapid adsorption and biodegradation increased the amount (by 70-93%) of 2-NSA removal from the influent phase as well as the bed-life of the GAC (from 40 to >120 d). A microbially conditioned GAC fixed-bed reactor containing 15 g GAC removed 100% 2-NSA (100 mg/l) from tannery wastewater at an empty bed contact time of 22 min for a minimum of 120 d without the need for GAC reconditioning or replacement. This suggests that small volume GAC bioreactors could be used for tannery wastewater recycling.     

Electrochemical regeneration of field spent GAC from two water treatment plants

The effectiveness of on-site thermal regeneration of field-spent granular activated carbon (GAC) from two municipal drinking water facilities was compared with bench-scale electrochemical regeneration, a novel regeneration technology. The regeneration method was evaluated using aqueous natural organic material (NOM) adsorption, iodine number analysis, and surface area analysis. In contrast to the large electrochemical regeneration efficiencies reported in the literature for GAC loaded with phenolics and other individual organic compounds, the electrochemical reactor tested was only able to regenerate 8-15% of the NOM adsorption capacity of the field spent GAC. In contrast, thermal reactivation achieved up to 103% regeneration efficiency. To more accurately assess the efficiency of regeneration processes for water treatment applications, GAC should be loaded in continuous-flow columns and not batch rectors. The iodine number analysis yielded higher efficiency values, however it did not give an accurate estimate of the regeneration efficiency. The small changes in GAC pore size distribution were consistent with the low electrochemical regeneration efficiencies. These low efficiencies appear to be related to the low reversibility of NOM adsorption and to pH-induced adsorbate desorption being the primary mechanism for this type of electrochemical regeneration system.     

Comparison between thermal and ozone regenerations of spent activated carbon exhausted with phenol

Thermal and ozone regenerations of granular activated carbons (GAC) used in the removal of phenol from aqueous solution have been studied. The phenol isotherms for virgin GAC could be well represented by the Langmuir equation. Direct ozonation of GAC introduced large amounts of acidic surface oxygen groups, which caused a decrease in the phenol uptake. Thermogravimetric methods were used to investigate the mechanism of phenol adsorption onto virgin and ozonated carbons. Thermal regeneration was carried out at 1123K using nitrogen (pyrolysis alone) or nitrogen and carbon dioxide (pyrolysis plus oxidation). Results showed that spent carbons do not recover their adsorption characteristics when heated under inert conditions whereas carbon dioxide regeneration was effective at about 15% wt burn-off. Regeneration of GAC was also carried out with ozone as oxidizing gas at room temperature. Ozone dose and the nature of GAC have much influence on the regeneration performance. For an individual GAC there exits an optimum ozone dose for which phenol is eliminated together with most of its oxidation by-products without incurring in carbon surface chemical alterations. However, if excessive ozone is applied some acidic surface groups are formed on the GAC, thereby decreasing the adsorption capacity for phenol. Results showed that spent carbons can recover most of their adsorption characteristics and specific surface areas when regenerated through a number of adsorption-ozone regeneration cycles.     

Regeneration of ortho-chlorophenol-exhausted activated carbons with liquid water at high pressure and temperature

A study was undertaken of the regeneration of three activated carbons exhausted with ortho-chlorophenol. The regeneration process was carried out using liquid water at 623 K and 150 atm in the absence of oxygen. The efficiency of this procedure was analyzed by determining the rate and amount of ortho-chlorophenol adsorbed in successive adsorption-regeneration cycles. The present procedure showed a much greater efficiency than that reported for chemical and/or thermal regeneration. Effects of this regeneration on the adsorption kinetics, adsorption capacity and textural characteristics of the carbon were investigated. The increase in adsorption capacity of the regenerated carbon compared with that of the original carbon seems mainly due to the opening of porosity during the regeneration treatment.     

改性炭对磺胺甲噁唑的吸附及解吸特性

采用商品活性炭和金属氧化物改性炭作为吸附剂,研究了几种活性炭对磺胺甲噁唑(SMZ)的吸附及解吸特性。结果表明:SMZ在几种活性炭上的吸附动力学符合拟二级动力学方程;SMZ的吸附均可采用Freundlich、Langmuir和Langmuir-Freundlich模型进行拟合,Langmuir-Freundlich吸附模型能更好地描述活性炭和改性炭对SMZ的吸附行为;铁、锰氧化物的存在对活性炭的比表面或者孔结构影响不大,并且其对活性炭吸附水中SMZ的性能影响甚微;与AC-Fe和AC-Mn相比,AC-0上吸附的SMZ更易解吸,改性炭负载的金属氧化物与SMZ的表面络合作用增强了AC-Fe和AC-Mn对SMZ的化学吸附,并且改性炭的MnOx和FeOx能氧化降解部分SMZ。     

Preliminary feasibility study for the use of an adsorption/bio-regeneration system for molinate removal from effluents

This work studies the feasibility of the use of a combined physical-biological remediation procedure for treatment of effluents contaminated with molinate, where the herbicide is removed through adsorption and biodegraded in a subsequent stage, with the regeneration of the adsorbent. In order to select the most adequate absorbent for molinate, different materials were tested, namely pine bark, activated carbon and resin Amberlite XAD-4. Activated carbon and resin Amberlite XAD-4 were the most efficient on the removal of molinate from solutions, although the activated carbon used proved not to be bio-regenerable. It was also observed that factors such as temperature, pH, and conductivity did not affect significantly molinate adsorption onto resin Amberlite XAD-4. Resin Amberlite XAD-4 was successfully bio-regenerated, being observed that biodegradation was mainly dependent on spontaneous desorption of the molinate. After bio-regeneration, the resin could be re-utilised as adsorbent.     

Adsorption-desorption characteristics of phenol and reactive dyes from aqueous solution on mesoporous activated carbon prepared from waste tires

Liquid-phase adsorption-desorption characteristics and ethanol regeneration efficiency of an activated carbon prepared from waste tires and a commercial activated carbon were investigated. Water vapor adsorption experiments reveal that both activated carbons showed hydrophobic surface characteristics. Adsorption experiments reveal that the prepared activated carbon possessed comparable phenol adsorption capacity as the commercial one but clearly larger adsorption capacity of two reactive dyes, Black 5 and Red 31. It was ascertained that the prepared activated carbon exhibited less irreversible adsorption of phenol and the two dyes than its commercial counterpart. Moreover, ethanol regeneration efficiency of the prepared AC saturated with either dye was higher than that of the commercial AC. Because of its superior liquid-phase adsorption-desorption characteristics as well as higher ethanol regeneration efficiency, the prepared activated carbon is more suitable for wastewater treatment, especially for adsorbing similarly bulky adsorbates.     

Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-I. Isotherms

The adsorption/desorption of pentachlorophenol (PCP) with Calgon F300 granular activated carbon (GAC) was studied and modelled. A modified Radke-Prausnitz (1972) isotherm model, incorporating a temperature- and pH-dependent proportionality constant, was found to best describe the observed PCP adsorption and desorption. The modified isotherm is valid in the ranges 4 ≤ pH ≤ 11 and 10 ≤ T ≤ 60°C. The activation energy of PCP adsorption was calculated to be 5.2 kJ/mol. At 30°C, PCP adsorbed strongly, and the rate of subsequent desorption was very low. However, the amount of PCP desorbed could be increased significantly by increasing the temperature to 60°C.     

Role of the physico-chemical factors in the purification process of water from surface-active matter by biosorption

Activated carbon adsorption with attached microorganisms (biosorption) has been studied. The approaches available do not account for an efficient role of activated carbon under a steady state of purification, considering it (carbon) as a carrier of biofilm only. This paper considers the role of physico-chemical factors in order to clear up and assess a contribution of both physical adsorption and biodegradation (influencing effectiveness of the biosorption process) into the cumulative effect of the biosorption. The nonionic and anionic surfactants as well as phenol were used as sorbates. The impact of such essential physico-chemical factors of the adsorption process as the change in the Gibbs free energy (−ΔG_a⁰) and the porous structure of the activated carbon on the effectiveness of the biosorption process has been established. The lower the contribution of the biological degradation into the biosorption process, the higher the −ΔG_a⁰. As a result of the biodegradation process, products differing in their −ΔG_a⁰ are generated on the active carbon. Separation of the biodegradation products characterized by different −ΔG_a⁰ in the biosorption column filled by active carbon results in redistribution of contributions of physical adsorption and biodegradation into a cumulative effect. The micropores of the active carbon in the course of the biosorption/bioregeneration process are occupied by adsorbed molecules and are not subjected to biological regeneration.     

两种碳基材料对二级出水中有机物的去除特性

针对活性炭与活性焦两种碳基吸附材料,分别开展静态吸附与动态过滤实验,考察了两者对城镇再生水厂二级出水中有机物的去除效果。结果表明:活性焦介孔及大孔丰富,对应孔体积为0.436 cm³/g,为活性炭的1.6倍;准二级动力学模型更适用于两种材料对COD的吸附动力学拟合,活性焦动力学吸附速率常数k₂为活性炭的2倍;水温为22℃时,活性焦与活性炭对COD的Langmuir饱和吸附量分别为230.38、94.14 mg/g。在近4个月的连续运行中,活性焦滤柱对有机物的去除效果全程优于活性炭滤柱,尽管两滤柱在由单纯吸附向生物吸附降解转化的过程中对有机物的去除率有所降低,但对COD的去除率仍可分别稳定在28.43%和22.26%。活性焦颗粒与活性炭颗粒表面ATP含量最高分别为7032.94、5753.52 ng/g。此外,活性焦滤柱对1~10 ku有机物组分,以及腐殖酸类物质、溶解性微生物代谢产物等不同荧光特性有机物均有较好的去除效果。与活性炭相比,活性焦对再生水厂二级出水中有机物的去除效果更优。     

Bioregeneration of the activated carbon layer spent in the dynamics of procaine biofiltration

This paper has investigated bioregeneration of biologically activated carbon (BAC) from procaine. The study has shown low efficiency (up to 25%) of desorption of procaine by aqueous solutions even at heating up to 80°C. In the course of bioregeneration media of spent BAC was recovered a small degree of adsorption capacity of the sorbent and by two times enhanced the ATP-ase activity of the biofilm, which increased the efficiency of the operation of biosorbents 2.5 and 3.25 times after respective 4 and 10 days of bioregeneration. A positive effect of bioregeneration affects further biofiltration about 1000 c.v. of the model solution.     

Reversibility of adsorption of aromatic compounds onto powdered activated carbon (PAC)

Desorption of sorbed compounds is an important process in the powdered activated carbon-activated sludge (PAC-AS) wastewater treatment system, where sorption and biodegradation interact. To assess the extent of desorption to be expected in the PAC-AS system, reversibility of adsorption was investigated using isotherm studies and a leaching technique under the conditions prevalent in the PAC-AS system. Two aromatic compounds, o-cresol and 3-chlorobenzoic acid (3-CB), and two types of powdered activated carbon (PAC) were used to study desorption. High degrees of irreversible adsorption were observed with both desorption techniques, depending on the type of PAC and the compound. The thermally activated, peat-based PAC (SA4) showed a high degree of irreversible adsorption compared to the chemically activated, wood-derived PAC (CA1). The phenolic compound, o-cresol, could be desorbed to a lesser extent than 3-CB from both types of PAC. Contact time between the PAC and the compound was found to affect the desorption of o-cresol adversely. Oxygen availability enhanced the adsorptive capacity of SA4 for o-cresol. Sorption of 3-CB proved unaffected by either contact time or oxygen. Oxidative polymerization as a probable mechanism for the irreversible adsorption observed is also discussed. Desorption kinetics from SA4 showed a first phase of rapid desorption followed by a second phase of slow desorption. CA1 displayed the first rapid desorption phase only.     

水源水中乐果污染物应急处理工艺的试验研究

以乐果为目标化合物,探讨了活性炭吸附、活性炭吸附-混凝沉淀工艺以及石灰碱解-活性炭吸附-混凝沉淀三种工艺对乐果的去除效果.结果表明,乐果的去除效果随着活性炭投加量与吸附时间的增加而增加,采用活性炭吸附-常规混凝沉淀工艺对乐果的去除效果要略好于单独采用活性炭吸附,但这两种工艺都不能有效去除水中的乐果.采用石灰碱解-活性炭吸附-混凝沉淀工艺时,乐果的去除率随着石灰碱解的pH值升高而增加.当原水乐果含量为0.182 mg/L,用石灰调节原水pH值为9,投加30 mg/L活性炭吸附20 min后,去除率达89.9%,沉淀出水乐果浓度为0.018 4 mg/L,满足标准要求.     

Desorption of dye from activated carbon beds: effects of temperature, pH, and alcohol.

The adsorption isotherms of yellow and red dye solutions onto granular activated carbon at varying solution pHs (2-8). temperatures (15-50 degrees C), and alcohol concentrations (0-20%) were experimentally determined by batch tests and the Tóth model was found to best fit the adsorption isotherm data for varying solution pHs. temperatures, and alcohol concentrations. The maximum adsorption capacity was found to decrease with increasing solution pH and alcohol concentration and could be predicted by the correlation equations obtained in this study. A correlation equation was also obtained to account for the effects of solution temperature on the adsorption equilibrium constant. The 25 degrees C water was found to be a very poor regenerant for the carbon bed presaturated with the yellow dye compared with 20% alcohol solution. A simple equation was derived, based on non-linear wave propagation theory, to predict the desorption curves of activated carbon bed. Given presaturation concentration, bed density and void fraction, and adsorption isotherm, the wave propagation theory predicted the desorption curves quite satisfactorily.