Characteristics of adsorbents made from biological, chemical and hybrid sludges and their effect on organics removal in wastewater treatment

Meso-macropore adsorbents were prepared from biological sludge, chemical sludge and hybrid sludge of biological and chemical sludges, by chemically activating with 18.0 M H₂SO₄ in the mass ratio of 1:3, and then pyrolyzing at 550 °C for 1 h in anoxic atmosphere. The physical and chemical characteristics of the sludge-based adsorbents were examined in terms of surface physical morphology, specific surface area and pore size distribution, aluminum and iron contents, surface functional groups and crystal structure. Furthermore, the adsorption effect of these adsorbents on the organic substances in wastewater was also investigated. The results indicated that the adsorption capacities of the sludge-based adsorbents for UV₂₅₄ were lower than that of commercial activated carbon (AC), whereas the adsorption capacities of the adsorbents prepared from hybrid sludge (HA) and chemical sludge (CA) for soluble COD_Cr (SCOD_Cr) were comparable or even higher than that of the commercial AC. The reasons might be that the HA and CA possessed well-developed mesopore and macropore structure, as well as abundant acidic surface functional groups. However, the lowest adsorption efficiency was observed for the biological sludge-based adsorbent, which might be due to the lowest metal content and overabundance of surface acidic functional groups in this adsorbent.     

Application of 'waste' metal hydroxide sludge for adsorption of azo reactive dyes

The capacity and mechanism of metal hydroxide sludge in removing azo reactive dyes from aqueous solution was investigated with different parameters, such as charge amount of dyes, system pH, adsorbent particle size, and adsorbent dosage. The three anionic dyes used were CI Reactive Red 2, CI Reactive Red 120, and CI Reactive Red 141, increasing in number of sulfonic groups, respectively. Only 0.2% (w/v) of powdered sludge (<75microm) achieved color removal from 30 mg l(-1) reactive dye solutions within 5 min without pH adjustment. The larger the charge amount of the dyes, the greater the adsorption (>90%) on the metal hydroxide sludge. The system pH played a significant role in the adsorption on metal hydroxides and formation of dye-metal complexes. The optimum system pH for dye adsorption was 8-9 which was close to the pH(zpc) of the sludge while the precipitation of dye-metal complexes occurred at system pH 2. The maximum adsorption capacity (Q degrees ) of the sludge for the reactive dyes was 48-62 mg dye g(-1) adsorbent. The Langmuir and Freundlich models showed that the higher charged dyes had a higher affinity of adsorption. The smaller particle size and the greater amount of adsorbent showed the faster process, due to an increase in surface area of adsorbent. Desorption studies elucidated that metal hydroxide sludge had a tendency for ion exchange adsorption of sulfonated azo reactive dyes. Leaching data showed that the treated water was nontoxic at a system pH above 5 or a solution pH above 2.     

Development and characterization of ferrihydrite-modified diatomite as a phosphorus adsorbent

A novel phosphorus adsorbent, ferrihydrite-modified diatomite was developed and characterized in this study. The ferrihydrite-modified diatomite was made through surface modification treatments including NaOH treatment and ferrihydrite deposition on raw diatomite. In the NaOH treatment, surface SiO₂ of diatomite was partially dissolved in the NaOH solution. The dissolved Si contributed to form the stable 2-line ferrihydrite which deposited into the macropores and mesopores of diatomite. Blocking macropores and larger mesopores of diatomite with 0.24 g Fe/g of 2-line ferrihydrite resulted in a specific surface area of 211.1 m²/g for the ferrihydrite-modified diatomite, which is 8.5-fold increase than the raw diatomite (24.77 m²/g). The surface modification also increased the point of zero charge (pH_PZC) values to 10 for the ferrihydrite-modified diatomite from 5.8 for the raw diatomite. Because of the increased surface area and surface charge, the maximum adsorption capacity of ferrihydrite-modified diatomite at pH 4 and pH 8.5 was increased from 10.2 mg P/g and 1.7 mg P/g of raw diatomite to 37.3 mg P/g and 13.6 mg P/g, respectively.     

Biological denitrification in an upflow sludge blanket reactor

A study was made of a denitrifying sludge blanket reactor without carrier material for the activated sludge. The reactor was fed with a solution of alcoholic waste and sodium nitrate. The highest surface load in our study was 2 m h^?1 and the sludge concentration in the sludge blanket at this flow was in the range of 40 g TS l^?1. To our opinion higher surface loads are attainable. The nitrate removal rate that at least can be obtained is 500 g NO^?₃ ? N m^?3 h^?1.     

Enhanced dewatering of waste sludge with microbial flocculant TJ-F1 as a novel conditioner

Microbial flocculant (MBF) TJ-F1 with high flocculating activity was investigated to be used as a novel conditioner for the enhanced dewaterability of the waste sludge from wastewater treatment plant (WWTP). The experimental results showed that TJ-F1 was better than poly(acrylamide [2-(Methacryloyloxy)ethyl]trimethylammonium chloride) (P(AM-DMC)), the most commonly used conditioner in China, in improving the dewaterability of the waste sludge in terms of both the specific resistance in filtration (SRF) and the time to filter (TTF). The key parameters influencing the dewaterability of the waste sludge conditioned by TJ-F1, including the system pH, CaCl₂ concentration and TJ-F1 concentration, were systematically investigated. The favorite pH for the conditioning process was around the neutral. CaCl₂ was found to be a good conditioning aid to TJ-F1. A right dosage of TJ-F1 was decisive for the conditioning process. The optimized conditioning process is that about 0.17% (w/w) TJ-F1 and 1.3% (w/w) CaCl₂ are added into the sludge, and then the system pH was adjusted to 7.5. The compound use of TJ-F1 and P(AM-DMC) was also testified to be feasible in improving the dewaterability of the waste sludge.     

Adsorption of Cu(II) from industrial liquid waste on Na-bentonite and Al-PILC following a full factorial design

The paper reports a study of the performance of Maghnia bentonite in a purified and modified state for the removal of Cu(II) from industrial liquid waste in the region of Oran (North West Algeria). Bentonite was firstly treated to produce a Na-bentonite, then modified with an aluminum solution containing molar ratio OH/Al of 1.8 and finally calcined at 450 °C. The polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ formed in solution was adsorbed by surface complexation on the bentonite, which is known to have a high capacity to fix metal cations. The prepared materials were characterized by DRX, BET and EDX. In order to find the optimum conditions, a full factorial design of 2⁴ allowed us to determine the main effects and interactions of the factors studied: pH, mass of materials, contact time and temperature. The results obtained show that the best rate of adsorption of copper requires a pH = 10, a mass = 0.8 g, a stirring time = 80 min, and a temperature = 25 °C. The adsorption capacity of treated bentonite increased considerably from 4.147 mg/g for Na-bentonite to 7.173 mg/g for pillared aluminum bentonite. This shows the strong adsorption of copper compared with Na-bentonite, caused by its high surface area.     

Piso sto Chorio … I Apantisi stin Krisi einai i Agrotiki Paragogi[Back to the Village … The Answer to the Crisis is Agricultural Production]

In this study, groups of batch experiments were designed to identify the characteristics of alum sludge for arsenic (As) adsorption. Air-dried alum sludge (moisture content 13.9%) collected from a water treatment works in Xi’an, China, was subjected to artificial As-rich wastewater adsorption tests using As₂O₃ as a model As source. Adsorption behaviours were investigated and the results have shown that the Langmuir adsorption isotherm well fits the experimental data (R² = 0.94957–0.99365). The maximum adsorption capacities range from 0.61 to 0.96 mg-As/g when the pH of the As solution was varied from 9.0 to 4.0. The prospects in China for the outcome of this study are discussed. This promising low-cost technique can eradicate As contamination in China.     

Defluoridation of wastewaters using waste carbon slurry

Adsorption of fluoride on waste carbon slurry was investigated. Waste carbon slurry was obtained from fuel oil based generators of a fertilizer industry. The work involves batch experiments to investigate the effects of contact time, pH, temperature and adsorbent dose on the extent of adsorption by carbon slurry. The contact time and pH for maximum fluoride uptake were found 1h and 7.58, respectively. Maximum adsorption capacity (4.861 mg g(-1)) of fluoride on carbon slurry was observed at 15.00 mg L(-1) initial fluoride concentration using 1.0 g L(-1) adsorbent dose. Among four applied models, the experimental isotherm data were found to follow Langmuir equation more closely. Thermodynamically, adsorption was found endothermic with values 7.348 kJ mol(-1), -25.410 kJ mol(-1) and 0.109 kJ mol(-1)K(-1) for enthalpy, free energy and entropy, respectively showing the feasibility of adsorption process. From kinetic analysis, the adsorption was found to follow second-order mechanism with rate constant 49.637 gm g(-1)min(-1). The rate-controlling step of the adsorption was found pore diffusion controlled. In order to investigate the potential of this adsorbent on industrial scale, column and desorption experiments were carried out. The breakthrough capacity of column was calculated 4.155 mg g(-1) with at a flow rate of 1.5 mL min(-1). The proposed adsorbent has been used to remove fluoride from groundwater and wastewater. Desorption has been achieved under alkaline conditions (pH 11.6) from exhausted carbon slurry. The performance of carbon slurry was compared with many other reported adsorbent for fluoride removal and it was observed that proposed adsorbent is effective in terms of performance and cost especially.     

蛭石微细粉的特性及其吸附亚甲基蓝的研究

为了探明天然蛭石对于有机阳离子染料的吸附特性,本文系统表征了气流粉粹得到的蛭石微细粉的物相组成、粒度分布、孔径分布、比表面积、Zeta电位;研究了在不同pH值、固液比、时间、亚甲基蓝浓度条件下蛭石微细粉对亚甲基蓝的吸附量和去除率.结果表明,该蛭石微细粉的主要矿物相为蛭石,含有少量的云母,平均粒径为21.65μm,比表面积为12.63m^2/g,表面呈负电荷.在pH值呈中碱性时蛭石对亚甲基蓝的吸附量最大.在固液比为3g/L、浓度为50mg/L、吸附时间为8h的条件下,蛭石对亚甲基蓝浓度的吸附量为16.42mg/g,去除率达到98.54％.     

Design parameters for sludge reduction in an aquatic worm reactor

Reduction and compaction of biological waste sludge from waste water treatment plants (WWTPs) can be achieved with the aquatic worm Lumbriculus variegatus. In our reactor concept for a worm reactor, the worms are immobilised in a carrier material. The size of a worm reactor will therefore mainly be determined by the sludge consumption rate per unit of surface area. This design parameter was determined in sequencing batch experiments using sludge from a municipal WWTP. Long-term experiments using carrier materials with 300 and 350 μm mesh sizes showed surface specific consumption rates of 45 and 58 g TSS/(m² d), respectively. Using a 350 μm mesh will therefore result in a 29% smaller reactor compared to using a 300 μm mesh. Large differences in consumption rates were found between different sludge types, although it was not clear what caused these differences. Worm biomass growth and decay rate were determined in sequencing batch experiments. The decay rate of 0.023 d⁻¹ for worms in a carrier material was considerably higher than the decay rate of 0.018 d⁻¹ for free worms. As a result, the net worm biomass growth rate for free worms of 0.026 d⁻¹ was much higher than the 0.009-0.011 d⁻¹ for immobilised worms. Finally, the specific oxygen uptake rate of the worms was determined at 4.9 mg O₂/(g ww d), which needs to be supplied to the worms by aeration of the water compartment in the worm reactor.     

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH₄⁺-N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.     

Study on the adsorption of Neutral Red from aqueous solution onto halloysite nanotubes

Halloysite nanotubes (HNTs), a low-cost available clay mineral, were tested for the ability to remove cationic dye, Neutral Red (NR), from aqueous solution. Natural HNTs used as adsorbent in this work were initially characterized by XRD, FT-IR, TEM and BET. The effect of adsorbent dose, initial pH, temperature, initial concentration and contact time were investigated. Adsorption increased with increase in adsorbent dose, initial pH, temperature and initial concentration. The equilibrium data were well described by both the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 54.85, 59.24 and 65.45 mg/g at 298, 308 and 318 K, respectively. Batch kinetic experiments showed that the adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. Thermodynamic parameters of ΔG⁰, ΔH⁰ and ΔS⁰ indicated the adsorption process was spontaneous and endothermic. The results above confirmed that HNTs had the potential to be utilized as low-cost and relatively effective adsorbent for cationic dyes removal.     

Pesticides removal from waste water by activated carbon prepared from waste rubber tire

Waste rubber tire has been used for the removal of pesticides from waste water by adsorption phenomenon. By applying successive chemical and thermal treatment, a basically cabonaceous adsorbent is prepared which has not only a higher mesopore, macropore content but also has a favorable surface chemistry. Presence of oxygen functional groups as evidenced by FTIR spectra along with excellent porous and surface properties were the driving force for good adsorption efficiency observed for the studied pesticides: methoxychlor, methyl parathion and atrazine. Batch adsorption studies revealed maximum adsorption of 112.0 mg g⁻¹, 104.9 mg g⁻¹ and 88.9 mg g⁻¹ for methoxychlor, atrazine and methyl parathion respectively occurring at a contact time of 60 min at pH 2 from an initial pesticide concentration of 12 mg/L. These promising results were confirmed by column experiments; thereby establishing the practicality of the developed system. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the adsorbent with a higher adsorption capacity than most other adsorbents. The adsorption equilibrium data obey Langmuir model and the kinetic data were well described by the pseudo-first-order model. Applicability of Bangham’s equation indicates that diffusion of pesticide molecules into pores of the adsorbent mainly controls the adsorption process. Spontaneous, exothermic and random characteristics of the process are confirmed by thermodynamic studies. The developed sorbent is inexpensive in comparison to commercial carbon and has a far better efficiency for pesticide removal than most other adsorbents reported in literature.     

Performance of granular zirconium-iron oxide in the removal of fluoride from drinking water

In this study, a granular zirconium-iron oxide (GZI) was successfully prepared using the extrusion method, and its defluoridation performance was systematically evaluated. The GZI was composed of amorphous and nano-scale oxide particles. The Zr and Fe were evenly distributed on its surface, with a Zr/Fe molar ratio of ∼2.3. The granular adsorbent was porous with high permeability potential. Moreover, it had excellent mechanical stability and high crushing strength, which ensured less material breakage and mass loss in practical use. In batch tests, the GZI showed a high adsorption capacity of 9.80 mg/g under an equilibrium concentration of 10 mg/L at pH 7.0, which outperformed many other reported granular adsorbents. The GZI performed well over a wide pH range, of 3.5-8.0, and especially well at pH 6.0-8.0, which was the preferred range for actual application. Fluoride adsorption on GZI followed pseudo-second-order kinetics and could be well described by the Freundlich equilibrium model. With the exception of HCO₃⁻, other co-existing anions and HA did not evidently inhibit fluoride removal by GZI when considering their real concentrations in natural groundwater, which showed that GZI had a high selectivity for fluoride. In column tests using real groundwater as influent, about 370, 239 and 128 bed volumes (BVs) of groundwater were treated before breakthrough was reached under space velocities (SVs) of 0.5, 1 and 3 h⁻¹, respectively. Additionally, the toxicity characteristic leaching procedure (TCLP) results suggested that the spent GZI was inert and could be safely disposed of in landfill. In conclusion, this granular adsorbent showed high potential for fluoride removal from real groundwater, due to its high performance and physical-chemical properties.     

Potassium hexacyanoferrate–clinoptilolite adsorbent for removal of Cs+ and Sr2+ from aqueous solutions

A new adsorbent was prepared by impregnation of nano-sized clinoptilolite by nickel hexacyanoferrate. The synthesized nano-adsorbent was changed to spherical beads by use of phenolsulphonic-formaldehyde resin. Techniques used to study the physicochemical properties of the adsorbent included Fourier transform infrared spectroscopy, X-ray diffraction, thermal methods (DTG-TGA), scanning electron microscopy, and energy dispersive X-ray spectroscopy. The adsorbent beads were used to remove Cs⁺ and Sr²⁺ from aqueous solutions in different experimental conditions. The maximum adsorption capacity of 171.3 and 70.5 mg g^?1 were obtained for Cs⁺ and Sr²⁺ respectively. The adsorption data were examined with the Langmuir and Freundlich isotherm models. It was concluded that the data were best modelled by the Langmuir equation indicating monolayer sorption of Cs⁺ and Sr²⁺ on the surface of the nano-composite. The data were well described by the pseudo-second-order model. Thermodynamic parameters, selectivity and regeneration capability of the adsorbent were determined and discussed.     

Removal of estrone and 17beta-estradiol from water by adsorption

Endocrine disrupting chemicals (EDCs) are the focus of current environment concern, as they can cause adverse health effects in an intact organism, or its progeny, subsequent to endocrine function. The paper reports on the removal of estrone (E1) and 17beta-estradiol (E2) from water through the use of various adsorbents including granular activated carbon (GAC), chitin, chitosan, ion exchange resin and a carbonaceous adsorbent prepared from industrial waste. The results show that the kinetics of adsorption were adsorbent and compound-dependent, with equilibration being reached within 2 h for a waste-derived carbonaceous adsorbent to 71 h for an ion-exchange resin for E1, and within 7 h for the waste-derived carbonaceous adsorbent to 125 h for GAC for E2. Of all the adsorbents tested, the carbonaceous adsorbent showed the highest adsorption capacity, with a maximum adsorption constant of 87500 ml/g for E1 and 116000 ml/g for E2. The GAC also had a very high adsorption capacity for the two compounds, with a maximum adsorption constant of 9290 ml/g for E1 and 12200 ml/g for E2. The effects of some fundamental environmental parameters including adsorbent concentration, pH, salinity and the presence of humic acid and surfactant on adsorption were studied. The results show that adsorption capacity of activated carbon was decreased with an increase in adsorbent concentration and by the presence of surfactant and humic acid. The results have demonstrated excellent performance of a waste derived adsorbent in removing E1 and E2 from water, and indicated the potential of converting certain solid waste into useful adsorbents for pollution-control purposes.     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

微波法制备污泥吸附剂的性能优化研究

通过向污泥中添加吸收微波能的物质实现了微波热解法制备污泥吸附剂,并考察了不同制备条件对污泥吸附剂性能的影响.结果表明,当污泥用量为35 g时,微波法制备污泥吸附剂的最佳务件:微波功率为1.2 kW、辐照时间为10 min、微波能吸收物质的用量为10 g,制得的污泥吸附剂的碘吸附值达585.95 mg/g.采用扫描电镜分析污泥吸附剂的表观结构可知,适宜的微波辐射通过有效热解污泥中的有机质可形成以炭骨架为主体的污泥吸附剂,该吸附剂可有效吸附酸、碱染料,但吸附量与商业活性炭仍存在一定差距.     

Laboratory study on the adsorption of Mn²⁺ on suspended and deposited amorphous Al(OH)₃ in drinking water distribution systems

Manganese (II) is commonly present in drinking water. This paper mainly focuses on the adsorption of manganese on suspended and deposited amorphous Al(OH)₃ solids. The effects of water flow rate and water quality parameters, including solution pH and the concentrations of Mn²⁺, humic acid, and co-existing cations on adsorption were investigated. It was found that chemical adsorption mainly took place in drinking water with pHs above 7.5; suspended Al(OH)₃ showed strong adsorption capacity for Mn²⁺. When the total Mn²⁺ input was 3 mg/L, 1.0 g solid could accumulate approximately 24.0 mg of Mn²⁺ at 15 °C. In drinking water with pHs below 7.5, because of H⁺ inhibition, active reaction sites on amorphous Al(OH)₃ surface were much less. The adsorption of Mn²⁺ on Al(OH)₃ changed gradually from chemical coordination to physical adsorption. In drinking water with high concentrations of Ca²⁺, Mg²⁺, Fe³⁺, and HA, the removal of Mn²⁺ was enhanced due to the effects of co-precipitation and adsorption. In solution with 1.0 mg/L HA, the residual concentration of Mn²⁺ was below 0.005 mg/L, much lower than the limit value required by the Chinese Standard for Drinking Water Quality. Unlike suspended Al(OH)₃, deposited Al(OH)₃ had a much lower adsorption capacity of 0.85 mg/g, and the variation in flow rate and major water quality parameters had little effect on it. Improved managements of water age, pipe flushing and mechanical cleaning were suggested to control residual Mn²⁺.     

Physical and chemical properties of activated sludge floc

Physical and chemical characteristics of activated sludge such as floc size, density, specific surface, carbohydrate content, dehydrogenase activity and settleability were investigated by seven parallel bench scale activated sludge units operated under different sludge ages (1.1–17.4 days). The analytical methods used included a dye adsorption technique for specific surface area determinations, the Coulter Counter method for floc size measurements and interference microscopy for floc density determinations. The typical floc sizes were found to be in the range 10–70 μm with floc densities in the range 1.015–1.034 g cm⁻³. A strong correlation between floc density and size was obtained. The specific surface areas measured (typically 100–200 m² g⁻¹ dry sludge) were found to be one to two orders of magnitude higher than the corresponding geometric floc surface areas, indicating a porous floc structure. Sludge settleability, for non-filamentous sludges, was well correlated to both floc size, density and specific surface area, but not to the sludge carbohydrate content, which was found to vary between 6 and 18%.