Adsorption of copper(II) onto sewage sludge-derived materials via microwave irradiation

Biosolids-based activated carbon for enhanced copper removal from citric-acid-rich aqueous media

In this study, we employed batch experiments to assess the effects of citric acid on the Cu(II) removal efficiencies of seven biosolids-based adsorbents. The adsorbents used were dried biosolids (BS), biosolids biochar (BSBC), biosolids-based activated carbon (SBAC), nitric-acid-modified BSBC (BSBC-HNO₃) and SBAC (SBAC-HNO₃), and amine-modified BSBC (BSBC-NH₂) and SBAC (SBAC-NH₂). However, with 100 mM citric acid in 1 mM Cu(II) solution, only SBAC showed an increase in Cu(II) removal efficiency (64.0-93.5%). Therefore, we used SBAC for further optimisation of the adsorption process. The kinetics data, optimally described by the pseudo-second-order model, indicated that bulk Cu(II) adsorption occurred within 10 min. The highest Cu(II) removal was at pH 3, with the estimated maximum Cu(II) adsorption capacity of SBAC increasing from 0.14 to 0.30 mmol/g, with 100 mM citric acid present. This result clearly indicated the positive effect of citric acid on Cu(II) adsorption. With citric acid present, the Freundlich model optimally fitted the adsorption isotherm data, suggesting adsorption of Cu(II) in multilayers. Further investigation of Cu(II) adsorption in a sequential setup proved that SBAC could lower the residual Cu(II) in the solution to below the discharge limit (0.05 mM) in 1 h. Overall, the production of activated carbon from BS has been proven an efficient Cu(II) adsorbent for Cu-citric-acid-rich aqueous media as a simulation of real wastewaters/leachates, as well as achieving waste-to-resources goals. This is the first study to identify an adsorbent (SBAC) with increased Cu(II) adsorption capacity in the presence of excess citric acid.

The effect of biochar mild air oxidation on the optimization of lead(II) adsorption from wastewater

In the present study, the effects of mild air oxidation of a biochar produced by the Pyrovac Inc. pyrolysis process, on the adsorption of lead(II) from synthetic wastewater under batch experimental conditions have been investigated. The adsorption experiments were performed under several conditions suggested by the response surface methodology, which allowed finding the optimal conditions, in order to maximize the adsorption capacity (Q(mgg^-1)), as well as the extraction efficiency (E (%)). The optimal conditions of lead ions adsorption were as follows: pH = 5, agitation time = 300 min, adsorbent mass = 0.5 g (per 50 cm³ of solution), and lead initial concentration = 100gm^-3, resulted in an adsorption capacity of 7.9 mg g^-1. Equilibrium adsorption was then obtained by keeping pH and adsorbent mass at the optimal values and changing the lead initial concentration for a sufficient agitation time. Results showed that mild air oxidation increased the equilibrium adsorption capacity of biochar from 2.5 to 44 mg g^-1. Oxidized biochar after equilibrium adsorption was submitted to SEM/EDX and XPS analysis. From SEM it was found that lead particles were distributed heterogeneously after adsorption. From XPS analysis, it was revealed that the external surface of oxidized biochar particles becomes saturated for the initial point of equilibrium diagram, obtained at lead initial concentration of 100gm^-3, suggesting that for a higher concentration, the internal surfaces of particles participate in the cations adsorption. The participation of surface functional groups in the adsorption process showed that carbonyl, carboxylic, and aromatic rings of oxidized biochar were involved in the adsorption. This work suggests that the very simple process of mild air oxidation can be used instead of the usual costly chemical activation, in order to improve biochar cation exchange capacity.

The thermochemical conversion of non-lignocellulosic biomass to form biochar: A review on characterizations and mechanism elucidation

Biochar obtained from non-lignocellulosic biomass (NLBM) has attracted wide interests in various fields like pollutants removal, catalysis, and energy storage. However, the thermochemical conversion processes from NLBM to non-lignocellulosic biochar (NLBC) have not been well summarized until now. To fill the knowledge gap, this review presents a systematical summary of NLBM characteristics, thermochemical behaviors of main components (e.g., C, O, N, P and metals), characterization methods for NLBC and conversion process, and the main applications of NLBC. Moreover, the vacancy and limitations of the current researches are pointed out to provide some guidance for future study. This review would contribute to deepen the understanding of NLBC, meanwhile optimize the efficient disposal and value-added utilization of NLBM wastes via thermochemical conversion.

Characteristics and adsorption study of the activated carbon derived from municipal sewage sludge

Sewage sludge-based activated carbon is proved to be an efficient and low-cost adsorbent in treatment of various industrial wastewaters. The produced carbon had a well-developed pore structure and relatively low Brunauer-Emmett-Teller (BET) surface area. Adsorptive capacity of typical pollutants, i.e. copper Cu(II) and methylene blue (MB) on the carbon was studied. Adsorptions were affected by the initial solution pH, contact time and adsorbent dose. Results showed that adsorption of Cu(II) and MB on the produced carbon could reach equilibrium after 240 min. The average removal rate for Cu(II) on the carbon was high, up to 97% in weak acidic conditions (pH = 4-6) and around 98% for MB in a very wide pH range (pH = 2-12). The adsorption kinetics were well fitted by the pseudo-second order model, and both Langmuir and Freundlich isotherm models could well describe the adsorption process at room temperature. The theoretical maximum adsorption capacities of Cu(II) and MB on sewage sludge-based activated carbon were 114.94 mg/g and 125 mg/g, respectively. Compared with commercial carbon, the sewage sludge-based carbon was more suitable for heavy metal ions' removal than dyes'.

Utilization of sludge based adsorbents for the removal of various pollutants: A review

Sludge based adsorbents are widely used for the removal of various pollutants from water and wastewater systems and the available data is much diversified. The purpose of this review is to organize and critically review the scattered available information on the potential of use of sludge based adsorbents for the removal of various pollutants. It was observed that performance of the sludge based adsorbents varies depending on the type of pollutants, type of precursor sludge, carbonization time-temperature profile and the type of activation conditions used. The variation in pyrolysis and activation conditions found to directly affect the adsorbent properties, adsorption capacity and the mechanism of pollutant removal by sludge based adsorbents. The interaction mechanisms of pollutants with adsorbent surface found to have a detrimental effect on desorption and regeneration of the adsorbents and its recycling potential. Therefore, desorption and regeneration technique used for recycle of the adsorbents is also discussed in detail. Moreover, life cycle and cost analysis of sludge based adsorbents is assessed to ensure the cost effectiveness of their application in water treatment operations.

Comparative study of the role of extracellular polymeric substances in biosorption of Ni(II) onto aerobic/anaerobic granular sludge

This study was carried out to comparatively evaluate the role of extracellular polymeric substances (EPS) in biosorption of Ni(II) onto aerobic/anaerobic granular sludge (AGS and AnGS). Batch sorption experiments data suggested that Ni(II) sorption onto AGS and AnGS were better fitted to Langmuir and Freundlich model, respectively. The contribution of EPS in the sorption of AnGS was higher than that of AGS. Interaction between EPS and Ni(II) was investigated by a combined three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra, two-dimensional correlation spectroscopy (2D-COS) and fourier transform infrared spectroscopy (FTIR). 3D-EEM showed that protein (PN)-like substances were the main peaks in EPS from AGS and AnGS. The quenched types of AGS and AnGS in the presence of Ni(II) belonged to dynamic and static quenching, respectively. Additionally, 2D-COS demonstrated that fluorescence change took place sequentially followed to humic-like region>PN-like region in AGS and fulvic-like fraction>PN-like and humic-like fractions in AnGS. According to FTIR spectra, hydroxyl group and amino group in both EPS were the key functional groups for Ni(II) sorption.

Chemical forms and risk assessment of heavy metals in sludge-biochar produced by microwave-induced low temperature pyrolysis

Microwave-induced low temperature pyrolysis can reduce the risk of most heavy metals in biochar prepared from sewage sludge, except the Cd and Pb.

Aqueous mercury adsorption by activated carbons

Due to serious public health threats resulting from mercury pollution and its rapid distribution in our food chain through the contamination of water bodies, stringent regulations have been enacted on mercury-laden wastewater discharge. Activated carbons have been widely used in the removal of mercuric ions from aqueous effluents. The surface and textural characteristics of activated carbons are the two decisive factors in their efficiency in mercury removal from wastewater. Herein, the structural properties and binding affinity of mercuric ions from effluents have been presented. Also, specific attention has been directed to the effect of sulfur-containing functional moieties on enhancing the mercury adsorption. It has been demonstrated that surface area, pore size, pore size distribution and surface functional groups should collectively be taken into consideration in designing the optimal mercury removal process. Moreover, the mercury adsorption mechanism has been addressed using equilibrium adsorption isotherm, thermodynamic and kinetic studies. Further recommendations have been proposed with the aim of increasing the mercury removal efficiency using carbon activation processes with lower energy input, while achieving similar or even higher efficiencies.

Development of sludge-based adsorbents: preparation, characterization, utilization and its feasibility assessment

The increasing generation of sludge and its subsequent treatment are very sensitive environmental problems. For a more stable and sustainable treatment of sludge, there have been many studies, including the conversion of sludge into sludge-based adsorbents (SBAs) for pollutants removal. In this review, current SBAs preparation conditions and use as adsorbent for contaminant removal in water treatment are summarized and discussed. Carbonization, physical activation and chemical activation are three common preparation methods. The controlling key parameters include pyrolysis temperature, dwell time, heating rate, activator and feedstock type. The efficacy of SBAs in contaminant adsorption depends on their surface area, pore size distribution, surface functional groups and ion-exchange capacity. It has been demonstrated that SBAs can attain high uptakes of dyes and metal ions due to their high cation exchange capacity; whereas the strong antibiotics adsorption performance of SBAs derives from high degree of mesoporosity. In addition, thermal treatment significantly stabilizes heavy metals contained in sludge. The paper also discusses the economic feasibility and environmental safety of preparation and application of SBAs. Further research will include investigations on the migration and transformation of element in sludge by thermal treatment, more economical and efficient chemical activation reagents, obtaining SBAs for designated application, combination of coagulation and SBAs adsorption, regeneration of SBAs and full-scale tests.

Characterization of top phase oil obtained from co-pyrolysis of sewage sludge and poplar sawdust

To research the impact of adding sawdust on top phase oil, a sewage sludge and poplar sawdust co-pyrolysis experiment was performed in a fixed bed. Gas chromatography (GC)/mass spectrometry (MS) was used to analyze the component distribution of top phase oil. Higher heating value, viscosity, water content, and pH of the top phase oil product were determined. The highest top phase oil yield (5.13 wt%) was obtained from the mixture containing 15% poplar sawdust, while the highest oil yield (16.51 wt%) was obtained from 20% poplar sawdust. Top phase oil collected from the 15% mixture also has the largest amount of aliphatics and the highest higher heating value (28.6 MJ/kg). Possible reaction pathways were proposed to explain the increase in the types of phenols present in the top phase oil as the proportion of poplar sawdust used in the mixture increased. It can be concluded that synergetic reactions occurred during co-pyrolysis of sewage sludge and poplar sawdust. The results indicate that the high ash content of the sewage sludge may be responsible for the characteristic change in the top phase oil obtained from the mixtures containing different proportions of sewage sludge and poplar sawdust. Consequently, co-pyrolysis of the mixture containing 15 % poplar sawdust can increase the yield and the higher heating value of top phase oil.

Structure and adsorption properties of sewage sludge-derived carbon with removal of inorganic impurities and high porosity

Purified sludge carbon (PSC) with removal of inorganic 'impurities' (Si, Al, etc.) is prepared from sewage sludge. Morphological structure, textural properties, surface elements and functional groups of sludge carbon (SC) and PSC are compared. SBET and pore volume of PSC are about three times higher than those of SC. PSC with large fluffy cavities remains some memory of SC parent structure. Removed fractions can be considered as a natural template for producing a hierarchical porous structure in PSC. Abundant oxygen-containing groups including hydroxyl and epoxide are generated in PSC, which are favorable for organic contaminant removal from wastewater. Diffraction peaks at 2θ = 45°, bending modes of Si-O-Si and Na1s peaks (1070.5 eV) jointly confirm that only a trace of adsorbed impurities (Na2O·(SiO2)x (x ≥ 1)) is retained on PSC surface. PSC is superior to SC and comparable to commercial activated carbon for rhodamine B and phenol adsorption capacity.

Emission factor of exhaust gas constituents during the pyrolysis of zinc chloride immersed biosolid

Pyrolysis enables ZnCl2 immersed biosolid to be reused, but some hazardous air pollutants are emitted during this process. Physical characteristics of biosolid adsorbents were investigated in this work. In addition, the constituents of pyrolytic exhaust were determined to evaluate the exhaust characteristics. Results indicated that the pyrolytic temperature was higher than 500 °C, the specific surface area was >900 m(2)/g, and the total pore volume was as much as 0.8 cm(3)/g at 600 °C. For non-ZnCl2 immersed biosolid pyrolytic exhaust, VOC emission factors increased from 0.677 to 3.170 mg-VOCs/g-biosolid with the pyrolytic temperature increase from 400 to 700 °C, and chlorinated VOCs and oxygenated VOCs were the dominant fraction of VOC groups. VOC emission factors increased about three to seven times, ranging from 1.813 to 21.448 mg/g for pyrolytic temperatures at 400-700 °C, corresponding to the mass ratio of ZnCl2 and biosolid ranging from 0.25-2.5.

Adsorption of Pb(II) from aqueous solution by silica-gel supported hyperbranched polyamidoamine dendrimers

The adsorption properties of silica-gel supported hyperbranched polyamidoamine dendrimers (SiO(2)-G0-SiO(2)-G4.0) have been investigated by batch method. The effect of pH of the solution, contact time, initial Pb(II) ion concentration, temperature and coexisting metal ions have been demonstrated. The results indicated that the optimum pH value was 5. Adsorption kinetics was found to follow the pseudo-second-order model and controlled by film diffusion. The adsorption isotherms were fitted by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Langmuir isotherm model was found to be more suitable to describe the equilibrium data, suggesting the uptake of Pb(II) ions by monolayer adsorption. From D-R isotherm model, the calculated mean free energy E demonstrated the adsorption processes occurred by chemical ion-exchange mechanism. FTIR analysis revealed that amine groups were mainly responsible for the adsorption of Pb(II) by amino-terminated adsorbents, while CO of ester groups also participated in the adsorption process of ester-terminated ones. The adsorbents can selectively adsorb Pb(II) from binary ion systems in the presence of Mn(II), Cu(II), Co(II), and Ni(II). Based on the results, it is concluded that SiO(2)-G0-SiO(2)-G4.0 had great potential for the removal of Pb(II) from aqueous solution.

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500°C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200 d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.

Characterisation of adsorbents prepared by pyrolysis of sludge and sludge/disposal filter cake mix

Copper and zinc removal from water (pH = 5.0) using adsorbents produced from slow and fast pyrolysis of industrial sludge and industrial sludge mixed with a disposal filter cake (FC), post treated with HCl, is investigated in comparison with a commercial adsorbent F400. The results show that a pseudo-second order kinetics model is followed. The Langmuir-Freundlich isotherm model is found to fit the data best. The capacity for heavy metal removal of studied adsorbents is generally better than that of commercial F400. The dominant heavy metal removal mechanism is cation exchange. Higher heavy metal removal capacity is associated with fast pyrolysis adsorbents and sludge/FC derived adsorbents, due to enhanced cation exchange. Improvement of Zn(2+) removal via 1 N HCl post-treatment is only effective when exchangeable cations of the adsorbent are substituted with H(+) ions, which boost the cation exchange capacity. Increase of temperature also enhances metal removal capacity. Fast pyrolysis sludge-based adsorbents can be reused after several adsorption-desorption cycles.

Utilization of municipal sewage sludge as additives for the production of eco-cement

The effects of using dried sewage sludge as additive on cement property in the process of clinker burning were investigated in this paper. The eco-cement samples were prepared by adding 0.50-15.0% of dried sewage sludge to unit raw meal, and then the mixtures were burned at 1450 °C for 2 h. The results indicated that the major components in the eco-cement clinkers were similar to those in ordinary Portland cement. Although the C(2)S phase formation increased with the increase of sewage sludge content, it was also found that the microstructure of the mixture containing 15.0% sewage sludge in raw meal was significantly different and that a larger amount of pores were distributed in the clinker. Moreover, all the eco-cement pastes had a longer initial setting time and final setting time than those of plain cement paste, which increased as the sewage sludge content in the raw meal increased. All the eco-cement pastes had lower early flexural strengths, which increased as the sewage sludge content increased, while the compressive strengths decreased slightly. However, this had no significant effect on all the strengths at later stages. Furthermore, the leaching concentrations of all the types of eco-cement clinkers met the standard of Chinese current regulatory thresholds.