Sludge-based Activated Carbon Research Articles

Using circular economy principles in the optimisation of sludge-based activated carbon production for the removal of perfluoroalkyl substances

Massive sewage sludge (SS) production from municipal wastewater treatment plants and the presence of numerous pollutant types render the process of SS treatment and disposal costly and complex. Here, resource recovery from SS was maximised via the optimisation of sludge-based activated carbon (SBAC) production for the removal of poly- and perfluoroalkyl substances (PFASs), while considering economic factors and minimising environmental impacts. SBAC production optimisation was realised under different operating conditions (different ZnCl2 impregnation ratios and different pyrolysis activation temperatures and durations). The sorption capacity of the optimised SBAC with respect to the removal of nine commonly detected PFASs, with environmentally relevant concentrations (∽50 μg/L), from simulated wastewater was evaluated. Economic analysis and life-cycle assessment (LCA) were also performed to determine the feasibility of the process and its potential role in the circular economy. Batch adsorption tests confirmed the high efficiency of the optimised SBACs for PFAS removal (93–100 %), highlighting the possibility of converting SS to SBAC. Economically speaking, the optimised SBAC at 1.5 M ZnCl2, 500 °C, and 0.75 h reduced total production cost by 49 %. Further, the cost could be reduced to as little as 1087 US $/metric-ton compared with that corresponding to the original conditions (2.5 M ZnCl2, 500 °C, 2 h; 2144 US $/metric-ton). LCA results also showed that freshwater ecotoxicity, marine ecotoxicity, and human non-carcinogenic toxicity were the most affected environmental impact indicators, showing a 49 % decrease when ZnCl2 impregnation ratio was reduced from 2.5 to 1.5 M. These findings highlighted the optimal conditions for the production of SBAC with high sorption capacity at a reduced cost and with reduced environmental impacts. Thus, they can serve as valuable tools for decision making regarding the selection of the most sustainable and economically feasible process for PFAS removal.

Circular economy in wastewater treatment plants: Treatment of contaminants of emerging concerns (CECs) in effluent using sludge-based activated carbon

Contaminants of Emerging Concern (CECs), including polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), and poly and perfluoroalkyl substances (PFASs), have been frequently detected at high concentrations in discharged wastewater effluents and biosolids. This study investigates the occurrence and removal of various PAHs, PFASs, and PBDEs from the final discharge effluent of a major Canadian wastewater treatment plant. We evaluated two seasons of the year (warm and cold) (effluents A and B) using sludge-based activated carbon (SBAC) samples synthesised from thickened waste secondary sludge and biosolids, named TS-SBAC and BioSBAC, respectively. The average removal efficiency of BioSBAC (at concentrations of 1 and 10 g SBAC in 1-L effluent) for PAHs and alkyl-PAHs in effluent A was 88–100% (residual concentrations below the reporting limit [RL] at 16.7 ng/L), and that of TS-SBAC (concentration of 1 g SBAC in 1-L effluent) in effluent B (below RL, at 20.8 ng/L) was 68–100%. The average removal efficiency of BioSBAC for PBDEs was 88–100% for effluent A (below RL, at 1.26 ng/L), and that of TS-SBAC for effluent B (below RL, at 1.14 ng/L) was 52–100%. The average BioSBAC removal range of PFASs from effluent B (below RL, at 5.37 ng/L) was 30–100%, with significant removal of long-chain (>C7) PFASs. These findings indicate that producing an efficient adsorbent (i.e., SBAC) from sewage sludge is a sustainable integrated circular economy solution for stabilising CECs, including PAHs, PFASs, and PBDEs, to improve the quality of wastewater effluents in a closed-loop system, with no waste being generated.

A comparative life-cycle assessment and cost analysis of biofilters amended with sludge-based activated carbon and commercial activated carbon for stormwater treatment

Environmental and economic issues resulting from the unsustainable management of sewage sludge from wastewater have necessitated the development of eco-friendly sewage sludge disposal methods, whereas stormwater effluent contains tremendous amounts of pollutants. This study compares the feasibility and environmental impacts associated with incorporating biofilters with sludge-based activated carbon (SBAC) versus commercial activated carbon (CAC) for stormwater treatment. The results demonstrate that the construction and disposal life-cycle stages are the dominant contributors to several environmental impact categories, including resource scarcity, carcinogenic toxicity, terrestrial ecotoxicity, and ozone formation indicators. Across multiple impact categories, the incorporation of biofilters with SBAC can reduce the negative environmental impacts associated with biofilter construction and disposal by 40% over a 50-year analysis period. In contrast, the most significant improvement is on construction-dominant indicators, where the decreased need for biofilter reconstruction results in a higher reduction in environmental impacts. Economically, amending the biofilter with SBAC can increase profits by up to 66% due to extending its lifespan. This study shows that SBAC has similar performance as CAC for lowering the negative environmental impacts resulting from biofilter construction, while increasing the overall net profits of the system. However, converting sewage sludge to an effective sorbent (SBAC) and incorporating SBAC into a biofilter to capture pollutants from stormwater is an economically and environmentally sustainable solution available to practitioners to manage sewage sludge and stormwater effluent. This solution protects the environment in a cost efficient, sustainable manner.

Sludge-based activated carbon from two municipal sewage sludge precursors for improved secondary wastewater-treatment discharge-effluent

This study investigated the use of sludge-based activated carbon (SBAC) sorbent as an integrated waste-to-resources approach for the removal of contaminants from wastewater. We measured the ability of SBAC sorbents from two types of municipal sewage sludge (SS) precursors (thickened waste SS “TWSS-SBAC” and biosolids “Bio-SBAC”) from a Canadian wastewater treatment plant (WWTP) to stabilise emerging contaminants (ECs) from precursor SS and to remove ECs from the discharged effluent. The ECs were from pharmaceutical and personal care products (PPCPs), including antibiotics, disinfectants, and antibacterial hand-sanitisers and soaps, which were commonly used during the COVID-19 (coronavirus disease of 2019) pandemic. We measured the removal efficacy of Bio-SBAC at two dosages (1 g/L and 10 g/L) and TWSS-SBAC at one dosage (1 g/L) via 30-min batch adsorption tests for eleven PPCPs at mean concentrations of 2–2337 ng/L in the discharged effluent, and compared the results with those of other techniques and sorbents reported in literature. At both dosages, Bio-SBAC removed PPCPs, including four blood regulator compounds that have been extensively used since the pandemic outbreak (furosemide, gemfibrozil, glyburide, and warfarin), with their levels decreasing below the detection limit. The percentage removal for ibuprofen, 2-hydroxy-ibuprofen, and naproxen were 91.6–99.8% using 1 g/L. The antimicrobial compounds triclosan and triclocarban were completely removed at both dosages. Ninety-nine percentage of bisphenol A was removed at 1 g/L dosage and was completely removed at 10 g/L. TWSS-SBAC showed similar performance as Bio-SBAC in removing PPCPs from the final effluent to improve the quality of wastewater discharged from a WWTP.

Efficient Removal of Organic Matter from Biotreated Coking Wastewater by Coagulation Combined with Sludge-Based Activated Carbon Adsorption

Coagulation–adsorption can be effective in the removal of the organic matters remaining in biotreated coking wastewater (BTCW), and cheap and efficient adsorbents benefit the widespread application of this technology. In this study, a sludge-based activated carbon (SAC) was prepared using zinc chloride to activate sludge pyrolysis carbon for the treatment of BTCW with coagulation as the pretreatment process. According to Brunauer-Emmett-Teller (BET) and the scanning electron microscope (SEM) analysis, the SAC exhibited a specific surface area of 710.175 m2/g and well-developed pore structure. The removal characteristics of the organic matter in BTCW were systematically studied. The results show that 76.79% of the COD in the BTCW was removed by coagulation combined with SAC adsorption, and the effluent COD was below the discharge limit (80 mg/L) (GB16171-2012), with the optimal dosages of polyaluminum chloride and SAC being 150 mg/L and 4 g/L, respectively. Compared with a commercial powdered activated carbon (PAC) (48.26%), the SAC achieved a similar COD removal efficiency (47.74%) at a higher adsorption speed. The removal efficiencies of the hydrophobic components (77.27%) and fluorescent components by SAC adsorption were higher than those by PAC adsorption. The SAC also had an excellent removal effect on complex organic compounds and colored substances in the BTCW, as revealed by UV-vis spectra analyses.

Sludge-based activated carbon and its application in the removal of perfluoroalkyl substances: A feasible approach towards a circular economy

This study explores the recovery of resources and energy from sewage sludge through the production of sludge-based activated carbon (SBAC) considering circular economy principles. The SBAC production costs were estimated under three scenarios considering various sludge dewatering/drying schemes to determine the production feasibility and its role in the circular economy. SBAC was tested in the removal of a mixture of nine commonly detected poly- and perfluoroalkyl substances (PFASs) in environmentally relevant concentrations of ∽50 μg/L in comparison to commercially available activated carbon (AC) using 5 mg of sorbent and 5 mL of a nine-PFAS mixture in deionised water. SBAC can be produced at approximately 1.2 US $/kg, which is substantially lower than the average production cost of commercial AC of >3 US $/kg. A net revenue ranging from 2 to 7 US $/kg SBAC was estimated by recycling the produced non-condensable gases and bio-oil to produce energy and selling the SBAC. Batch adsorption tests showed that the PFASs removal of SBAC was superior to that of granular AC and similar to that of powdered AC, reaching >91% to below the detection limit. The kinetics tests revealed that adsorption by SBAC and AC occurred within 15 min. The overall results demonstrate the potential of SBAC as an effective sorbent for PFASs, achieving waste-to-resources circular economy via resource and energy recovery from sewage sludge, eliminating sludge disposal and contaminant-leaching to the environment, and in enhancing the quality of wastewater effluent before discharge.

Multiple chemical modifications and Cd2+ adsorption characteristics of sludge-based activated carbon.

Sludge resource utilization is commonly realized through carbonization, but the use of direct carbonization to obtain sludge-based activated carbon (SAC) is not functional yet. The multiple chemical modifications were carried out to achieve N-doping and pore-making to modify SAC. The SACU–PF′ was synthesized by activating sludge simultaneously with uric acid and potassium ferrate. Moreover, SACN′, SACU, and SACPF′ were prepared with no additives, uric acid, and potassium ferrate, respectively. The results indicated that the different modifications affected the chemical properties and structure of SAC. The BET of SACU–PF′ was 56.73 m2 g−1, which was higher than that of SACN′ and SACPF′. SACU–PF′ possessed abundant functional groups, such as C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N and C–O. The adsorption capacity of SACU–PF′ for Cd2+ was 9.69 mg g−1, 5.5 times that of SACN′, the adsorption process of Cd2+ by SACU–PF′ fitted well for the second-order kinetic model and Langmuir isothermal adsorption model. The XPS and chemical analysis revealed that SACU–PF′ and Cd2+ were bonded by functional groups, and the Cd2+ removal by SACU–PF′ was through complexation, anion exchange, electrostatic attraction, and pore filling. The SACU–PF′ was exhibited different removal capacities for different metals, Pb2+ and Mn2+ correspond to adsorption capacities of 4.9 and 8.1 mg g−1. In addition, the adsorbed SACU–PF′ can be regenerated by sodium hydroxide. The study highlights the importance of multiple chemical modifications performed on SAC, the double coupled chemical modifications to ensure its good performance in the treatment of heavy metals in wastewater treatment.

Preparation of sludge-based materials and their environmentally friendly applications in wastewater treatment by heterogeneous oxidation technology.

The sludge resource utilization and the high value-added development are environmentally friendly means for sludge treatment. With its rich organic substances and metals content, sludge can replace activated carbon and become a widely used carbon-based material, such as sludge-based activated carbon (SBAC). Meanwhile, as a heterogeneous catalyst, sludge-based catalyst (SBC) can solve the requirements of traditional Fenton catalysts for pH, metal ion leaching, and catalyst recycling. In this paper, combining the properties of SBAC/SBCs, the characteristics of the three methods of activation, support, and hydrothermal preparation of SBAC/SBCs are reviewed. In general, it is necessary to select an appropriate preparation method based on pollutants and environmental treatment goals. Furthermore, compared with other catalysts, SBC heterogeneous oxidation has obvious advantages in refractory organic pollutants. And the reaction mechanism usually involves SO4·-, ·OH, O2·-, and 1O2 processes. Finally, some possible directions for future research involving environmentally friendly SBAC/SBCs are proposed.

A comprehensive review on the synthesis, performance, modifications, and regeneration of activated carbon for the adsorptive removal of various water pollutants

Rapid urbanization has led to the generation of a large quantum of complex wastewater comprising of recalcitrant organic and inorganic pollutants. The inability of the conventional treatment techniques to bring down the recalcitrant pollutant concentrations below desired standards has paved the way for the emergence of tertiary treatment technologies. Among various tertiary treatment techniques, adsorption is widely preferred due to the ease of operation, high removal performances, and diverse on-field applications. Activated carbon (AC) has found immense popularity due to easy synthesis routes, high stability, large specific surface area (SSA), etc. The synthesis and performance of AC derived from different carbonaceous precursors for pollutants removal, the role of activation techniques, pollutant specific modifications, regeneration techniques, and their disposal, are covered in this article. Trend analysis showed that research on AC derived from agricultural waste and sludge has a high potential for at least another 50 and 25 years, respectively. Most of the precursors are chemically activated to prepare the AC, which may be further modified using the metal impregnation technique for removing specific pollutants. Among various ACs, maximum mean pore volume has been shown by sludge-based AC (1.17 cm3/g) and the maximum mean SSA value has been exhibited by husk-based AC (1339 m2/g). AC is mostly used to treat dyes and metals, followed by pharmaceuticals, pesticides, and other recalcitrant organics. Moreover, by implementing microwave-assisted and biological-based regeneration techniques, the life of the AC can be increased and may serve as an efficient adsorbent for wastewater treatment for a prolonged duration.

Preparation of sludge-based activated carbon for adsorption of dimethyl sulfide and dimethyl disulfide during sludge aerobic composting

Emission of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) during sludge aerobic composting has limited the use and development of this economical sludge treatment process. In this study, cheap and easily available sludge was used as raw material for the preparation of adsorbents to eliminate DMS and DMDS. A series of sludge-based activated carbons (SACs) were prepared by acid or base activation, and coconut shell mix was also assessed. The results revealed that SAC preparation by KOH activation without coconut shell mix could significantly enhance the surface area and pore volume of SAC, and showed the maximum adsorption capacity for DMS (53.45 mg g−1) and DMDS (151.28 mg g−1). In addition, SAC had a good adsorption effect on a mixture of DMS and DMDS. The SAC adsorbents could efficiently adsorb DMS and DMDS after four cycles of regeneration. Thermodynamic and kinetic analyses demonstrated that adsorption between the SAC and DMS/DMDS was via physical adsorption. The SAC developed in this study utilized waste in a useful way that could significantly reduce the cost of adsorbents and use them for odor elimination during sludge aerobic composting.

Effect of iron nitrate modification on elimination of organic matter from landfill leachate by sludge-based activated carbon.

Sludge-based activated carbons (SACs) prepared from sewage sludge and corn straw, were modified by ferric nitrate, and the unmodified SAC and modified SAC were used as the adsorbing agent to treat the landfill leachate, the elimination capacity for chemical oxygen demand (COD) and organic matter in leachate were studied. Based on this, the physicochemical properties of SACs and the components changes in leachate were analyzed and characterized by X-ray photoelectron spectroscopy and three-dimensional fluorescence spectroscopy. The results showed that under optimal experimental conditions, the elimination capacities of SAC372 for COD, biological oxygen demand over 5 days, and NH4+-N in the leachate were 81.58%, 54.73%, and 69.08%, respectively; while the adsorption capacities of modified SAC for these three substances were 86.25%, 63.51%, and 79.15%, respectively. The ferric nitrate modification improved the ability of SAC to eliminate COD and organic matter from leachate slightly, and made the adsorption occurred easily. The adsorption process of unmodified SAC was dominated by multi-layer adsorption, while the adsorption process of modified SAC was dominated by monolayer adsorption. The mass fraction of Fe (2p) in modified SAC remarkably increased, from 0.70% to 26.01%, organic functional groups certain phase of Fe oxides with different valence states were generated in SAC, which provided a substrate for iron-carbon micro electrolysis. After adsorbed by unmodified SAC and modified SAC adsorption, the total fluorescence intensity of in the leachate increased by 17.01% and 116.84%, respectively. Both two SACs could decompose the humic acid-like substances into aromatic protein organic compounds, and modified SAC could further decompose the soluble microbial byproduct-like substances.

Effects of chemical modification on physicochemical properties and adsorption behavior of sludge-based activated carbon

This study aimed to explore the adsorption performance of sludge-based activated carbon (SBC) towards dissolved organic matters (DOMs) removal from sewage, and investigated the modification effect of different types of chemicals on the structure of synthesized SBC. Waste activated sludge (WAS) was used as a carbon source, and HCl, HNO3, and NaOH were used as different types of chemicals to modify the SBC. With the aid of chemical activation, the modified SBC showed higher adsorption performances on DOMs removal with maximum adsorption of 29.05 mg/g and second-order constant (k) of 0.1367 (L/mol/sec) due to the surface elution of ash and minerals by chemicals. The surface elemental composition of MSBC suggested that the content of C-C and C-O functional groups on the surface of modified sludge-based activated carbon (MSBC) played an important role on the adsorption capacities of MSBC towards DOMs removal in sewage. Additionally, the residual molecular weight of DOMs in sewage was investigated using a 3-dimension fluorescence excitation-emission matrix (3D-EEM) and high-performance size exclusion chromatography (HP-SEC). Results showed that the chemical modification significantly improved the adsorption capacity of MSBC on humic acids (HA) and aromatic proteins (APN), and both of NaOH-MSBC and HCl-MSBC were effective for a wide range of different AMW DOMs removal from sewage, while the HNO3-MSBC exhibited poorly on AMW organics of 2,617 Da and 409 Da due to the reducing content of macropore. In brief, this study provides reference values for the impact of the chemicals of the activation stage before the SBCs application.

Adsorption of dissolved organic matter from landfill leachate using activated carbon prepared from sewage sludge and cabbage by ZnCl2.

Sewage sludge and cabbage (Brassica oleracea) were used to prepare activated carbon by high-temperature inert carbonization with the activator ZnCl2. The physicochemical characteristics of the sludge-based activated carbon (SAC) were analyzed, and the effects on the removal of chemical oxygen demand (COD) from the landfill leachate by the adsorbent dosage, adsorption time, and the solution pH were investigated in different adsorbents. Three-dimensional fluorescence spectroscopy and gas chromatography-mass spectrometry were used to analyze the organic compounds in the leachate before and after adsorption. The results demonstrated that the average iodine content of the SAC was 535.01mg/g. The average specific surface area was 917.72m2/g, and the dominant pore size was in the mesoporous range. The optimum parameters for adsorption were a dosage of 3%, adsorption time of 60min, and pH = 8, and the COD removal rate reached 85.61%. The adsorption of COD on the SAC was best fitted by the Freundlich model. Additionally, the SAC was found to have a high removal efficiency for refractory organic matter and short-chain alkanes, such as humic acid-like substances, in the leachate but was not effective for long-chain alkanes.

Life cycle assessment approach to sustainable sewage sludge management for water pollution control

Increase in population growth coupled with industrialization, urbanization and requirements for implementation of stricter effluent discharge standards, sludge from wastewater treatment plants (WWTP) is expected to be produced in a continually increasing amount globally. The management of the huge volume of sludge generation becomes an integral component of environmental sustainability. Therefore, the need for environmentally friendly approach to sludge management strategy couldn’t be overemphasized. This paper proposes a rational and more sustainable approach directed towards devising means to solve the problem of the huge amount of WWTPs sludge by converting it to granular activated carbon (GAC) for utilization in water pollution control via incorporating Life Cycle Assessment (LCA). The paper reviews the various approaches and techniques for drying, pyrolysis and activation techniques and the best operating conditions for sludge based activated carbon (SBAC) for optimal pollution control. Based on that, a holistic decision making tool was recommended which incorporates major production, treatment and disposal options for each stage using Life Cycle Assessment (LCA) approach (from-cradle-to-grave), from which wide range of alternative scenarios will be generated vis-à-vis water pollution control efficacy in relation to environmental, cost as well as energy implications.

Waste-to-resources: Exploratory surface modification of sludge-based activated carbon by nitric acid for heavy metal adsorption

Sewage sludge has the potential to be utilised as a sorbent for dissolved pollutant removal. This study investigated metal removal efficiency of carbonised sewage sludges obtained via pyrolysis at 500 °C: biochar/carbonised sludge (CS), ZnCl2-activated sludge-based active carbon (SBAC), and three SBACs modified by nitric acid at different concentration and temperature (MSBACs). Batch adsorption kinetic tests indicated that the Pb2+ adsorption equilibrated in <5 min. Efficiencies of these sludge-based sorbents for Pb2+ adsorption followed the order MSBAC > SBAC > CS. Metal leachabilities were low or negligible for the SBAC and MSBACs. A comparison of 5-min adsorption of the best-performing MSBAC with different sorbents indicates that performance followed the trend MSBAC > grundite (illite) > zeolite (clinoptilolite) > commercial activated carbon (CAC) > kaolinite > perlite. Furthermore, MSBAC achieved 98.9%, 42.6%, and 34.6% removal of Cu, Zn, and Al, respectively, from spiked natural acid rock drainage in <5 min. The modified sludge-based activated carbon is an effective and sustainable sorbent for removing metals from aqueous environments.

Production of activated carbon from sludge and herb residue of traditional Chinese medicine industry and its application for methylene blue removal

Sludge-based activated carbon (SAC) was prepared with sewage sludge and Chinese medicine herbal residues (CMHR’s). An orthogonal experimental design method was used to determine the optimum preparation conditions. The effects of the impregnation ratio, activation temperature, activation time, and addition ratio of CMHR’s on the iodine value and Brunauer-Emmett-Teller surface area of activated carbon were studied. X-ray diffraction, Fourier-transform infrared spectrometer, and scanning electron microscopy were used to characterize the prepared SAC. The results showed that the optimal process conditions for preparing the SAC were as follows: an impregnation ratio of 1:4, an activation time of 30 min, an activation temperature of 700 °C, and an addition ratio of CMHR’s of 40%. The adsorption balance of the methylene blue dye was examined at room temperature. Adsorption isotherms were obtained by fitting the data using the Langmuir and Freundlich models, which showed that methylene blue adsorption was most suitable for the Langmuir equation. The results demonstrated that SAC prepared from SS and CMHR’s from a Chinese medicine factory could effectively expel dyes from wastewater.

Recycling of Waste Sludge: Preparation and Application of Sludge-Based Activated Carbon

With the rapidly increasing industrial and agricultural development, a large amount of sludge has been produced from much water treatment. Sludge treatment has become one of the most important environmental issues. Resource utilization of sludge is one of the important efficient methods for solving this issue. Sludge-based activated carbon (SBAC) materials have high adsorption performance and can effectively remove environmental pollutants including typical organic matter and heavy metals through physical and chemical processes. Therefore, developing efficient SBAC materials is important and valuable. At present, preparation, modification, and application of SBAC materials have gained widespread attention. This paper provides a review of the research on SBAC preparation and modification and its utilization in removing environmental pollutants. It included the following topics present in this review: conventional and new methods for preparation of SBAC were clearly present; the effective methods for improving SBAC performance via physical and chemical modification were reviewed; and the correlation of their physic-chemical properties of SBAC with pollutants’ removal efficiencies as well as the removal mechanisms was revealed. SBAC has a better adsorption performance than commercial activated carbon in some aspects. Furthermore, it is a cost-effective technique and has a wide range of raw materials. However, there are still some drawbacks to its research; thus, some suggestions for further research were given in this review.

Advanced anaerobic digested sludge dewaterability enhancement using sludge based activated carbon (SBAC) in combination with organic polymers

Wastewater sludge is difficult to dewater because the extracellular polymeric substances (EPS) it contains are highly hydrated and sticky. Anaerobic digestion generally results in further deterioration of sludge dewaterability due to the release of large quantities of biopolymers and fine particles. Chemical conditioning is required prior to mechanical dewatering and is of great importance in the operation of the dewatering process. In this work, a novel anaerobically digested (AD) sludge conditioning process that combines sludge based activated carbon (SBAC) as a skeleton builder with organic polymers (cationic polyacrylamide, CPAM, and chitosan, CTS) for flocculation is proposed to simultaneously remove soluble biopolymers and improve sludge dewaterability. Results indicate that the specific resistance to filtration (SRF) of AD sludge was decreased and that tryptophan-like proteins and humic substances in soluble EPS and loosely-bound EPS were effectively removed by SBAC adsorption through hydrophobic interaction. Flocs formed through CTS conditioning were smaller but aggregated more strongly and formed less compressible cake than those formed through CPAM conditioning. SBAC and cationic organic polymers showed a significant synergistic effect in improving sludge dewatering. The incorporation of SBAC into conditioning with organic polymers increased the strength of sludge floc aggregation and improved recover ability from mechanical shearing. Confocal laser scanning microscopy showed that conditioning with SBAC in combination with organic polymers resulted in protein molecules forming large aggregates, while polysaccharide molecules were uniformly distributed in sludge floc. This work provides a green and promising strategy for improved AD biosolid dewatering using sludge based activated carbon in combination with CTS.

Adsorption of organic stormwater pollutants onto activated carbon from sewage sludge

Adsorption filters have the potential to retain suspended pollutants physically, as well as attracting and chemically attaching dissolved compounds onto the adsorbent. This study investigated the adsorption of eight hydrophobic organic compounds (HOCs) frequently detected in stormwater – including four polycyclic aromatic hydrocarbons (PAHs), two phthalates and two alkylphenols – onto activated carbon produced from domestic sewage sludge. Adsorption was studied using batch tests. Kinetic studies indicated that bulk adsorption of HOCs occurred within 10 min. Sludge-based activated carbon (SBAC) was as efficient as tested commercial carbons for adsorbing HOCs; adsorption capacities ranged from 70 to 2800 μg/g (Cinitial = 10–300 μg/L; 15 mg SBAC in 150 mL solution; 24 h contact time) for each HOC. In the batch tests, the adsorption capacity was generally negatively correlated to the compounds' hydrophobicity (log Kow) and positively associated with decreasing molecule size, suggesting that molecular sieving limited adsorption. However, in repeated adsorption tests, where competition between HOCs was more likely to occur, adsorbed pollutant loads exhibited strong positive correlation with log Kow. Sewage sludge as a carbon source for activated carbon has great potential as a sustainable alternative for sludge waste management practices and production of a high-capacity adsorption material.

Characterization of ferromagnetic sludge-based activated carbon and its application in catalytic ozonation of p-chlorobenzoic acid.

In order to solve the separation problem of powdered sludge-based activated carbon (SAC), a series of novel ferromagnetic sludge-based activated carbons (FMSACs, with different iron content 2.3, 4.3, and 9.5wt%) with a good magnetic separation ability were prepared through co-precipitation method in this study. The structure and physicochemical properties of FMSACs and their catalytic ozonation performance on the removal of p-chlorobenzoic acid (p-CBA) were investigated. The saturation magnetization (Ms) of FMSACs was determined in the range of 0.3674-5.7992emug-1, and experiments confirmed that these FMSACs could be easily separated by magnetic fields. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that magnetite and maghemite were the main magnetic phases in FMSACs. Comparing with ozonation alone and SAC catalytic ozonation, the presence of 2.3wt% - FMSAC improved the degradation of p-CBA during catalytic ozonation from 44 and 70 to 80%. The tertiary butanol inhibition experiment indicated that FMSACs catalytic ozonation process followed hydroxyl radical reaction mechanism. Furthermore, after six repetitive catalytic ozonation runs, 2.3wt% - FMSAC still showed relatively high catalytic activity for the removal of p-CBA. Consequently, the novel FMSACs with magnetic separation ability and catalytic performance provide a practical pathway for the sludge utilization.