Capillary Suction Time Research Articles

Comparison of Anaerobic Co-Digestion of Buffalo Manure and Excess Sludge with Different Mixing Ratios under Thermophilic and Mesophilic Conditions

In this study, the main aim is to evaluate the mixing ratio of co-digestion of buffalo manure (BM) and excess sludge (ES) influenced for methane yield and digestate dewaterability. Five batch experiments with different BM and ES mixing ratios were carried out under thermophilic and mesophilic conditions. The methane yield of co-digestion of BM and ES increased by 10.1–73.5% under thermophilic conditions and 87.9–153.3% under mesophilic conditions, compared with the mono-anaerobic digestion of ES under the same conditions. Shannon and Chao1 indices showed that the bacterial species of the mesophilic digesters were more abundant than that of the thermophilic digesters. With the increase in the BM proportion in the substrate, the normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased. The NCST at thermophilic temperature (8.98–12.54 s∙g−1-TS) was greater than that at the mesophilic temperatures (5.45–12.32 s∙g−1-TS). However, the TS of sediment was not directly related to the digestion temperature. This study has shown that anaerobic co-digestion of BM and ES at the appropriate ratio (BM/ES = 1:1.5) has a significant meaning in a high methane yield.

Bioflocculants as Alternative to Synthetic Polymers to Enhance Wastewater Sludge Dewaterability: A Review

The dewatering process reduces the water quantity in sludge, allowing the decrease in its volume, which facilitates its storage, transport, stabilization, and improves the post-treatment efficiency. Chemical polymers including aluminum sulphate and polyaluminum chloride were applied as flocculants in the conditioning process in order to prepare sludge for dewatering. However, these synthetic polymers may cause risks for human health, and should be substituted with ecofriendly and safe materials. These materials include plant-based flocculants, animal-based flocculants, and microbial-based flocculants. Sludge dewaterability was evaluated by considering many parameters, such as moisture content (MC), dry solids (DS), specific resistance to filtration (SRF), capillary suction time (CST), and sludge volume index (SVI). The use of microorganisms for sludge dewatering is an available option, since many strains (R. erythropolis, A. ferrooxidans, P. mirabilis, T. flavus, etc.) demonstrated their ability to produce polymers useful for dewatering sludge from various origins (chemically treated primary sludge, activated sludge, anaerobically digested sludge, etc.). For plant-based flocculants, only okra (Abelmoschus esculentus), cactus (Opuntia ficus Indica), moringa (M. oleifera), and aloe (A. vera) plants are examined for sludge dewatering. Compared to synthetic polymers, plant-based flocculants showed a viable alternative to chemicals and a step forward in green sludge treatment technology. Among the animal-based flocculants, chitosan and aminated chitosan were able to reduce the SRF (SRF reduction rate > 80%) of the anaerobically digested sludge. A new strategy using methylated hemoglobin also showed a significant enhancement in cake solid content of sludge (47%) and a decrease in sludge bound water content of 17.30%. Generally, extensive investigations are needed to explore and optimize all the related parameters (operating conditions, preparation procedure, production cost, etc.) and to choose the appropriate materials for large-scale application.

Long-term effect of free ammonia pretreatment on the semi-continuous anaerobic primary sludge digester for enhancing performance: Towards sustainable sludge treatment

Primary sludge (PS) is one of the major sludge sources for anaerobic digesters in wastewater treatment plants. Although the impact of free ammonia (FA) pretreatment on methane production from anaerobic PS digestion was previously investigated using batch biochemical methane potential tests, these tests could not fully represent the continuous/semi-continuous anaerobic digestion that is currently used in practice. This study comprehensively evaluated the impact of FA pretreatment on the performance of anaerobic PS digestion for the first time using semi-continuous systems that run for over 120 days. FA pretreatment (560 mg NH3-N/L, 24 h) improved the volatile solids (VS) removal of PS by 12.2 % from 60.5 % to 67.9 %, with a similar improvement in total chemical oxygen demand removal of 14.9 % and methane production of 16.1 %. FA pretreatment increased the biomass-specific hydrolysis rate of digesters by 23.5 %. Model-based analysis revealed that the enhanced anaerobic digestion performance may be due to both the increased apparent hydrolysis rate (increased by 26.7 %) and the enhanced degradability extent (increased by 9.5 %) of PS, caused by FA pretreatment. The dewaterability of digested sludge was enhanced by 14.0 % due to FA pretreatment, which is also supported by the reduced capillary suction time from 15.1 s to 10.9 s. Removals of Fecal Coliform and E. Coli were enhanced by 0.6 and 1.4 log Most Probable Number/g vS by FA pretreatment. This study firstly manifested that FA pretreatment is a favourable approach to improve the performance of anaerobic PS digestion with extra benefits in pathogen removal and dewaterability.

Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Polymer flocculants are used to promote solid-liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

One-pot production of 5-methylfurfural (5-MF) and enhanced dewaterability of waste activated sludge by hydrothermal treatment with natural deep eutectic solvents (NADES): Experimental and theoretical studies

Natural deep eutectic solvents (NADES) coupled with hydrothermal treatment was innovatively proposed to process waste activated sludge for sustainable production of 5-methylfurfural (5-MF) and enhanced dewaterability. The yield of 5-MF up to 11.54 kg/t volatile solids (VS) with a NADES dosage of 2.0 mL, hydrothermal temperature of 180 °C and holding time of 30 min. The decreased capillary suction time (CST) and bound water content indicated that NADES with hydrothermal treatment substantially improved the dewaterability of sludge. The variations of sludge physicochemical properties and extracellular polymeric substances (EPS) compositions revealed that NADES disrupted the structure of sludge biopolymers. Density functional theory (DFT) calculations indicated that NADES weakened the hydrogen bond strength between EPS components, and thus promoted the solubilization of proteins and polysaccharides. Besides, transition state analysis showed that NADES also lowered the energy barrier of polypeptide hydrolysis and carbohydrates dehydration reactions for the production of 5-MF.

Insights into the role of ·OH generated in Fe2+/CaO2/coal slime system for efficient extracellular polymeric substances degradation to improve dewaterability of sewage sludge

The disposal of massive sewage sludge and coal slime is a problem facing municipalities in China. A hypothesis for the co-disposal of sludge and coal slime is proposed to improve dewaterability by utilizing the beneficial role of coal slime as a filter assist and CaO2 enhanced system in this research. Results showed that capillary suction time, specific resistance to filtration and water content decreased dramatically from 49.3 s, 13.2 × 1012 m/kg and 84.85% to 19.1 s, 1.0 × 1012 m/kg and 50.07%, respectively, under the optimal conditions with 0.3/0.1/0.3-Fe2+/CaO2/coal slime g/g DS. The hydroxyl radicals generated in the Fe2+/CaO2 process acted on extracellular polymeric substances (EPS), resulting in a drop in the ratio of α-helix/(β-sheet + random coil) in the secondary structure of EPS proteins and a reduction in the concentration of aromatic proteins and tryptophan-like substances in TB-EPS, thereby enhancing the sludge dewaterability. Furthermore, coal slime as the skeleton building material induced a rise in sludge particle size and contact angle, lowering the hydrophilicity, compressibility of sludge and providing more channels to facilitate water flow. This work verified the promising application prospect of the Fe2+/CaO2/coal slime combined system in the enhancement of sludge dewaterability.

Metal Cation and Surfactant-Assisted Flocculation for Enhanced Dewatering of Anaerobically Digested Sludge

Flocculation and dewatering of anaerobically digested sludge is known to be a major cost factor in the economy of wastewater treatment plants. Hence, several endeavors have been underway in search of affordable and effective alternatives. This study focuses on the effects of different metal cations, including FeCl3, CaCl2 and MgSO4, on the dewaterability of digested sludge. The effects of these metal flocculants were also investigated in the presence of co-polymers and surfactants, which can be considered the novelty of this study. The polymers and surfactants investigated in this study were emulsion polymer, CTAB and SDS. Sampling and characterization of digested sludge was conducted, and total solid (TS), volatile solid (VS), dewaterability in capillary suction time (CST), total dissolved solids (TDS), chemical oxygen demand (COD), pH and conductivity of the unconditioned digested sludge samples were determined. The dewaterability of FeCl3, CaCl2 and MgSO4 conditioned digested sludge samples were compared, and MgSO4 conditioned digested sludge showed better dewaterability compared to the other two metal conditioning agents at a pH of 6.8. The dewaterability was further improved by the addition of emulsion polymer (EMA 8854), cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). Fe Cl3 was found to perform better under an acidic pH of around 3. The dual conditioning using polymer and CTAB resulted in better dewaterability, with CaCl2 as metal conditioning agent. Moreover, the effects of pH, metal dose and polymer dose on the dewaterability of digested sludge were also investigated. The effects of metal and polymer conditioning on the particle size of the sludge flocs was also investigated. Optimum dewatering performance was achieved for metal doses of 0.16 v/v, 0.075 v/v and 0.16 v/v for FeCl3, CaCl2 and MgSO4, respectively, and a corresponding CTAB dose of 0.1 v/v and EMA dose of 15 kg/TDS were found to be the optimum. SDS as a polymer conditioning agent resulted in the deterioration of dewatering performance.

Combined conditioning of inorganic coagulant and polyamine to improve the dewaterability of municipal sludge, minimize dosage and reduce the influence of filtrate.

Efficient dewatering of sludge is necessary for its cost-effective transportation and final disposal. However, the common method of using polyferric sulfate (PFS) and polyacrylamide (PAM) requires a large amount of dosage and produces high iron ion content in the filtrate. This study examined a solution of applying polyamine (PA) coupled with inorganic coagulant PFS. The results demonstrated that using PFS + PA together could achieve the same or similar filtering rates as using PFS + PAM. The capillary suction time (CST) of PFS + PA (89.0 s) was equivalent to that of PFS (75.1 s) and better than that of PA (117.1 s) and raw sludge (RS, 403.8 s). Compared with PFS + PAM, the combination of PFS and PA efficiently removed Fe ions and chemical oxygen demand (COD) in sludge water content, with Fe ions in the sludge filtrate reduced by 97.8% and COD reduced by 78.9%, respectively. By analyzing the basic physicochemical properties of the sludge system, including the synergistic effect of coagulation and flocculation, sludge hydrolysis and flocculation, it indicated that PA + PFS could reduce bound water. These results demonstrated that combining PFS and PA to improve sludge dewatering performance is more beneficial than utilizing a coagulant or flocculant alone, even PFS + PAM.

In situ generation of H2O2 for Fenton oxidation in electrochemical system for the enhancement of sludge dehydration

Fenton methods can effectively improve the dewatering performance of waste activated sludge (WAS). However, the explosive properties of H2O2 and demand of real-time dosing often incur transportation difficulties and high operational costs. It limits large-scale applications of Fenton processes on WAS dewatering. This study introduced the electro-Fenton technique by in-situ H2O2 generation into sludge dewatering for the first time. The responding surface methodology indicated that the yield of H2O2 could reach 10.11 mg/g DS (dry solids) at an optimal iron dose of 8 mg/g DS within 60 min. Compared to WAS, the capillary suction time (CST) and specific resistance to filtration (SRF) of treated sludge decreased from 87.7 ± 0.57 s and 3.67 × 1012 m/kg to 57.65 ± 0.92 s and 3.14 × 1012 m/kg, respectively. The mechanism investigations showed that electro-Fenton treatment reduced surface negative charge of WAS and caused disruption of extracellular polymeric substances and release of intracellular substances, which enhanced the flocculability and filtering performance, but decreased the moisture content, fractal dimension of WAS. Additionally, electro-Fenton treatment altered the secondary structure of proteins, which led to a loose structure of protein, benefiting the exposure of hydrophobic sites or groups in EPS proteins. Furthermore, the dewatering mechanisms involved in the electro-Fenton process were explored and the contribution of individual reactions in sludge dewatering was revealed. Overall, this work will provide both theoretical basis and practical knowledge for electro-Fenton sludge dewatering.

Analysis of the effect of using divalent and trivalent iron compounds on sludge dewatering performance in thickening units

Abstract Sludge is one of the by-products of wastewater treatment plants (WWTPs). To assist biological processes, part of the produced sludge is returned to the treatment process and the excess is removed from the treatment plant whereby it undergoes thickening and dewatering. Numerous studies have been conducted to investigate the effect of different coagulants on dewatering from sludge, but the effect of using divalent iron for this purpose has not been investigated so far. In this research, the effect of divalent and trivalent iron compounds (ferrous sulfate and ferric chloride) on the dewatering of excess sludge of the first module of the Bojnourd WWTP (Iran) has been investigated. In this regard, first, the effect of different doses of each coagulant to optimize the dewatering characteristics of sludge was investigated and then the effect of pH change by adding lime was investigated. The results showed that the addition of optimal doses of FeSO4 (0.6 and 0.4 g/l) and lime (0.664 and 1.5866 g/l) reduced the capillary suction time of sludge by 30.6 and 32.7%, respectively, while reducing the moisture content of sludge cake by 26 and 30.6%.

Behavior of Sludge Dewaterability and Nutrient Contents after Treatment with Cellulose-Based Flocculants with Combined PTS and Catalytic Behavior of Sludge towards Tetracycline Degradation

Wastewater treatment plants are increasingly interested in adopting inorganic coagulants and organic flocculants in their sludge treatment process since sludge disposal costs more than half of the overall operational costs. This study synthesized poly titanium sulfate (PTS) by different molar ratios and used the best one with cellulose-based flocculants for sludge conditioning. PTS synthesized with a 1:2 molar ratio showed the lowest capillary suction time (CST) of sludge and was selected for further studies with cellulose-based flocculants. As bio-based flocculants have gained popularity due to current environmental problems, cationized cellulose-based flocculants (Ce-CTA) were used in this work with or without PTS for sludge treatment. After coagulation–flocculation, dewaterability of sludge enhanced, and the Lowry and Anthrone method was used to assess proteins and polysaccharides. Next, metal content and nutrients such as total phosphorus, phosphate, and nitrate were measured by ICP-OES and IC, and we found promising results of phosphate especially at pH 3. Higher total phosphorus content was found at pH 3 and 9, and even at pH 6 after PTS or PTS+Ce-CTA treatment. In addition, PTS-treated sludge materials also showed catalytic behavior, suggesting a new research avenue for future development. Based on this study, the PTS+Ce-CTA combination is promising for sludge treatment and nutrient recovery, along with the possibility for the further valorization of the sludge materials.

Enhancing sludge dewatering efficiency through bioleaching facilitated by increasing reactive oxygen species

Bioleaching facilitated by iron-oxidizing bacteria is regarded as a promising sludge dewatering method due to excellent dewaterability and low cost. However, a two-days bioleaching time for sludge conditioning decreased its daily treatment capacity. In fact, Fe2+ easily reacts with O2 to produce reactive oxygen species (ROS) with high oxidizing activity. Can bioleaching performed in Fe2+-rich system generate ROS to decompose sludge extracellular polymeric substances (EPS)? Here both contribution of ROS produced in bioleaching to improve sludge dewaterability and the increase of ROS content to shorten sludge bioleaching treatment time were investigated. The introduction of H2O2 in sludge bioleaching treatment (BS+H2O2) to increase ROS could simultaneously improve sludge dewaterability and decrease bioleaching time. Specific resistance to filtration (SRF) and capillary suction time (CST) reduction ratios (90.3% and 80.9%) in BS+H2O2 process were much higher than those in other processes after only 30 min reaction. Mechanisms of improving sludge dewaterability in BS+H2O2 mainly included ROS oxidation and Fe3+ flocculation by analysis of the contribution factors. These findings not only provide an effectively method to promote sludge dewatering efficiency of bioleaching, but also give new sights into the design of cost-efficient processes for improving the sludge dewatering.

The enhanced dewaterability of sludge by a starch-based flocculant combined with attapulgite

Coagulation/flocculation is one of the most widely used and cost-effective pretreatment methods for improving the dewaterability of sludge. In this study, a cationic modified starch-based flocculant (St-CTA) in conjunction with a popular clay, attapulgite (ATP), was used for the conditioning of waste-activated sludge. The dewatering properties, including the filter cake moisture content, filtration specific resistance, capillary suction time, filtration rate and compressibility coefficient, were measured and compared by varying the doses of St-CTA and ATP. By combination of the apparent dewatering performance and the changes in the contents and distributions of the extracellular polymeric substance (EPS) fractions and components, sludge flocs, and microstructures of sludge cakes, the dewatering mechanisms were discussed in detail. St-CTA in conjunction with ATP can exhibit an enhanced dewaterability of sludge and the water content in final sludge cake can be stably reduced below 80% owing to the synergistic effects of St-CTA and ATP. In addition to the efficient charge neutralization of St-CTA, ATP not only acts as a skeleton builder in the sludge dewatering process which makes the sludge flocs more compact and improves the filterability and permeability, but also tightly interacts with the proteins in EPS of the sludge which reduces the protein content and further enhances the dewatering effect. This study provides an economical, green, and effective way to further improve the dewaterability of sludge.

Evaluation of pre-magnetization on the dewaterability of waste activated sludge treated by ozonation

The dewaterability of waste activated sludge (WAS) plays the key role in sludge dewatering in wastewater treatment plants. The magnetic field as a source of clean energy has been reported to be able to cause changes in sludge properties and to enhance sludge dewatering by chemical treatment. This paper focuses on the effect of pre-magnetization on the sludge dewatering performance by ozonation. The results showed that ozonation reduced the capillary suction time (CST) and water content of sludge cake (Wsc) of WAS. The CST reduced from 21.5 ​s to 12.7 ​s; and the Wsc reduced from 85.6% to 85%. However, the addition of pre-magnetization with a magnetic field did not make much improvement of the dewaterability. Further investigation on sludge properties such as EPS, TOC, particle size, and the SEM images of the treated WAS showed that the pre-magnetization prior to ozonation led to stronger oxidation and WAS particle broken, which was proofed not necessarily correlated to sludge dewaterability enhancement.

Unraveling the impacts of Cu+-based treatments on sludge dewaterability: The overlooked role of Cu3+

The high water content of sewage sludge increases the processing costs and hampers its further disposal. Fenton technology has proven to be efficient and been widely used to enhance sludge dewaterability, but it usually needs acidification and subsequent neutralization, thus consuming a lot of chemicals. It’s well documented that hydroxyl radicals produced in various Fenton or Fenton-like reactions play a crucial role in sludge dewatering. Based on the latest study, Cu+ and Cu+/H2O2 pretreatments for the enhanced dewaterability of sludge without extra pH adjustment were proposed. Results showed that Cu+ with and without H2O2 can significantly improve the dewatering performance of sludge, which was ascertained by a capillary suction time (CST) reduction rate of about 80 %. The proteins and polysaccharides in tightly-bound extracellular polymeric substance (TB-EPS) were decreased, while increased in soluble extracellular polymeric substance (S-EPS). In addition, a hydrophobic and porous surface was formed, and zeta potential increased after conditioned. These changes may release bound water and thus improve sludge dewaterability. The results of electron spin resonance and scavenging tests signaled that the Cu3+ was mainly accountable for the dissolution of EPS, rather than the hydroxyl radicals (OH). Our results substantiate and untangle a distinct reinforcement mechanisms for sludge dewatering by high valent copper (Cu3+). This study demonstrates for the first time that Cu3+ plays an important role in sludge dewatering, which has long been credited to hydroxyl radicals. It also urges re-evaluation of the Fenton(-like) system for sludge dewatering, given that Cu3+ could also cause potential oxidative destruction of EPS compared with reactive oxygen species.

Optimization of operating conditions in the biological enzymes for efficient waste activated sludge dewatering

The sludge dewaterability is essential for waste activated sludge (WAS) treatment and disposal in wastewater treatment plants (WWTPs). The biological enzyme conditioning process is a promising method to enhance the dewaterability of WAS. In this study, the optimal conditions in terms of pH, temperature, bio-enzyme dosage, and treatment time for five kinds of biological enzymes (α-amylase, cellulase, acidic protease, neutral protease, and alkaline protease) were investigated. Among them, α-amylase and neutral protease showed good performance in conditional optimization experiments. After biological enzyme conditioning, the sludge supernatant of proteins, polysaccharides, and SCOD contents increased. The sludge water content (Wc) decreased, while the capillary suction time (CST) increased. The optimal conditions for α-amylase were pH 6, 45 ℃ of temperature, 30 mg/g TSS of dosage, and 3 h of treatment time, under which the lowest Wc can reach 68.67%. The optimal conditions for neutral protease were pH 6.5, 40 ℃ of temperature, 30 mg/g TSS of dosage, and 2 h of treatment time, under which the lowest Wc can reach 69.82%. Using biological enzymes is an environmentally friendly conditioning process for efficient WAS dewatering. The optimization of operating conditions in the biological enzymes conditioning process may be beneficial to WAS dewatering and further disposal in actual WWTPs.

An all-organic conditioning method to achieve deep dewatering of waste activated sludge and the underlying mechanism

Among the common treatment/disposal routes of excessive activated sludge from municipal wastewater treatment plant, dewatering process functions as an essential pre-/post-treatment for volume minimization and transportation facilitation. Since inorganic coagulants have long been criticized for their high dosage and solid residue in sludge cake, there is an urgent need for investigations regarding the potential of applying organic chemicals as the conditioner. In this study, combined use of poly dimethyldiallylammonium chloride (PDMD) and tannic acid (TA) were investigated as an all-organic co-conditioning method for sewage sludge pre-treatment. Results showed that this all-organic conditioning strategy can effectively improve the dewaterability of sewage sludge. The capillary suction time reduced from 128.8 s to 23.1 s, and the filtration resistance reduced from 1.24 × 1012 cm/g to 7.38 × 1010 cm/g. The moisture content of dewatered sludge cake decreased to as low as 55.83%, showing the highest dewatering efficiency reported so far. In addition, the combination of PDMD and TA maximized the treating efficiency with very limited consumption of conditioners (added up to 4% of total solid). Based on the physic-chemical and rheological property investigation, it was proposed that the intermediate molecular weight polymer-based flocculation process and the TA agent-based protein precipitation process, could remarkably strengthen the compactness and structure robustness of sludge. In all, this PDMD-TA-based conditioning method suggested practical significance in consideration of its cost-effectiveness and disposal convenience of sludge cake.

Comprehensive effects of grain-size modification of electrolytic manganese residue on deep dehydration performance and microstructure of sludge

As the by-product accompanied by sewage treatment, sludge has complex composition and high moisture content, therefore, its reutilization and disposal are still a challenge. In this paper, five kinds of quartz sand conditioners with different particle sizes (denoted as QS1, QS2, QS3, QS4 and QS5, respectively) were used to explore the effect of particle size distribution of conditioners on sludge dewatering performance. The moisture content, capillary suction time (CST), time to filter (TTF), specific resistance of filtration (SRF), particle size distribution curve, pore distribution law, scanning electron microscopy, isothermal adsorption-desorption curve and extracellular polymeric substances distribution were employed to characterize the modified sludge and explore the improvement mechanism. The results show that the particle size distribution of the conditioner significantly affects the efficiency of sludge dewatering. The wt% of sludge regulated with QS1 (QS1-S) could be reduced to 52%, and its CST value, TTF value and SRF value is 57.93 s, 278 s and 1.84 × 108 s2 g−1, respectively. The conjecture about the effect of difference of particle size distribution on sludge dewatering performance was verified with the original Electrolytic Manganese Residue (EMR) and the grain-size modified Electrolytic Manganese Residue (EMR6). Compared with those of the EMR-conditioned sludge, the CST, TTF and SRF of EMR6-conditioned sludge was decreased by 8.7%, 22.3% and 11.2%, respectively. According to analysis of surface microstructure, the surface of the sludge cake modified with QS1 is rough and sparse with rich pore structure. Compared with those of the undisturbed sludge (A0), the pore volume and specific surface area of the sludge modified with QS1 was increased by 61.65% and 38.62%, respectively. After grain-size modification, the dehydration effect of EMR6 (D10 4.25 μm, D50 19.65 μm, D90 73.26 μm) was significantly enhanced, and the D10, D50 and D90 value was close to that of QS1. It can be concluded that the particle size of QS1 (D10 3.27 μm, D50 15.66 μm, and D90 62.23 μm) can improve the dewatering performance of sludge by shearing the sludge particles to change the original sludge particle size distribution and improving the blockage of sludge dewatering channels.

Mechanism of thermally activated sodium persulfate–biochar skeleton treatment to improve the dewaterability of waste activated sludge

Sludge dewatering is a necessary process in the disposal of waste activated sludge (WAS). In this study, thermally activated sodium persulfate–biochar skeleton pretreatment was performed to improve the dewaterability of sludge, and its internal mechanism was systematically elucidated. The experimental results showed that, under optimal operating conditions, the water content of WAS could be reduced from 89.7% to 61.3% of the raw sludge. Under these conditions, the capillary suction time and specific resistance to filtration were roughly 23.23% and 59.57% of those in the raw sludge, respectively. This study proposes a relationship between organic matter migration and sludge physical structure that explains the dewaterability improvement mechanism. Separate thermal treatment caused organic matter such as proteins, polysaccharides, and humic substances to dissolve, releasing their bound water. Simultaneously, changes in the surface structure (pore size reductions and BET surface area increases) deteriorated the dewaterability of WAS. The reactive oxygen species generated by the thermally activated sodium persulfate further mineralized the organic matter, simplifying the floc surface structure (pore size increases and BET surface area decreases) and finally improving the dewaterability. Under these conditions, the addition of biochar increased the pore size, and further improved sludge dewaterability.

Particle size as a driver of dewatering performance and its relationship to stabilization in fecal sludge

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 μm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 μm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 μm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.