Solid-liquid Separation Processes Research Articles

Octopus-inspired flocculant for oily wastewater decontamination: Hydrophilic-hydrophobic convertibility and auto-separation characters

Unilateral hydrophobic flocculant and unsatisfactory floc separation constrained the efficacious purification of oil-containing wastewater. Illumined by the hunting behavior of mimic octopus, a biomimetic flocculant (CNSDA) with temperature-sensitive chains (color pouch) and hollow silica cores (mantle) was manufactured to derive hydrophilic-hydrophobic convertibility and auto-separation capabilities. Physical-chemical information of CNSDA was elucidated through characterization analysis. The flocculation behaviors of temperature-sensitive chains and hollow silica cores were evaluated by flocculation experiments. Results indicated that the configuration of CNSDA molecular chains varied from extension to constriction and revealed hydrophobicity as the temperature crossed 29.6 ℃. Compared with 20 ℃, the flocculation efficiencies rocketed at 40 ℃ by CNSDA, and excess flocculants were adsorbed by as-formed flocs through nonpolar interactions (the residual was low to 2.27 % at 160 mg/L). Concomitantly, the contracted molecular chains were contributed to generating dense flocs with low moisture content that flocked into large ones and expedited the solid-liquid separation process (60 % shorter than cationic polyacrylamide) with the auxiliary of low-density cores. The hydrophobic adsorption mechanism actuated by temperature-sensitive character was the decisive factor for high-efficiency flocculation. This study can provide meaningful references for the conception and exploitation of oily wastewater disposal agents.

Reducing operational risks during suspensions separation in rare metals technology

The work presents the results of studies of the solid-liquid separation processes of different mineralogical and granulometric compositions, different viscosity and concentrations of uranium, zirconium, nitric acid, soda, sodium nitrate. It has been shown that the process of industrial filtration is impossible for finely dispersed phases due to the low separation rate. Requirements for the purity of technological solutions of uranium and zirconium for the extraction process are limited by the technological ability of the filter fabric to retain the smallest particles, including chemical compounds with a particle size of 1–5 μm. The control filtration process is only possible under pressure, for which a new disk press filter was created, which reduced the concentration of the solid phase in the filtrate to 0.06 g/L. For difficult-to-filter suspensions, a screw centrifuge was developed, which ensured minimum sediment moisture after separating the finely dispersed phase from a solution of soda and sodium silicate and created conditions for maximum extraction of zirconium and hafnium from the solid phase. The separation of water-soluble sodium silicate ensured the stability of the process of extraction separation of zirconium and hafnium and made it possible to isolate silicon oxide.

Multidimensional Separation by Magnetic Seeded Filtration: Theoretical Study

Magnetic seeded filtration (MSF) is a multidimensional solid–liquid separation process capable of fractionating a multimaterial suspension based on particle size and surface properties. It relies on the selective hetero-agglomeration between nonmagnetic target and magnetic seed particles followed by a magnetic separation. Experimental investigations of multimaterial suspensions are challenging and limited. Therefore, a Monte Carlo model for the simulation of hetero-agglomeration processes is developed, validated, and compared to a discrete population balance model. The numerical investigation of both charge-based and hydrophobicity-based separation in an 11-material system, using synthetic agglomeration kernels based on real-world observations, yields results consistent with prior experimental studies and expectations: Although a multidimensional separation is indeed possible, unwanted hetero-agglomeration between target particles results in a reduced selectivity. This effect is more pronounced when separation is based on a dissimilarity rather than a similarity in the separation criterion and emphasizes the advantages of hydrophobicity-based systems. For the first time, 2D grade efficiency functions T(φ,d) are presented for MSF. However, it is shown that these functions strongly depend on the initial state of the suspension, which casts doubt on their general definition for agglomeration-based processes and underlines the importance of a simulation tool like the developed MC model.

Dimensional analysis for sedimentation behavior of magnetorheological fluids

Magnetorheological fluids (MRFs) are primarily composed of magnetic particles suspended in carrier liquids, exhibiting a remarkable capacity to respond dynamically to external magnetic fields. However, the phenomenon of solid–liquid phase separation, attributable to particle sedimentation, represents a formidable barrier to the real-world application of MRFs in engineering contexts. As a result, it becomes critically imperative to conduct a thorough investigation into the sedimentation behavior of MRFs under static conditions, to significantly enhance their practical utility. In the study, computational analysis through COMSOL was utilized to elucidate the sedimentation dynamics of MRFs. The findings indicated that particle sedimentation harbored the potential to induce localized turbulence within the flow field, thereby significantly impacting the sedimentation dynamics of MRFs. The motion of particles consistently followed a pattern where sedimentation rates decreased as the viscosity of the carrier liquids increased. Moreover, the elucidation of the settling behavior of MRFs was facilitated by the introduction of two dimensionless numbers. These dimensionless numbers were employed to systematically characterize the temporal evolution of the supernatant height throughout the settling process. This investigation further explored the intricate interdependence between these dimensionless parameters via a comprehensive series of settling experiments. The outcomes of this research uncovered a unique pattern in the solid–liquid separation process of MRFs, marked by a phase of gradual initiation, followed by acceleration, and culminating in deceleration. However, as the viscosity of the carrier liquids increased, this pattern became less pronounced, gradually shifting toward a more uniform settling trajectory.

Thermally enhanced solid-liquid separation process in food waste biorefinery: modelling the anaerobic digestion of solid residues.

The biochemical valorization potential of food waste (FW) could be exploited by extracting decreasing added-value bio-based products and converting the final residues into energy. In this context, multi-purpose and versatile schemes integrating thermal and biochemical conversion processes will play a key role. An upstream thermal pretreatment + solid-liquid separation unit was here proposed to optimize the conversion of the liquid fraction of FW into valuable chemicals through semi-continuous fermentation process, and the conversion of the residual solid fraction into biomethane through anaerobic digestion. The solid residues obtained after thermal pretreatment presented a higher soluble COD fraction, which resulted in higher methane production with respect to the raw residues (0.33 vs. 0.29 Nm3CH4 kg-1VSfed) and higher risk of acidification and failure of methanogenesis when operating at lower HRT (20d). On the contrary, at HRT = 40 d, the pretreatment did not affect the methane conversion rates and both tests evidenced similar methane productions of 0.33 Nm3CH4 kg-1VSfed. In the reactor fed with pretreated residue, the association of hydrogenotrophic methanogens with syntrophic bacteria prevented the acidification of the system. Modelling proved the eligibility of the FW solid residues as substrates for anaerobic digestion, given their small inert fractions that ranged between 0% and 30% of the total COD content.

Soluble carbon source recovery using preconditioning coagulants for applicable short-term fermentation of waste activated sludge in WWTPs

A huge production of waste activated sludge (WAS) has been a burden for wastewater treatment plants (WWTPs) with high disposal cost and little benefit back to wastewater purification. The short-chain fatty acids (SCFAs) produced by a short-term acidogenic fermentation of WAS before methane production have been proven to be a high-quality carbon source available for microbial denitrification process. The dual purpose of full recovery of fermentation liquid products and facilitating disposal of residual solid waste necessitate an efficient solid-liquid separation process of short-term fermentation liquid. The transformation and loss of various soluble carbon sources between solid and liquid are very important issues for carbon recovery efficiency when combining short-term fermentation and sludge dewatering in WWTPs. Here we testified the three conventional preconditioning coagulants, Polyferric Sulfate (PFS), Poly Aluminum Chloride (PAC) and Polyacrylamide (PAM), to improve the efficiency of subsequent solid-liquid separation. The results show that conversion yield of SCFAs in the liquid phase of sludge after short-term fermentation was 195 mg COD/g VSS, when using the coagulants PFS, PAC, and PAM for recovery, the recovery ratio was 79.5%, 82.0%, and 85.9%, respectively, while the dewaterability could be improved after preconditioning short-term fermentation sludge. The complexation of Al3+/Fe3+ in metal coagulants with carboxyl groups of SCFA demonstrated by Density Functional Theory calculation led to small part of soluble carbons co-migration to the solid phase, mainly a loss of high molecular weight organic compounds (carbohydrate, proteins, humic acids), while the application of PAM had little impact on carbon recovery. Economic calculations further showed PAM preconditioning short-term fermentation liquid of WAS could achieve higher recovery benefits.

Improved solid/liquid separation performance of hydrochar from sludge via hydrothermal carbonization

A solid–liquid separation process is crucial for the utilization of hydrochar from biomasses through hydrothermal carbonization (HTC). This study aimed to evaluate the separation performance of hydrochar from coking sludge (CS) and municipal sludge (MS) via HTC and propose its mechanistic insights. The results indicated that the separation performance of hydrochar was enhanced, and relatively severe hydrothermal temperatures exerted a relatively stronger dewatering effect (53.25% and 77.05% reductions in the total water contents in CS and MS, respectively) and a superior separation efficiency (the specific resistance to filtration of products obtained from CS and MS decreased form 7.21 × 1011 and 2.46 × 1012 to 1.92 × 1010 m/kg and 2.14 × 1011 m/kg, respectively). Mechanism investigation involved analyzing the surface functional groups of hydrochar and changes in organic components. It was demonstrated that the improvement in dewatering effect predominantly resulted from the release of bound water due to the decomposition of carbohydrates and proteins. Specifically, the release of bound water depended on the decomposition of carbohydrates at 180 °C, while it relied on the decomposition of proteins in the 210–300 °C range. Compared with particle size, the hydrophilicity of the particle played a more important role in improving the separation efficiency. The HTC reaction eliminated hydrophilic groups, such as hydroxyl and carboxyl groups, and induced the formation of aromatic structures, thus reducing the hydrophilicity of hydrochar particles. Moreover, it was found that the lower heating value of hydrochar from CS and MS increased from 3.51 to 1.94 to 8.32 and 4.60 MJ/kg due to the improvement of the separation efficiency. These comprehensive findings provide valuable mechanistic insights into the solid–liquid separation process and controlling the dewaterability of hydrochar.

Towards Solving the Complexity Associated with Continuous Countercurrent Decantation (CCD) System in Solid–Liquid Separation Processes

Towards Solving the Complexity Associated with Continuous Countercurrent Decantation (CCD) System in Solid–Liquid Separation Processes

Synergistic mechanism of CTAB and nonionic polyacrylamide on pore structure of kaolinite filter cake

Filtration rate and water content of filter cake are decisive indicators in tailings solid–liquid separation processes, with the pore structure of the filter cake playing crucial roles in determining these outcomes. This work aims to investigate the effect of different filter aids on filter cake characteristic and to elucidate the mechanism of surface wettability regulation and flocculation on the pore structure of the filter cake using X-ray microtomography (XMT) to capture the porous structure of the filter cake. The results indicated that the filtration rate of the kaolinite suspension reached 12.25 × 10 -3 mL/(s·cm2) when the dose of cetyl trimethyl ammonium bromide (CTAB) was 0.3 mmol/L and nonionic polyacrylamide (NPAM) was 40 g/t. In comparison to the case without CTAB, the water content of the kaolinite filter cake decreased from 40.21% to 34.91%. Analysis of the filter cake structure demonstrated that the percentage of isolated pores in the filter cake, obtained via CTAB pretreatment followed by NPAM flocculation, was reduced to 10.12%, with uniform pore space development, good homogeneity, and an increased pore throat coordination number. These enhancements effectively improved the connectivity of the filter cake pores and created more pathways for water migration during the filtration process. Concurrently, the pore throat radius ratio in the filter cake decreased from 1.15 to 1.10, minimizing capillary resistance during water migration, resulting in a significant increase in filtration speed and efficacy.

Synthesis of magnetic NaY zeolite for plasma proteomics application

Magnetically modified NaY zeolite has shown advantages in high-throughput and large-scale clinical plasma proteomic studies. In this study, magnetic NaY zeolite was prepared via an improved method, "layer by layer adhesion", using epoxy adhesive. The morphology, structure, and magnetic properties of magnetic NaY zeolite were characterized and tested by scanning electron microscope (SEM), fourier transform infrared spectrometer (FT-IR), X-ray diffractometer (XRD), and vibrating sample magnetometer (VSM), and using sodium dodecyl sulfonate-polyacrylamide gelelectrophoresis (SDS-PAGE) and liquid chromatography-tandem mass spectrometry (LC-MS) for plasma proteomics studies. The results showed that NaY zeolite was coated on the surface of Fe3O4 by epoxy adhesive, and such coating did not affect the surface properties of the magnetic zeolite. The saturation magnetization of magnetic NaY zeolite was measured as 9.964 emu g−1. Approximately 2929 proteins could be identified from plasma protein corona formed on magnetic NaY zeolite, reaching 97.6 % of the identification number of pure NaY zeolite. Furthermore, compared with NaY zeolite, the solid-liquid separation processes of magnetic zeolite during plasma proteomics studies were significantly reduced from half an hour to few minutes. Due to excellent plasma protein adsorption performance and rapid magnetic separation property, magnetic NaY zeolite is expected to become a powerful tool for the large-scale adsorption of low-abundant plasma proteins and high-throughput proteomic studies.

In-situ growth of MOF-based composites on nylon membrane for effective phosphate removal

A membrane adsorbent has been rationally designed to simplify the solid-liquid separation process and avoid adsorbent loss and leakage. The iron-based MOF was grown in situ on the surface of nylon membrane substrates by layer-by-layer method, and the as-synthesized MIL@nylon was post-treated with sodium borohydride to generate iron oxide nanoparticles within the MOF, named HFO@MIL@nylon. SEM, XRD, FT-IR and XPS characterization confirmed successful loading of MOF and the generation of nanoparticles in the MOF. The adsorption properties of HFO@MIL@nylon were tested. The results show that the adsorption process of phosphate accords with Langmuir and quasi-second-order kinetic model, with an adsorption capacity of 63.3 mg/g based on the mass of HFO@MIL. HFO@MIL@nylon could maintain high performance in a wide pH range. And the common interference ions SO42-, NO3-, Cl- only extended minus effect on the removal which means HFO@MIL@nylon has a good selectivity towards phosphorus. In addition, HFO@MIL@nylon membrane could work as a filter membrane, purifying 550 mL water of 200 μg-P/L with a water permeance of 1054 L/m2 h MPa.

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.

Specific lignin and cellulose depolymerization of sugarcane bagasse for maximum bioethanol production under optimal chemical fertilizer pretreatment with hemicellulose retention and liquid recycling

By screening out total nine sugarcane cultivars that contain directly-fermentable sugars, this study examined largely varied hexoses yields from direct enzymatic hydrolysis of bagasse residues. Using two representative sugarcane bagasse substrates, this study sorted out optimal K3PO4 pretreatments by performing classic response surface methodology, which respectively extracted 58% and 63% lignin and significantly reduced cellulose CrI and DP values in two pretreated bagasse residues. These consequently led to remarkably raised cellulose accessibility by 1.4- and 3.6 folds for near-complete biomass enzymatic saccharification with hexoses yields close to 100% (% cellulose). Notably, unlike physical (hot water, steam explosion) and chemical (acid, alkali) pretreatments as previously examined, this optimal pretreatment (6.4% K3PO4, 144.0 °C, 1 h) could not significantly extract arabinose-rich hemicellulose, suggesting that almost all xylose of hemicelluloses was applicable for engineered yeast co-fermentation to achieve maximum bioethanol at 29% (% dry matter) without the necessity of solid-liquid separation, water washing, and detoxification process. Furthermore, this study collected all K3PO4 liquid waste as chemical fertilizer into rice culture for much enhanced plant growth and biomass production up to 1.5 folds. Therefore, this work has proposed a mechanism model to highlight a cost-effective and green-like strategy for high yield of bioethanol with potential value-added bioproducts by using sugarcane bagasse and other lignocellulose residues.

Determination of five nonsteroidal anti-inflammatory drugs in water by dispersive solid phase extraction-ultra performance liquid chromatography-tandem mass spectrometry based on metal-organic framework composite aerogel

非甾体类抗炎药(NSAIDs)能在环境水体中长期稳定存在,不仅对生物有慢性毒性还能增加病原体的耐药性,开发可靠的测定水样中痕量非甾体抗炎药的分析方法至关重要。该文制备新型金属有机骨架/壳聚糖复合气凝胶材料Co-UiO-67(bpy)/CS分散固相萃取吸附剂,将其用于环境水体中酮洛芬、萘普生、氟比洛芬、双氯芬酸、布洛芬5种非甾体类抗炎药的富集,结合超高效液相色谱-串联质谱法(UPLC-MS/MS),建立了基于金属有机骨架材料(MOFs)复合气凝胶环境水体中药物残留检测的新方法。为获得最佳的萃取效率,对影响萃取效果的主要因素(材料类型、MOFs用量、萃取时间、水样pH值、离子强度、甲酸体积分数、洗脱时间、洗脱剂体积)进行条件考察及优化。优化结果显示,吸附剂5 min内就可实现目标化合物的完全吸附,用总体积为5 mL的1%甲酸甲醇溶液洗脱6 min,目标化合物就能充分解吸。在最优的固相萃取条件下建立分析方法,结果表明,5种非甾体类抗炎药在各自范围内线性关系良好,线性相关系数均大于0.9937,方法的检出限(LOD)和定量限(LOQ)分别为0.32~2.06 ng/L和1.05~6.78 ng/L。在40、250和1500 ng/L 3个加标水平下进行加标回收试验,5种待测物的平均回收率为74.5%~114.1%。日内、日间相对标准偏差分别为1.3%~12.3%和1.3%~11.5%。将该方法用于实际水样的检测,市政污水检测出微量的酮洛芬和氟比洛芬,含量分别为14.52 ng/L和10.05 ng/L。该方法具有良好的灵敏度、准确度和精密度,操作简便,耗时短,为环境水体中痕量非甾体抗炎药富集检测提供了新方法。

A Population Balance Model for Shear-Induced Polymer-Bridging Flocculation of Total Tailings

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process of total tailings. The PBM leads to a system of ordinary differential equations describing the evolution of the size distribution, and incorporates an aggregation kernel and a breakage kernel. In the aggregation kernel, a collision frequency model describes the particle collision under the combined effects of Brownian motions, shear flow, and differential sedimentation. A semi-empirical collision efficiency model with three fitting parameters is applied. In the breakage kernel, a new breakage rate coefficient model with another three fitting parameters is introduced. Values of the six fitting parameters are determined by minimizing the difference between experimental data obtained from FBRM and modeling result through particle swarm global optimization. All of the six fitting parameters vary with flocculation conditions. The six fitting parameters are regressed with the flocculation factors with six regression models obtained. The validation modeling demonstrates that the proposed PBM quantifies well the dynamic evolution of the floc size during flocculation under the given experimental setup. The investigation will provide significant new insights into the flocculation kinetics of total tailings and lay a foundation for studying the performance of the feedwell of a gravity thickener.

Metal Sulfide Precipitation: Recent Breakthroughs and Future Outlooks

The interest in metal sulfide precipitation has recently increased given its capacity to efficiently recover several metals and metalloids from different aqueous sources, including wastewaters and hydrometallurgical solutions. This article reviews recent studies about metal sulfide precipitation, considering that the most relevant review article on the topic was published in 2010. Thus, our review emphasizes and focuses on the overall process and its main unit operations. This study follows the flow diagram definition, discussing the recent progress in the application of this process on different aqueous matrices to recover/remove diverse metals/metalloids from them, in addition to kinetic reaction and reactor types, different sulfide sources, precipitate behavior, improvements in solid–liquid separation, and future perspectives. The features included in this review are: operational conditions in terms of pH and Eh to perform a selective recovery of different metals contained in an aqueous source, the aggregation/colloidal behavior of precipitates, new materials for controlling sulfide release, and novel solid–liquid separation processes based on membrane filtration. It is therefore relevant that the direct production of nanoparticles (Nps) from this method could potentially become a future research approach with important implications on unit operations, which could possibly expand to several applications.

Simulation of particles screening in pulsating negative pressure shale shaker by coupling CFD and DEM

PurposeThe purpose of this paper is to obtain the combination of working parameters suitable for pulsating negative pressure shale shaker through simulation, which is conducive to efficient recovery of clean drilling fluid and relatively dry cuttings.Design/methodology/approachShale shaker is still one of the main equipment in solid–solid and solid–liquid separation processes in drilling industry. This research is based on a new drilling fluids circulation treatment device, namely pulsating negative pressure shale shaker. In this work, a numerical study of particle flow and separation in the pulsating negative pressure shale shaker is carried out by coupling computational fluid dynamics/discrete element method (CFD-DEM). The effect of vibration parameters and negative pressure parameters are studied in terms of conveyance velocity and percent through screen.FindingsThe results show that, conveyance velocity of particle is mainly affected by vibration parameters, negative pressure in pulsating form can effectively prevent cuttings from sticking to the screen. Vibration parameters and pulsating airflow velocity peak have great influence on percent through screen, while vibration frequency and screen slope have influence on the time when the percent through screen reaches stability.Originality/valueIn this paper, the authors put forward a new kind of drilling waste fluid treatment equipment, and focused on the study of particle movement law. The results have important guiding significance for the selection of structural design parameters and rational use of equipment. In addition, the new device provides a new idea for solid–liquid separation method, which is one of the hot topics in current research.

A facile route of mesoporous TiO2 shell for enhanced arsenic removal

The commercial application of metal oxide composites adsorbent for arsenic removal was limited by some problems, such as low adsorption capacity and difficult recycling. Herein, monodispersed core-shell mesoporous H-Fe3O4@mTiO2 magnetic microspheres adsorbent for efficient arsenic removal was prepared by facile pre-modification of titania precursor and boiling water assisted crystallization treatment. The obtained H-Fe3O4@mTiO2 composite microspheres possessed high-quality core-shell structure with a high specific surface area of 179.98 m2 g−1 and an available magnetic susceptibility of 31.91 emu g−1 which is easy to separate adsorbent from waste water. The batch adsorption experimental results showed that the Langmuir maximum capacities of the obtained H-Fe3O4@mTiO2 for As(V) and As(III) were 7.74 and 18.22 mg g−1, respectively. Particularly, H-Fe3O4@mTiO2 exhibited excellent performance for As(III) removal at a broad pH range of 3–10. Moreover, as-made adsorbent showed excellent stability after 5 regeneration cycles because the preponderant magnetic inner-core can realize fast solid-liquid separation process of adsorbent without any loss.

Assessing inter and intra-variation in the characteristics of faecal sludge from Vadgaon Maval, Maharashtra: For better faecal sludge management in India

Faecal Sludge (FS) produced in developing countries has become a significant source of water pollution. The optimal treatment of FS can lead to a sustainable economy. In India, the second phase of the open defecation free (ODF) initiative (energy recovery by providing city- or town-level centralised FS treatment plants) has begun from 2019 to sustain millions of toilets. However, to achieve this goal, India must address significant knowledge gaps such as the type of available on-site sanitation treatments (OSTs), optimal time of emptying the OSTs, and variations in the FS characteristics with age. Thus, the present study analysed FS samples collected from Vadgaon Maval, Maharashtra, India, to understand the inter- and intra-variation in FS characteristics. The pH, electrical conductivity, total solids (TS), specific gravity (SG), organic matter (OM), chemical oxygen demand (COD), and pathogen content of FS samples were observed to be in the range of 7–7.65, 1.19–4.01 mS/cm, 1–123 g/L, 0.88–1.26, 18.4%–100%, 960–6080 mg/L, and 105–109 number/L of FS, respectively. The inter-variation of FS characteristics exhibited that the pH, EC, TS, and SG increased, whereas OM, settling, and drying capacity decreased with an increase in age. Fresh FS (excreta degraded for ≤3 years) was yellowish-brown in colour and exhibited low TS, low SG, and high OM. On the other hand, older FS (excreta degraded for >3 years) was blackish-brown in colour and exhibited high TS, SG, and pathogen content. This observation indicates that FS vacuum pumping may be difficult in the sludge zone after 3 years of excreta degradation, which may encourage the manual scavenging practice. Additionally, the analysis of FS treatment plant (FSTP) process control parameters (settled sludge volume, sludge volume index, and sludge drying capacity) indicated that the treatment time required for older FS is long, which increases the FSTP cost. Furthermore, FS intra-variation in OST exhibited that effluent FS could be directly sent for effluent treatment without any solid–liquid separation process. Thus, the present study can help practitioners in establishing or modifying FS treatment systems for addressing conditions based on the variation in FS characteristics at the town level in India.

A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

A simple criterion is proposed to quantitatively estimate the resistance of aggregates based on incremental mechanical shear disturbances. Aggregate strength can be affected by the hydrodynamic conditions under which flocculation occurs; therefore, an experimental method is standardized to determine the resistance of aggregate structures that are formed under defined conditions of salinity (NaCl 0–0.1 M), mixing time (3 min), and mean shear rate (G = 273 s−1). Kaolin particles were flocculated in saline solutions with an anionic flocculant of high molecular weight. The method involves increasing the mean shear rate (G = 0–1516 s−1). Each increment represents a new experiment that starts from the base of 273 s−1. Target aggregates are increasingly fragmented as mechanical disturbance increases. The monotonic relationship between the mean shear rate increments (ΔG) and the final size of the aggregates is used for a quantitative estimate of the resistance of the target aggregates since this resistance underlies this relationship. The evolution of aggregate size is analyzed by the Focused Beam Reflectance Measurement (FBRM) method, which may capture the chord length distribution on concentrated slurries. To estimate and compare the resistance of the target aggregates in solutions with different salinities, a pseudo-first-order model that describes the rupture degree as a function of shear rate increments obtains the characteristic shear rate. The rupture percentage is reached with considerably lower agitation increments at higher salinity than at low salinity. This criterion is expected to help improve the efficiency of solid–liquid separation processes, especially in plants operating with seawater, be it raw or partially desalinated.