Dewatering Of Wastewater Sludge Research Articles

A Mini Review on Electroosmotic Phenomena in Porous Media

Electroosmosis phenomenon in porous media finds widespread applications in various fields such as microfluidic systems, polymer electrolyte membrane fuel cells, oil and gas engineering, wastewater sludge dewatering and groundwater dynamics etc. Therefore, the electroosmotic flow mechanism in porous media have attracted broad interests from multiple disciplines. This paper provides an overview on the physical mechanisms and mathematical models for electroosmosis in porous media. The background of electric double layer theory and state-of-art research progress on pore-scale models for electroosmotic flow through porous media are reviewed. Two typical and significant research topics, electroosmosis under pressure coupling effect and nanoscale electroosmotic phenomena, are then focused on. The advances in theoretical analysis, numerical simulation and experimental measurements are summarized. Finally, the potential research directions for the electroosmotic flow in porous media are addressed out.

Characterization and Performance of Sludge Derived Biochar as Conditioner in Textile Wastewater Sludge Dewatering

Characterization and Performance of Sludge Derived Biochar as Conditioner in Textile Wastewater Sludge Dewatering

Factors affecting the mechanical deep dewatering of sludge from wastewater treatment

Effects of pressure, dewatering time, and sludge cake thickness on the dewatering of wastewater sludge by the hydraulic dehydrator under the condition of adding CaO and FeSO4 were analyzed using the response surface method (RSM). It was found that when the parameters of pressure, dewatering time, and sludge cake thickness were changed, the trends of dewatering papermaking sludge and municipal sludge were similar under the condition of raw sludge with 3% CaO and 3% FeSO4. Specifically, the increase of pressure and dewatering time promotes the dewatering effect of wastewater sludge, and the thinner the sludge cake is, the better the dewatering effect. The water content can be affected by the change of pressure, dewatering time, and sludge cake thickness. In response surface analysis, the model F-value and coefficient of determination (R2) were 541.43 and 0.9986, respectively, indicating high significance and good correlation. In the model, the change of pressure, dewatering time, and sludge cake thickness affected the water content of paper sludge. Particularly, the increase of pressure and compression time enhanced the dewatering efficiency. The thinner the sludge cake was, the better the dewatering effect of paper sludge was.

Malodorous volatile organic compounds (MVOCs) formation after dewatering of wastewater sludge: Correlation with the extracellular polymeric substances (EPS) and microbial communities

Malodorous volatile organic compounds (MVOCs) are often the key odorants in determining sludge odor character and odor impact. However, the emission characterization and generation mechanisms of MVOCs from various dewatered sludge have not been sufficiently understood partly due to the diverse and complex composition and low concentration of odorants. In this study, waste activated sludge (WAS) was collected to examine the variation of MVOC emission from sludge after different dewatering treatment in lab-scale trials. The MVOCs were measured using the electronic nose (eNose), headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS). The results showed that centrifugation treatment promoted the generation of various odorous volatiles. The identified key odorants included dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), geosmin, and p-cresol according to their odor activity values (OAVs). The effects of the enhanced dewatering on volatile production were greater than thickening, however, the key odorants of dewatered sludge using gravity thickening varied more greatly than sludges from centrifuge thickening. The distribution of extracellular polymeric substances (EPS) and variation of microbial community showed correlations with the production of key odorants. Tryptophan-like substances in the inner layer of EPS (LB-EPS and TB-EPS) were better correlated with the key odorants. The bound EPS released by centrifugation may play the role of precursor for odorous microbial volatiles. According to the predicted functions of differential microbial genera, Desulfobulbus (Desulfobacterota), Gordonia (Actinobacteriota), and Hyphomicrobium (Proteobacteria) were associated with the production of DMS, DMDS, and DMTS, while Gordonia and Hyphomicrobium were related to p-cresol production.

A comparative study of electro-dewatering process performance for activated and digested wastewater sludge

Electro-dewatering (EDW) is an alternative emerging and energy-efficient technology that provides improved liquid/solids separations in the dewatering of wastewater sludge. The EDW technology is not only an innovative dewatering method for significantly reducing the volume of wastewater sludge before re-utilization or disposal, but is also a promising emerging method which may potentially be used for decontamination purposes. In this study, the influence of the sludge properties (e.g. electrical conductivity, zeta potential, specific cake resistance, among others) on their mechanical and electrical behaviour in terms of dewaterability and electro-dewaterability, the applied current (current density from 20 to 80 A/m2), and filter cloth position relative to the electrode was investigated. A two-sided filter press at lab-scale with moving anode was used, and the treatment performance of the EDW process on two different types of wastewater sludge (activated and digested) was thoroughly assessed from both an electrochemical viewpoint and in terms of the dewatering rate. The results showed that the conditioned digested sludge was more easily dewatered by mechanical dewatering (MDW) with 34–35% (w%) of dry solids content compared to 19–20% (w%) for the activated sludge, thanks to the lower content of both the microbial extracellular polymeric substances (EPS) and the volatile suspended solids fraction.For the EDW results, the electrical conductivity of the sludge was pivotal to the dryness of the final solids and therefore also to the dewatering kinetics. The results demonstrated that the activated sludge arrived at an equilibrium much faster (after approximately 3600 s) compared with digested sludge, thanks to its lower electrical conductivity (0.8 mS/cm) providing a greater voltage drop across the cathode and therefore more repulsion of the solids from the cathode leading to continuously high filtrate flowrate. Also the EDW performance was analysed by comparing the ratio of the filtrate volume collected at the anode to the volume collected at the cathode side. For digested sludge at 5 bar, 40 A/m2 different positions of the filter cloth were tested but these configurations barely impacted the EDW performance, despite having a significant impact on the energy requirements. At industrial scale, it would be useful to position the filter cloths at some distance from the electrodes, but this study shows that this benefit may be quickly outweighed by the loss in EDW energy efficiency.

Ferrrate(VI) and freeze-thaw treatment for oxidation of hormones and inactivation of fecal coliforms in sludge.

This study examined the individual and combined effects of potassium ferrate(VI) additions and freeze-thaw conditioning for the treatment and dewatering of wastewater sludge in cold climates, with particular focus on the inactivation of fecal coliforms and oxidation of estrogens, androgens, and progestogens. The first phase of the study evaluated the effects of potassium ferrate(VI) pre-treatment followed by freeze-thaw at -20 °C using a low (0.5 g/L) and high (5.0 g/L) dose of potassium ferrate(VI). The results showed that pre-treatment of anaerobically digested sludge with 5 g/L of potassium ferrate(VI) reduced the concentration of fecal coliforms in the sludge cake to below 100 MPN/g DS. The second phase evaluated the ability of ferrate(VI) to oxidise selected hormones in sludge. Anaerobically digested sludge samples were spiked with 10 different hormones: estrone (E1), 17α-estradiol, 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), equilin, mestranol, testosterone, norethindrone and norgestrel in two groups of low (3-75 ng/mL) and high (12-300 ng/L) concentration ranges of hormones. The samples were treated with either 0.5 or 1.0 g/L of potassium ferrate(VI), and hormone concentrations were measured again after treatment. Potassium ferrate(VI) additions as low as 1.0 g/L reduced the concentration of estrogens in sludge. Potassium ferrate(VI) additions of 0.5 and 1.0 g/L were less effective at reducing the concentrations of androgens and progestogens. Increasing ferrate(VI) dose would likely result in more substantial decreases in the concentrations of fecal coliforms and hormones. The results of this study indicate that the combined use of freeze-thaw and ferrate(VI) has the potential to provide a complete sludge treatment solution in cold regions.

Influence of process operating parameters on dryness level and energy saving during wastewater sludge electro-dewatering

Electrically assisted mechanical dewatering, known as electro-dewatering (EDW), is an alternative emerging technology for energy-efficient liquid/solids separation in the dewatering of wastewater sludge. In this study, the performance of the electro-dewatering (EDW) process for activated wastewater sludge was investigated. The influence of the operating modes; being the timing of voltage (U-EDW) or current (I-EDW) application to either or both the filtration and compression stages, and the influence of the applied pressure (in successive 30 min pressure steps) were studied. The results showed that by delaying the application of the electric field to the filter cake compression stage, there was a potential saving in power consumption of around 10–12% in the case of U-EDW and about 30–46% in the case of I-EDW.The increase of the applied pressure from 0.5 to 12 bar during the filter cake compression stage leads to an increase in electro-dewatering kinetics. The results also reveal that at a low electric field level the increase of the processing pressure has a relatively pronounced effect on the dewatering process. At high levels of the electric field, a minimum processing pressure (4–6 bar) is required to improve the electrical contact between the electrode and the sludge and thus lower the energy consumption.

Clay Fabric in Electrokinetic Dewatering

Electrokinetic dewatering, a promising way to separate the clay particles from water in suspensions, has been researched for many years on topics like equipment design, parametric optimization, and ion migration.1 However, little work has been done on the clay fabric which affects the performance to a considerable degree during electrokinetic dewatering since different fabrics have different electrokinetic properties. Therefore, if we could figure out fabric and control it intentionally, a breakthrough in improving the productivity and lowering the energy consumption will be possible.Suspensions come from four corners mining plant in central Florida, which contains approximately one-third phosphate, one-third sand and one- third clay. Clay, mainly smectite here, plays the key role in dewatering due to the relatively small particle size and large surface area. Smectite plate is a 2:1 structure with permanent negative charge on the two faces, and pH-dependent charge on the edge.2 It is this property that makes the behavior of smectite complex in electrokinetic dewatering under the effect of both pH and electrical force simultaneously. To dissociate the effect of the two mechanisms, a natural settling experiment at different pH and an electrokinetic dewatering experiment were conducted.In the natural settling experiment, suspensions at acid environment reach stable state very fast and show a “gel” like behavior. However, suspensions in neutral and alkaline environment remains to be liquid like ones. The SEM results (Fig 1) of the sediments samples prepared by freeze-drying show that smectite particles in the presence of acid show edge-face fabric and flocculate into “honeycomb” structure as a result of the edge-face attraction and face-face repulsion (Fig 1a), while particles in neutral suspensions mainly display edge-edge, and in alkaline environment show all fabrics (edge-edge, edge-face, face-face) without dominating part.In the electrokinetic dewatering experiment, an electric field of 4V/cm was applied for 13 minutes. The SEM results (Fig 1b) elucidates that honeycomb forms at lower layer near anode where H+ exists due to electrolysis of water during the separation process, but appears to be more compressed compared with that of natural settling (Fig. 1a), which should be due to the electrical force. The middle and upper layer with a slightly alkaline environment looks much more disordered than the lower layer.Intuitively, we could infer that the rigid “gel” like honeycomb is not desirable for separation of particles compared with “soft” suspensions. In addition, the cells of the honeycomb are likely to trap water, which weakens electro-osmosis. The significance of this work exists in the difference of the electrokinetic properties between disordered plates and flocculated honeycomb. If the difference is quantified, then measures could be taken to control the fabric intentionally. Thus, we can predict the process more accurately and achieve a better performance. References A. Mahmoud, J. Olivier, J. Vaxelaire, A. F. Hoadley, Electrical field: a historical review of its application and contributions in wastewater sludge dewatering,Water research, 44(2010), 8. G. Lagaly, S. Ziesme . Colloid chemistry of clay minerals : the coagulation of montmorillonite dispersions. Advances in Colloid and Interface Science, 100-102(2003), 105–128.

Structure Evolution of Wastewater Sludge During Electroosmotic Dewatering

An experimental investigation was conducted to explore the characteristics of electroosmotic dewatering of wastewater sludge. Inner pore structure images of sludge were obtained by microcomputed tomography (micro-CT) scanning; the 3D pore structures of sludge and its dynamical evolution were studied by means of pore size distribution (PSD), box-counting fractal dimension, and volume change of sludge matrix. Transport of water content inside sludge was also associated with interactions between local capillary stress and global structural force during electroosmotic dewatering; its impact on the change of pore structure was analyzed. As water content decreased, the local capillary force split the pore surface and created cracks, and the global structural force shrank the sludge matrix and constricted the pore surface. Inner water transport and the evolution of pore structure closely depended on the location between the anode and cathode of electroosmosis.

Dewatering of wastewater sludge through a solar still

Wastewater sludge was passed through a laboratory solar still in order to determine the dewatering process. A number of parameters describing the distillate and the sludge were measured at the end of each day in order to determine the process behavior under conditions of relatively high solar radiation and temperature levels. It was realized that dewatering is accelerated and further analysis is needed in order to determine optimum conditions and design parameters for a demonstration plant that will operate towards reducing the sludge volume.