Explore the vast range of titles available.

Dewatering of sludge from sewage treatment plants is proving to be a significant challenge due to the large amounts of residual sludges generated annually. In recent years, research and development have focused on improving the dewatering process in order to reduce subsequent costs of sludge management and transport. To achieve this goal, it is necessary to establish reliable indices that reflect the efficiency of sludge dewatering. However, the evaluation of sludge dewaterability is not an easy task due to the highly complex nature of sewage sludge and variations in solid–liquid separation methods. Most traditional dewatering indices fail to predict the maximum cake solids content achievable during full-scale dewatering. This paper reviews the difficulties in assessing sludge dewatering performance, and the main techniques used to evaluate dewatering performance are compared and discussed in detail. Finally, the paper suggests a new dewatering index, namely the modified centrifugal index, which is demonstrated to be an appropriate indicator for estimating the final cake solids content as well as simulating the prototype dewatering process.

Municipal sludge is characterized by high organic matter content, high viscosity, and fine particles, resulting in poor dewatering performance. This article analyzes the composition and properties of municipal sludge, examines the factors affecting the dewatering performance of sludge and the mechanisms corresponding to each influencing factor, and introduces chemical conditioning in detail. Chemical conditioning includes flocculation conditioning, oxidation conditioning, acid-base conditioning, and aggregate conditioning. The principles and applications of existing sludge conditioning technologies are systematically analyzed. By comparing the advantages and disadvantages of different technologies, it is pointed out that the key to developing sludge conditioning technology lies in developing a more appropriate combination of the sludge conditioning and dewatering process according to the sludge quality of different municipal wastewater treatment plants, taking into account their local environment, input costs, subsequent sludge disposal methods, and other factors, and further optimizing the sludge dewatering process by developing new efficient and environmentally friendly sludge conditioning agents.

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.

Producing tissue paper is an energy-demanding process; a significant amount of energy is expended when removing water by vacuum, mechanical pressing, and thermal drying. Because the water is most energy-demanding to remove in drying, making the preceding step of vacuum dewatering more efficient would benefit the whole process. This article focuses on developing a laboratory-scale method for verifying the nature of diminishing returns of water removal and investigating efficiency strategies of the vacuum dewatering. The theoretical concept of successive vacuum suction boxes with progressing vacuum levels was tested at the laboratory scale in order to show quantifiable results of the previously solely theoretical concept. The results confirmed that vacuum dewatering can be improved by adding progressively higher vacuum levels and that such a practice can benefit both outgoing dryness levels and expended vacuum pump energy. To truly examine the power of progression of vacuum levels, rewetting can be included in the calculations, by using an approximate value collected from pilot or full-scale measurements. For any new fiber mix, pulp type, vacuum level setup, basis weight, etc. the vacuum levels, rewetting, and dwell times need to be tuned to that specific case.

Chemical crosslinking of cellulosic fibers increases their brittleness, making them more susceptible to dry powdering. In this study, bleached eucalyptus kraft pulp (BEKP) sheets were crosslinked with glyoxal (GO) and citric acid (CA) and subsequently dry cut into powders using a Wiley cutting mill. Key variables in the powder preparation were dosages of GO and CA, as well as their respective catalysts, aluminum sulphate (alum) and sodium hypophosphite (SHP). The average fiber length of the GO and CA crosslinked pulps was reduced, at most down to 0.12 and 0.17 mm by the dry cutting, using a 0.5 mm perforated screen in the final dry-cutting stage. The powders exhibited reduced water retention, lower sedimentation volume in water, and, when dry, showed increased tapped and bulk densities. When mixed with refined BEKP, the powders enhanced dewatering during handsheet formation and improved the resulting sheets’ bulk, light scattering, and opacity, while reducing tensile strength. These findings suggest that chemically crosslinked pulp powders have potential as a bulking and dewatering aid in papermaking. Furthermore, due to their low water absorbency and presumable low abrasiveness, the powder may have potential applications beyond papermaking, such as filler of plastics, glues, and coating materials.

Coagulation/flocculation is a major phenomenon occurring during industrial and municipal water treatment to remove suspended particles. Common coagulants are metal salts, whereas flocculants are synthetic organic polymers. Those materials are appreciated for their high performance, low cost, ease of use, availability and efficiency. Nonetheless, their use has induced environmental health issues such as water pollution by metals and production of large amounts of sludges. As a consequence, alternative coagulants and flocculants, named biocoagulants and bioflocculants due to their biological origin and biodegradability, have been recently developed for water and wastewater treatment. In particular, chitosan and chitosan-based products have found applications as bioflocculants for the removal of particulate and dissolved pollutants by direct bioflocculation. Direct flocculation is done with water-soluble, ionic organic polymers without classical metal-based coagulants, thus limiting water pollution. Chitosan is a partially deacetylated polysaccharide obtained from chitin, a biopolymer extracted from shellfish sources. This polysaccharide exhibits a variety of physicochemical and functional properties resulting in numerous practical applications. Key findings show that chitosan removed more than 90% of solids and more than 95% of residual oil from palm oil mill effluents. Chitosan reduced efficiently the turbidity of agricultural wastewater and of seawater, below 0.4 NTU for the latter. 99% turbidity removal and 97% phosphate removal were observed over a wide pH range using 3-chloro-2-hydroxypropyl trimethylammonium chloride grafted onto carboxymethyl chitosan. Chitosan also removed 99% Microcystis aeruginosa cells and more than 50% of microcystins. Here, we review advantages and drawbacks of chitosan as bioflocculant. Then, we present examples in water and wastewater treatment, sludge dewatering and post-treatment of sanitary landfill leachate.

Soil electrokinetics (SEK) research has been widely used in various fields such as soil remediation, dewatering, land restoration, geophysics, sedimentation, pollution prevention, consolidation, and seed germination. According to our most recent published research on SEK process design modifications during the last 30 years (1993–2022), more than 150 designs have been introduced to assure SEK’s maximum performance. Incorporating lateral electrodes/anodes was not documented in the existing literature, which motivated us to investigate the output of this design. In this study, we aimed to enhance the performance of the perforated cathode pipe soil electrokinetic remediation (SEKR) system (PCPSS) for removing inorganic pollutants by installing lateral anodes (LA-PCPSS) using two approaches. In the first approach, the LA-PCPSS was connected to different sources of applied voltages (DSAV) from different power supplies, while in the second approach, the entire operation system was connected to the same source of applied voltage (SSAV). We used the Taguchi approach (L 9 OA) to determine the optimal levels of applied voltages for the DSAV system. The results indicated that the DSAV-(LA-PCPSS) could be optimized at an applied voltage of 1 V cm −1 for the surface and the first and second lateral anodes. The indigenous Sr (elements found in the tested soil without artificial pollution) in kaolinite showed the best response among other elements (Ni and other indigenous elements) when optimizing the DSAV-(LA-PCPSS) using the Taguchi approach. Installing lateral anodes (position B) supplied to low applied voltage (0.5 V cm −1 ) improved the electroosmosis (EO) rate/dewatering. Reverse migration of ions was observed during the remediation of real contaminated soil using the SSAV-(LA-PCPSS). The DSAV-(LA-PCPSS) is considered an appropriate design for the SEKR of inorganic pollutants, and increases the EO flow/dewatering. Additionally, the increased energy consumption employing the DSAV-(LA-PCPSS) was extremely minimal compared to the traditional PCPSS, which is an economic advantage for SEKR research. The DSAV-(LA-PCPSS) is still under optimization/intensification process, and subsequent processes will be examined to achieve high efficiency.

For a foundation pit adjacent to a structure with a common retaining wall, current mathematical models do not consider the interactions between seepage resulting from dewatering and the adjacent structures with the common retaining wall. In this study, the steady-state continuity equation of the seepage field considering an adjacent structure and retaining wall thickness is formulated by region dividing. The hydraulic head and water pressure are solved respectively using Fourier series expression and Bernoulli’s principle. A numerical model is established in FLAC3D to validate the accuracy of the analytical solution. The maximum deviation of analytical results is merely 2.76%, and the computation time is only two thousandths of that required by the numerical simulation. Further analysis is conducted on the effects of various engineering parameters on water pressure distribution, resultant water pressure and exit gradient, revealing that retaining wall thickness, adjacent structure width and upper/lower soil permeability ratio have non-negligible inhibitory effects on seepage, while pervious layer thickness exhibits a promotive effect and adjacent structure depth shows no influence on seepage. In conclusion, the proposed analytical solution can produce efficiently produce accurate results, making it valuable for practical applications in foundation engineering.

The process of disposing the tailings from mining activities generally involves the construction of large storage structures, either because of the large volume of residue generated by industrial processing plants or the difficulties in obtaining grants for new disposal areas. Over the past few years, such storage structures have been maximized to astonishing dimensions, considerably increasing the risk associated with possible rupture. Therefore, new management techniques, such as the integration of several mining areas involved in the exploration, and processing and residue disposal, need to be developed for reducing the generated residue volume and for optimizing the disposal processes of such materials. One of the residue disposal methodologies currently under study is the acceleration of the dewatering/consolidation process of the so-called fine residues, using electrokinetic techniques. In this context, this study conducts electrokinetic dewatering tests on fine bauxite tailing, using samples with initial solid content by weight ranging from 20 to 30%; final values between 43 and 66% are achieved. The estimated power consumption per volume of drained water ranges from 31.4 to 375.2 kWh/m3. The obtained results establish that the utilization of electrokinetic processes in the dewatering of tailings is a technique worthy of further investigation.

Sludge electro-dewatering technology is an attractive dewatering technology, but its application is limited by high energy consumption and filter cloth clogging caused by the dissolution of extracellular polymeric substances (EPSs). Thus, the addition of inorganic coagulants is expected to enhance the electro-dewatering efficiency of waste activated sludge (WAS). In this study, we evaluated the effects of the three typical inorganic coagulants (HPAC, PAC, and FeCl3) on sludge electro-dewatering behavior. The results show that the electro-dewatering rate at the cathode was increased with the raising of the inorganic coagulants dosage, and FeCl3 exhibited the best effect on the improvement of sludge electro-dewatering among the three inorganic coagulants. The zeta potential of the sludge flocs and the electro-osmotic effect were raised with the increasing of the inorganic coagulants dosage. The sludge floc conditioned by FeCl3 is more compact than HPAC and PAC. Moreover, the dissolved EPS content reduced in the sludge electro-dewatering process when inorganic coagulant was added. In comparison to increasing ionic strength, the compression of extracellular polymeric substances (EPSs) plays a more critical role in enhancing the electro-dewatering process of sludge. The addition of inorganic coagulants also reduced the energy consumption during water removal in the electro-dewatering process.