Energy-efficient coal dewatering using liquefied dimethyl ether

In this study, we dewatered sub-bituminous coal mined in Warra, Indonesia, by using liquefied dimethyl ether (DME); no heating was required in this dewatering process. We achieved this dewatering both in a laboratory-scale experiment and using previously developed bench-scale equipment. We also examined the properties of the coal before and after dewatering and measured the amount of energy required by the equipment. We found that the maximum water extraction efficiency of liquefied DME was 98.3%. Further, the properties of the coal did not change after the dewatering treatment. The wastewater obtained by dewatering can be treated by existing wastewater treatment technologies. The energy consumed by the bench-scale equipment was 2069 kJ/kg-water; thus, this dewatering process using liquefied DME was confirmed to be effective and energy efficient.     

A Study for Development of Real-Scale Thermal Filter Press Dewatering (TFPD)

Real-scale thermal filter press dewatering equipment (plate size: 630 mm × 630 mm) was installed and operated at a waterworks for one year in an attempt to achieve sludge reduction. During the period, the dewaterability was evaluated according to the seasonal sludge properties in order to compare the dewaterability of thermal dewatering and mechanical dewatering, as well as to determine the economics of thermal dewatering. According to the results, the winter season sludge showed a 36% decrease in water content and a two-thirds reduction in dewatering velocity compared to the summertime sludge. In addition, the dewatered cakes of the thermal filter press dewatering equipment showed a lower specific cake resistance and water content in the dewatered cakes than the mechanical filter press dewatering equipment, indicating superior dewaterability. This was attributed to the easier removal of the filtrate remaining in the capillary tubes due to thermal dewatering. The energy consumption for thermal dewatering was 300 kJ/dry solids (DS) kg. A comparison of the sludge dryers indicated that it is possible to produce dewatered cakes that consume less energy and can be recycled. According to the performance evaluation results, the real-scale thermal filter press dewatering equipment had high adaptability to the changes in seasonal sludge, showing excellent dewaterability compared to the mechanical filter press dewatering equipment, and was economical due to the lower energy consumption.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Experimental Study on Thermal Hydrolysis and Dewatering Characteristics of Mechanically Dewatered Sewage Sludge

After mechanical dewatering, sewage sludge has a moisture content of around 80 wt% and further disposal is required. A new sewage sludge semi-drying (dewatering) process is proposed and verified. It combines thermal hydrolysis and subsequent mechanical dewatering, with less energy consumption than traditional thermal drying. Sludge treated using this new process satisfies further disposal requirements (e.g., landfill or autothermal incineration). In the present study, a high-pressure test reactor was used to study the thermal hydrolysis of dewatered sludge. Thermally hydrolyzed sludge was subsequently dewatered by centrifugal sedimentation or by pressure filtration. The amount of organic compounds returning to the water phase was also measured. According to the results from centrifugal settling tests, the optimal thermal hydrolysis treatment temperature was 180°C. The moisture content then dropped to 1.44 kg/kg dry solids (DS; 59 wt%) after dewatering under relative centrifugal force of 9,000 × g from 5.67 kg/kg DS (85 wt%). Pressure filtration further reduced the moisture content of filter cakes to only 0.5 kg/kg DS (33 wt%, hydrolysis temperature 180°C). After thermal hydrolysis, the heating value of sludge (moisture-free basis) was about 80% that of the untreated sludge.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Involvement of Gypsum (CaSO4 · 2H2O) in Water Treatment Sludge Dewatering: A Potential Benefit in Disposal and Reuse

Abstract

This research assessed the use of gypsum (CaSO₄ · 2H₂O) as a skeleton builder for sludge dewatering since polymer conditioning of sludge affected only the rate of water release, not the extent of dewatering. The use of gypsum as a physical conditioner, in association with a polymer, could improve sludge filterability. More significantly, gypsum serves as a skeleton builder, forming a permeable and rigid lattice structure that can remain porous under high positive pressure during the compression step after the cake growth of the filtration, thereby maintaining the size of the micro‐passages through which water is expressed. Experiments using a high pressure cell apparatus showed that a further decrease of two to seven percent of the equilibrium moisture content of the sludge cake was achieved, for sludge thicknesses for dewatering of 1 to 10 cm, by the addition of gypsum with 60% of the original sludge solids when compared to the single polymer conditioning. The importance of the addition of gypsum in alum sludge dewatering is not only the improvement in the extent of dewatering, but also the potential application of transforming dewatered alum sludge from “waste” for landfill to useful “fertilizer” or to be used as a filter medium/adsorbent for wastewater treatment engineering.     

A study of the improvement in dewatering behavior of wastewater sludge through the addition of fly ash

Wastewater sludge is classified as a difficult dewatering material (DDM) due to the high cake specific resistance (CSR). On the other hand, fly ash is classified as an easy dewatering material (EDM), which suggests that it might be able to improve the dewaterability of wastewater sludge. The water content and cake specific resistance of dewatered sludge without the addition of fly ash were 80% and 2.9×10¹⁴ kg/m, respectively. When 50% (by dry weight) fly ash was added to the sludge, the water content and cake specific resistance decreased to 29.4% and 2.9×10¹³ kg/m, respectively. The cake specific resistance and water content decreased with increasing fly ash additions. Therefore, the production of sludge cake can be reduced by adding fly ash, which can help minimize the social and environmental problems caused by the need to dispose of wastewater sludge.     

Dewatering of Biomass Using Liquid Bio Dimethyl Ether

An interesting integrated configuration in a thermochemical conversion biorefinery that is producing dimethyl ether (DME) is to use a small fraction of the BioDME for dewatering of the solid biomass feedstock. Therefore, the use of liquid BioDME was investigated in this study for pressurized dewatering of biomass at room temperature. Water was removed in liquid form from wet sawdust and wet wood chips using liquid DME in a laboratory-scale batch unit. Both the sawdust and the wood chips could be dewatered in a short time (minutes) to a moisture content of 15% (w/w) from an initial content of approximately 55% (w/w). Longer DME treatment times (hours) lowered the moisture content even further down to 8% (w/w), indicating that the transport phenomena in the porous biomass and the solubility of DME in water influence the dewatering characteristics. The DME dewatering performance, 12–22 g DME per g water removed, was similar to literature data on coal dewatering using liquid DME. The present study showed that DME dewatering of the solid biomass feedstock has potential as an energy-efficient dewatering process, especially in an integrated thermochemical conversion biorefinery.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Effect of Polyelectrolyte Conditioning and Voltages on Fractionation of Macro and Trace Metals due to Sludge Electro-Dewatering

The purpose of this laboratory study was to investigate the simultaneous impacts of the electro-dewatering process on dry solids (DS) content and mobilization of metals in sewage sludge. The results suggested that the use of polyelectrolytes is necessary in mechanical pressure-driven dewatering and also in electro-dewatering. With polyelectrolyte conditioning, the DS content in the final sludge cake could be increased to 39%. Dewatering with slightly cationic polymer was not effective, but medium, strongly and very strongly cationic polymers performed equally. During electro-dewatering, an increase of voltage from 10 to 40 V resulted in a dryer sludge cake. Polyelectrolyte addition reduced the content of exchangeable metal species and increased less mobile, reducible species in the sludge. Furthermore, the more stable or immobile metal fractions were more likely to remain intact in dewatered sludge. Among heavy metals, Cu and Pb were immobile but Cr, Co, Ni, and Zn could more easily be mobilized during electro-dewatering. The application of high voltage had a direct effect on the migration of metal fractions, whereas, the sludge conditioning by a different cationic polymer had an indirect effect on the migration of these metals during electro-dewatering.     

Effect of Hydrodynamics During Crystallization on Mechanical Dewatering of Salicylic Acid

Mechanical cake dewatering is always desired to reduce the load on thermal dewatering (drying). Any change in the upstream process such as crystallization can have a significant influence on the filtration as well as cake dewatering characteristics. The present study deals with the effect of hydrodynamics (mixing intensity) during salicylic acid crystallization on the air dewatering characteristics in the subsequent pressure filtration. The mixing conditions during crystallization were varied by using three different types of agitators (anchor impeller [AI], curved blade turbine [CBT], and bar turbine [BT]) and by varying the speed of agitation. The effect of operating pressure and dewatering time on the final moisture content of the cake was also studied.

The crystal properties (crystal size and size distribution) were found to vary with the mixing intensity, which further influenced the cake dewatering kinetics as well as the residual moisture content. An AI, which is a laminar flow impeller, produced crystals with a wide size distribution and higher mean particle size, which resulted in cake with high porosity and hence higher moisture content. The high porosity (as well as high cake permeability) caused early air breakthrough, which resulted in ineffective dewatering of cake. Therefore, in this case the residual moisture in cake was found to be higher (27%) even at higher dewatering pressure (1.5 bar gauge) and longer dewatering time (90 s). A BT creates high turbulence during mixing and produced crystals with a relatively narrow size distribution and lower mean particle size, which provided low-porosity cakes. Such cakes could be efficiently dewatered and the final cake moisture content was found to decrease to about 15%, a significant improvement in the filterability of the cake. The dewatering data were modeled according to the correlation between irreducible cake saturation and capillary number for predicting the cake dewatering characteristics (residual moisture as well as dewatering kinetics) and the results were compared with the experimental data.     

高盐高有机制药废水污泥电渗透高干脱水

为研究高盐高有机制药废水污泥的电渗透脱水效果,深入认识化学污泥的电脱水过程,本文采用电渗透高干脱水技术对经抽滤脱水的高盐高有机制药废水化学污泥进行深度脱水,考察了泥饼初始pH的改变对污泥电渗透高干脱水过程中阴阳极污泥的含水率、电流、电导率、pH、zeta电位与能耗的影响,验证了对高盐高有机制药废水污泥实行电渗透高干脱水的可行性,解析了化学污泥电渗透脱水过程的机制。结果表明,泥饼pH为2、3、4时,zeta电位为正值,电渗流反向流动,无法脱水;pH增至5时,zeta电位为负值,电渗流从阴极脱除,污泥含水率从53.2%降至44.8%,脱水效果最好;但pH增至6时,脱水量有所降低。污泥电导率随pH的增加而降低。pH为5时初始电流最大。脱水15min时,即污泥含水率降至45.5%时,能源利用率最高。     

Tannery Waste Treatment: Leaching,Filtration and Cake Dewatering Using a Membrane Filter Press (a Pilot Plant Study)

Abstract

In Alcanena (Portugal) the waste water treatment plant (WWTP) receives tannery waste, after a pretreatment for sulphides and the tanning exhaust baths have been sent to a recovery unit and the municipal waste water from Alcanena residential area. Physical, chemical, and biological treatment processes are involved, and the end products are sludge of ～71% moisture containing mainly organic matter, sulfides, iron, chromium, and other metals. The sludge is dumped, after stabilization, in a specially designed hazardous waste landfill.

In this study, tannery mixed sludge (from chemical and biological treatments) was leached and filtered. Leaching was carried out using sulfuric acid (pH 0.5) to release residual sulfides and metals from the slurry. Hydrogen sulfide (H₂S) was flushed out into an oxidation trap (hypochlorite/alkaline tank) in which H₂S transforms to soluble sulfate. The acidified sludge was fed into a membrane filter press where it was filtered, acid‐washed, water–washed, membrane‐squeezed, and vacuum‐dried reaching lower moisture levels (20–30%). The process cycle is approximately 101–137 min in our experiments; however, from this work, a cycle of 90 min to produce cakes with 0.9 cm thickness in the industrial scale through cutting some operational time, reaching final moisture of ～20% at the end of the dewatering cycle, can be estimated. Filtration was carried out at different feed pressure (3–5 bar) with and without diatomite precoating. The effect of different amounts of diatomite body‐feed was studied. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite precoating and the increased amounts of diatomite body feed. Cake washing was accomplished using 0.05 M H₂SO₄ (acid washing), to remove residual metals, followed by water washing, to remove cake acidity. Cake dewatering via membrane squeezing was applied using hot water (65°C), and cake moisture was dropped from ～71% before squeezing to 42% after squeezing. With vacuum application over the hot cakes, for 30 min, cake moisture decreased to ～20% for cakes with an average thickness of 0.9 cm. Cake chemical analysis showed chromium levels lower than 1000 mg/kg (the maximum Cr concentration allowed by the Portuguese legislation in a solid residue for use in agricultural soil). In addition, produced cake (without diatomite body feed) has a calorific value of 11,000 kJ/kg and accordingly it can be used as a source of energy.     

Thermal Dewatering (TDW) to Reduce the Water Content of Sludge

Thermal dewatering describes the process whereby a heating plate and heat supply unit are incorporated into a filter press system to improve separation of water from sludge. The performance of our thermal dewatering system for both wastewater and waterworks sludge was measured and compared with mechanical dewatering in terms of water content, dewatering velocity, cake specific resistance, and energy consumption. Dewatering velocity was improved by a factor of two, cake water content was lower, and specific cake resistance was improved. However, energy consumption was higher. Thermal dewatering systems may be economical and have practical application to improving dewaterability.     

自来水厂排泥水处理技术

自来水厂排泥水中含有大量的悬浮物和其它污染物,直接排放会对水环境造成较大的影响.本文简述了自来水厂排泥水的性质,介绍了排泥水处理中有关污泥量确定、污泥调质、污泥浓缩、污泥脱水和脱水泥饼等的处置方法.     

电渗透/Fe-过硫酸盐氧化协同强化污泥深度脱水

利用电渗透和高级氧化技术,采用自制实验装置对城市污水处理厂的脱水污泥进行了脱水研究,系统研究了过硫酸盐投加量、铁盐与过硫酸盐比例、电压梯度、脱水时间和污泥厚度对污泥脱水的影响。结果表明,电渗透-高级氧化复合技术可以改善污泥的脱水性能,在污泥样品为140 g、过硫酸盐投加量为100（mg·g DS）^-1、Fe²⁺与过硫酸盐比例为1：1、机械压力为17.59 kPa、控制初始电压为11 V·cm^-1时,污泥的含水率可以降低至60%以下,与单独使用电渗透技术相比,泥饼具有更好的均匀性,便于后续的运输和安置。     

Compression Dewatering of Particulate Suspensions and Sludge: Effect of Shear

Experiments were carried out at the lab-scale to study the effect of a shearing action in a compression dewatering process. The impact of different process parameters, such as shear rate, filter-cake thickness, and pressure, on the final dry solid fraction was analyzed. Also, materials with different degrees of compressibility have been used. For slightly and moderately compressible materials (talc and kaolin, respectively), significantly higher final dry solid fractions (up to 0.79 wt/wt with talc and 0.75 wt/wt with kaolin) were obtained in the presence of a torsion shear. This behavior may mainly be explained by a rearrangement of the solid particles within the cake induced by the radial forces. A low shear rate (around 0.7 s^?1) was generally sufficient to cause a quite significant increase in the cake dryness (a 12.8% increase was observed with 11-mm-thick talc cakes). A further increase in the shear did not lead to noticeable changes in the final dry solid fraction in the cakes. Otherwise, reducing the filter-cake thickness was beneficial for the dewatering. For talc cakes, the dry solid fraction was increased by 21% for a 3 mm thickness against 7% for a 25 mm thickness. With a highly compressible material, such as activated sludge, the filter-cake dryness did not change with the application of a shearing action. This behavior may be mainly attributed to the fact that biological sludge dewatering is markedly influenced by a low permeability skin at the cake/medium interface, which is very thin and not perturbed by shear forces, due to the cake thickness. The low rigidity of the solid matter in this particular case may also limit the reorientation of the particles.     

市政污泥水热法脱水试验研究

市政污泥具有水分含量高、脱水困难的特点,水热法工艺可改善其脱水性能,降低污泥含水率,有利于实现污泥的无害化、稳定化及资源化利用.考察了反应温度、pH值、泥浆浓度、保温时间、泥浆过滤温度等工艺条件对污泥脱水效果的影响.结果 显示,在反应温度为180℃、pH值为6.85、生污泥与水的质量比约为2:1、保温时间为30 min...     

Fate and Effects of Fry-Drying Application on Municipal Dewatered Sludge

The present experimental investigation examined the applicability of fry-drying technology for municipal dewatered sludge by using waste engine oil for frying. The process was studied in a 100–180°C temperature range for 2 to 20 min frying times. The cakes were shaped in a diameter range of 1 to 3 cm with 3-cm-length prior to the frying. Experimental points were determined by the Box–Wilson experimental method. Statistical analysis was employed for determining the response function coefficients for variables. The response functions were as dry solids content (DS), volatile solids content (VS), and low heating value (LHV). Experimental and predicted results indicated good agreement with high correlation coefficients. The results showed that fry-drying is an alternative, fast process for sludge drying. In addition, it makes fry-dried sludge as a product with noteworthy LHV. This study provides further insight into the fry-drying of municipal dewatered sludges.