Performance evaluation of electrocoagulation and electrodewatering system for reduction of water content in sewage sludge

Electrocoagulation is applied to sewage sludge as a pretreatment process of an electrodewatering system to reduce the water content of sludge generated in wastewater treatment. The electrodewatering system, by incorporating an electric field as an additional driving force to the conventional pressure dewatering, has been evaluated as a function of an electrode material, applied voltage and filtration time. Experiments were carried out using sewage sludge with a pressure up to 392.4 kPa and applied electrical field ranging up to 120 V/cm. Mass median diameter of the sewage sludge by the effect of electrocoagulation increases from 34.7 μm to the 41.3 μm. The final water content of sewage sludge in the combination of both electrocoagulation and electrodewatering system can be reduced to 55 wt%, as compared to 78 wt% achieved with pressure dewatering alone. The combination of electrocoagulation and electrodewatering system shows a potential to be an effective method for reducing the water content in sludge.     

Fractionation of Macro and Trace Metals Due to Off-Time Interrupted Electrodewatering

Electrodewatering with interrupted voltage was set up to investigate the effects of long off-time interruption on solid content in the final sludge cake and the fractionation of macro and trace elements in the sludge matrix. In comparison to continuous direct current (DC) electrodewatering, long off-time interruption had a negative effect on water removal, resulting in a high water content in sludge at anode and the final sludge cake. However, long off-time interrupted electrodewatering significantly increased dry solid (DS) content in the final sludge cake in comparison to control experiments. Removal of Na⁺ and K⁺ from sludge was affected by long off-time interruption. The long off-time interruption also negatively influenced the dissolution and migration of macro (Ca, Mg, and Fe) and trace (Ni, Mn, and Zn) metals in sludge cake matrix. The long off-time interrupted voltage application did not have any effect on the chromium concentrations in sludge at the anode; however, the chromium concentrations in the removed water at the anode significantly depended on off-time interruption.     

Study of bio-oils and solids from flash pyrolysis of sewage sludges

The aim of this study was to evaluate the production of pyrolysis oil from three types of sewage sludges. The flash pyrolysis was performed at 500 °C, the maximum oil yield was 43.1%, and the water content in bio-oils obtained from secondary sludges was relatively low - 10.3% and 17.0%. GC-MS results showed that pyrolytic bio-oils of studied sludges dominantly contained fatty acids and nitrogenous compounds with potential added value.Obtained solids had high ash content and low calorific value which make them unattractive for use in incineration. FT-IR results showed that solids gave similar IR features as notified alumino silicates; utilization of these solids as adsorbents could be a potential valorization.     

Bound water in sewage sludges and its relationship to sludge surfaces and sludge viscosities

An examination of activated and digested sludges has shown that surface components are significant in determining the rheological characteristics of these sludges. On the basis of a series of enzymic treatments, it would appear that in activated sludge the most important constituents are polysaccharide and protein; whilst in digested sludge, lipopolysaccharide and, at times, proteins are the most significant surface polymers. Subsidiary studies showed that the bound water content of the sludges was associated with the rheology and that this association could be modified by the action of metal ions.     

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 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.     

Attribution of sewage sludge and sludge-based char in a fluidized bed reactor

Fluidized bed pyrolysis has been recognized as an innovative technology for sewage sludge treatment. The physical and attrition properties of sewage sludge are changed through the fluidized bed pyrolysis. The minimum fluidization velocities and attribution rate constants for sewage sludge and sludge based-char were obtained from pressure drop and attribution tests. As a result, sewage sludge with 20% moisture content and char were classified as Geldart B solids and the superficial gas velocity for bubbling fluidization was 0.2142-0.8755 m/s. In addition, attribution of the sewage sludge and char was more affected by particle size than by material type. The equations for the overall attrition rate constants are K _a × 10⁵ = 1.09U − 14.82 for sludge and ln k _a = 0.1(U−U _mf )− 13.63 for char, respectively.     

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.     

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.     

Pilot study for reclamation of secondary treated sewage effluent

A pilot study for reclamation of secondary treated sewage effluent in Singapore was conducted using a MF/RO system with the capacity of 20 m³/d. A 0.1 μm MF membrane from Asahi and RE-4040-FL RO membrane from Saehan were used in this study. The pilot plant consists of six spiral-wound RO elements. The RO train was configured in single stage. The pilot plant was designed with automatic control system and it was operated continuously (24 h) during the study. Trial runs on various flux rates of the RO membrane at different operating pressures were conducted over 3 months. The pilot results showed that the optimal operation flux rate of the RO membrane ranged from 10 to 15 gal/f²/d (GFD) for this application. The normalized flux after CIP was 97% of the initial one. At a flux rate of 10 GFD and water recovery of 50%, the average operating pressure of 57 psi was noted corresponding to a high normalized flux of 38 L m⁻² h⁻¹ MPa⁻¹ at 25°C. Rejections of the RO membrane in terms of conductivity, TOC, ammonium and nitrate were higher than 96%,97%,90% and 85%, respectively. It was concluded that the RO permeate quality in terms of conductivity, turbidity, TOC, ammonium, nitrate, hardness, total bacteria and total coliform matched the quality of high-grade water (NEWater) for use in the electronics industry.     

Effect of sewage sludge mix ratio on the biodegradation of diesel-oil in a contaminated soil composting

The objective of this research was an evaluation of amendments for supplementing organic matter for composting of diesel-contaminated soil. The materials used for this study were soil and sewage sludge, which was added as amendments for supplementing organic matter. The ratios of contaminated soil to these materials were 1: 0.1, 1: 0.3, 1: 0.5, and 1: 1 as wet weight basis. Experiments with only additives were carried out as control, and biocide control experiments were also tested by the addition of HgCl². Degradation of diesel was affected by the sewage sludge mix ratio, and the most rapid degradation of TPH was observed in the mix ratios of 1:0.3 and 1:0.5 of contaminated soil to sewage sludge. However, excess addition of these materials did not necessarily facilitate degradation rate. Appropriate mix ratio for effective degradation was 1: 0.5 as a wet weight, and 98.1% of TPH was degraded during the composting period. In biocide control experiments, 8.3% of TPH removal of diesel oil occurred, while 95.3% of TPH was removed in experiment without adding biocide. This indicated inactivation of microbial activity for degrading diesel oil was not completely occurring although significant suppress of microbial activity was observed. Carbon dioxide evolution rate and dehydrogenase activity were matched with the degradation of diesel oil well.     

Dewatering behaviour of water treatment sludges associated with contaminated site remediation in Antarctica

Sludge reduction and dewatering is an important aspect of water and waste water treatment. This is especially true in the case of Australia's Antarctic contaminated site remediation program, where the reduction in volume of wastes to be returned to Australia can lead to significant transport and handling cost savings. The dewatering characterisation of water treatment sludges from an Antarctic contaminated site was conducted using a theory of suspension dewatering developed by Buscall, Landman and White. This theory uses fundamental material properties of compressibility and permeability to determine the diffusivity of a suspension. Diffusivity is a useful property that can be used to directly compare the dewaterability of various sludges. In this investigation, several water treatment sludges were collected and characterised in the field to determine the impact of temperature and additives on compressibility, permeability and diffusivity. The Antarctic sludges were found to be less compressible and less permeable than materials such as mineral suspensions and alum water treatment sludges. Compressibility was found to decrease with the addition of powdered coagulation aids such as bentonite and chitosan.     

Investigations on twenty Australian sewage sludges — their evaluation by means of chemical analysis

To evaluate twenty sludges from different places in Australia for disposal on arable land, these sludges were extracted with (a) HNO₃ to determine the ‘total’ contents of some heavy metals and other elements; (b) a solution containing DTPA to determine contents of ‘available’ heavy metals; and (c) with a CaCl₂-solution to determine contents of water-soluble heavy metals and some other elements. Measurements of the pH of the sludges, their electrolytic conductivity, NaHCO₃-extractable P, water-extractable Cl, and contents of ash and organic carbon were also made. The HNO₃-extractable Cd, Cu, Mn, Ni, Pb, and Zn in the sludges were compared with those in sludges from three other countries. High correlations between HNO₃-extractable and DTPA-extractable metals were found in the Australian sludges; therefore, the HNO₃ is equally good as the DTPA as an extractant of heavy metals in sewage sludges. The correlations between HNO₃- and CaCl₂-extractable Cd, Cu, Mn, and Zn were not significant. ‘Young’ and ‘aged’ sludges from the same treatment plants consistently differed in their Na and Cl contents, which were lower in the ‘aged’ sludges. A wheat experiment treated with high application rates of a saline and metalliferous sludge showed that the balance of nutrients and the amount of soluble salts in a sewage sludge are of greater direct importance to the growth of plants than the heavy metal content of that sludge.     

离子交换纤维在污水处理中的应用

离子交换纤维是一种新型的功能纤维材料,能够有效地吸附污水中的重金属离子。介绍了离子交换纤维吸附重金属离子的原理、性能特点、应用和发展趋势。     

Modelling two-sided electrofiltration of quartz suspensions: Importance of electrochemical reactions

A new phenomenological model is proposed for two-sided electrofiltration of incompressible micron-sized particles with infinite electric resistance and negligible surface conductivity under application of a constant pressure and voltage. The model includes pressure-driven filtrate generation, electroosmosis and electrophoresis effects. Corrections are also discussed for varying electric fields and suspension concentration changes during the electrofiltration run due to a changing particle zeta potential as a consequence of the different electrochemical reactions occurring at the cathode and anode. The model, with the particle zeta potential as the sole adjustable parameter at each electrode side, appeared to fit very well to the experimental data, yielding physically sound zeta potential values. Electrofiltration experiments using both buffered and unbuffered quartz suspensions revealed the importance of electrochemical effects and the migration of hydroxide ions and especially protons into the filter chamber, altering the cake surface properties and even influencing the suspension particle flocculation state and as such the cake resistance and porosity. These effects may have biased modelling attempts and discussions regarding the beneficial effect of electrofiltration in some cases in the available literature.     

含油污泥脱水设备与技术

分析了含油污泥的性质 ,介绍了国内外含油污泥处理技术与脱水设备的现状 ,并比较各方法及设备的优缺点。提出了含油污泥脱水设备与技术的发展趋势和几点建议。     

石脑油脱硫剂性能评价

对拟投入使用的SY-1、SY-2、XBH三种商品脱硫剂进行性能对比研究,考察了空速、反应温度对脱硫剂穿透硫容的影响;通过浸水实验,考察了三种脱硫剂的耐水性。结果表明,三种脱硫剂常规使用稳定性均可靠,SY-2具有更高的穿透硫容,但耐水性略差;而SY-1具有更强的耐水性,穿透硫容略低;XBH指标性能居中。     

Comparing different methods of analysing sewage sludge, dewatered sewage sludge and sewage sludge ash

The following article compares different ways of characterising sewage sludge. Against the background of sludge recycling in agriculture as well as treatment with subsequent phosphorus recovery in mind, the article starts by collating and evaluating the levels of phosphorus, heavy metals, chlorine and sulphur in sludge as reported in the literature. Sewage sludge from the sewage treatment plant at Kaditz in Dresden was analysed using standardised and adjusted methods, which produced different results. In the course of this analysis the results were produced by using elemental analysis, atomic absorption spectroscopy, X-ray fluorescence spectroscopy (X-RFA) and ion chromatography (IC). The second part of the article therefore seeks reasons for the differences in the findings and tries to give solution statements. The article closes by calculating transfer coefficients for selected parameters during the incineration process and solid-liquid separation and weighing up the analysis techniques compared. Basically this article will show significant differences in sludge composition and the effects on the specific elements by ashing or mechanical dewatering of the different sludges. An essential attention obtains the analysis by using the X-RFA.     

Effects of double-layer polarization and electroosmotic flow on the electrophoresis of a finite cylinder along the axis of a cylindrical pore

The electrophoresis of a rigid, finite cylindrical particle along the axis of a long cylindrical pore is analyzed theoretically under the conditions of arbitrary surface potential and double-layer thickness. The effects of double-layer polarization and electroosmotic flow on the electrophoretic behavior of the particle are discussed. We show that if both the particle and the pore are positively charged, the mobility of the particle has a local minimum as the thickness of double layer varies. Also, if the level of the surface potential of the particle is sufficiently high and its aspect ratio is sufficiently large, then its mobility may change its sign twice as the thickness of double layer (or the concentration of electrolytes) varies. These findings are of practical significance in designing an electrophoresis operation because it will influence the prediction of the charged conditions on a particle if electrophoresis is used as an analytical tool, and the separation efficiency, if it is adopted as a separation technique.     

Performance evaluation of saponin over other organic acid and tap water for removal of chromium in tannery sludge by electrokinetic enhancement

The performance of Saponin over different electrolyte-mediated electrokinetic (EK) process for removal of Cr(III) from tannery sludge was assessed. Saponin exhibited maximum Cr(III) removal efficiency, i.e. 67.6–80.75% as compared to other groups of processing fluids. The possible mechanistic approach for the highest removal efficiency of saponin over other electrolytes may be attributed to synchronized effect of micelle formation and subsequent complexation and sorption of chromium ions. The highest electroosmotic flow rate of saponin indicated low electroosmotic resistance during EK process, which validates the observed trend. Therefore, saponin can be considered as a promising electrolyte for EK treatment of tannery sludge.

Abbreviation: CA: Citric acid; LA: lactic acid; OA: oxalic acid; BOD: biochemical oxygen demand; COD: chemical oxygen demand; EK: electokinetic.