Sludge Dewatering and Aggregate Formation Effects through Taylor Vortex Assisted Flocculation

Abstract

For polymer induced flocculation processes, the effects of flow patterns in a gap of a conical stirrer on aggregate formation and subsequent sludge dewatering efficiency were analysed. Different flow regimes were identified by lab scale investigations with model substances and summarized in a Ta and Re number plane. An enhancement of sludge dewaterability for polymer induced flocculation processes was identified through post‐treatment of flocculated sludge aggregates by the specific flow pattern of stable and wavy Taylor vortices. Photo‐optical image analysis of flocculated aggregates shows a clear change of aggregate size distribution with less small particles during aggregate forming by Taylor vortices compared to classical flocculation procedure by stirrer. Results from technical scale dewatering analyses confirmed enhancement of sludge dewatering efficiency for six different dewatering machines using the identified wavy and stable Taylor vortex flow pattern regime.     

Optimization Study of Municipal Sludge Conditioning,Filtering, and Expressing Dewatering by Partial Least Squares Regression

The effect of different conditioner doses and different applied pressures on the dewaterability of municipal sludge during the filtration and expression stage was assessed using a series of experiments referred to as a uniform design. The relative importance of conditioner dose and applied pressure on the dewatering characteristics of municipal sludge was evaluated with a quadratic model using partial least squares (PLS) regression analysis. It was shown that the developed quadratic model was able to accurately predict the dewatering characteristics during the whole process. It was further shown that lime as a physical conditioner had the most significant impact on filtration rate, expression rate, cake dry solids content, net sludge solids yield, and total cycle time. Aluminum polychloride as the inorganic flocculant had a quite complex effect although not as significant as lime. Filtration pressure had only a slight effect on dewaterability of the municipal sludge, though higher feeding pressure was needed in order to enhance the total feeding amount. Furthermore, expression pressure was only of benefit to cake dry solids content and expression rate and failed to improve other dewatering characteristics of the municipal sludge.     

Anwendung von Polyelektrolyten bei der mechanischen Fest/Flüssig-Trennung

Use of Polyelectrolytes in Mechanical Solids/Liquid Separation. This article shows how optimisation tasks for the dewatering of sludge can be solved by starting from studies of chemical structure and steric properties of polyelectrolytes and laboratory experiments based thereon with a trans-portable computer-aided flocculation and dewatering apparatus. The optimum polyelectrolyte dosage lies in the range of the critical concentration c* (viscosimetric measurements) of the dissolved polyelectrolytes. On optimisation of the flocculant regime for mechanical solids/liquid separation by combined addition of anionic and cationic polyelectrolytes (dual process), it is necessary to consider the overall system of sedimentation and filtration. In an industrial scale plant, the consumption of flocculant could be reduced by up to 10% compared to laboratory studies. At the same time, the dewatering behaviour could be improved by up to 60%, a shearing strength of the sludge in excess of 20 kN/m² reliably established, and plant operating reliability achieved for changing sedimentation properties.     

Improved Sludge Dewaterability for Sequential Ozonation – Aerobic Treatment

Chemical treatment processes such as ozonation have mostly been considered as an efficient way for bio-solids minimization. The improvement of sludge dewatering was more a welcoming side-effect in these sequential processes. However, sometimes the loaded ozone dose to the sludge has a negative effect on dewaterability. This work address the most important issue found — the effect of ozone on sludge dewaterability in a single ozonation processes as well as in a sequential ozonation biological processes. It was found that the maximum sludge dewaterability was achieved with an ozone dose of 0.05 gO₃/gTSS. This value was found to be less than the required ozone dosage that leads to sludge disintegration. However, it was observed that the sequential ozone and aerobic treatment allows further strong improvement of dewatering efficiencies.     

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.     

Effects of current density and electrode material on the dewaterability of the thickened activated sludge by electro‐flotation

BACKGROUND: Electro‐flotation (EF) could improve thickening and subsequent dewatering characteristics of activated sludge although the settling characteristics of the sludge were very poor. The objectives of this study were to evaluate the performance of EF in the thickening and dewatering of activated sludge and the effects of current density and electrode material on the dewaterability of the sludge. RESULTS: The specific resistance to filtration (SRF) of the sludges thickened by EF was much lower than that by gravity sedimentation. The SRF of the thickened sludge decreased exponentially with increase of gas generation rate of the EF system. Gas generation rate could be controlled by varying the current density of the electrode. Degassing of the microbubbles by moderate mixing of the thickened sludge layer deteriorated the dewaterability of the sludge. Therefore, it is obvious that the gas bubbles entrapped in the thickened sludge play a key role in the observed dewaterability improvement. The effect of electrode material on the thickening and dewatering efficiency was trivial compared with the effect of current density of the electrode. CONCLUSION: The EF system was quite promising as an alternative to gravity sedimentation for thickening of activated sludge and the dewaterability was also improved by microbubbles generated in the system. Copyright © 2009 Society of Chemical Industry     

壳聚糖絮凝剂的投加量对污泥脱水性能的影响

通过污泥比阻的测定,分析絮凝剂剂量对污泥脱水性能的影响。同时对三氯化铝、阳离子聚丙烯酰胺、壳聚糖以及复合絮凝剂的絮凝效果进行比较。结果表明,无论是无机絮凝剂和有机絮凝剂都存在最佳剂量,小于或大于最佳投加量,絮凝效果都不好。阳离子聚丙烯酰胺(CPAM)、壳聚糖、三氯化铝的最佳投加质量浓度分别为0．2g/L、10g/L、35g/L。与三氯化铝相比,阳离子聚丙烯酰胺的药剂消耗量要低得多。壳聚糖与CPAM相比,在达到相同的絮凝效果时,壳聚糖的用量大于CPAM的用量。将壳聚糖与氯化铝复合,用两段法应用于污泥调理,研究这种复合絮凝剂的脱水性能,实验表明壳聚糖和三氯化铝复合,能大大提高污泥的脱水性能。     

Conditioning and Dewatering of Phosphorus-Rich Biological Sludge

The conditioning and dewatering of phosphorus-rich biological sludge, obtained from a pilot-scale biological phosphorus removal plant, was investigated. Dual conditioning utilizing a polyampholyte (AC4601) in combination with aluminum chloride (AlCl₃), ferric chloride (FeCl₃), and calcium chloride (CaCl₂) was studied. Capillary suction time (CST) and specific resistance to filtration (SRF) were utilized to assess sludge dewaterability. The dewaterability and removal of dissolved phosphorus from the phosphorus-rich sludge were examined. Compared with conditioning with only AC 4601, dual conditioning by adding 49 kg/ton of AlCl₃ prior to addition of AC4601 resulted in formation of large flocs, better dewaterability, and removal of 50% of soluble phosphorus. Better dewaterability, even larger flocs (> 1 cm), and 75% removal of soluble phosphorus were found when dosage of AlCl₃ increased to 189.2 kg/ton. The use of alumina (Al₂O₃) in combination with AC4601 could achieve equivalent dewaterability. However, only insignificant removal of soluble phosphorus (ca. 10%) was found. Sludge conditioning utilizing FeCl₃ and AC4601 was also very effective. A higher dosage of AC4601 was required and insignificant removal of soluble phosphorus was found when CaCl₂ was used in combination with AC4601. The interactions between hydrolyzed species of trivalent metal ions and polyampholyte contributed to enhanced dewaterability. Precipitates acted as skeleton builder and assisted in dewaterability as well. In addition, the removal of phosphorus was due to its precipitation reactions with metal ions. This study demonstrated an alternative way to condition phosphorus-rich sludge that could control the release of phosphorus from sludge to aqueous phase under anaerobic environment and achieve enhanced dewaterability simultaneously.     

Enhancing dewaterability of sewage sludge by the application of tween-20 during bioleaching: Performance evaluation and mechanistic study

Dewatering is recognized as an important method for treating sewage sludge before its disposal. In this paper, the nonionic surfactant Tween-20 was used for the first time to improve the dewaterability of sewage sludge during bioleaching. The specific resistance to filtration (SRF), water content (WC) and bound water content (BW) of the sludge cake were used to evaluate sludge dewaterability. The results indicated that a 1?g/L Tween-20 dosage with an inoculum ratio of 20%, a S⁰ dosage of 2?g/L and a FeSO₄?·?7H₂O dosage of 10?g/L provided oxidation efficiencies up to 100% for Fe²⁺ and 65.8% for S⁰. The SRF of the bioleached sludge decreased to as low as 0.81?×?10¹²?m/kg from the initial 12.6?×?10¹²?m/kg for raw sludge. A WC of 47.16% was achieved while 48.1% of BW was released during bioleaching. The results from this study indicate that adding of an appropriate amount of Tween-20 to sewage sludge is a promising method to enhance dewaterability by bioleaching.     

Comparison of initiation methods in the structure of CPAM and sludge flocs properties

Cationic polyacrylamides (CPAMs) synthesized by thermal, ultrasonic, microwave, and UV initiation were characterized through magnetic resonance hydrogen spectroscopy (¹H NMR), Fourier transform infrared spectra, scanning electron microscopy, and thermal gravimetric analysis. The CPAMs for flocculation and dewatering of alum sludge produced through drinking water treatment were evaluated based on the residual turbidity of the supernatant, dry solid content, mean volume diameter and floc size distribution, fractal dimension of the flocs, and zeta potential as a function of flocculant dosage. Comparisons of the characteristics and performance of CPAMs synthesized through different initiation methods were systematically conducted. Flocculation and dewatering test results demonstrated that CPAMs synthesized through microwave and UV initiation had better flocculation performance and dewatering capability than those synthesized through thermal and ultrasonic initiation. All four CPAMs exhibited a similar final floc size distribution but different mean volume diameters and floc structures. The fractal dimension of the flocs and the zeta potential were in the following order: CPAM3 (microwave initiation) > CPAM4 (UV initiation) > CPAM1 (thermal initiation) > CPAM2 (ultrasonic initiation). Discussions on fractal dimension and zeta potential indicated that the electrostatic patches model and adsorption/bridging effect mechanisms played the main role in the formation of sludge flocs. Lastly, microwave and UV initiation were found to be alternative and recommendable initiation methods for the synthesis of CPAMs with improved flocculation performance and sludge dewatering capability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44071.     

Breakage–reflocculation implemented by two-stage shear for enhancing waste-activated sludge dewaterability: Effects of shear condition and extracellular polymeric substances

The conditioning of waste-activated sludge (WAS) before dewatering is crucial for enhancing sludge dewaterability. The breakage–reflocculation that was implemented by two-stage shear (drastic first-stage shear for breakage and moderate second-stage shear for reflocculation utilizing the bioflocculation function) which was proposed as a novel WAS conditioning method with several advantages (simple operation, lower cost, and none added reagent) compared to traditional methods. Effects of the shear condition and extracellular polymeric substances (EPS) on breakage–reflocculation were orderly investigated. Two equations were developed by response surface methodology for predicting breakage–reflocculation conditioning performance. Analysis of variance (ANOVA) indicated that individual effects of first-stage shear rate (G₁), second-stage shear rate (G₂), second-stage shear time (t₂), and interactive effect of G₁G₂ were significant. More compact WAS flocs with better dewaterability and larger floc size formed through breakage–reflocculation. This was reflected in that the capillary suction time decreased by 16.9% and mean floc size increased by 24% under the optimum shear condition. In addition, the loosely bound EPS was revealed to be closely negatively correlated with breakage–reflocculation conditioning performance, indicating its adverse role in breakage–reflocculation. The breakage–reflocculation could be used as an independent conditioning method with low cost or a part of combined method.     

超声波或生石灰单独及联合作用对污泥脱水性能的影响

研究了超声处理时间和生石灰添加量对污泥脱水性能的影响。超声波单独对污泥进行处理时,超声3 min后污泥的沉降性能最好。但是污泥经超声波处理后又能释放大量的胞外聚合物,增加污泥离心出水的COD,使出水水质变差。CaO对污泥单独处理时,采用10‰的投加量可以显著改善污泥的脱水性能。超声波和CaO对污泥联合处理时,以1 min的超声波处理时间和6‰的CaO投加量为最优条件,在保证污泥离心脱水效率的前提下,不仅减少了CaO的投加量,还能降低污泥离心出水的COD,改善出水水质。     

Preparation of Quaternized Lignin Derived from Oil Palm Empty Fruit Bunches and its Flocculation Properties

Quaternized lignin-based flocculant (QL) was prepared by a single-step reaction of an extracted lignin (EL) derived from oil palm empty fruit bunches (OPEFB) with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC) under alkaline condition. The performance of QLs was studied for various β values (molar ratios of CHPTAC to phenylpropanoid unit of lignin), flocculant dosages, pH values, kaolin concentrations, slow mixing rates and sedimentation times. The QL10 achieved the highest turbidity removal efficiency (ε_t) with increasing flocculant dosage, pH and kaolin concentration to the optimal conditions of 5?mg?L^?1, pH 7 and 1000?mg?L^?1, and required 20?min of sedimentation time at all the mixing rates tested. The flocculation kinetics agreed well with the particle collision model. The QL10 has good sludge dewatering properties compared to the alum. It also showed encouraging results in water quality analysis for sewage wastewater flocculation in comparison to that of the alum. This indicates the potential application of QL in treating water and wastewater.     

Sewage Sludge Dewatering Process Using Liquefied Dimethyl Ether as Solid Fuel

This article describes the dewatering of sewage sludge using liquefied dimethyl ether (DME), which clarified the effect of sludge type and its particle size. Changes in the heating value of the dewatered sludge were also examined. In addition, the change in dewaterability upon reuse of the liquefied DME was investigated experimentally.

Regardless of the nature of the sludge, its dewatering behavior was similar. The amount of dewatered water could be increased by decreasing the diameter of the sludge cake. Complete drying of the sludge cake via DME dewatering resulted in retention of approximately 96% of the heating value (17.7 MJ/kg-sludge) of the original sludge cake dry base (18.4 MJ/kg db). The DME could be recovered after extraction, and reuse experiments showed that liquefied DME dewatering performance was unchanged after five reuses.     

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.     

Sludge filterability and dewaterability in a membrane bioreactor for municipal wastewater treatment

The physical properties of excess sludge wasted from a large pilot scale membrane bioreactor (MBR) have been routinely monitored over almost two years. A statistical analysis highlighted the significant impact of temperature on the capillary suction time and sludge filterability, due to the increase of organic matter in the liquid phase. Suspended solids have resulted to be the most important component affecting sludge filterability, although the impact of colloids and solutes increased when temperature decrease, thus confirming the generally worse characteristics of sludge in such conditions. Conditioning and dewatering test have been performed on a pilot scale fixed volume recessed plate filter press. Six different chemicals were used for sludge pre-conditioning and, for each additive, three dosages were tested in the range 5-25 g_polymer kgMLSS^− 1. After about sixty filtration trials at three different pressure values (7, 11 and 15 bar), the kind of polymer seem to be the most important factor influencing the final cake-dryness, with less evident impact for dosage and operational pressure. Finally, when performed on the aerobically digested excess sludge wasted from a conventional activated sludge plant, the filtration tests show no differences with the MBR sludge.     

The Impact of Intermittent Aeration on the Operation of Air‐Lift Tubular Membrane Bioreactors under Sub‐Critical Conditions

Abstract

An air‐lift sidestream polymeric multi‐tube membrane module has been investigated to compare the hydraulic performance of an MBR challenged with municipal wastewater and landfill leachate. In both cases the MBRs were operated under the same conditions of membrane aeration rate and sludge retention time, but with hydraulic retention time for the leachate set by scoping trials based on porous pots to 48 hours. Operation under conventional continuous aeration conditions yielded critical flux values, based on classical flux step experiments, of 36–42 l m^?2 hr^?1 for the sewage‐fed trial compared with ～24 l m^?2 hr^?1 for the leachate‐fed trial. Substantial improvements in operating flux, between 20 and 100%, were obtained when operating with air pulsing (1s on/s off). Intermittent operation under more conventional conditions (5s on/5s off) yielded no improvement.     

Enhancement of biological fermented sludge dewaterability by inoculation of filamentous fungi Mucor circinelloides XY-Z and Penicillium oxalicum LY-1

Abstract

The two filamentous fungi of Mucor circinelloides XY-Z and Penicillium oxalicum LY-1 isolated from citric acid wastewater sludge collectively enhanced sludge dewaterability by 85.83% to achieve the lowest value of normalized sludge specific resistance (SRF) to 6.8?×?10¹¹ m·L/kg·g-TSS. The results showed that 75.77% of slime extracellular polymeric substances (EPS), 42.99% of protein in slime EPS and 60.27% of polysaccharide in LB-EPS were degraded during activated sludge treatment by the two mixed fungi of Mucor circinelloides XY-Z and Penicillium oxalicum LY-1, contributing to the conversion of 64.61% of bound water wrapped in EPS into free water, thereby improving activated sludge dewaterability.     

Application of Enhanced Vacuum Filtration to Dewatering of Fine Coal Refuse

Abstract

It is difficult to reduce the moisture content of fine coal refuse to a satisfactory level because of the high mineral content and the large capillary forces associated with small particle sizes. An experimental investigation of important operating variables on dewatering of fine coal refuse is reported. The cake permeability, cake formation time and final moisture content are used to measure the efficiency of moisture removal. Factors that were studied are the addition of coarse particles, level of vacuum, pH and the use of coagulants, flocculants and surfactants as additives. Addition of a flocculant was the most effective single means of improving dewatering and the permeability could be increased by more than an order of magnitude and the moisture content lowered by as much as 0.05 kg water/kg dry cake. It was found that the ionic nature and molecular weight of the flocculant, the flocculant dosage, the mixing time and the mixing intensity must be carefully studied to obtain optimal performance.     

阳离子絮凝剂PDA的合成与应用——对再生造纸废水的污泥脱水处理

研究了阳离子聚丙烯酰胺絮凝剂PDA对一种废纸再生造纸废水中的污泥的絮凝脱水处理过程，探讨了絮凝剂PDA的投加量，电荷密度，平均相对分子质量对絮凝脱水效果的影响，并比较了各种不同絮凝剂的处理效果，研究结果表明，絮凝剂PDA的电荷密度越大，相对分子质量越高，其絮凝脱水效果越好，在与无机絮凝剂PAC复配使用的相同条件下，实验室自制的絮凝剂PDA的絮凝脱水效果优于其他作对比的市售多种阳离子聚丙烯酰胺类絮凝剂。