Dual Conditioning of Sludge Utilizing Polyampholyte

Dual conditioning of activated sludge utilizing polyampholyte (T204) in combination with ferric chloride or cationic polyelectrolyte, polydiallyldimethyl ammonium chloride (PDADMAC) was investigated. Capillary suction time, specific resistance to filtration, and settling rate were utilized to assess sludge dewaterability. Floc structure and strength were evaluated. Experimental results indicated that dual conditioning of sludge exhibited better dewaterability at lower doses when compared with single conditioning. Much larger and stronger flocs were formed in dual conditioning. In addition, the sludge dewaterability did not deteriorate significantly when overdosed. It was found that dual polyelectrolytes conditioning (PDADMAC and T204) performed better than the combined use of ferric chloride and T204. It is postulated that in dual conditioning, the negative charge of sludge surfaces was partially neutralized by ferric chloride or PDADMAC, and the relatively more compact primary flocs were formed. The later added T204 could then become adsorbed either onto positively charged patch, or onto the un-neutralized part of the primary flocs. The enhanced flocculation is attributed to the interactions between PDADMAC and T204 that results in the improved dewaterability. The advantages of PDADMAC over ferric chloride as applied in dual conditioning in combination with T204 are discussed.     

Mathematical Model to Predict Solids Content of Water Treatment Residuals during Drying

Dewatering and drying of residuals are extremely energy intensive processes, which are necessary to reduce the quantity of wet residuals produced from the water and wastewater treatment operations. Meteorological conditions are a major factor in the drying of residuals, which can greatly affect the drying period. A mathematical model is developed for the process of drying of water treatment residuals. A steady-state heat-balance equation is applied for a control volume of residuals that takes into account the heat transfer by radiation, convection, and evaporation. The mathematical model was validated using drying experiments conducted in a wind tunnel as well as other experiments conducted in an open environment equipped with a weather monitoring station. Good agreement was obtained between model predictions and experimental observations. The model can be used to predict the drying time of a given application of water treatment residuals with the knowledge of meteorological conditions.     

Rheological Characterization of Sludges during Belt Filtration Dewatering Using an Immobilization Cell

An immobilization cell was successfully coupled to a controlled stress rheometer to quantify rheological properties of a sludge during its dewatering. An anaerobically digested sludge and a synthetic sludge were analyzed and conditioned at various doses with a cationic flocculant. Direct strain-controlled oscillatory analyses could not be performed due to rapid dewatering, but controlled shear rate analysis quantified the increases in sludge viscosity as the solid’s concentration increased. Immobilization times determined by these experiments—viscosity versus dewatering time—agree with capillary suction times, since both indicate the time required for water removal (r2 from 0.81 to 0.99). However, capillary suction time tests were more strongly influenced by filtrate viscosity at high polymer doses. The immobilization cell allowed quantified amounts of shear to be imposed during dewatering, with greater shearing found to provide more rapid immobilization. This finding is consistent with the design of belt filtration dewatering devices, but demonstrates that current models do not account for a critical aspect of this process.     

Measuring Sludge Network Strength Using Rheology and Relation to Dewaterability, Filtration, and Thickening—Laboratory and Full-Scale Experiments

Researchers ?rmeci and Abu-Orf used rheology; a fundamental character of sludge, to arrive at a standard protocol for measuring network strength in terms of energy required to break up the structure of a certain volume of sludge. A mathematical derivation showed that the area under the rheograms indicated energy dissipation within the sludge system, which was related to the network strength. The research described in this paper investigates the use of this protocol for measuring sludge network strength at different polymer doses and relates the results to filtration, thickening, and dewatering. Laboratory tests used anaerobically digested sludge and both capillary suction time and filtration tests to indicate dewaterability and filtration. Network strength measurements used a torque rheometer. At full scale, dose response testing was used to correlate the measured network strength of the conditioned sludge to both centrifugation and gravity belt thickening performance as indicated by solids output. Both laboratory and full-scale testing showed that the network strength could be used to identify the optimum polymer conditioning to achieve good water removal from the sludge. The network strength increased with increasing the polymer dose, however, within the optimum dose range, a “drop” in the network strength occurred. This paper also discusses how to use the sludge network strength information to achieve the desired dryness from a dewatering device, and ultimately automate conditioning and dewatering processes.     

Protocol to Measure Network Strength of Sludges and Its Implications for Dewatering

The ability to measure network strength is important in sludge conditioning and dewatering applications. Previous research has mostly focused on determining sludge floc strength indirectly through measuring other parameters such as floc size, floc density, and dewaterability of sludge. Few methods were developed for direct measurement of floc strength but these methods are not very practical for sludge applications. For the purpose of sludge characterization, it is more appropriate to determine the overall network strength of sludge rather than determining the strength of individual sludge flocs. This is because individual floc strengths will vary greatly, especially during conditioning, and therefore network strength is a more meaningful measurement compared to floc strength. This paper refers to raw or conditioned sludge as “network,” and provides a protocol to measure “network strength” which can be used to evaluate the dewaterability of water and wastewater sludges. The proposed protocol uses rheology, a fundamental character of sludge, to measure network strength in terms of energy required to break up the structure of a certain volume of sludge. Two methods are presented to directly measure network strength using either torque or concentric cylinder rheometers. A mathematical derivation showed that the area under a shear stress–shear rate or a torque–time rheogram is representative of the energy dissipation within the sludge system, and the total dissipated energy is related to the network strength. This study does not intend to measure the absolute network strength, rather a comparative strength of different sludges using the same instrument and measurement conditions.     

Quantitative Model of Coagulation with Inorganic Polymer Flocculant PACl: Application of the PCNM

In this paper, a quantitative model of coagulation with inorganic polymer flocculants (IPFs) was investigated, using polyauminum chloride (PACl) as an example. Application of a modified precipitation charge-neutralization model (M-PCNM) was examined and discussed, including variation of dose, pH, and B value on the resulting coagulation diagram. The model was modified by using measured Al fractions as model inputs. The experimental results show that there exists a remarkable difference in coagulation with various PACl formulations in accordance with the different species being preformed. This indicates that the assumption of all the surface species consisting of the same aluminum hydroxide solids is not correct, and some modification of the PCNM is therefore needed. By invoking different final hydroxide precipitates, the M-PCNM can be used quite well to predict the general behavior of coagulation with IPF-PACl.     

Relevance of Expression Phase in Dewatering of Sludge with Chamber Filter Presses

Biological sludge contains a large quantity of water and the decrease of its content constitutes one of the main issues for wastewater treatment plant operation. Laboratory tests to estimate the sludge dewaterability, i.e., its capability of being dehydrated, have been developed in the past, but there is no evidence of the tests’ direct correlation with the behavior of the real-scale dewatering devices. Different methods (specific resistance to filtration at different pressure, capillary suction time, expression tests, and drying test) have been applied on civil sludge conditioned with ferric chloride/lime or polymer/ferric chloride and results have been compared with operational data obtained from a full scale plant. The results presented in this paper highlight the role of the expression phase in the sludge dewatering using frame filter presses. To predict the sludge behavior and then to optimize the conditioning step, the laboratory procedure used for selecting the chemicals and doses has also to consider the effect of the expression of the cake.     

Effects of Surfactant Addition on Dewatering of Alum Sludges

In Taiwan, surfactants are frequently used in the flotation process to aid in solid/liquid separation. Their effect on the dewatering of alum sludge was investigated. Various amounts of cationic and anionic surfactants were added to sludge samples, and the dewatering characteristics of the sludge and the water content of sludge cakes were evaluated. Both surfactants improved the dewatering of the sludge by lowering the specific resistance to filtration, decreasing the bound water content, and increasing the dewatering rate of the sludge. Different combinations of anionic and cationic surfactants and polyelectrolytes were also experimented on to study the effect of surfactant addition on the dewatering characteristics of polyelectrolyte-conditioned sludge. Experimental results indicated that both cationic and anionic surfactants adversely affected the dewatering of the conditioned sludge. The addition of surfactant to the oppositely charged polyelectrolyte proved to be most detrimental to sludge dewatering due to the precipitation between surfactant and polyelectrolyte. The addition of cationic surfactant to the cationic polyelectrolyte-conditioned sludge had the least effect.     

Modeling a Retention Treatment Basin for CSO

Combined sewer overflows (CSOs) result in hazardous and unsightly contamination of receiving waters, particularly swimming areas. The removal of suspended solids and associated biological oxygen demand (BOD) can accelerate the recovery following a CSO event. This paper presents a numerical model to simulate the solids removal efficiency of a retention treatment basin (RTB) that utilizes polymers to improve the flocculation and settling rates for the suspended solids. The model includes settleable, nonsettleable, and floatable solids. The sludge is treated as a non-Newtonian fluid. Discrete, zone, and compression settling/floatation regimes are included. In-tank flocculation and a storage zone for sludge flushing are also included in the model. The model was calibrated and validated with data from a RTB pilot plant, and was applied to evaluate preliminary designs for a prototype RTB for the City of Windsor. The calibrated model showed that the optimum location of the target baffle was approximately 30% of the distance to the scum baffle. For design flows of 20?m/h and run durations of up to 2?h, it was found that the removal was insensitive to slopes from ?1 to ?3% and depths greater than 2.5?m (L/H = 10). The simulations indicate that 70 to 78% of solids removal can be achieved at surface overflow rates up to 25?m/h.     

转炉烟气净化水污泥处理常见设备问题的处理

介绍了转炉烟气净化水沉淀后,在烧结配料过程中污泥处理常见设备问题的处理     

Methods for Quantifying Lime Incorporation into Dewatered Sludge. II: Field-Scale Application

Postlime stabilization of municipal sludge requires methods for assessing the degree of lime incorporation and stability of the final product, as well as for evaluating and monitoring the performance of individual components in the process. The goal of this research was to systematically apply selected measures of lime incorporation and stability at the District of Columbia Water and Sewer Authority’s Blue Plains advanced wastewater treatment plant (see the companion paper). The transfer of sludge by screw conveyance prior to the lime blender did not appear to make it more difficult to incorporate lime in a bench-scale mixer. However, in the full-scale system, it may impede mixing by rolling the sludge into large plugs, and thus creating a discontinuous supply of sludge to the blender. Screw conveyance of limed sludge downstream from the blender appears to subject the limed sludge to additional mixing, resulting in improved lime incorporation and stabilization. The impact of lime purity (CaO%) appeared to be minimal within the range tested; however, increasing the lime particle diameter did significantly lengthen the mixing time required for stabilization. In addition, overdosing of lime was shown to be ineffective for compensating for poor lime incorporation.     

Crack Bridging in Polymer Nanocomposites

Carbon nanotube reinforced composites offer enhancements in fracture properties since the reinforcing nanotubes provide a bridging mechanism to resist crack growth. In this paper, a study of crack bridging by nanotubes in a nanotube-reinforced polymer composite is presented. The process of crack bridging is idealized as normal pullout of the participating nanotubes from the polymer matrix. The resistance to crack growth due to bridging is taken as the aggregate of the resistance offered by all the nanotubes, ignoring any interaction among the nanotubes themselves. The pullout of a single nanotube from the polymer matrix is modeled as an axisymmetric, nearly one-dimensional problem. This is done by assuming that fracture along the nanotube–polymer interface is dominated by shear openings, and that the nanotube behaves as a rigid body. When the polymer is a linear elastic material, the force–displacement relation for pullout is obtained as a function of dimensionless variables representing the interfacial fracture energy and the pullout length scale. Applying the correspondence principle, the elastic results are extended to the case where the polymer is a linear viscoelastic material with a single relaxation time. The force–displacement relation is then a function of the viscoelastic properties of the polymer and the pullout velocity as well. Using these results, the apparent enhancement in the fracture energy of the composite is obtained. This provides a guideline to design these composites for desired fracture properties in terms of the interfacial strength of the nanotube–polymer interface and the volume fraction of the nanotubes. Results of numerical simulations of nanotube pullout are compared to the predictions of the analytical model.     

Comparative study of dewatering characteristics of metal precipitates generated during treatment synthetic polymetallic and AMD solutions

The sludge dewatering characteristics expressed in terms of settling, filtration and centrifugation of metal precipitates generated during treatment of polymetallic solutions and synthetic acid mine drainage have been evaluated in this research. Results show that dewatering properties of metallic sludge vary depending on the type of matrix (Cl⁻; SO₄²⁻), precipitating agent, and metals present in effluent. Metal hydroxides (at pH 10.0) and metal phosphates precipitates (at pH 7.0) are amorphous in nature, thus difficult to dewater. In these treatment methods, the substitution of chloride matrix by sulphate one improves considerably dewatering properties (specific resistance to filtration = 6.60 × 10¹³ and 2.35 × 10¹³ m/kg for the chloride and sulphate matrix, respectively). In the case of sulphide and carbonate treatments (pH 8.0), precipitates obtained are semi crystalline, and crystalline form, respectively, and no influence of the matrix was detected on dewatering characteristics.     

阳离子淀粉的合成及在选矿废水处理中的应用

去除选矿废水中的大量悬浮物需要使用絮凝剂，用正交实验来找到了最主要的影响因素，根据正交实验表，选4因素3水平，主要分析了絮凝荆的各种应用状况，并通过实验说明有机絮凝剂和无机絮凝剂共同使用，其协同效果较等量单独加入更好。     

Conditioning of Wastewater Sludge from Science-Based Industrial Park Using Freezing and Thawing

The Hsinchu Science-based Industrial Park (HSIP) is the main manufacturing base of “high-tech” commodities of Taiwan. The treatment of wastewater of HSIP produces hard-to-dewater sludge, at a rate of 80 Mg/day, which is resistant to chemical conditioning, whose disposal is costly. The use of chemical flocculation and physical conditioning, including heating and freezing and thawing, on the dewaterability of HSIP sludge was examined in this Note. The dewaterability of the original sludge was poor, and neither chemical flocculation nor thermal heating enhanced its dewatering. However, the freezing and thawing could release up to 83% of moisture from the sludge body; in line with this occurrence, the settleability and filterability of the sludge were considerably enhanced. The ice front developed during freezing, which could destroy the floc network, release the interstitial water, and might correspond to the successful conditioning using freezing and thawing.     

Mixing Water Treatment Residual with Excavation Waste Soil in Brick and Artificial Aggregate Making

A large quantity of water treatment residual is generated each year from fresh water treatment plants in Taiwan. Landfill disposal of the nonhazardous sludge is impractical because of the high cost of transportation and an increasing scarcity of landfill sites in Taiwan. The water treatment residual was characterized; the ceramic bodies were prepared and sintered to formulate into building bricks and artificial aggregates. The sintering temperature requirement by the water treatment residual was higher than normally practiced in brick works due to the higher Al2O3 and lower SiO2 content. The excavation waste soil, practically clay, was blended with water treatment residual to improve the brick quality. Under the commonly practiced brick-making condition, up to 15% of water treatment residual could be added to produce first grade brick specified by the National Science Council (NSC). Test results of specific gravity, water absorption, and compressive strength of the artificial aggregates confirmed its applicability in constructions as various degrees of light-weight aggregates.     

Explosive Testing of Polymer Retrofit Masonry Walls

The most widely used terrorist tactic is the improvised explosive device, which can range in size from hand-held to truck-size. Most casualties and injuries sustained in such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of walls, the shattering of windows, and by nonsecured objects propelled at high velocities by the blast. Since 1995, the Air Force Research Laboratory at Tyndall Air Force Base has investigated methods of retrofitting wall structures to better resist blast loads from external explosions. This paper summarizes results from recent tests that involve an innovative use of a sprayed-on polymer to increase blast resistance of unreinforced concrete masonry walls. Test methodology, retrofit materials considered, material properties, mechanisms of effectiveness, and research challenges are discussed.     

Methods for Quantifying Lime Incorporation into Dewatered Sludge. I: Bench-Scale Evaluation

The addition of alkaline material (usually lime) to treated municipal sludge can be used to raise the pH to ≥ 12 and generate Class A or B biosolids. When lime is added to dewatered sludge, it must first be made into a slurry before the pH can be measured to demonstrate regulatory compliance. In this study, pH 12 was achieved in slurries prepared from lime-amended dewatered sludge, even when the lime was poorly incorporated and relatively high fecal coliform levels were detected. Thus, quantitative indicators of lime incorporation are needed to complement slurry pH measurements and ensure that sufficient contact occurs between lime and sludge particles to achieve adequate stabilization. In this study, the usefulness of several potential measures of lime incorporation—pH, CO2 consumption, distribution of calcium, fecal coliforms, NH3 and reduced sulfur compound production, and ATP—was systematically evaluated using a bench-scale system. Sludge pH and CO2 consumption were not influenced by the extent of lime incorporation. The distribution of calcium and fecal coliform levels appear to be useful measures of lime incorporation. NH3 and reduced sulfur compound emissions and ATP levels can also be used to assess lime incorporation provided recommended experimental techniques are used.     

Predicting Chlorine Residuals and Formation of TTHMs in Drinking Water

Chlorination is the most widely practiced form of disinfection in the United States. It is highly effective against most microbiological contaminants. However, there is concern that the disinfection by-products (DBPs) formed by the use of chlorine might be carcinogenic. One class of DBPs that are formed and the only class of DBPs that currently are regulated are total trihalomethanes (TTHMs). Therefore, much effort is being expended in developing models that can be used to predict both TTHMs and chlorine residual levels in treated drinking water. This paper presents a model that predicts both TTHMs and chlorine residuals based on the consumption of chlorine and can be used to assist in evaluating the complex balance between microbial and DBP risks associated with disinfecting drinking water with chlorine. The parameters of the model have been found to be functions of total organic carbon, pH, temperature, and initial chlorine residual level. Bromide and the subsequent formation of brominated by-products were not considered in this paper.     

Moisture Distribution in Sludge: Effects of Polymer Conditioning

This work investigated the effects of cationic polymer flocculation on the continuous moisture distributions of two sludges by means of combined thermal gravitational analysis and differential thermal analysis tests. At a specific moisture content, the solid-water bond strength first decreases with increasing polymer dose, after it reaches a charge neutralization point, and then increases in the overdose regime. Effects of polymer conditioning on the moisture distribution in sludge, as well as the correlation with the bound water data measured by expression and drying, were discussed.