Density and Activity Characterization of Activated Sludge Flocs

Activated sludge flocs are made up of a conglomerate of materials including microorganisms, exocellular polymers, inert particulates, slow and nonbiodegradable organic particles, and water. The goal of this study was to determine if inert/unbiodegradable aggregates had higher densities than active biomass. It was also desired to determine whether mixed liquor could be gravimetrically settled to differentially stratify flocs based on density and biological activity. In this manner, if activity stratification is possible, then less active biomass could be wasted preferentially during wastewater treatment operations (e.g., during daily wastage), thereby increasing the effective solids retention time and improving process performance. This paper reports the initial set of results, which focused on establishing density values of inert/unbiodegradable fractions of activated sludge floc, and the heterotrophic activity measurements of faster settling flocs compared to slower settling flocs. The results indicate that activated sludge from a local wastewater treatment plant had aggregate densities as low as 1.038?g/mL for slower settling floc particles and as high as 1.065?g/mL for faster settling floc particles. Primary effluent “inert+unbiodegradable particulate organic” fractions, which ultimately accumulate in mixed liquor and contribute to the inactive activated sludge floc fraction, had densities of approximately 1.24?g/mL. Mixed liquor that was digested in excess of 90 days to reduce any degradable organics revealed aggregate densities between 1.11 and 1.12?g/mL. Settling column experiments indicated that floc particles settled at rates ranging from less than 5?m/h to greater than 30?m/h. Specific oxygen uptake rates signified that the heterotrophic activity was homogeneous across all settling velocities except those flocs with a settling velocity of less than 5?m/h. These flocs exhibited a specific oxygen uptake rate of between 31 and 110% higher than the remaining floc. Determination of the mass fraction of these flocs indicates that they account for approximately 2% of the overall biomass. This low fraction limits the usefulness of differentially settling unaltered waste activated sludge to recover portions with higher activity.     

有机底物对活性污泥胞外聚合物的影响

研究了有机底物对3种活性污泥胞外聚合物(G-EPS、P-EPS、W-EPS)的影响。G-EPS和P-EPS在相同试验条件下以不同有机底物(葡萄糖、蛋白胨)培养得到,W-EPS由污水处理厂污泥中提取。3种EPS量的顺序为G-EPS>P-EPS>W-EPS,其中所含多糖和蛋白质的比值分别为22.9、4.8、6.7,且EPS中的多糖含量明显高于蛋白质的含量;在一个培养周期内,G-EPS中多糖、蛋白质及其总量达到最大值的时间均比P-EPS的短;3种EPS中,碳、氮元素比分别为8.5、5.5、6.1;红外光谱显示,3种EPS中所含的官能团种类很相近,主要是羟基、羧基、氨基和酰胺基团,但每种EPS中所含各种官能团的量有差异。     

Mechanisms of Ballasted Floc Formation

Ballasted flocculation processes were studied at laboratory scale to evaluate the mode of transport of ballasting agent from bulk liquid into the chemical floc and establish a new model for assessing the mechanisms of ballasted floc formation. For this purpose, a test program consisting of bench scale observations, microscopic observations, density tests, and centrifugal settling tests was developed. Ballasted flocs were found to be formed by a mechanism in which the ballasting agent is incorporated into the floc matrix by inertial forces, and the ballasting agent taking the place of the bound water content (ΦW). Bulk density of ballasted flocs (ρb) was found to be linearly related to the ballasting agent dose (M). This study provided a better understanding of the mechanisms controlling the interaction between ballasting agent and coagulant/polymer chemical floc.     

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.     

Sludge Floc Behavior in an Elongated Rectangular Settling Tank

The different sludge floc distributions along the rectangular secondary settling tank were confirmed experimentally. Along the settling tank, three different regions can be formed: the fast settling zone near the inlet, the compaction zone in the middle, and the slowly settling zone near the outlet. Further investigation of morphological change of sludge flocs also showed corresponding floc characteristics: the bigger size of particles in the front, the relatively smaller particles with high density in the middle, and the small loose flocs in the rear. These were determined by the hydraulics and floc construction. The preceding results can be used as a guide to design systems to collect loose sludge solids.     

不同pH值下胞外聚合物对污泥脱水性能及束缚水含量的影响

研究了不同pH值下污泥脱水性能和束缚水含量的变化,通过测定污泥调理过程中各层胞外聚合物(S-EPS、LB-EPS和TB-EPS)中蛋白质和多糖的含量、S-EPS中有机官能团以及有机酸的含量,探讨了胞外聚合物对污泥脱水性能及束缚水含量的影响.酸性条件下,污泥的脱水性能明显好于中性条件,并且pH值为3.03时,污泥滤饼含水率(WC)和毛细吸水时间(CST)均降至最低,分别为60.8%和25.4 s;碱性条件下,污泥中束缚水的含量明显增加,WC和CST均大幅升高,污泥脱水性能恶化.酸碱的加入导致污泥中TB-EPS含量降低,LB-EPS和S-EPS含量升高,并且EPS各层组均与WC、CST以及束缚水含量具有很强的相关性,其中S-EPS与污泥脱水性能以及束缚水含量的相关性最显著.酸碱调理过程中,部分EPS水解生成有机酸等小分子有机物,S-EPS中有机官能团的总量和种类都有明显增多.     

Effect of Ozone on Filamentous Bulking in a Laboratory Scale Activated Sludge Reactor Using Respirometry and INT-Dehydrogenase Activity

Filamentous bulking can be controlled by the addition of oxidant chemical agents such as ozone. To evaluate the ozone effect on activated sludge from a laboratory scale reactor, different techniques were applied: Settleability test, respirometry (oxygen uptake rate), and the INT-dehydrogenase activity test carried out both by spectrophotometry (DHAa) and image analysis (DHAi). In activated sludge, the respirometric technique and the spectrophotometric DHAa quantified ozone action on the total respiratory activity of flocs; in contrast, the image DHAi test was applied to evaluate the specific action of ozone on filamentous microorganisms. The conditions for application of the INT-dehydrogenase activity test were standardized using pure cultures of a filamentous microorganism (Sphaerotilus natans) and a floc-forming bacterium (Acinetobacter anitratus). For activated sludge with filamentous bulking, ozone doses and treatment times necessary to improve settleability were established. Ozone dose levels and contact times influence the viability of bacteria in flocs and filaments and the finding of appropriate parameters to preserve floc viability and, at the same time, inhibiting filaments is essential to filament control by ozonation.     

Effects of Sodium Chloride on the Performance of a Sequencing Batch Reactor

In this study, we investigated the effects of sodium chloride (concentrations ranging from 0?to?60?g/L) on the performance of sequencing batch reactors (SBRs) using a microbial culture developed from a domestic sewage treatment plant. The lab-scale SBRs were fed with synthetic wastewater (acetate as the organic substrate) containing either sodium chloride solution or seawater to ensure consistency in feed composition. It was found that sodium chloride concentrations of up to 10?g/L stimulated substrate removal. The organic removal efficiency decreased from 96%, when no sodium chloride was added, to 86% when 60?g/L of sodium chloride was introduced into the influent wastewater. Effluent turbidity increased significantly when the sodium chloride concentration in the wastewater was equal to or above 30?g/L even though the sludge volume index (SVI) decreased. The increase in effluent turbidity could be caused by the release of nondissolved cellular components due to plasmolysis of microorganisms as observed by scanning electron microscopy. Experiments involving seawater (with 20?g/L total dissolved solids) showed that organic removal efficiency improved from 87 to 95% while effluent turbidity and SVI values were lowered when the loading rate parameter (Li) was lowered from 0.6?to?0.3?mg total chemical oxygen demand (mg?VSS?day). Optical microscopy and scanning electron microscopy indicated morphological changes in the microbial population. From this study, it was concluded that microbial culture from domestic wastewater facilities could be acclimated in a SBR to treat wastewater containing sodium chloride concentrations of up to 60?g/L.     

Dosage Control of the Fenton Process for Color Removal of Textile Wastewater Applying ORP Monitoring and Artificial Neural Networks

Textile wastewater containing a high level of color and refractory chemical oxidation demand (COD) is difficult to treat using traditional wastewater treatment processes. Typically, a chemical process was suggested as a pretreatment to remove color and increase biodegradability of refractory organic materials. A biological process was then used to remove organic materials and reduce chemical costs for textile wastewater treatment. Fenton oxidation is one of the most effective chemical processes for removing color and COD for textile wastewater. In Fenton processes, oxidations by generated hydroxyl radical are the key factor for color removal in textile wastewaters; thus, monitoring oxidation reduction potential (ORP) should have high potential in Fenton dosage control for color removal in textile wastewater treatment. The main object of this study is to build a Fenton dosage control strategy that uses ORP monitoring and artificial neural network (ANN) models for removing color from textile wastewaters. Two wastewaters, synthetic and real textile, were used in this study. Experimental results have shown that the ANN models precisely represent the correlation between monitoring ORP, Fenton doses, color removal efficiency, and effluent color value, and therefore can be used to control Fenton doses for removing color from textile wastewater. Finally, another series of Fenton dose-control experiments for different color removal control targets were conducted to evaluate this proposed Fenton dose control strategy. Experimental results indicate that the proposed control strategy precisely controls the required Fenton doses for different control targets for both synthetic and real textile wastewaters, and result in reduced chemical costs.     

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.     

Floc Characteristics and Removal of Turbidity and Humic Acid from High-Turbidity Storm Water

This study considered the removal efficiency of turbidity and organic content from high-turbidity storm water of tropical storm Nari, using polyaluminum chloride (PACl) as a coagulant. The resulting floc size and compactness (fractal dimension) were determined using a small-angle light scattering technique. The response surface method, and the Box-Behnken design, was adopted to examine how the hydrogen ion concentration (pH), turbidity, and alkalinity of the suspension, the PACl dosage, and the dosed amount of humic acid affect the removal efficiency. Flocs with a looser interior structure more efficiently removed turbidity and humic acid. An acidic suspension and moderate PACl dosage and alkalinity level favor the production of loose flocs. Optimal conditions for generating large flocs includé pH neutrality and high PACl dosage. Producing both large and loose flocs depends on a compromise. The removal of turbidity/humic acid from high-turbidity storm water does not proceed by a charge neutralization mechanism.     

水相中砷的形态分析及相关修复技术研究

在矿山有色和贵金属资源开发过程中,大量的伴生矿物砷被开采而裸露于地表,增加了对周围水体及土壤环境污染的风险。为充分了解水体中砷的存在形态与具体除砷工艺选择的关系,在结合前人工作的基础上,分析了含砷废水中溶液pH值、氧化还原电位（Eh）、共存阴阳离子和溶解性有机物等各种影响因素对砷的存在形态的影响,总结了化学法、物理法及生态修复等各种除砷技术的适用范围和应用条件;结合具体工程案例,对矿山实际选冶过程中产生的含砷废水的处理情况进行了说明,以期为其他工业生产中含砷废水的无害化处理和修复技术开发提供技术参考。     

湿法冶金中胞外聚合物(EPS)的研究进展

针对当前国内外关于胞外聚合物在湿法冶金中的研究状况,介绍了胞外聚合物的来源、组成、物化性质和提取方法,以及胞外聚合物在湿法冶金中的应用现状。胞外聚合物在湿法冶金过程中的作用形式主要是帮助矿物在水溶液中溶解、改变矿物表面化学性质和吸附冶金废水中的金属离子。     

不同pH下好氧颗粒污泥的稳定性

为考察好氧颗粒污泥（AGS）对不同pH环境下的耐受力,研究了不同pH废水（pH分别为3、4、5、10、11、12）下AGS的稳定性变化规律.在酸性环境中,AGS的理化特性随pH下降而变差（胞外聚合物（EPS）含量由102.5 mg/g下降到76.43 mg/g MLSS,比耗氧速率（SOUR）由17.94 mg O₂/（g MLSS·h））下降到16.19 mg O₂/（g MLSS·h））,pH为3和4时均出现不同程度的污泥上浮,对污染物的去除效果也呈下降趋势,但COD和TP的去除率维持在80 %以上.在碱性环境中,AGS出现了明显的上浮及解体.随着pH的增大,AGS的理化特性不断恶化（EPS由93.27 mg/g MLSS上升到178.45 mg/g MLSS,SOUR由6.81 mg O₂/（g MLSS·h））下降到4.30 mg O₂/（g MLSS·h））.同时,AGS对污染物的去除能力急剧下降,对COD、TN、TP的去除率均下降到50 %以下.研究结果表明AGS在酸性环境中有较强的耐冲击负荷能力,而碱性环境对AGS有较大的抑制作用.      

Extradural temporopolar approach for giant pituitary adenomas invading the cavernous sinus and parasellar regions]

Natural organic matter (NOM) was extracted from a raw water source (Forge Pond, Granby, Mass.) and fractionated into eight groups: fulvic acid, humic acid, hydrophilic acid, weak hydrophobic acids, hydrophilic neutrals, hydrophobic neutrals, hydrophilic bases, and hydrophobic bases. The extent of adsorption of these fractions on preformed aluminum hydroxide flocs was determined. Also, the adsorption affinities of various fractions were correlated to selected NOM properties, i.e., organic charge, molecular weight, and specific ultraviolet absorbance. The nature of the reactions leading to adsorption was discussed, along with the induced dissolution of aluminum from the floc surface and its resulting association with NOM in particulate or colloidal forms.     

Simple Rule-Based Algorithm for Optimizing Volatile Fatty Acids Production in Primary Sludge Fermentation Schemes

In this paper, a model-based algorithm for optimizing the primary sludge fermentation process design and operation is described and evaluated. This is a recently used method to obtain the volatile fatty acid (VFA), needed for the enhanced biological phosphorus removal process, directly from raw wastewater. The proposed algorithm consists of a heuristic reasoning algorithm based on the expert knowledge of the process. Only effluent VFA and the sludge blanket height have to be set as design criteria, and the optimization algorithm obtains the minimum return sludge and waste sludge flow rates which fulfill those design criteria. It has been evaluated by simulating different temperature and sludge volume index (SVI) influent conditions in order to evaluate the algorithm performance under different conditions, as well as its sensitivity with respect to temperature and SVI, which are the most important parameters in these systems. The same tendencies observed by simulation were observed afterward in pilot plant experiments.     

UASB Treatment of Tapioca Starch Wastewater

Feasibility of the upflow anaerobic sludge blanket (UASB) process was investigated for the treatment of tapioca starch industry wastewater. After removal of suspended solids by simple gravity settling, starch wastewater was used as a feed. Start-up of a 21.5-L reactor with diluted feed of approximately 3,000 mg∕L chemical oxygen demand (COD) was accomplished in about 6 weeks using seed sludge from an anaerobic pond treating tapioca starch wastewater. By the end of the start-up period, gas productivity of 4–5 m3/m3r?day was obtained. Undiluted supernatant wastewater with a COD concentration of 12,000–24,000 mg∕L was fed during steady-state reactor operation at an organic loading rate of 10–16 kg COD/m3r?day. The upflow velocity was maintained at 0.5 m∕h with a recirculation ratio of 4:1. COD conversion efficiencies >95% and gas productivity of 5–8 m3/m3r?day were obtained. These results indicated that removal of starch solids from wastewater by simple gravity settling was sufficient to obtain satisfactory performance of the UASB process.     

Treatment and Decolorization of Dyes in an Anaerobic Baffled Reactor

Synthetic organic colorants, the majority of which are recalcitrant in nature, are used universally in many different manufacturing processes. The dyes are released into the environment in industrial effluents and are highly visible even at low concentrations (<1 mg∕L). Added to this, certain dyes, dye precursors, and aromatic amines have been shown to be carcinogenic. Thus, appropriate treatment of dye wastewaters to remove color and the dye compounds is clearly an important issue. Methanogenic toxicity tests on several food dyes provided a range of toxicity results, from noninhibitory (IC50 >20 g∕L) to inhibitory (IC50 0.2 mg∕L). Batch biodegradability assays indicated that the dyes were not readily utilized by the anaerobic microorganisms as a sole substrate. Decolorization of the dye tartrazine was investigated in a laboratory-scale anaerobic baffled reactor at a concentration of 250 mg∕L. Reduction in COD of 50–60% and color reduction of about 95% was achieved. Initially the tartrazine was not readily decolorized; however, decolorization improved with acclimation of the biomass. An industrial wastewater from a food dye manufacturer was fed to a second laboratory-scale anaerobic baffled reactor at a concentration of 5% (volume-to-volume ratio) and then increased to 10% (volume-to-volume ratio). Anaerobic degradation of the wastewater was efficient. Methanogenic activity was high; the organic content of the influent was reduced by about 70%, and color was reduced by almost 90%     

Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. II: Experimental Verification

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes: rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume that hydrolysis is the rate-limiting step, but none considers the role that the kinetics of biological flocculation and the sludge-settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetics of biological flocculation, and have analyzed its role on the removal of particulate chemical oxygen demand in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. The first paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge-settling properties with the aeration tank behavior, and the second paper presents experimental evidence that the proposed model is a reasonable first approximation that can be used for activated sludge system design and operation.     

Radiation-Assisted Process Enhancement in Wastewater Treatment

Laboratory and pilot tests were conducted to investigate the use of ionizing radiation at an activated sludge wastewater treatment facility with residuals processing. Operational enhancements were investigated with respect to bulking control, thickening enhancement, and anaerobic stabilization processes. Radiation caused permanent effects in measured sludge parameters including solids content, chemical oxygen demand, ammonia-nitrogen, zeta potential, specific surface area, resistance to filtration, sludge volume index, pH, organic acid production, and digester gas evolution. Analysis of beneficial effects from preliminary studies and pilot tests demonstrated that a dose of 2–3 kGy would be potentially successful for bulking control and to a lesser degree, enhanced thickening and radiation-assisted anaerobic digestion. A cost analysis based on preliminary tests determined that a centralized electron beam irradiator could be applied economically in an integrated approach at an estimated annual savings of $0.2–2.7 million depending upon the application. Considering that the annual cost of operating an accelerator unit was estimated at $2.4 million ($2.16/m3), this might translate into an important savings for a large-scale wastewater treatment facility.