FENTON AND FENTON-LIKE AOPs FOR ALUM SLUDGE CONDITIONING: EFFECTIVENESS COMPARISON WITH DIFFERENT Fe2+ AND Fe3+ SALTS

Currently, organic polymers are adopted in alum sludge (aluminum-coagulated drinking water treatment sludge) conditioning. However, there are important concerns regarding the use of these polymers because of the unknown and long-term effects of the potential release of excess polymer to the surrounding environment when the sludge is landfilled. Therefore, as an initial action, this study aimed at investigating alternative chemical conditioning methods and focused mainly on exploiting Fenton (Fe²⁺/H₂O₂) and Fenton-like (Fe³⁺/H₂O₂) reagents as the conditioner. Experiments have been conducted to test the effectiveness of Fenton's reagent (containing the ferrous salts of chloride, sulfate, or oxalate), Fenton-like reagent (containing ferric salts of chloride and sulfate), and the coagulation method using FeCl₃ for alum sludge conditioning at constant hydrogen peroxide and iron salt concentrations of 125 and 20 mg/g DS (dry solids), respectively. The effectiveness on dewaterability of the alum sludge demonstrated that the maximum reduction (%) of SRF (specific resistance to filtration) and CST (capillary suction time) of 74% and 47%, respectively, can be obtained when Fenton's reagent was adopted for sludge conditioning. Such reduction of 64% for SRF and 38% for CST can be achieved when Fenton-like reagents were applied.     

Enhancement of Coagulation Flocculation Process Using Anionic Polymer for the Post Treatment of UASB Reactor Effluent

This study was conducted for the treatment of up-flow anaerobic sludge blanket (UASB) reactor effluent by polymer assisted coagulation–flocculation process. The efficiency of alum, FeCl₃, and polyaluminum chloride (PAC) was observed alone and in coupled with anionic polymer (Synpol). The results revealed that FeCl₃ and PAC are efficient to remove 99% of turbidity, 83% of total suspended solids (TSS), 82% and 85% of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), respectively, and 99.5% removal of total coliforms (TC) and fecal coliforms (FC). The addition of anionic polymer to alum, FeCl₃, and PAC reduces the sludge volume upto 25%.     

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.     

Effect of polyaluminum chloride on enhanced softening for the typical organic-polluted high hardness North-China surface waters

The treatment of organic-polluted high hardness surface water by enhanced softening via precipitation using various coagulants, such as FeCl₃, AlCl₃ and polyaluminum chloride (PACl), was investigated in bench scale experiments. Higher removal of natural organic matter (NOM) (UV₂₅₄ removal reaches about 50%) is achieved by enhanced softening with coagulant addition conditions as compared with conventional coagulation at natural pH or by softening alone without coagulation. It is found that PACl could enhance the formation of Mg(OH)₂ precipitate to remove NOM efficiently at relative lower pH range (pH <10). Under this circumstance, the pH for enhanced softening can be decreased significantly into the practical pH range for treatment plant operation. The efficiency of enhanced softening is affected significantly not only by pH, coagulant type and dose, but also by raw water quality such as NOM characteristics, magnesium content and hardness. NOM with more hydrophobic content and higher molecular weight may be removed more easily in some situations. For water with higher content of Mg²⁺, the inflexion pH for favorable UV₂₅₄ removal is lower. It is of practical value for organic-polluted water with high content of magnesium to be treated by enhanced softening with PACl.     

Improving Dewaterability and Other Properties of Citric Acid Wastewater Treatment Sludge by Ozone and Peroxone

ABSTRACT

The efficacies of ozonation and peroxone (O₃/H₂O₂) pretreatments were compared for citric acid wastewater sludge conditioning with the objective of improving dewatering characteristics of the sludge. Treatment with 84 mg O₃/g dry solid (DS) and 12.5 mg/g DS H₂O₂ greatly enhanced the effectiveness of ozonation, providing sludge dewaterability similar to that obtained by ozonation at 250 mg O₃/g DS. Most importantly, treatment of citric acid wastewater sludge with 84 mg O₃/g DS and 12.5 mg/g DS H₂O₂ led to the preservation of the nutrient elements nitrogen, phosphorus, and potassium in the sludge with a minimal volatile suspended solids/total suspended solids reduction of 5.5%, which is much lower than that with ozonation at 250 mg O₃/g DS.     

碱性发酵污泥脱水性能的变化及其原因分析

通过控制温度在25℃和35℃,利用Ca(OH)₂和NaOH调节碱性发酵过程中pH至10,研究了碱性产酸发酵过程中碱性发酵液脱水性能的变化,并且分析了影响碱性发酵液脱水性能的因素。研究发现NaOH条件下得到的发酵污泥的脱水性能比Ca(OH)₂条件下得到的发酵污泥的脱水性能差,同种碱试剂条件下,35℃条件下的发酵污泥脱水性能比25℃条件下差。通过对溶解的蛋白和多糖含量的分析,得出在一定范围内,两者的含量与标准化CST(毛细吸水时间)存在较好的线性关系,并且单位多糖比单位蛋白更能引起发酵污泥脱水性能的恶化。通过对溶解的蛋白多糖结合Zeta电位、平均粒径分析,得出温度和Ca²⁺可能是引起碱性发酵污泥脱水性能差异的根本原因,Ca²⁺能中和胶体表面较多的负电荷,在污泥絮体之间起到良好的吸附架桥作用,从而不利于污泥的水解,抑制有机物的溶出,而有利于污泥的脱水。从脱水成本和产酸量综合分析,Ca(OH)₂比NaOH更适合作为碱试剂调节pH,25℃条件下更适合作为碱性发酵的温度。     

Sludge Ozonation and its Application to a New Advanced Wastewater Treatment Process with Sludge Disintegration

The applicability of sludge ozonation on wastewater treatment processes was investigated to reduce the amount of excess sludge without losing phosphorus removal efficiency. Solubilization degree per ozone consumption for general sludge was in the range from 2.4 to 5.8 gSS/O₃ and from 4.1 to 7.7 gCOD/gO₃. Around 80 to 90% of solubilized organics was biodegradable at a solubilization degree of 0.3. Based on the experimental results, a lab-scale plant with sludge ozonation and phosphorus crystallization was constructed to investigate the treatment performance. Amount of excess sludge was reduced by 93% with almost complete removal of soluble BOD and phosphorus removal efficiency of more than 80%. The percentage of the effluent COD_Cr discharge increased from 10% to 14–17% after installing ozonation and crystallization because of the formation of non-biodegradable organic substances in ozonation process. Energy consumption of the innovative advanced process is comparable or can be even smaller than that of the conventional anaerobic/oxic (A/O) process in spite of the installation of ozonation and crystallization.     

Ozonation of Primary Sludge and Digested Sludge to Increase Methane Production in a Chemically Enhanced Primary Treatment Facility

The purpose of this research was the investigation of the ozonation of sludge as a method to improve anaerobic digestion performance in a chemically enhanced primary treatment facility. Batch tests were conducted to evaluate the effect of ozonation on the physicochemical characteristics of both primary and digested sludge. Then, the performance of semi-continuous anaerobic digesters in combination with ozone treatment was investigated (pre-ozonation and post-ozonation). Ozonation of primary sludge did not increase the soluble COD nor the biodegradable COD, but resulted in the mineralization of a fraction of the organic matter into CO₂. However, the ozonation of anaerobic digested sludge resulted in an increase in soluble COD and biodegradable COD and in a small level of mineralization at the dose of 90 mg O₃/g COD. Pre-ozonation of primary sludge was not effective in enhancing the performance of the anaerobic digester. The coupling of ozonation and anaerobic digestion by means of the post-ozonation of digested sludge was found to be effective in improving methane production (+16%), for COD removal efficiency and for the dewaterability of anaerobic digesters compared to the control digester.     

Acylation desulfurization of oil via reactive adsorption

Excellent desulfurization is achieved via reactive adsorption using Friedel‐Crafts acylation materials, that is, acylating reagents and Lewis acids, such as acetyl chloride (AC) and AlCl₃, being named as acylation desulfurization (ACDS). For model oil, thiophenic compounds, namely, dibenzothiophene, benzothiophene, and thiophene, are removed completely by AC–AlCl₃ within 30 min at room temperature. In this process, thiophenic compounds are acylated by AC under the catalysis of AlCl₃, and the acylated derivatives are stronger base than original ones due to incorporation of O‐containing carbonyl group (C?O) and, thus, adsorbed more easily by AlCl₃ via Lewis acid–base complexation. Further, ACDS mechanism is identified by acylated product characterization and quantum chemistry calculation. Satisfactorily, ACDS is still effective for toluene‐rich and real oils, and real oil quality is improved with desulfurization proceeding. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2966–2976, 2013     

Mode of action of ferric and ferrous iron salts in activated sludge

BACKGROUND: Both ferric iron Fe(III) and ferrous iron Fe(II) salts are commonly used for chemical phosphorus removal (CPR) in the activated sludge (AS) process but only a few studies have compared Fe(III) and Fe(II) salts regarding their effect on the physical and biological properties of AS. In this research, the units of a continuous flow laboratory‐scale AS plant were dosed with Fe(III) and Fe(II) salts at a concentration of 25 mg Fe dm^?3 feed and changes in the AS properties were measured as Fe accumulated or washed out during startup, normal operation and withdrawal of dosing. RESULTS: The morphological characteristics of the flocs showed marked differences depending on the type of ion used. Fe(II) dosed flocs were more compact, less filamentous and smaller in size than Fe(III) dosed flocs. The settleability index of the Fe(II) dosed sludge was lower than that of the Fe(III) dosed sludge. The activity of ammonium (NH₄⁺‐N) and nitrite (NO₂^?‐N) oxidizing bacteria was found to be affected by the accumulation of Fe relating products into the sludge. CONCLUSIONS: Fe(II) was a more effective flocculent than Fe(III) and this was attributed to its ability to form stronger ionic bonds with the flocs prior to its oxidation to Fe(III). A hypothesis explaining the mode of action of Fe(II) is proposed. Floc surface properties were enhanced, this being beneficial to the morphological characteristics and settleability with further implications for the operation of AS. However, the effect may be reversed at high Fe contents. Copyright © 2010 Society of Chemical Industry     

强化生物除磷体系中颗粒污泥的形成及机理探讨

以实验室小试SBR反应器为载体接种普通活性污泥,研究了强化生物除磷系统对颗粒污泥形成的促进作用并探讨了其形成机理。试验结果发现：在生物脱氮运行阶段,SBR中的活性污泥能维持较稳定的絮体状态,平均SVI为138.9 ml·g^-1;当系统转为生物除磷方式运行时,随着除磷效果的好转,反应器中的污泥逐渐转化为颗粒污泥,平均SVI降低至74.1 ml·g^-1,颗粒污泥的平均粒径为0.8 mm。因此,SBR生物除磷系统有利于颗粒污泥的形成。试验发现在强化生物除磷系统厌氧释磷的过程中会有带正电的微粒大量生成,它们可以作为颗粒污泥的晶核吸附带负电的细胞体,进而促进颗粒污泥的形成。强化生物除磷颗粒污泥系统有着较为稳定的磷去除性能,除磷效率接近100%。     

AlCl3 promoting living-radical polymerization of MMA based on sec-butyl chlorine in n-butanol

The effect of metal halide AlCl₃ as additive on the living-radical polymerization of methyl methacrylate (MMA) in n-butanol at 80 °C was investigated. The initiator was sec-butyl chlorine (SBC), which was used as a model initiator containing secondary R-Cl bond and the catalyst was FeCl₂/(PPh₃)₄. The polymerization reaction of MMA, using SBC/FeCl₂ (PPh₃)₄ as initiating system, was very slow or even did not take place without AlCl₃. The addition of AlCl₃ accelerated the polymerization to some great extent and the polymers obtained have almost controlled molecular weights and narrow molecular weight distribution. These experimental results were different from those of the literatures, in which metal chlorides would slow down the polymerization rate of MMA for ATRP reactions.     

FeCl3对污泥酸性发酵产物中丙酸比率的影响

采用半连续运行的序批式反应器进行污泥酸性发酵试验,研究了发酵液中FeCl₃浓度对污泥发酵产物中丙酸比率的影响。实验表明：在温度32℃、HRT 6.6 d、进泥VS浓度 20.43 g·L^-1、pH5.5～6.0的条件下,FeCl₃浓度由0增加到232 mg·L^-1时,发酵液中ORP逐渐提高,丙酸比率变化不大;FeCl₃相似文献   

Effects of Acidification on Dewaterability and Aluminum Concentration of Alum Sludge

This study utilizes the Terzaghi-Voigt model to characterize the effects of acidification on the dewaterability of alum sludge. Alum sludge, which was obtained from the sedimentation basins of a water treatment plant using poly aluminum chloride as coagulant, was acidified to different pH levels with sulfuric acid. The dewaterability of the acidified sludge was characterized by expression tests. The results show dewaterability enhancement was insignificant until pH was below 4. Further improvement in dewaterability can be achieved by polymer conditioning. The Terzaghi-Voigt model can be applied to explain the difference in dewaterability between acidified and original sludges. Results also show dissolved aluminum concentrations were controlled by minerals in the influent rather than amorphous aluminum hydroxide.     

Feasibility of Sludge Ozonation for Stabilization and Conditioning

A pilot-scale sludge treatment plant was built to investigate the feasibility of ozonation processes for waste activated sludge treatment. Ozonation of wastewater sludge resulted in mass reduction by mineralization as well as by supernatant and filtrate recycle. Another advantage of sludge ozonation is a significant improvement of settleability and dewaterability. Experimental results showed that mass reduction of 70% and volume reduction of 85% compared with the control sludge was achieved through the sludge ozonation at a dose of 0.5?gO₃/gDS. It is also interesting to note that the filterability deteriorates up to ozone dose of 0.2?gO₃/gDS and then improves considerably at a higher ozone dose. The filterability could be improved by chemical conditioning even at a low ozone dose. The economic feasibility by cost analysis reveals that ozonation processes can be more economical than other alternative processes for sludge treatment and disposal at small-sized wastewater treatment plants.     

Effect of Ferric Chloride on the Properties of Biological Sludge in Co-precipitation Phosphorus Removal Process

This paper studied the effect of ferric chloride on waste sludge digestion, dewatering and sedimentation under the optimized doses in co-precipitation phosphorus removal process. The experimental results showed that the concentration of mixed liquid suspended solid (MLSS) was 2436 mg稬^-1 and 2385 mg稬^-1 in co-precipitation phosphorus removal process (CPR) and biological phosphorous removal process (BPR), respectively. The sludge reduction ratio for each process was 22.6% and 24.6% in aerobic digestion, and 27.6% and 29.9% in anaerobic digestion, respectively. Due to the addition of chemical to the end of aeration tank, the sludge content of CPR was slightly higher than that of BPR, but the sludge reduction rate for both processes had no distinct difference. The sludge volume index (SVI) and sludge specific resistance of BPR were 126 ml穏^-1 and 11.7?10¹² m穔g^-1, respectively, while those of CPR were only 98 ml穏^-1 and 7.1?10¹² m穔g^-1, indicating that CPR chemical could improve sludge settling and dewatering.     

Structural Analysis and Dewatering Characteristics of Waste Sludge from WWTP MBR

Abstract

A pilot‐scale UF membrane bioreactor (MBR) of 1 m³/day capacity was set up in an industrial wastewater treatment plant to evaluate its performance. This study mainly focused on testing the dewaterability and structural analysis of MBR sludge. MBR had 14% reduction of excess sludge production in relative to the conventional activated sludge process (CAS sludge). For dewatering, MBR sludge had comparable dewaterability with the CAS sludge but required nearly 20% less flocculant to reach the highest filterability χ and lowest specific filtration resistance (SRF). This could reduce the cost for running the dewatering facilities and final disposal. Meanwhile the chemical and morphological analyses on MBR sludge exhibited lower EPS (exocellular polymeric substances) content, slightly smaller flocs and more compact morphology. Additionally, to estimate the appropriate polyelectrolyte dose prior to dewatering, we measured the hysteresis loop area of the sludge rheogram (shear stress vs. shear rate) using a co‐axial cylinder viscometer. For both sludges, the area dramatically increased at some critical flocculant dosage and then plateaued off. The critical dosage, though not optimal, still led to an acceptable dewatering performance for the sludge.     

Reactions of a bituminous coal with metal chlorides in carbon tetrachloride

The interaction of a bituminous coal (87.2% C) with several metal chlorides in carbon tetrachloride was studied using the conditions under which graphite forms intercalation compounds. Adducts with SbCl₅, AlCl₃, FeCl₃ and MoCl₅ were isolated by filtration and washing with carbon tetrachloride. Atomic ratios versus coal carbon are as follows: C_10.0SbCl_7.4; C_6.2AlCl_4.1; C_6.3FeCl_3.3; and C_11.3MoCl_3.8. X-ray diffraction patterns of the adducts show no 002-band, the latter being partially recovered after extraction with diluted hydrochloric acid. The g-value of the e.s.r. signal of the coal vitrain shows a characteristic increase because of adduct formation with SbCl₅ and AlCl₃ and is reversible by hydrolysis extraction. The results obtained indicate that the bonding with SbCl₅ and AlCl₃ is mainly due to formation of chloro-complexes and with FeCl₃ and MoCl₅ — to formation of organo-metal complexes.     

Effects of Fe- and Ca-based additives on NO emission during gasification of N-containing model compound under different atmospheres

The effects of iron and calcium compounds on NO emission during CZC (carbazole char) gasification under different O₂ concentrations have been investigated in a quartz tube fixed bed reactor. Temperature-programmed gasification was preformed to determine the influence of O₂ concentration and catalytic effects of iron and calcium on NO emission. The results show that the O₂ concentration strongly influences NO emission during CZC gasification; suitable O₂ concentration could largely reduce NO emission, but high or low O₂ concentration is unfavorable to reduce NO pollution. Iron catalysts increase NO emission during CZC gasification in O₂ concentration ranging from 20.9 to 1.2%, and their catalytic effects are strongly depended on O₂ concentration. The order of their catalytic effects is Fe(AC)₂>FeCl₂≈FeCl₃. Different kinds of iron compounds show different catalytic activities for their different dispersion on CZC and their different decomposition tendency to form active sites. Calcium compounds show different effects on NO emission depending on O₂ concentration. Ca(AC)₂ and CaCl₂ increase NO emission under high O₂ concentration (such as 20.9%), but they decrease NO under low O₂ concentration (such as 1.2%). When CZC gasification under 4.8% O₂-Ar, Ca(AC)₂ decreases NO emission, but CaCl₂ increases NO emission.     

Catalytic dehydrochlorination of the solid poly(vinyl chloride) in the presence of aluminium chloride (friedel-crafts) catalyst: Studies of the structure by spectroscopical methods

Catalytic dehydrochlorination (100%) of solid poly(vinyl chloride) (PVC) in the presence of AlCl₃ at 200°C gives a product which has a similar structure to the product of catalytic dehydrochlorination of 1,2-dichloroethane in the presence of AlCl₃ at 60°C. Both products have brown-black color, are completely insoluble, thermally resistant up to more than 400°C, and exhibit conductivities in the range 10^?6 S cm^?1 (after doping with FeCl₃ or I₂ conductivities: 10^?5 S cm^?1). Different spectroscopical methods such as UV/VIS, IR, Raman, ESCA, and ¹³C-NMR were employed to the structure study of both products, which are crosslinked polyenes with a number of aromatic rings.