Ultrasonic reduction of excess sludge from activated sludge system II: urban sewage treatment

Previous study showed that sonication was effective to reduce waste activated sludge (WAS) using artificial wastewater. This paper confirms the viability and evaluates the performance of this method in practical wastewater treatment using urban sewage without temperature control. The results showed that sonication significantly lowered the WAS and biomass synthesis, and greatly enhanced the mineralization of sewage organics. The optimal specific energy for sludge lysis was 20.0k Wh/kg DS. Further energy-increase had little benefit on WAS reduction. When the specific energy was 20.0kWh/kgDS and the sludge recycle ratio was 0.007, the WAS decreased by 54%, the biomass synthesis abated by 59%, and the sewage mineralization ratio increased from 31% to 58%. The effluent COD and nitrogen were stable but phosphorus was higher than that of the control bioreactor. The COD removal was lower but the WAS reduction was higher for urban sewage than for artificial wastewater. The accumulation pattern of heavy metals in sludge was greatly alternated by the sonication-cryptic growth; and different metals behaved differently. The sludge Ni concentration increased by 141% while As decreased by 53%.     

Enhancing the use of waste activated sludge as bio-fuel through selectively reducing its heavy metal content

Power plant or cement kiln co-incineration are important disposal routes for the large amounts of waste activated sludge (WAS) which are generated annually. The presence of significant amounts of heavy metals in the sludge however poses serious problems since they are partly emitted with the flue gases (and collected in the flue gas dedusting) and partly incorporated in the ashes of the incinerator: in both cases, the disposal or reuse of the fly ash and bottom ashes can be jeopardized since subsequent leaching in landfill disposal can occur, or their "pozzolanic" incorporation in cement cannot be applied. The present paper studies some physicochemical methods for reducing the heavy metal content of WAS. The used techniques include acid and alkaline thermal hydrolysis and Fenton's peroxidation. By degrading the extracellular polymeric substances, binding sites for a large amount of heavy metals, the latter are released into the sludge water. The behaviour of several heavy metals (Cd, Cr, Cu, Hg, Pb, Ni, Zn) was assessed in laboratory tests. Results of these show a significant reduction of most heavy metals.     

Magnetic nanostructures functionalized with a derived lysine coating applied to simultaneously remove heavy metal pollutants from environmental systems

ABSTRACT

The pollution of environmental systems with heavy metals is becoming a serious problem worldwide. These contaminants are one of the main issues in sludge (which is considered waste) and can even have harmful effects if the sludge is not treated properly. Thus, the development of a novel functional magnetic nanoadsorbent based on a derived lysine is reported here, which can be efficiently applied for metal removal from sludge. Magnetic nanoparticles were coated with silica layer and further modified by covalent bonding of derived lysine. The morphology of the nanomaterial, its nano-size and the silica layer thickness were analyzed by transmission electron microscopy. The successful silanization of the lysine derivative to the silica-coated magnetic nanostructures was investigated by several physicochemical characterization techniques, while the magnetic properties were measured with a vibrating sample magnetometer. The synthesized nanostructures were used as adsorbents for simultaneous removal of most critical heavy metals (Cr, Zn, Cu) from real complex sludge suspensions. The main practical adsorption parameters, pH of the native stabilized sludge, adsorbent amount, time, and adsorbent regeneration were investigated. The results show promising adsorption properties among currently available adsorbents (the total equilibrium adsorption capacity was 24.5 mg/g) from the sludge with satisfactory nanoadsorbent reusability and its rapid removal. The stability of the nanoadsorbent in the sludge, an important but often neglected practical parameter for efficient removal, was verified. This work opens up new possibilities for the development of high-quality magnetic nanoadsorbents for metal pollutants applied in various complicated environmental fields and enables waste recovery.     

Heavy metal adsorption by a formulated zeolite-Portland cement mixture

Large amounts of fine zeolite by-product were produced when natural zeolite was processed into a powder with a specific particle size. In Korea, large piles of this by-product exist with no disposal options. We conducted studies to determine whether mixtures of this by-product with other materials could be used as a substitute to activated carbon for wastewater treatment. A granular material was formulated by mixing zeolite by-product with Portland cement (ZeoAds), and this material was tested for its efficiency for heavy metal removal from aqueous solutions. The ZeoAds removed Pb and Cu in an aqueous solution up to 27.03 and 23.25 mg g(-1), respectively. Adsorption kinetics of the ZeoAds for heavy metals was first-order, and the ZeoAds removed about 90% of the Cu within 30 min. At solution pH lower than five, the adsorption specificity of the ZeoAds for metals was Pb>Cu>Cd>or=Zn. Langmuir isotherms adequately described the adsorption, and adsorption capacity increased as the particle size decreased to 2 mm in diameter. The maximum adsorption capacities of the metals for the ZeoAds were, irrespective of the kinds of metals, about two times greater than those of activated carbon. Column experiments demonstrated that the ZeoAds was more efficient and had a higher sorptive capacity than activated carbon for removing metals from industrial wastewater.     

Solidification/stabilization of hazardous sludges with Portland cement

Abstract

Studies were conducted to investigate the feasibility and effectiveness of solidification/stabilization of hazardous heavy metal‐laden sludges with portland cement. The results indicated that the sludge properties had a significant effect on the compressive strength of the solidified samples. Additives such as lime, sodium silicate, calcium chloride, and fly ash could enhance the compressive strength and reduce the leachability of heavy metal. Also, leaching studies indicated that stabilization minimized or prevented the release of heavy metals and created a nonhazardous product.     

Total concentrations and fractions of Cd, Cr, Pb, Cu, Ni and Zn in sewage sludge from municipal and industrial wastewater treatment plants

Heavy metals are one of the important factors that affect the final disposal of sewage sludge. In this paper, the metal mobility and bioavailability of heavy metals in sewage sludge were studied by using Community Bureau of Reference (BCR) sequential extraction procedure to get more information for the reasonable disposal of sludge. Sewage sludge was collected from five municipal wastewater treatment plants and three industrial wastewater treatment plants. The sludge was examined for and the total concentrations and different chemical fractions of Cd, Cr, Pb, Cu, Ni and Zn. The total metal concentrations of heavy metals in sludge varied greatly. The contents of Zn and Cu were the highest, followed by then Cr, Ni and Pb and the content of Cd was the least. There was no significant difference in total metal concentration between municipal and industrial wastewater treatment plants. Fractions extracted by the BCR sequential procedure were acid soluble/exchangeable, reducible and oxidizable fraction. Sludge pH was found to have profound effect on the chemical fractions of heavy metals. Acidic sludges (Xiamen and Jinlin Petrochemical Group Co., wastewater treatment plant) had higher proportion of the acid soluble/exchangeable fractions than in neutral sludge. In neutral sludges, Pb and Cr were principally distributed in between the oxidizable fraction and the residual fraction; Cu was in the oxidizable fraction; Cd mainly in the residual fraction in municipal wastewater treatment plants and had high percentage of acid soluble/exchangeable and reducible fractions in industrial wastewater treatment plants; Ni and Zn had higher percentage in the acid soluble/exchangeable and the oxidizable fraction.     

燃煤电厂脱硫废水及污泥中重金属污染物控制研究进展

燃煤发电中常采用湿法烟气脱硫技术,该工艺会产生含有重金属污染物的脱硫废水和污泥,潜在环境危害性强,需谨慎处理。介绍了燃煤电厂脱硫废水和脱硫污泥的产生来源、成分组成、重金属污染物含量水平和排放处置标准,对沉淀法等脱硫废水重金属处理技术和脱硫污泥重金属去除及固化技术的原理、优点、适用性和局限性进行总结对比分析。脱硫废水重金属控制方法中,目前普遍使用的三联箱工艺难以满足日益严格的排放标准,需进行改进;吸附法、微生物法等新型方法也因成本和技术等问题而难以普及;零排放技术因其无污染的特性将逐渐成为研究和推广的主流。脱硫污泥重金属控制方法大多仍处于研究中,化学修复和药剂固化方法因效果好、适用性强将逐渐在电厂生产实践中推广。     

The distribution of heavy metals during fluidized bed combustion of sludge (FBSC)

During combustion of wastewater treatment sludge, the inorganic constituents are converted into ash which contains the major fraction of the heavy metals present. The behaviour of heavy metals in combustion processes has been studied extensively for mostly coal combustion and waste incineration. For biomass and sludge, literature data are scarce and mostly limited to laboratory experiments. The present paper assesses the partitioning of eight heavy metals (Hg, As, Cd, Cu, Pb, Cr, Ni and Zn) in the different residues from a large-scale fluidized bed sludge combustor of 4.4 m i.d. The origin of the sludge is mostly from treating urban wastewaters (>90%), although some mixed sludge (urban+industrial, <10%) is also burnt. The different residues (bottom ash, fly ash, filter cake, scrubber effluent and stack emissions) were sampled and analysed during 33 weeks, spread over a period of 1 year. The mass balance of relevant heavy metals closes for 96.5%, inaccuracies being related to the unsteadiness of the process, the accuracy of the mass flow data monitored at the plant, and on collecting representative samples. It is also shown that all heavy metals under scrutiny, except Hg, are concentrated in the fly ash as collected in the electrostatic precipitator.     

Potential use of treated wastewater and sludge in the agricultural sector of the Gaza Strip

Twelve elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were analyzed in 120 composite samples of influent and effluent wastewater; the results revealed that domestic wastewater influent contains considerable amounts of heavy metals and the partially functional treatment plants of Gaza are able to remove 40–70% of most metals during the treatment process. Heavy metals in 31 industrial wastewater effluents are within the ranges of international standards. All industries of Gaza are light; although they have no treatment facilities, their effluents are being discharged to municipal sewerage system and the existing treatment plants are capable of absorbing the industrial effluents with no significant impact on treatment bioprocesses.Thirty parameters were determined in 35 sludge samples: P, AOX, C, S, CaCO₃, Mg, Ca, Na, K, Li, Cu, Zn, Ni, Pb, Mn, Fe, Cr, Co, Cd, As, Hg, Ti, Se, Br, Rb, Th, Sr, Y, U, and Zr. Although there are no treatment facilities for sludge within the treatment plants, the results indicated that sludge in general is clean of heavy metals. Only Zinc and AOX showed anomalous concentrations; more than 85% of sludge samples showed that averages of zinc and AOX are 2,000 mg/kg and 550 mg Cl/kg, respectively, which exceed the standards of all industrial countries for sludge to be used in land application.     

Evaluation of electrokinetic removal of heavy metals from sewage sludge

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.     

Amalgamation and application of nano chitosan cross‐linked with fish scales based activated carbon as an adsorbent for the removal of reactive dye (RB9)

The extensive discomfort in the expulsion of toxic pollutants even at mild concentrations has demanded the need for prompt methods for the evacuation of dyes and heavy metals. The effective method for depuration of dye from the effluent is by sorption. Chitosan is a bio‐polymer which is gaining an increasing interest as one of the sorbents. It was obtained from the crab shells by undergoing several chemical processes and used as an adsorbent for dye, metal removal and also for pharmaceutical purposes. Cross linking it with other co polymers will increase the capacity of adsorption to a maximum level. Fish scales are considered to be a major waste in the food industry and since it takes a long time for decomposing it is considered to be one of the pollutants. Hence it is utilised by converting it into activated carbon by preliminary treatment and into a muffle furnace. The obtained activated carbon is combined with chitosan by using a cross linker and utilised for adsorption mechanism. To analyse the effect of chitosan cross linked with activated carbon obtained from fish scales in adsorption of dye Reactive Blue 9 (RB9) to evaluate the adsorption studies, kinetics, mass transfer studies, thermodynamics of the bio adsorbent.Inspec keywords: dyes, wastewater treatment, effluents, mass transfer, activated carbon, adsorption, polymer blends, water pollution control, thermodynamics, reaction kinetics, furnaces, recycling, industrial waste, waste recovery, food processing industry, pharmaceutical industry, renewable materials, nanoparticles, toxicologyOther keywords: fish scales, activated carbon, reactive dye removal, toxic pollutants, heavy metals, bio‐polymer, nanochitosan, bio adsorbent, amalgamation, RB9 dye, industrial effluent, crab shells, adsorption method, pharmaceutical purposes, copolymers, food industry waste, waste recovery, recycling process, muffle furnace, reaction kinetics, mass transfer, thermodynamic analysis, ReactiveBlue 9, wastewater treatment, water pollution control, C     

污泥基活性炭的制备及其在环境污染治理中的应用进展

从污泥基活性炭的制备及其在水和大气环境领域的应用两个部分进行了综述。主要总结了3种传统制备方法的原理;同时,对比了7种不同制备方法的优缺点和主要用途,汇总了通过添加农作物秸秆和矿物来提升污泥活性炭性质的相关研究。污泥基活性炭在环境领域的应用主要包括其对废水中有机染料、有机药物、小分子有机化合物和重金属的吸附以及其对硫化氢等工业废气和甲醛等室内废气的净化。另外,分别举例说明了不同来源污泥基活性炭的用途和性能。最后,总结分析了污泥基活性炭在研究中存在的问题以及今后的主要发展方向。     

Alkaline thermal sludge hydrolysis

The waste activated sludge (WAS) treatment of wastewater produces excess sludge which needs further treatment prior to disposal or incineration. A reduction in the amount of excess sludge produced, and the increased dewaterability of the sludge are, therefore, subject of renewed attention and research. A lot of research covers the nature of the sludge solids and associated water. An improved dewaterability requires the disruption of the sludge cell structure. Previous investigations are reviewed in the paper. Thermal hydrolysis is recognized as having the best potential to meet the objectives and acid thermal hydrolysis is most frequently used, despite its serious drawbacks (corrosion, required post-neutralization, solubilization of heavy metals and phosphates, etc.). Alkaline thermal hydrolysis has been studied to a lesser extent, and is the subject of the detailed laboratory-scale research reported in this paper. After assessing the effect of monovalent/divalent cations (respectively, K(+)/Na(+) and Ca(2+)/Mg(2+)) on the sludge dewaterability, only the use of Ca(2+) appears to offer the best solution. The lesser effects of K(+), Na(+) and Mg(2+) confirm previous experimental findings.As a result of the experimental investigations, it can be concluded that alkaline thermal hydrolysis using Ca(OH)(2) is efficient in reducing the residual sludge amounts and in improving the dewaterability. The objectives are fully met at a temperature of 100 degrees C; at a pH approximately 10 and for a 60-min reaction time, where all pathogens are moreover killed. Under these optimum conditions, the rate of mechanical dewatering increases (the capillary suction time (CST) value is decreased from approximately 34s for the initial untreated sample to approximately 22s for the hydrolyzed sludge sample) and the amount of DS to be dewatered is reduced to approximately 60% of the initial untreated amount. The DS-content of the dewatered cake will be increased from 28 (untreated) to 46%.Finally, the mass and energy balances of a wastewater treatment plant with/without advanced sludge treatment (AST) are compared. The data clearly illustrate the benefits of using an alkaline AST-step in the system.     

杭州市典型污水处理厂所产污泥重金属含量及资源化分析

以杭州市内4所典型城市污水处理公司产生的城市污泥为研究对象,对污泥中的重金属种类及含量进行了分析.结果表明,四种污泥中主要含Pb、Ni、Cr、Zn、Cu、Mn、Sn、Fe、Hg等重金属,且毒性较大的元素Hg、As和Pb的含量较高.四种污泥中Ni的含量均超出《城镇污水处理厂污染物排放标准》（GB18918--2002）中污泥农用标准限值（土壤pH＜6.5）.尤其是富阳污泥,其Pb、Hg和Cr的含量较高,且Pb及Hg的含量超出农用标准限值,污泥的资源化利用受限.除富阳污泥外,其他三种污泥可采用掺烧方式实现污泥的资源化利用.     

The synthesis,activation and characterization of charcoal powder for the removal of methylene blue and cadmium from wastewater

Charcoal prepared from biomass, wastes of the local forest (tree branches), activated with NaOH solution and with Degussa P25 (TiO₂) was used as adsorbent and photocatalyst for the removal of cadmium cations and methylene blue from wastewater. These materials were characterized by using atomic force microscopy for roughness surface. The energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis indicate the existence of nano TiO₂ on the charcoal surface. Additionally, the FT-IR spectroscopy measurements indicate that the alkali treatment develops hydroxyl groups on charcoal surface which could adsorb methylene blue, heavy metals and other pollutants via the synergistic effect. The activities of the charcoal (BC), activated charcoal (BCA) and BCA/TiO₂ mixture (BCA-D) depend on the contact time, adsorbent dosage and pH. The adsorption kinetic data were tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The kinetic studies showed that the adsorption is followed by the pseudo-second-order reaction with regard to the intraparticle diffusion rate kinetics.     

A study on the dewatering of industrial waste sludge by fry-drying technology

In sludge treatment, drying sludge using typical technology with high water content to a water content of approximately 10% is always difficult because of adhesive characteristics of sludge. Many methods have been applied, including direct and indirect heat drying, but these approaches of reducing water content to below 40% after drying is very inefficient in energy utilization of drying sludge. In this study, fry-drying technology with a high heat transfer coefficient of approximately 500 W/m² °C was used to dry industrial wastewater sludge. Also waste oil was used in the fry-drying process, and because the oil's boiling point is between 240 and 340 °C and the specific heat is approximately 60% of that of water. In the fry-drying system, the sludge is input by molding it into a designated form after heating the waste oil at temperatures between 120 and 170 °C. At these temperatures, the heated oil rapidly evaporates the water contained in the sludge, leaving the oil itself. After approximately 10 min, the water content of the sludge was less than 10%, and its heating value surpassed 5300 kcal/kg. Indeed, this makes the organic sludge appropriate for use as a solid fuel. The wastewater sludge used in this study was the designated waste discharged from chemical, leather and plating plants. These samples varied in characteristics, especially with regard to heavy metal concentration. After drying the three kinds of wastewater sludge at oil temperatures 160 °C for 10 min, it was found that the water content in the sludge from the chemical, leather, and plating plants reduced from 80.0 to 5.5%, 81.6 to 1.0%, and 65.4 to 0.8%, respectively. Furthermore, the heat values of the sludge from the chemical, leather, and plating plants prior to fry-drying were 217, 264, and 428 kcal/kg, respectively. After drying, these values of sludge increased to 5317, 5983 and 6031 kcal/kg, respectively. The heavy metals detected in the sludge after drying were aluminum, lead, zinc, mercury, and cadmium. Most importantly, if the dried sludge is used as a solid fuel, these heavy metals can be collected from the dust collector after combustion.     

Effects of organic complexing ligands and soil organic matter on the metal adsorption/migration in soil

Abstract

The adsorption of heavy metals on soil from the Neihu Landfill Site in Taipei City was investigated in order to assess the ground water pollution problems. The effects of soil organic matter and the behaviors of organic complexing ligands like EDTA and humic acid to the overall adsorption process were studied and discussed. In explaining the results, the pH of soil system and the properties of the soil/aqueous interface were chosen as two significant and interacting factors for discussion. The concept of the specific adsorption mechanism was also demonstrated and discussed. The results showed that the complexing ligands existing in soil liquid phase have more influences than natural organic matter does. The competitive sequences of different organic matter contents indicated that organic functional sites preferentially bind with Cu and Cd. The presence of EDTA and humic acid which formed ligandlike complexes will reduce Cd adsorption efficiency. These effects will induce mobility and the fate of heavy metals in soils, such as bioavailability.     

Ammonium removal by a novel magnetically modified excess sludge

Disposal of nitrogen nutrient and excess sludge is a keen concern in wastewater treatment plants. This study describes a simple method of preparing an economical adsorbent, i.e., magnetic excess sludge (MES) by compounding the excess sludge with Fe₃O₄ nanoparticles. Ammonia–nitrogen removal from simulated wastewater was investigated by using the MES as an adsorbent. The MES had an adsorption efficiency of up to 90% for ammonium removal. Highly efficient separation of adsorbed ammonium on the MES could be magnetically separated from wastewater within 30 s. The operating conditions for ammonium adsorption were optimized at MES dose of 20 g/L, initial ammonium concentration of 45 mg/L and operating temperature of 298–308 K. The equilibrium data of ammonium adsorption on the MES showed a good agreement with the Langmuir isotherm, while the kinetic data were best fitted by the pseudo-second-order model. FTIR analysis indicated that various functional groups, such as hydroxyl and carboxyl groups, existed on the surface of the MES and contributed to the excellent capability for ammonium adsorption. These results suggest that the MES is a promising candidate for removing ammonium from wastewater and recycling excess sludge to ease its disposal at low cost.     

Single and combined effects of nickel (Ni(II)) and cobalt (Co(II)) ions on activated sludge and on other aerobic microorganisms: a review

Nickel (N(II)) and cobalt (Co(II)) are often encountered in wastewaters. As conventional wastewater treatment may only partially remove nickel and cobalt, a large fraction of the above metals is released to the aquatic environment. Both metals have been identified as micronutrients, at trace concentrations; however, they are both microbial growth inhibitors, at relatively high concentrations. On the other hand, the combined effects (e.g.: growth stimulation or toxicity) of the above metals have been found to differ from the summation of the effects which occur when the metals are applied individually. Moreover, a number of environmental factors (e.g.: pH, biomedium composition, biomass concentration, presence of other heavy metals) can affect the microbial toxicity of the above metallic species. The present review discusses, in a systematic way, the individual and joint effects of the above heavy metals to the growth of microorganisms grown under aerobic conditions, with focus on the growth of activated sludge. Data on multi-metal toxicity are particularly useful in establishing criteria for heavy metal tolerance levels in the environment.