High-frequency ultrasound treatment of sludge: combined effect of surfactants removal and floc disintegration

Ultrasounds represent an effective technology in many research fields. In sewage sludge treatment, low-frequency ultrasound, particularly at 20 kHz, are widely used for sludge disintegration before the anaerobic digestion, while in the last years novel application of high-frequency ultrasound regards the decontamination of water and wastewater through sonochemical reactions. The innovative approach presented in this paper is the treatment of sewage sludge with ultrasound at 200 kHz for obtaining efficient sludge disintegration and the removal of the linear alkylbenzenesulphonates (LAS) at the same time. Results of the sonolysis experiments showed that native LAS degradation up to 40% can be achieved with low power input in less than 1 h. The degradation pattern was different for each LAS homologue (from C10 to C13), because of their physical-chemical properties, in particular as regards the alkyl chain length. This high-frequency ultrasound irradiation resulted effective also in terms of floc disintegration and soluble organic matter release, in particular for energy inputs higher than 30,000 kJ/kg TS. The disrupting effect of the 200 kHz treatment was also evaluated by microscope analyses and determination of the extracellular polymeric substances release in the liquid phase.     

Stabilization of biosolids with nanoscale zero-valent iron (nZVI)

Biosolids are the treated organic residuals, also known as sludge, that are generated from domestic wastewater treatment plants. According to the USEPA, over 7 millions tons (dry weight) of biosolids are generated every year in the US by more than the 16,000 wastewater treatment plants and a large portion of these biosolids is disposed on land. Nuisance odors, the potential of pathogen transmission, and presence of toxic and persistent organic chemicals and metals in biosolids have for the most part limited the use of land applications. This paper presents zero-valent iron nanoparticles (1–100 nm) for the treatment and stabilization of biosolids. Iron nanoparticles have been shown to form stable and nonvolatile surface complexes with malodorous sulfur compounds such as hydrogen sulfide and methyl sulfides, degrade persistent organic pollutants such as PCBs and chlorinated pesticides, and sequestrate toxic metal ions such as mercury and lead. The end products from the nanoparticle reactions are iron oxides and oxyhydroxides, similar to the ubiquitous iron minerals in the environment. Due to the large surface area and high surface reactivity, only a relatively low dose (<0.1% wt) of iron nanoparticles is needed for effective biosolids stabilization. The iron nanoparticle technology may thus offer an economically and environmentally sustainable and unique solution to one of the most vexing environmental problems.     

超声波强化一次污泥沉降与脱水性能的研究

本文就超声波处理对一次污泥强化沉降与脱水性能进行了研究。对污泥性质中的SV、滤饼含水率、比阻、粘度等进行了分析。分析表明短时间的超声作用可以提高污泥脱水和沉降性能,超声处理7s后滤饼含水率降低2.9%；超声10s时粘度和比阻值最小,比原污泥分别减小29.4%和24.2%；15s后污泥沉降速率是原污泥的3.7倍。如投加絮凝剂,投加量为0.054g/L时污泥沉降速率最快,最终污泥体积为84.5%,粘度值最低,为84.5mpa·s。加入超声10s作用后,最佳絮凝剂投加量为0.027g/L,且最终污泥体积比单独投加0.054g/L时减小4%,粘度值降低14.8%。超声波与絮凝剂的联用可以改善污泥脱水性能和沉降性能,减小絮凝剂的量达一半以上。     

Assessment of sonotrode and tube reactors for ultrasonic pre-treatment of two different sewage sludge types

The effectiveness of tube and sonotrode reactors for the sonication of sewage sludge under identical conditions was compared for the first time. Despite the considerable structural differences, sonication with each ultrasonic reactor led to an accelerated degradation rate and an increased methane production within the first five days for the majority of the sewage sludge samples tested. On closer examination, however, it becomes clear that the investigated sonication systems are not equally suitable for the substrates considered. While the use of a sonotrode proved to be particularly advantageous for the treatment of waste activated sludge (+25% methane yield at 300 kJ/kg_TS), the use of a 2-inch tube reactor achieved the highest enhancement for low-intensity sonication in digested sludge (+22% methane yield at 300 kJ/kg_TS). With increasing energy input, more chemical oxygen demand was solubilized, but this did not result in an increase in methane yield for all samples. Sonication of waste activated sludge led to a significant reduction in viscosity of up to 50%, and a reduction of up to 60% was observed after sonication of digested sludge with low energy inputs. The study, therefore, demonstrates that the choice of the most suitable sonication system essentially depends on the properties of the sludge to be sonicated.     

Ultrasonic treatment on activated sewage sludge from petro-plant for reduction

In this essay, the influences of low frequency ultrasound (20 kHz) on dewater ability and anaerobic digestion behaviors of activated sewage sludge, obtained from Yangzi Water Treatment Plant, Yangzi Petrochemical Corporation, were discussed. Ultrasound pretreatment could enhance the filtration progress and decrease the moisture content of the sludge from 99% to 80%. Together with flocculant, the ultrasound pretreatment decreased the specific filtration resistance (SFR) of the sludge from 3.59 x 10(12) m/kg to 1.18 x 10(12) m/kg and saved about 25-50% of the flocculant dosage. Bound water of the sludge was measured by dilatometer. After 2-4 min treatment of ultrasound under intensity of 400 W/m(2), the bound water of sludge decreased from 16.7 g/g (dry base) to above 2.0 g/g (dry base). Ultrasound pretreatment could also enhance digestion and reduce digestion time. To the same resolution ratio, such as 49%, the digestion time of sludge with ultrasound pretreatment was 7 days less than that without ultrasound. Proper ultrasound pretreatment could also improve the dewater ability of the digested sludge, the final moisture of which was 73.7%.     

Ultrasound assisted method to increase soluble chemical oxygen demand (SCOD) of sewage sludge for digestion

The aim of this study was to clarify the possibilities to increase the amount of soluble chemical oxygen demand (SCOD) and methane production of sludge using ultrasound technologies with and without oxidising agents. The study was done using multivariate data analyses. The most important factors affected were discovered. Ultrasonically assisted disintegration increased clearly the amount of SCOD of sludge. Also more methane was produced from treated sludge in anaerobic batch assays compared to the sludge with no ultrasonic treatment. Multivariate data analysis showed that ultrasonic power, dry solid content of sludge (DS), sludge temperature and ultrasonic treatment time have the most significant effect on the disintegration. It was also observed that in the reactor studied energy efficiency with high ultrasound power together with short treatment time was higher than with low ultrasound power with long treatment time. When oxidising agents were used together with ultrasound no increase in SCOD was achieved compared the ultrasonic treatment alone and only a slight increase in total organic carbon of sludge was observed. However, no enhancement in methane production was observed when using oxidising agents together with ultrasound compared the ultrasonic treatment alone. Ultrasound propagation is an important factor in ultrasonic reactor scale up. Ultrasound efficiency rose linearly with input power in sludge at small distances from the transducer. Instead, ultrasound efficiency started even to decrease with input power at long distances from the transducer.     

Effect of electric field on activated sludge in water

The results of the study of the effect of a dc electric field on activated sludge of aeration tanks. It is experimentally detected that the specific oxidation rate of organic compounds by activated sludge increases up to 90.5% with electric field processing, and then decreases. The observed effect is substantiated. The results obtained can find wide application in purification of sewage polluted by organic compounds.     

A review on hybrid techniques for the degradation of organic pollutants in aqueous environment

The creation of the modern world requires many industrial sectors, however, sustainability needs to be considered while developing industries. In particular, organic pollutants generated by many of these industries contaminate the environment leading to health and other issues. Advanced oxidation processes (AOPs) have been introduced to remove organic pollutants present in wastewater. Sonolytic degradation of organic pollutants is considered as one of the AOPs, however, this process has its limitations. In order to overcome the limitations, hybrid techniques involving ultrasound and other AOPs have been developed. That is, ultrasound combined with heterogeneous AOPs (ultrasound/metal ions, ultrasound/metal oxides, and ultrasound/photocatalysis) and homogeneous AOPs (ultrasound/ozone, ultrasound/H₂O₂, and ultrasound/persulfate) for the degradation/mineralization of organic pollutants. This review highlights the advantages of using hybrid techniques involving ultrasound for the degradation of organic pollutants in aqueous solutions.     

电感耦合等离子体质谱法测定城市污泥中重金属的活性形态

以沈阳北部、满堂河、仙女河三个污水处理厂的污泥为研究对象,选择水、醋酸和不同极性的有机溶剂对其进行浸提分离,采用ICP-MS测定了污泥中主要污染的重金属元素各活性形态的含量,并探讨了Cr,Cu,Zn,Cd和Pb随环境条件的改变其活性形态含量的变化规律及其影响因素。结果表明：城市污泥中重金属的醋酸浸提态含量较高,水溶态含量较低,二者随时间和温度条件的变化呈一致的规律性,有机浸提态重金属的含量与溶剂极性大小呈正相关性。醋酸浸提态重金属在迁移转化过程中具有较大活性,同一形态重金属的活性次序为：水溶态Zn＞Cu＞Cd＞Pb＞Cr,醋酸浸提态Cd＞Cr＞Cu＞Zn＞Pb,有机浸提态Pb＞Cd＞Cr＞Cu＞Zn。     

Ultrasonic cell disruption of stabilised sludge with subsequent anaerobic digestion

The world-wide increasing environmental awareness and its subsequent regulations have led to the application of improved technologies in wastewater purification plants. This has resulted in higher wastewater and sludge productions. Sludge is the by-product of such plants and it is not only rich in organic carbon and pathogens but also in heavy metals and other environmental pollutants. In Europe, agricultural application of dried sludge (bio-solids) is confronted with negative reactions from the citizens, governmental organisations, farmers and the food industry. Ultrasonic disruption of sludge is a popular mechanical disruption process in sludge treatment. During ultrasonic treatment, high frequency acoustic signals are used to initiate the cavitation process. The applied ultrasonic field leads to a breakdown of cohesive forces of the liquid molecules resulting in the generation of cavitation bubbles. A shock wave is released by the collapse of the cavitation bubbles and propagates in the surrounding medium forming jet streams that cause the disruption of cells in sludge. Disruption of sludge cells enables the release of light organic substances into the sludge water thereby exposing them for further anaerobic digestion. This paper presents results on the disruption of conventionally stabilised sludge through the application of the ultrasonic field. In order to reduce the specific energy input (i.e. ratio of the consumed energy during ultrasonic disruption to the input sludge mass) and improve biogas production, the total solids content of the stabilised sludge was increased before disruption. The anaerobic digestion of sludge samples was carried out in a set of specially constructed laboratory anaerobic digesters. Results showed that subsequent anaerobic digestion of the ultrasonically disrupted sludge could improve biogas production with reduced sludge quantity that is vital to the economic consideration of the wastewater treatment plants. This process encourages the exploitation of valuable materials and energy from stabilised sewage sludge just before its final disposal. The negative effects of mixing disrupted sludge with its separated sludge water are also shown in this paper. This expresses the microbiological instability of the anaerobic process caused by the mixing process.     

Coupled high and low-frequency ultrasound remediation of PFAS-contaminated soils

Solids such as soils and sediments contaminated with per- and polyfluorinated alkyl substances (PFAS) from exposure to impacted media, e.g., landfill leachate or biosolids, direct contaminated discharge, and contaminant transport from atmospheric deposition, have caused significant environmental pollution. Such solids can act as secondary sources of PFAS for groundwater and surface water contamination. There are currently no proven technologies that can degrade PFAS in soil and sediments in a cost-effective, environmentally-friendly, and energy-efficient manner. This study examines the use of coupled high and low-frequency ultrasound in desorbing and degrading PFAS in soil, thereby achieving concurrent treatment and destruction of PFAS in soil. Two common PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were used to evaluate treatment performance in soils with both low and high organic matter contents. The test results showed that the ultrasound treatment could significantly reduce PFAS concentrations in artificially contaminated soil; however, no significant degradation was achieved. Ultrasound treatment did improve desorption of PFAS from solid particles, particularly from the highly absorbent organic soil; 68.8 ± 1.8% of PFOA and 45.4 ± 4.1% of PFOS were leached from the soil after ultrasound treatment compared to only 28 ± 0.2% of PFOA and 1 ± 3.1% of PFOS after desorption in water. This work shows that sonication treatment is an effective technology for the removal of PFAS from solids, however, the presence of solids in the solid–liquid slurry can negatively impact ultrasonic cavitation, inhibiting the sonolytic degradation of desorbed PFAS.     

生物炭对活性污泥沉降性能和反硝化作用的影响研究

Biochar is a massively produced by-product of biomass pyrolysis to obtain renewable energy and has not been fully used.Incomplete separation of sludge and effluent and insufficient denitrification of sewage are two of main factors that influence the efficiency of activated sludge process.In this work,we proposed a new utilization of biochar and investigated the effect of biochar addition on the performance of settleability and denitrification of activated sludge.Results show that the addition of biochar can improve the settleability of activated sludge by changing the physicochemical characteristics of sludge (e.g.,flocculating ability,zeta-potential,hydrophobicity,and extracellular polymeric substances constituents).Moreover,the dissolved organic carbon released from biochar obtained at lower pyrolysis temperature can improve the nitrate removal efficiency to a certain extent.     

超声波降解溴苯:操作参数与环境因素的影响

本文考察了用超声波降解水中溴苯的动力学与脱卤效应,并研究了重要的操作参数如强度与饱和气体,以及环境干扰因素如悬浮物、地表水其他杂质的影响。结果表明,超声波可以有效地处理溴苯,在20kHz,7.5W／cm2下一级反应常数达0.044／min,脱卤效率达58％。本研究范围内,声强度越高,反应越快。氧气和氩气下降解速率高于空气下。超声降解不受地表水中杂质、纳米级微粒、无机颗粒的影响,但有机悬浮物能在一定程度上干扰溴苯的超声降解。     

Multifractality analysis of crack images from indirect thermal drying of thin-film dewatered sludge

Crack formation is inevitable during sludge drying because of the existence of uneven thermal stress. Experiments have been conducted to study crack pattern formation in thin film sludge. Crack images show that the thinner the sewage sludge film, the more even the crack distribution. The crack changes from a flaky texture to a banded structure with increasing thickness. Multifractal methods are proposed to analyze the crack image of four different thicknesses of dried sludge. Several parameters are conducted for quantification of the crack image and the results indicate that the width of spectra increases with thicker sludge film, that is to say, nonunifromity of crack distribution increases with increasing thickness, which proves that the multifractal method is sensitive enough to quantify the crack distribution and can be seen as a new approach for the changing research of crack images of sewage sludge drying.     

Evaluation of focused ultrasound and ozonolysis as sample treatment for direct determination of mercury by FI-CV-AAS. Optimization of parameters by full factorial design

Different oxidation methodologies based on ozone and focused ultrasound for the degradation of organic matter and organic-mercury compounds (spiked) present in human urine are discussed. Inorganic and total mercury can be determined in human urine. A flow-injection cold-vapour atomic absorption spectrometer system was used for mercury measurements. Optimization of cold vapour generation was performed with NaBH4 and SnCl2. A two-level full factorial design (2(4)) was applied to understand the cross-effects among the variables influencing the degradation of organic-mercurials and organic matter in urine by KMnO4/HCl/focused ultrasound, namely, KMnO4 and HCl concentration, ultrasonication time and ultrasonication amplitude. Optimization results showed that all variables were significant. New trends in the application of focused ultrasound and ozone are highlighted. As a result of the optimization procedure, one simple, rapid and accurate method was developed for the determination of total mercury in urine samples The method is based on the ultrasound assisted degradation of organo-mercurials and organic matter in urine in the presence of KMnO4/HCl/Focused Ultrasound. The procedure can be accomplished within 3 min, using 50% sonication amplitude provided by a probe ultrasonic device (63 W maximum output power, 22.5 kHz frequency). The method was applied to measure the mercury content in spiked urine from different non-exposed volunteers.     

Evaluation on the air-borne ultrasound-assisted hot air convection thin-layer drying performance of municipal sewage sludge

The thin-layer drying behavior of the municipal sewage sludge in a laboratory-scale hot air forced convective dryer assisted with air-borne ultrasound was investigated in between 70 and 130 °C hot air temperatures. The drying kinetics in the convective process alone were compared to that for ultrasound-assist process at three ultrasound powers (30, 90, 150 W). The average drying rates within whole drying temperature range at ultrasound powers of 30, 90 and 150 W increased by about 22.6%, 27.8% and 32.2% compared with the convective drying alone (without ultrasound). As the temperature increasing from 70 °C to 130 °C, there were maximum increasing ratios for the effective moisture diffusivities of the sewage sludge in both falling rate periods at ultrasonic power of 30 W in comparison with other two high powers. In between the ultrasound powers of 0 and 30 W, the effect of the power on the drying rate was significant, while its effect was not obvious over 30 W. Therefore, the low ultrasonic power can be just set in the drying process. The values of the apparent activation energy in the first falling rate period were down from 13.52 to 12.78 kJ mol⁻¹, and from 17.21 to 15.10 kJ mol⁻¹ for the second falling rate period with increasing the ultrasonic power from 30 to 150 W. The values of the apparent activation energy in two falling rate periods with the ultrasound-assist were less than that for the hot air convective drying alone.     

Ultrasonics in the dehydration process of sludge

This paper discusses from the physico-chemical point of view the increase of the dehydration efficiency of sludge from some selected mineral and organic sewages as a result of preliminary ultrasound irradiation and the addition of ion-active flocculants.     

Oxygen-induced concurrent ultrasonic degradation of volatile and non-volatile aromatic compounds

Acoustic cavitation, induced by ultrasound, can be used to eliminate organic pollutants from water. This type of ultrasonic treatment of polluted water can be grouped with those generally referred to as advanced oxidative processes since it involves hydroxyl radicals. In this case these highly active species are generated from the dissociation of water and oxygen dissociation caused by cavitation bubble collapse. The cavitation induced degradation rates of organic compounds in water are mainly linked to their vapor pressure and solubility and here we will further explore these links by examining the degradation of a mixture of two materials with different physical properties, chlorobenzene and 4-chlorophenol. The results obtained when a dilute solution of a mixture of these compounds saturated with argon is subjected to sonication at 300 kHz, parallels previous observations achieved in an aerated aqueous medium at 500 kHz. The two compounds exhibit sequential degradation with the more volatile chlorobenzene entering the cavitation bubble and being destroyed first. The 4-chlorophenol degradation occurs subsequently only when the chlorobenzene has been completely destroyed. The two compounds exhibit different behavior when sonicated in water saturated with oxygen. Under these conditions the two compounds are degraded simultaneously, a remarkable result for which two explanations can be proposed, both of which are based on the formation of additional OH radical species: The ability to produce conditions for the simultaneous elimination of two organic compounds by the use of oxygen is of great importance in the developing field of ultrasonic water treatment.     

CFBC混烧城市污泥与煤:N2O和NO的排放

在0.15MWth CFBC试验台上混烧城市污泥与煤,当城市污泥的含水率和混烧率分别变化在30％～60％和25％～100％之间时,可以实现稳定燃烧。分析了炉膛温度和城市污泥混烧率对NO和N_oO生成浓度的影响。结果显示,在焚烧氮含量很高的城市污泥过程中,通过适当提高炉膛温度,可以控制N_2O的生成,但是NO的生成浓度主要与混烧率有关。     

Degradation of chlortetracycline in wastewater sludge by ultrasonication,Fenton oxidation,and ferro-sonication

Residual emerging contaminants in wastewater sludge remain an obstacle for its wide and safe applications such as landfilling and bio-fertilizer. In this study, the feasibility of individual ultrasonication (UlS) and Fenton oxidation (FO) and combined, Ferro-sonication processes (FO) on the degradation of chlortetracycline (CTC) in wastewater sludge was investigated. UlS parameters such as amplitude and sonication time were optimized by response surface methodology (RSM) for further optimization of FS process. Generation of highly reactive hydroxyl radicals in FO and FS processes were compared to evaluate the degradation efficiency of CTC. Increasing in the ratio of hydrogen peroxide and iron concentration showed increased CTC degradation in FO process; whereas in FS, an increase in iron concentration did not show any significant effect (p > 0.05) on CTC degradation in sludge. The estimated iron concentration in sludge (115 mg/kg) was enough to degrade CTC without the addition of external iron. The only adjustment of sludge pH to 3 was enough to generate in-situ hydroxyl radicals by utilizing iron which is already present in the sludge. This observation was further supported by hydroxyl radical estimation with adjustment of water pH to 3 and with and without the addition of iron. The optimum operating UlS conditions were found to be 60% amplitude for 106 min by using RSM. Compared to standalone UlS and FO at 1:1 ratio, FS showed 15% and 8% increased CTC degradation respectively. In addition, UlS of sludge increased estrogenic activity 1.5 times higher compared to FO. FS treated samples did not show any estrogenic activity.