Effects of ultrasonic disintegration of excess sewage sludge

Ultrasonic disintegration of excess sludge is used as a process preceding the stabilization of sludge in wastewater treatment plants. It has a task of intensifying the anaerobic digestion of the organic fraction of sludge due to the fragmentation of its particles and destruction of microorganisms. Amount of energy put into process is the strongest factor determining type and intensity of disintegration. Physicochemical properties of sludge, operational variables and construction of installation have to be considered as well. The research have shown the effects of disintegration of various sludge conducted in disintegrators of varying heads and emitter structures, but at the same energy density E_V kW h m⁻³.     

Optimizing dewaterability of drinking water treatment sludge by ultrasound treatment: Correlations to sludge physicochemical properties

Sludge dewatering has proven to be an effective method to reduce the volume of sludge. In this study, drinking water treatment sludge (DWTS) was treated by ultra-sonication under variable conditions comparing two sonoreactor types (bath and probe), four frequencies (25, 40, 68, 160 kHz) and four energy density levels (0.03, 1, 3, 5 W/mL). The effects of these conditions were studied using specific resistance to filtration and capillary suction time as measures of dewaterability, and floc size, the Brunauer, Emmett and Teller (BET) specific surface area and Zeta potential to determine treated sludge characteristics. The results indicated that the dewaterability of sonicated sludge improved at relatively low energy densities of 0.03 and 1.0 W/mL, while an optimum for sonication duration (within 10 min) was also identified. Higher frequencies (tested up to 160 kHz) with acoustic energy density of 0.03 W/mL also reduced the dewatering property. At higher energy densities of 3.0 and 5.0 W/mL, dewaterability of sludge deteriorated regardless of ultra-sonication time, with an increase of solubilized organic matter content and severely changed floc characteristics. The deterioration of the dewatering capacity was closely related to the considerably reduced floc sizes, dissolution of proteins and polysaccharides, and to the Zeta potential of sonicated sludge flocs. The dewaterability was not correlated with BET specific surface area. Mechanistic explanations for the observations were discussed by analyzing corrosion patterns of aluminum foil as a measure for cavitation field distribution.     

Development of a novel electric field-assisted modified hydrodynamic cavitation system for disintegration of waste activated sludge

In this current study, we present a modified hydrodynamic cavitation device that combines an electric field to substitute for the chemical addition. A modified HC system is basically an orifice plate and crisscross pipe assembly, in which the crisscross pipe imparts some turbulence, which creates collision events. This study shows that for maximizing disintegration, combining HC system, which called electric field-assisted modified orifice plate hydrodynamic cavitation (EFM-HC) in this study, with an electric field is important. Various HC systems were compared in terms of disintegration of WAS, and, among them, the EFM-HC system exhibited the best performance with the highest disintegration efficiency of 47.0 ± 2.0% as well as the destruction of WAS morphological characteristics. The experimental results clearly show that a conventional HC system was successfully modified. In addition, electric field has a great potential for efficient disintegration of WAS for as a additional option in a combination treatment. This study suggests continued research in this field may lead to an appropriate design for commercial use.     

Effects of ultrasonic reactor design on sewage sludge disintegration

The impact of ultrasound (US) reactor design on cavitation intensity distribution and disintegration efficiency was studied for sewage sludge pre-treatment, using a US flatbed reactor of variable reaction chamber height (RCH, 20–100 mm). Mapping of cavitation intensity and treatment effects was conducted using (i) hydrophone measurements, (ii) aluminum foil tests, and (iii) soluble chemical oxygen demand (COD) analyses. The overall disintegration efficiency was evaluated based on average COD solubilization. The impact of flow on treatment (in)homogeneity was additionally examined using computational fluid dynamics (CFD). Results of all measurement techniques suggest that small RCHs (20 mm, for instance) enable uniform and intense treatments, while large RCHs, which are subjected to strong sound wave attenuation, entail inhomogeneous treatments where large fractions of substrate are no longer exposed to notable cavitation activity. For instance, COD solubilization (relative to alkaline hydrolysis) measured in the channel center dropped from 6.4% to zero as RCH widened from 20 mm to 100 mm. Flow-through sonication further aggravates treatment inhomogeneity due to the high flow rates in the low-cavitation channel centers. Overall disintegration efficiency declined with increasing RCH, showing a drop in average COD solubilization by 73% from RCH = 20 mm to RCH = 100 mm. The drop correlated with average cavitation noise levels (R² = 0.82), indicating that hydrophone measurements may be a suitable tool for US reactor design optimization. Overall, results suggest that reactor geometry has a critical impact on both treatment (in)homogeneity and treatment efficiency and that equal specific energy inputs do not imply equal US treatments.     

A review on pharmaceuticals removal from waters by single and combined biological,membrane filtration and ultrasound systems

Contaminants of emerging concern (CEC) such as pharmaceuticals commonly found in urban and industrial wastewater are a potential threat to human health and have negative environmental impact. Most wastewater treatment plants cannot efficiently remove these compounds and therefore, many pharmaceuticals end up in aquatic ecosystems, inducing problems such as toxicity and antibiotic-resistance. This review reports the extent of pharmaceutical removal by individual processes such as bioreactors, advanced oxidation processes and membrane filtration systems, all of which are not 100% efficient and can lead to the direct discharge of pharmaceuticals into water bodies. Also, the importance of understanding biotransformation of pharmaceutical compounds during biological and ultrasound treatment, and its impact on treatment efficacy will be reviewed. Different combinations of the processes above, either as an integrated configuration or in series, will be discussed in terms of their degradation efficiency and scale-up capabilities. The trace quantities of pharmaceutical compounds in wastewater and scale-up issues of ultrasound highlight the importance of membrane filtration as a concentration and volume reduction treatment step for wastewater, which could subsequently be treated by ultrasound.     

Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters.     

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。     

Effect of ultrasound assisted cleaning on pesticide removal and quality characteristics of Vitis vinifera leaves

In this study, the pesticide (acetamiprid, deltamethrin, and pyridaben) removal and physicochemical quality improvement of vine (Vitis vinifera) leaf were examined using ultrasonic and traditional cleaning for 5, 10, and 15 min. After an ultrasonic cleaning procedure at 37 kHz for 10 min, acetamiprid, deltamethrin, and pyridaben in vine leaf were reduced by 54.76, 58.22, and 54.55 %, respectively. Furthermore, the total phenolic content (TPC) in vine leaf increased to 13.45 mg GAE/g DW compared to that in control samples using traditional cleaning (10.37 mg GAE/g DW), but there were no significant differences in DPPH radical scavenging activity. After 15 min of conventional cleaning, the total chlorophyll and total carotenoid content of leaves were found to be lowest among all samples, at 6.52 mg/kg and 0.48 mg/kg, respectively. In conclusion, when compared to conventional cleaning methods, ultrasonic cleaning with no chemicals or heat treatment has proven to be a successful and environmentally friendly application in reducing commonly used pesticides and improving the physicochemical qualities of leaves.     

The removal characteristics of natural organic matter in the recycling of drinking water treatment sludge: Role of solubilized organics

To clarify the role of solubilized organics derived from drinking water treatment sludge (DWTS) in the elimination of natural organic matter (NOM) in the DWTS recycling process, a probe sonoreactor at a frequency of 25 kHz was used to solubilize the organics at varied specific energies. The coagulation behavior related to NOM removal in recycling the sonicated DWTS with and without solubilized organics was evaluated, and the effect on organic fractionations in coagulated water was determined. The study results could provide useful implications in designing DWTS recycling processes that avoid the enrichment of organic matter. Our results indicate that DWTS was disrupted through a low release of soluble chemical oxygen demand (SCOD) and proteins, which could deteriorate the coagulated water quality under the specific energy of 37.87–1212.1 kW h/kg TS. The optimal coagulation behavior for NOM removal was achieved by recycling the sonicated DWTS without solubilized organics at 151.5 kW h/kg TS specific energy. Recycling the sonicated DWTS could increase the enrichment potential of weakly hydrophobic acid, hydrophilic matter, and <3 kDa fractions; the enrichment risks could be reduced by discharging the solubilized organics. Fluorescent characteristic analysis indicated that when recycling the sonicated DWTS without solubilized organics, the removal of humic-like substances was limited, whereas removal of protein-like substances was enhanced, lowering the enrichment potential of protein-like substances.     

Sonochemical effect of flat sweep frequency and pulsed ultrasound (FSFP) treatment on stability of phenolic acids in a model system

To obtain greater knowledge on the stability of phenolic acids for the application of FSFP ultrasound technique in the extraction, the sonochemical effects of ultrasonic factors were investigated. The kinetic model and mechanism of degradation reaction were developed and identified by FT-IR and HPLC-ESIMS. The results showed that caffeic and sinapic acids were degraded under FSFP ultrasound treatment. The ultrasonic temperature, frequency, sweep range, sweep cycle, and pulse ratio were proved to be important factors in affecting the degradation rates of caffeic and sinapic acids. Relatively high temperature, frequency away from the resonance frequency, narrow sweep range, moderate sweep cycle, and relatively low or high pulse ratio were recommended to maintain high stability of caffeic and sinapic acids. The degradation kinetics of these two phenolic acids under FSFP ultrasound treatment were conformed to zeroth-order reaction at 10–50 °C. Moreover, FSFP ultrasound had a stronger sonochemical effect on sinapic acid than caffeic acid. The FT-IR and HPLC-ESIMS proved that decomposition and polymerization reactions occurred when caffeic and sinapic acids were subjected to FSFP ultrasound. Degradation products, such as the corresponding decarboxylation products and their dimers, were tentatively identified.     

Effective removal of organics from Bayer liquor through combined sonolysis and ozonation: Kinetics and mechanism

The presence of organic compounds in the waste liquor is of serious environmental concern that has plagued the development of alumina industry (Bayer Process). The present work attempts to develop a green and efficient process for removal of organics utilizing combined effect of sonolysis and ozonation (US/O₃). The effects of reaction duration, ozone concentration and ultrasonic power are assessed for sonolysis (US), ozonation (O₃) and combination of sonolysis and ozonation (US/O₃). The optimal conditions for US/O₃ treatment system is identified to be a reaction duration of 7 h, ozone concentration of 7.65 g/h, and ultrasonic power of 600 W. The total organic carbon (TOC) removal and decolorization are 60.13% and 87.1%, respectively. The process can be scaled-up to industrial scale, which could potentially serve to be a convenient, safe and sustainable alternative to the exisiting treatment technologies. Additionally, the treated waste water can be reused contributing to an improvement in the overall economics.     

Alternate pulses of ultrasound and electricity enhanced electrochemical process for p-nitrophenol degradation

A novel alternated ultrasonic and electric pulse enhanced electrochemical process was developed and used for investigating its effectiveness on the degradation of p-nitrophenol (PNP) in an aqueous solution. The impacts of pulse mode, pH, cell voltage, supporting electrolyte concentration, ultrasonic power and the initial concentration of PNP on the performance of PNP degradation were evaluated. Possible pathway of PNP degradation in this system was proposed based on the intermediates identified by GC–MS. Experimental results showed that 94.1% of PNP could be removed at 2 h in the dual-pulse ultrasound enhanced electrochemical (dual-pulse US-EC) process at mild operating conditions (i.e., pulse mode of electrochemical pulse time (T_EC) = 50 ms and ultrasonic pulse time (T_US) = 100 ms, initial pH of 3.0, cell voltage of 10 V, Na₂SO₄ concentration of 0.05 M, ultrasonic powder of 48.8 W and initial concentration of PNP of 100 mg/L), compared with 89.0%, 58.9%, 2.4% in simultaneous ultrasound enhanced electrochemical (US-EC) process, pulsed electrochemical (EC) process and pulsed ultrasound (US), respectively. Moreover, energy used in the dual-pulse US-EC process was reduced by 50.4% as compared to the US-EC process. The degradation of PNP in the pulsed EC process, US-EC process and dual-pulse process followed pseudo-first-order kinetics. Therefore, the dual-pulse US-EC process was found to be a more effective technique for the degradation of PNP and would have a promising application in wastewater treatment.     

The effects and mechanism of phycocyanin removal from water by high-frequency ultrasound treatment

The effects and mechanism of phycocyanin removal from water by high-frequency ultrasound treatment were studied. The efficiency of sonication treatment in removing proteins derived from algal cells was investigated, and the factors influencing the process, including the effects of coagulation, were also studied. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the three-dimensional fluorescence spectrum, and mass spectrum were used to illustrate the removal mechanism. The results indicated that phycocyanin can be degraded to the point where it is barely detectable in water samples after 180 min of high-frequency sonication. While the total nitrogen (TN) concentration remained consistent during the entire sonication process (240 min), about 78.9% of the dissolved organic nitrogen (DON) was oxidized into inorganic nitrogen. The sonication effect was greatly influenced by the ultrasound frequency, with 200 kHz having the highest removal performance due to the large production of hydroxyl (HO) radicals. Coagulation was adversely influenced by sonication in the first 60 min due to the cross-linking reaction between protein molecules caused by the sonication. The influence of sonication weakened with sonication time due to the further degradation of the proteins by ultrasound. The variation of the TN, DON, and inorganic nitrogen indicated that the main mechanism occurring during the high-frequency sonication of the phycocyanin was the direct oxidation of the radicals, which was totally different from of the mechanism occurring during ultrasound with low frequency.     

Biological effects of combined ultrasound and cisplatin treatment on ovarian carcinoma cells

The effects of low-power ultrasound, the anti-cancer drug cisplatin, and their combined application were studied in two lines of human ovarian carcinoma cells, A2780 and A2780cis. Four modes of treatment were used: exposure to ultrasonic field, application of cisplatin, exposure to ultrasound followed by cisplatin, and presence of cisplatin followed by exposure to application ultrasound. Ultrasound was used at intensities of 0.5 W/cm² and 1.0 W/cm² for 10 min, cisplatin was applied at concentrations of 1 μM and 6 μM per cell suspension treated in A2780 and cisplatin-resistant A2780cis cells, respectively. The results of each experimental treatment were assessed by the resultant cell viability related to the viability of control cells, using a standard MTT test. It was shown that a combined effect of ultrasound and cisplatin was more effective than that of ultrasound or cisplatin alone. It also appeared that the order of application played a role, with the cisplatin-ultrasound treatment lowering cell viability more than the ultrasound-cisplatin treatment. It can be assumed that the exposure of cells to a low-power ultrasonic field has an immediate effect on the structure of cell surfaces and, consequently, on entry of cisplatin into the cell.The study also included observations on changes in the cell cycle associated with the treatments used in both cell lines and their evaluation by flow cytometry.     

The effect of ultrasound on the structure and properties of the water-soluble corn hull heteroxylan

Ultrasonic irradiation of a water-soluble corn hull xylan fraction in neutral and alkaline aqueous medium has been found to produce significant changes in its molecular properties. Degradation is first manifested by a decrease in the large molar mass component under generation of polymer chains with about the same size as those of the main molar mass component. The latter is slightly shifted to the lower molar mass region only at stronger irradiation conditions. Ultrasonication of the xylan in neutral aqueous medium at high ultrasound power and/or long irradiation caused no significant changes in its sugar composition, primary structure and viscoelastic properties.     

Effect of hydrodynamic disintegration on the solubilisation and bioavailability of thickened excess sludge

The main objective of the study was the verification whether conducting the hydrodynamic disintegration (HD) of thickened excess sludge (TES) before the anaerobic hydrolysis (AH) can cause an increase in the efficiency of the hydrolysis process, and therefore a reduction in its duration, or allow for complete omission of the stage before the anaerobic digestion (AD). For this purpose, the HD (conducted in five levels of energy density (E_L): 140, 280, 420, 560 and 700 kJ/L) of TES was carried out, and then all sludges (before and after disintegration) were subjected to the AH. The obtained results confirmed that the process of HD can be an effective method of increasing the solubilisation and bioavailability of TES. In the process of HD, the maximum increase in ΔVFA (308–428 mg VFA/L), was reported when E_L was increased from 140 to 280 kJ/L (the solubilisation degree increased from approximately 2 to 8%). The obtained results also showed that the ΔSTN and ΔSTP were related to solubilisation degree. The most intensive increase in the ΔSTN was determined for solubilisation degree in a range of 15–20%. In the case of ΔSTP, constant intensity of release of the compounds to the sludge liquid was observed. The obtained results also confirmed that conducting the process of AH of disintegrated TES proved to change the SCOD value when contrasted with the value of this indicator at the start of the experiment (before hydrolysis): (i) the E_L equal to 140 and 280 kJ/L allowed for a higher SCOD value; (ii) at E_L higher or equal to 560 kJ/L it caused a decrease in the SCOD value.     

Combined treatment approaches based on ultrasound for removal of triazophos from wastewater

Pesticides have been the major contributors to the growth of agricultural productivity, but the wide spread use in the fields and discharge from the manufacturing industries have also contributed to environmental concerns. In the present work, degradation of triazophos (O,O-diethyl-O-(1-phenyl-1H-1,2,4-triazol-3-yl) phosphorothioate) as a model pollutant has been investigated using high volume continuous ultrasonic flow cell for the first time. Effect of power dissipation and initial pH on the extent of triazophos degradation using acoustic cavitation has been investigated initially. Under the optimized set of operating power dissipation and pH, effect of addition of hydrogen peroxide (ratio of C₁₂H₁₆N₃O₃PS (Triazophos):H₂O₂ over the range of 1:1–1:5), ozone (over the flow rate of 100–400 mg/h) and Fenton’s reagent (C₁₂H₁₆N₃O₃PS:FeSO₄:H₂O₂ ratio over the range of 1:1:1–1:4:4) has been investigated as possible process intensification strategy. Combined operation of US with H₂O₂ and Ozone resulted in 48.6% and 54.6% triazophos degradation respectively whereas combination of US and Fenton’s reagent resulted in maximum degradation as 92.2% and also resulted in maximum COD removal as 88.5%. The study also focused on identification of intermediate products formed during the degradation as well as establishing the kinetic rate constants and the synergistic index for different approaches. The study has established that cavitation can be effectively used for triazophos degradation with significant intensification benefits based on the use of combination approach.     

Effects of Ca and Na acetates on nitrogen transformation during sewage sludge pyrolysis

The study reports the effects of Ca and Na acetates on the transformation of nitrogen species during sewage sludge pyrolysis. Sludge samples, with or without acetates, were pyrolysed in a fix-bed reactor at 150–550 °C, and the nitrogen species in the pyrolysis products (char, tar, and gas) were characterised and quantified. Ca and Na acetates distinctly affect nitrogen transformation during sludge pyrolysis, which is ascribable to their different catalytic activities for the decomposition of nitrogen species in sludge. The addition of Ca acetate is found to increase nitrogen retention in char and reduce the formation of nitrogen species in tar, which is mainly due to the suppressed decomposition of protein-N as well as the promoted formation of stable nitrogen species in char. On the other hand, the addition of Na acetate enhances the decomposition of nitrogen species in sludge, such as protein- and inorganic-N. The levels of both Ca and Na acetates are significantly reduced in the nitrogen-containing gas emissions because acetone is produced when acetates are heated, and acetone readily reacts with NH₃ to produce binary clusters or amines. Our results show that acetate addition is an important strategy for the reduction of NH₃ emission during sludge pyrolysis.     

Optimal dosage of ultrasound contrast agent for ultrasound surgery: Thermal effect of linear plane wave

The optimal dosage of ultrasound contrast agent model for ultrasound surgery was explored. A specific ultrasound contrast agent Albunex^® was chosen for simulation. The model was developed based on a dilute bubbly liquid model proposed by Ye and Ding [Z. Ye, L. Ding, Acoustic dispersion and attenuation relations in bubbly mixture, J. Acoust. Soc. Am. 98 (3) (1995) 1629–1636]. The numerical simulation suggests that 2 MHz is more efficient than 1 MHz to thermally treat cancer in deep tissue with the optimal dosage of 3 ml. On the other hand, the simulation also suggests 3 MHz center frequency with the optimal dosage of 1.6 ml is adequate for prostate cancer treatment with transrectal equipment. The simulation is expected to valid up to 2 MPa incident pressure due to the limitation of the linearized UCA model. Even though it is developed from a single ultrasound contrast agent, this model is expected to be useful for any ultrasound contrast agent as long as the necessary parameters are provided.     

Ultrasonic degradation, mineralization and detoxification of diclofenac in water: Optimization of operating parameters

The 20 kHz ultrasound-induced degradation of non-steroidal, anti-inflammatory drug diclofenac (DCF) was investigated. Several operating conditions, such as power density (25–100 W/L), substrate concentration (2.5–80 mg/L), initial solution pH (3.5–11), liquid bulk temperature and the type of sparging gas (air, oxygen, argon), were tested concerning their effect on DCF degradation (as assessed measuring absorbance at 276 nm) and hydroxyl radicals generation (as assessed measuring H₂O₂ concentration). Sample mineralization (in terms of TOC and COD removal), aerobic biodegradability (as assessed by the BOD₅/COD ratio) and ecotoxicity to Daphnia magna and Artemia salina were followed too.DCF conversion is enhanced at increased applied power densities and liquid bulk temperatures, acidic conditions and in the presence of dissolved air or oxygen. The reaction rate increases with increasing DCF concentration in the range 2.5–5 mg/L but it remains constant in the range 40–80 mg/L, indicating different kinetic regimes (i.e. first and zero order, respectively). H₂O₂ production rates in pure water are higher than those in DCF solutions, implying that decomposition basically proceeds through hydroxyl radical reactions. Mineralization is a slow process as reaction by-products are more stable than DCF to total oxidation; nonetheless, they are also more readily biodegradable. Toxicity to D. magna increases during the early stages of the reaction and then decreases progressively upon degradation of reaction by-products; nevertheless, complete toxicity elimination cannot be achieved at the conditions in question. Neither the original nor the treated DCF samples are toxic to A. salina.