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Effect of the sequence ultrasonic operation on anaerobic degradation of sewage sludge
... For raw sludge, the COD concentration in the overlying liquid was 152 ± 14 mgO 2 /L [33]. Other studies focused on the use of ultrasonic disintegration for the pretreatment of excessive sewage sludge [75]. They showed that the COD concentration in the supernatant reached 4537.5 mg/L after 30 min of ultrasonic exposure. ...
... For raw sludge, the COD concentration in the overlying liquid was 152 ± 14 mgO2/L [33]. Other studies focused on the use of ultrasonic disintegration for the pretreatment of excessive sewage sludge [75]. They showed that the COD concentration in the supernatant reached 4537.5 mg/L after 30 min of ultrasonic exposure. ...
... They showed that the COD concentration in the supernatant reached 4537.5 mg/L after 30 min of ultrasonic exposure. In the raw sludge, the COD content in the overlying liquid was 227.5 ± 27.5 mg/L [75]. Park et al. (2013) [76], on the other hand, used ultrasonic disintegration to process microalgal biomass. ...
There is a need to find methods to intensify the anaerobic digestion process. One possibility is the use of pretreatment techniques. Many laboratory tests confirm their effectiveness, but in most cases, there is no verification work carried out on industrial plants. A reliable and complete evaluation of new solutions can only be carried out in plants that reflect operating conditions at a higher readiness technological level. This has a direct impact on the scientific value and, above all, on the high application value of innovative technologies. The aim of our research carried out under laboratory conditions and on a large scale was to determine the technological and energy efficiency of the use of hydrodynamic cavitation in the pretreatment of a waste mixture from dairy farms. It has been shown that hydrodynamic cavitation significantly increases the concentration of organic compounds in the dissolved phase. In the most effective variants, the increase in the content of these indicators was over 90% for both COD and TOC. The degree of solubilisation achieved was 49 ± 2.6% for COD and almost 52 ± 4.4% for TOC. Under laboratory conditions, the highest effects of anaerobic digestion were achieved after 10 min of pretreatment. The amount of biogas was, on average, 367 ± 18 mL/gCOD, and the amount of methane was 233 ± 13 mL/gCOD. Further large-scale optimisation trials showed that after 8 min of hydrodynamic cavitation, the biogas yield was 327 ± 8 L/kgCOD with a CH4 content of 62.9 ± 1.9%. With this variant, the net energy yield was 66.4 ± 2.6 kWh/day, a value that was 13.9% higher than the original variant with 10 min of disintegration and 3.1% higher than the variant without pretreatment.
... For raw sludge, the COD concentration in the overlying liquid was 152±14 mgO2/L [33]. Other studies focused on the use of ultrasonic disintegration for the pretreatment of excessive sewage sludge [72]. They showed that the COD concentration in the supernatant reached 4537.5 mg/L after 30 minutes of ultrasonic exposure. ...
... They showed that the COD concentration in the supernatant reached 4537.5 mg/L after 30 minutes of ultrasonic exposure. In the raw sludge, the COD content in the overlying liquid was 227.5±27.5 mg/L [72]. Park et. ...
There is a need to find methods to intensify the anaerobic digestion process. One possibility is the use of pre-treatment techniques. Many laboratory tests confirm their effectiveness, but in most cases, there is no verification work carried out on industrial plants. The aim of the research carried out under laboratory conditions and on a large scale was to determine the technological and energy efficiency of the use of hydrodynamic cavitation in the pre-treatment of a waste mixture from dairy farms. It has been shown that hydrodynamic cavitation significantly increases the concentration of organic compounds in the dissolved phase. In the most effective variants, the increase in the content of these indicators was over 90% for both COD and TOC. The degree of solubilisation achieved was 49±2.6% for COD and almost 52±4.4% for TOC. Under laboratory conditions, the highest effects of anaerobic digestion were achieved after 10 minutes of pre-treatment. The amount of biogas was on average 367±18 mL/gCOD and the amount of methane 233±13 mL/gCOD. Further large-scale optimisation trials showed that after 8 minutes of hydrodynamic cavitation, the biogas yield was 327±8 L/kgCOD with a CH4 content of 62.9±1.9%. With this variant, the net energy yield was 66.4±2.6 kWh/day, a value that was 13.9% higher than the original variant with 10 minutes of disintegration and 3.1% higher than the variant without pre-treatment.
... Compared to other sludge pretreatment methods such as electric pulse, acid/alkali treatment and ozone oxidation, the operations and required devices for TH, EH and FNA hydrolysis (FNAH) are relatively simple and environmentfriendly. However, current research and application of sludge pretreatment methods mostly aim to reduce the sludge volume or to recover carbon sources by promoting sludge disaggregation (Li et al., 2016;Chi et al., 2018;Yu et al., 2018). Few studies have focused on the N, P release and recovery from the sludge hydrolysate after pretreatments. ...
... It is composed of various physical (pressure pulses, shear forces, high local temperatures) and chemical side effects (decomposition of H 2 O mainly to % OH and other radicals). Ultrasonic cavitation has been proven to be efficient for the intensification of oxidation reactions (H 2 O 2 and % OH) [9,10] and for the destruction of bacteria [11][12][13]. It provides significantly higher rates for the Weissler reaction (oxidation of iodide to https://doi.org/10.1016/j.ultsonch.2020.105002 ...
Please cite this article as: J. Kosel, M. Šuštaršič, M. Petkovšek, M. Zupanc, M. Sežun, M. Dular, Application of (super)cavitation for the recycling of process waters in paper producing industry, Ultrasonics Sonochemistry (2020), Abstract In paper production industry, microbial contaminations of process waters are common and can cause damage to paper products and equipment as well as the occurrence of pathogens in the end products. Chlorine omission has led to the usage of costly reagents and products of lower mechanical quality. In this study, we have tested a rotation generator equipped with two sets of rotor and stator assemblies to generate developed cavitation (unsteady cloud shedding with pressure pulsations) or supercavitation (a steady cavity in chocked cavitation conditions) for the destruction of a persistent bacteria Bacillus subtilis. Our results showed that only supercavitation was effective and was further employed for the treatment of waters isolated from an enclosed water recycle system in a paper producing plant. The water quality was monitored and assessed according to the chemical (COD, redox potential and dissolved oxygen), physical (settleable solids, insolubles and colour intensity) and biological methods (yeasts, aerobic and anaerobic bacteria, bacterial spores and moulds). After one hour of treatment, a strong 4 logs reduction was achieved for the anaerobic sulphate reducing bacteria and for the yeasts; a 3 logs reduction for the aerobic bacteria; and a 1.3 logs reduction for the heat resistant bacterial spores. A 22 % reduction in COD and an increase in the redox potential (37 %) were observed. Sediments were reduced by 50 % and the insoluble particles by 67 %. For bacterial destruction in real industrial process waters, the rotation generator of supercavitation spent 4 times less electrical energy in comparison to the previously published cavitation treatments inside the Venturi constriction design.
... 4 Moreover, the utilization of UT in the AD process can facilitate the disintegration of solids while enhancing the effects of ultrasonic cavitation. 5 Intermittent UT exposure achieved high degradation efficiency because both high and low density ultrasound radiations were applied within the same ultrasound system. Therefore, the utilization of intermittent UT inside the sludge disintegration reactor was justied. ...
This study proposed a sludge degradation system comprised of: (i) an ultrasound treatment (UT) system to disintegrate sludge; (ii) an up flow anaerobic sludge blanket (UASB) reactor to degrade the disintegrated sludge; and (iii) a microbial electrolysis cell (MEC) in replacement of a three-phase UASB separator to deeply degrade the disintegrated sludge. The influence of the ultrasound power, the temperature, and the voltage on the sludge degradation process was discussed. The experimental results showed that the UT unit effectively promoted sludge disintegration, thereby leading to deterioration of the quality of the reactor effluent. The temperature and the voltage parameters were found to be key for the anaerobic degradation (AD) process within this system. The volatile suspended solid concentration in the effluent was maintained at 320–380 mg L⁻¹ (ca. 0.08 times the raw sludge concentration), thereby validating the utilization of MEC as a three-phase separation unit. The total chemical oxygen demand removal was maintained at 61.3% during 5 days of AD upon intermittent exposure of the sludge to the UT unit, thereby showing that the system can effectively degrade solid organic matter. The bacterial community structure of the raw sludge significantly changed, with the high biodiversity of this system increasing the ecological stability. This system can degrade sludge with high efficiency and could be used in further engineering applications.
... Some researchers indicated that transesterification process affected the biodiesel yield from excess sludge (Mondala et al., 2009;Li et al., 2016a). Ultrasonic pretreatment could improve treatment efficiency of sludge anaerobic degradation (Li et al., 2016b). The addition of n-hexane could improve fat solubility from microorganisms (Wu et al., 2017). ...
Biodiesel is a renewable and environmentally friendly energy source. The use of biological wastewater treatment systems for excess sludge in the biodiesel production can achieve both sludge reduction and resource recovery. In this study, an in situ one-step method for producing biodiesel from excess secondary sludge was investigated; then the differences in both biodiesel yield and composition produced from the five industrial wastewater sludges and two municipal wastewater sludges were studied. The results showed that ultrasonic pretreatment of sludge was not necessary for biodiesel production by in situ acid-catalyzed transesterification. The addition of n-hexane during transesterification was significant to determine the performance of biodiesel production. Significant differences were found in yield and composition of the sludge lipid from seven different types of wastewater. The sludge oil of starch wastewater and restaurant wastewater was significantly higher than those of tannery wastewater, landfill leachate, and livestock wastewater, which was mainly due to the significant differences on wastewater quality and sludge microbial structure. The higher organic content (especially sugar), COD/TN and COD/TP ratios and better biodegradability in wastewater led to the dominance of Saprospiraceae and Anaerolineaceae, finally benefited the lipid accumulation in excess secondary sludge for biodiesel production.
... This results in a faster assimilation of the hydrolyzed components by the microorganisms, resulting in a higher rate of transformation and degradation in the reactors with sonicated sludge compared to the control reactor fed raw WAS. Other studies have also reported an increase in the soluble fraction of organic components through the sonication of sludge (Houtmeyers et al., 2014;Li et al., 2016). ...
Anaerobic digestion (AD) is the most widely used method to stabilize and recover energy from waste activated sludge (WAS). However, AD of sludge results in a low biogas yield. Ultrasonic pretreatment (USp) is the most effective sludge disintegration technology and has elicited interest to increase the biodegradability and improve the efficiency of the AD. This study investigated the influence of USp on the semicontinuous AD of WAS as a strategy to increase its performance. During an experiment lasting 90 days, 0.8-L digesters were semicontinuously fed under different conditions: raw sludge and sonicated at 15000, 25000 and 35000 kJ/kg TS (total solids); and an increase of the organic loading rate (OLR) from 1 to 3 kgVS/m³·d, for 30 days each. The maximum biogas rate (0.218 L/d) was reached at 25000 kJ/kg TS and 3 kgVS/m³·d. The highest VS removal efficiency (23.7%) was observed at the highest USp and the lowest OLR. The reactors fed with raw sludge had a lower performance compared to the sonicated WAS in terms of VS reduction and biogas production. In contrast, the USp allowed the bioreactors to be operated at a high OLR (3 kgVS/m³·d) without inhibition. Finally, a kinetic analysis of accumulated biogas was performed.
... We recently reported that UT can mitigate solids disintegration while enhancing the effects of ultrasonic cavitation during AD. Thus, intermittent UT achieved higher degradation efficiencies in the same ultrasound system [14]. This system effectively disintegrated flocs in the sludge while releasing organic components from the sludge solids into the liquid phase, thereby accelerating the degradation of the organic matter in the sludge [3,10]. ...
This study proposes a process with the following steps: (i) use of ultrasound treatment (UT) to disintegrate sludge; (ii) application of an up-flow anaerobic sludge blanket (UASB) reactor to degrade the disintegrated sludge; and (iii) utilization of a microbial electrolysis cell (MEC) composed of graphite fiber brush and titanium in replacement of a three-phase UASB separator. The soluble chemical oxygen demand (SCOD) and protein concentration in the MEC effluent reached 569.5 and 373.1 mg/L, respectively, after 7 days of anaerobic degradation. The concentration of volatile suspended solid (VSS) in the MEC effluent was maintained at 320–380 mg/L (ca. 0.08% of raw sludge concentration), thereby revealing successful separation by MEC during sludge degradation. The total chemical oxygen demand (TCOD) concentration, TCOD removal, and VSS/SS ratio in the UT reactor reached 1885.8 mg/L, 71.4%, and 24.7%, respectively. The proposed sludge degradation system can potentially minimize the energy consumption during ultrasound disintegration while simultaneously accelerating the anaerobic sludge degradation process. This study provides the basis for a further development of sludge mineralization processes.
Nowadays, ultrasonic cavitation has been successfully used for the degradation of organic pollutants. However, many sonotrodes employed for wastewater treatment are excited to present a longitudinal vibration mode. Thus, the strongest cavitation generally occurs at the tip end of the sonotrodes or the inner walls of ultrasound baths, resulting in severe erosion of the vibrating metal surface caused by ultrasonic cavitation, even though the sonotrodes are made of titanium alloy. In addition, recontamination is possible due to corrosion of the sonotrode. To avoid the above issues, a novel ultrasound system composed of a cylindrical sonotrode and a Langevin-type transducer, is proposed for generating cavitation only in the concentric zone of the cylindrical sonotrode. The first-order longitudinal vibration and the radial vibration are simultaneously stimulated in the Langevin transducer and the cylindrical sonotrode, respectively, to produce the focused cavitation at the concentric zone of the sonotrode. At first, the finite element simulation is conducted to confirm the planned vibration of the ultrasound system and to compute its sound pressure. Subsequently, the prototype of the proposed ultrasound system is manufactured and assembled for vibration measurements. Finally, experimental investigations are carried out on the ultrasound system prototype. By the aluminum foil experiments, the cavitation bubbles occurred in the center of the cylindrical sonotrode. The erosion area increased with the increase of the working power and processing time. After treating the methyl violet solution by ultrasonic cavitation for 60 minutes, the methyl violet in the solution is reduced by 60%, which certainly will help the development of an appropriate flow system for dye degradation.
Anaerobic digestion (AD) is the most widely used technology for the treatment of sewage sludge. It allows the production of biogas, prevents environmental and health negative impacts, and generates biosolids. However, despite its potential, the sludge AD has certain disadvantages such as low biodegradability of sludge, high hydraulic retention time, instability at high organic loading rates and long periods, and low pathogen inactivation. These disadvantages make it necessary to improve the process, especially using pretreatments. Ultrasonic pretreatment is the most effective sludge disintegration technology. Therefore, the main objectives of this work were reviewing the effects of sonication on the sludge AD, highlighting effects on solubilization of sludge, dewaterability, pathogen inactivation, and biosolid quality. As well as the current developments, challenges, and future perspectives, such as coupling with other pretreatments or the nanomaterials incorporation, highlighting the novel process of nanoferrosonication.
Excess sludge is rich in proteins that can be recovered to prepare protein foaming agents and other products with high added value. To extract sludge proteins efficiently, more sludge proteins can be dissolved into the liquid phase by destroying sludge flocs and microbial cell structures. The commonly used alkali-thermal hydrolysis method has the disadvantages of high energy consumption and the additional Maillard reaction. Ultrasonic-alkali hydrolysis (UA) has been widely used as pretreatment for sludge anaerobic digestion, and the effect of UA on cell wall cracking gives it potential application prospects in sludge protein extraction. This study evaluated the potential of UA for sludge protein extraction, and the experimental conditions were optimized to explore the foaming performance of sludge proteins based on a single-factor experiment and orthogonal experiment. The results showed that under optimum hydrolysis conditions (pH of 12, sludge moisture content of 94%, ultrasonic power density of 1.7 W/mL, and ultrasonication duration of 24 min), the protein yield and protein extraction efficiency (RP) were 366.3 mg/g total solids (TS) and 81.4%, respectively. UA converted more than half of the proteins into polypeptides and thus promoted the foaming performance of the sludge proteins to meet the relevant standards for foaming agents. The dewatering performance of the hydrolysed sludge was improved by 93.4%, which was convenient for subsequent treatment. Further research illustrated that UA could shorten the treatment time of alkali hydrolysis (AH) by 36 times when achieving a similar protein yield, and the protein yield produced by UA was 11.4 times greater than that produced solely by ultrasonic hydrolysis (US), indicating that a synergistic effect occurred when AH was combined with US.
In this study, anaerobic digestion of sewage sludge with different ultrasonic pretreatment (USp) conditions was investigated. USp were applied at a constant ultrasonic density of 0.5 W/mL with sonication times of 0–240 min. While the methane yield of the untreated (control) reactor was 170.1 ± 4.7 mL/g volatile solids (VS), the highest methane yield was 266.1 ± 7.5 mL/g VS in the reactor where sonication was applied for 120 min. Actual specific energy input (SEA)/nominal specific energy input (SEN) ratios after USps were measured for pretreatment yield. These values varied between 77.0 and 14.87% according to different sonication times. Sonication times of more than 30 min did not significantly increase the methane yield due to possible reflocculation. After the USps, various cumulative methane yields were predicted via the modified Gompertz Model, modified Logistic Model, and Artificial Neural Network (ANN) model (Scenario 1); of these the ANN model made predictions that were closest to the experimental data. In the other part of the study, ANN was trained by experimental pretreatment conditions and methane yields were successfully predicted by taking different USp parameters (different sonication times, SEA values and incremental soluble chemical oxygen demand % values) as input variables (Scenarios 2, 3 and 4). Regression analyses showed values close to 1, indicating that the prediction of the ANN model correlated linearly with experimental data.
The correlation between sludge reduction induced by 2,4,6-trichlorophenol (2,4,6-TCP) as an uncoupler and sludge toxicity was investigated in sequence batch reactors over a 100-d operation period. The influent concentrations of 2,4,6-TCP tested were 10 mg/L, 30 mg/L, and 50 mg/L. Sludge reduction, chemical oxygen demand (COD) removal rate, and sludge toxicity were measured. The results showed that from 30 to 80 d, when the COD removal rate was at an acceptable level, the sludge reduction levels for the 10 mg/L, 30 mg/L, and 50 mg/L groups were 9.7%, 31.6%, and 41.5%, respectively, and the average sludge toxicity values were 24.2%, 38.0%, and 53.0%, respectively. Sludge reduction was positively correlated with sludge toxicity. The two-dimensional polyacrylamide gel electrophoresis/results showed that extracellular and intracellular proteins secreted by the activated sludge during uncoupling metabolism were positively correlated with sludge toxicity. Taking the COD removal rate, sludge reduction, and sludge toxicity into consideration, the optimal influent concentration of the uncoupler 2,4,6-TCP was 30 mg/L when the initial mixed liquid suspended solids of sludge was 2,500 mg/L.
Excess sludge contains a large amount of organic matter, most of which is present in the form of bacteria and extracellular polymeric substances. In this study, a photosynthetic bioelectrochemical system (BES) combined with ultrasonic treatment (UT) was investigated to mineralize sludge. The sludge was disintegrated by the UT and the supernatant separated from the treated sludge was further degraded through a bioelectrochemical system containing photosynthetic bacteria (PSB‐BES). The UT efficiency was enhanced by supernatant separation. The PSB‐BES method effectively improved the degradation of the soluble chemical oxygen demand (SCOD) from the supernatant. The SCOD and protein removal were increased 1.4 and 1.5 times, respectively, compared to BES without PSB. In addition, the effects of several key operating factors including illumination, voltage and temperature were systematically investigated. This study provides a basis for further development of sludge mineralization processes.
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Waste activated sludge (WAS) is a polluting waste with severe management problems that must be treated to prevent pollution and human health risks. Anaerobic digestion (AD) is the most used process to stabilize sludge; however, it must be improved because the biomethanation of sludge entails low biodegradability, pathogen inactivation, and biogas production. This study investigated the effects of ultrasonic pretreatment (USp) of WAS as a strategy to improve AD. Macromolecule solubilization, heavy metal behavior, pathogen inactivation and biogas production were evaluated. USp was applied at a range of 5000–35000 kJ/kg TS (total solids). The maximum solubilization degree of soluble chemical oxygen demand was 26%, and 22.9% of proteins at 35000 kJ/kg TS. The highest USp reduced only 2 log units of pathogens; nevertheless, a high inactivation was obtained when TS were reduced to 2% and continuous stirring was applied. AD of raw and sonicated WAS were compared with biochemical methane potential tests, and a biogas overproduction of 31.43% (219.5 mL/g VS) was achieved at highest USp. A modified Gompertz model was used for kinetic study of biogas production. The kinetic parameters at highest energy were: biogas production potential, G0 = 634.2 mL; maximum biogas production rate, Rmax = 57.23 mL/day.
To improve the excess sludge disintegration efficiency, reduce the sludge disintegration cost, and increase sludge biodegradability, a combined pretreatment of anaerobic hydrolysis (AH) and ultrasonic treatment (UT) was proposed for excess sludge. Results showed that AH had an advantage in dissolving flocs, modifying sludge characteristics, and reducing the difficulty of sludge disintegration, whereas UT was advantageous in damaging cell walls, releasing intracellular substances, and decomposing macromolecular material. The combined AH-UT process was an efficient method for excess sludge pretreatment. The optimized solution involved AH for 3 days, followed by UT for 10 min. After treatment, chemical oxygen demand, protein, and peptidoglycan concentrations reached 3,949.5 mg O2/L, 752.5 mg/L and 619.1 mg/L, respectively. This work has great significance for further engineering applications, namely, reducing energy consumption, increasing the sludge disintegration rate, and improving the biochemical properties of sludge.
Biogas production from renewable resources is attracting increased attention as an alternative energy source due to the limited availability of traditional fossil fuels. Many countries are promoting the use of alternative energy sources for sustainable energy production. In this study, a metagenome from a production-scale biogas fermenter was analysed employing Roche's GS FLX Titanium technology and compared to a previous dataset obtained from the same community DNA sample that was sequenced on the GS FLX platform. Taxonomic profiling based on 16S rRNA-specific sequences and an Environmental Gene Tag (EGT) analysis employing CARMA demonstrated that both approaches benefit from the longer read lengths obtained on the Titanium platform. Results confirmed Clostridia as the most prevalent taxonomic class, whereas species of the order Methanomicrobiales are dominant among methanogenic Archaea. However, the analyses also identified additional taxa that were missed by the previous study, including members of the genera Streptococcus, Acetivibrio, Garciella, Tissierella, and Gelria, which might also play a role in the fermentation process leading to the formation of methane. Taking advantage of the CARMA feature to correlate taxonomic information of sequences with their assigned functions, it appeared that Firmicutes, followed by Bacteroidetes and Proteobacteria, dominate within the functional context of polysaccharide degradation whereas Methanomicrobiales represent the most abundant taxonomic group responsible for methane production. Clostridia is the most important class involved in the reductive CoA pathway (Wood-Ljungdahl pathway) that is characteristic for acetogenesis. Based on binning of 16S rRNA-specific sequences allocated to the dominant genus Methanoculleus, it could be shown that this genus is represented by several different species. Phylogenetic analysis of these sequences placed them in close proximity to the hydrogenotrophic methanogen Methanoculleus bourgensis. While rarefaction analyses still indicate incomplete coverage, examination of the GS FLX Titanium dataset resulted in the identification of additional genera and functional elements, providing a far more complete coverage of the community involved in anaerobic fermentative pathways leading to methane formation.
During two-phase sludge anaerobic digestion, sludge is usually hydrolyzed and acidified in the first phase, then methane is produced in the second stage. To get more methane from sludge, most studies in literature focused on the increase of sludge hydrolysis. In this paper a different sludge pretreatment method, i.e., pretreating sludge at pH 10 for 8 d is reported, by which both waste activated sludge hydrolysis and acidification were increased, and the methane production was significantly improved. First, the effect of different sludge pretreatment methods on methane yield was compared. The pH 10 pretreated sludge showed the highest accumulative methane yield (398 mL per g of volatile suspended solids), which was 4.4-, 3.5-, 3.1-, and 2.3-fold of the blank (unpretreated), ultrasonic, thermal, and thermal-alkaline pretreated sludge, respectively. Nevertheless, its total time involved in the first (hydrolysis and acidification) and second (methanogenesis) stages was 17 (8 + 9) d, which was almost the same as other pretreatments. Then, the mechanisms for pH 10 pretreatment significantly improving methane yield were investigated. It was found that pretreating sludge at pH 10 caused the greatest sludge hydrolysis, acidification, soluble C:N and C:P ratios, and Fe(3+) concentration with a suitable short-chain fatty acids composition in the first stage, which resulted in the highest microorganism activity (ATP) and methane production in the second phase. Further investigation on the second phase microorganisms with fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) indicated that there were much greater active methanogenesis Archaea when methane was produced with the pH 10 pretreated sludge, and the predominant morphology of the microcolonies suggest a shift to Methanosarcina sp. like.
During the last 50 years extensive experimental investigation has been carried out on the chemical effects of ultrasound, but limited work has been reported on modeling. This paper presents a new model in which a numerical calculation of the three-dimensional linear sound pressure field distribution in a commonly used sonoreactor containing three transducers is carried out. In this model the inhomogeneous three-dimensional time-dependent wave equation was solved using the finite difference approach. The modeled results are then compared with the experimentally measured values, and the agreement, in general, is found to be good. Further, our modeling studies have an advantage, since they clearly describe the continuous sound pressure field structure, unlike previously reported results in which some information is missing due to limited intermittent measured points.
Anaerobic digestion is an effective waste treatment method both for the pollution control and energy recovery, such as treating many agricultural and industrial wastes which contain high level of easily biodegradable substances. However, there are also many problems to be resolved, such as low methane yield, long retention time and process instability, preventing this technique from being widely applied. Variety of inhibitory substances and intermediate products are the primary cause of anaerobic digester upset or failure, including free ammonia (FA), volatile fatty acids (VFAs) and sulfide/sulfate, though they are essential nutrients for bacterial growth and anaerobic digestion process. Many researches have been conducted to investigate the inhibition mechanisms and the controlling factors during the overall anaerobic digestion process. In this paper, a detailed summary of the researches was discussed on the inhibition of the anaerobic digestion process. Furthermore, the controlling and recovery of the inhibitors as valuable products were also reviewed in detail. Co-digestion with other wastes, acclimation of microorganisms, and incorporation of methods could significantly improve the efficiency of sewage sludge anaerobic digestion.
A critical review on the effect of ultrasound (US) on enzymes and their biocatalytic action is presented here. Discussion on the information users of US acquire before utilizing the different devices, and the importance they give to US frequency is constant along the review. The authors have gone into the different areas in which the US-enzyme binomial has been applied. The lack of enough information on the US-enzyme-working conditions under which each piece of research has been developed, and the necessity to provide complete information on the data and metadata to give enough light on each piece of research (and thus on the potential comparison of results from different studies) are critically exposed. With this aim, the study has been divided into the positive effect of US on enzymes to favor the production of metabolites, polymers or proteins; and the degradation, inhibition or activation of the biocatalyst under US application. Also the effect of US on enzyme production and the main fields of application of the US-enzyme binomial are discussed.
In this study, batch tests were conducted to investigate the effect of extracellular polymeric substances (EPS) disintegration on anaerobic fermentation of waste activated sludge (WAS). Ultrasonic pretreatment was used to disintegrate EPS and accelerate WAS hydrolysis. The experimental results showed that more organic substances were released from sludge with increase of ultrasonic density, and the EPS were completely disintegrated at ultrasonic parameters beyond 2.0 W/mL and 15 min. The optimal ultrasonic density for short chain fatty acids (SCFAs) accumulation was 2.0 W/mL, and the SCFAs concentration reached 3166 mg/L after 5 days of anaerobic fermentation. The SCFAs mainly consisted of acetic and propionic acids, accounting for 88% of total SCFAs. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that ultrasonic density significantly altered the bacterial communities by affecting the EPS disintegration degree. Firmicutes, Proteobacteria and Bacteroidetes were main species, contributing to proteins (PN) and polysaccharides (PS) degradation and SCFAs production.
The present study is aimed at enhanced cell production in together with pollution removal in photosynthetic bacteria wastewater treatment through low-strength ultrasound stimulation. The ultrasound strength was 0.3W/cm(2) with 40kHz frequency. Results showed 1-10min sonication significantly improved the cell production. The optimal sonication time was 2min. When the irradiation period was over 10min, a strong mechanical damage occurred. These phenomena could be explained by the changes of PSB dehydrogenase activity. Sonication stimulated the initial dehydrogenase activity; moderate sonication increased the cell activity while too-long sonication led to quick enzyme activity decrease. The optimal sonication strategy was 1min at the 0th hour and 1min at the 27th hour. The corresponding cell production and cell yield increased by 110% and 93% respectively, and the COD removal reached 98%. The cost of low-strength ultrasound was only 1% of the incremental sales value of cells.
The effect of short-time aerobic digestion on bioflocculation of extracellular polymeric substances (EPSs) from waste activated sludge (WAS) was investigated. Bioflocculation of the EPS was found to be enhanced by 2∼6 h of WAS aerobic digestion under the conditions of natural sludge pH (about 7), high sludge concentration by gravity thickening, and dissolved oxygen of about 2 mg/L. With the same EPS extraction method, the total suspended solid content reduction of 0.20 and 0.36 g/L and the volatile suspended solid content reduction of 0.19 and 0.26 g/L were found for the WAS samples before and after aerobic digestion of 4 h. It indicates that more EPS is produced by short-time aerobic digestion of WAS. The scanning electron microscopy images of the WAS samples before and after aerobic digestion of 4 h showed that more EPS appeared on the surface of zoogloea by aerobic digestion, which reconfirmed that WAS aerobic digestion induced abundant formation of EPS. By WAS aerobic digestion, the flocculating rate of the EPS showed about 31 % growth, almost consistent with the growth of its yield (about 34 %). The EPSs obtained before and after the aerobic digestion presented nearly the same components, structures, and Fourier transform infrared spectra. These results revealed that short-time aerobic digestion of WAS enhanced the flocculation of the EPS by promoting its production.
The effect of sludge lysis using ultrasonic waves on the sludge yield coefficient was investigated using pilot-scale SBR reactors. Our results revealed that reduction of excess sludge is affected by multiple factors including the energy supplied to sludge mass, the power used for wave generation, duration of wave usage, and percentage of sludge exposed to the waves. Increasing the energy supplied to the sludge mass resulted in more reduction of sludge yield but energies greater than 35,000 kJ/kg VSS showed no significant effect on sludge reduction. Moreover, less power and more retention time showed better performance in sludge reduction. Using ultrasonic waves for reducing sludge yield deteriorated the quality of the reactor effluent and also increasing volume of the sludge lysed by waves at every run brought about decreasing COD removal efficiency. In order to meet standards for effluent discharge to surface and groundwater bodies, a maximum 30% of the system sludge could be lysed resulting in approximately 78% reduction of sludge yield. In this case, the sludge SOUR decreased down to 9 mg DO/g SS.h, but the sludge sedimentation property was improved and SVI was reduced.Research Highlights► Specific supplied energy has effect in excess sludge reduction. ► Sludge sonication deteriorates the quality of the effluent. ► Sludge sonication decreases SOUR but improves sludge sedimentation characteristic.
High-pressure homogenization (HPH) technology was applied as a pretreatment to disintegrate sewage sludge. The effects of homogenization pressure, homogenization cycle number, and total solid content on sludge disintegration were investigated. The sludge disintegration degree (DD(COD)), protein concentration, and polysaccharide concentration increased with the increase of homogenization pressure and homogenization cycle number, and decreased with the increase of sludge total solid (TS) content. The maximum DD(COD) of 43.94% was achieved at 80 MPa with four homogenization cycles for a 9.58 g/L TS sludge sample. A HPH sludge disintegration model of DD(COD) = kNaPb was established by multivariable linear regression to quantify the effects of homogenization parameters. The homogenization cycle exponent a and homogenization pressure exponent b were 0.4763 and 0.7324 respectively, showing that the effect of homogenization pressure (P) was more significant than that of homogenization cycle number (N). The value of the rate constant k decreased with the increase of sludge total solid content. The specific energy consumption increased with the increment of sludge disintegration efficiency. Lower specific energy consumption was required for higher total solid content sludge.
To improve anaerobic sludge digestion efficiency, the effects of high-pressure homogenization (HPH) conditions on the anaerobic sludge digestion were investigated. The VS and TCOD were significantly removed with the anaerobic digestion, and the VS removal and TCOD removal increased with increasing the homogenization pressure and homogenization cycle number; correspondingly, the accumulative biogas production also increased with increasing the homogenization pressure and homogenization cycle number. The optimal homogenization pressure was 50 MPa for one homogenization cycle and 40 MPa for two homogenization cycles. The SCOD of the sludge supernatant significantly increased with increasing the homogenization pressure and homogenization cycle number due to the sludge disintegration. The relationship between the biogas production and the sludge disintegration showed that the accumulative biogas and methane production were mainly enhanced by the sludge disintegration, which accelerated the anaerobic digestion process and improved the methane content in the biogas.
Five individual pretreatment methods, including three widely-used protocols (heat, acid and base) and two novel attempts (ultrasonic and ultraviolet), were conducted in batch tests to compare their effects on mixed microflora to enhance hydrogen (H2) production from corn stover hydrolysate. Experimental results indicated that heat and base pretreatments significantly increased H2 yield with the values of 5.03 and 4.45 mmol H2/g sugar utilized, respectively, followed by acid pretreatment of 3.21 mmol H2/g sugar utilized. However, compared with the control (2.70 mmol H2/g sugar utilized), ultrasonic and ultraviolet pretreatments caused indistinctive effects on H2 production with the values of 2.92 and 2.87 mmol H2/g sugar utilized, respectively. The changes of soluble metabolites composition caused by pretreatment were in accordance with H2-producing behavior. Concretely, more acetate accumulation and less ethanol production were found in pretreated processes, meaning that more reduced nicotinamide adenine dinucleotide (NADH) might be saved and flowed into H2-producing pathways. PCR-DGGE analysis indicated that the pretreatment led to the enrichment of some species, which appeared in large amounts and even dominated the microbial community. Most of the dominated species were affiliated to Enterobacter spp. and Escherichia spp. As another efficient H2 producer, Clostridium bifermentan was only found in a large quantity after heat pretreatment. This strain might be mainly responsible for better performance of H2 production in this case.
The effect of low power ultrasound on aerobic/anoxic digestion of activated sludge was investigated. First, dehydrogenate activity (DHA) and special oxygen uptake rate (SOUR) were detected to indicate the change of biological activity of sludge induced by ultrasound. Single-factor experiments showed that when the ultrasonic frequency was 28 kHz, the optimal ultrasonic density and exposure time were 0.15 W/mL and 10 min, respectively. Through orthogonal tests, the optimal ultrasonic parameters for aerobic/anoxic digestion were found to be a ultrasonic density of 0.15 W/mL, ultrasonic exposure time of 10 min and interval time of 12 h. The aerobic/anoxic digestion was improved by ultrasonic pretreatment, the VSS reduction at the optimal conditions was increased by 35.73%, compared with the control. It can be concluded that low power ultrasonic pretreatment is a valid method for improving aerobic/anoxic biodegradability of activated sludge.
The activated sludge process is an essential process for treating domestic and industrial wastewaters in most wastewater treatment plants (WWTPs). This process consists of a mixture of general and special microorganisms in a form of a complex enrichment population. Thus, the exploration of activated sludge microbial communities is crucial to improve the performance of activated sludge process. In this study, we investigated the phylogenetic diversity and metabolic potential of activated sludge microbial communities in full-scale WWTPs. Four 16S rRNA gene clone libraries were constructed from activated sludge samples. In all samples, Proteobacteria was the most abundant phylogenetic group, followed by Bacteroidetes and Firmicutes. The dominance of Proteobacteria was further demonstrated by denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP). Some specific genera, e.g., Nitrosomonas, Thauera, and Dechloromonas, which significantly correlate with the functions and performance of wastewater treatment, were abundant in all samples. A large number of unclassified sequences were found in the library, suggesting that a wide variety of novel species may inhabit complex activated sludge communities. The structures of the bacterial community did not differ significantly among samples. All samples utilized the vast majority of 31 carbon sources of an EcoPlate (Biolog), suggesting that activated sludge microbial communities possess high metabolic potential and equivalent functions required for wastewater treatment.
Five different mesophilic systems were evaluated in this study for the anaerobic treatment of food waste. Systems A and B were one stage methane with unsonicated and sonicated feeds, respectively, while, systems C and D were two-stage hydrogen and methane with unsonicated and sonicated feeds, respectively. System E comprised a novel sonicated biological hydrogen reactor (SBHR) followed by methane reactor. The results showed that sonication inside the reactor in the first stage (system E) showed superior results compared to all other systems. Overall VSS removal efficiencies of 67%, 59%, 51%, 44%, and 36% were achieved in systems E, D, C, B, and A, respectively. Volumetric hydrogen production rates of 4.8, 3.3, and 2.6L H(2)/L(reactor)d were achieved in the SBHR, CSTR with and without sonicated feed, respectively, while, methane production rates of 1.6, 2.1, 2.3, 2.6, and 3.2L CH(4)/L(reactor)d were achieved in systems A-E, respectively.
The individual effects of alkaline (pH 8-13) and ultrasonic (3750-45,000kJ/kg TS) pretreatments on the disintegration of sewage sludge were separately tested, and then the effect of combining these two methods at different intensity levels was investigated using response surface methodology (RSM). In the combined pretreatment, ultrasonic treatment was applied to the alkali-pretreated sludge. While the solubilization (SCOD/TCOD) increase was limited to 50% in individual pretreatments, it reached 70% in combined pretreatment, and the results clearly showed that preconditioning of sludge at high pH levels played a crucial role in enhancing the disintegration efficiency of the subsequent ultrasonic pretreatment. By applying regression analysis, the disintegration degree (DD) was fitted based on the actual value to a second order polynomial equation: Y=-172.44+29.82X(1)+5.30x10(-3)X(2)-7.53x10(-5)X(1)X(2)-1.10X(1)(2)-1.043x10(-7)X(2)(2), where X(1), X(2), and Y are pH, specific energy input (kJ/kg TS), and DD, respectively. In a 2D contour plot describing the tendency of DD with respect to pH and specific energy input, it was clear that DD increased as pH increased, but it seemed that DD decreased when the specific energy input exceeded about 20,000kJ/kg TS. This phenomenon tells us that there exists a certain point where additional energy input is ineffective in achieving further disintegration. A synergetic disintegration effect was also found in the combined pretreatment, with lower specific energy input in ultrasonic pretreatment yielding higher synergetic effect. Finally, in order to see the combined pretreatment effect in continuous operation, the sludge pretreated with low intensity alkaline (pH 9)/ultrasonic (7500kJ/kg TS) treatment was fed to a 3 L of anaerobic sequencing batch reactor after 70 days of control operation. CH(4) production yield significantly increased from 81.9+/-4.5mL CH(4)/g COD(added) to 127.3+/-5.0mL CH(4)/g COD(added) by pretreatment, and this enhanced performance was closely related to the solubilization increase of the sludge by pretreatment. However, enhanced anaerobic digestion resulted in 20% higher soluble N concentration in the reactor, which would be an additional burden in the subsequent nitrogen removal system.
The pretreatment of waste activated sludge by ultrasonic disintegration was studied in order to improve the anaerobic sludge stabilization. The ultrasound frequency was varied within a range from 41 to 3217 kHz. The impact of different ultrasound intensities and treatment times was examined. Sludge disintegration was most significant at low frequencies. Low-frequency ultrasound creates large cavitation bubbles which upon collapse initiate powerful jet streams exerting strong shear forces in the liquid. The decreasing sludge disintegration efficiency observed at higher frequencies was attributed to smaller cavitation bubbles which do not allow the initiation of such strong shear forces. Short sonication times resulted in sludge floc deagglomeration without the destruction of bacteria cells. Longer sonication brought about the break-up of cell walls, the sludge solids were distintegrated and dissolved organic compounds were released. The anaerobic digestion of waste activated sludge following ultrasonic pretreatment causing microbial cell lysis was significantly improved. There was an increase in the volatile solids degradation as well as an increase in the biogas production. The increase in digestion efficiency was proportional to the degree of sludge disintegration. To a lesser degree the deagglomeration of sludge flocs also augmented the anaerobic volatile solids degradation.
The effects of pretreatment process variables [straw concentration between 20 and 90 kg volatile solids (VS)/m(3), temperature between 30 and 85 degrees C, and alkaline dosage between 0 and 80 g NaOH/kg VS] on acidogenesis and methanogenesis were investigated. Rates of acidogenesis and methanogenesis were determined using firstorder kinetics, and ultimate acid and methane yields were measured. The acid yield was not affected by pretreatment concentration or temperature, but increased as alkaline dosage increased. The acidogenesis rate was not affected by pretreatment temperature or alkaline dosage, but decreased as the substrate concentration increased. This decrease in the acidogenesis rate was attributed to a decrease in the inoculum: substrate ratio as the substrate concentration increased. The methane yield and methanogenesis rate were not affected by pretreatment substrate concentration or temperature, and both increased with alkaline dosage up to about 40 g NaOH/kg VS, then remained relatively constant above 40 g NaOH/kg VS.
Effects of various Fig. 4. Transmission electron microscope micrographs of sludge: (a) raw sludge
- K Zhang
- N Q Ren
- C H Guo
- A J Wang
- G L Cao
Zhang, K., Ren, N.Q., Guo, C.H., Wang, A.J., Cao, G.L., 2011. Effects of various
Fig. 4. Transmission electron microscope micrographs of sludge: (a) raw sludge; (b) treated sludge.