Open Access This article is
- freely available
Energies 2019, 12(1), 21; https://doi.org/10.3390/en12010021
Disintegration of Wastewater Activated Sludge (WAS) for Improved Biogas Production
Centre for Nanomaterials, Advanced Technologies and Innovation, Technical University of Liberec, 461 17 Studentska, Czech Republic
Institute of Environmental Protection and Engineering, University of Bielsko-Biala, Willowa 2, 43-309 Bielsko-Biala, Poland
Faculty of Natural Sciences and Technology, University of Opole, ul. kard. B. Kominka 6, 45-032 Opole, Poland
Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palacky University in Olomouc, Slechtitelu 27, 783 71 Olomouc, Czech Republic
Authors to whom correspondence should be addressed.
Received: 16 November 2018 / Accepted: 18 December 2018 / Published: 21 December 2018
Due to rapid urbanization, the number of wastewater treatment plants (WWTP) has increased, and so has the associated waste generated by them. Sustainable management of this waste can lead to the creation of energy-rich biogas via fermentation processes. This review presents recent advances in the anaerobic digestion processes that have led to greater biogas production. Disintegration techniques for enhancing the fermentation of waste activated sludge can be apportioned into biological, physical and chemical means, which are included in this review; they were mainly compared and contrasted in terms of the ensuing biogas yield. It was found that ultrasonic- and microwave-assisted disintegration provides the highest biogas yield (>500%) although they tend to be the most energy demanding processes (>10,000 kJ kg−1 total solids).
Keywords:biogas; renewable energy; anaerobic digestion; waste activated sludge; disintegration
The continuous increase in the use of fossil fuel in modern society and the harmful effects of greenhouse gases on the environment has prompted the search for alternative energy sources which are becoming increasingly important and even mandatory in the future. In this context, research focusing on the improvement of biogas production has become essential. Moreover, due to the increase in urbanization, the number of wastewater treatment plants (WWTP) have increased, and since the wastes (e.g., waste activated sludge (WAS)) generated from the WWTP are considered hazardous for the environment, it is important to develop efficient processes for their pre-treatment .
Untreated activated sludge is hydrated to a level of 97–99% and the rest is comprised of solid and dissolved matter, minerals and organic substances, coagulants, gels and trapped gas bubbles. The stabilized sediment, on the other hand, is often hydrated only to a level of 60–88% [1,2,3].
The basic process of sludge utilization predominantly involves spreading it over the surface of the soil to fertilize it or improve its properties. Final disposal of sewage sludge is used in the following areas:
- In agriculture, for growing crops,
- For the reclamation of land, including land for agricultural purposes,
- For the adaptation of land to specific needs resulting from waste management plans, spatial development plans or decisions on building and land development conditions,
- For the production of compost,
- For the cultivation of flora not intended for consumption .
Unless it contains excessive amounts of heavy metals, stabilized sludge can improve the agrotechnical state of fertilized soils, because it contains a high concentration of micro- and macronutrients .
Most waste generators, including WAS, are obligated to handle it in a manner consistent with the principles of waste management and the requirements of environmental protection and waste management plans . Firstly, waste should be subject to a recovery process and if it is impossible for technological reasons or is not justified for ecological or economic reasons, it should be subjected to disposal . The composition of WAS varies enormously and depends on many factors, for example, the type and origin of WAS (e.g., the impact of industry in a settlement unit) and the method of treatment applied in the WWTP . There are many issues concerning WAS including, dissolved heavy metals and/or toxic organic substances : dioxins and furans, polychlorinated biphenyls (PCBs), and pesticides. At present, there are 500 substances classified in 15 different categories. With the exception of heavy metals, European Union regulations still lack strict limits on these substances in WAS.
Anaerobic digestion (AD) is one of the most commonly applied processes for WAS treatment as it is considered to be sustainable. Although it main purpose is the stabilization of WAS, however, it does decrease the water content of the sludge and associated toxicity. Another advantage of this method is that it produces biofuel (biogas), rendering the whole operation not only an environmentally feasible but also cost-beneficial. In this context, it is not surprising that the number of WWTPs producing and storing biogas is increasing each year. For example, in 2009 there were 6227 of these plants in Europe, by 2015 there were 17,376, an almost three -fold increase in only six years . In China alone there are currently more than one million of these plants .
Biogas can be made from a range of organic substances and can be used to produce heat, power, heat and power (combined) or as a fuel for vehicles. Biogas contains methane, carbon dioxide, and nitrogen in different proportions and in trace concentrations also hydrogen sulphide, hydrogen, ammonia, oxygen, and carbon monoxide , siloxanes and aromatic and halogenated compounds (also depending on the fermentation/pre-treatment type) . Primary production of biogas in the European Union is shown in Figure 1 and the typical characteristic of biogas can be found in Table 1 .
Anaerobic digestion process entails four steps, i.e., hydrolysis, acidogenesis, acetogenesis and methanogenesis ; the complex process is attainable only under strict anaerobic conditions, with hydrolysis being a rate limiting step . During hydrolysis, lipids, proteins, polysaccharides and soluble organic matter are all degraded, with the final products being further treated through acidogenesis to yield volatile fatty acids (acidogenesis = generation of acids; VFAs) and other by-products [15,16]. The acidogenesis step is followed by acetogenesis, during which the VFAs are digested by acetogenic microorganisms producing an even simpler molecule, acetate. The last step is methanogenesis, during which methane is generated; the process involves two methanogenic microorganisms, one group uses acetate to generate methane and CO2 while the other uses hydrogen to produce methane . This whole process, including the contribution of organic substances (chemical oxygen demand (COD)) and bacteria involved in it, is illustrated in Figure 2.
Biogas is a renewable fuel, which is considered to be more eco-friendly than conventional energy reserves; therefore, rapid development in this field is based on improving the biogas yield and especially by improving the pre-treatment process of WAS.
Pre-treatment of WAS is one of the most crucial steps before AD as it eliminates the disadvantages of the rate-limiting, hydrolysis step, and can often significantly enhance the yield of biogas with a simultaneous reduction of the sludge cake. In addition, several of these methods can efficiently reduce the toxicity of WAS by degrading the toxic and persistent microorganisms and molecules.
For various reasons, it is hard to compare the effectiveness of different pre-treatment methods used in wastewater technologies. The most important variables that make unambiguous comparison impossible are the type of sludge (inter alia: waste activated, primary, digested, sludge age) and the operational conditions used (inter alia: temperature, continuous/batch, hydraulic retention time (HRT)).
However, this paper focuses only on the recent advances in WAS pre-treatment methods, which positively impacts subsequent biogas production.
2. Pre-Treatment Methods
Pre-treatment methods, be either separate or hybrid processes (not discussed here), are applied to provide the optimum results for various purposes . Before selecting the technology, the pre-treatment goals must be clearly defined, because improvement of one of the processes can negatively affect another treatment stage.
As mentioned above, selection of the disintegration method depends heavily on the type of sludge. Müller  suggests that the most effectively method for primary sludges and sludges with high lignocellulose content is enzymatic pre-treatment. However, it could be less suitable for WAS or secondary sludges as they degrade themselves before enzymatic hydrolysis starts.
The vast majority of studies devoted to disintegration methods focus on the implementation of these methods for activated sludge or secondary sludge. This is due to the fact that primary sludges are most frequently composed of easily-degradable components (no treatment needed) or secondary sludges, and are mainly formed by microorganisms whose cell walls prevent rapid degradation.
One of the major components of WAS flocs are extracellular polymeric substances (EPS) comprised mainly of a proteins (e.g., enzymes), carbohydrates, humic matter and, to a smaller amount, uronic and deoxyribonucleic (DNA) acids and lipids. Multivalent cations and EPS interact and the associated hydrogen bonds results in the formation of a network of polymeric substances in the waste activated sludge [20,21]. All of this leads to longer retention times required for biological stabilisation. Many pre-treatment methods have received attention recently pertaining to EPS degradation and there are also many methods for their extraction [22,23].
Several different pre-treatment/disintegration methods are used specifically to improve anaerobic digestion e.g., biological, chemical and physical methods as well as combinations thereof. Essentially, sludge pre-treatment is used to break down the cell walls of microbes generally to reduce the molecular weight of substances in WAS, releasing the intracellular matter, which becomes more accessible to anaerobic microbes and consequently enhancement of the anaerobic digestion.
The most important objectives of disintegration/pre-treatment methods include:
- Simple access to the organic substances that were trapped inside the biomass and their release into the supernatant/liquid phase, as well as to intracellular enzymes that cause direct decomposition of pollutants,
- Release of organic substrate (in the case of disintegration of surplus activated sludge; often represented as chemical oxygen demand (COD)) that can be an easily digestible organic carbon source for the denitrification process. The increase in COD solubilization can be often correlated with the increase in methane production ,
- Removing activated sludge foam generated on the surface of bioreactors as well as elimination of foaming in digestion chambers and secondary settling tanks,
- Increase in the biogas production and biogas yield and hence energy production with faster digestion.
In recent years, several pre-treatment/disintegration methods have been applied both on a bench and technical scale, for example by using thermal energy [25,26], enzymes , ozonisation , acidification , alkalization [30,31], high pressure [32,33], mechanical grinding  and ultrasound energy [35,36]. In general, these techniques can be classified into three categories: biological, physical and chemical (Figure 3).
Biological pre-treatment (Table 2) can utilise either anaerobic or aerobic processes [37,38]. Anaerobic pre-treatment is one of the most commonly used in sludge pre-treatment , this process can effectively destroy pathogens, reduce volatile solids and enhance biogas production [40,41,42,43,44]. So-called bioaugmentation can be used as a pre-treatment of WAS for reducing the molecular weight of substances therein [45,46]. Indeed, many authors have reported on the effectiveness of this technique e.g., addition of cellulolytic bacteria, that are capable of generating an enzymatic complex, cellulosome, can enhance the digestion rates of cellulose (and subsequent improvement of biogas production) .
Ai et al.  concluded that adding Bacillus coagulants can promote the hydrolysis and acidogenesis process with no negative effect on the methanogenesis process. In order to obtain the sludge disintegration, it is possible to use enzymes, which are biologically derived molecules that work as a catalyst (also termed biocatalyst). It is possible to classify these enzymes into six basic classes: oxidoreductases, ligases, transferases, lyases, hydrolysases, and isomerases. Enzymatic lysis by the enzyme catalysing the reaction leads to the breaking down of bonds and compounds constituting the cell wall of the microorganisms. The enzymes can help decompose the organic matter, i.e., turn it into smaller molecules [27,38,39,49,50,51,52,53,54,55,56,57,58,59,60,61,62]. Recently, Prajapati et al.  successfully used a bio-electrochemical process to enhance the methane production from sewage sludge by augmenting it with food waste.
Chemical pre-treatment is another efficient and cost-effective process for hydrolysing the membranes and the cell walls and thus increasing the solubility of the organic matter that is located inside the cells; the most common used before anaerobic digestion are alkalization  or acidification [58,65,66].
The often used alkaline reagents are NaOH , Ca(OH)2  and KOH . Alkali pre-treatment can solubilize the cell membranes, releasing the intracellular matter from the cells in solution, which becomes available for the fermentation process. The intracellular matter essentially formed by lipid proteins and hydrocarbons is decomposed in the soluble substances that are available for the microorganisms . The advantages of alkali methods are their high efficiency and the ease of performance during the process .
On the other hand, oxidation techniques are used because of their enormous efficiency. Traditional oxidation techniques include Fenton reactions, and photocatalytic and ozonation processes. All the aforementioned techniques have one thing in common, namely the formation of a hydroxyl radical; these processes are also known as advanced oxidation processes (AOP). Ozonation pre-treatment includes two different types of oxidation processes i.e., ozonolysis and hydroxyl radical reactions, which depend mainly on the pH values. It has been reported that at low pH ozone reacts selectively with the organic molecules comprising C=C, –OH, CH3, –OCH3 and other functionalities , and at pH > 8 the ozone generates ∙O2− and HO2∙ radicals ; more details are available [71,73,74,75,76,77,78,79,80,81,82,83,84,85,86] On the other hand, Fenton reactions involve the reaction of hydrogen peroxide with divalent iron producing hydroxyl radicals, and have been used in environmental matrices (including WAS) for a long period of time [87,88]. Although, these methods have been tested for many years for WAS pre-treatment, there are still some innovative solutions being uncovered. For example, in a recent study Hallaji et al.  reported the possibility to increase the methane production by 72% with a combined free nitrous acid (FNA)/Fenton reaction pre-treatment process. The possibility to increase methane production by ~200% with a combination of micro aerobic hydrolysis and the addition of trace metals has also been reported . Anjum et al.  recently reported the possibility to enhance the biogas production using photocatalytic disintegration of WAS, whereby this procedure increased the biogas production by 1.6 times.
It should be noted that whereas the hydroxyl radical pre-treatment of WAS have been known for some time, sulphate radical pre-treatment (activated peroxydisulfate or peroxymonosulphate (persulphates)) has only been introduced in the last few years; however, several limitations disable their in situ application. Peroxydisulphate (PDS) is a strong oxidant used with success for the disintegration of WAS by several authors [22,92,93,94,95]. In order to form sulphate and hydroxyl radicals, persulphates need to be activated, usually by heat , metal , UV  and alkaline conditions , among others .
Many oxidation techniques, including Fenton reactions ) and new reactions concerning peroxomonosulphate (PMS; ), nano-layered TiO2  and dimethyldioxirane (DMDO), can cause the alteration of refractory organic matter into easily accessible and soluble biochemical oxygen demand (BOD), and subsequently improve the biogas yield  (Table 2). Recently, a newly greener oxidant for this purpose, peracetic acid (PAA), has been proposed to improve anaerobic digestion .
2.3. Physical Methods
Physical and mechanical treatments of WAS work in basically the same way, the cell walls are broken and flocs break up by the application of force/external energy. Disintegration of the WAS with the use of mechanical forces causes the fragmentation of flocks and effective lysis of bacterial cells, leading to the release of organic substances and therefore an increase in biogas production.
The effect of mechanical disintegration of WAS on the efficiency of AD has been investigated for a long period. Mechanical shearing, lysate-thickening centrifuge , milling technology , and high pressure technology [61,107,108,109,110,111,112] are some of the main techniques.
Hydrodynamic cavitation triggered by the Venturi effect is a promising process for pretreatment of waste activated sludge prior to mesophilic fermentation according to many authors, including Machnicka et al. . Furthermore, mesophilic digestion trials have reported a significant increase in the biogas production of approximately 36.1% and 62.16% for 10% and 30% of the volume of foam added to the digestion chamber, respectively.
Ultrasonic methods have been included as physical treatment in this review but they can also be included as AOPs. These methods involve two different processes: cavitation, which is promoted at low frequencies, and the formation of radicals (∙OH, HO2∙, H∙) due to the chemical reactions at high frequencies . To induce cavitation, the process has to operate at a certain frequency (<100 kHz), the ultrasound creates gas bubbles that up on collapsing produce hydromechanical forces, which disintegrate the macromolecules [33,114,115]. The extreme conditions that occur during the cavitation process can cause generation of hydroxyl radicals, which can degrade volatile and non-volatile pollutants. Ultrasonication can enhance the WAS digestibility by damaging the physical, chemical and biological properties of the sludge; lysis accelerates the hydrolysis reactions by disrupting the cells. Within the explosion (cavitational) of transient bubbles, a certain amount of soluble particulate organic matter can be rendered completely soluble. Ultrasound is considered as one of the most efficient sludge pre-treatments for sludge floc disintegration [85,114,116,117,118,119,120,121]; Lizama et al.  reported an increase in biogas production after ultrasonic treatment of 560% (Table 2).
Compared to mechanical techniques, thermal disintegration processes consume more energy, but they can be deployed e.g., by using heat exchangers, or by the use of steam to the WAS. Thermal pre-treatment processes can occur at a wide range of temperatures from 60 to 270 °C; processes at a temperature of <100 °C are considered as low temperature processes and those taking place at a temperature of >100 °C are high temperature processes [60,61,85,137,138,139,140,141].
The optimal temperature treatment is frequently stated to be around 170 °C ; Ennouri et al.  reported that at a thermal pre-treatment temperature of 120 °C, the biogas yield increased by 37%.
However, Dwyer et al.  reported that COD solubilisation increased at temperatures above 150 °C but there was no increase in the methane production. According to Batstone et al. , the main disadvantages of thermal pre-treatment are associated with the costs and increased ammonia inhibition.
Another pre-treatment process that has already shown to improve the anaerobic digestion is microwave pre-treatment ; which is a good substitute for thermal pre-treatment, increasing the concentration of soluble proteins in solution  and improving biogas [148,149] production and disinfection . Microwave irradiation has two main effects, thermal and non-thermal; they involve the interaction of rapidly alternating electric field with polar proteins, fats and H2O and the breakdown of hydrogen bonds and the consequent death of microorganisms . Other recent methods involve the application of low temperatures for WAS treatment known as freezing/thawing [25,26,152].
In conclusion, we have evaluated various disintegration protocols pertaining to the waste activated sludge for the enhanced production of eco-fuel–biogas. The pre-treatments are focused mainly on augmenting the disintegration method and improving the hydrolysis and gaining more biogas in the anaerobic digestion (AD) process. Three types of pre-treatment processes (biological, chemical and physical) are presented with their associated strengths, weaknesses and recent advances. Some pre-treatment processes are more efficient in reducing the biomass, while the others work better for the solubilization of organic matter or for the cell disintegration. Additionally, the diverse pre-treatment processes generate fluctuating costs depending on e.g., the volume of WAS used, varying reaction times and effects on biogas generation. Biological pre-treatment is usually slower than other types of treatment and can last several days. Moreover, despite its advantages e.g., often lower costs, it is less effective in terms of solubilization of the organic matter and corresponding increase of the biogas yield (<40%). Regarding the chemical treatments, one could distinctly identify peroxydisulfate one, which produced 180% increase of biogas yield (the highest in comparison to all other chemical treatments reported herein), however, further studies are needed to verify the quality of thus produced biogas, since the sulfate ion (end-product of the treatment) can negatively influence anaerobic digestion process. Chemical and physical methods are faster and are rather easier to implement; however, they can be more energy demanding as described in recent findings, where the application of microwaves or ultrasonic energy increased biogas production by >500% but tend to be very energy-demanding (>10,000 kJ kg−1 TS). In keeping with the aim of attaining sustainability, the newer pathways need to be explored which may use photochemical approach exploiting the visible light or solar energy, an abundant energy source, to facilitate the processability of the sludge and reduction of water contents.
S.W. conceived the idea.; S.W., K.G. and D.S. collected the references; K.G. and D.S. analyzed the references and reorganized the pictures and the tables; S.W., K.G., D.S., V.V.T.P., M.W., M.Č. and R.S.V. wrote and edited the manuscript; M.Č. and R.S.V. reviewed the manuscript; all authors read and approved the manuscript.
The research presented in this article was supported by the Ministry of Education, Youth and Sports in the framework of the targeted support of the OPR & DI project “Extension of CxI facilities” (CZ.1.05/2.1.00/19.0386). The authors also acknowledge the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project no. LM2015073. This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic and the European Union—European Structural and Investment Funds in the frames of Operational Program Research, Development and Education—Project Hybrid Materials for Hierarchical Structures (HyHi, Reg. No. CZ.02.1.01/0.0/0.0/16_019/0000843).
Conflicts of Interest
The authors declare no conflict of interest.
- Den, W.; Sharma, V.K.; Lee, M.; Nadadur, G.; Varma, R.S. Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals. Front. Chem. 2018, 6, 141. [Google Scholar] [CrossRef] [PubMed]
- De Lemos Chernicharo, C.A. Anaerobic Reactors; IWA Publishing: London, UK, 2007; ISBN 1843391643. [Google Scholar]
- Begum, L. Advanced Processes and Technologies for Enhanced Anaerobic Digestion; Green Nook Press: Toronto, ON, Canada, 2014; ISBN 0993904505. [Google Scholar]
- De Vrieze, J.; De Lathouwer, L.; Verstraete, W.; Boon, N. High-rate iron-rich activated sludge as stabilizing agent for the anaerobic digestion of kitchen waste. Water Res. 2013, 47, 3732–3741. [Google Scholar] [CrossRef]
- United States Environmental Protection Agency. National Hazardous Waste Management Plan 2008–2012; United States Environmental Protection Agency: Washington, DC, USA, 2008; ISBN 9781840952988.
- Fytili, D.; Zabaniotou, A. Utilization of sewage sludge in EU application of old and new methods—A review. Renew. Sustain. Energy Rev. 2008, 12, 116–140. [Google Scholar] [CrossRef]
- Wzorek, M. Characterisation of the properties of alternative fuels containing sewage sludge. Fuel Process. Technol. 2012, 104, 80–89. [Google Scholar] [CrossRef]
- Mathiasson, A. Future of Biogas Europe. Available online: www.european-biogas.eu (accessed on 6 October 2018).
- Banu, J.R.; Kavitha, S. Various Sludge Pretreatments: Their Impact on Biogas Generation. In Waste Biomass Management—A Holistic Approach; Springer International Publishing: Cham, Switzerland, 2017; pp. 39–71. [Google Scholar]
- Ullah Khan, I.; Hafiz Dzarfan Othman, M.; Hashim, H.; Matsuura, T.; Ismail, A.F.; Rezaei-DashtArzhandi, M.; Wan Azelee, I. Biogas as a renewable energy fuel—A review of biogas upgrading, utilisation and storage. Energy Convers. Manag. 2017, 150, 277–294. [Google Scholar] [CrossRef]
- Rasi, S.; Veijanen, A.; Rintala, J. Trace compounds of biogas from different biogas production plants. Energy 2007, 32, 1375–1380. [Google Scholar] [CrossRef]
- Deublein, D.; Steinhauser, A. Biogas from Waste and Renewable Resources: An Introduction; Wiley-VCH: Weinheim, Germany, 2008; ISBN 9783527621705. [Google Scholar]
- Meyer, T.; Edwards, E.A. Anaerobic digestion of pulp and paper mill wastewater and sludge. Water Res. 2014, 65, 321–349. [Google Scholar] [CrossRef]
- Aquino, S.F.; Stuckey, D.C. Integrated model of the production of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in anaerobic chemostats during transient conditions. Biochem. Eng. J. 2008, 38, 138–146. [Google Scholar] [CrossRef]
- Pham, H.D.; Seon, J.; Lee, S.C.; Song, M.; Woo, H.-C. Maximization of volatile fatty acids production from alginate in acidogenesis. Bioresour. Technol. 2013, 148, 601–604. [Google Scholar] [CrossRef] [PubMed]
- Zhen, G.; Lu, X.; Kato, H.; Zhao, Y.; Li, Y.-Y. Overview of pretreatment strategies for enhancing sewage sludge disintegration and subsequent anaerobic digestion: Current advances, full-scale application and future perspectives. Renew. Sustain. Energy Rev. 2017, 69, 559–577. [Google Scholar] [CrossRef]
- Mao, C.; Feng, Y.; Wang, X.; Ren, G. Review on research achievements of biogas from anaerobic digestion. Renew. Sustain. Energy Rev. 2015, 45, 540–555. [Google Scholar] [CrossRef]
- Gujer, W.; Zehnder, A.J.B. Conversion processes in anaerobic digestion. Water Sci. Technol. 1983, 15, 127–167. [Google Scholar] [CrossRef]
- Müller, J.A. Prospects and problems of sludge pre-treatment processes. Water Sci. Technol. 2001, 44, 121–128. [Google Scholar] [CrossRef]
- Wawrzynczyk, J. Enzymatic Treatment of Wastewater Sludge. Sludge Solubilisation, Improvement of Anaerobic Digestion and Extraction of Extracellular Polymeric Substances. Ph.D. Thesis, Lund University, Lund, Sweden, 2007. [Google Scholar]
- Beijer, R. Enzymatic Treatement of Wastewater Sludge in Presence of a Cation Binding Agent: Improved Solubilisation and Increased Methane Production. Master’s Thesis, Linköping University, Linköping, Sweden, 2008. [Google Scholar]
- Shi, Y.; Yang, J.; Yu, W.; Zhang, S.; Liang, S.; Song, J.; Xu, Q.; Ye, N.; He, S.; Yang, C.; et al. Synergetic conditioning of sewage sludge via Fe2+/persulfate and skeleton builder: Effect on sludge characteristics and dewaterability. Chem. Eng. J. 2015, 270, 572–581. [Google Scholar] [CrossRef]
- Li, X.Y.; Yang, S.F. Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge. Water Res. 2007, 41, 1022–1030. [Google Scholar] [CrossRef]
- Carrère, H.; Bougrier, C.; Castets, D.; Delgenès, J.P. Impact of initial biodegradability on sludge anaerobic digestion enhancement by thermal pretreatment. J. Environ. Sci. Health A 2008, 43, 1551–1555. [Google Scholar] [CrossRef]
- Hu, K.; Jiang, J.-Q.; Zhao, Q.-L.; Lee, D.-J.; Wang, K.; Qiu, W. Conditioning of wastewater sludge using freezing and thawing: Role of curing. Water Res. 2011, 45, 5969–5976. [Google Scholar] [CrossRef] [PubMed]
- Nowicka, E.; Machnicka, A.; Grübel, K. Improving of anaerobic digestion by dry ice disintegration of activated sludge. Ecol. Chem. Eng. A 2014, 21, 211–219. [Google Scholar] [CrossRef]
- Yu, S.; Zhang, G.; Li, J.; Zhao, Z.; Kang, X. Effect of endogenous hydrolytic enzymes pretreatment on the anaerobic digestion of sludge. Bioresour. Technol. 2013, 146, 758–761. [Google Scholar] [CrossRef]
- Glaze, W.H.; Kang, J.-W.; Chapin, D.H. The Chemistry of Water Treatment Processes Involving Ozone, Hydrogen Peroxide and Ultraviolet Radiation. Ozone Sci. Eng. 1987, 9, 335–352. [Google Scholar] [CrossRef]
- Woodard, S.E.; Wukasch, R.F. A hydrolysis/thickening/filtration process for the treatment of waste activated sludge. Water Sci. Technol. 1994, 30, 29–38. [Google Scholar] [CrossRef]
- Grübel, K.; Suschka, J. Hybrid alkali-hydrodynamic disintegration of waste-activated sludge before two-stage anaerobic digestion process. Environ. Sci. Pollut. Res. 2015, 22, 7258–7270. [Google Scholar] [CrossRef] [PubMed]
- Grubel, K.; Machnicka, A.; Waclawek, S. Impact of alkalization of surplus activated sludge on biogas production. Ecol. Chem. Eng. S 2013, 20, 343–351. [Google Scholar] [CrossRef]
- Gogate, P.R.; Shirgaonkar, I.Z.; Sivakumar, M.; Senthilkumar, P.; Vichare, N.P.; Pandit, A.B. Cavitation reactors: Efficiency assessment using a model reaction. AIChE J. 2001, 47, 2526–2538. [Google Scholar] [CrossRef]
- Machnicka, A.; Grubel, K.; Suschka, J. The use of hydrodynamic disintegration as a means to improve anaerobic digestion of activated sludge. Water SA 2009, 35, 129–132. [Google Scholar] [CrossRef]
- Müller, J. Disintegration as a key-step in sewage sludge treatment. Water Sci. Technol. 2000, 41, 123–130. [Google Scholar] [CrossRef]
- Antoniadis, A.; Poulios, I.; Nikolakaki, E.; Mantzavinos, D. Sonochemical disinfection of municipal wastewater. J. Hazard. Mater. 2007, 146, 492–495. [Google Scholar] [CrossRef] [PubMed]
- Zhang, P.; Zhang, G.; Wang, W. Ultrasonic treatment of biological sludge: Floc disintegration, cell lysis and inactivation. Bioresour. Technol. 2007, 98, 207–210. [Google Scholar] [CrossRef]
- Ali, M.; Zhang, J.; Raga, R.; Lavagnolo, M.C.; Pivato, A.; Wang, X.; Zhang, Y.; Cossu, R.; Yue, D. Effectiveness of aerobic pretreatment of municipal solid waste for accelerating biogas generation during simulated landfilling. Front. Environ. Sci. Eng. 2018, 12, 5. [Google Scholar] [CrossRef]
- Carrère, H.; Dumas, C.; Battimelli, A.; Batstone, D.J.; Delgenès, J.P.; Steyer, J.P.; Ferrer, I. Pretreatment methods to improve sludge anaerobic degradability: A review. J. Hazard. Mater. 2010, 183, 1–15. [Google Scholar] [CrossRef]
- Merrylin, J.; Kumar, S.A.; Kaliappan, S.; Yeom, I.-T.; Banu, J.R. Biological pretreatment of non-flocculated sludge augments the biogas production in the anaerobic digestion of the pretreated waste activated sludge. Environ. Technol. 2013, 34, 2113–2123. [Google Scholar] [CrossRef] [PubMed]
- Gebreeyessus, G.D.; Jenicek, P. Thermophilic versus Mesophilic Anaerobic Digestion of Sewage Sludge: A Comparative Review. Bioengineering 2016, 3, 15. [Google Scholar] [CrossRef] [PubMed]
- Ferrer, I.; Vázquez, F.; Font, X. Long term operation of a thermophilic anaerobic reactor: Process stability and efficiency at decreasing sludge retention time. Bioresour. Technol. 2010, 101, 2972–2980. [Google Scholar] [CrossRef]
- Ponsá, S.; Ferrer, I.; Vázquez, F.; Font, X. Optimization of the hydrolytic–acidogenic anaerobic digestion stage (55 °C) of sewage sludge: Influence of pH and solid content. Water Res. 2008, 42, 3972–3980. [Google Scholar] [CrossRef] [PubMed]
- Ge, H.; Jensen, P.D.; Batstone, D.J. Temperature phased anaerobic digestion increases apparent hydrolysis rate for waste activated sludge. Water Res. 2011, 45, 1597–1606. [Google Scholar] [CrossRef] [PubMed]
- Jang, H.M.; Park, S.K.; Ha, J.H.; Park, J.M. Microbial community structure in a thermophilic aerobic digester used as a sludge pretreatment process for the mesophilic anaerobic digestion and the enhancement of methane production. Bioresour. Technol. 2013, 145, 80–89. [Google Scholar] [CrossRef] [PubMed]
- Romero-Güiza, M.S.; Vila, J.; Mata-Alvarez, J.; Chimenos, J.M.; Astals, S. The role of additives on anaerobic digestion: A review. Renew. Sustain. Energy Rev. 2016, 58, 1486–1499. [Google Scholar] [CrossRef]
- Nzila, A. Mini review: Update on bioaugmentation in anaerobic processes for biogas production. Anaerobe 2017, 46, 3–12. [Google Scholar] [CrossRef]
- Prapinagsorn, W.; Sittijunda, S.; Reungsang, A. Co-digestion of napier grass and its silage with cow dung for methane production. Energies 2017, 10, 1654. [Google Scholar] [CrossRef]
- Ai, S.; Liu, H.; Wu, M.; Zeng, G.; Yang, C. Roles of acid-producing bacteria in anaerobic digestion of waste activated sludge. Front. Environ. Sci. Eng. 2018, 12. [Google Scholar] [CrossRef]
- You, M.Y.; Chai, T.Y.; Pan, Y.; Zhu, Y.N.; Cao, Y.H.; Li, X.J.; Xie, Y.H.; Han, J.; Zhu, T. Review of Excess Sludge Disintegration Research. Adv. Mater. Res. 2013, 726–731, 2949–2955. [Google Scholar] [CrossRef]
- Gopi Kumar, S.; Merrylin, J.; Kaliappan, S.; Adish Kumar, S.; Tae Yeom, I.; Rajesh Banu, J. Effect of cation binding agents on sludge solubilization potential of bacteria. Biotechnol. Bioprocess Eng. 2012, 17, 346–352. [Google Scholar] [CrossRef]
- Mayhew, M.E.; Le, M.S.; Ratcliff, R. A novel approach to pathogen reduction in biosolids: The enzymic hydrolyser. Water Sci. Technol. 2002, 46, 427–434. [Google Scholar] [CrossRef] [PubMed]
- Mayhew, M.; Le, M.S.; Brade, C.E.; Harrison, D. The united utitlities ‘enzymic hydrolysis process’—Validation of phased digestion at full scale to enhance pathogen removal. Proc. Water Environ. Fed. 2003, 2003, 1000–1013. [Google Scholar] [CrossRef]
- Miah, M.S.; Tada, C.; Sawayama, S. Enhancement of Biogas Production from Sewage Sludge with the Addition of Geobacillus sp. Strain AT1 Culture. Jpn. J. Water Treat. Biol. 2004, 40, 97–104. [Google Scholar] [CrossRef]
- Wawrzynczyk, J.; Norrlöw, O.; Dey, E.; la Cour Jansen, J. Alternative Method for Sludge Reduction Using Commercial Enzymes. In Proceedings of the Aqua Enviro European Biosolids and Organic Residuals Conference, Wakefield, West Yorkshire, UK, 24–26 November 2003; pp. 1–5. [Google Scholar]
- Davidsson, Å.; Wawrzynczyk, J.; Norrlöw, O.; la Cour Jansen, J. Strategies for enzyme dosing to enhance anaerobic digestion of sewage sludge. J. Residuals Sci. Technol. 2007, 4, 1–7. [Google Scholar]
- Recktenwald, M.; Wawrzynczyk, J.; Dey, E.S.; Norrlöw, O. Enhanced efficiency of industrial-scale anaerobic digestion by the addition of glycosidic enzymes. J. Environ. Sci. Health Part A 2008, 43, 1536–1540. [Google Scholar] [CrossRef]
- Jang, H.M.; Cho, H.U.; Park, S.K.; Ha, J.H.; Park, J.M. Influence of thermophilic aerobic digestion as a sludge pre-treatment and solids retention time of mesophilic anaerobic digestion on the methane production, sludge digestion and microbial communities in a sequential digestion process. Water Res. 2014, 48, 1–14. [Google Scholar] [CrossRef]
- Bayr, S.; Kaparaju, P.; Rintala, J. Screening pretreatment methods to enhance thermophilic anaerobic digestion of pulp and paper mill wastewater treatment secondary sludge. Chem. Eng. J. 2013, 223, 479–486. [Google Scholar] [CrossRef][Green Version]
- Kavitha, S.; Jayashree, C.; Adish Kumar, S.; Yeom, I.T.; Rajesh Banu, J. The enhancement of anaerobic biodegradability of waste activated sludge by surfactant mediated biological pretreatment. Bioresour. Technol. 2014, 168, 159–166. [Google Scholar] [CrossRef]
- Climent, M.; Ferrer, I.; Baeza, M.; Artola, A.; Vázquez, F.; Font, X. Effects of thermal and mechanical pretreatments of secondary sludge on biogas production under thermophilic conditions. Chem. Eng. J. 2007, 133, 335–342. [Google Scholar] [CrossRef]
- Barjenbruch, M.; Kopplow, O. Enzymatic, mechanical and thermal pre-treatment of surplus sludge. Adv. Environ. Res. 2003, 7, 715–720. [Google Scholar] [CrossRef]
- Hasegawa, S.; Shiota, N.; Katsura, K.; Akashi, A. Solubilization of organic sludge by thermophilic aerobic bacteria as a pretreatment for anaerobic digestion. Water Sci. Technol. 2000, 41, 163–169. [Google Scholar] [CrossRef] [PubMed]
- Prajapati, K.B.; Singh, R. Kinetic modelling of methane production during bio-electrolysis from anaerobic co-digestion of sewage sludge and food waste. Bioresour. Technol. 2018, 263, 491–498. [Google Scholar] [CrossRef] [PubMed]
- Kim, J.; Park, C.; Kim, T.; Lee, M.; Kim, S.; Eung-wook Kim, S.; Lee, J. Effects of Various Pretreatments for Enhanced Anaerobic Digestion with Waste Activated Sludge. J. Biosci. Bioeng. 2003, 95, 271–275. [Google Scholar] [CrossRef]
- Parthiba Karthikeyan, O.; Trably, E.; Mehariya, S.; Bernet, N.; Wong, J.W.C.; Carrere, H. Pretreatment of food waste for methane and hydrogen recovery: A review. Bioresour. Technol. 2018, 249, 1025–1039. [Google Scholar] [CrossRef][Green Version]
- Wang, Q.; Jiang, G.; Ye, L.; Yuan, Z. Enhancing methane production from waste activated sludge using combined free nitrous acid and heat pre-treatment. Water Res. 2014, 63, 71–80. [Google Scholar] [CrossRef][Green Version]
- Silvestri, D.; Wacławek, S.; Gončuková, Z.; Padil, V.V.T.; Grübel, K.; Černík, M. A new method for assessment of the sludge disintegration degree with the use of differential centrifugal sedimentation. Environ. Technol. 2018, 1–8. [Google Scholar] [CrossRef]
- Lee, I.; Han, J.-I. The effects of waste-activated sludge pretreatment using hydrodynamic cavitation for methane production. Ultrason. Sonochem. 2013, 20, 1450–1455. [Google Scholar] [CrossRef]
- Modenbach, A.A.; Nokes, S.E. The use of high-solids loadings in biomass pretreatment—A review. Biotechnol. Bioeng. 2012, 109, 1430–1442. [Google Scholar] [CrossRef]
- Wonglertarak, W.; Wichitsathian, B. Alkaline Pretreatment of Waste Activated Sludge in Anaerobic Digestion. J. Clean Energy Technol. 2014, 118–121. [Google Scholar] [CrossRef]
- Ikehata, K.; El-Din, M.G. Degradation of recalcitrant surfactants in wastewater by ozonation and advanced oxidation processes: A review. Ozone Sci. Eng. 2004, 26, 327–343. [Google Scholar] [CrossRef]
- Wang, F.; Smith, D.W.; El-Din, M.G. Application of advanced oxidation methods for landfill leachate treatment—A review. J. Environ. Eng. Sci. 2003, 2, 413–427. [Google Scholar] [CrossRef]
- Sievers, M.; Ried, A.; Koll, R. Sludge treatment by ozonation Ð evaluation of full-scale results. Water Sci. Technol. 2004, 49, 247–253. [Google Scholar] [CrossRef] [PubMed]
- Carbajo, J.B.; Petre, A.L.; Rosal, R.; Berná, A.; Letón, P.; García-Calvo, E.; Perdigón-Melón, J.A. Ozonation as pre-treatment of activated sludge process of a wastewater containing benzalkonium chloride and NiO nanoparticles. Chem. Eng. J. 2016, 283, 740–749. [Google Scholar] [CrossRef]
- Oller, I.; Malato, S.; Sánchez-Pérez, J.A. Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination—A review. Sci. Total Environ. 2011, 409, 4141–4166. [Google Scholar] [CrossRef] [PubMed]
- Chu, C.; Lee, D.; Chang, B.-V.; You, C.; Tay, J. “Weak” ultrasonic pre-treatment on anaerobic digestion of flocculated activated biosolids. Water Res. 2002, 36, 2681–2688. [Google Scholar] [CrossRef]
- Paul, E.; Camacho, P.; Sperandio, M.; Ginestet, P. Technical and Economical Evaluation of a Thermal, and Two Oxidative Techniques for the Reduction of Excess Sludge Production. Process Saf. Environ. Prot. 2006, 84, 247–252. [Google Scholar] [CrossRef]
- Saktaywin, W.; Tsuno, H.; Nagare, H.; Soyama, T.; Weerapakkaroon, J. Advanced sewage treatment process with excess sludge reduction and phosphorus recovery. Water Res. 2005, 39, 902–910. [Google Scholar] [CrossRef]
- Yeom, I.T.; Lee, K.R.; Ahn, K.H.; Lee, S.H. Effects of ozone treatment on the biodegradability of sludge from municipal wastewater treatment plants. Water Sci. Technol. 2002, 46, 421–425. [Google Scholar] [CrossRef]
- Bougrier, C.; Battimelli, A.; Delgenes, J.-P.; Carrere, H. Combined Ozone Pretreatment and Anaerobic Digestion for the Reduction of Biological Sludge Production in Wastewater Treatment. Ozone Sci. Eng. 2007, 29, 201–206. [Google Scholar] [CrossRef]
- Valo, A.; Carrère, H.; Delgenès, J.P. Thermal, chemical and thermo-chemical pre-treatment of waste activated sludge for anaerobic digestion. J. Chem. Technol. Biotechnol. 2004, 79, 1197–1203. [Google Scholar] [CrossRef]
- Ak, M.S.; Muz, M.; Komesli, O.T.; Gökçay, C.F. Enhancement of bio-gas production and xenobiotics degradation during anaerobic sludge digestion by ozone treated feed sludge. Chem. Eng. J. 2013, 230, 499–505. [Google Scholar] [CrossRef]
- Silvestre, G.; Ruiz, B.; Fiter, M.; Ferrer, C.; Berlanga, J.G.; Alonso, S.; Canut, A. Ozonation as a Pre-treatment for Anaerobic Digestion of Waste-Activated Sludge: Effect of the Ozone Doses. Ozone Sci. Eng. 2015, 37, 316–322. [Google Scholar] [CrossRef]
- Carballa, M.; Manterola, G.; Larrea, L.; Ternes, T.; Omil, F.; Lema, J.M. Influence of ozone pre-treatment on sludge anaerobic digestion: Removal of pharmaceutical and personal care products. Chemosphere 2007, 67, 1444–1452. [Google Scholar] [CrossRef] [PubMed]
- Bougrier, C.; Delgenès, J.-P.; Carrère, H. Combination of Thermal Treatments and Anaerobic Digestion to Reduce Sewage Sludge Quantity and Improve Biogas Yield. Process Saf. Environ. Prot. 2006, 84, 280–284. [Google Scholar] [CrossRef]
- Battimelli, A.; Millet, C.; Delgenès, J.P.; Moletta, R. Anaerobic digestion of waste activated sludge combined with ozone post-treatment and recycling. Water Sci. Technol. 2003, 48, 61–68. [Google Scholar] [CrossRef] [PubMed]
- Barbusinski, K. Fenton reaction—Controversy concerning the chemistry. Ecol. Chem. Eng. S 2009, 16, 347–358. [Google Scholar]
- Dewil, R.; Appels, L.; Baeyens, J.; Degrève, J. Peroxidation enhances the biogas production in the anaerobic digestion of biosolids. J. Hazard. Mater. 2007, 146, 577–581. [Google Scholar] [CrossRef]
- Hallaji, S.M.; Torabian, A.; Aminzadeh, B.; Zahedi, S.; Eshtiaghi, N. Improvement of anaerobic digestion of sewage mixed sludge using free nitrous acid and Fenton pre-treatment. Biotechnol. Biofuels 2018, 11, 233. [Google Scholar] [CrossRef]
- Montalvo, S.; Vielma, S.; Borja, R.; Huiliñir, C.; Guerrero, L. Increase in biogas production in anaerobic sludge digestion by combining aerobic hydrolysis and addition of metallic wastes. Renew. Energy 2018, 123, 541–548. [Google Scholar] [CrossRef]
- Anjum, M.; Al-Talhi, H.A.; Mohamed, S.A.; Kumar, R.; Barakat, M.A. Visible light photocatalytic disintegration of waste activated sludge for enhancing biogas production. J. Environ. Manag. 2018, 216, 120–127. [Google Scholar] [CrossRef] [PubMed]
- Wacławek, S.; Grübel, K.; Chłąd, Z.; Dudziak, M.; Chład, Z.; Dudziak, M.; Chłąd, Z.; Dudziak, M. Impact of peroxydisulphate on disintegration and sedimentation properties of municipal wastewater activated sludge. Chem. Pap. 2015, 69, 1473–1480. [Google Scholar] [CrossRef]
- Sun, D.D.; Liang, H.M.; Ma, C. Enhancement of Sewage Sludge Anaerobic Digestibility by Sulfate Radical Pretreatment. Adv. Mater. Res. 2012, 518–523, 3358–3362. [Google Scholar] [CrossRef]
- Liu, C.; Wu, B.; Chen, X. Sulfate radical-based oxidation for sludge treatment: A review. Chem. Eng. J. 2018, 335, 865–875. [Google Scholar] [CrossRef]
- Wang, S.; Wang, J. Activation of peroxymonosulfate by sludge-derived biochar for the degradation of triclosan in water and wastewater. Chem. Eng. J. 2018, 356, 350–358. [Google Scholar] [CrossRef]
- Ji, Y.; Xie, W.; Fan, Y.; Shi, Y.; Kong, D.; Lu, J. Degradation of trimethoprim by thermo-activated persulfate oxidation: Reaction kinetics and transformation mechanisms. Chem. Eng. J. 2016, 286, 16–24. [Google Scholar] [CrossRef]
- Kim, C.; Ahn, J.Y.; Kim, T.Y.; Shin, W.S.; Hwang, I. Activation of Persulfate by Nanosized Zero-Valent Iron (NZVI): Mechanisms and Transformation Products of NZVI. Environ. Sci. Technol. 2018, 52, 3625–3633. [Google Scholar] [CrossRef]
- Zhang, R.; Sun, P.; Boyer, T.H.; Zhao, L.; Huang, C.-H. Degradation of Pharmaceuticals and Metabolite in Synthetic Human Urine by UV, UV/H2O2, and UV/PDS. Environ. Sci. Technol. 2015, 49, 3056–3066. [Google Scholar] [CrossRef]
- Siegrist, R.L.; Crimi, M.; Brown, R. In Situ Chemical Oxidation: Technology Description and Status; Springer: New York, NY, USA, 2011; ISBN 978-1-4419-7825-7. [Google Scholar]
- Wacławek, S.; Lutze, H.V.; Grübel, K.; Padil, V.V.T.; Černík, M.; Dionysiou, D.D. Chemistry of persulfates in water and wastewater treatment: A review. Chem. Eng. J. 2017, 330, 44–62. [Google Scholar] [CrossRef]
- Neyens, E.; Baeyens, J. A review of classic Fenton’s peroxidation as an advanced oxidation technique. J. Hazard. Mater. 2003, 98, 33–50. [Google Scholar] [CrossRef]
- Jin, B.; Niu, J.; Dai, J.; Li, N.; Zhou, P.; Niu, J.; Zhang, J.; Tao, H.; Ma, Z.; Zhang, Z. New insights into the enhancement of biochemical degradation potential from waste activated sludge with low organic content by Potassium Monopersulfate treatment. Bioresour. Technol. 2018, 265, 8–16. [Google Scholar] [CrossRef] [PubMed]
- Godvin Sharmila, V.; Rajesh Banu, J.; Gunasekaran, M.; Angappane, S.; Yeom, I.T. Nano-layered TiO2 for effective bacterial disintegration of waste activated sludge and biogas production. J. Chem. Technol. Biotechnol. 2018, 93, 2701–2709. [Google Scholar] [CrossRef]
- Shang, M.; Hou, H. Studies on Effect of Peracetic Acid Pretreatment on Anaerobic Fermentation Biogas Production from Sludge. In Proceedings of the 2009 Asia-Pacific Power and Energy Engineering Conference, Wuhan, China, 27–31 March 2009; pp. 1–3. [Google Scholar]
- Zábranská, J.; Dohányos, M.; Jenícek, P.; Kutil, J. Disintegration of excess activated sludge—Evaluation and experience of full-scale applications. Water Sci. Technol. 2006, 53, 229–236. [Google Scholar] [CrossRef] [PubMed]
- Elliott, A.; Mahmood, T. Pretreatment technologies for advancing anaerobic digestion of pulp and paper biotreatment residues. Water Res. 2007, 41, 4273–4286. [Google Scholar] [CrossRef] [PubMed]
- Engelhart, M.; Krueger, M.; Kopp, J.; Dichtl, N. Effects of disintegration on anaerobic degradation of sewage excess sludge in downflow stationary fixed film digesters. Water Sci. Technol. 2000, 41, 171–179. [Google Scholar] [CrossRef] [PubMed]
- Kumar, P.S.; Pandit, A.B. Modeling Hydrodynamic Cavitation. Chem. Eng. Technol. 1999, 22, 1017–1027. [Google Scholar] [CrossRef]
- Grűbel, K.; Machnicka, A. Use of Hydrodynamic Disintegration to Accelerate Anaerobic Digestion of Surplus Activated Sludge. Water Environ. Res. 2009, 81, 2420–2426. [Google Scholar] [CrossRef]
- Mirota, K.; Grubel, K.; Machnicka, A. Design and assessment of cavitational device for enhancement of sewage sludge fermentation. Ochr. Śr. 2011, 33, 47–52. [Google Scholar]
- Senthil Kumar, P.; Siva Kumar, M.; Pandit, A. Experimental quantification of chemical effects of hydrodynamic cavitation. Chem. Eng. Sci. 2000, 55, 1633–1639. [Google Scholar] [CrossRef]
- Vichare, N.P.; Gogate, P.R.; Pandit, A.B. Optimization of Hydrodynamic Cavitation Using a Model Reaction. Chem. Eng. Technol. 2000, 23, 683–690. [Google Scholar] [CrossRef]
- Machnicka, A.; Grübel, K.; Mirota, K. Considerations of impact of Venturi effect on mesophilic digestion. Ecol. Chem. Eng. S 2015, 22, 645–658. [Google Scholar] [CrossRef]
- Tiehm, A.; Nickel, K.; Zellhorn, M.; Neis, U. Ultrasonic waste activated sludge disintegration for improving anaerobic stabilization. Water Res. 2001, 35, 2003–2009. [Google Scholar] [CrossRef]
- Machnicka, A.; Grübel, K.; Suschka, J. The use of disintegrated foam to accelerate anaerobic digestion of activated sludge. Arch. Environ. Prot. 2009, 35, 11–19. [Google Scholar] [CrossRef]
- Zhou, Z.; Yang, Y.; Li, X. Effects of ultrasound pretreatment on the characteristic evolutions of drinking water treatment sludge and its impact on coagulation property of sludge recycling process. Ultrason. Sonochem. 2015, 27, 62–71. [Google Scholar] [CrossRef] [PubMed]
- Aylin Alagöz, B.; Yenigün, O.; Erdinçler, A. Ultrasound assisted biogas production from co-digestion of wastewater sludges and agricultural wastes: Comparison with microwave pre-treatment. Ultrason. Sonochem. 2018, 40, 193–200. [Google Scholar] [CrossRef] [PubMed]
- Bougrier, C.; Carrère, H.; Delgenès, J.P. Solubilisation of waste-activated sludge by ultrasonic treatment. Chem. Eng. J. 2005, 106, 163–169. [Google Scholar] [CrossRef]
- Salsabil, M.R.; Prorot, A.; Casellas, M.; Dagot, C. Pre-treatment of activated sludge: Effect of sonication on aerobic and anaerobic digestibility. Chem. Eng. J. 2009, 148, 327–335. [Google Scholar] [CrossRef]
- Mao, T.; Show, K.-Y. Influence of ultrasonication on anaerobic bioconversion of sludge. Water Environ. Res. 2007, 79, 436–441. [Google Scholar] [CrossRef]
- Mao, T.; Show, K.Y. Performance of high-rate sludge digesters fed with sonicated sludge. Water Sci. Technol. 2006, 54, 27–33. [Google Scholar] [CrossRef]
- Lizama, A.C.; Figueiras, C.C.; Pedreguera, A.Z.; Ruiz Espinoza, J.E. Effect of ultrasonic pretreatment on the semicontinuous anaerobic digestion of waste activated sludge with increasing loading rates. Int. Biodeterior. Biodegrad. 2018, 130, 32–39. [Google Scholar] [CrossRef]
- Odnell, A.; Recktenwald, M.; Stensén, K.; Jonsson, B.H.; Karlsson, M. Activity, life time and effect of hydrolytic enzymes for enhanced biogas production from sludge anaerobic digestion. Water Res. 2016, 103, 462–471. [Google Scholar] [CrossRef] [PubMed]
- Ding, H.H.; Chang, S.; Liu, Y. Biological hydrolysis pretreatment on secondary sludge: Enhancement of anaerobic digestion and mechanism study. Bioresour. Technol. 2017, 244, 989–995. [Google Scholar] [CrossRef] [PubMed]
- Zhang, S.; Guo, H.; Du, L.; Liang, J.; Lu, X.; Li, N.; Zhang, K. Influence of NaOH and thermal pretreatment on dewatered activated sludge solubilisation and subsequent anaerobic digestion: Focused on high-solid state. Bioresour. Technol. 2015, 185, 171–177. [Google Scholar] [CrossRef] [PubMed]
- Ruiz-Hernando, M.; Martín-Díaz, J.; Labanda, J.; Mata-Alvarez, J.; Llorens, J.; Lucena, F.; Astals, S. Effect of ultrasound, low-temperature thermal and alkali pre-treatments on waste activated sludge rheology, hygienization and methane potential. Water Res. 2014, 61, 119–129. [Google Scholar] [CrossRef] [PubMed][Green Version]
- Alqaralleh, R.M.; Kennedy, K.; Delatolla, R. Improving biogas production from anaerobic co-digestion of Thickened Waste Activated Sludge (TWAS) and fat, oil and grease (FOG) using a dual-stage hyper-thermophilic/thermophilic semi-continuous reactor. J. Environ. Manag. 2018, 217, 416–428. [Google Scholar] [CrossRef] [PubMed]
- Mirmasoumi, S.; Khoshbakhti Saray, R.; Ebrahimi, S. Evaluation of thermal pretreatment and digestion temperature rise in a biogas fueled combined cooling, heat, and power system using exergo-economic analysis. Energy Convers. Manag. 2018, 163, 219–238. [Google Scholar] [CrossRef]
- Kang, X.; Liu, Y.; Li, X.; Yuan, Y.; Du, M. Two-stage mesophilic anaerobic digestion from waste activated sludge enhanced by low-temperature thermal hydrolysis. Desalin. Water Treat. 2016, 57, 7607–7614. [Google Scholar] [CrossRef]
- Gagliano, M.C.; Braguglia, C.M.; Gianico, A.; Mininni, G.; Nakamura, K.; Rossetti, S. Thermophilic anaerobic digestion of thermal pretreated sludge: Role of microbial community structure and correlation with process performances. Water Res. 2015, 68, 498–509. [Google Scholar] [CrossRef]
- Ebenezer, A.V.; Arulazhagan, P.; Adish Kumar, S.; Yeom, I.-T.; Rajesh Banu, J. Effect of deflocculation on the efficiency of low-energy microwave pretreatment and anaerobic biodegradation of waste activated sludge. Appl. Energy 2015, 145, 104–110. [Google Scholar] [CrossRef]
- Houtmeyers, S.; Degrève, J.; Willems, K.; Dewil, R.; Appels, L. Comparing the influence of low power ultrasonic and microwave pre-treatments on the solubilisation and semi-continuous anaerobic digestion of waste activated sludge. Bioresour. Technol. 2014, 171, 44–49. [Google Scholar] [CrossRef] [PubMed]
- Zieliński, M.; Dębowski, M.; Krzemieniewski, M.; Rusanowska, P.; Zielińska, M.; Cydzik-Kwiatkowska, A.; Głowacka-Gil, A. Application of an Innovative Ultrasound Disintegrator for Sewage Sludge Conditioning Before Methane Fermentation. J. Ecol. Eng. 2018, 19, 240–247. [Google Scholar] [CrossRef]
- Martín, M.Á.; González, I.; Serrano, A.; Siles, J.Á. Evaluation of the improvement of sonication pre-treatment in the anaerobic digestion of sewage sludge. J. Environ. Manag. 2015, 147, 330–337. [Google Scholar] [CrossRef]
- Lu, D.; Xiao, K.; Chen, Y.; Soh, Y.N.A.; Zhou, Y. Transformation of dissolved organic matters produced from alkaline-ultrasonic sludge pretreatment in anaerobic digestion: From macro to micro. Water Res. 2018, 142, 138–146. [Google Scholar] [CrossRef] [PubMed]
- Liu, X.; Xu, Q.; Wang, D.; Zhao, J.; Wu, Y.; Liu, Y.; Ni, B.-J.; Wang, Q.; Zeng, G.; Li, X.; et al. Improved methane production from waste activated sludge by combining free ammonia with heat pretreatment: Performance, mechanisms and applications. Bioresour. Technol. 2018, 268, 230–236. [Google Scholar] [CrossRef] [PubMed]
- Ferrer, I.; Ponsá, S.; Vázquez, F.; Font, X. Increasing biogas production by thermal (70 °C) sludge pre-treatment prior to thermophilic anaerobic digestion. Biochem. Eng. J. 2008, 42, 186–192. [Google Scholar] [CrossRef]
- Ferrer, I.; Serrano, E.; Ponsa, S.; Vazquez, F.; Font, X. Enhancement of thermophilic anaerobic sludge digestion by 70 °C pre-treatment: Energy considerations. J. Residuals Sci. Technol. 2009, 6, 8. [Google Scholar]
- Hendriks, A.T.W.M.; Zeeman, G. Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresour. Technol. 2009, 100, 10–18. [Google Scholar] [CrossRef]
- Delgenès, J.P.; Penaud, V.; Torrijos, M.; Moletta, R. Investigations on the changes in anaerobic biodegradability and biotoxicity of an industrial microbial biomass induced by a thermochemical pretreatment. Water Sci. Technol. 2000, 41, 137–144. [Google Scholar] [CrossRef]
- Aboulfotoh, A.M.; EI Gohary, E.H.; EI Monayeri, O.D. Effect Of Thermal Pretreatment On The Solubilization Of Organic Matters In A Mixture Of Primary And Waste Activated Sludge. J. Urban Environ. Eng. 2015, 9, 82–88. [Google Scholar] [CrossRef]
- Kepp, U.; Machenbach, I.; Weisz, N.; Solheim, O.E. Enhanced stabilisation of sewage sludge through thermal hydrolysis—Three years of experience with full scale plant. Water Sci. Technol. 2000, 42, 89–96. [Google Scholar] [CrossRef]
- Ennouri, H.; Miladi, B.; Diaz, S.Z.; Güelfo, L.A.F.; Solera, R.; Hamdi, M.; Bouallagui, H. Effect of thermal pretreatment on the biogas production and microbial communities balance during anaerobic digestion of urban and industrial waste activated sludge. Bioresour. Technol. 2016, 214, 184–191. [Google Scholar] [CrossRef] [PubMed]
- Dwyer, J.; Starrenburg, D.; Tait, S.; Barr, K.; Batstone, D.J.; Lant, P. Decreasing activated sludge thermal hydrolysis temperature reduces product colour, without decreasing degradability. Water Res. 2008, 42, 4699–4709. [Google Scholar] [CrossRef]
- Batstone, D.J.; Balthes, C.; Barr, K. Model assisted startup of anaerobic digesters fed with thermally hydrolysed activated sludge. Water Sci. Technol. 2010, 62, 1661–1666. [Google Scholar] [CrossRef] [PubMed]
- Bohdziewicz, J.; Kuglarz, M.; Grubel, K. Influence of microwave pre-treatment on the digestion and higienisation of waste activated sludge. Ecol. Chem. Eng. S 2014, 21, 447–464. [Google Scholar] [CrossRef]
- Yi, W.G.; Lo, K.V.; Mavinic, D.S. Effects of microwave, ultrasonic and enzymatic treatment on chemical and physical properties of waste-activated sludge. J. Environ. Sci. Health Part A 2014, 49, 203–209. [Google Scholar] [CrossRef] [PubMed]
- Park, W.-J.; Ahn, J.-H. Effects of Microwave Pretreatment on Mesophilic Anaerobic Digestion for Mixture of Primary and Secondary Sludges Compared with Thermal Pretreatment. Environ. Eng. Res. 2011, 16, 103–109. [Google Scholar] [CrossRef]
- Kuglarz, M.; Karakashev, D.; Angelidaki, I. Microwave and thermal pretreatment as methods for increasing the biogas potential of secondary sludge from municipal wastewater treatment plants. Bioresour. Technol. 2013, 134, 290–297. [Google Scholar] [CrossRef]
- Eskicioglu, C.; Kennedy, K.J.; Droste, R.L. Enhanced disinfection and methane production from sewage sludge by microwave irradiation. Desalination 2009, 248, 279–285. [Google Scholar] [CrossRef]
- Tang, B.; Yu, L.; Huang, S.; Luo, J.; Zhuo, Y. Energy efficiency of pre-treating excess sewage sludge with microwave irradiation. Bioresour. Technol. 2010, 101, 5092–5097. [Google Scholar] [CrossRef]
- Montusiewicz, A.; Lebiocka, M.; Rożej, A.; Zacharska, E.; Pawłowski, L. Freezing/thawing effects on anaerobic digestion of mixed sewage sludge. Bioresour. Technol. 2010, 101, 3466–3473. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Primary production of biogas in the EU (tonnes of oil equivalent·1000; source: https://ec.europa.eu/eurostat; 2018).
Figure 2. Proposed diagram of methane production during anaerobic digestion (based on ).
Figure 3. Diagram showing the available disintegration methods for waste activated sludge.
Table 1. Typical characteristic of biogas.
|Constituents||Energy (kW m−3)||Fuel Equivalent (L oil m−3 biogas)||Ignition Temperature (°C)||Critical Pressure (bar)||Critical Temperature (°C)||Normal Density (kg m−3)|
Table 2. Recent advances in the pretreatment of WAS for biogas production enhancement.
|Disintegration Type||Treatment Type/Condition||Anaerobic Digestion Condition||Results||Reference|
|Biological||Amylase + protease||37 °C||+23% biogas yield|||
|Subtilisin||38 °C||+37% biogas yield|||
|Biological hydrolysis||35 °C||“significantly higher methane generation”|||
|Micro-aerobic hydrolysis||35 °C||38% methane yield|||
|Chemical||Acidification: 0.52–1.42 mg HNO2-N L−1||37 °C||+12–16% methane yield|||
|Acidification: 2.5 mg L−1 HNO2||37 °C||+25% methane yield|||
|Alkalization: 20 mg NaOH g−1 TS||37 °C||+35% methane yield|||
|Alkalization: 157 mg NaOH g−1 TS||37 °C||+34% methane yield|||
|Oxidation: H2O2: 5 mg L−1||37 °C||+27% methane yield|||
|Oxidation: 0.1 g K2S2O8 g−1 SS||35 °C||180% methane yield|||
|Oxidation: [email protected]||35 °C||62% methane yield|||
|Hybrid: HNO2/H2O2||37 °C||+72% methane yield|||
|Physical and hybrid||Thermal:70 °C||55 °C||+148% methane yield|||
|Thermal: 90 °C||55 °C||+161% methane yield|||
|Thermal: 100 °C||33 °C||+343% biogas production|||
|Thermal: 120 °C||33 °C||+345% biogas production|||
|Thermal: 134 °C||55 °C||+47% biogas yield|||
|Microwaves: 14,000 kJ kg−1 TS||35 °C||+570% biogas yield|||
|Ultrasounds: 96 kJ kg−1 Sludge||37 °C||+27% biogas yield|||
|Ultrasounds: 750 kJ||37 °C||+52% methane yield|||
|Ultrasounds: 1000 kJ kg−1 TS||35 °C||+95% methane yield|||
|Ultrasounds: 25,000 kJ kg−1 TS||36 °C||+560% biogas yield|||
|Hybrid: Alkalization + Ultrasounds||35 °C||+33% biogas yield|||
|Hybrid: Free ammonia (135 mg L−1) + 70 °C||35 °C||+25% biogas yield|||
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).