Towards hydrogen production from waste activated sludge: Principles, challenges and perspectives
Graphical abstract
Introduction
With the development of society, people need more and more energy, which inevitably leads to the shortage of fossil fuels. In addition, the combustion of fossil fuels makes large amounts of greenhouse gas (i.e., carbon dioxide) release in the atmosphere, causing the climate change and global warming. The issues of energy shortage and global warming drive the efforts to seek clean, recyclable, and renewable energy. Compared with methane, hydrogen possesses higher energy yield (i.e., 142.35 kJ/g which is 2.75 folds than that of other hydrocarbons) and generates water rather than greenhouse gases while it is combusted [1]. Therefore, hydrogen is considered as the green energy and widely accepted to be the most promising alternative to fossil fuels.
Hydrogen can be produced from valuable resources such as water and fossil fuels, and also from wastes such as sewage and food waste via a series of chemical-physical and biological methods. There are many publications that reported hydrogen production by utilizing the chemical-physical methods and biological methods [2]. Currently, most of the hydrogen (>85%) is produced through the pyrolysis of fossil fuels, and the gasification of biomass [3]. Although these chemical-physical methods could obtain high hydrogen yield, they are not sustainable due to high energy consumption [4,5]. By contrast, biological hydrogen production is a more cost-effective and environmental friendly method to produce hydrogen from varieties of organic wastes (e.g., waste activated sludge) due to the simple operational conditions, steady H2 yield and low energy consumption [6,7]. As for different substrates, using wastes to produce hydrogen is an environmentally favorable and economically sustainable way. With the growing energy crisis worldwide, this aspect is becoming more important and pushing forward new attempts employing more wastes.
Waste activated sludge (WAS), which is the main byproduct of municipal wastewater treatment plants (WWTPs), is generated with large amounts annually [8]. For instance, it was documented that 11.2 million metric tons of dry sludge were generated in China while 10 million tons were produced in EU countries [9]. On one hand, treatment and disposal of such massive amount of WAS are costly, accounting for up to 60% of the total operation cost of a WWTP [10]. On the other hand, WAS contains high levels (50–70%) of organic compounds such as protein, carbohydrate, and lipid [11,12], which makes it an ideal renewable resource. For example, Jiang et al. investigate the physicochemical characteristics of WAS and found that when the volatile suspended solid (VSS) of WAS was 10.81 g/L, WAS contained 14.88 g/L total chemical oxygen demand (TCOD), 9.94 g COD/L total protein, 0.86 g COD/L total carbohydrate, and 0.17 g COD/L lipid and oil [13]. Similar WAS characteristics were also reported in other papers [14,15]. In addition, it was reported that ~35% of carbon element, ~3.8% of nitrogen element, ~1.6% of phosphorus element, and other trace elements contained in WAS [16].
Many publications showed that various wastes containing high organic substrates could be utilized to produce hydrogen by anaerobic fermentation process [17,18], indicating that WAS is a potential substrate for hydrogen production. Although WAS is generally treated by the anaerobic digestion to produce methane, several hydrogen producers are found to be present in the digester such as Clostridium pasteurianum [19] and Thermoanaerobacterium [20,21]. In fact, hydrogen is observed as an important intermediate in the anaerobic digestion process [22]. Thus, hydrogen production from WAS attracted much attention in the past decades, by which fossil fuels are saved, greenhouse gas (e.g., CO2) emission is reduced, WAS is reused and reduced, and sustainable clean energy H2 and volatile fatty acids (VFAs) are also obtained. However, practical application of hydrogen production from WAS has not yet been achieved. On the contrary, some doubts and debates have been arisen recently about its technical and economic feasible in full-scale situations due to the low hydrogen yield. There are many challenges in reactor control, system development, and energy recovery. For example, hydrogen is an intermediate product in the anaerobic digestion, thus the produced hydrogen would be quickly consumed by hydrogen-utilizing methanogens to produce methane, homoacetogens to produce acetic acid, or sulfate-reducing bacteria to produce hydrogen sulfide. The highest hydrogen yield from WAS reported so far has been only 20.30 mg per gram volatile suspended solids [23].
Several review papers were published on hydrogen production using the various wastes such as biodegradable municipal wastes [24], food waste [25], agriculture waste, wastewater [26], and lignocellulosic materials [27,28]. These works were mainly to review the progress of hydrogen production in one aspect or several aspects. For example, Yang et al. provided a review on fermentative hydrogen production from sewage sludge but only focus on pretreatment methods and co-fermentation with other substrates [5]. Systematic summarization and critical thinking of the application niche of hydrogen production from WAS is still lacking. In addition, many endeavors were dedicated recently to improve hydrogen yield from WAS through enhanced the disintegration of WAS and suppressed or killed the competitive microorganisms (e.g., methanogens), which have made great progress [7,29]. Hence, this review article aimed to comprehensively sum up the knowledge obtained in this field and critically think the prospect of biohydrogen production from WAS. To find out whether and how to recover hydrogen in a future paradigm of WAS treatment, the principles and advances of hydrogen production from WAS were needed to systematically review, its opportunities and challenges were required to critically re-examine, and the possible solutions were essential to carefully think about.
Based on reviewing more than 200 publications and critically analyzing the opportunities and challenges of hydrogen production from WAS, this review aims to offer useful information to remove key barriers that hinder hydrogen production from WAS to be applied in full-scale situations, and to stimulate more thinking and discussion of a probable application niche for hydrogen production from WAS. To guide the application and development of hydrogen recovery, a more promising hybrid process through rational integration of the available technologies is proposed as an example, and how this hybrid process works is illustrate d and future efforts to be made in the future is discussed.
Section snippets
The pathways of hydrogen production from waste activated sludge
Several methods such as direct-biophotolysis, indirect-biophotolysis, photo-fermentation, dark-fermentation, and microbial electrolysis cell can be theoretically used for hydrogen production [30]. To date, however, only three approaches, i.e., dark-fermentation, photo-fermentation, and microbial eletrolysis cell, have been documented to produce hydrogen from WAS (Fig. 1). Dark-fermentative hydrogen production is a process that uses organic matters in either soluble or solid state as electron
The potential of hydrogen production from WAS
WAS shows huge theoretical potential in hydrogen production. The theoretical methane yield of 354 mg-CH4 can be produced from WAS anaerobic digestion if 1 g sludge cells (expressed as C5H7NO2) are completely digested [64]. It is reported that 28% methane is produced from the hydrogenotrophic methonogenesis pathway [65], this indicates ~50 mg-H2 would be consumed theoretically in this process. Besides, two other processes, i.e., homoacetogenesis and sulfate-reducing processes, are known to
Recent progress in hydrogen production from WAS dark fermentation
In the past years, many endeavors were dedicated to improving hydrogen yield from WAS (Table 1). In order to enhance the disintegration of WAS and to suppress or kill the competitive microorganisms (e.g., methanogens) in dark fermentative systems, many WAS pretreatment methods such as heating [87], acid [88], alkaline, and ultrasonic [89,90] pretreatments were tested. Xiao et al. [91] found that compared with the control, thermal pretreatment at 121 °C for 30 min enhanced soluble chemical
Research gap and perspective
Although numerous efforts have been performed, hydrogen production from WAS is still far from achieving at practical scales due to low hydrogen yield, high energy (chemical) input in WAS pretreatment and fermenter control, or cost-prohibitive materials in photo-bioreactors (or anodes). In view of the state of the art relate to hydrogen bioproduction from WAS, further research on the following perspectives is urgently needed:
- (1)
Many pretreatments were developed to promote sludge disintegration, but
The hybrid process for the operation of WWTPs
It is widely acceptable that WWTPs are not only the places to purify sewage but also the facilities to recovery energy and resource. The yield of each useful product (e.g., hydrogen) from WWTPs should be maximized, and meanwhile the operation input should be minimized as far as possible. In addition, the investment of WWTPs to recovery resource should be controlled at a reasonable level. Based on these principles, the combining dark fermentation technology with other available technologies
Conclusions
In this paper, the principles and potentials, microorganisms, possible technologies, and process parameters of hydrogen production were reviewed. Besides, both the opportunities and challenges of hydrogen production were analyzed. Microbial electrolysis cells were regarded as the prospective technology for hydrogen production due to high theoretical hydrogen yield and the ability of using varieties of organics as substrate. Nonetheless, the low organics utilization from WAS and the quick
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was financially supported by the project of National Natural Science Foundation of China (51779089), the Natural Science Funds of Hunan Province for Distinguished Young Scholar (2018JJ1002), and Huxiang High Level Talent Gathering Project (2019RS1029).
References (155)
- et al.
Progress in energy from microalgae: a review
Renew Sustain Energy Rev
(2013) - et al.
Air gasification of dried sewage sludge in a two-stage gasifier. Part 2: calcined dolomite as a bed material and effect of moisture content of dried sewage sludge for the hydrogen production and tar removal
Int J Hydrogen Energy
(2013) - et al.
Hydrogen production from agricultural waste by dark fermentation: a review
Int J Hydrogen Energy
(2010) - et al.
Free nitrous acid promotes hydrogen production from dark fermentation of waste activated sludge
Water Res
(2018) - et al.
Full-scale evaluation of aerobic/extended-idle regime inducing biological phosphorus removal and its integration with intermittent sand filter to treat domestic sewage discharged from highway rest area
Biochem Eng J
(2016) - et al.
Mechanisms of peroxymonosulfate pretreatment enhancing production of short-chain fatty acids from waste activated sludge
Water Res
(2019) - et al.
Wastewater opportunities for denitrifying anaerobic methane oxidation
Trends Biotechnol
(2017) - et al.
Free nitrous acid serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge
Water Res
(2015) - et al.
Effect of initial pH on short chain fatty acid production during the anaerobic fermentation of membrane bioreactor sludge enhanced by alkyl polyglcoside
Int Biodeterior Biodegrad
(2015) - et al.
Biological short-chain fatty acids (SCFAs) production from waste-activated sludge affected by surfactant
Water Res
(2007)
Free ammonia-based pretreatment enhances phosphorus release and recovery from waste activated sludge
Chemosphere
Physical and chemical properties of activated sludge floc
Fermentative hydrogen production from wastewaters: a review and prognosis
Int J Hydrogen Energy
A bench scale study of fermentative hydrogen and methane production from food waste in integrated two-stage process
Int J Hydrogen Energy
A nutrient formulation for fermentative hydrogen production using anaerobic sewage sludge microflora
Int J Hydrogen Energy
Thermophilic hydrogen production from sludge pretreated by thermophilic bacteria: analysis of the advantages of microbial community and metabolism
Bioresour Technol
Microbial hydrogen production from sewage sludge bioaugmented with a constructed microbial consortium
Int J Hydrogen Energy
Effect of polyhydroxyalkanoates on dark fermentative hydrogen production from waste activated sludge
Water Res
A review of dark fermentative hydrogen production from biodegradable municipal waste fractions
Waste Manag
Food waste and food processing waste for biohydrogen production: a review
J Environ Manag
Microbial electrolysis cells: an emerging technology for wastewater treatment and energy recovery. From laboratory to pilot plant and beyond
Renew Sustain Energy Rev
Microbial electrolysis cells for waste biorefinery: a state of the art review
Bioresour Technol
Freezing in the presence of nitrite pretreatment enhances hydrogen production from dark fermentation of waste activated sludge
J Clean Prod
An efficient and green pretreatment to stimulate short-chain fatty acids production from waste activated sludge anaerobic fermentation using free nitrous acid
Chemosphere
Photobiological production of hydrogen gas as a biofuel
Curr Opin Biotechnol
Hydrogen production by mixed bacteria through dark and photo fermentation
Int J Hydrogen Energy
Principle and perspectives of hydrogen production through biocatalyzed electrolysis
Int J Hydrogen Energy
Enhancing anaerobic digestion of lignocellulosic materials in excess sludge by bioaugmentation and pre-treatment
Waste Manag
Principles and potential of the anaerobic digestion of waste-activated sludge
Prog Energy Combust Sci
Anaerobic bio-hydrogen production from ethanol fermentation: the role of pH
J Biotechnol
Hydrogen production of Enterobacter aerogenes altered by extracellular and intracellular redox states
Int J Hydrogen Energy
Hydrogen evolution of Enterobacter aerogenes depending on culture pH: mechanism of hydrogen evolution from NADH by means of membrane-bound hydrogenase
Degradation of volatile fatty acids in highly efficient anaerobic digestion
Biomass Bioenergy
High hydrogen yield from a two-step process of dark- and photo-fermentation of sucrose
Int J Hydrogen Energy
Acetate as a carbon source for hydrogen production by photosyntheticbacteria
J Biotechnol
Enhanced hydrogen production from waste activated sludge by cascade utilization of organic matter in microbial electrolysis cells
Water Res
Enhanced biohydrogen production from waste activated sludge in combined strategy of chemical pretreatment and microbial electrolysis
Int J Hydrogen Energy
Pyrosequencing reveals highly diverse microbial communities in microbial electrolysis cells involved in enhanced H2 production from waste activated sludge
Water Res
Comparison of biohydrogen production processes
Int J Hydrogen Energy
Hydrogen production by fermentative consortia
Renew Sustain Energy Rev
Homoacetogenesis during hydrogen production by mixed cultures dark fermentation: unresolved challenge
Int J Hydrogen Energy
Developing a statistical model to predict hydrogen production by a mixed anaerobic mesophilic culture
Int J Hydrogen Energy
Perspectives on cultivation strategies and photobioreactor designs for photo-fermentative hydrogen production
Bioresour Technol
Effect of light intensity, wavelength and illumination protocol on hydrogen production in photobioreactors
Int J Hydrogen Energy
Biotechnological potentials of anoxygenic phototrophic bacteria. I. Production of single-cell protein, vitamins, ubiquinones, hormones, and enzymes and use in waste treatment
Adv Appl Microbiol
Performance of a semi-pilot tubular microbial electrolysis cell (MEC) under several hydraulic retention times and applied voltages
Bioresour Technol
Assessment of biotic and abiotic graphite cathodes for hydrogen production in microbial electrolysis cells
Int J Hydrogen Energy
Steady-state performance and chemical efficiency of microbial electrolysis cells
Int J Hydrogen Energy
Heat pretreatment assists free ammonia to enhance hydrogen production from waste activated sludge
Bioresour Technol
Hydrogen production from sewage sludge using mixed microflora inoculum: effect of pH and enzymatic pretreatment
Bioresour Technol
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