Elsevier

Chemosphere

Volume 253, August 2020, 126687
Chemosphere

Simultaneous H2S mitigation and methanization enhancement of chicken manure through the introduction of the micro-aeration approach

https://doi.org/10.1016/j.chemosphere.2020.126687Get rights and content

Highlights

  • Micro-aerobic approach was applied to remove/mitigate H2S of chicken manure biogas.

  • Accelerated hydrolysis and lower VFAs content were achieved due to micro-aeration.

  • The most efficient micro-aeration trial with 58% removed H2S was 30 ml air/gVSin.

  • Microbial community dynamics were characterized by 16S rDNA cloning library.

  • Bacterial richness and diversity were enhanced with micro-aerated digesters.

Abstract

The impact on H2S alleviation and methane yield enhancement after submitting the anaerobic digestion of chicken manure to a finite amount of air was investigated. The largest reduction in the H2S biogas content (58% lower) occurred when air intensity of 30 ml/g VSin was injected into the reactors. Consequently, a maximum methane yield (335 mL-g VSin−1), which was 77% higher than the control, was concurrently achieved. Slight sulfate accumulation (<330 mg L−1) was observed inside the micro-aerated digesters with higher air intensities, suggesting a suppression of sulfide inhibition. Bacterial diversity/richness was enhanced in these digesters while the relative abundance of Methanocelleus increased by 36%. The most important contributing factor to enhancement was the synergistic effect resulting from increments in the hydrolysis rate and the suppression of sulfide inhibition. The results highlighted the potential of in situ H2S mitigation with the added benefit of methane yield enhancement.

Introduction

In the last decade the amount of livestock manure in China has rapidly increased, and it is estimated to reach 2.78 billon tons by the year 2020 (Yan et al., 2017). This type of waste is both energy-rich and bio-digestible, making anaerobic digestion (AD) an optimal solution for its management (Anjum et al., 2017; Zhang et al., 2019). However, the high content of sulfurous matter has been identified as a barrier to livestock AD as it can induce the inhibition of anaerobic microbes by H2S. Methionine, for instance, a sulfur-containing amino acid, is nutritionally essential in feeding regime for both laying hens and broiler chickens to support feather growth and protein synthesis. Thus, chicken manure becomes rich in sulfur-containing amino acids which their anaerobic digestion forms sulfurous compounds. The presence of sulfurous compounds in the AD concert highlights current challenges such as the out-competition among indigenous organisms accompanied by these compounds with methane producers resulting in the decreasing of not only the quality but also the quantity of the biogas. At the same time, the removal of H2S from biogas makes the whole AD process less economical.

Specifically, sulfate-reducing bacteria (SRB) will be promoted in the presence of organic matters and sulfates under anaerobic condition where sulfate will be used as the terminal electron acceptor and methanogenic substrates (acetate, H2) will act as electron donors leading to H2S formation as the main product (Reaction 1 and 2). H2S is toxic to methanogens at relatively low concentrations. It is also highly reactive, has a bad odour, and is corrosive to piping and equipments associated with the biogas industry. Extra investment costs are thus required in order to maintain the system (Krayzelova et al., 2015). On the other hand, in an AD process, SRB will compete with methanogens to utilize electron and this negatively affects the methane production. Various approaches have been put forward to mitigate the formation of H2S during the AD process including chemical methods such as precipitation (Dhar et al., 2011), scrubbing (Couvert et al., 2008), oxidation (Khanal and Huang, 2006), pH elevation (Yan et al., 2018), and biological methods (Show et al., 2013). Nevertheless, even if these techniques can remove H2S from biogas and thus increase the quality and quantity of biogas production, the final economic balance is still not positive.4H2 + SO42− + H+→HS + 4H2O ΔG0 = −38.0 KJCH3COO + SO42− → HS+ 2HCO3 ΔG0 = −39.5 KJ

Recent studies have demonstrated that micro-aeration could provide an innovative solution for addressing the H2S issues (Nguyen and Khanal, 2018). Micro-aeration refers to the addition of a finite amount of air or oxygen into the anaerobic system to support a partial oxidation of H2S to elemental sulfur by sulfide-oxidizing bacteria (Reaction 3) (Guerrero et al., 2016).H2S + 0.5 O2 → S0 + H2O ΔG0 = −209.4 KJ

Micro-aeration could also have a positive impact on the overall AD performance of the process, including hydrolysis efficiency improvement, methane yield enhancement, and the scavenging of hydrogen sulfide; however, other studies were more contradictory. For instance, Botheju et al. (2010) demonstrated an enhancement in the methane yield of starch by 30–55%, and Tertakovsky et al. (2011) increased the methane yield of synthetic wastewater by 26% after adding limited oxygen to anaerobic digesters. However, Ramos et al. (2014) and Diaz et al. (2011) reported a negligible impact of micro-aeration on the process performance of sewage sludge and the methane yield of cellulose, respectively. Overall, a wide range of H2S removal efficiency, from 30% to more than 99%, has been reported in the literatures (Zhou et al., 2007; Krayzelova et al., 2014; Fdz-Polanco et al., 2009); therefore, more accurate knowledge about micro-aeration optimization i.e., air intensity (Tsapekos et al., 2017) could help clarify these variations and maximize the potential application of this approach.

In addition to this, the dynamic of the microbial community in micro-aerated AD reactors is also not quite clear. Some studies have reported that micro-aeration has no strong impact on the dynamics of microorganisms (Tang et al., 2004) while other studies have stated that micro-aerated systems have a higher diversity and relative abundance of hydrolytic microorganism, i.e. Firmicutes, compared to a strict AD system (Yin et al., 2016). Lim et al. (2014) have reported a 14% enhancement in the relative abundance of Firmicutes in a micro-aerated system compared to a strict AD one. In addition to the diversity, methanogenic activity has, on occasion, been found to improve more under micro-aeration conditions in comparison to the conventional AD system (Fu et al., 2016). However, it has also been demonstrated that methanogenic activity inhibition depends more on sulfide concentration than micro-aeration (Jenicek et al., 2011a, 2011b). While Brioukhanov and Netrusov (2007) reported the suppression of SRB growth and activity by oxygen. Jenicek et al. (2011a, 2011b) found that SRB activity was not negatively affected under micro-aeration conditions, and the activity of sulfide-oxidizing bacteria was significantly enhanced. Such a technology is affected by many other factors and these are often referred in the relevant literature (Nguyen and Khanal, 2018). Accordingly, it seems likely that although several studies have been performed to elucidate the role of providing microaerobic environment into AD treating different organic wastes, controversial results have been reported. Furthermore, to our knowledge, the underlying mechanisms of the potential impact of micro-aerated approach in terms of microbial dynamics, methane production, hydrolysis performance and H2S reduction have not been addressed concurrently. Therefore, a devoted investigation to entirely evaluate and define the potential impact of micro-aeration approach in the entire AD process is necessary.

The current study, therefore, aimed to estimate the role of a micro-aeration strategy in H2S removal, hydrolysis performance and methane yield enhancement. Chicken manure batch AD reactors were supplemented with different air dosages and the H2S removal efficiencies and methane yields of the different trials were assessed. 16S rRNA gene sequencing was performed to determine if, and to what extent the micro-aeration strategy would shape the profile of the microbial community structure.

Section snippets

Substrate and inoculum

The substrate used in this study was chicken manure and was obtained from an egg-laying farm belonged to China Agriculture University. The large particles i.e. feathers, were separated and then the manure was sieved to avoid a blockage of tools and kept at 4 °C until usage. The fed chicken manure had a TS, volatile solid (VS), and total chemical oxygen demand (TCOD) of 10%, 7% and 104 g/L respectively. Sludge from a long-term laboratory-scale mesophilic (37 °C) digester fed with chicken manure

The effect of micro-aeration injection on H2S mitigation

The cumulative emission of H2S in biogas when the micro-aeration technology was applied is illustrated in Fig. 1. The cumulative emission of H2S in the control digesters (10,400 ppm) was used as a baseline to determine the efficiency of H2S removal in micro-aerated AD. The achieved desulfurization efficiency in micro-aerated AD was between 28% and 58% (Fig. 1b). However, even though the sulfide concentration decreased noticeably, not all the sulfide was removed from the biogas. It is clear,

Conclusion

The simultaneous suppression of sulfide toxicity and the enhancement of the methane yield (77% higher) using micro-aeration technology in order to upgrade the biogas production of chicken manure, were the main findings of the current study. Proper air intensity (30 ml/g VSin) led to the highest H2S removal (58%) and the maximum methane yield enhancement. The richness and the diversity of bacteria were enhanced and the archaeal Methanocelleus exclusively became the dominant methanogens in the

CRediT authorship contribution statement

Ahmed Mahdy: Writing - original draft, Data curation. Yunlong Song: Writing - original draft, Data curation. Ali Salama: Writing - review & editing. Wei Qiao: Writing - review & editing, Writing - original draft, Formal analysis, Methodology, Conceptualization, Project administration, Funding acquisition, Supervision. Renjie Dong: Project administration.

Declaration of competing interests

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 work was partially supported by the National Key Research and Development Program of China (2016YFD0501403) and the Beijing Natural Science Foundation (6182017). Ahmed Mahdy would like to thank State Administration of Foreign Experts Affairs P.R.China. (Project No. WQ20180011) for the financial support.

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