Fate of Biological Contaminants During Recycling of Organic Wastes

Fate of Biological Contaminants During Recycling of Organic Wastes covers the fate of viruses, HPBs, and ARGs in organic wastes, and their eliminating methods, including composting, vermicomposting and anaerobic digestion. In addition, this work describes the environmental risks associated with the application of excess sludge, livestock and other bio-wastes in soils Fate of Biological Contaminants During Recycling of Organic Wastes will benefit environmental and soil scientists engaged in the latest research regarding risk assessment and remediation techniques in wastewater, and solid wastes, and agricultural wastes.

• Covers the fate of viruses, HPBs, and ARGs in wastes as well as their environmental risk to the ecosystem
• Includes applications of earthworm remediation techniques, composting, and anaerobic digestion for organic wastes
• Introduce the key relationship between viruses, HPBs, ARGs and the microbial community during biological treatment of excess sludge and livestock manure

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 24, 2022
• ISBN: 9780323959971

Book preview

Chapter One: Occurrence, fate, and behavior of antibiotic resistance genes in organic wastes during biological treatments and current elimination strategies

Wenjiao Lia,b; Sartaj Ahmad Bhata; Yongfen Weia; Fusheng Lia; Shuhei Tanakab    a River Basin Research Center, Gifu University, Gifu, Japan

b Graduate School of Global Environmental Studies, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, Japan

Abstract

Antibiotic resistance genes (ARGs) are concerned worldwide as newly emerging contaminants since their proliferation can bring about serious environmental and public health issues. Organic wastes such as activated sludge, animal manures, and food wastes are generated in large quantities and recognized as significant reservoirs of ARGs. Moreover, treatments for converting organic wastes to fertilizers or soil modifiers are biological processes involving aerobic and/or anaerobic bacteria (e.g., anaerobic digestion, aerobic composting, and vermicomposting) that possess a possibility of being a new spot for ARGs proliferation. For better handling, treating and recycling of the organic wastes to meet the sustainable development goals by 2030, current knowledge gaps including the behavior of ARGs organic wastes during treatment and efficient treatment approaches for eliminating the antibiotic resistance needed to be bridged. For this, this chapter aimed to propose an overview of established studies on the occurrence, fate, and behavior of ARGs in various organic wastes during different biological treatments, as well as the current elimination strategies, hence providing critical insights for mitigating the proliferation of antibiotic resistance in the total environment.

Keywords

Antibiotic resistance genes; Organic wastes; Activated sludge; Vermicomposting, biochar

1: Introduction

Antibiotics are widely used not only in humans but also in animals to prevent or treat infections caused by bacteria. However, their overuse and misuse have caused the emergence and prosperity of antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs), which led to environmental and public health issues and are of great concern worldwide. According to the World Health Organization (WHO, 2016), the ARGs problem already claims the lives of 70,000 people worldwide every year. It is estimated that as many as 10 million people could be dying of ARGs-related causes every year globally, and about 40% of those deaths will occur in Asia. The rising levels of ARGs can also hinder progress toward many of the Sustainable Development Goals, especially those regarding health, food security, and the environment (FAO et al., 2021). Three possible reasons for ARGs proliferation in the environment were described by Lee et al. (2017a) as follows: (1) not fully metabolized antibiotics are significantly excreted, which account for 30%–90% of the total amount; (2) selection pressure exerted by antibiotics can facilitate the proliferation of ARB; and (3) horizontal gene transfer (HGT) between bacteria by mobile genetic elements (MGEs) can promote the spread of ARGs. Among different MEGs, integrons were widely investigated and found in approximately 9% of sequenced bacterial genomes (Wang et al., 2020a). Accordingly, clarification of the occurrence and behavior of antibiotics, ARGs and MGEs in various environmental samples, is considered as one of the key points for mitigating the ARGs proliferation in the environment.

Organic wastes such as activated sludge (Huang et al., 2020b; Wei et al., 2020), animal manures ARGs (Chen et al., 2021; Tian et al., 2021), and food wastes (Li et al., 2021; Zhao et al., 2022) have been recognized as significant reservoirs of ARGs. Treatments for converting organic wastes to fertilizers or soil modifiers are biological processes involving aerobic and/or anaerobic bacteria (e.g., anaerobic digestion, aerobic composting, and vermicomposting) that possess a possibility of being a new spot for ARGs proliferation. Moreover, the not fully metabolized and improperly handled antibiotics with related ARB can be also transferred into the wastes treatment systems (Bhat et al., 2022), leading to higher selection pressure for ARGs spreading. Furthermore, the antibiotics, ARB, ARGs, and MGEs persisting in the treated organic wastes can enter the soil or surrounding water environment after being applied as fertilizers or soil modifiers, thus affecting the total environment including water resources and the food chain (Li et al., 2021). The spreading pathways of ARB with ARGs and MGEs, as well as the antibiotics in the environment, are shown in Fig. 1. Therefore, not only the fate and behavior of ARGs in various organic wastes during treatments but also the occurrence and proliferation potential of ARGs in the final products after treatments are highly required to be clarified. However, the comprehensive information on the occurrence, fate, and behavior of ARGs and MGEs during different biological treatments for organic wastes as well as the current elimination strategies is not systemically summarized so far. In this chapter, research progress on ARGs and HGT-related MGEs in typical organic wastes and their fate and behavior during different biological treatments were summarized. Additionally, the current elimination strategies for ARGs and MGEs as well as the possible mechanisms behind them were also discussed. The critical insights pointed out here may provide new avenues in the aspect of the elimination of ARGs and MGEs during biological treatments for organic wastes in further studies.

Fig. 1

Fig. 1 Speading pathways of antibiotics, antibiotic resistance bacteria (ARB) harboring antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in the emviroment.

2: Occurrence of antibiotics, ARGs, and MGEs in various organic wastes

Table 1 summarized the recent studies in detecting antibiotics, ARGs, and MGEs from typical organic wastes. Tetracyclines, β-lactams, macrolides, quinolones, and sulfonamides with their related ARGs were detected worldwide in different types of organic wastes, which lined with the commonly used antibiotics described by Pazda et al. (2019). The presence of antibiotics is closely associated with ARB and ARGs since the main mechanisms for bacteria to be resistant are linked with the antibiotics: (1) efflux pump of antibiotics; (2) modification of antibiotic targets; (3) inactivation of antibiotics; and (4) enhancement of membrane impermeability, as could be seen in Fig. 2. Concentrations of antibiotics varied in different organic wastes and regions as a result of the variation of applied types and doses. Antibiotics recorded in sludge from China by Huang et al. (2020a) were extremely higher than other studies on sludge about 2–4 orders of magnitude. Compared with the activated sludge and animal manure, food waste such as fruits and vegetables contain fewer antibiotics, ARGs, and MGEs (Chen et al., 2021; Li et al., 2021). Karkman et al. (2018) indicated that some bacteria could acquire resistance even under the very low selection pressure of antibiotics. Cui et al. (2019) reported a significant difference of tet genes with other targeted genes in domestic activated sludge and explained it as the reason for selective pressure from the usage of large quantities of tetracycline in clinics, livestock, and poultry breeding. The original antibiotics and ARB in organic wastes may also impact the fate and behavior of ARGs during the biological treatment process, thus influencing the safety of final products if applied into the soil environment (Li et al., 2021). Except for antibiotics, a recent review paper summarized that the occurrence of ARGs in organic waste is also related to other different factors such as microbial profiles, heavy metals, and chemical properties (Cui et al., 2020). These previous studies evidenced again that the proliferation of ARGs occurred everywhere with a complex mechanism, actions are immediately required. Another point worth to be noted is that studies focusing on both antibiotics and ARGs and MGEs simultaneously are very limited, remaining unknowns of the interaction of the occurrence of antibiotics with their related genes.

Table 1

N.D.: Not detected. /: No data.

Fig. 2

Fig. 2 Main mechanisms for bacteria to be antibiotic-resistant.

3: Fate and behavior of ARGs and MGEs during different organic wastes treatments

Biological treatments, including traditional anaerobic digestion and aerobic composting, and advanced composting with earthworms (vermicomposting), are broadly used for treating organic wastes before disposal or application into the environment. Our previous publication has summarized the advantages, efficiencies, and final products of these treating technologies (Li et al., 2020b) and indicated that vermicomposting is one of the most sustainable methods to treat organic wastes such as fruit and vegetable wastes and excess activated sludge. However, the evaluation was judged only based on the utilization value of final products, remaining a lack of safety issue caused by newly emerging contaminants. Table 2 exhibited the results and main findings from recent studies on the fate and behavior of antibiotics (a few studies), ARGs, and MGEs in typical organic wastes during anaerobic digestion, composting, and vermicomposting. By reviewing previous studies, new insights on ARGs proliferation during biological treatments involving bacteria are expected to be gained.

Table 2

(1), (2), (3) and (4): different treatments. /: No data.

4: Anaerobic digestion

Anaerobic digestion is conducted by involving various bacteria, such as hydrolytic bacteria, hydrogen- and acid-producing bacteria, and methane-producing bacteria during different treating phases (Cui et al., 2020), representing very complex and various changes of microbial communities. Inoculum of seeding sludge from wastewater treatment plants or previous anaerobic digesters can also bring about rich bacteria that could be the host bacteria of ARGs and MGEs, leading to ARGs transfer during digestion (Wu et al., 2016; Bai et al., 2019; Zhang et al., 2019a). Moreover, anaerobic digestion consists of mesophilic and thermophilic conditions, which could also influence the spreading of ARGs. Wu et al. (2016) investigated the fate and behavior of ARGs and MGEs in municipal wastewater sludge and found that most ARGs reduced during the acidogenic period and then increased during the methanogenic period, while the MGEs (intl1) slightly reduced during both two periods. It seems like acid-forming conditions can play a role in the elimination of ARGs. They also clarified that the thermophilic condition at 55°C could mitigate the presence of ARGs compared with the mesophilic condition at 35°C (Wu et al., 2016). Similarly, a previous study on anaerobic digestion of dairy manure also revealed that ARGs were significantly enriched during the mesophilic period at 37°C and then reduced during the thermophilic period at 55°C, indicating a potential risk of ARGs spreading in the environment if applied the treated solid fraction. For the effects of antibiotics on ARGs and MGEs, Bai et al. (2019) conducted mesophilic anaerobic digestion (35 ± 1°C) to treat dewatered sludge with and without the addition of six types of antibiotics (2 mg/L) and found that the enrichment of ARGs in the treatment added with antibiotics was about twice higher than that in the treatment without addition of antibiotics. These studies all suggested that higher temperature can effectively inhibit the proliferation of ARGs during anaerobic digestion, while rich ARGs still remain in the final products or will rebound again if the temperature decreased.

5: Aerobic composting

Traditional composting under aerobic conditions is also recognized as a sustainable technology for treating organic wastes worldwide. It can be applied for a full treatment course or combined with other treatment approaches such as anaerobic digestion. Wang et al. (2020b) investigated the ARGs and MGEs in the initial and biologically treated food waste after aerobic and anaerobic co-digestion processes and found that the absolute abundances of ARGs and MGEs decreased obviously after the aerobic process while enriched after the anaerobic process. However, the total relative abundances of ARGs and MGEs significantly increased in both treatments. The usage of inoculum sludge containing rich ARGs could be one of the possible reasons for the higher enriched ARGs after anaerobic co-digestion. A recent study comprehensively confirmed the fate and behavior of antibiotics, ARGs, and MGEs in kitchen wastes during composting under different temperatures (Zhao et al., 2022). It is recorded that abundances of some targeted ARGs increased with different extents between a range of 5.4%–8534.7% and the reduction of antibiotics differed among different types. Although the kitchen waste was composted, however, it persisted underestimated sources of antibiotics and ARGs. Ezzariai et al. (2018) also reported that reduction efficiencies of antibiotics were different depending on their chemical structures, while almost could be removed with a range from 70% to 99%. In addition, Zhao et al. (2022) indicated that temperature, pH, and water content also considerably affected the reduction of antibiotics and MGEs. Likewise, Cui et al. (2020) concluded that chemical factors including pH, NH4+, and NO3− could also influence the ARGs in organic wastes such as excess activated sludge and animal manure. Another more detailed report of temperature effects on ARGs is given by Fahad et al. (2021) via carrying out a temperature-controlled aerobic composting of cow manure mixed with corn straw. ARGs significantly decreased in the initial 10 days of the thermophilic phase (45°C–55°C) but increased greatly after 30 days (35°C–25°C). It is designated that the positive effect on the abundance of ARGs could be explained as the temperature impacted the bacterial community. The composition of potential host bacteria for ARGs changed during composting, indicating a close association with the maintenance of ARGs, Liao et al. (2019) also pointed out based on the results obtained from food waste composting. In contrast to the studies above, an earlier study on the changes of ARGs and their potential host bacteria during composting of swine manure described that the maturity period (lower temperature) is the main stage of ARGs reduction (Guo et al., 2021). However, the targeted ARGs increased by 427% on average throughout the composting process. The results from those studies on the behavior of ARGs and MGEs in organic wastes are inconsistent showing either decrease or increase during composting, while rich ARGs in the final product.

6: Vermicomposting

Compared with composting, vermicomposting has more effective functions of biodegradation and stabilization of the organic wastes through the joint action of earthworms and microorganisms (Li et al., 2020a). Due to the joint of earthworms and the bacteria in their gut, the fate and behavior of ARGs during vermicomposting are more complex than that in composting because the latter relies only on mesophilic and/or thermophilic bacteria (Cui et al., 2020). Besides the evaluation based on the stabilization efficiency of sewage sludge or nutrition values of final products (Huang et al., 2014, 2017), the elimination potentials for antibiotics and ARGs in the sludge of traditional composting and vermicomposting were also investigated by (Huang et al., 2018). Through conducting the sludge stabilization experiment with and without earthworms, significant inhibition effects of earthworms on the tetracycline and related ARGs, as well as MGEs, were observed. This phenomenon was explained as the reason that earthworms can strongly affect the possible host bacteria encoding ARGs and MGEs, hence abating the pathogenic bacteria in the final product. An earlier study on treating excess sludge also reported that vermicomposting greatly attenuated the targeted ARGs in sludge by 85.6%–100% bringing about the changes of microbial profiles (Cui et al., 2018). As was mentioned in the previous sections, temperature plays a critical role in the mitigation of ARGs and MGEs during biological treatments either under anaerobic or aerobic conditions, a lack of information for the effect on earthworms and ARGs in vermicomposting products. Temperature-controlled (15°C, 20°C, and 25°C) vermicomposting of excess activated sludge was established, and the fate of ARGs was clarified (Cui et al., 2022). Results showed that 25°C cannot significantly attenuate ARGs in sludge compared with lower temperatures. In addition, the bacterial diversity in the final product was also impacted presenting a lower Shannon index, indicating that the growth of some species of possible host bacteria may rebound the ARGs. However, it is found that the dynamics of targeted ARGs at 15°C and 20°C (higher kinetic coefficient) fitted to the first-order kinetic equation, proposing that the vermicomposting at 20°C had more significant removal of ARGs. To explore the mechanisms of ARGs elimination by earthworms, studies focusing on the bacteria from earthworms’ gut by investigating the fresh casts were carried out. Cui et al. (2019) clarified that earthworm casts contained significantly lower absolute abundances of ARGs compared with the initial sludge before gut digestion. Additionally, the bacterial number and diversity were remarkably reduced due to the digestion of the earthworm’s gut. Another recent study investigated the changes of ARGs and MGEs in the fresh cast derived from earthworms before and after vermicomposting of five types of fruit and vegetable wastes, excess activated sludge and their mixtures, respectively (Li et al., 2021). The relative abundances of ARGs and MGEs against 16S rDNA in fresh cast samples were reduced markedly and much lower than those in all different organic wastes after vermicomposting (about 1–3 orders of magnitude). It is indicated that the gut of earthworms could selectively reduce the host bacteria harboring ARGs and MGEs through activation of non-antibiotic resistance bacteria or digestion of the