How do earthworms affect the pathway of sludge bio-stabilization via vermicomposting?

The synergy effects between earthworms and microorganisms promote nitrogen mineralization and enhance stabilization of organic matters in a vermicomposting system. However, the stabilization pathways of vermicomposting in the system remain unknown. The aim of this study was to investigate the effect of earthworms on the stabilization pathway and associated microbial population of waste activated sludge recycled by vermicomposting. The treatment of sludge with and without earthworms was conducted at 20 °C for 60 days. The trends in organic matter (OM), dissolved organic carbon (DOC), NH4+-N, electrical conductivity (EC), microbial biomass carbon (MBC), and dehydrogenase activity (DHA) were similar in both systems over time. At the end of the treatment, OM and DOC were significantly lower (p < 0.05), and EC, NH4+-N, and NO3--N were significantly higher (p < 0.05) in the vermicomposting group than in the control. Based on the statistical results of principal component analysis (PCA), it was proposed that the stabilization pathway in both treatment systems required a sequence of reactions characterized by the degradation of organic matter, accumulation of dissolved organic carbon, ammonification, and nitrification. Vermicomposting led to greater abundance and diversity (Shannon index) of 16S rDNA microbial species, but more even distribution in microbial community composition (Simpson index) than the control. However, the opposite performance for 18S rDNA microbes was observed. Vermicomposting enhanced the abundance of microorganisms involved in organic matter degradation and nitrification, facilitating the conversion of organic matter and favoring the nitrification. In short, the pathway of sludge bio-stabilization is not altered regardless of the addition of earthworms or not, which enables us to better understand vermicomposting process of sludge.

Inhibition insights of hydrothermal liquid digestate in anaerobic digestion: Impact on organics conversion and inhibitor degradation.

Hydrothermal liquid digestate has been widely accepted as a substrate in anaerobic digestion (AD) for energy recovery. However, the potential negative impacts of hydrothermal liquid digestate on AD remain unclear. In this study, the organic biodegradability of hydrothermal liquid digestate produced from hydrothermal treatment (HTT) at different temperatures was analyzed, and the formation and degradation process of potential inhibitory substances were discussed. Results demonstrated that the AD lag phase of hydrothermal liquid digestate increased from 3 days at raw liquid digestate to 5-21 days. When the HTT temperature reached 220 °C, the methane yield decreased by 48%, and more than 71% of the organics in the hydrothermal liquid digestate were not utilized by AD. Biorefractory substances, such as fulvic and humic acids, accumulate in the hydrothermal liquid digestate. Potential inhibitory substances from Maillard reactions mainly affect the methanogenesis of AD. Most inhibitory substances were degraded within 7-22 days, with the degradation rate following the order of pyrroles > pyrazines > ketones > imidazoles > indoles. The AD community structure and methane conversion were partially re-established after most inhibitory substances were degraded. This study provides valuable information on eliminating the potential negative effects of hydrothermal liquid digestate on AD.

Practice and performance of domestic waste source segregation in Chinese universities: A case study in Shanghai.

The importance and urgency of domestic solid waste (DSW) source segregation in universities is self-evident. Although many universities have carried out waste management, however, a comprehensive summary for successful implementation work of DSW segregation is lacking. This study summarizes the mechanism of DSW segregation in Chinese university based on questionnaire survey, on-site inquiry and sampling analysis in a comprehensive university in Shanghai. Questionnaire survey show that it is critical for encouraging students to participate in waste segregation to build convenient segregation facilities and humanized segregation reward and punishment method. The strengthened publicity and education due to the advantages in environmental discipline, easy-operating waste dumping site/facility as well as personalized solutions for different functional areas (teaching building) were considerably important strategies for implementing efficient waste segregation. The recyclables that were collected by intelligent recycling device and mobile recycling enterprise were dominated by paper, and the amounts increased dramatically during the graduation season. Therefore, the university correspondingly increased the collection frequencies of waste and the number of segregation guiders in the period to decrease the potential risk of fire safety. The study could provide a valuable reference for efficient implementation of waste segregation on university/college in China.

Feasibility of housefly larvae-mediated vermicomposting for recycling food waste added digestate as additive.

The development of methods for the efficient treatment and application of food waste digestate is an important research goal. Vermicomposting via housefly larvae is an efficient way to reduce food waste and achieve its valorization, however, studies on the application and performance of digestate in vermicomposting are rarely. The present study aimed to investigate the feasibility of the co-treatment of food waste and digestate as an additive via larvae. Restaurant food waste (RFW) and household food waste (HFW) were selected to assess the effects of waste type on vermicomposting performance and larval quality. Waste reduction rates of 50.9%-57.8% were observed in the vermicomposting of food waste mixed with digestate at a ratio of 25%, which were slightly lower than those for treatments without the addition of digestate (62.8%-65.9%). The addition of digestate increased the germination index, with a maximum value of 82% in the RFW treatments with 25% digestate, and decreased the respiration activity, with a minimum value of 30 mg-O2/g-TS. The larval productivity of 13.9% in the RFW treatment system with a digestate rate of 25% was lower that without digestate (19.5%). Materials balance shows that larval biomass and metabolic equivalent had decreasing trends as the amount of digestate increased and HFW vermicomposting exhibited lower bioconversion efficiency than that of RFW treatment system regardless of the addition of digestate. These results suggest that mixing digestate at a low ratio (25%) during vermicomposting of food waste especially RFW could lead to considerable larval biomass and generate relatively stable residues.

Co-digestion of food waste and hydrothermal liquid digestate: Promotion effect of self-generated hydrochars.

Hydrothermal treatment (HTT) can efficiently valorize the digestate after anaerobic digestion. However, the disposal of the HTT liquid is challenging. This paper proposes a method to recover energy through the anaerobic co-digestion of food waste and HTT liquid fraction. The effect of HTT liquid recirculation on anaerobic co-digestion performance was investigated. This study focused on the self-generated hydrochars that remained in the HTT supernatant after centrifugation. The effect of the self-generated hydrochars on the methane (CH4) yield and microbial communities were discussed. After adding HTT liquids treated at 140 and 180 °C, the maximum CH4 production increased to 309.36 and 331.61 mL per g COD, respectively. The HTT liquid exhibited a pH buffering effect and kept a favorable pH for the anaerobic co-digestion. In addition, the self-generated hydrochars with higher carbon content and large oxygen-containing functional groups remained in HTT liquid. They increased the electron transferring rate of the anaerobic co-digestion. The increased relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota was observed with adding HTT liquid. The results of the principal component analysis indicate that the electron transferring rate constant had positive correlationships with the relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota. This study can provide a good reference for the disposal of the HTT liquid and a novel insight regarding the mechanism for the anaerobic co-digestion.

B(C6F5)3-catalyzed metal-free hydrogenation of 2-oxazolones.

A metal-free hydrogenation of 2-oxazolones was successfully realized by using 10 mol% of B(C6F5)3 as the catalyst, giving a variety of 2-oxazolidinones in 70-98% yields. An enamine to imine process was believed to be involved in this reaction.

Vermicomposting leads to more abundant microplastics in the municipal excess sludge.

Municipal excess activated sludge is not only an important reservoir of microplastics particles, but is also a vehicle of entry of microplastics into the environments as soil amendments or organic fertilizer. Vermicomposting is a cost-effective technology for sludge valorization. However, it is not clear whether vermicomposting affects the occurrence of microplastics in residual sludge. Here, the variation of microplastics (0.05-5 mm) in sludge, including the abundance, type, size, and morphology, before and after vermicomposting by epigeic earthworms under different temperature conditions (15 °C, 20 °C and 25 °C) were investigated by micro Fourier Transform Infrared Spectroscopy (µ-FTIR) and Scanning Electronic Microscopy (SEM). More abundant (over 104 particles ∙kg-1 (dry weight)), and smaller microplastics (over 60% in total with 0.05-0.5 mm) in the treated sludge via earthworms were observed compared to the raw sludge. The increment of vermicomposting temperature was more obvious (p < 0.05) for the enrichment of the microplastics, especially for polyethylene particle. Gizzard grinding and microbial digestion in the gut of earthworms may contribute to the fragment of microplastics. The present study suggests that the sludge-sourced vermicompost is still an important hotspot of microplastics, posing a potential threat to the receiving environments.

Temperature impacts fate of antibiotic resistance genes during vermicomposting of domestic excess activated sludge.

Effect of temperature on antibiotic resistance genes (ARGs) during vermicomposting of domestic excess sludge remains poorly understood. Vermicomposting experiment with excess sludge was conducted at three different temperatures (15 °C, 20 °C, and 25 °C) to investigate the fate of ARGs, bacterial community and their relationship in the process. The vermicomposting at 25 °C did not significantly attenuate the targeted ARGs relative to that at 15 °C and 20 °C. The dynamics of qnrA, qnrS, and tetM genes during vermicomposting at 15 °C and 20 °C followed the first-order kinetic model. Temperature remarkably impacted bacterial diversity of the final products with the lowest Shannon index at 25 °C. The presence of the genus (Aeromonas and Chitinophagaceae) at 25 °C may contribute to the rebound of the genes (qnrA, qnrS and tetM). The study indicates that 20 °C is a suitable vermicomposting temperature to simultaneously reach the highest removal efficiency of the ARGs and the good biostability of the final product.

Changes in physicochemical properties and microfauna community during vermicomposting of municipal sludge under different moisture conditions.

The present study aimed to explore the effect of a range of moisture content levels, including 65%, 72%, and 78%, on physicochemical properties and microfauna communities during vermicomposting of municipal sludge. As a result, death of perishable microfauna together with the degradation of organic matter was the dominant response in all groups in the early period of vermicomposting, while the effects of moisture content levels on various physiochemical parameters did not appear until the mid-later period. After the treatment with 78% moisture content, the content of mineral nitrogen was 1.186 g/kg in the sludge, with a 9.36 × 103 ind./g of microfauna quantity and 663.01 g of earthworm biomass. The values of these three measurements in 78% group were significantly higher than other two groups (p < 0.05), indicating that the effects of 78% moisture content were more pronounced for promoting nitrogen mineralization as well as microfauna and earthworms growth during vermicomposting. Specifically, testate amoebae were strongly associated with nitrification process, while nematodes were related to ammonification and phosphorus mineralization, of which testate amoebae had great potential of being bioindicators during vermicomposting of municipal sludge.

Distribution of extracellular and intracellular antibiotic resistance genes in sludge fractionated in terms of settleability.

The widespread proliferation of antibiotic resistance genes (ARGs) is a serious environmental and human health issue. Wastewater treatment facilities (WWTFs) are potential sources to spread ARGs to natural environment, for which, the presence state of ARGs in the sludge, as extracellular ones (eARGs) or intracellular ones (iARGs), along with the sludge settleability, are very important factors. The sludge settleability is closely associated with its floc size and density, bacterial activity, and the proportion of intact/damaged bacterial cells that aggregate together to form flocs for separation in the sedimentation process. It is reasonable to hypothesize that the distribution of eARGs and iARGs may differ with the sludge fractions of different settleability, a topic of great academic and practical significance requiring clarification. In this study, sludge samples from the aerobic contact tank of six household WWTFs were fractionated into fractions with different settling velocities: sludge of low settleability (LS), medium settleability (MS) and high settleability (HS); and the distribution of eARGs and iARGs in the obtained fractions for the widely detected tet G, tet M and sul 1 in water environment was evaluated based on the PMA-qPCR method, together with the evaluation for the well reported mobile genomic element intl 1 and total bacterial 16S rDNA. For the LS fractions, which contained more damaged bacterial cells, the distribution percentages of eARGs were generally higher than those of iARGs. For the HS fractions, which contained flocs with larger sizes formed by both intact and damaged bacterial cells, the relative abundances of ARGs and intl 1 were found apparently lower even if the presence percentages of eARGs were comparatively higher. It is thus inferable that sludge fractions of LS may possess higher transfer potential for ARGs and enhancing their settleability through optimization of the operation conditions is important for mitigating the proliferation of ARGs.

Critical insight into the fate of antibiotic resistance genes during biological treatment of typical biowastes.

Antibiotic resistance genes (ARGs) in biowaste, such as livestock manure and excess activated sludge, pose potential threat to human and ecological health when applied to agricultural fields. Biological treatment approaches, such as thermophilic composting/vermicomposting and anaerobic digestion, widely adopted to stabilize biowaste have demonstrated significant effects on the fate of ARGs. However, the influence of these biological treatments on ARGs is not known. This review summarizes the occurrence of ARGs in biowaste and the impact of thermophilic composting, vermicomposting, and anaerobic digestion on the fate of ARGs with discussion on factors, including substrate properties, pretreatments, additives, and operational parameters, associated with ARGs during biological treatment of biowaste. Finally, this review explores the research implications and proposes new avenues in the field of biological treatment of organic waste.

Effect of excess activated sludge on vermicomposting of fruit and vegetable waste by using novel vermireactor.

This study aimed to clarify the effect of excess activated sludge (EAS) on vermicomposting of fruit and vegetable wastes (FVW). For this, a novel vermireactor consists of substrate and bed compartments was used for treating five types of FVW (banana peels, cabbage, lettuce, carrot, and potato) with and without the addition of EAS by earthworms. The EAS promoted the growth and cocoon production of earthworms, and the decomposition efficiency of FVW. The changes of dehydrogenase activity revealed that the EAS enhanced the microbial activity in all treatments except for the carrot. The organic matter content, total carbon and the C/N ratio showed a significant decrease after addition of EAS into FVW. The content of nitrogen and phosphorus was also improved in the final products after vermicomposting. This study suggested that the addition of EAS could be a feasible option to enhance the vermicomposting of FVW.

Effect of heavy metals on the performance and bacterial profiles of activated sludge in a semi-continuous reactor.

Heavy metals are toxic to microorganisms at specific concentrations and can have a serious effect on the efficiency of biological wastewater treatment plants. The wastewater treatment performance and bacterial communities of activated sludge were investigated at different heavy metal concentrations (0.1-10 mg L-1 for Cd(II), Pb(II) and 1-100 mg L-1 for Cu(II)) in a well-controlled semi-continuous reactor in 30 d period. Glucose was added once every 8 h as the carbon source throughout the experiment. The heavy metal toxicity was related to chemical oxygen demand (COD), total organic carbon (TOC), three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy, bacterial activity and community composition. The first-order consumption rate for glucose showed that the activity was decreasing in comparison to the control. The COD removal efficiency was also decreased from 87% to 26% in all the reactors under different heavy metal concentrations treatment. The PCR-DGGE and sequencing results revealed that the bacterial diversity showed evident variations under heavy metal stress owing to the potential toxicity of heavy metals. At the genus level, Pedobacter steynii and Flavobacterium, were only tolerant to Cu(II) at 100 mg L-1, while Rhodanobacter thiooxydans resisted to all heavy metal concentrations except Cu(II) 100 mg L-1. Cluster analysis and Principal component analysis (PCA) revealed that the microbial community in Cu(II) was different from the sludge samples treated with Cd(II) and Pb(II) concentrations. The study indicated that it is necessary to identify the metal tolerant species of bacteria for maintaining good performance of biological wastewater treatment plants.

Elimination of antibiotic resistance genes and human pathogenic bacteria by earthworms during vermicomposting of dewatered sludge by metagenomic analysis.

This study used a metagenomic approach to investigate the effects of earthworms on ARGs and HPB during the vermicomposting of dewatered sludge. Results showed that 139 types of ARGs were found in sludge vermicompost, affiliated to 30 classes. Compared with the control, the total abundance of ARGs in sludge vermicompost decreased by 41.5%. Moreover, the types and sequences of plasmids and integrons were also decreased by vermicomposting. Proteobacteria and Actinobacteria were the most dominant hosts of ARGs in sludge vermicompost. In addition, earthworms reduced the total HPB abundance and modified their diversity, thus leading to higher abundance of Enterobacteriaceae in sludge vermicompost. However, the sludge vermicompost was still ARG and HPB enriched, indicating a remaining environmental risk for agricultural purpose. The observed change of microbial community and the reduction of mobile genetic elements caused by earthworm activity are the main reasons for the alleviation of ARG pollution during vermicomposting.

Gut digestion of earthworms significantly attenuates cell-free and -associated antibiotic resistance genes in excess activated sludge by affecting bacterial profiles.

Vermicomposting can significantly attenuate antibiotic resistance genes (ARGs) in the excess activated sludge (EAS). However, the effect of earthworms, especially the effect of gut digestion as a critical step in the vermicomposting process, remains unclarified. The purpose of this study was to investigate the response of ARGs (cell-free and -associated) in EAS to gut digestion of earthworms and to clarify the possible mechanism from the viewpoint of bacterial community through quantitative polymer chain reaction (q-PCR) and high throughput sequencing. Compared to the initial sludge, the earthworm casts were observed to have significantly lower absolute abundances of ARGs, especially qnrS, tetM, and tetX with the removal exceeding 90%. Cell-free and -associated ARGs (except sul1 and tetG) had equivalent contributions to the attenuation of each ARG. Remarkable reductions of bacterial number and alpha diversity (chao1 and Shannon) were detected in the casts. Spearman correlation analysis between the targeted genes and bacterial community indicates that twelve different phyla mainly including Acidobacteria, Euryarchaeota, Deinococcus-Thermus, Chlorobi, Firmicutes, Fibrobacteres, and Proteobacteria are the potential ARGs hosts, suggesting that the fate and behaviour of these hosts during gut digestion of EAS by earthworms substantially determined the dynamics of the ARGs. These findings increase our understanding of earthworm gut digestion as an important process for the attenuation of ARGs in EAS, and contribute towards preventing their release into the total environment.

Changes of quinolone resistance genes and their relations with microbial profiles during vermicomposting of municipal excess sludge.

Antibiotic resistance genes abundant in municipal excess sludge reduce the agricultural value of vermicompost. However, little attention has been paid on the fate and behavior of the problem-causing agents in vermicomposting. In this study, the fate and behavior of quinolone resistance genes in excess activated sludge during vermicomposting were studied with reactors introduced with Eisenia fetida for three different densities. The substrate pile without earthworms was operated as control in parallel. The results showed that earthworms could significantly reduce the absolute abundance of quinolone resistance genes in the excess sludge, with a reduction ratio of 85.6-100% for qnr A and 92.3-95.3% for qnr S, respectively (p < 0.05). For microbial profiles, both the dehydrogenase activity and the abundance of microbes (16S rDNA) revealed a distinct decreasing trend after 7 days from the start of the experiment; however, the bacterial diversity in the final products seemed to be enriched with the emergence of the uncultured Flavobacteriales bacterium and uncultured Anaerolineaceae bacterium. Redundancy analysis revealed clearly that the qnr genes had positive correlations with the targeted indexes of microbial profiles, with the correlations with the bacterial abundance and dehydrogenase activity being more statistically significant than the bacterial diversity (p < 0.05). The results of this study suggested that earthworms could promote the attenuation of quinolone resistance genes in the excess sludge through lowering the bacterial abundance and activity, and the promotion effect could be enhanced by increasing the density of earthworms.

Effects of earthworms on the fate of tetracycline and fluoroquinolone resistance genes of sewage sludge during vermicomposting.

Diverse antibiotic resistance genes (ARGs) present in sewage sludge are difficult to be eliminated using conventional sludge treatment processes. To date, little remains known on the fate of the ARGs during vermicomposting of sludge. This study aimed to investigate the effect of earthworms on the fate of tetracycline and fluoroquinolone resistance genes, and integrons during vermicomposting of sewage sludge through contrasting two systems of sludge stabilization with and without earthworms. Compared to the control without earthworms, vermicomposting significantly (p < 0.05) decreased the abundances of tetracycline and fluoroquinolone resistance genes and int1, with complete removal for parC. Variations in ARGs were associated with environmental factors, horizontal gene transfer, bacterial community composition, and earthworms during vermicomposting. In addition, earthworms strongly affected the possible host bacteria encoding ARGs and Int1, abating the pathogenic bacteria in vermicomposting product. These results imply that vermicomposting could effectively reduce tetracycline and fluoroquinolone resistance genes in the sludge.

An Interactive Care System Based on a Depth Image and EEG for Aged Patients with Dementia.

Due to the limitations of the body movement and functional decline of the aged with dementia, they can hardly make an efficient communication with nurses by language and gesture language like a normal person. In order to improve the efficiency in the healthcare communication, an intelligent interactive care system is proposed in this paper based on a multimodal deep neural network (DNN). The input vector of the DNN includes motion and mental features and was extracted from a depth image and electroencephalogram that were acquired by Kinect and OpenBCI, respectively. Experimental results show that the proposed algorithm simplified the process of the recognition and achieved 96.5% and 96.4%, respectively, for the shuffled dataset and 90.9% and 92.6%, respectively, for the continuous dataset in terms of accuracy and recall rate.

Effects of earthworms on nitrification and ammonia oxidizers in vermicomposting systems for recycling of fruit and vegetable wastes.

Although it is known that earthworms enrich the nitrate content in their final products, the detailed mechanisms behind this are not well understood, and this is important for determining the agricultural value of vermicomposting. Hence, this study aimed to investigate the effects of earthworms on ammonia oxidization and to clarify the functions of ammonia-oxidizing bacteria and archaea (AOB and AOA) during vermicomposting of fruit and vegetable wastes (FVWs). For this, two dry systems using dry FVWs and a fresh system using fresh FVWs were adopted and compared during 60days of vermicomposting. Each system included two treatments, with earthworms and without earthworms. The results revealed that vermicomposting could facilitate the stabilization of FVWs, forming high value-added products. Based on the results of fluorescent excitation-emission matrix analysis, humification indices of the dry and fresh vermicomposts were 4.0 and 4.2, respectively. Moreover, compared to the minus net nitrification rates in groups without worm treatment, the net nitrification rates of 17.5mgN/kg/d and 9.3mgN/g/d, respectively, were found in dry and fresh vermicomposting systems, indicating that earthworms could significantly accelerate the nitrification process. Compost treated with earthworms exhibited elevated numbers of ammonia oxidizers (AOA and AOB) and greater community diversity in final products, compared to the counterparts without earthworms. Final vermicompost products were abundant in the AOB members of Nitrosomonas and Nitrosospira along with AOA groups including Crenarchaeota and Thaumarchaeota. By contrast, AOA were the dominate members completing ammonia oxidization during vermicomposting of dry and fresh FVWs. This study suggests that earthworms facilitate the ammonia oxidization process by promoting both numbers and diversity of AOA and AOB during vermicomposting of FVWs.

Optimal growth condition of earthworms and their vermicompost features during recycling of five different fresh fruit and vegetable wastes.

This study aimed to promote vermicomposting performance for recycling fresh fruit and vegetable wastes (FVWs) and to assess microbial population and community of final products. Five fresh FVWs including banana peels, cabbage, lettuce, potato, and watermelon peels were chosen as earthworms' food. The fate test of earthworms showed that 30 g fresh FVWs/day was the optimal loading and the banana peels was harmful for the survival of Eisenia fetida. The followed vermicomposting test revealed lower contents of total carbon and weaker microbial activity in final vermicomposts, relative to those in compared systems without earthworms worked. The leachate from FVWs carried away great amounts of nutrients from reactors. Additionally, different fresh FVWs displayed dissimilar stabilization process. Molecular biological approaches revealed that earthworms could broaden bacterial diversity in their products, with significant greater populations of actinobacteria and ammonia oxidizing bacteria than in control. This study evidences that vermicomposting efficiency differs with the types and loadings of fresh FVWs and vermicomposts are rich in agricultural probiotics.