Anaerobic digestion of municipal solid waste composed of food waste, wastepaper, and plastic in a single-stage system: performance and microbial community structure characterization

Tracking the extracellular and intracellular antibiotic resistance genes across whole year in wastewater of intensive dairy farm

Monitoring the annual variation of antibiotic resistance genes (ARGs) in livestock wastewater is important for determining the high-risk period of transfer and spread of animal-derived antibiotic resistance into the environment. However, the knowledge regarding the variation patterns of ARGs, especially intracellular ARGs (iARGs) and extracellular ARGs (eARGs), over time in livestock wastewater is still unclear. Herein, we conducted a year-round study to trace the profiles of ARGs at a Chinese-intensive dairy farm, focusing on the shifts observed in different months. The results showed significant differences in the composition and variation between iARGs and eARGs. Tetracycline, sulfonamide, and macrolide resistance genes were the major types of iARGs, while cfr was the major type of eARG. The environmental adaptations of the host bacteria determine whether ARGs appear as intracellular or extracellular forms. The total abundance of ARGs was higher from April to September, which can be attributed to the favorable climatic conditions for bacterial colonization and increased antibiotic administration during this period. Integron was found to be highly correlated with most iARGs, potentially playing a role in the presence of these genes within cells and their similar transmission patterns in wastewater. The intracellular and extracellular bacterial communities were significantly different, primarily because of variations in bacterial adaptability to the high salt and anaerobic environment. The intracellular co-occurrence network indicated that some dominant genera in wastewater, such as Turicibacter, Clostridium IV, Cloacibacillus, Subdivision5_genera_incertae_sedis, Saccharibacteria_genera_incertae_sedis and Halomonas, were potential hosts for many ARGs. To the best of our knowledge, this study demonstrates, for the first time, the annual variation of ARGs at critical points in the reuse of dairy farm wastewater. It also offers valuable insights into the prevention and control of ARGs derived from animals.

Anaerobic co-digestion of three commercial bio-plastic bags with food waste: Effects on methane production and microbial community structure

The emergence of bioplastic bags as a replacement for traditional petroleum-based plastic bags is promising for their simultaneous anaerobic digestion with food waste. In this study, the degradation of three bioplastic bags is evaluated during anaerobic co-digestion with food waste under mesophilic/thermophilic conditions, and the results indicated PBAT/PLA/starch > PLA > PBAT for methane production rate. The PBAT/PLA/starch mixture produced 23.4 ml/g of methane at 55 °C, and the cumulative methane production increased by 28.4 % compared to the control. In addition, the lag time before methane production was reduced by one to four days when anaerobic co-digestion was performed under thermophilic conditions, and the conversion of the bioplastics improved by 9.11-11.2 %. Microscopy further showed obvious physical degradation of the PBAT/PLA/starch material. The FTIR analysis showed that the characteristic peaks of the material at 3320, 2957, and 934 cm^-1 decreased significantly after anaerobic fermentation. The biodegradability of the polymer decreased with an increase in the content of the crystalline area in the structure. The addition of a comonomer reduced the crystallinity of the polymer. In addition, the biodegradability was increased by adjusting the hydrolysis reaction and microbial activity of the polymer surface. An analysis of the structural features of the microbial communities revealed that Archaea exhibited different biodiversity at distinct temperatures. In particular, under thermophilic conditions, the relative abundance of Methanothermobacter was 56.0 %, and it plays an important role in the anaerobic degradation of PBAT/PLA/starch materials, while bacterial communities showed smaller differences. Overall, the bioplastic was able to be co-digested anaerobically with food waste to produce renewable energy. This study provides a plan for the practical application of biodegradable plastic bag collection for the combined treatment of food waste in anaerobic digesters. It provides a theoretical basis for modifications of bioplastic and domestication of anaerobic microorganisms.

Utilization of nanoparticles for biogas production focusing on process stability and effluent quality

Abstract

One of the most important techniques for converting complex organic waste into renewable energy in the form of biogas and effluent is anaerobic digestion. Several issues have been raised related to the effectiveness of the anaerobic digestion process in recent years. Hence nanoparticles (NPs) have been used widely in anaerobic digestion process for converting organic wastes into useful biogas and effluent in an effective way. This review addresses the knowledge gaps and summarizes recent researchers’ findings concentrating on the stability and effluent quality of the cattle manure anaerobic digestion process using single and combinations nanoparticle. In summary, the utilization of NPs have beneficial effects on CH4 production, process optimization, and effluent quality. Their function, as key nutrient providers, aid in the synthesis of key enzymes and co-enzymes, and thus stimulate anaerobic microorganism activities when present at an optimum concentration (e.g., Fe NPs 100 mg/L; Ni NPs 2 mg/L; Co NPs 1 mg/L). Furthermore, utilizing Fe NPs at concentrations higher than 100 mg/L is more effective at reducing H2S production than increasing CH4, whereas Ni NPs and Co NPs at concentrations greater than 2 mg/L and 1 mg/L, respectively, reduce CH4 production. Effluent with Fe and Ni NPs showed stronger fertilizer values more than Co NPs. Fe/Ni/Co NP combinations are more efficient in enhancing CH4 production than single NPs. Therefore, it is possible to utilize NPs combinations as additives to improve the effectiveness of anaerobic digestion.

Article highlights

Biogas Production and Microbial Communities of Mesophilic and Thermophilic Anaerobic Co-Digestion of Animal Manures and Food Wastes in Costa Rica

Biomass generated from agricultural operations in Costa Rica represents an untapped renewable resource for bioenergy generation. This study investigated the effects of two temperatures and three mixture ratios of manures and food wastes on biogas production and microbial community structure. Increasing the amount of fruit and restaurant wastes in the feed mixture significantly enhanced the productivity of the systems (16% increase in the mesophilic systems and 41% in the thermophilic). The methane content of biogas was also favored at higher temperatures. Beta diversity analysis, based on high-throughput sequencing of 16S rRNA gene, showed that microbial communities of the thermophilic digestions were more similar to each other than the mesophilic digestions. Species richness of the thermophilic digestions was significantly greater than the corresponding mesophilic digestions (F = 40.08, p = 0.003). The mesophilic digesters were dominated by Firmicutes and Bacteroidetes while in thermophilic digesters, the phyla Firmicutes and Chloroflexi accounted for up to 90% of all sequences. Methanosarcina represented the key methanogen and was more abundant in thermophilic digestions. These results demonstrate that increasing digestion temperature and adding food wastes can alleviate the negative impact of low C:N ratios on anaerobic digestion.

Urban Metabolism of Food-Sourced Nitrogen among Different Income Households: A Case Study Based on Large Sample Survey in Xiamen City, China

Food consumption is fundamental for urban households if they are to sustain production and daily life. Nitrogen resulting from food consumption has significantly contributed to pollutant emissions in urban ecosystems. Taking Xiamen city, a rapid urbanizing area of southeast China as a case study, we evaluated the food-sourced nitrogen consumption of households based on a large simple onsite questionnaire survey, as well as differences between households in the consumption of plant-based and animal-based foods. A material flow analysis (MFA) was conducted to simulate the urban metabolism of food-sourced nitrogen and environmental emissions among different income groups. The impacts of household attributes, plant-based food consumption, and animal-based food consumption on environmental nitrogen emissions were examined with a structural equation model (SEM). Our results show that the surveyed households' diets were more plant-based and less animal-based. Aquatic products and livestock were the source of 43.7% of food-sourced nitrogen, and 84.5% of the food-sourced nitrogen was discharge into the environment through direct discharge and waste treatment. Soil, water, and air emissions accounted for 62.8%, 30.1%, and 7.1% of the food-sourced nitrogen, respectively. Household income, household size, and household area are all associated with accelerating increases of nitrogen emissions released into the environment, though middle-income group households have the highest food-sourced environmental nitrogen emissions. On this basis, we discuss how to better manage the urban metabolism of food-sourced nitrogen, so as to improve urban household consumption, lower nitrogen emissions, and improve food security.

Metagenomic insights into aniline effects on microbial community and biological sulfate reduction pathways during anaerobic treatment of high-sulfate wastewater

For comprehensive insights into the change of sulfate reduction pathway responding to the toxic stress and the shift of microbial community and performance of sulfate reduction, we built a laboratory-scale expanded granular sludge bed reactor (EGSB) treating high-sulfate wastewater with elevated aniline concentrations from 0 to 480 mg/L. High-throughput sequencing and metagenomic approaches were applied to decipher the molecular mechanisms of sulfate reduction under aniline stress through taxonomic and functional profiles. The increasing aniline in the anaerobic system induced the accumulation of volatile fatty acids (VFA), further turned the bioreactor into acidification, which was the principal reason for the deterioration of system performance and finally resulted in the accumulation of toxic free sulfide. Moreover, aniline triggered the change of bacterial community and genes relating to sulfate reduction pathways. The increase of aniline from 0 to 320 mg/L enriched total sulfate-reducing bacteria (SRB), and the most abundant genus was Desulfomicrobium, accounting for 66.85-91.25% of total SRB. The assimilatory sulfate reduction pathway was obviously inhibited when aniline was over 160 mg/L, while genes associated with dissimilatory sulfate reduction pathways all exhibited an upward tendency with the increasing aniline content. The enrichment of aniline-resistant SRB (e.g. Desulfomicrobium) carrying genes associated with the dissimilatory sulfate reduction pathway also confirmed the underlying mechanism that sulfate reduction turned into dissimilation under high aniline condition. Taken together, these results comprehensively provided solid evidence for the effects of aniline on the biological sulfate reduction processes treating high-sulfate wastewater and the underlying molecular mechanisms which may highlight the important roles of SRB and related sulfate reduction genes during treatment.

Potential of Sustainable Concept for Handling Organic Waste in Tunisia

Nowadays, Tunisia is seeking to implement cost-efficient and sustainable solutions in relation to the treatment of organic waste which, at up to 65%, makes up the largest proportion of total waste generated in the country. Therefore, an efficient tool for decision makers is needed to provide a clear approach about the potential of organic waste as well as the treatment concept, which can be adapted based on technical requirements and local conditions. Results revealed that there is a high variation in terms of the nature of the collected biowaste, which affects the selection of the adopted bioprocess for each geographical zone of the study area. Three main categories of biowaste are produced along the coastline of Tunisia: food waste (FW) (102.543 t/a); green waste (GW) (1.326.930 t/a); and cattle manure (CM) (1.548.350 t/a). Based on the results of similar projects and laboratory-scale research work, anaerobic and aerobic digestion were examined. Regarding aerobic digestion, the monitoring of several physicochemical parameters ascertained that the co-composting of FW and GW at different ratios (GW: FW = 100:0, 75:25, 50:50, and 25:75) allowed the production of a stable and mature compost. A highly qualified end-product was generated from each trial categorized as a finished compost of class V with reference to German Standards of compost. Regarding the anaerobic process, different feedstock mixtures (FW:CM = 0:1, 1:1, 2:1, and 3:1) were prepared to feed semi-continuous anaerobic reactors. However, a significant improvement in the process development was recorded for digesters including a higher fraction of FW, which produced 0.846 LN/kg VSin as the maximum biogas production. Therefore, biological treatments of food waste and different co-substrates seems to be a suitable technique for Tunisia in terms of waste management, environmental, and energy aspects. However, the evaluation of the efficiency of the proposed biological treatments was also verified by a draw-up of a technical and economic feasibility analysis. Although the cost–benefit estimations proved that the profits from both the compost and biogas plants would be very modest, the feasibility of such sustainable projects should not only be evaluated on an economic basis, but also by taking into account socio-environmental considerations including decreasing environmental threats, providing work opportunities, increasing incomes, stimulating public awareness as well as reducing the operating costs linked to landfilling.

Malodorous gases production from food wastes decomposition by indigenous microorganisms

Volatile organic compounds (VOCs) produced during the degradation of food wastes may harm to the health of people and create annoyance in adjacent communities. In this work, the VOCs emitted from the decomposition food wastes including fruit, meat and vegetable, and their microbial communities were measured in three individual 57-L reactors for 61 days. Total of 232.8, 373.5, and 191.1 μg·kg^-1·h^-1 VOCs with oxygenated VOCs (57.6%), volatile organic sulfur compounds (VOSCs, 58.6%) and VOSCs (54.9%) as the main group were detected during fruit, meat and vegetable fermentation, respectively. 2-Butanone (55.1%) and ethyl acetate (13.8%) were the two most abundant VOCs from fruit wastes, while dimethyl sulfide (68.0 and 26.6%) and dimethyl disulfide (89.2 and 10.1%) were in vegetable and meat wastes. The predominant Firmicutes represented 93.0-99.9% of the bacterial communities of meat decomposition, while Firmicutes and Proteobacteria were the dominant phyla throughout the fruit digestion process. Proteobacteria (16.9%-83.6%) was the dominant phylum in vegetable wastes, followed by Bacteroidetes, Firmicutes, and Actinobacteria. Malodorous VOCs emissions were highly affected by microbial activity, the abundant Weissella, Leuconostoc and Enterobacteriaceae in vegetable wastes showed correlation with carbon disulfide and dimethyl sulfide, while dominant Peptococcus, Bacteroides, Lactobacillales and Peptoniphilus in meat wastes was related to dimethyl disulfide. Overall, significant differences and correlation between VOCs emission profiles and bacterial communities among different food wastes decomposition were observed. These data contribute to a more comprehensive understanding the relationship between microbial community dynamics and malodorous VOCs emission.

New insights into the effect of sludge proteins on the hydrophilic/hydrophobic properties that improve sludge dewaterability during anaerobic digestion

Extracellular polymer proteins have been reported to play an important role in enhancing sludge dewaterability during anaerobic digestion in our previous study. However, how the proteins in sludge determine sludge dewaterability remains to be determined. In this work, proteins from digested sludge were identified using label free proteomics analysis, and its hydrophilicity/hydrophobicity properties and functional groups were analysed. We determined that the microbial community variation between the three stages during the anaerobic digestion process was responsible for enhancing sludge dewaterability; The transformation from hydrophilicity to hydrophobicity of digested sludge surface is the result of functional groups distribution variation which caused by the proteins and microbial communities. This study provides a new insight into the development of anaerobic digestion based on sludge dewaterability.

Bacterial communities, metabolic functions and resistance genes to antibiotics and metals in two saline seafood wastewater treatment systems

This study investigated the bacterial communities, metabolic functions, antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in two alternating anaerobic/aerobic biological filters (A/O-BFs) treating saline seafood wastewater (SSW). Firmicutes was the most abundant phylum in both systems, and halophilic and alkaliphilic bacteria were largely enriched. 15 potential pathogens were obtained. Metabolism was the predominant bacterial function. 49 ARGs and 7 MRGs were detected, and the total abundance of ARGs increased while that of MRGs decreased. Clear shifts in bacterial structure and function, ARGs and MRGs were observed in both systems and at different heights. Co-occurrence of ARGs and MRGs and their hosts were identified. ARGs and MRGs mainly negatively correlated with bacterial functions, which were also the important contributors to shifts in bacterial communities and functions. This study highlights the importance of investigating ARGs and MRGs in SSW treatment systems and their complex interactions with bacterial communities and functions.

Effects of thermal hydrolysis on the metabolism of amino acids in sewage sludge in anaerobic digestion

Three semi-continuous anaerobic digesters with raw sludge (R1) or thermally hydrolyzed sludge (120 °C (R2) or 160 °C (R3)) were operated to investigate the effects of thermal hydrolysis on the metabolism of amino acids during high solid anaerobic digestion with sewage sludge. Thermal hydrolysis pretreatment (THP) decomposed protein in terms of hydrolytic amino acid in raw sludge by 8.90% and 26.69% under 120 °C and 160 °C, respectively. The decomposition of amino acids during THP was the main contributor to the final enhanced amino acids degradation in sewage sludge with THP after anaerobic digestion. The dominating bacterial genera related to amino acids degradation in R2 and R3 shifted to Fastidiosipila and Proteiniphilum/Tissierella, respectively, from Gelria in R1, influencing the utilization of amino acids, especially glutamic acid, glycine and proline. Different from 120 °C, THP at 160 °C played an important role in promoting amino acid metabolism during AD through the Stickland pathway by the bacteria belonged to order Clostridiales.

Fermentative hydrogen and methane co-production from anaerobic co-digestion of organic wastes at high loading rate coupling continuously and sequencing batch digesters

The anaerobic co-digestion of the most abundant organic wastes was investigated for enhancing biogas production rate and quality. The used feedstock was composed of fruit and vegetable waste (FVW), waste-activated sludge (WAS), olive mill wastewater (OMW) and cattle manure (CM). A considerable methane yield of 340 L/kg volatile solid (VS) inlet was obtained using single-stage anaerobic sequencing batch reactors (ASBRs). However, VS biodegradation becomes difficult at high organic loading rate (OLR). Therefore, a continuously stirred tank reactor (CSTR) was integrated to the ASBR for waste pre-digestion. The dark fermentation leads to the improvement of organic matter solubilisation and bio-hydrogen productivity, reaching 0.73 L/L/day (H₂ content of 49.8%) when pH decreased to 5.8. Therefore, methane productivity increased from 0.6 to 1.86 L/L/day in the methanogenic reactor with a better VS biodegradation (91.1%) at high OLR. Furthermore, the bio-hythane production was performed through a controlled biogas recirculation from the dark fermentation stage into the methaniser to reach 842.4 L/kg VS inlet. The produced biogas was composed of 8% H₂, 28.5% CO₂ and 63.5% CH₄. Therefore, two-stage anaerobic co-digestion with coupled CH₄ and H₂ recuperation may be an important contribution for pollution control and high-rate bioenergy recovery (21.1 kJ/g VS inlet) from organic wastes.

Potential for Methane Generation by Lignocellulosic Household Waste

The contribution of domestic lignocellulosic waste and its potential for biodegradation by components, for each category of paper and cardboard, have scarcely been reported. To achieve integral proposals, for managing this type of waste, is essential to know each individual contribution to the “paper and cardboard” category. The objective of this study was to characterize the paper and cardboard waste from the domestic solid waste stream, in the city of Morelia, Mexico, and estimate its methane generation potential (CH4). The generation of lignocellulosic waste was studied in a housing complex of social interest. The domestic lignocellulosic residues (DLW) that were chemically characterized were derived from paper and cardboard. The average daily generation was 0.5 kg/inhabitant. The highest content of lignin was found in newspaper (24.5%), and toilet paper was the material with the lowest lignin content (1%). The bond paper had a DLW of higher YCH4, when degraded anaerobically, in a semi-solid phase and a mesophilic regime. The variety of paper and cardboard, such as DLW, presented differences in their generation (kg/person), chemical composition (lignin content), and their potential for anaerobic biodegradability.

Effects of disposable plastics and wooden chopsticks on the anaerobic digestion of food waste

A common challenge for the anaerobic digestion (AD) of food waste (FW) is the contamination by disposable plastic materials and utensils. The objective of this batch study was to investigate the effects of disposable plastic materials - polystyrene (PS), polypropylene (PP), high density polyethylene (HDPE) and wooden chopsticks (WC) on the AD of FW. Results showed that methane production from the AD of FW was inhibited to different extents when different materials were present in FW. PS and PP were found to reduce methane production from food waste more than HDPE and WC. The reduction in methane production was hypothesized to be due to the production of toxic plastic by-products or due to reduced contact between microbes and FW. Pyrosequencing and Field Emission Scanning Electron Microscope (FESEM) results indicated that the reduction in methane production was more likely due to the interference of good contact necessary between microbes and FW for biodegradation, and that the biological processes of AD were not affected by the contamination of plastics. Greater reductions in methane yields were also observed when the surface areas of the disposable materials were increased. Studying the effects of disposable materials on the AD of FW would provide plant operators with more information that could optimise the process of resource recovery from food waste.

Global trends and future prospects of food waste research: a bibliometric analysis

The unregulated discharge reams of food waste (FW) causes severe resource loss and environmental pollution. In the present study, a bibliometric analysis was used for research activities and tendencies of food waste from 1991 to 2015. The results indicated that the amount of FW research continually grew by the years, and the number of publications rose significantly from 2012. Bioresource Technology and Waste Management were the two most frequently published journals in the field of FW research. China took a leading position and had a high h-index (38) out of 94 countries/territories, followed by the USA and South Korea. Presently, anaerobic digestion for methane and dark fermentation for hydrogen production are the mainstream techniques in FW disposal. Lactic and ethanol fermentation from FW received more and more attention in recent years. Life cycle assessment (LCA) was an ever-increasingly popular evaluation method for FW-related research. Moreover, cluster analysis indicated microbial community structure, food security, leachate, and pathogens were also the research hotspots.

New insights into the enhanced performance of high solid anaerobic digestion with dewatered sludge by thermal hydrolysis: Organic matter degradation and methanogenic pathways

Two lab-scale high solid anaerobic digesters fed with untreated sludge (R1) and thermally hydrolyzed sludge (R2) were operated to investigate the influence of thermal hydrolysis pretreatment (THP) on the degradation of individual macromolecular organic components (MOCs), as well as the functional and metabolic responses of microbes during anaerobic digestion (AD). The degradation of MOCs was improved by THP at different rates, in which improved degradation of proteins (by 49.0%) and hemicelluloses (by 25.0%) were the main factors contributing to the increase in volatile solids (VS) reduction. However, no enhancement of final degradation extent of MOCs was observed. With a more densified microbial population, R2 was also enriched in genes involved in amino acid and carbohydrate metabolism, reflected in the enhanced degradation of proteins and carbohydrates. After THP, the methanogenic pathway shifted from strict acetoclastic methanogenesis to acetoclastic/hydrogenotrophic methanogenesis, consistent with the enhanced methane production and the increase of methane content.

Microbial characteristics in anaerobic digestion process of food waste for methane production-A review

Food waste (FW) is rich in starch, fat, protein and cellulose. It is easy to decay and brings environmental pollution and other social problems. FW shows a high potential to produce methane by anaerobic digestion (AD) due to its high organic content. However, many inhibitors, such as accumulation of ammonia and volatile fatty acids (VFAs), usually result in inefficient performances and even process failure. Microorganisms play an important role in the process of hydrolysis, acidogenesis, acetogenesis and methanogenesis. This review provided a critical summary of microbial characteristics to obtain connects of microbial community structure with operational conditions at various states of AD, such as mesophilic and thermophilic, wet and dry, success and failure, pretreated or not, lab-scale and full-scale. This article emphasizes that it is necessary to analyze changes and mechanisms of microbial communities in unbalanced system and seek efficiency dynamic succession rules of the dominant microorganisms.

Dry anaerobic digestion of food waste and cardboard at different substrate loads, solid contents and co-digestion proportions

The increasing food waste production calls for developing efficient technologies for its treatment. Anaerobic processes provide an effective waste valorization. The influence of the initial substrate load on the performance of batch dry anaerobic co-digestion reactors treating food waste and cardboard was investigated. The load was varied by modifying the substrate to inoculum ratio (S/X), the total solids content and the co-digestion proportions. The results showed that the S/X was a crucial parameter. Within the tested values (0.25, 1 and 4gVS·gVS^-1), only the reactors working at 0.25 produced methane. Methanosarcina was the main archaea, indicating its importance for efficient methanogenesis. Acidogenic fermentation was predominant at higher S/X, producing hydrogen and other metabolites. Higher substrate conversions (≤48%) and hydrogen yields (≤62mL·gVS^-1) were achieved at low loads. This study suggests that different value-added compounds can be produced in dry conditions, with the initial substrate load as easy-to-control operational parameter.

The dynamic changes and interactional networks of prokaryotic community between co-digestion and mono-digestions of corn stalk and pig manure

Anaerobic co-digestion is considered to be an efficient way to improve the biogas production. The abundance, dynamic and interactional networks of prokaryotic community were investigated between co-digestion and mono-digestions of corn stalk and pig manure in mesophilic batch test. Co-digestion showed higher methane production, and contributed to suitable microenvironment as well as stable prokaryotic community structure. The highest methane production was achieved with the highest relative abundance of Methanosaeta. Prokaryotic community in mono-digestions might inhibited by FA or FVFA. The functional modules in co-digestion and mono-digestion of pig manure clustered together with bigger size and higher degree, and the connections of metabolic functions were better-organized, which means high-efficient utilization of substrate and prevention of the two digestion systems crash. The partial mantel tests showed the functional modules were significantly affected by environmental factors. These results further explained that why co-digestion was more efficient than mono-digestion owing to suitable microenvironment.

Application of nanoscale zero valent iron and iron powder during sludge anaerobic digestion: Impact on methane yield and pharmaceutical and personal care products degradation

Lab scale and single stage high solid anaerobic digestion of sewage sludge spiked with freshly synthesized nanoscale zero valent iron (nZVI) and commercial iron powder (IP) under mesophilic condition (37±1°C) was performed. The effects of both additives on methane yield, and pharmaceutical and personal care product (PPCP) removal were investigated. Results showed that methane yield was increased by 25.2% and 40.8% in the presence of nZVI (0.1%) and IP (1.6%), respectively. Removal efficiencies of chemical oxygen demand were 54.4% and 66.2% in the presence of nZVI and IP, respectively, which were higher compared to the control group (44.6%). In addition, most PPCPs could be partly or completely removed during the anaerobic digestion process. The application of nZVI and IP showed positive impact on the removal of chlorinated PPCPs (p<0.05), but did not show significant impact on other PPCPs (p>0.05). Our finding suggests that the application of nZVI and IP in anaerobic digestion could be a promising way to enhance methane yield but had less improvement on PPCP degradation.

Waste biorefinery in arid/semi-arid regions

The utilization of waste biorefineries in arid/semi-arid regions is advisable due to the reduced sustainable resources in arid/semi-arid regions, e.g. fresh water and biomass. This review focuses on biomass residues available in arid/semi-arid regions, palm trees residues, seawater biomass based residues (coastal arid/semi-arid regions), and the organic fraction of municipal solid waste. The present review aims to describe and discuss the availability of these waste biomasses, their conversion to value chemicals by waste biorefinery processes. For the case of seawater biomass based residues it was reviewed and advise the use of seawater in the biorefinery processes, in order to decrease the use of fresh water.

Microbial ecology overview during anaerobic codigestion of dairy wastewater and cattle manure and use in agriculture of obtained bio-fertilisers

The anaerobic co-digestion of dairy wastewater (DW) and cattle manure (CM) was examined and associated with microbial community's structures using Denaturing Gradient Gel Electrophoresis (DGGE). The highest volatile solids (VS) reduction yield of 88.6% and biogas production of 0.87 L/g VS removed were obtained for the C/N ratio of 24.7 at hydraulic retention time (HRT) of 20 days. The bacterial DGGE profile showed significant abundance of Uncultured Bacteroidetes, Firmicutes and Synergistetes bacterium. The Syntrophomonas strains were discovered in dependent association to H2-using bacteria such as Methanospirillum sp., Methanosphaera sp. and Methanobacterium formicicum. These syntrophic associations are essential in anaerobic digesters allow them to keep low hydrogen partial pressure. However, high concentrations of VFA produced from dairy wastes acidification allow the growth of Methanosarcina species. The application of the stabilised anaerobic effluent on the agriculture soil showed significant beneficial effects on the forage corn and tomato plants growth and crops.

Hygienic treatment and energy recovery of dead animals by high solid co-digestion with vinasse under mesophilic condition: feasibility study

In the present study, the feasibility of hygienic treatment and energy recovery of dead animals (pork as an experimental alternative) by high solid co-digestion with vinasse under mesophilic condition was investigated. A lab-scale digester was operated for 125 days with SRT of 20 days. The volatile solid (VS) reduction, biogas yield, and CH4 content finally achieved stability after two obvious fluctuations, and were 55±1%, 0.40±0.02 m(3)/kg VS feed and 68%, respectively. Meanwhile, the shifts of microbial communities of the samples taken on typical days with different performance (day 40 (stable), day 65 (deteriorated), day 75 (in recovery), day 90 (recovered) and day 110 (stable)) were monitored by the application of pyrosequencing technology and the bioinformatical analysis with QIIME 1.8. In consequence, the details of changes in bacterial and archaeal communities elaborately explained the intrinsic reasons for the deterioration and recovery of the digester, and provided the proofs for the feasibility of hygienic treatment and energy recovery of dead animals by high solid co-digestion with vinasse under mesophilic condition.

Managing urban nutrient biogeochemistry for sustainable urbanization

Urban ecosystems are unique in the sense that human activities are the major drivers of biogeochemical processes. Along with the demographic movement into cities, nutrients flow towards the urban zone (nutrient urbanization), causing the degradation of environmental quality and ecosystem health. In this paper, we summarize the characteristics of nutrient cycling within the urban ecosystem compared to natural ecosystems. The dynamic process of nutrient urbanization is then explored taking Xiamen city, China, as an example to examine the influence of rapid urbanization on food sourced nitrogen and phosphorus metabolism. Subsequently, the concept of a nutrient footprint and calculation method is introduced from a lifecycle perspective. Finally, we propose three system approaches to mend the broken biogeochemical cycling. Our study will contribute to a holistic solution which achieves synergies between environmental quality and food security, by integrating technologies for nutrient recovery and waste reduction.