Microbial ecology of anaerobic digesters: the key players of anaerobiosis

Effects of ciprofloxacin on biogas production and microbial community composition in anaerobic digestion of swine wastewater in ASBR type reactor

In swine farming, antibiotics are often used to reduce disease and promote animal growth. Part of these compounds is not absorbed by the swine body, being excreted and later reaching the treatment systems, soil, and nearby waterbodies. This research sought to investigate the influence of adding ciprofloxacin (CIP) on the anaerobic digestion of swine wastewater. For that, a bench-scale anaerobic sequential batch reactor (ASBR) was used, with 5 L of working volume in six different phases, with volumetric organic loading rate (VOLR) and CIP dosage variation. According to the results, the optimal VOLR for the reactor was 0.60 ± 0.11 gSV L-1 d-1, resulting in biogas productivity of 0.51 ± 0.03 Lbiogas L-1 d-1. After initial stability, adding substrate with 0.5 mgCIP L-1 resulted in an abrupt drop of 82% in the productivity from the 7th to 11th day of addition, coinciding with volatile acids accumulation. Afterward, the reactor recovered and reached apparent stability, with productivity similar to the previous step without the drug. For 2.5 mgCIP L-1 in the substrate, the biogas productivity at equilibrium was 11.8% lower than in the phases with the same VOLR and 0.0 and 0.5 mgCIP L-1. Organic matter removals near 80% were achieved for both dosages. The 16S rRNA metagenomic analyses showed an increase in the relative abundance of most of the phyla found, indicating that the dosages used allowed the acclimatization of microorganisms and possibly the compound biodegradation.

Stabilization of microbial network by co-digestion of swine manure and organic wastes

The production of biogas from organic waste has attracted considerable interest as a solution to current energy and waste management challenges. This study explored the methane (CH4) production potential of swine manure (SM), food waste (FW), and tomato waste (TW) and the changes in the microbial community involved in the anaerobic digestion process. The results revealed that the CH4 production potentials of the four kinds of SM samples were influenced by the characteristics of SM (e.g., age and storage period). Among the four kinds of SM samples, the CH4 yield from the manure directly sampled from primiparous sows (SM3) was the highest. The CH4 yield was significantly improved when SM3 was co-digested with FW, but not with TW. The addition of SM fostered a stable CH4 production community by enhancing the interaction between methanogens and syntrophic bacteria. Furthermore, the addition of FW as a co-substrate may improve the functional redundancy structure of the methanogenesis-associated network. Overall, the characteristics of SM must be considered to achieve consistent CH4 yield efficiency from anaerobic digestion since CH4 production potentials of SM can be different. Also, the contribution of co-substrate to the synergistic relationship between methanogens and syntrophic bacteria can be considered when a co-substrate is selected in order to enhace CH4 yield from SM.

Potential of biofuel production from leather solid wastes: Indian scenario

India is one among the major leather-producing countries in the world which shares close to one-fourth of the world's leather solid wastes and most of these wastes are not effectively utilized. These wastes are rich in protein and lipids that could be a potential feedstock for biofuel production, i.e., biogas, biodiesel, etc. Among the 150,000 tons of daily leather solid wastes in India, approximately 87,150 tons are shared by pre-tanning operations (i.e., raw trimmings, fleshing, and hair wastes) while the rest of the 62,850 tons are shared by tanning, post-tanning, and finishing operations (i.e., wet blue trimmings, chrome splits, shavings, buffing dust, crust trimming wastes). This review article shows that there is considerable bioenergy potential for the use of leather solid wastes as a green fuel. The biogas potential of leather solid wastes is estimated to be 40,532.9 m3/day whereas the biodiesel potential is estimated as 15,452.6 L/day. The bio-oil and bio-char potential of leather solid wastes is estimated to be 80,513.0 L/day and 45.8 tons/day, respectively. Several factors influence the biofuel process efficacy, which needs to be taken into consideration while setting up a biofuel recovery plant. The overall biofuel potential of leather solid wastes shows that this feedstock is an untapped resource for energy recovery to add commercial benefits to India's energy supply. Furthermore, in addition to the economic benefits for investors, the use of leather solid wastes for biofuel production will yield a positive environmental impact.

Impact of innovative nanoadditives on biodigesters microbiome

Nanoparticles (NPs) supplementation to biodigesters improves the digestibility of biowaste and the generation of biogas. This study investigates the impact of innovative nanoadditives on the microbiome of biodigesters. Fresh cow manure was anaerobically incubated in a water bath under mesophilic conditions for 30 days. Three different NPs (zinc ferrite, zinc ferrite with 10% carbon nanotubes and zinc ferrite with 10% C76 fullerene) were separately supplemented to the biodigesters at the beginning of the incubation period. Methane and hydrogen production were monitored daily. Manure samples were collected from the digesters at different time points and the microbial communities inside the biodigesters were investigated via real-time PCR and 16 S rRNA gene amplicon-sequencing. The results indicate that zinc ferrite NPs enhanced biogas production the most. The microbial community was significantly affected by NPs addition in terms of archaeal and bacterial 16 S rRNAgene copy numbers. The three ZF formulations NPs augmented the abundance of members within the hydrogenotrophic methanogenic phyla Methanobacteriaceae. While Methanomassiliicoccacaea were enriched in ZF/C76 supplemented biodigester due to a significant increase in hydrogen partial pressure, probably caused by the enrichment of Spirochaetaceae (genus Treponema). Overall, NPs supplementation significantly enriched acetate-producing members within Hungateiclostridiaceae in ZF/CNTs, Dysgonomonadaceae in ZF and Spirochaetaceae ZF/C76 biodigesters.

The role of restaurant wastewater for producing bioenergy towards a circular bioeconomy: A review on composition, environmental impacts, and sustainable integrated management

Population inflation has led to the unprecedented increase in urbanization, thus causing negative impacts on environmental sustainability. Recently, there is an upsurge in the number of restaurants due to the changing lifestyles of the people round the globe. For instance, there were 167,490 food and beverage establishments in 2015, representing an annual growth rate of 5.1% since 2010 in Malaysia. The rapid growth of restaurants has implicated a negative impact due to the generation of highly polluted restaurant wastewater (RWW). RWW is mainly generated during the cooking, washing, and cleaning operations. RWW typically contain fat, oil, and grease (FOG) resulting from residues of meat, deep-fried food, baked items and butter, and has caused serious blockages of sewer due to clogging and eventually sewage backup. This has increased the required frequency of cleaning and sanitary sewer overflows (SSOs). Results from the previous studies have shown that FOG can be treated using physical, chemical, and biological processes. Different technologies have been applied for the treatment of FOG and other pollutants (COD, BOD, SS and NH₄-N) present in RWW. Therefore, this review aims to provide an in-depth understanding of the characteristics of RWW, chemical and physical characteristics of FOG with the mechanism of its formation and utilization for biocomposites, biogas and biodiesel productions for circular bioeconomy. Besides, this review has discussed the potential treatment technologies comprehensively for RWW which is currently remain understudied. Integrated sustainable management of FOG with technoeconomic analysis of bioproducts, sustainable management with international initiatives and previous studies are also summarized. Hence, this review aims towards providing better alternatives in managing RWW at sources, including its treatment and potential of its biorefinery, therefore eventually contributing towards environmental sustainability.

Deciphering the internal mechanisms of ciprofloxacin affected anaerobic digestion, its degradation and detoxification mechanism

Ciprofloxacin (CIP) is widely used in livestock farms, but the internal mechanism of the effect of residual CIP in actual livestock wastewater on anaerobic digestion (AD) performance remains unknown. This study examined the dose-specific effects of CIP (0.5-2 mg/L) on livestock wastewater AD by analyzing acidogenesis and methanogenesis. 0.5 mg/L CIP promoted methane production by facilitating acidogenesis and acetogenesis. Compared with the control, the cumulative methane production increased from 331.38 to 407.44 mL/g VS at a dose of 0.5 mg/L, an increase of 22.95 %. However, as the dose of CIP increased, the cumulative methane production gradually decreased to 217.64 mL/g VS (2 mg/L). Microbial community analysis revealed that CIP had the greatest impact on methane production by influencing the activity of acidogenic bacteria. Meanwhile, acidogenesis was critical for CIP degradation. In acidogenesis, hydroxylation, amination, defluorination, decarboxylation, and piperazine ring breaking not only degraded CIP but also reduced its toxicity. Therefore, a large number of intermediates could be continuously degraded by microorganisms. However, as the dosage of CIP increased, the ability of microorganisms to degrade intermediates decreased.

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

Cultured and uncultured microbial community associated with biogas production in anaerobic digestion processes

The search for sustainable development has increased interest in the improvement of technologies that use renewable energy sources. One of the alternatives in the production of renewable energy comes from the use of waste including urban solids, animal excrement from livestock, and biomass residues from agro-industrial plants. These materials may be used in the production of biogas, making its production highly sustainable and environmentally friendly. The present study aimed to evaluate the cultivated and uncultivated microbial community from a substrate (starter) used as an adapter for biogas production in anaerobic digestion processes. 16S rDNA metabarcoding revealed the domain of bacteria belonging to the phyla Firmicutes, Bacteroidota, Chloroflexi and Synergistota. The methanogenic group was represented by the phyla Halobacterota and Euryarchaeota. Through 16S rRNA sequencing of isolates recovered from the starter culture, the genera Rhodococcus (Actinobacteria phylum), Vagococcus, Lysinibacillus, Niallia, Priestia, Robertmurraya, Proteiniclasticum (Firmicutes phylum), and Luteimonas (Proteobacteria phylum) were identified, genera that were not observed in the metabarcoding data. The volatile solids, volatile organic acids, and total inorganic carbon reached 659.10 g kg^-1, 717.70 g kg^-1, 70,005.0 g kg^-1, respectively. The cultured groups are involved in the metabolism of sugars and other compounds derived from lignocellulosic material, as well as in anaerobic methane production processes. The results demonstrate that culture-dependent approaches, such as isolation and sequencing, and culture-independent studies, such as the Metabarcoding approach, are complementary methodologies that, when integrated provide robust and comprehensive information about the microbial communities involved in processes of the production of biogas in anaerobic digestion processes.

Prolonged acetogenic phase and biological succession during anaerobic digestion using swine manure

In recent years, global warming and the limitation of fossil fuels have been causing the governments of different countries to think about the search for more sustainable fuel sources. Biomethane (CH₄) has gained increasing attention in recent years as an alternative option for a sustainable source of energy. Biogas is generated during the anaerobic digestion of organic materials by the metabolism of complex microbial communities in the substrates that make up this digestion. The microbial community evaluation using 16S rDNA metabarcoding in a bench covered pond bioreactor using swine effluent revealed the dominant bacteria belonging to Firmicutes, Proteobacteria, and Bacteroidetes phyla. The methanogenic group was represented by the Euryarchaeota phylum. It was possible to observe that the relative frequency of the methanogenic archaea community decreased with the anaerobic digestion, indicating a biological succession stage. On the other hand, there was a predominant acetogenic diversity in this final stage. These data showed stabilization of biomethane production, although the microbial community of methanogens has drastically reduced in the late process.

Physico-Chemical and Metagenomic Profile Analyses of Animal Manures Routinely Used as Inocula in Anaerobic Digestion for Biogas Production

Anaerobic digestion (AD) of organic waste is considered a sustainable solution to energy shortage and waste management challenges. The process is facilitated by complex communities of micro-organisms, yet most wastes do not have these and thus need microbial inoculation using animal manures to initiate the process. However, the degradation efficiency and methane yield achieved in using different inocula vary due to their different microbial diversities. This study used metagenomics tools to compare the autochthonous microbial composition of cow, pig, chicken, and horse manures commonly used for biogas production. Cows exhibited the highest carbon utilisation (>30%) and showed a carbon to nitrogen ratio (C/N) favourable for microbial growth. Pigs showed the least nitrogen utilisation (<3%) which explains their low C/N whilst horses showed the highest nitrogen utilisation (>40%), which explains its high C/N above the optimal range of 20−30 for efficient AD. Manures from animals with similar gastrointestinal tract (GIT) physiologies were observed to largely harbour similar microbial communities. Conversely, some samples from animals with different GITs also shared common microbial communities plausibly because of similar diets and rearing conditions. Insights from this study will lay a foundation upon which in-depth studies of AD metabolic pathways and strategies to boost methane production through efficient catalysis can be derived.

Archaeal and Bacterial Content in a Two-Stage Anaerobic System for Efficient Energy Production from Agricultural Wastes

Anaerobic digestion (AD) is a microbially-driven process enabling energy production. Microorganisms are the core of anaerobic digesters and play an important role in the succession of hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes. The diversity of participating microbial communities can provide new information on digester performance for biomass valorization and biofuel production. In this study anaerobic systems were used, operating under mesophilic conditions that realized biodegradation processes of waste wheat straw pretreated with NaOH-a renewable source for hydrogen and methane production. These processes could be managed and optimized for hydrogen and methane separately but combining them in a two-stage system can lead to higher yields and a positive energy balance. The aim of the study was to depict a process of biohydrogen production from lignocellulosic waste followed by a second one leading to the production of biomethane. Archaeal and bacterial consortia in a two-stage system operating with wheat straw were identified for the first time and the role of the most important representatives was elucidated. The mixed cultures were identified by the molecular-biological methods of metagenomics. The results showed that biohydrogen generation is most probably due to the presence of Proteiniphilum saccharofermentans, which was 28.2% to 45.4% of the microbial community in the first and the second bioreactor, respectively. Archaeal representatives belonging to Methanobacterium formicicum (0.71% of the community), Methanosarcina spelaei (0.03%), Methanothrix soehngenii (0.012%), and Methanobacterium beijingense (0.01%) were proven in the methane-generating reactor. The correlation between substrate degradation and biogas accumulation was calculated, together with the profile of fatty acids as intermediates produced during the processes. The hydrogen concentration in the biogas reached 14.43%, and the Methane concentration was 69%. Calculations of the energy yield during the two-stage process showed 1195.89 kWh·t-1 compared to a 361.62 kWh·t-1 cumulative yield of energy carrier for a one-stage process.

Biofilm formation as a method of improved treatment during anaerobic digestion of organic matter for biogas recovery

The efficiency of anaerobic digestion could be increased by promoting microbial retention through biofilm development. The inclusion of certain types of biofilm carriers has differentiated existing AD biofilm reactors through their respective mode of biofilm growth. Bacteria and archaea engaged in methanogenesis during anaerobic processes potentially build biofilms by adhering or attaching to biofilm carriers. Meta-analyzed results depicted varying degrees of biogas enhancement within AD biofilm reactors. Furthermore, different carrier materials highly induced the dynamicity of the dominant microbial population in each system. It is suggested that the promotion of surface contact and improvement of interspecies electron transport have greatly impacted the treatment results. Modern spectroscopy techniques have been and will continue to give essential information regarding biofilm's composition and structural organization which can be useful in elucidating the added function of this special layer of microbial cells.

Synergistic Effect of Magnetite and Bioelectrochemical Systems on Anaerobic Digestion

Conventionally, the anaerobic digestion of industrial effluent to biogas constitutes less than 65% methane, which warrants its potential methanation to mitigate carbon dioxide and other anthropogenic gas emissions. The performance of the anaerobic digestion process can be enhanced by improving biochemical activities. The aim of this study was to examine the synergistic effect of the magnetite and bioelectrochemical systems (BES) on anaerobic digestion by comparing four digesters, namely a microbial fuel cell (MFC), microbial electrolysis cell (MEC), MEC with 1 g of magnetite nanoparticles (MECM), and a control digester with only sewage sludge (500 mL) and inoculum (300 mL). The MFC digester was equipped with zinc and copper electrodes including a 100 Ω resistor, whereas the MEC was supplied with 0.4 V on the electrodes. The MECM digester performed better as it improved microbial activity, increased the content of methane (by 43% compared to 41% of the control), and reduced contaminants (carbon oxygen demand, phosphates, colour, turbidity, total suspended solids, and total organic carbon) by more than 81.9%. Current density (jmax = 25.0 mA/m²) and electrical conductivity (275 µS/cm) were also high. The prospects of combining magnetite and bioelectrochemical systems seem very promising as they showed a great possibility for use in bioelectrochemical methane generation and wastewater treatment.

Valorisation of CO2 into Value-Added Products via Microbial Electrosynthesis (MES) and Electro-Fermentation Technology

Microbial electrocatalysis reckons on microbes as catalysts for reactions occurring at electrodes. Microbial fuel cells and microbial electrolysis cells are well-known in this context; both prefer the oxidation of organic and inorganic matter for producing electricity. Notably, the synthesis of high energy-density chemicals (fuels) or their precursors by microorganisms using bio-cathode to yield electrical energy is called Microbial Electrosynthesis (MES), giving an exceptionally appealing novel way for producing beneficial products from electricity and wastewater. This review accentuates the concept, importance and opportunities of MES, as an emerging discipline at the nexus of microbiology and electrochemistry. Production of organic compounds from MES is considered as an effective technique for the generation of various beneficial reduced end-products (like acetate and butyrate) as well as in reducing the load of CO2 from the atmosphere to mitigate the harmful effect of greenhouse gases in global warming. Although MES is still an emerging technology, this method is not thoroughly known. The authors have focused on MES, as it is the next transformative, viable alternative technology to decrease the repercussions of surplus carbon dioxide in the environment along with conserving energy.

Solid state anaerobic digestion of food waste and sewage sludge: Impact of mixing ratios and temperature on microbial diversity, reactor stability and methane yield

Food waste (FW) and sewage sludge (SS) were anaerobically co digested under solid state conditions (Total solids >15%) and observed that mixing ratio of 3:1 and 2:1 is optimum for mesophilic and thermophilic conditions respectively. The VS reduction and methane yield at optimized ratio was 76% and 0.35 L CH₄/(g VS reduced) respectively at mesophilic temperature whereas it was 88% and 0.42 L CH₄/(g VS reduced) at thermophilic temperature. The metagenomic analysis for these cases were done and high throughput DNA sequencing revealed that diversified bacterial groups that participate in the different metabolisms (hydrolysis, acidogenesis and acetogenesis) were mainly dominated by the phylum Firmicutes and Bacteriodetes. Genus Methanothrix is found to be dominant which is capable of generating methane by any methanogenic pathway among all the archaeal communities in the reactors followed by Methanolinea and Methanoculleus. However, it was understood through metagenomic studies that acetotrophic pathway is observed to be the major metabolic pathway in the reactors.

Effects of combined tannic acid/fluoride on sulfur transformations and methanogenic pathways in swine manure

Livestock manure emits reduced sulfur compounds and methane, which affect nature and the climate. These gases are efficiently mitigated by addition of a tannic acid-sodium fluoride combination inhibitor (TA-NaF), and to some extent by acidification. In this paper, TA-NaF treatment was performed on swine manure to study the treatment influence on methanogenic pathways and sulfur transformation pathways in various laboratory experiments. Stable carbon isotope labeling revealed that both untreated and TA-NaF treated swine manures were dominated by hydrogenotrophic methanogenesis. However, in supplementary experiments in wastewater sludge, TA-NaF clearly inhibited acetoclastic methanogenesis, whereas acidification inhibited hydrogenotrophic methanogenesis. In swine manure, TA-NaF inhibited s-amino acid catabolism to a larger extent than sulfate reduction. Conversely, acidification reduced sulfate reduction activity more than s-amino acid degradation. TA-NaF treatment had no significant effect on methanogenic community structure, which was surprising considering clear effects on isotope ratios of methane and carbon dioxide. Halophile sulfate reducers adapted well to TA-NaF treatment, but the community change also depended on temperature. The combined experimental work resulted in a proposed inhibition scheme for sulfur transformations and methanogenic pathways as affected by TA-NaF and acidification in swine manure and in other inocula.

Potential Valorization of Organic Waste Streams to Valuable Organic Acids through Microbial Conversion: A South African Case Study

The notion of a “biobased economy” in the context of a developing country such as South Africa (SA) necessitates the development of technologies that utilize sustainable feedstocks, have simple and robust operations, are feasible at small scale and produce a variety of valuable bioproducts, thus fitting the biorefinery concept. This case study focuses on the microbial production of higher-value products from selected organic waste streams abundant in the South African agricultural sector using microbes adapted to utilize different parts of biomass waste streams. A ruminant-based carboxylate platform based on mixed or undefined anaerobic co-cultures of rumen microorganisms can convert the carbohydrate polymers in the lignocellulosic part of organic waste streams to carboxylic acids that can be upgraded to biofuels or green chemicals. Furthermore, yeast and fungi can convert the simpler carbohydrates (such as the sugars and malic acid in grape and apple pomace) to ethanol and high-value carboxylic acids, such as lactic, fumaric, succinic and citric acid. This review will discuss the combinational use of the ruminal carboxylate platform and native or recombinant yeasts to valorize biomass waste streams through the production of higher-value organic acids with various applications.

Biogas Production from Coffee Pulp and Chicken Feathers Using Liquid- and Solid-State Anaerobic Digestions

Agricultural waste, particularly lignocellulose, has been used in the second generation of biogas. Coffee pulp and chicken feathers can be developed as biogas raw materials because of their suitability as a biogas substrate. This study investigates the effect of the percentage of total solids (TS), carbon to nitrogen ratio (C/N, g/g), and delignification pretreatment on biogas production from coffee pulp and chicken feathers, and aims to compose kinetics using the modified Gompertz model. The results show that adjusting the percentage of TS at low-level speeds up the degradation process, which increases chemical oxygen demand (COD) reduction and biogas production. COD reduction and biogas production increase optimally at the 25 (g/g) C/N ratio. Pretreatment delignification aids microorganisms in substrate decomposition, resulting in faster COD reduction and biogas conversion. The 25% TS and 25 (g/g) C/N ratio with the delignification process achieved the best biogas production, with biogas production of 10,438.04 mL. The Gompertz method shows that the difference in TS percentage can influence biogas production. Moreover, the method shows that biogas production is higher with the delignification process than without it.

Haloarchaea as Cell Factories to Produce Bioplastics

Plastic pollution is a worldwide concern causing the death of animals (mainly aquatic fauna) and environmental deterioration. Plastic recycling is, in most cases, difficult or even impossible. For this reason, new research lines are emerging to identify highly biodegradable bioplastics or plastic formulations that are more environmentally friendly than current ones. In this context, microbes, capable of synthesizing bioplastics, were revealed to be good models to design strategies in which microorganisms can be used as cell factories. Recently, special interest has been paid to haloarchaea due to the capability of some species to produce significant concentrations of polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), and polyhydroxyvalerate (PHV) when growing under a specific nutritional status. The growth of those microorganisms at the pilot or industrial scale offers several advantages compared to that of other microbes that are bioplastic producers. This review summarizes the state of the art of bioplastic production and the most recent findings regarding the production of bioplastics by halophilic microorganisms with special emphasis on haloarchaea. Some protocols to produce/analyze bioplastics are highlighted here to shed light on the potential use of haloarchaea at the industrial scale to produce valuable products, thus minimizing environmental pollution by plastics made from petroleum.

Combined fungal and bacterial pretreatment of wheat and pearl millet straw for biogas production - A study from batch to continuous stirred tank reactors

In present study, chitinolytic bacteria were employed to bioaugment the biogas production from fungal pretreated agricultural residues. The fungal pretreatment of wheat and pearl millet straw was done by Chaetomium globosporum. Pretreated straw were digested anaerobically at batch scale with and without the presence of chitinolytic bacteria. Contrary to untreated samples, the addition of chitionolytic bacteria with pretreated wheat and pearl millet straw provided 41 and 57% higher biogas yield. The study was further upscaled to continuous stirred tank reactors. At continuous scale too, wheat straw pretreated with Chaetomium globosporum combined with chitinolytic bacteria resulted in 16% higher biogas yield in contrast to untreated straw. Higher abundance of methanogens was detected in reactors running with pretreated wheat straw during microbial community analysis. The identified bacteria belonged mostly to Firmicutes, Bacteroidetes, Proteobacteria phyla.

Biomethanation Potential (BMP) Study of Mesophilic Anaerobic Co-Digestion of Abundant Bio-Wastes in Southern Regions of Tunisia

Tunisia is a country that suffers from energy demand problems and environmental matters. Thus, Tunisian authorities desire to encourage the development of renewable energy sources, especially from biological processes, like anaerobic digestion. Therefore, this study is focused on the evaluation of biogas and bio-methane yield from the co-digestion of three available and abundant bio-wastes in the southern regions of Tunisia. The three different raw materials are an organic fraction of municipal solid waste, chicken manure, and olive mill wastewater. In this context, experimental work to evaluate the potential of biogas and bio-methane production was carried out at mesophilic temperature 35 °C and batch mode. The present work highlights the possibility of generating biogas from these organic wastes and reducing the amounts of the wastes to dispose of in landfills. The experimental study of the co-digestion process under specific conditions of carbon to nitrogen ratio (C/N), T, pH, and inoculums to substrate ratio ISR provided a high yield of net methane and net biogas, in comparison with other research works. Results showed a higher specific net methane production per kg of volatile solids, which is equal to 0.338 Nm3 methane/kg VS and 0.430 Nm3 methane/kg VS for two studied cases. The obtained volatile solids reduction was found to be 91% of the initial content, for a hydraulic retention time (HRT) of 40 days.

Enhancing anaerobic syntrophic propionate degradation using modified polyvinyl alcohol gel beads

Modified polyvinyl alcohol (PVA) beads serve as effective anaerobic microbe immobilization carriers. PVA beads were mixed with different conductive materials, activated carbon, magnetite, and green tuff stone powder. In this study, modified PVA beads were used to investigate the effect of using, promote methane production, and enhance direct interspecies electron transfer (DIET) on the anaerobic syntrophic degradation of propionate, which is an essential intermediate process for generating methane in anaerobic digesters. The batch experiment showed that PVA mixed with activated carbon had the highest methane conversion rate of 72%, whereas the rates for control (sludge) was 61%. Moreover, the lag time during the second and third feedings was shorter by 5-fold than for the first feeding when modified PVA beads were added. The syntrophic propionate degrading microorganisms in the modified PVA beads was Syntrophobacter and Methanobacterium, either Methanoculleus or Methanosaeta. The modified PVA beads hold at least 10 times larger syntrophs than normal PVA. Therefore, composite PVA with conductive materials can promote methane production, accelerate propionate consumption, and enhance electron transfer in related microbial species.

Anaerobic mono and co-digestion of organic fraction of municipal solid waste and landfill leachate at industrial scale: Impact of volatile organic loading rate on reaction kinetics, biogas yield and microbial diversity

The present study was aimed to demonstrate a semi-commercial biomethanation plant based on anaerobic gas lift reactor (AGR) for the mono and co-digestion of organic fraction of municipal solid waste (OFMSW) and landfill leachate (LL) for 47 weeks. The reactors were commissioned at a volatile organic loading rate (VOLR) starting from 0.4 to 6.2 kg VS/(m³·day) to investigate the impact of VOLR on the organic matter removal rates, substrate utilization rate using Stover-Kincannon reaction kinetics, biogas yield and microbial diversity. 16s-metagenomic sequencing of the species present in the inoculum that was acclimatized with OFMSW, LL separately and in combination was also performed to identify the dominant microbial species in the mixed microbial consortia. Results revealed that the VS reduction in AGR 1, AGR 2 and AGR 3 at full load was 46%, 42% and 47% respectively with a corresponding biogas generation of 73.8 m³/day, 42 m³/day and 60.8 m³/day. The biodegradability in AGR 1 was between 73% and 81% whereas in AGR 2 and AGR 3, it was between 57% and 78% and 64% and 86% respectively. The operational strategy of digestate recirculation facilitated in the reduced usage of buffering chemicals which impacted on overall financials of the plant. The techno-economic analysis suggests that these kinds of biomethanation plants are remunerative.

Rapid Two Stage Anaerobic Digestion of Nejayote through Microaeration and Direct Interspecies Electron Transfer

Corn is one of the main food products in Mexico. The elaboration of corn-derived products generates wastewater with a high organic load (nejayote). Anaerobic digestion is an indicated treatment for wastewater with high organic loads. The results of this study show that the application of microaeration in the hydrolysis-fermentative reactor increased the percentage of volatile fatty acids (VFA) available in the medium by 62%. The addition of a conductive material, such as granulated activated carbon (GAC), promotes DIET (Direct interspecies electrons transfer) in the methanogenic UASB reactor increasing the methane yield by 55%. Likewise, a great diversity of exoelectrogenic bacteria, with the ability to donate electrons DIET mechanisms, were developed in the GAC biofilm, though interestingly, Peptoclostridium and Clostridium (17.3% and 12.75%, respectively) were detected with a great abundance in the GAC biofilm. Peptoclostridium has not been previously reported as a participant in DIET process.

Hydrolysis and Methanogenesis in UASB-AnMBR Treating Municipal Wastewater Under Psychrophilic Conditions: Importance of Reactor Configuration and Inoculum

Three upflow anaerobic sludge blanket (UASB) pilot scale reactors with different configurations and inocula: flocculent biomass (F-UASB), flocculent biomass and membrane solids separation (F-AnMBR) and granular biomass and membrane solids separation (G-AnMBR) were operated to compare start-up, solids hydrolysis and effluent quality. The parallel operation of UASBs with these different configurations at low temperatures (9.7 ± 2.4°C) and the low COD content (sCOD 54.1 ± 10.3 mg/L and pCOD 84.1 ± 48.5 mg/L), was novel and not previously reported. A quick start-up was observed for the three reactors and could be attributed to the previous acclimation of the seed sludge to the settled wastewater and to low temperatures. The results obtained for the first 45 days of operation showed that solids management was critical to reach a high effluent quality. Overall, the F-AnMBR showed higher rates of hydrolysis per solid removed (38%) among the three different UASB configurations tested. Flocculent biomass promoted slightly higher hydrolysis than granular biomass. The effluent quality obtained in the F-AnMBR was 38.0 ± 5.9 mg pCOD/L, 0.4 ± 0.9 mg sCOD/L, 9.9 ± 1.3 mg BOD₅/L and <1 mg TSS/L. The microbial diversity of the biomass was also assessed. Bacteroidales and Clostridiales were the major bacterial fermenter orders detected and a relative high abundance of syntrophic bacteria was also detected. Additionally, an elevated abundance of sulfate reducing bacteria (SRB) was also identified and was attributed to the low COD/SO₄ ^2- ratio of the wastewater (0.5). Also, the coexistence of acetoclastic and hydrogenotrophic methanogenesis was suggested. Overall this study demonstrates the suitability of UASB reactors coupled with membrane can achieve a high effluent quality when treating municipal wastewater under psychrophilic temperatures with F-AnMBR promoting slightly higher hydrolysis rates.

Characterisation of microbial communities for improved management of anaerobic digestion of food waste

Anaerobic digestion of food waste is an attractive and increasingly popular technology within waste management and energy recovery. A better understanding of the microbiology associated with anaerobic digestion of food waste will provide new insight into the operational conditions required for optimizing this process, as well as its potential for utilisation in co-digestion systems. Eighteen full-scale reactors processing varying proportions of food waste under diverse operational configurations were subjected to microbial community analysis by amplicon sequencing of the 16S rRNA and mcrA genes to capture the bacterial and methanogenic populations. Statistical correlations between microbial populations, plant design and operating conditions revealed that the microbial communities were shaped by operational parameters such as the primary substrate type and operational temperature, while the methanogenic communities showed a more reactor specific distribution. The distribution of microbes based on the waste processed in the surveyed digesters was explored, as well as the presence of specialist populations such as syntrophs and methanogens. Food waste digester communities were not associated with a strong microbial fingerprint compared to other waste types (wastewater and manure) but contained greater abundance and unique syntrophic acetate oxidising populations, suggesting that co-digestion with food waste may improve the functional diversity of anaerobic digesters.

Enhancement of biogas production from wastewater sludge via anaerobic digestion assisted with biochar amendment

Studies have shown that biochar enhances methane formation due to the presence of redox active moieties and its conductive properties. This study investigated the influence of biochar, which was produced from Douglas fir pyrolysis, on biogas production and microbial community during anaerobic digestion (AD) of wastewater sludge. The results showed that biochar significantly enhances methane (CH₄) production rate and increases its final yield during AD. The cumulative highest CH₄ production obtaining in cultures with DF500 (biochar from Douglas fir at 500 °C) were about 11% and 98% more than the culture without biochar at 37 °C and 25 °C AD temperature, respectively. At 55 °C, the maximum CH₄ yield reached 172.3 ml/g COD with DF730, which was about 48.3% more than control culture. The microbial community analysis results showed that biochar could up-regulate the role of micro-ecology especially the methanogens and improve the AD process.

Effects of dicyandiamide and Mg/P on the global warming potential of swine slurry and sawdust cocomposting

Composting is an emerging strategy for swine slurry treatment; nonetheless, significant greenhouse gases (GHG) emissions may occur during this process. We carried out two separate assays with increasing doses of dicyandiamide (DCD; up to 1.1% w/w) as a nitrification inhibitor and solutions of MgCl₂ and H₃PO₄ (Mg/P; up to 0.09/0.06 mol kg^-1) to promote struvite crystallization in order to assess their efficiencies as additives to decrease GHG emission during swine slurry cocomposting with sawdust (1:1v/v). We monitored the nitrous oxide (N₂O-N), methane (CH₄-C), and carbon dioxide (CO₂-C) emissions and the ammonia (NH₄⁺-N) and nitrate/nitrite (NOx-N) concentrations in compost reactors (35 L) during the first 4-5 weeks of composting. DCD had no effect on CH₄-C and CO₂-C emissions but decreased N₂O-N losses by up to 56% compared with control. However, DCD inactivation was favored by thermophilic conditions and N₂O-N emissions increased to same levels of control after 13 days. Mg/P was effective to decrease N₂O-N losses only at the highest dose, which also sustained higher [NH₄⁺-N] in the compost by the end of the assessment. Nonetheless, the use of 0.09/0.06 mol kg^-1 of Mg/P also decreased CH₄-C and CO₂-C emissions compared with lower doses of Mg/P and unamended treatments. Overall, DCD and Mg/P amendments decreased the global warming potential (GWP) of swine slurry composting by up to 46 and 28%, respectively. The Mg/P application may be also interesting to increase the compost quality by increasing its NH₄⁺-N availability. Graphical abstract.

Annual microbial community dynamics in a full-scale anaerobic sludge digester from a wastewater treatment plant in Colombia

Anaerobic digestion is a microbe-driven process widely applied to treat activated sludge from municipal wastewater treatment plants. It is one of the most efficient solutions for sludge reduction along with biogas production. However, the knowledge of the microbial consortium involved in this process is still unknown in full-scale anaerobic digesters from Latin America. This study aimed to elucidate the dynamics of the microbial community of a full-scale anaerobic digester for a year using 16S rDNA amplicon sequencing with the Illumina Miseq platform. The results showed fluctuations in the frequencies of dominant phyla with a decrease of Proteobacteria and Bacteroidetes after a temporary suspension of anaerobic digester. The core community was affiliated with bacterial phyla Firmicutes, Actinobacteria, Proteobacteria, and Chloroflexi. The core community was represented by 154 OTUs that accounted for 74% of all the processed reads. The Anaerolineaceae family, within Chloroflexi phylum, was the most frequently observed taxonomic group in all samples analyzed. Despite the microbial fluctuations, the biogas production was stable over the studied year (average 66% methane production), which might indicate a functional redundancy in the microbial consortium.

Microbial Community Redundancy and Resilience Underpins High-Rate Anaerobic Treatment of Dairy-Processing Wastewater at Ambient Temperatures

High-rate anaerobic digestion (AD) is a reliable, efficient process to treat wastewaters and is often operated at temperatures exceeding 30°C, involving energy consumption of biogas in temperate regions, where wastewaters are often discharged at variable temperatures generally below 20°C. High-rate ambient temperature AD, without temperature control, is an economically attractive alternative that has been proven to be feasible at laboratory-scale. In this study, an ambient temperature pilot scale anaerobic reactor (2 m³) was employed to treat real dairy wastewater in situ at a milk processing plant, at organic loading rates of 1.3 ± 0.6 to 10.6 ± 3.7 kg COD/m³/day and hydraulic retention times (HRT) ranging from 36 to 6 h. Consistent high levels of COD removal efficiencies, ranging from 50 to 70% for total COD removal and 70 to 84% for soluble COD removal, were achieved during the trial. Within the reactor biomass, stable active archaeal populations were observed, consisting mainly of Methanothrix (previously Methanosaeta) species, which represented up to 47% of the relative abundant active species in the reactor. The decrease in HRT, combined with increases in the loading rate had a clear effect on shaping the structure and composition of the bacterial fraction of the microbial community, however, without affecting reactor performance. On the other hand, perturbances in influent pH had a strong impact, especially when pH went higher than 8.5, inducing shifts in the microbial community composition and, in some cases, affecting negatively the performance of the reactor in terms of COD removal and biogas methane content. For example, the main pH shock led to a drop in the methane content to 15%, COD removals decreased to 0%, while the archaeal population decreased to ~11% both at DNA and cDNA levels. Functional redundancy in the microbial community underpinned stable reactor performance and rapid reactor recovery after perturbations.

Acetate Production from Cafeteria Wastes and Corn Stover Using a Thermophilic Anaerobic Consortium: A Prelude Study for the Use of Acetate for the Production of Value-Added Products

Efficient and sustainable biochemical production using low-cost waste assumes considerable industrial and ecological importance. Solid organic wastes (SOWs) are inexpensive, abundantly available resources and their bioconversion to volatile fatty acids, especially acetate, aids in relieving the requirements of pure sugars for microbial biochemical productions in industries. Acetate production from SOW that utilizes the organic carbon of these wastes is used as an efficient solid waste reduction strategy if the environmental factors are optimized. This study screens and optimizes influential factors (physical and chemical) for acetate production by a thermophilic acetogenic consortium using two SOWs-cafeteria wastes and corn stover. The screening experiment revealed significant effects of temperature, bromoethane sulfonate, and shaking on acetate production. Temperature, medium pH, and C:N ratio were further optimized using statistical optimization with response surface methodology. The maximum acetate concentration of 8061 mg L-1 (>200% improvement) was achieved at temperature, pH, and C:N ratio of 60 °C, 6, 25, respectively, and acetate accounted for more than 85% of metabolites. This study also demonstrated the feasibility of using acetate-rich fermentate (obtained from SOWs) as a substrate for the growth of industrially relevant yeast Yarrowia lipolytica, which can convert acetate into higher-value biochemicals.

Anaerobic digestion of biorefinery lignin: Effect of different wet explosion pretreatment conditions

This study examine ways to make biorefinery lignin accessible for anaerobic digestion. The raw material was the residue after removing carbohydrates by Wet Explosion pretreatment at 190 °C and 7.5% O₂ followed by enzymatic hydrolysis. The residual solid was mainly composed of lignin and was the raw material for a second WEx pretreatment operated at 220 °C with 4% oxygen and variable concentrations of NaOH (0-2%). Lignin B was the residue after pretreated without NaOH, Lignin C was pretreated at 1% NaOH, and Lignin E at 2% NaOH. Anaerobic digestion was carried out on all lignin fractions (Lignin A, B, C and E) at thermophilic conditions (52 °C) by mixing 70% of each lignin fractions with 30% clarified manure. The results showed that the lignin samples were demethoxylated as part of the biodegradation and that the highest severity pretreatment (with oxygen and 2% NaOH) resulted in the highest methane yield.

Enhanced hydrolysis of waste activated sludge for methane production via anaerobic digestion under N2-nanobubble water addition

Anaerobic digestion (AD) is a relatively safe and economically feasible disposal technique for waste activated sludge (WAS), in which hydrolysis of complex organic matters is the rate-limiting step. The aim of this study is to explore the efficiency of applying nitrogen gas nanobubble water (N₂-NBW) to AD of WAS and reveal the possible mechanisms. The possible effects of N₂-NBW on different processes during AD of WAS were investigated and N₂-NBW was expected to enhance the hydrolysis step. Results showed that after N₂-NBW addition, sludge particles possessed more negative charges (indicated by zeta potential) than the control with deionized water (DW) addition. The total methane production of NBW group was 402 mL/g-VS_reduced, 29% higher than the control group. Moreover, mechanism investigations revealed that N₂-NBW addition not only improved the disintegration of high molecular weight compounds (proteins and polysaccharides), but also enhanced the activities of four extracellular hydrolases by 14-17%. Results from the present work showed that the enhancement of N₂-NBW addition on methane production from AD of WAS was mainly through the augmentation of hydrolysis of WAS, as little effect on methanogenesis and VS reduction was discerned. The promotion effect of N₂-NBW on hydrolysis suggests that N₂-NBW addition is a promising pretreatment strategy for AD of WAS with no chemical addition at low energy consumption, thus, increasing the economic feasibility of WAS disposal.

Microbial communities in co-digestion of food wastes and wastewater biosolids

The effect of food waste (FW) co-digestion with wastewater biosolids (WWB) on microbial communities was investigated through running thirteen lab-scale digesters for 100 days at different operational conditions i.e. organic loading rates (2 and 4 kgCOD/m³·day), feed types (WWB and FW), and FW content (10%, 90%, 100%). Compared with mono-digestion of WWB, FW co-digestion enhanced biogas production by 13% and COD degradation rates by up to 101%. Among fermentative bacteria/acetogens, Syntrophomonas was the dominant genus in FW digesters in contrast to the dominance of Clostridium in WWB digesters. The predominant methanogen was Methanosarcina in FW digesters in contrast to Methanosaeta in WWB digesters. COD degradation rates and methane yields were well correlated with Bacteroidetes population. Methane production rate was well correlated with Clostridium for FW digesters, with syntrophs for WWB digesters, and with aceticlastic methanogens for both digesters. Synergism was associated with hydrolytic bacteria, Clostridium, Syntrophomonas, syntrophs, Methanosarcina, and Methanobacterium.

Petroleum Hydrocarbon Contamination in Terrestrial Ecosystems-Fate and Microbial Responses

Petroleum hydrocarbons represent the most frequent environmental contaminant. The introduction of petroleum hydrocarbons into a pristine environment immediately changes the nature of that environment, resulting in reduced ecosystem functionality. Natural attenuation represents the single, most important biological process which removes petroleum hydrocarbons from the environment. It is a process where microorganisms present at the site degrade the organic contaminants without the input of external bioremediation enhancers (i.e., electron donors, electron acceptors, other microorganisms or nutrients). So successful is this natural attenuation process that in environmental biotechnology, bioremediation has developed steadily over the past 50 years based on this natural biodegradation process. Bioremediation is recognized as the most environmentally friendly remediation approach for the removal of petroleum hydrocarbons from an environment as it does not require intensive chemical, mechanical, and costly interventions. However, it is under-utilized as a commercial remediation strategy due to incomplete hydrocarbon catabolism and lengthy remediation times when compared with rival technologies. This review aims to describe the fate of petroleum hydrocarbons in the environment and discuss their interactions with abiotic and biotic components of the environment under both aerobic and anaerobic conditions. Furthermore, the mechanisms for dealing with petroleum hydrocarbon contamination in the environment will be examined. When petroleum hydrocarbons contaminate land, they start to interact with its surrounding, including physical (dispersion), physiochemical (evaporation, dissolution, sorption), chemical (photo-oxidation, auto-oxidation), and biological (plant and microbial catabolism of hydrocarbons) interactions. As microorganism (including bacteria and fungi) play an important role in the degradation of petroleum hydrocarbons, investigations into the microbial communities within contaminated soils is essential for any bioremediation project. This review highlights the fate of petroleum hydrocarbons in tertial environments, as well as the contributions of different microbial consortia for optimum petroleum hydrocarbon bioremediation potential. The impact of high-throughput metagenomic sequencing in determining the underlying degradation mechanisms is also discussed. This knowledge will aid the development of more efficient, cost-effective commercial bioremediation technologies.

Performance Analysis of Biocathode in Bioelectrochemical CO2 Reduction

Microbial electrosynthesis (MES) biogas upgrading is done via reduction of carbon dioxide to methane through electroactive microbial catalysis. The baseline MES mode of operation showed about a 39% increase in the methane production rate compared to the open circuit mode of operation. MES is capable of producing acetic acid at relatively more negative potential (−0.80 to –0.90 V vs. Standard Hydrogen Electrode (SHE)) than the potential at which it produces methane (−0.65 V vs. SHE). The optimum pH for enhancing the electroactive acetogens is found to be around 6.8–7.0 while a pH of around 7.0–7.5 enhances the electroactive methanogens performance. The biocathode adaptation test reveals that 45% of the methane was produced through the electrochemical pathway with a coulombic efficiency of 100% while maintaining heterotrophic efficiency above 99%.

Kinetic modeling of Stickland reactions-coupled methanogenesis for a methanogenic culture

Studying amino acid catabolism-coupled methanogenesis is the important standpoints to decipher the metabolic behavior of a methanogenic culture. l-Glycine and l-alanine are acted as sole carbon and nitrogen sources for acidogenic bacteria. One amino acid is oxidized and another one is reduced for acetate production via pyruvate by oxidative deamination process in the Stickland reactions. Herein, we have developed a kinetic model for the Stickland reactions-coupled methanogenesis (SRCM) and simulated objectively to maximize the rate of methane production. We collected the metabolic information from enzyme kinetic parameters for amino acid catabolism of Clostridium acetobutylicum ATCC 824 and methanogenesis of Methanosarcina acetivorans C2A. The SRCM model of this study consisted of 18 reactions and 61 metabolites with enzyme kinetic parameters derived experimental data. The internal or external metabolic flux rate of this system found to control the acidogenesis and methanogenesis in a methanogenic culture. Using the SRCM model, flux distributions were calculated for each reaction and metabolite in order to maximize the methane production rate from the glycine–alanine pair. Results of this study, we demonstrated the metabolic behavior, metabolite pairing while mutually interact, and advantages of syntrophic metabolism of amino acid-directed methane production in a methanogenic starter culture.

Benefit of solid-liquid separation on volatile fatty acid production from grass clipping with ultrasound-calcium hydroxide pretreatment

Ultrasound-calcium hydroxide (US-Ca(OH)₂) pretreatment effectively enhanced volatile fatty acid (VFA) production from lignocellulosic biomass. In this paper, solid and liquid fraction of pretreated grass clipping was for the first time separately fermented in order to improve organic recovery from liquid fraction and reduce inhibition due to alkaline pretreatment. The total VFA yield and VS removal reached 515 mg/g TS and 59.7% after solid-liquid separation, exhibiting an increase of 116.7% and 91.9% comparing to that of mixture sample. The dominate components of VFAs are acetic and propionate acid, accounting for 80-90% of total VFAs. Kinetic analysis showed that the highest maximum VFA production rate of 690 mg/L·d and the highest cumulative VFA production potential of 3299 mg/L were achieved in the fermentation of solid fraction. Microbial analysis showed that the dominate genera for VFA production were Halocella and Ruminiclostridium, both with a relative abundance of 20.1% in fermentation of solid fraction.

Microbiota of a Full-scale UASB Reactor Treating Brewery Wastewater Using Illumina MiSeq Sequencing

Background:

The efficiency of biological wastewater treatment plant is determined by bacterial metabolism. There are data on the effect of operational parameters on microbial consortia present in laboratory scale reactor. However, knowledge on the full-scale reactor is still limited at present, hence the need to define the relations between the microbial structure and the performance of full-scale reactor.

Objective:

In this study, the microbial community structure in a full-scale UASB reactor treating brewery wastewater was assessed using metagenomics Next-Generation Sequencing technique.

Method:

Granular sludge samples were collected from the UASB reactor treating brewery wastewater and extracted genomic DNA was amplified using barcoded bacterial primer sets targeting V3-V4 region of the 16S rRNA genes on sequencing Illumina MiSeq platform.

Results:

The taxonomic analysis revealed the abundance of bacteria (~95%) with considerable Archaea community (~2%) in the granular sludge. After trimming, 18 bacterial phyla, 29 orders, 36 families and 44 genera were recovered from the 48,488 sequences reads of the 16S rRNA genes analysed, where the most abundant community belongs to Firmicutes, Bacteroidetes, Synergistetes and Proteobacteria phyla.

Conclusion:

For a sustainable bioenergy generation, understanding the mechanisms of anaerobic system in relation to microbial community is an important factor to increase the production of biogas production during wastewater treatment. To the best of our knowledge, this report is one of the studies that explored and described bacterial diversity and community structure of a full-scale UASB reactor treating brewery wastewater using high-throughput sequencing. This study provides insight into the dominant microbial community and their phylogenetic diversity in biogas producing reactor.

Metagenomic assessment of the microbial community and methanogenic pathways in biosolids from a municipal wastewater treatment plant in Medellín, Colombia

Abundance and diversity of microbial communities in biosolids are variable and poorly studied in the tropics, and it is known that rainfall is one of the events that could affect the phylogenetic and functional microbial structure. In the present study, using NGS technics, we studied the microbial diversity as well as the methanogenesis pathway in one of the largest WWTP in Colombia. Besides, we sampled and analyzed biosolids from rainy season and dry season. Phylogenetic classification showed a predominance of bacteria in both samples and difference in the dominant groups depending on the rainfall season. Whereas Pseudomonas was the dominant bacteria in the dry season, Coprothermobacter was in the rainy season. Archaea abundance was higher in the rainy season (11.5%) doubling dry season proportion. The bioreactor biogas production and total solids content showed similar results between rainy and dry season at the sampling dates. The most abundant Archaea related with methanogenesis was Methanosaeta, which is a methanogenic microorganism that exclusively uses acetate to produce methane. Moreover, annotation of the methanogenic pathway in the metagenome showed abundance in genes encoding Acetyl-CoA synthetases (ACSS), an enzyme that catalyzes acetate activation. Our results suggest that the microbial diversity was stable among the two time points tested, rainy season and dry season; and, although there were changes in the microbial abundance of dominant bacterial species, anaerobic digester performance is not affected.

Optimization of co-culture inoculated microbial fuel cell performance using response surface methodology

Microbial fuel cells (MFCs) are considered as promising technology to achieve simultaneous wastewater treatment and electricity generation. However, operational and technological developments are still required to make it as a sustainable technology. In the present study, response surface methodology (RSM) was used to evaluate the effects of substrate concentration, co-culture composition, pH and time on the performance of co-culture (Klebsiella variicola and Pseudomonas aeruginosa) inoculated double chamber MFC. From the statistical analysis, it can be seen that the performance of MFC was not influenced by the interaction between the initial COD and time, pH and time, pH and initial COD, time and initial COD. However, the interaction between the inoculum composition and time, pH and the inoculum composition, initial COD and inoculum composition significantly influenced the performance of MFC. Based on the RSM results, best performance (power density and COD removal efficiency) was obtained when the inoculum composition, initial COD, pH and time were about 1:1, 26.690 mg/L, 7.21 and 15.50 days, respectively. The predictions from the model were in close agreement with the experimental results suggesting that the proposed model could adequately represent the actual relationships between the independent variables generating electricity and the COD removal efficiency.

Support media can steer methanogenesis in the presence of phenol through biotic and abiotic effects

A wide variety of inhibitors can induce anaerobic digester disruption. To avoid performance losses, support media can be used to mitigate inhibitions. However, distinguishing the physico-chemical from the biological mechanisms of such strategies remains delicate. In this framework, the impact of 10  g/L of different types of zeolites and activated carbons (AC) on microbial community dynamics during anaerobic digestion of biowaste in the presence of 1.3 g/L of phenol was evaluated with 16 S rRNA gene sequencing. In the presence of AC, methanogenesis inhibition was rapidly removed due to a decrease of phenol concentration. This abiotic effect related to the physico-chemical properties of AC led to increased final CH4 and CO2 productions by 29-31% compared to digesters incubated without support. Interestingly, although zeolite did not adsorb phenol, final CH4 and CO2 production reached comparable levels as with AC. Nevertheless, compared to digesters incubated without support, methanogenesis lag phase duration was less reduced in the presence of zeolites (5 ± 1 days) than in the presence of activated carbons (12 ± 2 days). Both types of support induced biotic effects. AC and zeolite both allowed the preservation of the major representative archaeal genus of the non-inhibited ecosystem, Methanosarcina. By contrast, they distinctly shaped bacterial populations. OTUs belonging to class W5 became dominant at the expense of OTUs assigned to orders Clostridiales, Bacteroidales and Anaerolinales in the presence of AC. Zeolite enhanced the implantation of OTUs assigned to bacterial phylum Cloacimonetes. This study highlighted that supports can induce biotic and abiotic effects within digesters inhibited with phenol, showing potentialities to enhance anaerobic digestion stability under disrupting conditions.

Anaerobic co-digestion of multiple agricultural residues to enhance biogas production in southern Italy

To valorize agricultural wastes and byproducts in southern Italy, anaerobic co-digestion of six feedstocks (citrus pulp, olive pomace, cattle manure, poultry litter, whey, and corn silage) was studied to produce biogas for renewable energy generation. Both batch and semi-continuous co-digestion approaches were adopted to carry out the investigation. The feedstocks were mixed at different percentages according to their availabilities in southern Italy. The batch anaerobic co-digestion demonstrated that six studied feedstock mixtures generated an average of 239 mL CH₄/g VS loading without significant difference between each other, which concluded that the feedstock mixtures can be used for biogas production. Considering the feedstock availability of citrus pulp and olive pomace in Sicily, three feedstock mixtures with the highest volatile solids concentration of citrus pulp (42% citrus pulp, 17% corn silage, 4% cattle manure, 8% poultry litter, and 18% whey; 34% citrus pulp, 8% olive pomace, 17% corn silage, 4% cattle manure, 8% poultry litter, and 18% whey; and 25% citrus pulp, 16% olive pomace, 17% corn silage, 4% cattle manure, 8% poultry litter, and 18% whey, respectively) were selected to run the semi-continuous anaerobic digestion. Under the stabilized culture condition, the feed mixture with 42% citrus pulp, 17% corn silage, 4% cattle manure, 8% poultry litter, and 18% whey presented the best biogas production (231 L methane/kg VS loading/day). The corresponding mass and energy balance concluded that all three tested feedstock mixtures have positive net energy outputs (1.5, 0.9, and 1.2 kWh-e/kg dry feedstock mixture, respectively).

Novel insights into freshwater hydrocarbon-rich sediments using metatranscriptomics: Opening the black box

Baseline biogeochemical surveys of natural environments is an often overlooked field of environmental studies. Too often research begins once contamination has occurred, with a knowledge gap as to how the affected area behaved prior to outside (often anthropogenic) influences. These baseline characterizations can provide insight into proposed bioremediation strategies crucial in cleaning up chemical spill sites or heavily mined regions. Hence, this study was conducted to survey the in-situ microbial activity within freshwater hydrocarbon-rich environments cutting through the McMurray formation - the geologic strata constituting the oil sands. We are the first to report in-situ functional variations among these freshwater microbial ecosystems using metatranscriptomics, providing insight into the in-situ gene expression within these naturally hydrocarbon-rich sites. Key genes involved in energy metabolism (nitrogen, sulfur and methane) and hydrocarbon degradation, including transcripts relating to the observed expression of methane oxidation are reported. This information provides better linkages between hydrocarbon impacted environments, closing knowledge gaps for optimizing not only oil sands mine reclamation but also enhancing microbial reclamation strategies in various freshwater environments. These finding can also be applied to existing contaminated environments, in need of efficient reclamation efforts.

Microbial community structure with trends in methylation gene diversity and abundance in mercury-contaminated rice paddy soils in Guizhou, China

Paddy soils from mercury (Hg)-contaminated rice fields in Guizhou, China were studied with respect to total mercury (THg) and methylmercury (MeHg) concentrations as well as Bacterial and Archaeal community composition. Total Hg (0.25-990 μg g-1) and MeHg (1.3-30.5 ng g-1) varied between samples. Pyrosequencing (454 FLX) of the hypervariable v1-v3 regions of the 16S rRNA genes showed that Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Euryarchaeota, and Crenarchaeota were dominant in all samples. The Bacterial α-diversity was higher in samples with relatively Low THg and MeHg and decreased with increasing THg and MeHg concentrations. In contrast, Archaeal α-diversity increased with increasing of MeHg concentrations but did not correlate with changes in THg concentrations. Overall, the methylation gene hgcAB copy number increased with both increasing THg and MeHg concentrations. The microbial communities at High THg and High MeHg appear to be adapted by species that are both Hg resistant and carry hgcAB genes for MeHg production. The relatively high abundance of both sulfate-reducing δ-Proteobacteria and methanogenic Archaea, as well as their positive correlations with increasing THg and MeHg concentrations, suggests that these microorganisms are the primary Hg-methylators in the rice paddy soils in Guizhou, China.

Exploration of the diversity and associated health benefits of traditional pickles from the Himalayan and adjacent hilly regions of Indian subcontinent

The Himalayas have provided shelter to the various communities for thousands of years and have remained the cradle for the origin of diverse cultures and traditions. The Himalayan belt is rich in biodiversity and have ushered mankind with numerous gifts for survival and existence. The art of pickling is believed to have developed independently among the different communities of this region. In this region, the main meal is supplemented with pickles or achar that not only adds flavour, but also enhances the value of the meal and often comes with inherent health benefits. The prime objective of this article was to enlist the diverse pickles that are being prepared and consumed by the different tribes and communities, and at the same time analyse the science behind pickle preparation and health benefits and concerns associated with pickles. We have enlisted about hundred monotypic pickles, that are prepared from single fruit or vegetable; but sometimes fungi such as Agaricus and ferns like Diplazium and Pteridium have also been used. Also, fish and meat pickles are common mostly in the Eastern Himalayan region. Traditional pickles constitute the medicinal values of the ingredients and other beneficial properties conferred by the associated microorganisms.

Dry anaerobic co-digestion of food waste and cattle manure: Impact of total solids, substrate ratio and thermal pre treatment on methane yield and quality of biomanure

The objective of the present study is to assess the impact of TS concentration, substrate mixing ratio (co digestion) and thermal pretreatment on biogas production, methane yield, VS reduction (%) and quality of biomanure through dry anaerobic digestion (DAD) of food waste (FW) and cattle manure (CM). Results divulged that the optimum methane yield and biomanure of 0.18 and 0.21 m³ CH₄/(kg VS reduced) and 3.15 and 2.8 kg/kg waste was obtained from FW at TS of 25% and 30% at an HRT of 41 and 31 days respectively whereas it was 0.32 and 0.43 m³ CH₄/(kg VS reduced) and 2.2 and 1.15 kg/kg waste from pretreated FW at an HRT of 16 and 20 days correspondingly. Improvement of methane from 62 to 81% was obtained due to thermal pretreatment. The highest nutrient recovery in terms of N, P, K was found to be 5.14, 2.6 and 3.2 respectively.