Waste lipids to energy: how to optimize methane production from long-chain fatty acids (LCFA)

Waste-to-energy barriers and solutions for developing countries with limited water and energy resources

The environmental risks of conventional waste disposal methods, along with the resource and energy value of waste, have formed the foundation for waste-to-energy (WtE) technology. WtE systems that work on recovering energy present a suitable solution to generate energy and sustainably manage waste. This type of waste management system in the Middle East and North Africa (MENA) region is still considered underutilized as WtE technology is rarely used due to a lack of experience in their specific local conditions, lack of qualified competencies, and the absence of an appropriate regulatory and legislative structure. This study reviews the existing WtE policies and regulations, and it investigates the potential of WtE techniques in the MENA region. Moreover, sustainability in water consumption is critical; therefore, various water-conservation techniques were reviewed and considered when selecting regulatory actions. The radiative sky cooling technique was recommended to reduce water consumption. Barriers to implementing WtE and solutions for developing countries were presented to enable proper WtE implementation.

Optimization of methane production from solid tuna waste: Thermal pretreatment and co-digestion

Fish canning industries generate large amounts of solid waste during their processing operations, creating a significant environmental challenge. Nonetheless, this waste can be efficiently and sustainably treated through anaerobic digestion. In this study, the potential of biogas production from anaerobic digestion of thermally pretreated and co-digested solid tuna waste was investigated. The thermal pretreatment of raw fish viscera resulted in a 50 % increase in methane yield, with a production of 0.27 g COD-CH4/g COD added. However, this pretreatment did not lead to a significant increase in biogas production for cooked tuna viscera. When non-thermally pretreated raw viscera was tested, a large accumulation of volatile fatty acids and long chain fatty acids was observed, with levels reaching 21 and 6 g COD/L, respectively. On the other hand, anaerobic co-digestion of cooked tuna viscera with fat waste significantly enhanced methane production, achieving 0.87 g COD-CH4/g COD added. In contrast, co-digestion of cooked tuna viscera with dairy waste and sewage sludge resulted in notably lower yields of 0.36 and 0.46 g COD-CH4/g COD added, respectively. These results may be related to the C/N ratio, which was found to be within the optimal range for anaerobic digestion only in the tuna and fat waste co-digestion assay.

Boosting anaerobic digestion of long chain fatty acid with microbial electrolysis cell combining metal organic framework as cathode: Biofilm construction and metabolic pathways

The role of metal organic framework (MOF) modified cathode in promoting long chain fatty acid (LCFA) methanation was identified in microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system. The maximum methane production rate of MEC-AD-MOF achieved 49.8 ± 3.4 mL/d, which increased by 41 % compared to MEC-AD-C. The analysis of bio-cathode biofilm revealed that microbial activity, distribution, population, and protein secretion prompted by MOF cathode, which in turn led to an acceleration of electron transfer between the cathode and microbes. Specifically, the relative abundance of acetate-oxidizing bacterium (Mesotoga) in MEC-AD-MOF was 1.5-3.6 times higher than that in MEC-AD-C, with a co-metabolized enrichment of Methanobacterium. Moreover, MOF cathode reinforced LCFA methanation by raising the relative abundance of genes coded key enzymes involved in CO2-reducing pathway, and elevating the tolerance of microbes to LCFA inhibition. These results indicate that MOF can enhance biofilm construction in MEC-AD, thereby improving the treatment performance of lipid wastewater.

Isotope-labeling in situ derivatization and HS-SPME arrow GC-MS/MS for simultaneous determination of fatty acids and fatty acid methyl esters in aqueous matrices

Fatty acids (FAs) and fatty acid methyl esters (FAMEs) co-occur in many samples, and analysis of both substance classes is frequently of high interest. To this end, this study introduces the first method for simultaneous determination of FAs and FAMEs including fully automated solvent-free solid-phase microextraction (SPME) arrow headspace extraction combined with isotope-labeling in situ FA derivatization with deuterated methanol (CD3OD). By using the chromatographic isotope effect (ΔRt = 0.03 min) and the + 3 m/z mass shift, FAs can be selectively differentiated from the FAMEs during gas chromatography tandem-mass spectrometry (GC-MS/MS) operated in the multiple reaction monitoring (MRM) aquisition mode. Additionally, an approach is presented to predict the retention times of deuterated compounds. Optimization of the derivatization conditions was accomplished by design of experiments and found to be 20 min, 50 °C, 4 v/v% CD3OD, and pH 2.1. During method validation, FAs and FAMEs were calibrated in different concentration ranges by standard addition in five real matrices and ultrapure water leading to good linearities and method detection limits for FAs ranging from 1-30 µg L-1 and for FAMEs from 0.003-0.72 µg L-1. FAs and FAMEs were detected in real samples from surface water, wastewater treatment plant effluent, and three different bioreactor samples and could be quantified in concentrations ranging from 2-1056 µg L-1 for FAs and 0.01-14 µg L-1 for FAMEs.

Excess methane production and operation stability for anaerobic digestion of oily food waste controlled by mixing intensity: Focusing on heterogeneity of long chain fatty acids

Long chain fatty acids (LCFAs) are the key intermediate of anaerobic digestion of oily food waste, not completely soluble in a water-dominant anaerobic system due to their long hydrocarbon chains with hydrophobic property. Their effective concentration affects release of high methanogenic potential and system stability. A long-term continuous anaerobic digestion of oily food waste demonstrated excess methane production of even more than feedstock in an anaerobic continuous stirred tank reactor (CSTR). Assuming feedstock COD at 100%, approximately 120% of COD as methane could be achieved. Oil floating and crystallization with Ca salt resulting from the distribution heterogeneity of LCFAs in the CSTR were found responsible for the excess methane production. Moreover, slow conversion and accumulation of saturated LCFAs with relatively lower solubility played an important role as well. Compared with unsaturated oleic (C18:1) and linoleic acids (C18:2), around twice slower methane production rate and longer lag time could be observed for those saturated LCFAs. Mixing intensity was proved to be a critical controlling factor for methanogenesis and stability possibly by affecting interaction between oil/LCFAs and anaerobes to change effective lipid loading.

A novel approach for the fractionation of organic components and microbial degraders in ADM1 and model validation based on the methanogenic potential

The anaerobic digestion model No 1 (ADM1), with fixed fractions of the substrate components, is currently used to simulate methane production during the anaerobic digestion (AD) of waste activated sludge (WAS). However, the goodness-of-fit for the simulation is not ideal due to the different characteristics of WAS from different regions. In this study, a novel methodology based on a modern instrumental analysis and 16S rRNA gene sequence analysis for the fractionation of organic components and microbial degraders in the WAS is investigated to modify the fractions of the components in the ADM1. The combination of Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) analyses were used to achieve a rapid and accurate fractionation of the primary organic matters in the WAS that was verified using both the sequential extraction method and the excitation-emission matrix (EEM). The protein, carbohydrate, and lipid contents in the four different sludge samples measured using the above combined instrumental analyses were 25.0 - 50.0%, 2.0 - 10.0%, and 0.9 - 2.3%. The microbial diversity based on 16S rRNA gene sequence analysis was utilized to re-set the initial fractions of the microbial degraders in the ADM1. A batch experiment was utilized to further calibrate the kinetic parameters in the ADM1. Based on the above optimization of the stoichiometric and kinetic parameters, the ADM1 with full parameter modification for WAS (ADM1-FPM) simulated the methane production of the WAS very well with a Theil's inequality coefficient (TIC) of 0.049, which was increased by 89.8% than that of the default ADM1 fit. The proposed approach, with its rapid and reliable performance, demonstrated a strong application potential for the fractionation of organic solid waste and the modification of ADM1, which contributed to a better simulation of methane production during the AD of organic solid wastes.

Molecular insights informing factors affecting low temperature anaerobic applications: Diversity, collated core microbiomes and complexity stability relationships in LCFA-fed systems

Fats, oil and grease, and their hydrolyzed counterparts-long chain fatty acids (LCFA) make up a large fraction of numerous wastewaters and are challenging to degrade anaerobically, more so, in low temperature anaerobic digestion (LtAD) systems. Herein, we perform a comparative analysis of publicly available Illumina 16S rRNA datasets generated from LCFA-degrading anaerobic microbiomes at low temperatures (10 and 20 °C) to comprehend the factors affecting microbial community dynamics. The various factors considered were the inoculum, substrate and operational characteristics, the reactor operation mode and reactor configuration, and the type of nucleic acid sequenced. We found that LCFA-degrading anaerobic microbiomes were differentiated primarily by inoculum characteristics (inoculum source and morphology) in comparison to the other factors tested. Inoculum characteristics prominently shaped the species richness, species evenness and beta-diversity patterns in the microbiomes even after long term operation of continuous reactors up to 150 days, implying the choice of inoculum needs careful consideration. The generalised additive models represented through beta diversity contour plots revealed that psychrophilic bacteria RBG-13-54-9 from family Anaerolineae, and taxa WCHB1-41 and Williamwhitmania were highly abundant in LCFA-fed microbial niches, suggesting their role in anaerobic treatment of LCFAs at low temperatures of 10-20 °C. Overall, we showed that the following bacterial genera: uncultured Propionibacteriaceae, Longilinea, Christensenellaceae R7 group, Lactivibrio, candidatus Caldatribacterium, Aminicenantales, Syntrophus, Syntrophomonas, Smithella, RBG-13-54-9, WCHB1-41, Trichococcus, Proteiniclasticum, SBR1031, Lutibacter and Lentimicrobium have prominent roles in LtAD of LCFA-rich wastewaters at 10-20 °C. This study provides molecular insights of anaerobic LCFA degradation under low temperatures from collated datasets and will aid in improving LtAD systems for treating LCFA-rich wastewaters.

Oleate Impacts on Acetoclastic and Hydrogenotrophic Methanogenesis under Mesophilic and Thermophilic Conditions

This study investigated oleate inhibition concentration on mesophilic and thermophilic sludge by utilizing acetate and H2/CO2 (80:20, v/v) as substrate, respectively. In addition, another batch experiment was carried out to explore the influence of oleate loads (mM-oleate/g-VS) on methane production. Generally, the mesophilic anaerobic system was more stable than the thermophilic system, which embodied higher microbial abundance, higher methane yield, and higher oleate tolerance. Furthermore, this study provides a possible methanogenic pathway impacted by oleate under mesophilic and thermophilic conditions according to functional microbial composition. Lastly, this paper provides noticeable and avoidable oleate concentrations and loads under different experimental conditions as a guide for future anaerobic bioreactors of lipidic waste biodegradation.

Effect of granular activated carbon adsorption and size of microbial aggregates in inoculum on stimulating direct interspecies electron transfer during anaerobic digestion of fat, oil, and grease

To investigate the effect of granular activated carbon (GAC) adsorption and size of microbial aggregates in inoculum on stimulating direct interspecies electron transfer (DIET) during anaerobic digestion of fat, oil, and grease (FOG), seed sludge was divided into two inocula (big (>0.85 mm)/small (0.15-0.85 mm)) for FOG digestion with/without GAC. More long-chain fatty acids (LCFAs) were adsorbed on GAC in the reactor with small aggregates than that with big aggregates, corresponding to 57 % and 10 % decreased methane production, respectively. Adsorption of unsaturated LCFAs (e.g., oleic acid) on GAC was found to reduce LCFA bioavailability, hinder DIET via GAC, and change community structure. Compared to pre-adsorption of oleic acid on GAC, pre-attachment of microbes on GAC resulted in 5.6-fold higher methane yield for oleic acid digestion. Together, competition of LCFA adsorption between GAC and microbial aggregates is essential for enhanced methane recovery from FOG digestion via GAC-induced DIET.

Volatile fatty acid production from food waste: The effect of retention time and lipid content

The bioconversion of food waste to renewable products has an important role in alleviating the environmental burden of food wastage. This study evaluates the effect of solids retention time (1.5, 4, and 7 days) and lipid content (up to 30 % DS) on the solid's destruction efficiency and VFA yield from food waste fermentation. Although SRT below 4 days and lipid content beyond 20 % reduced the solids destruction efficiency (SRT -12 %, lipids -13 %), the VFA yield improved (SRT 0.36 to 0.48 g COD_VFA/TCOD_FED; lipids 0.17 to 0.39 g COD_VFA/TCOD_FED). This appeared to be a mechanism of improved acidification which doubled to 0.77 gCOD_VFA/g SCOD at 1.5-day SRT. The introduction of easily degradable organics in waste oils and methanogen inhibition by LCFAs were likely causes of process instability when lipids >20 %. Further research is needed considering the COD fractionation of the feed to maximize recoverable products on a commercial scale.

Enhanced sewage sludge treatment via parallel anaerobic digestion at the upper mesophilic level

Sewage mixed sludge (MS) digestion performance was ameliorated implementing the parallel digestion model for primary sludge (PS) and secondary sludge (SS) (waste activated sludge) as domestic sewage sludge fractions rich in oil and grease content at the upper mesophilic level (40 °C). Optimization of the organic loading rate (OLR) was conducted in parallel semi-continuous bench-scale digesters for PS, SS and MS. Comparatively evaluated performance and biosolid quality parameters were methane production rates, volatile solid (VS) reduction, oil and grease and nutrient content, dewaterability and electrical conductivity (EC). OLR optimization indicated different retention time needs for PS and SS stabilization and enabled 18% and 93% higher VS loading and reduction, respectively, compared to MS digestion. Inhibitory effect followed an ascending pattern as a result of OLR increase in each digestion line acting on the hydrolysis of proteinaceous matter and acetogenesis rather than methanogenesis. A high number of long chain fatty acids was detected in the raw sludges. The enhancing effect of the upper mesophilic temperature was significant in SS digestion with increased biodegradability, oil and grease removal and microbial growth compared to digestion at 35 °C. The parallel digestion system and upper mesophilic temperature proved a useful tool to enhance VS loading and reduction without worsening the stabilized biosolids' dewaterability as a feasible model in the existing and prospective municipal wastewater treatment plants (WWTPs). The weakness of the MS digestion was diagnosed as the lower synthesis degree of biomass induced by the dilution of the substrate in PS by SS mixing which weakened the microbial tolerance to high OLR and inhibition. The output indicated the potential of parallel AD, importance of the optimization for OLR and temperature to advance the performance and flexibility of the sludge line practice in municipal WWTPs.

Biogas production performance and system stability monitoring in thermophilic anaerobic co-digestion of lipids and food waste

A thermophilic anaerobic co-digestion system treating lipids and food waste was demonstrated by a long-term operation (over 600 days) with different lipid/TS ratios (from 10 % to 80 %). The lipids degradation efficiency achieved 90 % in the system when the lipid/TS ratio was less than 70 %. Addition of lipids significantly enhanced methane production, as the lipid/TS ratio increased from 10% to 70 %, the biogas production rate increased from 2.36 g/L/d to 3.42 g/L/d with 59.7 % to 67.7 % of methane. From the view of system stability, the increase of lipid/TS ratio reduced the alkalinity of the system and eventually caused the system collapse. In order to avoid losses due to overload, the results suggested that the ratio of total ammonia nitrogen to alklinity-6.5 could be used as a monitoring indicator. And the system could maintain efficient operation when the indicator was less than 0.6.

Biological Aspects, Advancements and Techno-Economical Evaluation of Biological Methanation for the Recycling and Valorization of CO2

Nowadays, sustainable and renewable energy production is a global priority. Over the past decade, several Power-to-X (PtX) technologies have been proposed to store and convert the surplus of renewable energies into chemical bonds of chemicals produced by different processes. CO2 is a major contributor to climate change, yet it is also an undervalued source of carbon that could be recycled and represents an opportunity to generate renewable energy. In this context, PtX technologies would allow for CO2 valorization into renewable fuels while reducing greenhouse gas (GHG) emissions. With this work we want to provide an up-to-date overview of biomethanation as a PtX technology by considering the biological aspects and the main parameters affecting its application and scalability at an industrial level. Particular attention will be paid to the concept of CO2-streams valorization and to the integration of the process with renewable energies. Aspects related to new promising technologies such as in situ, ex situ, hybrid biomethanation and the concept of underground methanation will be discussed, also in connection with recent application cases. Furthermore, the technical and economic feasibility will be critically analyzed to highlight current options and limitations for implementing a sustainable process.

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids

Several problems associated with the presence of lipids in wastewater treatment plants are usually overcome by removing them ahead of the biological treatment. However, because of their high energy content, waste lipids are interesting yet challenging pollutants in anaerobic wastewater treatment and codigestion processes. The maximal amount of waste lipids that can be sustainably accommodated, and effectively converted to methane in anaerobic reactors, is limited by several problems including adsorption, sludge flotation, washout, and inhibition. These difficulties can be circumvented by appropriate feeding, mixing, and solids separation strategies, provided by suitable reactor technology and operation. In recent years, membrane bioreactors and flotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on the diversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extend the knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids in anaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent key discoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps in the field is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobic technology.

Influence of cysteine, serine, sulfate, and sulfide on anaerobic conversion of unsaturated long-chain fatty acid, oleate, to methane

This study aims to elucidate the role of sulfide and its precursors in anaerobic digestion (i.e., cysteine, representing sulfur-containing amino acids, and sulfate) on microbial oleate conversion to methane. Serine, with a similar structure to cysteine but with a hydroxyl group instead of a thiol, was included as a control to assess potential effects on methane formation that were not related to sulfur functionalities. The results showed that copresence of sulfide and oleate in anaerobic batch assays accelerated the methane formation compared to assays with only oleate and mitigated negative effect on methane formation caused by increased sulfide level. Nuclear magnetic resonance spectroscopy of sulfide-exposed oleate suggested that sulfide reaction with oleate double bonds likely contributed to negation of the negative effect on the methanogenic activity. Methane formation from oleate was also accelerated in the presence of cysteine or serine, while sulfate decreased the cumulative methane formation from oleate. Neither cysteine nor serine was converted to methane, and their accelerating effects was associated to different mechanisms due to establishment of microbial communities with different structures, as evidenced by high-throughput sequencing of 16S rRNA gene. These outcomes contribute with new knowledge to develop strategies for optimum use of sulfur- and lipid-rich wastes in anaerobic digestion processes.

Microbial β-oxidation of synthetic long-chain fatty acids to improve lipid biomethanation

β-oxidation is a well-known pathway for fatty acid (FA) degradation. However, the wide range of feedstocks, their intermediates, and complex microbial networks involved in anaerobic digestion (AD) make β-oxidation unclear during lipid digestion having a variety of long-chain fatty acids (LCFAs). Here, we demonstrated the detailed metabolic pathway of major bacteria and enzymes responsible for the β-oxidation of individual saturated FAs (C16:0 and C18:0) and unsaturated FAs (C18:1 and C18:2). C16:0 showed no negative impact on AD. The relative enzyme abundance and production of shorter-chain FAs ( Collapse

Key Words

• Biomethanation
• Community response
• Saturated fatty acids
• Unsaturated fatty acids
• Β-oxidation

Collapse

MESH Headings Collapse

Grants Collapse

Affiliation(s)

Muhammad Usman MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China; Department of Occupational and Environmental Health, School of Public Health, Lanzhou University Lanzhou 730000, Gansu, China
Shuai Zhao MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China
Byong-Hun Jeon Department of Earth Resources and Environmental Engineering, Hanyang University, Seoul 04763, Korea
El-Sayed Salama Department of Occupational and Environmental Health, School of Public Health, Lanzhou University Lanzhou 730000, Gansu, China.
Xiangkai Li MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China.

Collapse

A Review on Biological Synthesis of the Biodegradable Polymers Polyhydroxyalkanoates and the Development of Multiple Applications

Polyhydroxyalkanoates, or PHAs, belong to a class of biopolyesters where the biodegradable PHA polymer is accumulated by microorganisms as intracellular granules known as carbonosomes. Microorganisms can accumulate PHA using a wide variety of substrates under specific inorganic nutrient limiting conditions, with many of the carbon-containing substrates coming from waste or low-value sources. PHAs are universally thermoplastic, with PHB and PHB copolymers having similar characteristics to conventional fossil-based polymers such as polypropylene. PHA properties are dependent on the composition of its monomers, meaning PHAs can have a diverse range of properties and, thus, functionalities within this biopolyester family. This diversity in functionality results in a wide array of applications in sectors such as food-packaging and biomedical industries. In order for PHAs to compete with the conventional plastic industry in terms of applications and economics, the scale of PHA production needs to grow from its current low base. Similar to all new polymers, PHAs need continuous technological developments in their production and material science developments to grow their market opportunities. The setup of end-of-life management (biodegradability, recyclability) system infrastructure is also critical to ensure that PHA and other biobased biodegradable polymers can be marketed with maximum benefits to society. The biobased nature and the biodegradability of PHAs mean they can be a key polymer in the materials sector of the future. The worldwide scale of plastic waste pollution demands a reformation of the current polymer industry, or humankind will face the consequences of having plastic in every step of the food chain and beyond. This review will discuss the aforementioned points in more detail, hoping to provide information that sheds light on how PHAs can be polymers of the future.

Influence of the Sludge Retention Time on Membrane Fouling in an Anaerobic Membrane Bioreactor (AnMBR) Treating Lipid-Rich Dairy Wastewater

This study evaluated the effects of sludge retention time (SRT) on the membrane filtration performance of an anaerobic membrane bioreactor (AnMBR) fed lipid-rich synthetic dairy wastewater. The membrane filtration performance was evaluated in two AnMBR systems operated at two different SRTs, i.e., 20 and 40 days. For the AnMBR operated at 40 days, SRT exhibited worse membrane filtration performance characterized by operational transmembrane pressures (TMP) exceeding the maximum allowed value and high total resistances to filtration (R_total). The sludge in the two reactors evaluated at the different SRTs showed similar sludge filterability properties. However, the sludge in the reactor operated at 40 days SRT was characterized by exhibiting the highest concentrations of: (i) total suspended solids (TSS), (ii) small-sized particles, (iii) extracellular polymeric substances (EPS), (iv) soluble microbial products (SMP), (v) fats, oils and grease (FOG), and (vi) long-chain fatty acids (LCFA). The cake layer resistance was the major contributor to the overall resistance to filtration. The high TSS concentration observed in the AnMBR systems apparently contributed to a less permeable cake layer introducing a negative effect on the membrane filtration performance.

Filamentous foam disintegration with free nitrous acid: Effect on anaerobic digestion

Sludge foaming is a common problem in wastewater treatment plants negatively affecting operation of anaerobic digestion reactors. Therefore, in common practice, foam is removed from reactors without being fermented, leading to increase in sludge mass for disposal. However, foam is rich in lipids and can be a good source of methane if operational problems can be overcome. In this paper, in a two-stage experiment, we show that foam disintegration with free nitrous acid (FNA) can boost methane production and decrease foaming potential. In the first stage, the biochemical methane potential (BMP) of foam was evaluated to be higher by 19-63% (191-263NmL/gVS) than the BMP of waste activated sludge (WAS) (161 ± 1NmL/gVS) confirming previous assumptions. The main findings of the second stage (continuous experiments) are: (1) foam and WAS co-digestion leads to sludge stratification and thickened biomass accumulation in the upper part of the reactor, (2) FNA disintegration destroyed foam structure, resulting in lower biomass stratification and 14% higher methane production (134 mL/gVS) than observed in the reference reactor, (3) FNA disintegration of both substrates (foam and WAS) does not provide noticeable benefits in terms of biomass stratification. However, it does enhance methane production to 140 mL/gVS and sludge mineralization efficiency. A significantly higher impact of FNA on methane yield from foam than WAS was attributed to the high content of M.parvicella and the ability of these bacteria to adsorb and accumulate lipids. Anaerobic digestion of FNA disintegrated foam leads to substantial benefits in terms of methane production, reactor volume, and reagents consumption.

Economic and environmental sustainability for anaerobic biological treatment of wastewater from paper and cardboard manufacturing industry

The sustainable application of an up-flow anaerobic baffled reactor (UABR) to treat real paper and cardboard industrial effluent (PCIE) containing bronopol (2-bromo-2-nitropropan-1, 3-diol) was investigated. At a hydraulic retention time (HRT) of 11.7 h and a bronopol concentration of 7.0 mg L^-1, the removal efficiencies of total chemical oxygen demand (COD_total), COD_soluble, COD_particulate, total suspended solids (TSS), volatile suspended solids (VSS), carbohydrates, and proteins were 55.3 ± 5.2%, 26.8 ± 2.3%, 94.4 ± 4.6%, 89.4 ± 2.6%, 84.5 ± 3.2%, 72.1 ± 1.8%, and 22.4 ± 1.8%, respectively. The conversion of complex organics (e.g., carbohydrates and proteins) into bio-methane (CH₄) was assisted via enzyme activities of, in U (100 mL)^-1, α-amylase (224-270), α-xylanase (171-188), carboxymethyl cellulase (CM-cellulase) (146-187), polygalacturonase (56-126), and protease (67,000-75300). The acidogenic condition was dominant at a short HRT of 2.9 h, where methane yield dropped by 32.5%. Under this condition, the growth of methanogenic bacteria could be inhibited by volatile fatty acids (VFA) accumulation. The analysis of Fourier-transform infrared (FTIR) spectra detected peaks relevant to methylene and nitro groups in the sludge samples, suggesting that entrapment/adsorption by the sludge bed could be a major mechanism for removing bronopol. The economic feasibility of UABR, as proposed to receive 100 m³ d^-1 of PCIE, showed a payback period (profits from environmental benefits, biogas recovery, and carbon credit) of 7.6 yr. The study outcomes showed a high connection to the environmental-, economic-, and social-related sustainable development goals (SDGs).

Saponification with calcium has different impacts on anaerobic digestion of saturated/unsaturated long chain fatty acids

Little is known about the influence of the saturation degree of long chain fatty acids (LCFAs) on the bio-methane potential of calcium-LCFAs salts. In this study, palmitic acid and oleic acid were chosen as the model compounds to investigate the impact of saponification between calcium and saturated/unsaturated LCFAs on the methane recovery from LCFAs in anaerobic digestion. A 2.2-fold enhancement of methane yield was obtained due to the formation of calcium palmitate, which was primarily attributed to the enhanced bio-aggregation and significant change of microbial community. However, saponification between calcium and oleic acid decreased the methane recovery from oleic acid digestion. Only partial saponification with excess oleic acid led to 4% increment of methane production. The low bio-accessibility of calcium oleate and the little change of microbial community may be responsible for the small difference of methane recovery due to the formation of calcium oleate.

Organic matter parameters in WWTP - a critical review and recommendations for application in activated sludge modelling

This paper includes a comprehensive literature review of sludge composition data from wastewater treatment plants. 722 data sets from 249 sources were used to establish typical ratios between COD and solids-based parameters and to verify rule-of-thumb values, respectively. Confirmation of these typical ratios can also be accomplished by using biochemical composition data. It is shown that a correlation between data from proteins, lipids and carbohydrates analysis can be related to COD/VSS ratios. Finally, using the findings from the literature review, the organic and inorganic conversion factors of COD fractions in activated sludge models are adjusted to solids-based parameters. It was shown that with the adjustments of the factors and a partition of the particulate inert fraction into a fraction assigned to the influent and a fraction assigned to the endogenous products, a better agreement with the ratios of COD/VSS in the individual sludge streams can be established.

Microbial assemblages and methanogenesis pathways impact methane production and foaming in manure deep-pit storages

Foam accumulation in swine manure deep-pits has been linked to explosions and flash fires that pose devastating threats to humans and livestock. It is clear that methane accumulation within these pits is the fuel for the fire; it is not understood what microbial drivers cause the accumulation and stabilization of methane. Here, we conducted a 13-month field study to survey the physical, chemical, and biological changes of pit-manure across 46 farms in Iowa. Our results showed that an increased methane production rate was associated with less digestible feed ingredients, suggesting that diet influences the storage pit’s microbiome. Targeted sequencing of the bacterial 16S rRNA and archaeal mcrA genes was used to identify microbial communities’ role and influence. We found that microbial communities in foaming and non-foaming manure were significantly different, and that the bacterial communities of foaming manure were more stable than those of non-foaming manure. Foaming manure methanogen communities were enriched with uncharacterized methanogens whose presence strongly correlated with high methane production rates. We also observed strong correlations between feed ration, manure characteristics, and the relative abundance of specific taxa, suggesting that manure foaming is linked to microbial community assemblage driven by efficient free long-chain fatty acid degradation by hydrogenotrophic methanogenesis.

Surveying the applicability of energy recovery technologies for waste treatment: Case study for anaerobic wastewater treatment in Minnesota

Waste treatment is an important part of the future global energy portfolio. Challenges associated with implementing energy recovery technology at waste treatment sites include interwoven technical, economic, and policy considerations. This work focuses on the tradeoff of input waste energy content to output electrical power, i.e. efficiency for waste-to-energy systems. Also presented is an approach for conversion technology selection based on characteristics of the waste stream, energy content of biogas generated from anaerobic waste treatment, and commercial applicability of five major prime movers across a large gradient of power output including: gas turbines, steam turbines, microturbines, reciprocating internal combustion engines, and solid oxide fuel cells. An efficiency model developed from fundamental thermodynamic principles is used to estimate the amount of power available from a waste treatment site, using data from a comprehensive data set of prime mover characteristics. A case study is presented, illustrating prime mover selection for three types of waste systems in Minnesota, United States: wastewater treatment plants, landfill sites and dairy farms. The results show that gas and steam turbines are recommended for large-scale systems with millions of gallons per day of wastewater generation, up to 60% of waste treatment sites. For small-scale systems applicable to distributed waste treatment and wastewater treatment facilities processing less than 10,000 gallons of water per day, fuel cells are recommended solely based on their high efficiency. Given the potential growth of decentralized waste-to-energy, the scarcity of highly efficient, affordable and fuel flexible power generation options necessitates further innovation in small-scale prime mover technologies.Implications: Energy recovery from waste has not reached its potential due to several decision-influencing factors and technical challenges. Here an efficiency model is presented that theoretically validates efficiency curves for prime movers often shown in previous literature, but without physical verification. The developed regime model has significant practical utility as it concisely estimates power generation potential of a given waste treatment site. This work decouples decision factors by providing a practical template to better identify applicability of a prime mover to waste processing scenarios. In addition, the applicability analysis highlights areas in need of innovation, technology, and policy to address the changing landscape of waste treatment scale and potential opportunity to recover energy from small-scale distributed treatment facilities.

Estimation of Energy Recovery Potential from Primary Residues of Four Municipal Wastewater Treatment Plants

Wastewater treatment plants have been traditionally developed for the aerobic degradation of effluent organic matter, and are associated with high energy consumption. The adoption of sustainable development targets favors the utilization of every available energy source, and the current work aims at the identification of biomethane potential from non-conventional sources derived from municipal wastewater treatment processes. Byproducts derived from the primary treatment process stage were collected from four sewage treatment plants in Greece with great variation in design capacity and servicing areas with wide human activities, affecting the quality of the influents and the corresponding primary wastes. The samples were characterized for the determination of their solids and fats content, as well as the concentration of leached organic matter and nutrients, and were subjected to anaerobic digestion treatment for the measurement of their biomethane production potential according to standardized procedures. All samples exhibited potential for biogas utilization, with screenings collected from a treatment plant receiving wastewater from an area with combined rural and agro-industrial activities presenting the highest potential. Nevertheless, these samples had a methanogens doubling time of around 1.3 days, while screenings from a high-capacity unit proved to have a methanogens doubling time of less than 1 day. On the other hand, floatings from grit chambers presented the smallest potential for energy utilization. Nevertheless, these wastes can be utilized for energy production, potentially in secondary sludge co-digestion units, converting a treatment plant from an energy demanding to a zero energy or even a power production process.

Combined Stochastic and Deterministic Processes Drive Community Assembly of Anaerobic Microbiomes During Granule Flotation

Advances in null-model approaches have resulted in a deeper understanding of community assembly mechanisms for a variety of complex microbiomes. One under-explored application is assembly of communities from the built-environment, especially during process disturbances. Anaerobic digestion for biological wastewater treatment is often underpinned by retaining millions of active granular biofilm aggregates. Flotation of granules is a major problem, resulting in process failure. Anaerobic aggregates were sampled from three identical bioreactors treating dairy wastewater. Microbiome structure was analysed using qPCR and 16S rRNA gene amplicon sequencing from DNA and cDNA. A comprehensive null-model approach quantified assembly mechanisms of floating and settled communities. Significant differences in diversity were observed between floating and settled granules, in particular, we highlight the changing abundances of Methanosaeta and Lactococcus. Both stochastic and deterministic processes were important for community assembly. Homogeneous selection was the primary mechanism for all categories, but dispersal processes also contributed. The lottery model was used to identify clade-level competition driving community assembly. Lottery “winners” were identified with different winners between floating and settled groups. Some groups changed their winner status when flotation occurred. Spirochaetaceae, for example, was only a winner in settled biomass (cDNA-level) and lost its winner status during flotation. Alternatively, Arcobacter butzerli gained winner status during flotation. This analysis provides a deeper understanding of changes that occur during process instabilities and identified groups which may be washed out—an important consideration for process control.

Determination of long-chain fatty acids in anaerobic digester supernatant and olive mill wastewater exploiting an in-syringe dispersive liquid-liquid microextraction and derivatization-free GC-MS method

Long-chain fatty acids (LCFA) are commonly found in lipid-rich wastewaters and are a key factor to monitor the anaerobic digesters. A new simple, fast, precise, and suitable method for routine analysis of LCFA is proposed. The system involves in-syringe-magnetic stirring-assisted dispersive liquid-liquid microextraction (DLLME) prior to gas chromatography-mass spectrometry (GC-MS) without a derivatization process. Calibration curves were prepared in an ethanol solution (R² ≥ 0.996), which was also useful as disperser solvent. Hexane was chosen as the extraction solvent. Several parameters (pH, ionic strength, extraction solvent volume, stirring time) were optimized in multivariate and univariate studies. Limits of detection (LODs) were found in the range 0.01-0.05 mg L^-1 and good precision inter-day (RSDs≤7.9%) and intra-day (RSDs≤4.4%) were obtained. The method was applied to quantify LCFA in supernatants of anaerobic digesters and olive mill wastewaters (OMW). Palmitic, stearic, and oleic acids were the most abundant fatty acid in the analyzed samples and the relative recoveries for all of them were between 81 and 113%.

Enhancement of nutrients removal and biomass accumulation of Chlorella vulgaris in pig manure anaerobic digestate effluent by the pretreatment of indigenous bacteria

High concentrations of pollutants in pig manure anaerobic digestate effluent (PMADE) can severely inhibit microalgal growth. In this study, two types of PMADE (PMADE-1, PMADE-2) were pretreated with indigenous bacteria which were selected from PMADE to alleviate their inhibition for the growth of Chlorella vulgaris. Indigenous bacteria could decrease 34.04% and 47.80% of total phosphorus (TP) and turbidity in PMADE-1, and 80.81%, 43.27%, and 57.51% of COD, TP, and turbidity in PMADE-2, respectively. And no significant reduction of NH₄⁺-N in both PMADE after 5 days pretreatment occurred. C. vulgaris failed to grow in unpretreated PMADE-2. Pretreatment of PMADE with indigenous bacteria could remarkably promote nutrients removal and cell growth of C. vulgaris compared to the unpretreated PMADE. The order of abiotic stress in the studied PMADE was COD > NH₄⁺-N > turbidity, and it is appropriate to pretreat the PMADE with indigenous bacteria for 2-3 days.

Investigation of Fats, Oils, and Grease Co-digestion With Food Waste in Anaerobic Membrane Bioreactors and the Associated Microbial Community Using MinION Sequencing

Co-digestion of fats, oils, and grease (FOG) with food waste (FW) can improve the energy recovery in anaerobic membrane bioreactors (AnMBRs). Here, we investigated the effect of co-digestion of FW and FOG in AnMBRs at fat mass loading of 0.5, 0.75, and 1.0 kg m^–3 day^–1 with a constant organic loading rate of 5.0 gCOD L^–1 day^–1 in both a single-phase (SP) and two-phase (TP) configuration. A separate mono-digestion of FW at an identical organic loading rate was used as the benchmark. During co-digestion, higher daily biogas production, ranging from 4.0 to 12.0%, was observed in the two-phase methane phase (TP-MP) reactor compared to the SP reactor, but the difference was statistically insignificant (p > 0.05) due to the high variability in daily biogas production. However, the co-digestion of FW with FOG at 1.0 kg m^–3 day^–1 fat loading rate significantly (p < 0.05) improved daily biogas production in both the SP (11.0%) and TP (13.0%) reactors compared to the mono-digestion of FW. Microbial community analyses using cDNA-based MinION sequencing of weekly biomass samples from the AnMBRs revealed the prevalence of Lactobacillus (92.2–95.7% relative activity) and Anaerolineaceae (13.3–57.5% relative activity), which are known as fermenters and fatty acid degraders. Syntrophic fatty acid oxidizers were mostly present in the SP and TP-MP reactors, possibly because of the low pH and short solid retention time (SRT) in the acid phase digesters. A greater abundance of the mcrA gene copies (and methanogens) was observed in the SP and MP reactors compared to the acid-phase (AP) reactors. This study demonstrates that FW and FOG can be effectively co-digested in AnMBRs and is expected to inform full-scale decisions on the optimum fat loading rate.

Effluent solids recirculation to municipal sludge digesters enhances long-chain fatty acids degradation capacity

BACKGROUND

Slow degradation kinetics of long-chain fatty acids (LCFA) and their accumulation in anaerobic digesters disrupt methanogenic activity and biogas production at high loads of waste lipids. In this study, we evaluated the effect of effluent solids recirculation on microbial LCFA (oleate) degradation capacity in continuous stirred-tank sludge digesters, with the overall aim of providing operating conditions for efficient co-digestion of waste lipids. Furthermore, the impacts of LCFA feeding frequency and sulfide on process performance and microbial community dynamics were investigated, as parameters that were previously shown to be influential on LCFA conversion to biogas.

RESULTS

Effluent solids recirculation to municipal sludge digesters enabled biogas production of up to 78% of the theoretical potential from 1.0 g oleate l-1 day-1. In digesters without effluent recirculation, comparable conversion efficiency could only be reached at oleate loading rates up to 0.5 g l-1 day-1. Pulse feeding of oleate (supplementation of 2.0 g oleate l-1 every second day instead of 1.0 g oleate l-1 every day) did not have a substantial impact on the degree of oleate conversion to biogas in the digesters that operated with effluent recirculation, while it marginally enhanced oleate conversion to biogas in the digesters without effluent recirculation. Next-generation sequencing of 16S rRNA gene amplicons of bacteria and archaea revealed that pulse feeding resulted in prevalence of fatty acid-degrading Smithella when effluent recirculation was applied, whereas Candidatus Cloacimonas prevailed after pulse feeding of oleate in the digesters without effluent recirculation. Combined oleate pulse feeding and elevated sulfide level contributed to increased relative abundance of LCFA-degrading Syntrophomonas and enhanced conversion efficiency of oleate, but only in the digesters without effluent recirculation.

CONCLUSIONS

Effluent solids recirculation improves microbial LCFA degradation capacity, providing possibilities for co-digestion of larger amounts of waste lipids with municipal sludge.

In-situ alkaline enhanced two-stage anaerobic digestion system for waste cooking oil and sewage sludge co-digestion

Anaerobic digestion is a promising way for resource recovery from waste cooking oil (WCO) due to its high bio-methanation potential. In-situ mild alkaline (pH 8) enhanced two-stage continuous stirred tank reactors (ALK-2-CSTRs) were implemented to explore its efficiency in co-digesting WCO and sewage sludge with stepwise increase of WCO in the co-substrates. Results demonstrate that the ALK-2-CSTRs effectively promoted methane yield from the co-substrates via promoting hydrolysis, long chain fatty acids (LCFAs) degradation and protecting methanogens from exposure to high concentration of LCFAs directly. The maximum methane yield of the ALK-2-CSTRs is 39.2% higher than that of a single stage CSTR system at the optimal feed mixture of 45:55 (WCO:SS [VS]). The thermophilic operation applied to the stage-1 of the ALK-2-CSTRs failed to improve the methane yield when the methanogenic performance was stable; while upon WCO overloaded, the elevated temperature mitigated the deterioration of methanogenesis by stimulating the bioconversion of the toxic LCFAs, especially the unsaturated oleic acid. Microbial community analysis reveals the ALK-2-CSTRs stimulated the growth of lipolytic bacteria and hydrogenotrophic methanogens, which suggests the hydrogenotrophic methanogenic pathway was promoted. Cost evaluation demonstrates the economical superiority of the ALK-2-CSTR over the prevailing strategies developed for enhancing methane yield from the co-substrates.

Long-Chain Fatty Acids Degradation by Desulfomonile Species and Proposal of "Candidatus Desulfomonile Palmitatoxidans"

Microbial communities with the ability to convert long-chain fatty acids (LCFA) coupled to sulfate reduction can be important in the removal of these compounds from wastewater. In this work, an enrichment culture, able to oxidize the long-chain fatty acid palmitate (C_{16 : 0}) coupled to sulfate reduction, was obtained from anaerobic granular sludge. Microscopic analysis of this culture, designated HP culture, revealed that it was mainly composed of one morphotype with a typical collar-like cell wall invagination, a distinct morphological feature of the Desulfomonile genus. 16S rRNA gene amplicon and metagenome-assembled genome (MAG) indeed confirmed that the abundant phylotype in HP culture belong to Desulfomonile genus [ca. 92% 16S rRNA gene sequences closely related to Desulfomonile spp.; and ca. 82% whole genome shotgun (WGS)]. Based on similar cell morphology and average nucleotide identity (ANI) (77%) between the Desulfomonile sp. in HP culture and the type strain Desulfomonile tiedjei strain DCB-1^T, we propose a novel species designated as "Candidatus Desulfomonile palmitatoxidans." This bacterium shares 94.3 and 93.6% 16S rRNA gene identity with Desulfomonile limimaris strain DCB-M^T and D. tiedjei strain DCB-1^T, respectively. Based on sequence abundance of Desulfomonile-morphotype in HP culture, its predominance in the microscopic observations, and presence of several genes coding for enzymes involved in LCFA degradation, the proposed species "Ca. Desulfomonile palmitatoxidans" most probably plays an important role in palmitate degradation in HP culture. Analysis of the growth of HP culture and D. tiedjei strain DCB-1^T with short- (butyrate), medium- (caprylate) and long-chain fatty acids (palmitate, stearate, and oleate) showed that both cultures degraded all fatty acids coupled to sulfate reduction, except oleate that was only utilized by HP culture. In the absence of sulfate, neither HP culture, nor D. tiedjei strain DCB-1^T degraded palmitate when incubated with Methanobacterium formicicum as a possible methanogenic syntrophic partner. Unlike D. tiedjei strain DCB-1^T, "Ca. Desulfomonile palmitatoxidans" lacks reductive dehalogenase genes in its genome, and HP culture was not able to grow by organohalide respiration. An emended description of the genus Desulfomonile is proposed. Our study reveals an unrecognized LCFA degradation feature of the Desulfomonile genus.

Impact of solids retention time on the biological performance of an AnMBR treating lipid-rich synthetic dairy wastewater

In this study, the impact of applied solids retention time (SRT) on the biological performance of an anaerobic membrane bioreactor (AnMBR) treating synthetic dairy wastewater with high lipid content was assessed. Two side-stream AnMBR systems were operated at an SRT of 20 and 40 days (R20 and R40, respectively), equipped with an inside-out tubular membrane operated in cross-flow mode under full-scale operational conditions, i.e. crossflow velocity, transmembrane pressure, membrane flux. Successful operation was achieved and removal efficiencies of both reactors were up to 99% applying an organic loading rate (OLR) of 4.7 g COD L^-1 d^-1. No precipitation of lipids was observed throughout the operational period, keeping the lipids available for the anaerobic degradation. Long chain fatty acid (LCFA) accumulation was very modest and amounted 148 and 115 mg LCFA-COD per gram of volatile suspended solids (VSS) for R20 and R40, respectively. At an SRT of 40 days, a slightly better biological conversion was obtained. Periodically performed specific methanogenic activity (SMA) tests showed stabilization of the SMA for R40 sludge, whereas for R20 sludge the SMA continued to decrease. This study revealed a more stable reactor performance operating the AnMBR at an SRT of 40 days compared to 20 days.

Methanogenic Microorganisms in Industrial Wastewater Anaerobic Treatment

Over the past decades, anaerobic biotechnology is commonly used for treating high-strength wastewaters from different industries. This biotechnology depends on interactions and co-operation between microorganisms in the anaerobic environment where many pollutants’ transformation to energy-rich biogas occurs. Properties of wastewater vary across industries and significantly affect microbiome composition in the anaerobic reactor. Methanogenic archaea play a crucial role during anaerobic wastewater treatment. The most abundant acetoclastic methanogens in the anaerobic reactors for industrial wastewater treatment are Methanosarcina sp. and Methanotrix sp. Hydrogenotrophic representatives of methanogens presented in the anaerobic reactors are characterized by a wide species diversity. Methanoculleus sp., Methanobacterium sp. and Methanospirillum sp. prevailed in this group. This work summarizes the relation of industrial wastewater composition and methanogen microbial communities present in different reactors treating these wastewaters.

First approaches to valorizate fat, oil and grease (FOG) as anaerobic co-substrate with slaughterhouse wastewater: Biomethane potential, settling capacity and microbial dynamics

Anaerobic digestion (AD) is the biological preferred treatment applied to Slaughterhouse wastewaters (SWW) due to its effectiveness. The aim of the study is to investigate the effect of different percentages of fats, oil and grease (FOG) on biomethane production in anaerobic co-digestion with slaughterhouse wastewater using BMP tests under mesophilic conditions (35 °C). For this purpose, three percentages of FOG from 1% to 10% were tested. Biodegradability, biomethane production and the microbial population were studied. In addition, settling capacity has been evaluated at different conditions: i) before and after anaerobic co-digestion; ii) at different temperature 25 °C and 35 °C. The settling rates as well as the characterization of the digestate were recorded. Experimental results showed that all the co-digestion mixtures (FOG percentages = 1-10%) enhanced biomethane production and biodegradability compared to AD of sole SWW. The best conditions were achieved at 5-10% of FOG, showing biodegradability of 66-70% CODt_removal and specific biomethane productions of 562 and 777 mL_CH4·g^-1_CODsremoved, respectively. Regarding microbial dynamics, Eubacteria was reduced with the increase in %FOG but Acetate utilizing methanogens was increased. Regarding settling capacity, mesophilic temperatures (35 °C) increased the settling rate of digestate in 1.76 times and reduced the lag-phase to 0.92 min; obtaining a more concentrated sludge and leaving a clarified whose TSS represent only 8% of TS.

Long Chain Fatty Acid Degradation Coupled to Biological Sulfidogenesis: A Prospect for Enhanced Metal Recovery

This research assessed the microbiological suitability of oleate degradation coupled to sulfidogenesis by enriching communities from anaerobic sludge treating dairy products with S⁰, SO 3 2 - , SO 4 2 - , and S₂ O 3 2 - as electron acceptors. The limiting factor hampering highly efficient oleate degradation was investigated in batch reactors. The best sulfidogenic performance coupled to specialization of the enriched bacterial community was obtained for S⁰- and S₂ O 3 2 - -reducing enrichments, with 15.6 (± 0.2) and 9.0 (± 0.0) mM of sulfide production, respectively. Microbial community analyses revealed predominance of Enterobacteraceae (50.6 ± 5.7%), Sulfurospirillum (23.1 ± 0.1%), Bacteroides (7.5 ± 1.5%) and Seleniivibrio (6.9 ± 1.1%) in S⁰-reducing cultures. In S₂ O 3 2 - -reducing enrichments, the genus Desulfurella predominated (49.2 ± 1.2%), followed by the Enterobacterales order (20.9 ± 2.3%). S⁰-reducing cultures were not affected by oleate concentrations up to 5 mM, while S₂ O 3 2 - -reducing cultures could degrade oleate in concentrations up to 10 mM, with no significant impact on sulfidogenesis. In sequencing batch reactors operated with sulfide stripping, the S⁰-reducing enrichment produced 145.8 mM sulfide, precipitating Zn as ZnS in a separate tank. The S₂ O 3 2 - fed bioreactor only produced 23.4 mM of sulfide precipitated as ZnS. The lower sulfide production likely happened due to sulfite toxicity, an intermediate of thiosulfate reduction. Therefore, elemental sulfur reduction represents an excellent alternative to the currently adopted approaches for LCFA degradation. To the best of our knowledge, this is the first report of oleate degradation with the flux of electrons totally diverted toward sulfide production for metal precipitation, showing great efficiency of LCFA degradation coupled to high levels of metals precipitated as metal sulfide.

Effect of Sub-Stoichiometric Fe(III) Amounts on LCFA Degradation by Methanogenic Communities

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H₂-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83-89%, 3-6%, and 0.2-10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

Molecular weight distribution of pretreated thickened waste activated sludge and fat, oil, and grease

Co-digestion samples containing thickened waste activated sludge and fat, oil and grease were subjected to three different pretreatment methods, i.e., microwave at 175 °C, hyper-thermophilic stage at 70 °C, and conventional heat at 70 °C. The soluble matter extracted from the un-pretreated and pretreated samples were subjected to an ultrafiltration (UF) process using four different membrane sizes (300, 100, 10, and 1 kDa) for molecular weight distribution analysis. Every pretreatment method had a different effect on the solubilization and redistribution of the soluble matter (SCOD and TVFA). For example while MW pretreatment resulted in a significant increase in the SCOD at the lowest molecular weight (< 1 kDa) and at the highest molecular weight (> 300 kDa), Hyper pretreatment caused the majority of the SCOD ( ̴ 62.7% of total SCOD) to be concentrated at the smaller molecular weight range (< 10 kDa). The MW and hyper-thermophilic pretreatments were much more effective in increasing samples solubilization and biogas production compared to the conventional heat pretreatment. The hyper-thermophilic samples had the maximum improvement in cumulative biogas production from all the molecular weights compared to MW- and Heat-pretreated samples; Hyper-pretreated samples achieved 86.5% higher cumulative biogas production compared to the control.

Effects of biochar addition on the anaerobic digestion of carbohydrate-rich, protein-rich, and lipid-rich substrates

Although biochar addition into the anaerobic digestion of food waste (FW) is an efficient means to enhance methane production, the effects of biochar on various FW components remain unclear. Laboratory batch experiments were conducted to investigate the impact of sewage sludge-derived biochar (SSB) supplementation on the anaerobic digestion (AD) of major FW components, including carbohydrate-rich, protein-rich, and lipid-rich substrates. The lag phase of AD with the carbohydrate-rich substrate was 48.6% shorter when SSB was added, and the cumulative methane yield was 4.74 times higher compared to AD without biochar. SSB supplementation also increased the rate of methane production from the lipid-rich substrate. However, the effect of SSB addition on AD of the protein-rich substrate was minor. Analysis of the microbial communities revealed that methanogen growth was enhanced during AD of the carbohydrate-rich and lipid-rich substrates, but not the protein-rich substrate, following SSB supplementation. Also, the most dominant methanogenic genus varied with the substrates. SSB addition promoted the growth of hydrolytic and fermentative bacteria, particularly phylum Bacteroidetes.Implications: Biochar supplementation has been studied to overcome the shortcomings of anaerobic digestion (AD). However, the effects of biochar on different substrates remain unclear. This study compared carbohydrate-rich, protein-rich, and lipid-rich substrates in anaerobic digestion with sewage sludge-derived biochar (SSB). SSB supplementation improved methane generation from all but the protein-rich substrate. The study results imply that the effect of SSB addition on AD varied with the substrate due to the substrates underwent different degradation processes with different microbial communities.

Exploring the potential of co-fermenting sewage sludge and lipids in a resource recovery scenario

In this study, co-fermentation of primary sludge (PS) or waste activated sludge (WAS) with lipids was explored to improve volatile fatty acid production. PS and WAS were used as base substrate to facilitate lipid fermentation at 20 °C under semi-aerobic conditions. Mono-fermentation tests showed higher VFA yields for PS (32-89 mgCOD gVS^-1) than for WAS (20-41 mgCOD gVS^-1) where propionate production was favoured. The principal component analysis showed that the base substrate had a notable influence on co-fermentation yields and profile. Co-fermentation with WAS resulted in a greater extent of oleic acid degradation (up to 4.7%) and evidence of chain elongation producing valerate. The occurrence of chain elongation suggests that co-fermentation can be engineered to favour medium-chain fatty acids without the addition of external commodity chemicals. BMP tests showed that neither mono-fermentation nor co-fermentation had an impact on downstream anaerobic digestion.

Enhanced Anaerobic Digestion of Long Chain Fatty Acid by Adding Magnetite and Carbon Nanotubes

This study investigated the impact of stimulating direct interspecies electron transfer (DIET), by supplementing nano-sized magnetite (nFe3O4, 0.5 g Fe/g VSS) and carbon nanotubes (CNT, 1 g/L), in anaerobic digestion of oleic acid (OA) at various concentrations (0.10 - 4.00 g chemical oxygen demand(COD)/L). Both supplementations could enhance CH4 production, and its beneficial impact increased with increased OA concentration. The biggest improvements of 114% and 165% compared to the control were achieved by nFe3O4 and CNT, respectively, at OA of 4 g COD/L. The enhancement can be attributed to the increased sludge conductivity: 7.1 ± 0.5 (control), 12.5 ± 0.8 (nFe3O4-added), and 15.7 ± 1.1 µS/cm (CNT-supplemented). Dissolved iron concentration, released from nFe3O4, seemed to have a negligible role in improving CH4 production. The excretion of electron shuttles, i.e., humic-like substances and protein-like substances, were found to be stimulated by supplementing nFe3O4 and CNT. Microbial diversity was found to be simplified under DIET-stimulating conditions, whereby five genera accounted for 88% of the total sequences in the control, while more than 82% were represented by only two genera (Methanotrix concilli and Methanosarcina flavescens) by supplementing nFe3O4 and CNT. In addition, the abudance of electro-active bacteria such as Syntrophomonas zehnderi was significantly increased from 17% to around 45%.

Direct interspecies electron transfer stimulated by granular activated carbon enhances anaerobic methanation efficiency from typical kitchen waste lipid-rapeseed oil

Due to long-chain fatty acids (LCFAs) and acidification, rapeseed oil as a typical lipid in kitchen waste is difficult to be biodegraded by anaerobic digestion. It has been reported that incorporation of some conductive materials into reactors treating complex organic matter could enhance reactor performance. In this study, the aim was to study this possibility of application of granular activated carbon (GAC) in anaerobic digestion of rapeseed oil. As expected, the GAC-amended reactor could significantly improve methane yield and reduce acidification. Besides, the GAC-amended broth could efficiently degrade palmitate into methane. Microbial community analysis showed that bacteria (Syntrophomonas) and methanogens (Methanosarcina) were greatly enriched on the GAC surface in GAC-amended system. These results, and the kwon of easy enrichment of Syntrophomonas on conductive materials or current-harvesting electrodes in methanogenic and/or electrogenic systems, suggest that Syntrophomonas could participate in direct interspecies electron transfer with Methanosarcina species, when GAC is available as an electron transfer mediator. Hence, the addition of GAC could efficiently, stably and environmentally enhance the methanogenic metabolism of rapeseed oil.

Characterisation and energy assessment of fats, oils and greases (FOG) waste at catchment level

Several of the waste materials that have a negative impact on the sewer system are produced by fats, oils and greases (FOG) discharged from commercial and domestic kitchens. These materials accumulate at different points in the sewer catchment, from kitchens to pumping stations, sewers and sewage treatment works (STWs), and comprise oily wastewater, floating agglomerates and hard deposits. Despite their detrimental effects, these waste materials have a high calorific content and are an ideal feedstock for energy recovery processes. So far, the overall volume of each type of waste and their physical-chemical properties in relation to their collection point are unknown. However, from a management point of view, knowledge on each feedstock quality and volumes is necessary to develop an economic viable solution for their collection and for energy recovery purposes. In this study, FOG wastes collected from households, food service establishments (FSEs), sewage pumping stations, sewers and STWs, were compared to sewage sludge in terms of organic contents and energy potentials. As expected, FOG recovered at source (households and FSEs) were 'cleaner' and had a higher energy content. Once mixed with wastewater the materials changed in composition and lost some of their energy per unit mass. Our results showed that around 94,730 tonnes.year^-1 of these materials could be recovered from the Thames Water Utilities' catchment, one of the most populated in the UK. These materials could produce up to 222 GWh.year^-1 as biogas, close to double of what is produced with sewage sludge digestion and around 19% of the company energy needs. Finally, even with over six million households in the catchment, the results showed that most of the FOG waste was produced by FSEs (over 48,000 premises) with an estimated average of 79,810 tonnes.year^-1 compared to 14,920 tonnes.year^-1 from private households. This is an important outcome as recovery from FSEs will be cheaper and easier if the company decides to implement a collection system for energy recovery.

Biohythane production from food processing wastes - Challenges and perspectives

The food industry generates enormous quantity of food waste (FW) either directly or indirectly including the processing sector, which turned into biofuels for waste remediation. Six types of food processing wastes (FPW) such as oil, fruit and vegetable, dairy, brewery, livestock and finally agriculture based materials that get treated via dark fermentation/anaerobic digestion has been discussed. Production of both hydrogen and methane is daunting for oil, fruit and vegetable processing wastes because of the presence of polyphenols and essential oils. Moreover, acidic pH and high protein are the reasons for increased concentration of ammonia and accumulation of volatile fatty acids in FPW, especially in dairy, brewery, and livestock waste streams. Moreover, the review brought to forefront the enhancing methods, (pretreatment and co-digestion) operational, and environmental parameters that can influence the production of biohythane. Finally, the nature of feedstock's role in achieving successful circular bio economy is also highlighted.