Lactic acid fermentation of food waste as storage method prior to biohydrogen production: Effect of storage temperature on biohydrogen potential and microbial communities.

This study aims to investigate the impact of utilizing lactic acid fermentation (LAF) as storage method of food waste (FW) prior to dark fermentation (DF). LAF of FW was carried out in batches at six temperatures (4 °C, 10 °C, 23 °C, 35 °C, 45 °C, and 55 °C) for 15 days followed by biological hydrogen potential (BHP) tests. Different storage temperatures resulted in different metabolites distribution, with either lactate or ethanol being dominant (159.2 ± 20.6 mM and 234.4 ± 38.2 mM respectively), but no negative impact on BHP (averaging at 94.6 ± 25.1 mL/gVS). Maximum hydrogen production rate for stored FW improved by at least 57%. Microbial analysis showed dominance of lactic acid bacteria (LAB) namely Lactobacillus sp., Lactococcus sp., Weisella sp., Streptococcus sp. and Bacillus sp. after LAF. Clostridium sp. emerged after DF, co-existing with LAB. Coupling LAF as a storage method was demonstrated as a novel strategy of FW management for DF, for a wide range of temperatures.

Use of additives to improve collective biogas plant performances: A comprehensive review.

Nowadays, anaerobic digestion (AD) is being increasingly encouraged to increase the production of biogas and thus of biomethane. Due to the high diversity among feedstocks used, the variability of operating parameters and the size of collective biogas plants, different incidents and limitations may occur (e.g., inhibitions, foaming, complex rheology). To improve performance and overcome these limitations, several additives can be used. This literature review aims to summarize the effects of the addition of various additives in co-digestion continuous or semi-continuous reactors to fit as much as possible with collective biogas plant challenges. The addition of (i) microbial strains or consortia, (ii) enzymes and (iii) inorganic additives (trace elements, carbon-based materials) in digester is analyzed and discussed. Several challenges associated with the use of additives for AD process at collective biogas plant scale requiring further research work are highlighted: elucidation of mechanisms, dosage and combination of additives, environmental assessment, economic feasibility, etc.

Screening and Application of Ligninolytic Microbial Consortia to Enhance Aerobic Degradation of Solid Digestate.

Recirculation of solid digestate through digesters has been demonstrated to be a potential simple strategy to increase continuous stirred-tank reactor biogas plant efficiency. This study extended this earlier work and investigated solid digestate post-treatment using liquid isolated ligninolytic aerobic consortia in order to increase methane recovery during the recirculation. Based on sampling in several natural environments, an enrichment and selection method was implemented using a Lab-scale Automated and Multiplexed (an)Aerobic Chemostat system to generate ligninolytic aerobic consortia. Then, obtained consortia were further cultivated under liquid form in bottles. Chitinophagia bacteria and Sordariomycetes fungi were the two dominant classes of microorganisms enriched through these steps. Finally, these consortia where mixed with the solid digestate before a short-term aerobic post-treatment. However, consortia addition did not increase the efficiency of aerobic post-treatment of solid digestate and lower methane yields were obtained in comparison to the untreated control. The main reason identified is the respiration of easily degradable fractions (e.g., sugars, proteins, amorphous cellulose) by the selected consortia. Thus, this paper highlights the difficulties of constraining microbial consortia to sole ligninolytic activities on complex feedstock, such as solid digestate, that does not only contain lignocellulosic structures.

Dataset of organic sample near infrared spectra acquired on different spectrometers.

This dataset presents 127 raw near infrared spectra of different organic samples acquired on three different spectrometers in three different labs. An example of data processing is shown to create six spectra transfer models between the three spectrometers (two by two). In order to build and validate these transfer models, the dataset was split into two sets of spectra: a first set was used to compute six spectra transfer models thanks to the Piecewise Direct standardisation function (PDS). A second set of spectra, independent of the first one was used to validate transfer models. Spectrum treatments and models were created on ChemFlow (https://vm-chemflow-francegrille.eu/), a free online chemometric software that includes all the necessary functions.

Effect of coupling alkaline pretreatment and sewage sludge co-digestion on methane production and fertilizer potential of digestate.

This study aims at investigating how organic waste co-digestion coupled with alkaline pretreatment can impact the methane production and agronomic value of produced digestates. For this purpose, sludge alone and mixed with olive pomace or macroalgal residues were subjected to anaerobic digestion with and without alkaline pretreatment. In addition, co-digestion of pretreated sludge with raw substrates was also carried out and compared to the whole mixture pretreatment. KOH pretreatment enhanced methane production by 39%, 15% and 49% from sludge, sludge mixed with olive pomace and sludge mixed with macroalgal residues, respectively. The digestates were characterised according to their physico-chemical and agronomic properties. They were then applied as biofertilizers for tomato growth during the first vegetative stage (28 days of culture). Concentrations in chlorophyll a and carotenoids in tomato plants, following sludge digestate addition, rose by 46% and 41% respectively. Sludge digestate enhanced tomato plant dry weight by 87%, while its nitrogen content increased by 90%. The impact of nitrogen and phosphorus contents in the digestate was strongest on tomato plant dry weight, thus explaining the efficiency of sludge digestate relative to other types of digestate. However, when methane production is considered, the combination of pre-treatment with co-digestion of macroalgal residues and sludge appears most beneficial for maximizing energy recovery and for biofertilizer generation.

Evaluation of agronomic properties of digestate from macroalgal residues anaerobic digestion: Impact of pretreatment and co-digestion with waste activated sludge.

The aim of this paper is to investigate the impact of pretreating macroalgal residue (MAR) from agar-agar extraction and its co-digestion with sewage sludge on methane production and the agronomic quality of the digestates produced. First, different pretreatments were assessed on BMP tests. Among milling technologies used, knife milling with a 4 mm-screen improved methane production by 25%. The MAR was then knife milled before alkaline, acid and thermal pretreatment. KOH pretreatment (5% TS basis, 25 °C for 2 days) led to the highest methane improvement. It was applied to semi-continuous anaerobic digestion and methane production achieved 237 Nml/gVS which was 20% higher than the control (198 Nml/gVS). In comparison to MAR mono-digestion, co-digestion with thickened activated sludge produced less methane (184 Nml/gVS) but reduced H2S emission by 91%. None of the digestates was toxic for the germination or growth of wheat and tomato plants. Particularly, co-digestion had the highest impact on tomato plant dry weight (+94% compared to soil alone) mainly due to the phosphorous brought by sludge. However, the impact of alkaline pretreatment on plant growth was not significant.

Impacts of Chemical-Assisted Thermal Pretreatments on Methane Production from Fruit and Vegetable Harvesting Wastes: Process Optimization.

The increasing population creates excess pressure on the plantation and production of fruits and vegetables across the world. Consumption demand during the whole year has made production compulsory in the covered production system (greenhouse). Production, harvesting, processing, transporting, and distribution chains of fruit and vegetables have resulted in a huge amount of wastes as an alternative source to produce biofuels. In this study, optimization of two pretreatment processes (NaOH and HCl assisted thermal) was investigated to enhance methane production from fruit and vegetable harvesting wastes (FVHW) that originate from greenhouses. NaOH concentration (0-6.5%), HCl concentration (0-5%), reaction temperature (60-100 °C), solid content (1-5%), time of reaction (1-5 h), and mixing speed (0-500 rpm) were chosen in a wide range of levels to optimize the process in a broad design boundary and to evaluate the positive and negative impacts of independent variables along with their ranges. Increasing NaOH and HCl concentrations resulted in higher COD solubilization but decreased the concentration of soluble sugars that can be converted directly into methane. Thus, the increasing concentrations of NaOH and HCl in the pretreatments have resulted in low methane production. The most important independent variables impacting COD and sugar solubilization were found to be chemical concentration (as NaOH and HCl), solid content and reaction temperature for the optimization of pretreatment processes. The high amount of methane productions in the range of 222-365 mL CH4 gVS-1 was obtained by the simple thermal application without using chemical agents as NaOH or HCl. Maximum enhancement of methane production was 47-68% compared to raw FVHW when 5% solid content, 1-hour reaction time and 60-100 °C reaction temperature were applied in pretreatments.

Mild microwaves, ultrasonic and alkaline pretreatments for improving methane production: Impact on biochemical and structural properties of olive pomace.

This study aims to investigate the effects of microwaves, ultrasonic and alkaline pretreatments on olive pomace properties and its biomethane potential. Alkaline pretreatment was found to reduce lipid and fiber contents (especially lignin) and to increase soluble matter. The alkali pretreatment at a dose of 8% (w/w TS) under 25 °C and for 1 day removed 96% of initial lipids from the solid olive pomace. Unlike NaOH addition, mild microwaves and ultrasonic pretreatments had no impact on lignin. However, in the case of long microwaves pretreatment (450 W-10 min), cellulose and lignin contents were reduced by 50% and 26% respectively. Similarly, the combination of ultrasonic and alkali reagent showed a positive effect on fiber degradation and lipid solubilization as well as a positive impact on methane production. Statistical analysis highlighted the correlation between NaOH dose, solubilization and methane production. The alkaline pretreatment at ambient temperature appeared the most energetically efficient.

Soft Microwave Pretreatment to Extract P-Hydroxycinnamic Acids from Grass Stalks.

The aim of this article is to provide an analysis of microwave effects on ferulic and coumaric acids (FA and CA, respectively) extraction from grass biomass (corn stalks and miscanthus). Microwave pretreatment using various solvents was first compared to conventional heating on corn stalks. Then, microwave operational conditions were extended in terms of incident power and treatment duration. Optimal conditions were chosen to increase p-hydroxycinnamic acids release. Finally, these optimal conditions determined on corn stalks were tested on miscanthus stalks to underlie the substrate incidence on p-hydroxycinnamic acids release yields. The optimal conditions-a treatment duration of 405 s under 1000 W-allowed extracting 1.38% FA and 1.97% CA in corn stalks and 0.58% FA and 3.89% CA in miscanthus stalks. The different bioaccessibility of these two molecules can explain the higher or lower yields between corn and miscanthus stalks.

Solid-state anaerobic digestion of wheat straw: Impact of S/I ratio and pilot-scale fungal pretreatment.

Solid State Anaerobic Digestion (SSAD) of fungal pretreated wheat straw was evaluated in a leach bed reactor. During a first experiment, the effect of Substrate/Inoculum (S/I) ratios on the start-up phase was investigated. High S/I increased methane productivity but also raised the risk of reactor failure due to Volatile Fatty Acid (VFA) accumulation. With S/I ratios between 1.2 and 3.6 (Volatile Solid (VS) basis), the SSAD start-up using wheat straw was successful. Moreover, reactors were able to recover from acidification when the Total VFA/alkalinity ratio was lower than 2 gHAc_eq/gCaCO3, with VFA concentrations lower than 10 g/L and a pH close to 5.5. The conventional threshold of 0.6 gHAc_eq/gCaCO3 for stable wet AD is therefore not adapted to SSAD. During a second experiment, after the wheat straw was submitted to a fungal pretreatment in a non-sterile pilot-scale reactor, it was digested with an S/I ratio of 2.8-2.9. Under batch SSAD conditions, the biodegradability of pretreated wheat straw was slightly improved in comparison to the control (254 versus 215 NmL/g VS, respectively). Considering mass losses occurring during the pretreatment step, suboptimal pretreatment conditions caused a slightly lower methane production (161 versus 171 NmL/gTSinitial after 60-days anaerobic digestion). Nevertheless, pretreatment improved the start-up phase with lower acidification relative to controls. It would be particularly beneficial to improve the methane production in reactors with short reaction times.