Semi-continuous Reactor Research Articles

Effects of high solid content and straw proportion on volatile fatty acids production from straw, sludge and food wastes: performance and microbial community characteristics

Anaerobic digestion (AD) is an efficient technology for treating organic solid wastes, and the volatile fatty acids (VFAs) produced during AD have significant value due to their wide range of applications and higher added value compared to methane. This study investigated the long-term effects of high solid content and straw proportion in mixed substrates (straw, sludge, and food wastes) on VFAs production through semi-continuous reactors under thermophilic and mesophilic conditions. Results showed that both reactors achieved a maximum VFAs concentration of ~ 22 g/L as the straw proportion increased to 50%. Acetate (48.3 – 64.5%) was the main component of produced VFAs in both reactors, while butyrate and propionate production in thermophilic temperature were superior compared to mesophilic conditions. Microbial community analysis revealed that Defluviitoga plays a pivotal role in acidogenesis within both reactors; besides, unclassified Hungateiclostridiaceae and Caproiciproducen were found to be dominant in thermophilic reactor, while Lachnospiraceae_NK3A20_group and Rikenellaceae_RC9_gut_group were essential for VFAs production under mesophilic conditions. These findings provide valuable insights for the biotechnological exploration of acidogenic fermentation for large-scale mechanized production of VFAs from agricultural wastes.

Establishing a High-Yield Chloroplast Cell-Free System for Prototyping Genetic Parts.

Plastid engineering offers the potential to carry multigene traits in plants; however, it requires reliable genetic parts to balance expression. The difficulty of chloroplast transformation and slow plant growth makes it challenging to build plants just to characterize genetic parts. To address these limitations, we developed a high-yield cell-free system from Nicotiana tabacum chloroplast extracts for prototyping genetic parts. Our cell-free system uses combined transcription and translation driven by T7 RNA polymerase and works with plasmid or linear template DNA. To develop our system, we optimized lysis, extract preparation procedures (e.g., runoff reaction, centrifugation, and dialysis), and the physiochemical reaction conditions. Our cell-free system can synthesize 34 ± 1 μg/mL luciferase in batch reactions and 60 ± 4 μg/mL in semicontinuous reactions. We apply our batch reaction system to test a library of 103 ribosome binding site (RBS) variants and rank them based on cell-free gene expression. We observe a 1300-fold dynamic range of luciferase expression when normalized by maximum mRNA expression, as assessed by the malachite green aptamer. We also find that the observed normalized gene expression in chloroplast extracts and the predictions made by the RBS Calculator are correlated. We anticipate that chloroplast cell-free systems will increase the speed and reliability of building genetic systems in plant chloroplasts for diverse applications.

Occurrence of 40 sanitary indicators in French digestates derived from different anaerobic digestion processes and raw organic wastes from agricultural and urban origin.

This study investigated the sanitary quality of digestates resulting from the mesophilic anaerobic digestion (AD) of urban and agricultural organic wastes (OWs). 40 sanitary indicators, including pathogenic bacteria, antimicrobial resistance genes, virulence factor genes, and mobile genetic elements were evaluated using real-time PCR and/or droplet digital PCR. 13 polycyclic aromatic hydrocarbons (PAHs) and 13 pharmaceutical products (PHPs) were also measured. We assessed agricultural OWs from three treatment plants to study the effect of different AD processes (feeding mode, number of stages, pH), and used three laboratory-scale reactors to study the effect of different feed-supplies (inputs). The lab-scale reactors included: Lab1 fed with 97% activated sludge (urban waste) and 3% cow manure; Lab2 fed with 85% sludge-manure mixture supplemented with 15% wheat straw (WS); and Lab3 fed with 81% sludge-manure mixture, 15% WS, and 4% zeolite powder. Activated sludge favored the survival of the food-borne pathogens Clostridium perfringens and Bacillus cereus, carrying the toxin-encoding genes cpe and ces, respectively. Globally, the reactors fed with fecal matter supplemented with straw (Lab2) or with straw and zeolite (Lab3) had a higher hygienization efficiency than the reactor fed uniquely with fecal matter (Lab1). Three pathogenic bacteria (Enterococcus faecalis, Enterococcus faecium, and Mycobacterium tuberculosis complex), a beta-lactam resistance gene (bla TEM), and three mobile genetic elements (intI1, intI2, and IS26) were significantly decreased in Lab2 and Lab3. Moreover, the concentrations of 11 PAHs and 11 PHPs were significantly lower in Lab2 and Lab3 samples than in Lab1 samples. The high concentrations of micropollutants, such as triclosan, found in Lab1, could explain the lower hygienization efficiency of this reactor. Furthermore, the batch-fed reactor had a more efficient hygienization effect than the semi-continuous reactors, with complete removal of the ybtA gene, which is involved in the production of the siderophore yersiniabactin, and significant reduction of intI2 and tetO. These data suggest that it is essential to control the level of chemical pollutants in raw OWs to optimize the sanitary quality of digestates, and that adding co-substrate, such as WS, may overcome the harmful effect of pollutants.

Simultaneously enhancement of methane production and active phosphorus transformation by sludge-based biochar during high solids anaerobic co-digestion of dewatered sludge and food waste: Performance and mechanism

Biochar has been proved to improve methane production in high solids anaerobic co-digestion (HS-AcoD) of dewatered sludge (DS) and food waste (FW), but its potential mechanism for simultaneous methane production and phosphorus (P) transformation has not been sufficiently revealed. Results showed that the optimal preparation temperature and dosage of sludge-based biochar were selected as 300 °C and 0.075 g·g−1, respectively. Under this optimized condition, the methane production of the semi-continuous reactor increased by 54%, and the active phosphorus increased by 18%. The functional microorganisms, such as Methanosarcina, hydrogen-producing, sulfate-reducing, and iron-reducing bacteria, were increased. Metabolic pathways associated with sulfate reduction and methanogenesis, especially hydrogenotrophic methanogenesis, were enhanced, which in turn promoted methanogenesis and phosphorus transformation and release. This study provides theoretical support for simultaneously recovery of carbon and phosphorus resources from DS and FW using biochar.

Innovative approach for semi‐continuous production of puerarin palmitate via transesterification with novel immobilized lipase

BackgroundPuerarin, a flavonoid abundantly found in the roots of Pueraria lobata, exhibits antioxidant, anti-cancer, anti-inflammatory, and anti-aging properties. Despite its numerous benefits, the low bioavailability of puerarin hinders its widespread industrial application. To improve this, flavonoid acylation is required. Lipase is a biocatalyst primarily used for flavonoid acylation; immobilized lipase is preferred given the limited stability of free lipase. Although research on flavonoid acylation for structural modification is actively being conducted, there is a need to explore continuous production for enhancing the industrial application of flavonoid esters. Therefore, in this study, we aimed to produce puerarin palmitate innovatively by selecting an effective lipase, developing an immobilized lipase, characterizing the enzymatic reaction, and designing a semi-continuous reactor system.ResultsLipase from Thermomyces lanuginosus (TL) was found to be the most suitable for the synthesis of puerarin palmitate; it was successfully immobilized on glutaraldehyde-activated silica gel (GASG). TL GASG showed greater solvent, thermal, and operational stability than those of commercial immobilized lipases. Furthermore, TL GASG use resulted in a puerarin palmitate conversion rate of 97.17% within 3 h. Additionally, the reusability of TL GASG for this reaction was higher than that of commercially available immobilized lipases. Upon using a semi-continuous reactor, the cumulative conversion rate of puerarin palmitate remained above 85% after more than ten substrate injections.ConclusionsThe results support the feasibility of the continuous production of flavonoid esters, underscoring their diverse industrial applications. A biorefinery strategy is anticipated to be proposed to utilize P. lobata extract biomass for flavonoid ester production. Moreover, optimizing continuous reactors through statistical experimental design is expected to enhance flavonoid ester production efficiency; these aspects will be explored in future research.Graphical

Source-Separated Industrial Wastewater Is a Candidate for Biogas Production through Anaerobic Digestion

Anaerobic digestion is a potential treatment for industrial wastewater that provides valuable end-products, including renewable energy (biogas). However, waste streams may be too variable, too dilute at high volumes, or missing key components for stable digestion; all factors that increase costs and operational difficulty, making optimisation crucial. Anaerobic digestion may benefit from process intensification, particularly the novel combination of high-strength source-separated wastewater to minimise volume, together with the use of biosolids biochar as a chemical and microbial stabiliser. This study investigates the stability, yield, and microbial community dynamics of the anaerobic digestion of source-separated industrial wastewater from a food manufacturer and a logistics company, using biosolids biochar as an additive, focusing on gas and volatile fatty acid (VFA) production, process stability, and the microbial community using bench-scale semi-continuous reactors at 30- and 45-day hydraulic retention time (HRT). While gas yields were lower than expected, stability was possible at high HRT. Methane production reached 0.24 and 0.43 L day−1 per litre reactor working volume at 30- and 45-day HRT, respectively, despite high VFA concentration, and was linked to the relative abundance of Methanosarcina in the microbial community. Interactions between substrate, VFA concentration, and the microbial community were observed. Biochar-assisted anaerobic digestion holds promise for the treatment of source-separated wastewater.

Bioleaching of secondary and critical raw materials from Red Mud by a mixed culture in a semi-continuous reactor

Red Mud (RM) is a byproduct of the Bayer Process, used to extract alumina from bauxite. This residue contains valuable metals and rare earth elements (REEs), which can be bioleached under acidic conditions and later recovered, eventually reducing the RM pollution potential. The focus of this study was to extract metals through bioleaching using biostimulated biomass. A sequencing batch reactor (SBR) was operated at two different solid to liquid ratios (S/L, 2% and 1.5%) under aerobic conditions, using a feeding strategy based on pH evolution over time. The lowest pH obtained at 2% S/L was 3.8. Metals extraction efficiencies were 68 ± 18% for Mn, 58 ± 4.5% for Mg, 51 ± 2.9% for Al, 0.6 ± 0.07% for Ti and < 0.1% for Fe. At 1.5% S/L, a slightly lower pH was achieved (3.4), with metals extraction efficiencies similar to those obtained at 2% S/L, but more stable over time. At 1.5% S/L, REEs (i.e., Nd, Ce, Y, Sc and La) extraction efficiencies were also evaluated, and the highest value was obtained for Nd (around 65%). The results were promising and provided useful information for further enhancing the efficiency of metals extraction, in the perspective of process scale-up.

Characteristics of the digestates from OFMSW methane production at psychrophilic, mesophilic, and thermophilic conditions under different organic loading rates

ABSTRACT The anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) has shown to be a viable alternative since it allows energy recovery in the form of methane and generates a residue (digestate) that can be applied effectively as a soil improver or fertiliser. The potential for methane production and the digestates’ characteristics depend on the substrate characteristics and the process variables such as temperature, solids retention time, and organic load. This study dealt with OFMSW anaerobic digestion under different organic loading rates and temperatures and the characteristics of the resulting digestates. Three semi-continuous reactors were operated at 20, 35, and 55°C and fed daily with ground, fresh OFMSW from Mexico City. The inoculum was temperature-adapted UASB granular sludge. The main results indicate that the anaerobic digestion was adequate, as the pH values were slightly alkaline, which is sufficient for methanization, and the alkalinity was not a limiting factor. Potassium and PO4-P increased with the organic load, and Kjeldahl nitrogen decreased. At 20°C, total organic carbon (TOC) increased substantially with the organic load; at 35°C, it remained without significant changes; and at 55°C, TOC slightly decreased with the organic load. The C/N ratio changed accordingly to TOC variations. At 20°C, the residual biogas potential increased with the organic load; at 35 and 55°C, it decreased with increasing organic load; the residual biogas potential increased with residual fatty acids concentrations. To comply with international standards for agricultural use, the digestates need only dewatering and supplementing with PO4-P.

Biohydrogen production from lactic acid: Use of food waste as substrate and evaluation of pretreated sludge and native microbial community as inoculum

Nowadays, lactic acid (HLa) has caught the eye as a precursor of H2 production from substrates that harbor a significant amount of lactic acid bacteria (LAB), such as Lactobacillus and Lactococcus. Since the native microbial community of food waste (FW) is dominated by LAB, the production of H2 during dark fermentation might be inhibited by the displacement of H2-producing bacteria by LAB. Therefore, lactate-driven dark fermentation in two steps is an alternative to overcome the overproliferation of LAB. In this process, FW is converted into HLa, which can subsequently be transformed into H2 by HLa-consuming bacteria during a cross-feeding mechanism with H2-producing bacteria. In the present study, FW was evaluated for HLa production at different organic loading rates (OLR) (12.5, 25.0, 37.5, and 50.0 gVS/L/d) in a semi-continuous reactor, and the HLa obtained was used for the H2 production. Results showed that OLR significantly influences HLa production during the self-fermentation of FW (p < 0.05). The highest ORL of 50.0 gVS/L/d and an HRT of 1.25 days generated the net maximum HLa production of 10.8 g/L. The HLa production was companied by the presence of acetate, propionate, and succinate, which accounted for only 20 % of the total organic acids produced. Then, effluent with HLa concentrations of 5.0, 10.0, 15.0, 20.0, and 25.0 g/L was evaluated for H2 production in batch tests using thermally pretreated sludge and the native microbial community of the effluent as inoculum. Even though different metabolic pathways for H2 production can be noted during the fermentation, which differs from one inoculum to another, the highest value of H2 production of 596.3 mL/Lreactor was obtained with the native microbial community at the highest concentration of HLa (25.0 g/L). During the fermentation process for H2 production, HLa and propionate were mainly transformed into butyrate and acetate. The present study demonstrated the feasibility of obtaining H2 from a complex substrate, such as effluent from a previous fermentation, using different inocula.

Winery and olive mill wastewaters treatment using nitrilotriacetic acid/UV-C/Fenton process: Batch and semi-continuous mode

In this work, both red and white winery wastewaters (WW) and olive mill wastewater (OMW) were submitted to a treatment by Fenton-based processes (FBPs). The main aim was to evaluate the most efficient and economic process. Initial tests, resorting to a batch reactor, demonstrated that UV-C/Fenton (λ = 254 nm) was the most effective process. Operational conditions such as pH, H2O2 and Fe2+ concentrations revealed to have a superior influence within dissolved organic carbon (DOC) removal as well as regarding the reactor's energy consumption. As a means to prevent iron precipitation, the addition of nitrilotriacetic acid (NTA) was tested. With experimental conditions pH = 3.0, [H2O2] = 194 mM, [Fe2+] = 1.0 mM, [NTA] = 1.0 mM, radiation UV-C (254 nm), time = 240 min, the kinetic rate related with DOC removal showed a kredWW = 0.0128 min−1 > kOMW = 0.0124 min−1 > kwhiteWW = 0.0104 min−1 and both the WW and OMW achieved the Portuguese legal limit values for wastewater discharge. Furthermore, comparative experiments were performed in a semi-continuous reactor, being that the results put in evidence that the concentration of H2O2 added and the flow rate of reagents' addition (F) had a significant effect on the efficiency of the reactor. Under an optimum experimental procedure pH = 3.0, [H2O2] = 97 mM, [Fe2+] = 1.0 mM, [NTA] = 1.0 mM, radiation UV-C (254 nm), F = 1 mL min−1, time = 240 min, there were observed higher DOC removal kinetic rates (kOMW = 15.20 × 10−3 min−1 > kredWW = 11.64 × 10−3 min−1 > kwhiteWW = 11.57 × 10−3 min−1) and a cost ranging between 0.0402 and 0.0419 €/g.DOC. These results showed that semi-continuous reactors have the potential to be applied to large scale treatments, with low reagents consumption and reduced energy requirements.

Complete recycling of Printed Circuit Boards: From base metal bioleaching in a semi-continuous reactor with dual regulation to gold biosorption with brewer's yeast

Bioleaching is a promising technology for recovering base metals and concentrating precious elements in secondary resources. In this study, the extraction of base metals from printed circuit boards (PCBs) was optimized using a dual control system including biomass encapsulation. Gold recovery was achieved in a second step by chemical dissolution followed by biosorption on brewer's yeast. A dual regulation system, controlling oxidoreduction potential (ORP) and copper concentration, was established. This system comprised two reactors interconnected in a loop: a leaching reactor and a biological reactor. Acidophilic bacteria in the biological reactor recycled ferrous into ferric iron in a low shear stress environment. The Fe3+ solution from the biological reactor recirculated to the leaching compartment (hosting the PCBs) based on ORP regulation (optimal setpoint: +410 mV vs Ag/AgCl). A second control aimed to maintain the copper concentration below the inhibitory level (15 g Cu2+ L−1) by addition of fresh medium and overflow of leachate. This configuration ensured the highest pulp density, operating consistently, in steady state, at the inhibitory concentration limit, the PCBs being added batch-wise when the stock within the leaching compartment was exhausted. Compared to planktonic cells, the encapsulated mode showed optimal base metals leaching yields: 100% for Cu, 24% for Al, 49% for Ni, and 100% for Zn, with a hydraulic retention time (HRT) of 92 h and an iron oxidation rate of 0.455 mg L−1 h−1. The reactor's productivity was 5.91 g Cu L−1d−1, corresponding to the leaching of 20.88 g PCBs L−1d−1. The gold enriched PCBs (from 290 to 450 mg Au kg−1) were then extracted using Aqua regia, with a 24:1 liquid/solid ratio at 80 °C for 2 h. Subsequent biosorption on brewer's yeast (10 g yeast L−1) selectively recovered gold, with 98% efficiency. Biosorption yields for “fresh” yeast resulting from a model brewing (90.8%) and commercial “active dry” yeast (88.7%) were comparable, indicating the potential use of spent yeast from brewing.

Upgrading Pyrolytic Oil via Catalytic Co-Pyrolysis of Beechwood and Polystyrene.

This study aims to investigate the catalytic co-pyrolysis of beech wood with polystyrene as a synergic and catalytic effect on liquid oil production. For this purpose, a tubular semi-continuous reactor under an inert nitrogen atmosphere was used. Several zeolite catalysts were modified via incipient wetness impregnation using iron and/or nickel. The liquid oil recovered was analyzed using GC-MS for the identification of the liquid products, and GC-FID was used for their quantification. The effects of catalyst type, beechwood-to-polystyrene ratio, and operating temperature were investigated. The results showed that the Fe/Ni-ZSM-5 catalyst had the best deoxygenation capability. The derived oil was mainly constituted of aromatics of about 92 wt.% for the 1:1 mixture of beechwood and polystyrene, with a remarkably high heating value of around 39 MJ/kg compared to 18 MJ/kg for beechwood-based bio-oil. The liquid oil experienced a great reduction in oxygen content of about 92% for the polystyrene-beechwood 50-50 mixture in comparison to beechwood alone. The catalytic and synergetic effects were more realized for high beechwood percentages as a 75-25 beechwood-polystyrene mix. Regarding the temperature variation between 450 and 600 °C, the catalyst seemed to deactivate faster at higher temperatures, thus constituting a quality reduction in the pyrolytic oil in high-temperature ranges.

Rumen microbe fermentation of corn stalk to produce volatile fatty acids in a semi-continuous reactor

Resource utilization of corn stalk is promising to relieve the problem of energy shortage and environmental pollution. Rumen microbes can improve the hydrolysis efficiency of corn stalk to produce volatile fatty acids (VFAs) efficiently. However, long-term rumen fermentation practice has not been conducted and performances of hydrolysis and acidogenesis are still unclear. In this study, the long-term hydrolysis and acidogenesis performances and microbial succession of rumen microbes for 120 d were explored in a semi-continuous reactor using corn stalk as substrate. Results showed that an average VFA yield was 0.310 g/g substrate for 120 d fermentation. VFA concentration rapidly increased to 10.34 g/L at Day 7, then gradually decreased, and finally stabilized from Day 30. VS removal reached the highest of 58.5% at Day 7, then gradually decreased, and finally fluctuated at 43.4%-48.2%. A high VFA/SCOD ratio indicated that rumen semi-continuous reactor had a good hydrolysis and acidogenesis capacity. Diversity and abundance of rumen bacterial communities in the stable stage (after Day 30) were significantly lower than those in the initiating stage (0–5 d). Rumen microbes formed a new community composition in the stable stage, and Prevotella, Succiniclasticum, Rikenellaceae_RC9_gut_group, and Ruminococcus were the main hydrolytic bacteria and acidogens to ensure the VFA production. Meanwhile, rumen bacteria co-occurring in the stable stage was simpler than that in the initiating stage. pH decrease and VFA accumulation might be the main reason for the community change in rumen bacteria, further leading to the decrease of VFA concentration in the rumen semi-continuous reactor. These findings provide a theoretical reference for long-term fermentation of lignocellulosic biomass with rumen microbes.

Hydrothermal carbonization vs. anaerobic digestion to valorize fruit and vegetable waste: A comparative technical and energy assessment

Herein, the valorization of vegetable and fruit waste was assessed via hydrothermal carbonization (HTC) and anaerobic digestion (AD) in terms of product characterization and energy requirements. HTC was conducted at reaction temperatures between 150 ºC and 190 ºC, and residence times between 20 min and 40 min. The increase in the process severity resulted in hydrochars with higher carbon contents and higher energy densification ratios. AD was performed in two different ways. i.e., batch and semi-continuous reactions. From the batch experiments a methane yield of 300 L CH4/kg VS was obtained, while for the semi-continuous, the average specific methane production estimated (for HRTs from 75 to 50 days) was 213 ± 32 L CH4/kg VS. To estimate the energy requirements, mass and energy balances were performed considering the basic stages of each process to obtain a suitable biofuel material. In this sense, it was concluded that for this specific waste, AD was a more suitable process with a positive energy net balance. On the contrary, HTC presented a negative energy net balance being required 1.29 MJ/kg of fresh food waste. A combined HTC-AD treatment may be an efficient method to take advantage of both technologies leading to higher energy efficiencies and other valuable products.

Valorization of brown macroalgae Sargassum plagiophyllum for biogas production under different salinity conditions

This study investigates the biogas production from Sargassum plagiophyllum under different salinity using a semi-continuous reactor. Inoculum preparation was conducted by mixing the two prepared S. plagiophyllum juice (deionized and saline water) with the cow manure using a ratio of 1:1. Once every two days, 5 % of the substrate was replaced with 5 % of fresh macroalgae juice continuously. The results found that cumulative biogas production in deionized water was 3.7 times higher than in saline water after 30 days. It could be attributed to anaerobic bacteria growth inhibited by salt. The maximum cumulative methane and biogas yields in the deionized water digester were 266.18 mL/g-VS and 371.76 mL/g-VS, respectively. The kinetics of the methane production was also determined, and the experimental data fitted well with the modified Gompertz model. These results indicate that S. plagiophyllum, under low salinity conditions, can be developed as a feedstock for biogas production.

Biochemical hydrogen potential assay for predicting the patterns of the kinetics of semi-continuous dark fermentation

The performance and kinetics response of thermophilic semi-continuous dark fermentation (DF) of simulated complex carbohydrate-rich waste was investigated at various hydraulic retention times (HRT) (2, 2.5, and 3 d) and compared with data obtained from biochemical hydrogen potential assay (BHP). A culture of Thermoanaerobacterium thermosaccharolyticum was used as the inoculum and dominated both in BHP and semi-continuous reactor. Both the modified Gompertz and first-order models described the DF kinetics well (R2 = 0.97–1.00). HRT of 2.5 d was found to be optimal in terms of maximum hydrogen production rate and hydrogen potential, which were 3.97 and 1.26 times higher, respectively, than in BHP. The hydrolysis constant was highest at HRT of 3 d and was closest to the value obtained in the BHP. Overall, BHP has been shown to be a useful tool for predicting H2 potential and the hydrolysis constant, while the maximum H2 production rate is greatly underestimated.

Volatile fatty acids production from municipal waste streams and use as a carbon source for denitrification: The journey towards full-scale application and revealing key microbial players

Volatile fatty acids (VFAs) production is attracting interest as a sustainable approach to maximize resource recovery from organic wastes. This study explored the interlink between long-term system resilience of VFA production from primary sludge (PS) and external organic waste (OW) without pH control and the microbial community dynamics as well as the effect of substrate variability. The study elucidated the practicality of using VFA-rich effluent as a carbon source for wastewater denitrification. A 15 L bench-scale semi-continuous reactor was operated for 315 days with a feed of 70% v/v PS and 30% v/v OW and scaled up to a 2 m3 pilot-scale continuous reactor operated for 264 days. In the bench-scale study, the system was resilient with VFA production of up to 24,700 ± 400 mg COD/L and a yield of 506 ± 25 mg COD/g VSfed. The VFA composition was dominated by caproic acid up to 62% w/w. In the pilot-scale reactor, substrate variability influenced VFA production with a concentration of up to 21,500 ± 500 mg COD/L. The system was shown to be economically viable. The microbial community was dominated by Lachnospiraceae, Streptococcaceae and Comamonadaceae. The relative abundance of Lachnospiraceae gave a strong positive statistical correlation with caproic acid concentrations. The VFA-rich effluent exhibited a higher specific denitrification rate than methanol and acetate. Moreover, a continuous denitrification experiment with real nitrified wastewater resulted in a high nitrate removal efficiency with a maximum of 98%. The study demonstrates the production of bio-based products from organic wastes as alternatives to fossil-based products.

Simulation of biowastes and biodegradable plastics co-digestion in semi-continuous reactors: Performances and agronomic evaluation

The development of selective biowaste collection in most European countries provides new opportunities for the anaerobic digestion sector. In parallel, extensive development of biodegradable plastics like polylactic-acid (PLA) and polyhydroxybutyrate (PHB), which facilitates the replacement of conventional plastics, has taken place in the past decade. This study investigated anaerobic co-digestion in semi-continuous reactors of biowastes (75 % Volatil Solids) and biodegradable plastics (25 % Volatil Solids, PLA and PHB). PHB was estimated to be fully biodegraded in the reactors. By contrast, PLA accumulated in the reactor, and an average biodegradation of 47.6 ± 17.9 % was estimated during the third hydraulic retention time. Pretreatment of PLA, by thermo-alkaline hydrolysis at 70 °C, with 2.5 w/v of Ca(OH)2 for 48 h, improved the biodegradation yield of PLA to 77.5 ± 9.3 %. Finally, it was highlighted that PLA or PHB addition to the feed did not further affect the agronomic properties of the digestate.

Pilot-Scale Modelling of Aerated Lagoon Technology for the Treatment of Landfill Leachate: Case Study Hrybovychi Plant

Results of experimental pilot-scale study of aerobic pre-treatment of the leachate of the Hrybovychi municipal solid waste (MSW) landfill (Ukraine) in batch reactor mode and in semi-continuous mode are presented. The dependencies of key pollution indicators, namely biological oxygen demand, chemical oxygen demand, pH, suspended solids, and total Kjeldahl nitrogen (TKN), during a 30-day periodical aeration process were obtained. The first 15 days treatment was in the batch reactor mode treating an initial volume of raw leachate. The second 15 days treatment was in a semi-continuous reactor mode: 400 L of aerobically pre-treated leachate were pumped to the next treatment stage and consequently the same volume of raw leachate was added in the bioreactor tank. Aerobic biological treatment of Hrybovychi landfill leachate using the developed method achieved significant treatment effects, namely 55.3% of the total Kjeldahl nitrogen, 27% of COD, 70.2% of BOD5 and 66.5% of BODtot. Time dependences of TKN, COD, BOD5, and BODtot are well fitted by simple exponential trends, which correspond to first-order reactions. Landfill leachate, aerobically pre-treated in the pilot-scale treatment unit, can be discharged for final treatment to the bio-plateau or to the wastewater treatment plant.

Effects of seasonal and local co-feedstocks on the performance of continuous anaerobic digestion of cattle slurry

The study's aim was to assess the robustness of farm-type anaerobic digestion with cattle slurry as the main feedstock under the change of co-feedstock type and quality. Fish biomass, rainbow trout offal, potato, and reindeer offal were investigated as possible co-feedstocks in a 428-day semi-continuous reactor experiment. Using fish biomass or rainbow trout offal as co-feedstock (19 % of VS of the feed) produced an average of 220 and 305 L CH4/kg VS compared to the 201 L CH4/kg VS for the manure control. For other co-feedstocks, the differences were not statistically significant. Despite recommendations to acclimate biogas process to new feedstocks with caution, no disturbances in the biogas process were observed, even with sudden changes in co-feedstocks. The use of locally available and seasonal co-feedstocks improved the agronomic quality of the digestates and could be important in securing farms' supply of and self-sufficiency in both energy and fertilizers.