Volatile Solids Basis Research Articles

Biomethanization of rigid packaging made entirely of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): Mono- and co-digestion tests and microbial insights

This study evaluates the anaerobic mesophilic mono- and co-digestion of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) plastic bottles as a proxy for rigid packaging materials. Initial tests showed a 97.3 ± 0.2 % reduction in weight and an observable alteration in the surface (thinning, color fading and pitting) of the PHBH bottles after eight weeks. Subsequent tests showed that PHBH squares (3 × 3 cm) produced 400 NmL-CH4/g-VSfed, at a slower rate compared to powdered PHBH but with similar methane yield. Co-digestion experiments with food waste, swine manure, or sewage sludge showed successful digestion of PHBH alongside organic waste (even at a high bioplastic loading of 20 % volatile solids basis), with methane production comparable to or slightly higher than that observed in mono-digestion. Molecular analyses suggested that the type of co-substrate influenced microbial activity and that methane production was mainly driven by hydrogenotrophic methanogenesis. These results suggest the potential for integrating rigid PHBH packaging into anaerobic digesters.

Enhanced methane production with co-feeding spent coffee grounds using spare capacity of existing anaerobic food waste digesters

With increasing coffee consumption worldwide, the efficient and sustainable management of spent coffee grounds (SCG) has become increasingly challenging. This study investigated the anaerobic co-digestion of small amounts of SCG with food waste (FW) at increasing co-feeding ratios of 1:100–1:10 (volatile solids basis) to assess the possibility of SCG treatment using the spare capacity of existing anaerobic digesters. Co-feeding SCG increased methane production compared to FW mono-digestion in the tested range of co-feeding ratios without compromising process stability. Methane yield did not further increase when the SCG/FW ratio increased above 4%, and process failure occurred at a 1:10 co-feeding ratio without trace element supplementation. The enhanced methanogenic performance was attributed to increased protein removal efficiency, which was potentially related to the promotion of peptide hydrolysis. The overall results suggest that co-feeding appropriate small amounts of SCG to FW digesters can be a realistic sustainable option for SCG management.

Enhancing anaerobic digestion of dewatered sewage sludge through thermal hydrolysis pretreatment: Performance evaluation and microbial community analysis

This study explored the effectiveness of thermal hydrolysis (TH) in conditioning dewatered sewage sludge (DSS) for enhanced anaerobic digestion (AD). The TH pretreatment employed in this study (30 min at 170°C and 6 bar) significantly improved the bioavailability of DSS. The degree of solubilization varied with the physicochemical characteristics of DSS collected over three seasons: 16.8–24.8% on a volatile solids (VS) basis and 9.4–33.7% on a chemical oxygen demand (COD) basis. Correspondingly, the dissolved fraction of VS in DSS increased by 2.1–3.4-fold, and the soluble fraction of COD rose by 1.4–2.9-fold. The duplicate anaerobic reactors treating the TH-pretreated DSS did not achieve steady-state operation at the intended design organic loading rate (OLR) of 3.8 g VS/L·d, but showed stable performance at an OLR of 3.4 g VS/L·d with significantly higher methane yield (0.26–0.29 L/g VS fed) and VS removal (35–38%) than those reported for untreated DSS and comparable to TH-pretreated DSS. The reactors' microbial community structures changed dynamically as the OLR varied, with shifts in dominance between acetoclastic and hydrogenotrophic methanogens. The results highlight the promising potential of TH-AD process for efficiently treating DSS while emphasizing the importance of optimizing OLR for stable operation.

A comprehensive evaluation of cheese whey to produce biogas in the Canary Islands

Cheese whey (CW) is a by-product of the cheese industry with pollution potential if not properly managed. This study evaluates biogas potential from CW samples from the Canary Islands. Empirical data were used to evaluate biogas potential at cheese factory, municipality, insular and regional level. 24 samples of CW were collected from 17 different farms across the Canaries, including different industries (artisan/industrial), different milk types (cow, goat, sheep, cow + goat, goat + sheep, cow + goat + sheep) and different post-treatments (cottage cheese production, filtering and skimming, inverse osmosis) to study their physical and chemical composition and biogas potential through Biochemical Methane Potential assays. Composition showed significant differences between industrial and artisan manufacturers, showing higher organic matter concentration in artisan CW. Methane potential varied from 450.6 ± 0.2 L kg−1 to 861.2 ± 28.8 L kg−1 (on basis of volatile solids). Artisan CW showed a higher methane potential (m3 t−1 of fresh matter) than industrial CW, whereas no differences were observed depending on the milk type. Post-treatments, further processing at factories and degradation at environmental conditions changed CW properties and biogas potential. Results showed that CW should be fed fast into digesters to avoid acidification and the loss of biogas potential. In the Canary Islands 81.95 million litres of CW are produced annually, which could be converted into 4.5 million m3 of biogas with the potential to contribute 108 TJ y−1 of renewable energy into the energy matrix. Valorisation of CW is a promising alternative for small and medium farms/industries in the Canary Islands, which could replace fossil energy with biogas.

The Role of Mild Alkaline Pretreatment in the Biorefinery Upgrade of Spent Coffee Grounds

This work proposes a valorization route for spent coffee grounds (SCG), a widespread lignocellulosic residue, encompassing the production of: biomethane, lignin, and oligosaccharides as value-added products obtained simultaneously during a mild alkaline (NaOH) pretreatment. The studied operational variables were the reaction time (60–240 min), temperature (25–75 °C), and the NaOH concentration (0–2.5 M). The severity factor suitably describes the global process kinetics, with higher severities (log Mo = 5.5) yielding high product yields, 18.02% and 13.25% (on dry SCG basis) for lignin and oligosaccharides (XGMOS), respectively. Solid yield is negatively impacted by all studied variables (at the 95% confidence level). Conversely, XGMOS yield is positively influenced both by time and catalyst concentration, whereas lignin yield is only (positively) influenced by catalyst concentration. Optimal balance between product formation and potential operational costs is putatively achieved when using 0.625 M NaOH, at 50 °C for 60 min. The mild alkaline pretreated biomass (MAP-SCG) was compared to untreated SCG for biomethane production by anaerobic co-digestion with pig slurry (PS), using a ratio of biomass/PS = 1/3 (volatile solids (VS) basis). The proposed valorization route enabled the sequential production of 6.25 kg lignin, 6.36 kg oligosaccharides, and 138.05 kg biomethane per 100 kg of non-extracted SCG (and 287.60 kg pig slurry), in an integrated process that is technically feasible and promotes the circular bioeconomy.

Application of a Full-Scale Horizontal Anaerobic Digester for the Co-Digestion of Pig Manure, Food Waste, Excretion, and Thickened Sewage Sludge

Many laboratory- and pilot-scale studies on anaerobic co-digestion have been conducted in Republic of Korea; however, studies on full-scale demonstration facilities are lacking. This study aimed to present a successful case of a large-scale anaerobic co-digestion facility in Republic of Korea for biogas generation from four organic wastes (pig manure, food waste, excretion, and thickened sewage sludge) using a horizontal anaerobic digester. A preliminary biochemical methane potential test was performed for the individual and mixed organic waste to design a treatment facility for 320 m3/day of organic waste generated in Seosan City. Subsequently, a horizontal anaerobic digester with a 35 day-retention time (based on 320 m3/day input) was constructed. Each organic waste was placed in an anaerobic reactor after pretreatment. The input was gradually increased after the first seeding, and the operation continued for 158 days. Total and volatile solids made up 4.1% and 3.3%, respectively. Throughout the operating period, the digester temperature was maintained at 35–40 °C for mesophilic digestion, and the pH was maintained at 7–8. The average organic matter removal efficiency (volatile solids basis) was 64% and the methane gas production rates were 0.35, 0.6, 0.26, 0.28, and 0.39 Nm3CH4/kg vs. for pig manure, food waste, excretion, thickened sewage sludge, and mixed waste, respectively, resulting in an average methane content of the biogas 68.8%.

Influence of Dairy Manure as Inoculum Source on Anaerobic Digestion of Swine Manure.

Inoculation is a widely used method to improve the efficiency of anaerobic digestion (AD) with a high organic load. This study was conducted to prove the potential of dairy manure as an inoculum source for AD of swine manure. Furthermore, an appropriate inoculum-to-substrate (I/S) ratio was determined to improve methane yield and reduce the required time of AD. We carried out 176 days of anaerobic digestion for five different I/S ratios (3, 1, and 0.3 on a volatile solid basis, dairy manure alone, and swine manure alone) of manure, using solid container submerged lab-scale reactors in mesophilic conditions. As a result, solid-state swine manure inoculated with dairy manure could be digested without inhibition caused by ammonia and volatile fatty acid accumulation. The highest methane yield potential was observed in I/S ratios 1 and 0.3, as 133 and 145 mL CH4·g-1-VS, respectively. The lag phase of swine manure alone was more extended, 41 to 47 days, than other treatments containing dairy manure, directly related to tardy startup. These results revealed that dairy manure can be used as an inoculum source for AD of swine manure. The proper I/S ratios leading to successful AD of swine manure were 1 and 0.3.

Methane and Hydrogen Sulfide Production from the Anaerobic Digestion of Fish Sludge from Recirculating Aquaculture Systems: Effect of Varying Initial Solid Concentrations

Recirculating aquaculture systems (RAS) are efficient at solid waste capture and collection but generate a concentrated waste stream. Anaerobic digestion (AD) could be one potential treatment option for RAS facilities. However, the concentration of organic matter in the sludge can significantly affect the biogas quality from AD. This study evaluated the effect of fish sludge (FS) solid concentration on biogas quality. Three FS treatments consisted of different initial total solid concentrations (1.5%, 2.5%, and 3.5%) from a mixture of sludge produced by Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). Methane (CH4) production was measured, quantified, and normalized on a volatile solids (VS) basis. The highest solid concentration treatment produced 23% more CH4 than the lowest solid concentration (519 mL/g VS versus 422 mL/g VS, respectively). Peak CH4 production occurred on Day 7 for the lowest FS concentration (78.2 mL/day), while the highest FS concentration peaked on Day 11 (96 mL/day). Peak hydrogen sulfide (H2S) concentrations ranged from 1803–2074 ppm across treatments, signifying the requirement of downstream unit processes for H2S removal from biogas. Overall, this study demonstrated that increasing the FS concentration can significantly enhance CH4 production without affecting the stability of the digestion process.

Anaerobic Co-Digestion of Bioplastics and Food Waste under Mesophilic and Thermophilic Conditions: Synergistic Effect and Biodegradation

To mitigate the various problems caused by using conventional plastics, bioplastic (BP) has emerged as a substitute for plastics. BP wastes after use are commonly treated using composting, causing many environmental problems. Anaerobic digestion (AD) has become prominent as an alternative method of producing renewable energy. The aim of this study was to estimate the methane production yield (MPY) of BPs (polylactic acid (PLA) and polyhydroxyalkanoate (PHA)) with mechanical pretreatment (particle size < 0.5 cm) and investigate the effect of co-digestion of BPs and food waste (FW). Batch experiments were conducted under mesophilic and thermophilic conditions at various mixing ratios (FW/PLA or PHA = 95:5 and 90:10 on a weight basis). During 20 d of digestion at temperatures of 37 and 55 °C, MPYs of PHA were 153.8–172.0 mL CH4/g chemical oxygen demand (COD), but that of PLA was significantly low (<25.6 mL CH4/g COD). Higher MPYs were attained at 55 °C than at 37 °C. The synergistic effects of FW addition on BP AD were observed at both temperatures, especially at 55 °C. By comparing theoretical (based on mono-digestion results) and actual (based on co-digestion results) MPYs, the synergistic effect of FW addition on MPY of co-digestion reached 8.5–26.6% and 12.7–25.5% for PLA- and PHA-fed tests, respectively. The biodegradation rates (on a volatile solids (VS) basis) of PLA and PHA were 6.0–13.7% and 49.1–52.3% and increased by 1.8–4.3 and 1.2–1.5 times in the PLA- and PHA-fed co-digestion tests, respectively. Co-digestion of FW might be a feasible treatment option for BPs combined with simple mechanical pretreatment.

Biochemical methane potential and active microbial communities during anaerobic digestion of biodegradable plastics at different inoculum-substrate ratios

The influence of the inoculum-substrate ratio (ISR) on the mesophilic and thermophilic biochemical methane potential test of two biodegradable plastics was evaluated. Poly(lactic acid) (PLA) and polyhydroxybutyrate (PHB) were selected for this study, the first for being recalcitrant to mesophilic anaerobic digestion (AD) and the second, by contrast, for being readily biodegradable. Several ISRs, calculated on the basis of volatile solids (VS), were tested: 1, 2, 2.85, 4, and 10 g(VS of inoculum).g(VS of substrate)−1. A high ISR was associated with an enhanced methane production rate (i.e., biodegradation kinetics). However, the ultimate methane production did not change, except when inhibition was observed. Indeed, applying the lowest ISR to readily biodegradable plastics such as PHB resulted in inhibition of methane production. Based on these experiments, in order to have reproducible degradation kinetics and optimal methane production, an ISR between 2.85 and 4 is recommended for biodegradable plastics. The active microbial communities were analyzed, and the active bacteria differed depending on the plastic digested (PLA versus PHB) and the temperature of the process (mesophilic versus thermophilic). Previously identified PHB degraders (Ilyobacter delafieldii and Enterobacter) were detected in PHB-fed reactors. Thermogutta and Tepidanaerobacter were detected during the thermophilic AD of PLA, and they are probably involved in PLA hydrolysis and lactate conversion, respectively.

The Three-stage High Solid Anaerobic Digestion (TSHS- AD) under Ambient Temperature for Enhanced Biogas Production from Cow Manure

This research aimed to investigate the three-stage high solid anaerobic digestion (TSHS-AD) at ambient temperature. BMP was conducted at the various substrate to inoculum (S: I) ratios of 2:1, 4:1, and 6:1 on a volatile solid (VS) basis, each of which was conducted at different total solid concentrations (15%, 20%, and 30%). The highest methane yield of 343.97 mL-CH4·gVS-1 was achieved at 2:1-S: I ratio and 15 %TS. Meanwhile, TSHS-AD operated at S: I 2:1 and 15 %TS (20g-TS/L-R1) provide a maximum methane yield of 316.09 mL-CH4·gVS-1. The stage separation of TSHS-AD reduces inhibitors in the methanogenesis step. Moreover, it could create a full microbial function in each stage. Accumulation of VFA and semi-continuous feeding have considerable influence in enhancing anaerobic microbes involved in the biogas system. The annual income from biogas has the greatest impact on the investment attractiveness of TSHS-AD, according to the computation of IRR, NPV, and PB. The results obtained in this research could be potentially helpful to scale up the TSHS-AD system.

Anaerobic Co-Digestion to Enhance Waste Management Sustainability at Yosemite National Park

This study evaluated the co-digestion of domestic wastewater solids (WWS) and food waste (FW) at the bench-scale for Yosemite National Park, California, which operates a 1900 m3/d wastewater treatment plant in El Portal, California. A 35-day biochemical methane potential test was performed on varying amounts of FW as a percentage of total waste (WWS plus FW) on a volatile solids basis (%FW). Specific methane yield and volumetric methane yield increased substantially with increasing %FW. A higher %FW was also associated with slower degradation kinetics but higher methane content in biogas. The 75 %FW treatment had relatively rapid kinetics, a high cumulative specific methane yield (453 mL CH4/g VS), and an elevated methane content in biogas, and is suggested as an upper limit %FW mixture for full-scale co-digestion. This, coincidently, is near the estimated ratio of WWS and FW production at the Park (70 %FW). Co-digesting the Park’s feedstock of FW with WWS in existing anaerobic digestion facilities could increase methane production five-fold. Combusting this methane in a combined heat and power system would produce about twice the energy needed to heat anaerobic digestors and power the treatment plant.

Energy and Nutrients from Apple Waste Using Anaerobic Digestion and Membrane Technology.

The worldwide increment of food waste requires innovative management solutions, aligned with sustainability, energy, and food security. Anaerobic digestion (AD), followed by nutrient recovery, may be considered an interesting approach. This study proposed a co-digestion of apple pomace (AP) with swine manure (SM) to study the effect of different proportions of AP (0, 7.5, 15, and 30%, on a volatile solids (VS) basis) on the methane production and the stability of the process. Subsequently, the gas-permeable membrane (GPM) technology was applied to recover nitrogen (N) as ammonium sulfate (bio-based fertilizer) from the digestates produced after the AD of 7.5% of AP and SM, and SM alone. The results showed that the co-digestion of 7.5% and 15% of AP with SM presented a methane production similar to the AD of SM alone (with 412.3 ± 62.6, 381.8 ± 134.1, and 421.7 ± 153.6 mL g VS−1 day−1, respectively). The later application of the GPM technology on the resulting digestates, with SM alone and with 7.5% of AP with SM, showed total ammoniacal N recovery rates of 33 and 25.8 g N m−2 d−1, respectively. Therefore, the AP valorization through the AD process, followed by N recovery from the digestate, could be a good management strategy.

In-situ sulphide control in the anaerobic co-digestion of residual biomass from the production of penicillin and cystine

This study was focused on the anaerobic digestion of residual biomass from the production of penicillin and l-cystine. The biogas potential tests of individual substrates and their mixture showed good anaerobic biodegradability. The highest measured specific biogas production was 712 l/kg volatile solids (VS) for penicillin biomass and 676 l/ kg VS for cystine biomass. The biogas potential tests were performed at different inoculum-to-substrate ratios (ISR) and showed that high concentrations of nitrogen and sulphur present in residual biomass have a major impact on the anaerobic processes. The long-term operation of the laboratory anaerobic reactor showed that the mono-digestion of the penicillin biomass was stable at an OLR of 1 kg/(m3.d). When co-digestion of penicillin and cystine biomass at a ratio of 0.9:0.1 (on a VS basis) and at the same OLR was enhanced, the operation of the laboratory model turned unstable. During this phase of the operation, the course of anaerobic processes was affected by ammonia and especially sulphide inhibition. Sulphide inhibition was effectively reduced by direct dosing of FeCl2 (in-situ sulphide control), at a molar iron-to-sulphur ratio of β = 1 (mol Fe/mol S). When suppressing sulphide inhibition, the operation of the laboratory model became stable even at a co-digestion ratio of 0.5:0.5 (VS basis). The results of this work open a new scope for future applications in the anaerobic digestion of waste biomass with high sulfur content, coming from industrial fermentation processes.

Anaerobic Co-Digestion of Sugarcane Leaves, Cow Dung and Food Waste: Focus on Methane Yield and Synergistic Effects

Anaerobic co-digestion (AcoD) of food waste (FW) and lignocellulose waste is a promising technology for methane production. This work investigated the methane generation from AcoD of FW, sugarcane leaves (SLs), and cow dung (CD) under mesophilic conditions in a batch test. As for AcoD of two feedstocks (SL and FW or CD and FW), introduction of SL and CD (25%, volatile solid (VS) basis) showed slight improvement in methane production from FW. In contrast, positive synergistic effect (synergy index = 1.03–1.14 > 1) was observed in all the AcoD reactors of the three feedstocks (SL, CD, and FW). The optimum mixing ratio of FW:SL:CD (VS basis) was 85:11.25:3.75 with a synergy index of 1.07, achieving a methane yield rate and methane content of 297.16 mL/g VS and 73.26%, respectively. This group cumulative methane production was an improvement of 110.45 and 444.72% higher than mono-digestion of SL and CD. The biodegradability, soluble chemical oxygen demand (SCOD), and VS removal rate were 56.44, 44.55 and 55.38%, respectively. The optimum results indicated that AcoD of FW, SL, and CD have higher potentials for energy recovery and provided forceful scientific evidence for their energy utilization.

Electrochemical pretreatment enhancing co-fermentation of waste activated sludge and food waste into volatile fatty acids: Performance, microbial community dynamics and metabolism

Waste activated sludge (WAS) has low biodegradability that restricts acidogenic fermentation (AF), thereby limiting the high-value volatile fatty acids (VFAs) production. This study investigated an alternative electrochemical pretreatment (EPT) approach that can facilitate AF of WAS and food waste (FW) and therefore enhance VFAs production. The results showed through introducing 50 % volatile solid basis of FW (containing massive chloride) into WAS, a 60-min EPT produced reactive chlorine species (RCS), which diffused into WAS-FW inner layers resulting in cell lysis, therefore significantly promoted and accelerated WAS-FW disintegration, contributing to more soluble and biodegradable dissolved organic matter (DOM). Then during the subsequent 15-day acidogenic co-fermentation (Co-AF), the residual RCS (approximate 5 mg Cl2/L) also caused acidogenic bacteria (including Prevotella_7, Lactobacillus and Veillonella) gradually outcompeted methanogens due to their different tolerance to residual RCS. Consequently, the maximum VFAs yield of the WAS-FW Co-AF with EPT was 40.8 % higher than WAS-AF without EPT.

Annual Physicochemical Characteristics and Biogas Potential of Food Waste in Korean Coastal Cities

Korea recycles approximately four million tons of food waste (FW) annually. Around 80% of this waste is treated as animal feed and compost. As the demand for animal feed and compost from FW decreases, there is an increasing need to find innovative solutions for this waste. Anaerobic digestion (AD) is currently the most realistic solution, and Korea has plans to construct more AD facilities by 2030. Before these facilities can be built, it is essential to study the indicators and frequencies representative of the characteristic changes in FW. The current literature is lacking in this area, as many studies only focus on a few critical indicators over short periods of time. This study aims to overcome this lack of information by analyzing two processes. The first process analyzes the monthly and seasonal variations in FW characteristics of Pohang city for one year. Biochemical methane potential (BMP) tests were performed, and their data was analyzed to provide basic information for AD design. The second process evaluates different methods of estimating methane production to determine which is the most suitable. The FW characterization study was conducted twice a month and the BMP analysis was conducted once a month. An analysis of the physicochemical parameters for one year indicated an average pH of 4.82, an average moisture content of 80.68%, an average volatile solid (VS) value of 174.48 g/L, an average chemical oxygen demand (COD) of 275.48 g/L, the average carbohydrate, protein, and lipid contents in VS basis were 41.87%, 33.59 %, and 14.34% respectively, and the average BMP was 259.97 ± 12.96 mL/g COD. Principal component analysis of FW characteristics resulted in two significantly different clusters - one for winter and spring and the other for summer and fall. The ANOSIM R-value for these characteristics was 0.821 (p < 0.01). Methane production levels were estimated from FW characteristics using COD, organic composition, and heat value basis. The data indicated that estimating methane production from FW using an organic composition basis rendered more accurate results than the other two methods. These results are beneficial for designing and managing food waste using AD processes as understanding the substrate characteristic change is important to maintaining stability.

Deploying two-stage anaerobic process to co-digest greasy sludge and waste activated sludge for effective waste treatment and biogas recovery

High-strength waste activated sludge (WAS) and greasy sludge (GS) were largely generated from canned tuna processing. This study reports the performance of the two-stage anaerobic process for co-digesting WAS and GS. Various WAS:GS mixing ratios of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:00 (volatile solids (VS) basis) were investigated in batch acidogenic stage at ambient (30 °C ± 3 °C), 55 °C, and 60 °C temperatures. Subsequently, the effluents from the first stage were used to produce methane in the second methanogenic stage at an ambient temperature. The highest methane yield of 609 mL CH4/g-VSadded was achieved using acidogenic effluents generated from a WAS:GS mixing ratio of 40:60 at an ambient temperature. The first-order kinetic constants (k) for the first (k1) and second (k2) stages were subsequently estimated to be 0.457 d−1 and 0.139 d−1, respectively. The obtained k constants were further used to predict the hydraulic retention time (HRT) for the two continuously stirred tank reactors (CSTR) in series. Consequently, the calculated 4-day HRT and 20-day HRT for 50-L CSTR1 and 250-L CSTR2, respectively, were used to operate the continuous two-stage process at an ambient temperature by feeding with a 40:60-WAS:GS mixing ratio. A satisfactory methane yield of 470-mL CH4/g-VS along with 75% chemical oxygen demand (COD) removal was generated. Furthermore, the predicted methane yield of 450-mL CH4/g-VS obtained from the simple kinetic CSTR model resembled the experimental yield with 96% accuracy. The obtained experimental results demonstrate that WAS and GS co-digestion could be successfully accomplished using a practical two-stage anaerobic process operated at an ambient temperature.

Effect of different digestates derived from anaerobic co-digestion of olive mill solid waste (omsw) and various microalgae as fertilizers for the cultivation of ryegrass

AimsThe aim of this work was to evaluate the fertilizing effect of three anaerobic co-digestates on the growth of the herbaceous plant Lolium rigidum.MethodsNine treatments, combining different nutritional solutions (organic and inorganic) and number of fertilizations (one or two) were evaluated. Organic nutritive solution: plants grown with different olive mill solid waste (OMSW) -microalgae co-digestates: 75% OMSW-25% Raphidocelis subcapitata, volatile solids (VS) basis (OMSW-Rs); 50% OMSW- 50% Chlamydomonas Reinhardtii, VS basis (OMSW-Chl); and 75% OMSW-25% Secenedesmus quadricauda, VS basis (OMSW-Sq). Inorganic nutritive solution (INS): plants grown with inorganic Hoagland nutrient solution at 50%. After 60 days of experimentation, biometric and nutritional characteristics and photosynthetic activity were measured.ResultsThe results showed a favourable growth, development and nutritional quality of L. rigidum plants when digestates obtained from the anaerobic co-digestion of OMSW-microalgae are used as organic nutritional solutions as opposed to INS ones. The highest total biomass of L. rigidum was obtained with the treatments that involved two fertilizations. No inhibition due to excess nutrients was observed. A higher root/shoot ratio was achieved with the digestates of OMSW-Rs and OMSW-Ch as compared to that obtained with OMSW-Sq (F = 17.23 p ≤ 0.001). The nitrogen shoot biomass obtained after the organic treatments with the above-mentioned co-digestates was higher than that obtained after the inorganic treatment. Net photosynthesis rates did not present differences in the co-digestates treatments, being equal or superior to the INS treatments.ConclusionsThe use of the anaerobic co-digestates from OMSW-microalgae can be considered a viable and promising alternative to inorganic fertilization.

Polyhydroxyalkanoates Production by Mixed Microbial Culture under High Salinity

The fishing industry produces vast amounts of saline organic side streams that require adequate treatment and disposal. The bioconversion of saline resources into value-added products, such as biodegradable polyhydroxyalkanoates (PHAs), has not yet been fully explored. This study investigated PHA production by mixed microbial cultures under 30 gNaCl/L, the highest NaCl concentration reported for the acclimatization of a PHA-accumulating mixed microbial culture (MMC). The operational conditions used during the culture-selection stage resulted in an enriched PHA-accumulating culture dominated by the Rhodobacteraceae family (95.2%) and capable of storing PHAs up to 84.1% wt. (volatile suspended solids (VSS) basis) for the highest organic loading rate (OLR) applied (120 Cmmol/(L.d)). This culture presented a higher preference for the consumption of valeric acid (0.23 ± 0.03 CmolHVal/(CmolX.h)), and the 3HV monomer polymerization (0.33 ± 0.04 CmmolHV/(CmmolX.h) was higher as well. As result, a P(3HB-co-3HV)) with high HV content (63% wt.) was produced in the accumulation tests conducted at higher OLRs and with 30 gNaCl/L. A global volumetric PHA productivity of 0.77 gPHA/(L.h) and a specific PHA productivity of 0.21 gPHA/(gX.h) were achieved. These results suggested the significant potential of the bioconversion of saline resources into value-added products, such as PHAs.