Mesophilic and thermophilic anaerobic co-digestion of winery wastewater sludge and wine lees: An integrated approach for sustainable wine production

Coupling anaerobic co-digestion of winery waste and waste activated sludge with a microalgae process: Optimization of a semi-continuous system

Wine production represents one of the most important agro-industrial sectors in Italy. Wine lees are the most significant waste in the winery industry and have high disposal and storage costs and few applications within the circular economy. In this study, anaerobic digestion and a microalgae coupled process was studied in order to treat wine lees and waste activated sludge produced within the same facility, with the aim of producing energy and valuable microalgae biomass that could be processed to recover biofuel or biostimulant. Chlorella vulgaris was cultivated on liquid digestate in a semi-continuous system without biomass recirculation. The best growth and phytoremediation performance were achieved applying a hydraulic retention time (HRT) of 20 days with a stable dry weight, lipid and protein storage of 1.85 ± 0.02 g l-1, 33.48 ± 7.54 % and 57.85 ± 10.14 % respectively. Lipid characterization highlighted the potential use in high quality biodiesel production, according to EN14214 (<12 % v/v linolenic acid). The microalgae reactor's liquid output showed high removal of ammonia (95.72 ± 2.10 %), but low organic soluble matter reduction. Further semi-continuous process optimization was carried out by increasing the time between digestate feeding and biomass recovery at HRT 10. These operative changes avoided biomass wash-out and provided a stable phytoremediation of the digestate with 84.58 ± 4.02 % ammonia removal, 33.01 ± 1.44 % sCOD removal, 38.06 ± 2.65 % of polyphenols removal.

Optimization of cobalt, nickel, and iron supplement for mesophilic and thermophilic anaerobic digestion treating high-solid food waste

ABSTRACTThe effects of trace metals (iron (Fe), cobalt (Co) + Fe, and Co + nickel (Ni) + Fe) on mesophilic and thermophilic anaerobic digestion of food waste were quantified experimentally. Supplementation with 0 ≤ [Co] ≤ 5 mg/L, 0 ≤ [Ni] ≤ 10 mg/L, or 0 ≤ [Fe] ≤ 200 mg/L can significantly improve the productivity of mesophilic (MD) and thermophilic (TD) digesters. Addition of micronutrients increased biogas production, but excessive addition of trace metals hindered the production. Supplementation with Fe + Co or Fe + Co + Ni increased biogas production more than the addition of only Fe did. Within the design boundaries, the optimal concentrations for supplementation with three trace metals in MD were [Co] = 0.33 mg/L, [Ni] = 0.43 mg/L, and [Fe] = 5.35 mg/L, and in TD were [Co] = 1.41 mg/L, [Ni] = 3.84 mg/L, and [Fe] = 200 mg/L. TD required larger amounts of the trace metals than MD (4.3-37.4 times). The results can give quantitative information on trace metal supplementation for successful anaerobic digestion.

Exploring the potential of thermophilic anaerobic co-digestion between agro-industrial waste and water hyacinth: operational performance, kinetic study and degradation pathway

Anaerobic co-digestion (co-AD) of agro-industrial waste, namely, palm oil mill effluent (POME) and sugarcane vinasse (Vn), with water hyacinth (WH) as co-substrate was carried out in two separate Anaerobic Suspended Growth Closed Bioreactors (ASGCBs) under thermophilic (55 °C) conditions. The highest chemical oxygen demand (COD) and soluble COD reduction in co-AD of POME-WH (78.61%, 78.86%) is slightly higher than co-AD of Vn-WH (75.75%, 78.24%). However, VFA reduction in co-AD of POME-WH (96.41%) is higher compared to co-AD of Vn-WH (85.94%). Subsequently, biogas production peaked at 13438 mL/day values and 16122 mL/day for co-AD of POME-WH and Vn-WH, respectively. However, the methane content was higher in the co-AD of POME-WH (72.04%) than in the co-AD of Vn-WH (69.86%). Growth yield (Y_G), maximum specific substrate utilization rate (r_x,max) and maximum specific biomass growth rate (μ_max) are higher in co-AD of POME-WH, as supported by the higher mixed liquor volatile suspended solids (MLVSS) and COD reduction efficiency compared to co-AD of Vn-WH. However, methane yield ([Formula: see text]) reported in the co-AD of POME-WH and Vn-WH are 0.2748 and 0.3112 L CH₄/g COD_reduction, respectively, which suggests that WH is a more suitable co-substrate for Vn compared to POME.

Effect of distillery sewage sludge addition on performance and bacterial community dynamics during distilled grain waste composting

This study evaluated the dynamics of physicochemical characteristics and bacterial communities during the co-composting of distilled grain waste (DGW) and distillery sewage sludge (SS), with DGW mono-composting as a control. Results showed that co-composting with SS significantly improved DGW degradation efficiency (61.38% vs. 54.13%) and end-product quality (seed germination index: 129.82% vs. 113.61%; N + P₂O₅ + K₂O: 9.08% vs. 5.28%), compared to DGW mono-composting. Microbial community analysis revealed that co-composting accelerated the bacterial community succession rate and enhanced the abundance of the phyla Proteobacteria, Firmicutes, Chloroflexi, and Deinococcota by 45.86%, 4.38%, 37.49%, and 15.29%, respectively. Network analysis showed that DGW-SS co-composting altered the interactions among the bacterial genera and improved bacterial community stability. Spearman correlation analysis indicated that the correlation between bacterial genera and environmental factors was more significant in DGW-SS co-composting. Therefore, co-composting of DGW and SS is a suitable strategy for the treatment of solid byproducts from spirit distilleries.

Comparison between thermophilic and mesophilic anaerobic digestion of waste activated sludge by combined NaOH-microwave pretreatment

The purpose of this study was to investigate the performance of the thermophilic and mesophilic anaerobic digestion process (TADP, MADP) fed with NaOH-microwave pretreated waste activated sludge. The experiment was conducted in anaerobic CSTR reactors. During this experiment, the reactors were stable in operation and were not inhibited by ammonia. The methane production and reduction of organic matters from MADP were less than those from TADP. The dewatering performance of mesophilic sludge was better than that of the thermophilic sludge. The experimental results showed that the continuous TADP and MADP were effective, when the reactors were fed with the waste activated sludge pretreated by NaOH-microwave. MADP was more suitable to combine the NaOH-MW pretreatment process than TADP.

Substrate-to-inoculum ratio drives solid-state anaerobic digestion of unamended grape marc and cheese whey

Inoculation dose is a key operational parameter for the solid-state anaerobic digestion (SS-AD) of lignocellulosic biomass, maximum methane recovery, and stable digester performance. The novelty of this study was the co-digestion of unamended full-strength grape marc and cheese whey for peak methane extraction at variable inoculation levels. An acclimatised digestate from a preceding anaerobic treatment was used as a downstream inoculum. The impact of inoculum size (wet weight) was evaluated at 0/10, 5/5, 7/3 and 9/1 substrate-to-inoculum (S/I) ratios, corresponding to an initial concentration of 20-30% total solids (TS) in digesters over 58 days at 45°C. The optimal 7/3 S/I produced the highest cumulative methane yield, 6.45 L CH4 kg-1 VS, coinciding with the lowest initial salinity at 11%; the highest volumetric methane productivity rate of 0.289±0.044 L CH4 LWork-1 d-1; the highest average COD/N ratio of 9.88; the highest final pH of 9.13, and a maximum 15.07% elemental carbon removal; for a lag time of 9.4 days. This study identified an optimal inoculation dose and opens up an avenue for the direct co-digestion of grape marc and cheese whey without requirements for substrate pretreatment, thus improving the overall bioenergy profile of the winery and dairy joint resource recovery operations.

C. vulgaris growth batch tests using winery waste digestate as promising raw material for biodiesel and stearin production

The recovery of high added value compound from waste stream is fundamental to keep biotechnological processes sustainable. In this study, anaerobic digestion of two highly produced organic waste was integrated with microalgae-based processes both to treat liquid digestate and recover high value compounds. Chlorella vulgaris growth was assessed for lipids accumulation and subsequent recovery, using two types of digestate: organic waste and sewage sludge digestate (DIG-OFMSW) and wine lees digestate (DIG-WL). Growth tests were carried out in batch mode and results showed a slightly higher final biomass concentration from DIG-WL (1.36 ± 0.09 g l^-1) compared to DIG-OFMSW (1.05 ± 0.13 g l^-1) and a clearly different lipids accumulation yield (28.86 ± 0.05% in DIG-WL compared to 6.1 ± 0.2% of DIG-OFMSW, on total solids). Lipid characterization showed a high oleic acid accumulation (69.52 ± 0.50%w/w in DIG-WL) that positively influence biodiesel properties and a low linolenic acids content (below 0.30%w/w) that comply with European law EN14214 for biodiesel (linolenic acid content lower than 12%w/w). In addition, due to the high concentration of palmitic and stearic acids detected at the end of test, this oil can be used as new substrate to produce stearin, normally produced from palm oil.

Dynamic Effect of Operational Regulation on the Mesophilic BioMethanation of Grape Marc

Wine production annually generates an estimated 11 million metric tonnes of grape marc (GM) worldwide. The diversion of this organic waste away from landfill and towards its use in the generation of renewable energy has been investigated. This study aimed to evaluate the effectiveness of operational parameters relating to the treatment regime and inoculum source in the extraction of methane from GM under unmixed anaerobic conditions at 35 °C. The study entailed the recirculation of a previously acclimated sludge (120 days) as downstream inoculum, an increased loading volume (1.3 kg) and a low substrate-to-inoculum ratio (10:3 SIR). The results showed that an incorporation of accessible operational controls can effectively enhance cumulative methane yield (0.145 m³ CH₄ kg⁻¹ VS), corresponding to higher amounts of digestible organics converted. The calculated average volumetric methane productivity equalled 0.8802 L CH₄ L_Work⁻¹ d⁻¹ over 33.6 days whilst moderate pollutant removal (43.50% COD removal efficiency) was achieved. Molecular analyses identified Firmicutes and Bacteroidetes phyla as core organisms for hydrolytic and fermentative stages in trophic relationships with terminal electron acceptors from the methane-producing Methanosarcina genus. Economic projections established that the cost-effective operational enhancements were sustainable for valorisation from grape marc by existing wineries and distilleries.

Methane production and active microbial communities during anaerobic digestion of three commercial biodegradable coffee capsules under mesophilic and thermophilic conditions

Biodegradable plastics market is increasing these last decades, including for coffee capsules. Anaerobic digestion, as a potential end-of-life scenario for plastic waste, has to be investigated. For this purpose, mesophilic (38 °C) and thermophilic (58 °C) anaerobic digestion tests on three coffee capsules made up with biodegradable plastic (Beanarella®, Launay® or Tintoretto®) and spent coffee (control) were compared by their methane production and the microbial communities active during the process. Mesophilic biodegradation of the capsules was slow and did not reach completion after 100 days, methane production ranged between 67 and 127 NL (CH₄) kg^-1 (VS). Thermophilic anaerobic digestion resulted in a better biodegradation and reached completion around 100 days, methane productions were between 257 and 294 NL (CH₄) kg^-1 (VS). The microbial populations from the reactors fed with plastics versus spent coffee grounds were significantly different, under both the mesophilic and the thermophilic conditions. However, the different biodegradable plastics only had a small impact on the main microbial community composition at a similar operational temperature and sampling time. Interestingly, the genus Tepidimicrobium was identified as a potential key microorganisms involved in the thermophilic conversion of biodegradable plastic in methane.

Analysis of uncontrolled phosphorus precipitation in anaerobic digesters under thermophilic and mesophilic conditions

This study compares the operation of mesophilic and thermophilic anaerobic digestion of sewage sludge and their effects in uncontrolled phosphorus precipitation. The research has been carried out using a pilot plant consisting of two digesters of 1.6 m³ working volume, treating the mixed sludge of Alzira WWTP (Valencia, Spain). The digesters were operated in parallel, at different conditions: mesophilic (38 ± 2.0°C) and thermophilic (55 ± 2.5°C) temperatures and organic loading rates (OLR) ranging from 1.1 to 1.7 kg volatile solids (VS) m^-3 d^-1 and different hydraulic retention times (HRT) 20, 15 and 12 days. Uncontrolled precipitation was evaluated through P, Mg and Ca mass balances in both digesters. The results revealed that up to 82% of the available P and 81% of the available Mg precipitated in the mesophilic digester at HRT = 20 days which suggests the possible formation of struvite in both digesters. At lower HRT (HRT = 12 days) Mg and Ca precipitation was negligible and P fixation has been attributed to the possible formation of iron phosphates or adsorption processes on solid surfaces.

Evaluation of Chlorella vulgaris and Scenedesmus obliquus growth on pretreated organic solid waste digestate

In this research Scenedesmus obliquus and Chlorella vulgaris growth was tested on digestate sludge obtained from the anaerobic co-digestion treatment of the organic fraction of municipal solid waste (OFMSW) together with waste activated sludge (WAS). Digestate was diluted 1:10 and tested in three batch experimental conditions: with no pre-treatments (noPT), after centrifugation (AC) and after filtration (AUF), in order to evaluate microalgae limiting growth factors. The best growth was obtained by C. vulgaris on digestate AC compared to S. obliquus, reaching 479 ± 31 cell million ml^-1 and 131 ± 12 cell million ml^-1 respectively. Ammonia removal evaluated in C. vulgaris and S. obliquus cultures was 99.2% ± 0.3 and 98.146% ± 0.008 in AC condition, respectively. Considering that AUF showed similar microalgae growth values, the digestate pretreatment for microalgae growth, could be limited to centrifugation.

Co-Digestion of Grape Marc and Cheese Whey at High Total Solids Holds Potential for Sustained Bioenergy Generation

At the end of fermentation, wine contains approximately 20% (w/v) of solid material, known as grape marc (GM), produced at a yield of 2 t/ha. Cheese manufacture produces cheese whey (CW), which is over 80% of the processed milk, per unit volume. Both waste types represent an important fraction of the organic waste being disposed of by the wine and dairy industries. The objective of this study was to investigate the bioenergy potential through anaerobic codigestion of these waste streams. The best bioenergy profile was obtained from the digestion setups of mixing ratio 3/1 GM/CW (wet weight/wet weight). At this ratio, the inhibitory salinity of CW was sufficiently diluted, resulting in 23.73% conversion of the organic material to methane. On average, 64 days of steady bioenergy productivity was achieved, reaching a maximum of 85 ± 0.4% CH₄ purity with a maximum cumulative methane yield of 24.4 ± 0.11 L CH₄ kg⁻¹ VS. During the fermentation there was 18.63% CODt removal, 21.18% reduction of conductivity whilst salinity rose by 36.19%. It can be concluded that wine and dairy industries could utilise these waste streams for enhanced treatment and energy recovery, thereby developing a circular economy.

Improving the Anaerobic Digestion of Wine-Industry Liquid Wastes: Treatment by Electro-Oxidation and Use of Biochar as an Additive

Wine lees have a great potential to obtain clean energy in the form of biogas through anaerobic digestion due to their high organic load. However, wine lees are a complex substrate and may likely give rise to instabilities leading to failure of the biological process. This work analysed the digestion of wine lees using two different approaches. First, electro-oxidation was applied as pre-treatment using boron-doped diamond-based electrodes. The voltage was 25 V and different treatment times were tested (ranging from 0.08 to 1.5 h) at 25 °C. Anaerobic digestion of wine lees was evaluated in batch tests to investigate the effect of electro-oxidation on biogas yield. Electro-oxidation exhibited a significant positive effect on biogas production increasing its value up to 330 L kg−1 of volatile solids after 1.5 h of treatment, compared to 180 L kg−1 of volatile solids measured from raw wine lees. As a second approach, the addition of biochar to the anaerobic digestion of wine lees was investigated; in the experimental conditions considered in the present study, the addition of biochar did not show any positive effect on anaerobic digestion performance.

Deciphering the effects of temperature on bio-methane generation through anaerobic digestion

Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300 mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55 °C) to produce methane (CH₄)-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH₄ generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1 μL CH₄ from 500 μL sample injected, obtained using 200 mg/L of phenol at 35 °C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35 °C followed by 55, 45, and 25 °C indicating 35 °C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35 °C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55 °C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real-time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temperature than the presence of phenol with the methanogens being the dominating species at 35 °C. The findings suggest that the planned operation of the ABR could be a promising choice for CH₄-enriched biogas and COD removal from phenolic wastewater.

Water and wastewater management for sustainable viticulture and oenology in South Portugal – a review

Assessing sustainability of the wine industry requires improved characterization of its environmental impacts, namely in terms of water use. Therefore, quantification of water inputs and wastewater (WW) outputs is needed to highlight inefficiencies in wine production and related consequences for the environment. Water use and WW generation in irrigated viticulture and oenology remains insufficiently quantified for dry Mediterranean regions (e.g. South Portugal). This paper is focused on wine production under warm and dry climate conditions in the winegrowing region of Alentejo (South Portugal). This region experiences increasingly dry conditions, while the irrigated area keeps expanding, which puts exacerbates the pressure on existing local and regional water resources. Additionally, more erratic variation in climate conditions and the tendency for increasingly extreme climate events (e.g. heat waves) pose more challenges to Alentejo’s wine sector. We conclude that quantitative information on water use and management is not always easy to obtain or access, which hinders improved strategies and/or policies for water use at farm, winery and region-level. Up-to-date statistics and robust metrics can help to better characterize water use and WW flows for Alentejo’s wine region, while optimizing management in vineyards and wineries, in companies and region-wide. The paper is focused on a “Farm-Winery” scenario, which is the most common in South Portugal’s wine sector

Organic wastes as alternative sources of phosphorus for plant nutrition in a calcareous soil

Recycled organic wastes (OW) can be a valuable P source; however, their P-fertilising capacity is still poorly known. In this study, we selected three anaerobic digestates [wastewater sludge (D₁), winery sludge (D₂), and bovine-slurry/energy crops (BD)] and two animal effluents [bovine slurry (BS) and swine slurry (SS)] to test their P-release and P-fertilising capacities via sequential chemical extraction (SCE), X-ray diffraction (XRD), and ³¹P-nuclear magnetic resonance (³¹P NMR). Subsequently, the three digestates (30 mg P kg^-1 of soil) were compared for the release of Olsen-P during a soil incubation and for plant-P apparent recovery (ARF) in a pot experiment using ryegrass (112 days) in a soil with poorly available-P (Olsen-P < 5 mg kg^-1), under a non-limiting N environment. The amount of labile-P (H₂O + NaHCO₃), as determined from SCE, related well to the Olsen-P following OW addition to the soil. It was shown via ³¹P NMR spectroscopy that orthophosphate was the leading P-form in highly P-releasing OW. The amount of labile-P, however, was affected by soil adsorption, thereby reducing plant-P uptake. The plant-P ARF (%) showed that the recycled P-sources were clustered in highly (BD and SS: ≈20%), intermediately (D₁ and BS: ≈15%), and poorly performing OWs (D₂: ≈10%) vs. chemical P-source (P-chem: 20%). Therefore, only BD and SS were effective alternatives to P-chem; however, the other OW can be efficient P-sources in soils with higher Olsen-P. Thus, crop fertilisation can be tailored on a P-basis by SCE as a function of soil adsorption capacity and on an N-basis according to the demand.

Assessment of the Health Risk Induced by Accumulated Heavy Metals from Anaerobic Digestion of Biological Sludge of the Lettuce

Heavy metals are a group of pollutants in biological sludge. Many agencies regulated guidelines for heavy metal concentrations for various applications of sludge such as agricultural application. In this study, we tried to determine heavy metal fate after anaerobic digestion. Additionally, we determined the bioaccumulation rate of heavy metals in lettuce cultivated on a sludge-applied land. Heavy metal (As, Pb, Hg, Cd) contents of solid and liquid parts of raw and anaerobically digested sludge were separately measured by ICP-OES. For this purpose, the samples were digested using nitric acid, hydrochloric acid, and boric acid. Then, the raw and anaerobically digested sludge were used for cultivation of lettuce in separate farms. The heavy metal concentrations in the harvested lettuce were measured by the same procedure. The results showed that the main part of heavy metals in the raw sludge was in the liquid part (67%), while, the main part of heavy metals in the anaerobically digested samples was in the solid part of the sludge. Because of washout of dissolved heavy metals in the liquid part of the sludge, the lettuce cultivated by anaerobically digested sludge had higher content of the heavy metals in comparison to that of the lettuce cultivated by the raw sludge. This study showed that application of anaerobically digested sludge can increase the bioaccumulation rate of heavy metals in the crops and induce more human health risk.

Influence of Added Nutrients and Substrate Concentration in Biohydrogen Production from Winery Wastewaters Coupled to Methane Production

Winery wastewaters are acidic effluents with high content of organic matter and nutrients. Different initial values of chemical oxygen demand (COD), ranging from 4 to 50 g L^-1, were tested in batch assays to evaluate the fermentative hydrogen production followed by a methane production step. The influence of adding a typical nutrient solution for hydrogen production was investigated. Nutrients include N-NH₄, Mg, Fe, Co, Mn, I, Ni, and Zn. The best hydrogen production potential was obtained at a COD of 50 g L^-1 without nutrient addition. This condition produced 528 mL H₂ L^-1. At a COD ≥ 35 g L^-1, tests with only WW had a hydrogen potential 1.6 to 1.9 times higher than did tests where nutrients were added. The use of added nutrients reduced the hydrogen production by producing additional reduced acids, such as propionate and valerate. In a second stage, biomethane potential was evaluated using the effluent of a selected condition from hydrogen production tests. The methane production reached values of 207 ± 2.2 mL CH₄ g^-1 COD at 10 g COD L^-1. The COD affected the specific methane production. The results of this study demonstrated the potential of winery effluents as a substrate for sequential hydrogen and methane production to increase the energy recovery from this effluent, with a maximum energetic yield and productivity of 7.15 kJ gCOD^-1 and 11.51 kJ d^-1.

The microbial community of a biofilm contact reactor for the treatment of winery wastewater

AIMS

To utilize a three-tiered approach to provide insight into the microbial community structure, the spatial distribution and the metabolic capabilities of organisms of a biofilm in the two towers of a high-rate biological contact reactor treating winery wastewater.

METHODS AND RESULTS

Next-generation sequencing indicated that bacteria primarily responsible for the removal of carbohydrates, sugars and alcohol were more abundant in tower 1 than tower 2 while nitrifying and denitrifying bacteria were more abundant in tower 2. Yeast populations differed in each tower. Fluorescent in situ hybridization coupled with confocal microscopy showed distribution of organisms confirming an oxygen gradient across the biofilm depth. The Biolog system (ECO plates) specified the different carbon-metabolizing profiles of the two biofilms.

CONCLUSIONS

The three-tiered approach confirmed that the addition of a second subunit to the bioreactor, expanded the treatment capacity by augmenting the microbial and metabolic diversity of the system, improving the treatment scope of the system.

SIGNIFICANCE AND IMPACT OF THE STUDY

A three-tiered biofilm analysis provided data required to optimize the design of a bioreactor to provide favourable conditions for the development of a microbial consortium, which has optimal waste removal properties for the treatment requirements at hand.