Final Digestate Research Articles

Selenium-Chelating Peptide Derived from Wheat Gluten: In Vitro Functional Properties.

The efficacy of selenium-chelating polypeptides derived from wheat protein hydrolysate (WPH-Se) includes enhancing antioxidant capacity, increasing bioavailability, promoting nutrient absorption, and improving overall health. This study aimed to enhance the bioavailability and functional benefits of exogenous selenium by chelating with wheat gluten protein peptides, thereby creating bioactive peptides with potentially higher antioxidant capabilities. In this study, WPH-Se was prepared with wheat peptide and selenium at a mass ratio of 2:1, under a reaction system at pH 8.0 and 80 °C. The in vitro antioxidant activity of WPH-Se was evaluated by determining the DPPH, OH, and ABTS radical scavenging rate and reducing capacity under different conditions, and the composition of free amino acids and bioavailability were also investigated at various digestion stages. The results showed that WPH-Se possessed significant antioxidant activities under different conditions, and DPPH, OH, and ABTS radical scavenging rates and reducing capacity remained high at different temperatures and pH values. During gastrointestinal digestion in vitro, both the individual digestate and the final digestate maintained high DPPH, OH, and ABTS radical scavenging rates and reducing capacity, indicating that WPH-Se was able to withstand gastrointestinal digestion and exert antioxidant effects. Post-digestion, there was a marked elevation in tryptophan, cysteine, and essential amino acids, along with the maintenance of high selenium content in the gastrointestinal tract. These findings indicate that WPH-Se, with its enhanced selenium and amino acid profile, serves as a promising ingredient for dietary selenium and antioxidant supplementation, potentially enhancing the nutritional value and functional benefits of wheat gluten peptides.

The dynamic duo of bioremediation: A case study on the efficacy of Penicellium spp and Bacillus spp

Anaerobic digestion (AD) is a biological process in which microorganisms break down organic matter with biogas. It is a series of chemical reactions during which organic material is decomposed through the metabolic pathways of naturally occurring microorganisms in an oxygen-depleted environment. Recently, anaerobic digestion (AD) has been recognized as one of the best options for treating food waste/cattle rumen mixtures since it results in two valuable final products, biogas and digestate that may be utilized for electricity production and as soil fertilizer, respectively. However, putting the digestate directly into the soil may bring environmental concerns because they contain certain pathogens and heavy metals which could be detrimental to plant and human health when consumed as food. The experimental study carried out in this project has shown that heavy metals contained in food waste/cattle rumen mixtures can be removed using indigenous microbes (Bacillus spp and Penicellium spp). From the results of the experiment carried out, it was deduced that bioremediation is effective in removing heavy metals from AD sludge. This finding is of special importance because this means that digestate can be freely used as manure without worrying about plants absorbing dangerous heavy metals which are more than their allowable limit from the soil. The use of indigenous microbes is cheap since they are readily available in the digestate.

Anaerobic Digestion of Poultry Droppings in Semi-Continuous Mode and Effect of Their Co-Digestion with Physico-Chemical Sludge on Methane Yield

Poultry waste is rich in organic matter, which allows its treatment by the process of anaerobic digestion (AD) to reinforce economic and environmental green strategies. The aim of this study is to assess the technical feasibility of poultry waste AD in semi-continuous mode and to intensify methane production by co-digestion with physico-chemical sludge, i.e., the product of the primary treatment of wastewater after the slaughtering process. First, the AD of poultry droppings is conducted in a continuous stirred anaerobic digester (CSAD) at 37 °C. A volume of 0.791 and 0.623 Nm3·Nm−3 reactor·days−1 of biogas and methane, respectively, were produced during the entire process stabilization period. Biochemical characterization of the substrate and the final digestate show high reduction rates of the biochemical fractions, which corroborates with methane yield. In addition, the co-digestion of poultry droppings with two different ratios of physico-chemical sludge (20% and 40% added sludge considering the amount of volatile solids) shows an increase in methane production versus droppings alone, with a higher increase of 54% with a sludge ratio of 40%. Altogether, these promising results were obtained in stable processes, highlighting the pertinence of our study.

COMPARATIVE EVALUATION OF THE CHEMICAL COMPOSITION OF BIOGAS DIGESTATE SLURRIES UNDER VARYING FEEDSTOCKS

Biogas production is increasingly considered a good source of clean energy and Biofertilizers in the form of digestate slurry. This study sought to characterize biogas digester slurries under varying Feedstocks and provide information useful for assessing the potential impact of their usage as organic fertilizer on crop productivity and environment. The study was informed by the need to allow agricultural scientists determine how individual biogas feeds affect the composition of the final digestate and hence the impact the digestates could have. Digestates from human waste, livestock waste, and abattoir waste feedstock were sampled for the study. The pellets from the samples were then analyzed using Energy Dispersive X-ray Fluoroscopy (EDXRF) spectroscopy for elemental components. After the requisite statistical analysis, the human waste digestate had the highest concentration values for most elements. In human waste, essential elements were determined at 40600 ± 2000, 19000 ± 1140, 1300 ± 400, 200 ± 30, 900 ± 260 ppm for Ca, Fe, Mn, Zn and Cu respectively, as compared to Ca (26400 ± 1400), Fe (9500 ± 440), Mn (820 ± 190), Zn (180 ± 40), Cu (360 ± 70), in livestock waste. In abattoir waste, the mean content was 49500 ± 4100 for Ca, 15220 ± 1350 for Fe, 1090 ± 90 for Mn, 200 ± 50 for Zn and 140 ± 50 for Cu. Potentially toxic elements Hg and Cd were determined below detection limits, while Pb concentrations were highest in human waste at 20.81 ppm. The high amounts are associated with the micro industrial activities in Kibera. Therefore, human wastes digestates might be the best nutrient supplement but is the most probable threat to environment. Indeed, an unchecked Bioaccumulation of the other elements might be counterproductive as well. For agronomists, crops need matching with digestates from which they would benefit the most, given unique crop requirements. 

Anaerobic digestion of organic waste allows recovering energy and enhancing the subsequent bioplastic degradation in soil

The bioplastics within organic municipal waste are a critical component for the future of waste management with particular reference to the quality of the final products, i.e., digestate and compost. Moreover, to promote a circular economy they need to be recovered to produce new material and/or energy. This study compared polylactic acid (PLA) and starch based (SB) materials which were subjected to anaerobic digestion (AD) treatments producing biomethane, and the fate of residual bioplastics when incubated in soil were then evaluated. Results indicated that AD processes affected both PLA and SB characteristics, influencing their subsequent degradation in soil. Comparative material balance, considering the whole process, indicated that SB bioplastics degraded by 50%, while PLA achieved overall degradation by 70% when thermophilic AD was applied. The insights obtained contribute to understanding the fate of bioplastics and confirmed the role of AD as method for waste valorization in a circular economy perspective.

Occurrence and risk assessment of trace organic contaminants and metals in anaerobically co-digested sludge

Anaerobic co-digestion of sludge increases biogas production and maintains anaerobic digestion stability. However, it is unclear whether the addition of co-substrates may increase the concentration of trace organic contaminants (TrOCs) and metals, limiting potential resource recovery opportunities when applied to agricultural land. This study explored the occurrence of 20 TrOCs and 18 metals in wastewater sludge anaerobically co-digested with beverage rejects (cola, beer and juice) and food wastes. TrOCs results showed that cola reject caused an accumulation of caffeine in final digestate. Bisphenol A also significantly increased in food waste co-digestion when compared with the mono-digestion (control). No significant difference in TrOCs was observed in the juice reject co-digestion. Analysis of the metal composition revealed a significant increase in Cr and Al in juice reject co-digested sludge. While restaurant food waste increased concentrations of K and Ca, both of which may be beneficial when applied to land. All metals in this study were below the maximum permissible concentrations specified for agricultural land use in Australia. Environmental risk assessment of sludge when used as soil fertiliser, showed that caffeine, diuron, triclocarban, triclosan, Cu and Zn exhibited high risks, with the largest risk quotient (RQ) posed by caffeine. Estrone and naproxen implied medium risks, and ibuprofen implied a high risk except for the co-digestion using cola reject (RQ = 0.9, medium risk). The results emphasise the importance for wastewater utility operators to understand the impact of co-substrate selection on the quality of sludge to minimise environmental risk from the use of biosolids on agricultural land.

Chemometric tools in the optimization of a microwave-assisted digestion procedure for guarana-based drink samples and data analysis from elemental, caffeine, and epicatechin contents

In this work, a method was developed for the determination of Na, K, Ca, Mg, P, S, Fe, Zn, Mn, and Cu by ICP OES and caffeine and epicatechin by HPLC-DAD in industrialized guarana-based beverages. The acid digestion in microwave oven was optimized by constrained mixture design. The optimum volumes found for the reagents were 2.60 mL (HNO3), 1.80 mL (H2O2), and 0.60 mL (HCl) for a final volume of 10 mL, resulting in a final digestate with residual acidity of 0.8 mol L−1 and 9% for residual carbon content. The detection limits found for the studied elements were between 0.0010 and 0.050 mg L−1. Precision (%RSD) was always below 6%. Accuracy was assessed by analyzing a certified reference material and addition and recovery tests. PCA and HCA were applied to caffeine, epicatechin and elemental concentrations aiming to evidence latent information.

Effect of Animal Waste Based Digestate Fertilization on Soil Microbial Activities, Greenhouse Gas Emissions and Spring Wheat Productivity in Loam and Sandy Loam Soil

The increasing quantities of organic residues are becoming one of the most important problems for climate change mitigation. Sustainable utilization technologies are required to minimize the effect of recycling on the environment. Nevertheless, treated residues should be part of the circular bioeconomy. One of the most promising processes is the biogas system, with the final products biogas and digestate, which contain valuable nutrients and are therefore suitable as agricultural fertilizers. However, there is lack of research data on the effectiveness of digestate on environmental factors including soil quality as well as crop productivity and quality. In this study, we compare the roles of different digestates (chicken manure digestate, cow manure digestate, and pig manure digestate) on spring wheat productivity, soil microbial activities, and greenhouse gas emissions in loam and sandy loam soil under controlled climate conditions. The liquid digestate applied was equivalent to 170 kg N ha−1 of total N presented. Overall, results showed that the two soil types responded differently to the addition of the digestates, and the benefits depended on soil characteristics as well as on the type of the digestate applied. There was a higher effect on soil microbial activity in sandy loam soil compared to that of loam soil. Chicken manure digestate had the highest value of dehydrogenase activity and soil microbial biomass C of 9.23 µg TPFg−1 h−1 and 175.6 µg g−1 across the two soil types. CO2 and N2O emissions were moderately higher in loam soil when compared to that of sandy loam soil. The highest CO2 peak emission at 0.0107 µg ha−1 h−1 occurred in pig manure digestate in the sandy loam soil, and regular peak patterns observed in loam soil fertilized with pig digestate manure. Chicken manure digestate had the highest peak emissions across both soil types at 0.007950 mg ha−1 h−1 and 0.5667 mg ha−1 h−1 in the loam and sandy loam soil, respectively. The biomass yield varied across the soil types irrespective of the digestate applied. The agricultural benefits of digestates in different receiving soil ecosystems supplying essential nutrients for crop productivity, coupled with its environmental benefits, makes it an encouraging prospect in temperate climate zones.

Biochemical Methane Potential of Cork Boiling Wastewater at Different Inoculum to Substrate Ratios

The present study evaluates the digestion of cork boiling wastewater (CBW) through a biochemical methane potential (BMP) test. BMP assays were carried out with a working volume of 600 mL at a constant mesophilic temperature (35 °C). The experiment bottles contained CBW and inoculum (digested sludge from a wastewater treatment plant (WWTP)), with a ratio of inoculum/substrate (Ino/CBW) of 1:1 and 2:1 on the basis of volatile solids (VSs); the codigestion with food waste (FW) had a ratio of 2/0.7:0.3 (Ino/CBW:FW) and the codigestion with cow manure (CM) had a ratio of 2/0.5:0.5 (Ino/CBW:CM). Biogas and methane production was proportional to the inoculum substrate ratio (ISR) used. BMP tests have proved to be valuable for inferring the adequacy of anaerobic digestion to treat wastewater from the cork industry. The results indicate that the biomethane potential of CBWs for Ino/CBW ratios 1:1 and 2:1 is very low compared to other organic substrates. For the codigestion tests, the test with the Ino/CBW:CM ratio of 2/0.7:0.3 showed better biomethane yields, being in the expected values. This demonstrated that it is possible to perform the anaerobic digestion (AD) of CBW using a cosubstrate to increase biogas production and biomethane and to improve the quality of the final digestate.

The effect of field application of food‐based anaerobic digestate on earthworm populations

AbstractIn general, farming systems that provide the greatest organic matter returns to the soil support the highest earthworm populations and typically the application of organic materials will increase earthworm numbers because of an abundance of food. There has been limited work on the effects of digestate applications on earthworm populations with most focus on the short‐term effects of digestate from manure or crop‐based feedstocks, not from food wastes. To address this gap in current knowledge, the objective of this study was to assess the impact of repeated food‐based digestate applications on earthworm populations/biomass in both the short term (c. 6 months after digestate application) and longer term (2 years later) in comparison with other commonly used inputs (manufactured nitrogen‐N fertilizer, compost and livestock manures). This multi‐site field experiment has shown that the application of food‐based digestate at application rates above current good practice can have a short‐term, negative impact on earthworm numbers under certain conditions. Six months after the final digestate addition, earthworm numbers were 32%–60% lower than following the additions of other organic materials at four of the seven sites investigated. A combination of high ammonium/low organic matter loadings and soil compaction most likely explained the observed effects.

Anaerobic Digestion of Mycotoxin-Contaminated Wheat: Effects on Methane Yield and Contamination Level

In this study, biogas and biomethane production during mesophilic anaerobic digestion of wheat substrates coming from national crops and naturally contaminated with deoxynivalenol (DON) and/or T-2/HT-2 toxins was investigated. Biochemical methane potential (BMP) tests of both wholewheat flour and of the main milling fractions were carried out to assess the effect on the concentration of mycotoxins on the anaerobic biological process and their residual presence in the final digestate. The good methane average production achieved (337.0 ± 24.5 NL CH4/kg VS) was substantially comparable with the yields gained from similar biomasses at mesophilic conditions. Moreover, an effective reduction (60.7–100%) of DON concentration was obtained in all the tested substrates (range of contamination in the samples, 368–12,916 μg/kg) whereas the sum of T-2 and HT-2 toxin levels in digestates was always <LOQ in all substrates analyzed (range of contamination in the samples, 5–65 μg/kg). The results supported an alternative exploitation of “non-compliant” lots of cereals destined for human consumption and/or animal feed which could represent a concrete benefit for agricultural producers. Anaerobic digestion could be employed as an effective tool to recover large amounts of trichothecene-contaminated cereals in an environmentally and economically sustainable way.

Ranking hazards pertaining to human health concerns from land application of anaerobic digestate

Anaerobic digestion (AD) has been identified as one of the cleanest producers of green energy. AD typically uses organic materials as feedstock and, through a series of biological processes, produces methane. Farmyard manure and slurry (FYM&S) are important AD feedstock and are typically mixed with agricultural waste, grass and/or food wastes. The feedstock may contain many different pathogens which can survive the AD process and hence also possibly be present in the final digestate. In this study, a semi-quantitative screening tool was developed to rank pathogens of potential health concern emerging from AD digestate. A scoring system was used to categorise likely inactivation during AD, hazard pathways and finally, severity as determined from reported human mortality rates, number of global human-deaths and infections per 100,000 populations. Five different conditions including mesophilic and thermophilic AD and three different pasteurisation conditions were assessed in terms of specific pathogen inactivation. In addition, a number of scenarios were assessed to consider foodborne incidence data from Ireland and Europe and to investigate the impact of raw FYM&S application (without AD and pasteurisation). A sensitivity analysis revealed that the score for the mortality rate (S3) was the most sensitive parameter (rank coefficient 0.49) to influence the final score S; followed by thermal inactivation score (S1, 0.25) and potential contamination pathways (S2, 0.16). Across all the scenarios considered, the screening tool prioritised Cryptosporidium parvum, Salmonella spp., norovirus, Streptococcus pyogenes, enteropathogenic E. coli (EPEC), Mycobacterium spp., Salmonella typhi (followed by S. paratyphi), Clostridium spp., Listeria monocytogenes and Campylobacter coli as the highest-ranking pathogens of human health concern resulting from AD digestate in Ireland. This tool prioritises potentially harmful pathogens which can emerge from AD digestate and highlights where regulation and intervention may be required.

Advances in combined enzymatic extraction of ferulic acid from wheat bran

Wheat bran could be utilised as feedstock for innovative and sustainable biorefinery processes. Here, an enzymatic hydrolysis process for ferulic acid (FA) extraction was optimised step by step for total wheat bran (Tritello) and then also applied to the outer bran layer (Bran 1). Proteins, reducing sugars, total phenols and FA were quantified. The highest FA yields (0.82–1.05 g/kg bran) were obtained either by rehydrating the bran by autoclaving (Tritello) or by steam explosion (Bran 1) using a bran/water ratio of 1:20, followed by enzymatic pre-treatment with Alcalase and Termamyl, to remove protein and sugars, and a final enzymatic hydrolysis with Pentopan and feruloyl esterase to solubilise phenol. FA was recovered from the final digestate via solid phase extraction. A 40-fold scale-up was also performed and the release of compounds along all the process steps and at increasing incubation times was monitored. Results showed that FA was initially present at a minimum level while it was specifically released during the enzymatic treatment. In the final optimized process, the FA extraction yield was higher than that obtained with NaOH control hydrolysis while, in comparison with other FA enzymatic extraction methods, fewer process steps were required and no buffers, strong acid/alkali nor toxic compounds were used. Furthermore, the proposed process may be easily scaled-up, confirming the feasibility of wheat bran valorisation by biorefinery processes to obtain valuable compounds having several areas of potential industrial exploitation.

Influence of feed/inoculum ratios and waste cooking oil content on the mesophilic anaerobic digestion of food waste

Information on the anaerobic digestion (AD) of food waste (FW) with different waste cooking oil contents is limited in terms of the effect of the initial substrate concentrations. In this work, batch tests were performed to evaluate the combined effects of waste cooking oil content (33–53%) and feed/inoculum (F/I) ratios (0.5–1.2) on biogas/methane yield, process stability parameters and organics reduction during the FW AD. Both waste cooking oil and the inoculation ratios were found to affect digestion parameters during the AD process start-up and the F/I ratio was the predominant factor affecting AD after the start-up phase. The possible inhibition due to acidification caused by volatile fatty acids accumulation, low pH values and long-chain fatty acids was reversible. The characteristics of the final digestate indicated a stable anaerobic system, whereas samples with F/I ratios ranging from 0.8 to 1.2 display higher propionic and valeric acid contents and high amounts of total ammonia nitrogen and free ammonia nitrogen. Overall, F/I ratios higher than 0.70 caused inhibition and resulted in low biogas/methane yields from the FW.

INCREASING METHANE PRODUCTION RATE THROUGH ANAEROBIC DIGESTION OF ACTIVATED HORSE DUNG BY CONVENTIONAL THERMAL AND MICROWAVE PRETREATMENTS

Conventional thermal, microwave and combination of thermal-microwave pretreatments were performed through anaerobic digestion of activated horse dung for improving biogas production and methane production rate. Evaluation of the different pretreatments was conducted in terms of daily and accumulative biogas productions and methane production rate. Final residual digestate from the digestion was analyzed as a rich fertilizer of macro and micro nutrients (Nitrogen, Phosphorus, Potassium and Calcium). Results indicated that biogas pretreatment would be a rapid method for enhancing biogas and methane production compared to without pretreatment. Conventional thermal pretreatment at 185oC in combination with microwave pretreatment of 8 minutes gave the highest values of daily biogas production of 2175 mL/day, accumulated biogas production of 29757 mL, methane percentage of 83 % and the highest concentration of nitrogen in the final residual digestate of 5.15 % as a rich fertilizer.

Effect of drying, composting and subsequent impurity removal by sieving on the properties of digestates from municipal organic waste

The application of organic soil amendments is a common measure to prevent structural degradation of agricultural soils and to maintain and improve long-term soil fertility. Solid residues from anaerobic digestion of municipal organic waste (MOW) are rich in nutrients and organic matter and have a promising potential to be used as soil amendment. However, no study has related amendment properties of MOW digestate of one origin to different treatment procedures. We therefore investigated the impact of drying, composting and sieving on final digestate properties and specifically nutrient availability and heavy metal and carbon elution.Samples were provided by a semi-industrial two-stage biogas plant with dry fermentation of MOW. Results confirm that in comparison to drying, composting of MOW digestates leads to a significant increase of K, P, Mg, Ca, Cd and Cr in the digestates. Sieving of composted digestates showed that heavy metals are not evenly distributed and that heavy metal concentration in the digestate increases with decreasing mesh sizes (highest concentrations in the fractions <1 mm). Although the element concentration is higher in composted batches, the water-extractability of nutrients, heavy metals and carbon is significantly lower from composted over dried digestates. A significant correlation was found between the dissolution of Zn, Ni, Ca and Mg and pH of eluate as well as dissolved organic carbon (DOC) release (R > 0.7, p<0.05). Results confirm that the extent of carbon elution depends on the degradation rate of digestates. DOC may therefore be a good measure to evaluate digestate stability and to decide on treatment measures.

Free nitrous acid pre-treatment of waste activated sludge enhances volatile solids destruction and improves sludge dewaterability in continuous anaerobic digestion

Previous work has demonstrated that pre-treatment of waste activated sludge (WAS) with free nitrous acid (FNA i.e. HNO2) enhances the biodegradability of WAS, identified by a 20–50% increase in specific methane production in biochemical methane potential (BMP) tests. This suggests that FNA pre-treatment would enhance the destruction of volatile solids (VS) in an anaerobic sludge digester, and reduce overall sludge disposal costs, provided that the dewaterability of the digested sludge is not negatively affected. This study experimentally evaluates the impact of FNA pre-treatment on the VS destruction in anaerobic sludge digestion and on the dewaterability of digested sludge, using continuously operated bench-scale anaerobic digesters. Pre-treatment of full-scale WAS for 24 h at an FNA concentration of 1.8 mg NN/L enhanced VS destruction by 17 ± 1% (from 29.2 ± 0.9% to 34.2 ± 1.1%) and increased dewaterability (centrifuge test) from 12.4 ± 0.4% to 14.1 ± 0.4%. Supporting the VS destruction data, methane production increased by 16 ± 1%. Biochemical methane potential tests indicated that the final digestate stability was also improved with a lower potential from FNA treated digestate. Further, a 2.1 ± 0.2 log improvement in pathogen reduction was also achieved. With inorganic solids representing 15–22% of the full-scale WAS used, FNA pre-treatment resulted in a 16–17% reduction in the volume of dewatered sludge for final disposal. This results in significantly reduced costs as assessed by economic analysis.

Low-temperature hydrothermal pretreatment followed by dry anaerobic digestion: A sustainable strategy for manure waste management regarding energy recovery and nutrients availability

This study evaluated the feasibility of low-temperature hydrothermal (HT) pretreatment for improving dry anaerobic digestion (AD) of swine manure (SM) and nutrient elements reclamation, with specific goals to minimize the drawbacks of conventional HT process including high energy consumption, inhibitory compounds formation and unfavorable pH/alkalinity decrease. Pretreatment at 110–130°C for holding 30min increased the soluble organic carbon (SOC) concentration in SM by 13–26%. After being mixed with inocula, the pretreated SM was applied for dry AD tests successfully without initial pH adjustment, achieving a CH4 yield of 280.18–328.93ml/g-VSfed (14–34% increase compared to that from raw SM). Energy assessment indicated a positive net gain of 0.95kJ/g-VS by adopting HT pretreatment at 130°C. Except for increment in CH4 yield, low-temperature HT pretreatment also promoted organic-N mineralization, increasing N fractions in the digestate available for plants. After 70days’ dry AD, a high ammonia-N to total nitrogen (TN) ratio of 71% was obtained for the SM sample pretreated at 130°C, in sharp contrast to that of 38% in raw SM. P bioavailability in the final digestate was not greatly affected by the HT pretreatment since the labile organics were mostly degraded after AD, in which P existing forms were influenced by the multivalent metals content in SM. Overall, 23–27% of the total P was potentially bioavailable in all digestates.

Synergistic effect of co-digestion to enhance anaerobic degradation of catering waste and orange peel for biogas production.

Catering waste and orange peel were co-digested using an anaerobic digestion process. Orange peel is difficult to degrade anaerobically due to the presence of antimicrobial agents such as limonene. The present study aimed to examine the feasibility of anaerobic co-digestion of catering waste with orange peel to provide the optimum nutrient balance with reduced inhibitory effects of orange peel. Batch experiments were conducted using catering waste as a potential substrate mixed in varying ratios (20-50%) with orange peel. Similar ratios were followed using green vegetable waste as co-substrate. The results showed that the highest organic matter degradation (49%) was achieved with co-digestion of catering waste and orange peel at a 50% mixing ratio (CF4). Similarly, the soluble chemical oxygen demand (sCOD) was increased by 51% and reached its maximum value (9040 mg l-1) due to conversion of organic matter from insoluble to soluble form. Biogas production was increased by 1.5 times in CF4 where accumulative biogas was 89.61 m3 t-1substrate compared with 57.35 m3 t-1substrate in the control after 80 days. The main reason behind the improved biogas production and degradation is the dilution of inhibitory factors (limonene), with subsequent provision of balanced nutrients in the co-digestion system. The tCOD of the final digestate was decreased by 79.9% in CF4, which was quite high as compared with 68.3% for the control. Overall, this study revealed that orange peel waste is a highly feasible co-substrate for anaerobic digestion with catering waste for enhanced biogas production.

Enhancing anaerobic digestion of poultry blood using activated carbon

The potential of using anaerobic digestion for the treatment of poultry blood has been evaluated in batch assays at the laboratory scale and in a mesophilic semi-continuous reactor. The biodegradability test performed on residual poultry blood was carried out in spite of high inhibitory levels of acid intermediaries. The use of activated carbon as a way to prevent inhibitory conditions demonstrated the feasibility of attaining anaerobic digestion under extreme ammonium and acid conditions. Batch assays with higher carbon content presented higher methane production rates, although the difference in the final cumulative biogas production was not as sharp. The digestion of residual blood was also studied under semi-continuous operation using granular and powdered activated carbon. The average specific methane production was 216±12mL CH4/g VS. This result was obtained in spite of a strong volatile fatty acid (VFA) accumulation, reaching values around 6g/L, along with high ammonium concentrations (in the range of 6–8g/L). The use of powdered activated carbon resulted in a better assimilation of C3-C5 acid forms, indicating that an enhancement in syntrophic metabolism may have taken place. Thermal analysis and scanning electron microscopy (SEM) were applied as analytical tools for measuring the presence of organic material in the final digestate and evidencing modifications on the carbon surface. The addition of activated carbon for the digestion of residual blood highly improved the digestion process. The adsorption capacity of ammonium, the protection this carrier may offer by limiting mass transfer of toxic compounds, and its capacity to act as a conductive material may explain the successful digestion of residual blood as the sole substrate.