Disposal Of Digestate Research Articles

Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach

While several researchers have investigated the anaerobic digestion (AD) of textile wastewater for dye degradation, their studies suffer from lower biogas productivity due to substrate inhibition and the occurrence of secondary pollution from digestate disposal. Hence, this study focuses on using the extract of wheat straw (WS) as a co-substrate to facilitate the dye AD process, followed by recycling the digestate sludge for biochar production. In the first study, the batch digesters were operated at different dye wastewater (DW)/WS ratios (0–50% v/v), substrate-to-inoculum ratio of 0.28–0.50 g/g, pH 7.0 ± 0.2, and 37 °C. The digester operated at a DW/WS fraction of 65/35% (v/v) showed the best chemical oxygen demand (COD) removal efficiency of 68.52 ± 3.40% with bio-CH4 of 270.52 ± 19.14 mL/g CODremoved. About 52.96 ± 3.61% of the initial COD mass was converted to CH4, avoiding inhibition caused by volatile fatty acid (VFA) accumulation. In the second experiment, the dry digestate was thermally treated at 550 °C for 2 h under an oxygen-deprived condition, yielding 0.613 ± 0.031 g biochar/g. This biochar exhibited multiple functional groups, mineral contents, and high stability (O/C = 0.193). The combined digestion/pyrolysis scenario treating 35 m3/d (106.75 kg COD/d) could maintain profits from pollution reduction, biogas, biochar, and carbon trading, obtaining a 6.5-year payback period.

Flexibilization or biomethane upgrading? Investment preference of German biogas plant operators for the follow‐up of guaranteed feed‐in tariffs

AbstractThis article reports the results of a discrete choice experiment with 183 German biogas plant operators designed to elicit the respondents' plans for biogas utilization pathways after the end of guaranteed feed‐in tariffs. Participants could choose between ‘flexibilization’ for demand‐based electricity generation and conversion to biomethane upgrading for direct feed‐in into the natural gas grid. A binomial logit model revealed a 37% probability of switching to biomethane upgrading. These plants are characterized by higher capacities, several involved shareholders, secured succession, costly digestate disposal and belonging to the upper performance quartile. Mixed logit estimations conducted separately for the two investment concepts revealed a very high overall willingness to invest: 71% for flexibilization and 82% for biomethane upgrading. The respondents demand a return on investment of 19% for flexibilization and 26% for biomethane upgrading. Within the flexibilization, twofold overbuilding (installed capacity equals 2 times the rated power) is clearly preferred to fivefold overbuilding. For the biomethane upgrading, private ownership of the upgrading plant is preferred to a joint investment in a central upgrading facility. Limiting the use of energy crops reduces the propensity to invest in both models, while a longer utilization period enhances it. The respondents consider lack of planning reliability as the biggest obstacle to invest, followed by long approval procedures and high investment costs due to restrictive legal requirements.

Ultrafiltration of digestate liquid fraction by hollow-fiber membranes: Influence of digestate pre-treatment on hydraulic capacity and nutrient removal efficiency

With the growing interest in anaerobic digestion as a processing method of agro-food waste, proper disposal of digestate has become a prominent problem. In the study, ultrafiltration of the sugar beet pulp digestate was conducted using hollow-fiber membranes with a cut-off of 150 kDa operating in an outside-in system. The effect of different pre-treatment strategies of digestate i.e. centrifugation alone or in combination with coagulation with polyaluminium chloride, biocoagulation with chitosan and flocculation with polyacrylamide on mitigation of membrane fouling and permeate quality was investigated. High ultrafiltration performance was obtained using centrifugation followed by flocculation with 416 mg/dm3 of polyacrylamide as digestate pre-treatment. Removal efficiencies of chemical oxygen demand (COD), total solids, phosphorus and nitrogen were 89.80, 90.08, 88.37 and 64.12%, respectively. Permeate flux and total membrane resistance averaged 22.33 dm3/m2/h and 5.32 • 1011 m−1. Hydraulic parameters and removal rates determined during ultrafiltration preceded by centrifugation and biocoagulation with 100 mg/dm3 of chitosan did not differ significantly from the values mentioned above for the pre-treatment consisting of centrifugation and flocculation with polyacrylamide. The results indicate the possibility of filtering the liquid fraction obtained by centrifugation, coagulation or flocculation of the digestate, and using natural auxiliary agents during its pre-treatment.

Artificial Sweetener Enhances the Spread of Antibiotic Resistance Genes During Anaerobic Digestion.

Artificial sweeteners have been frequently detected in the feedstocks of anaerobic digestion. As these sweeteners can lead to the shift of anaerobic microbiota in the gut similar to that caused by antibiotics, we hypothesize that they may have an antibiotic-like impact on antibiotic resistance genes (ARGs) in anaerobic digestion. However, current understanding on this topic is scarce. This investigation aimed to examine the potential impact of acesulfame, a typical artificial sweetener, on ARGs in anaerobic digestion by using metagenomics sequencing and qPCR. It was found that acesulfame increased the number of detected ARG classes and the abundance of ARGs during anaerobic digestion. The abundance of typical mobile genetic elements (MGEs) and the number of potential hosts of ARGs also increased under acesulfame exposure, suggesting the enhanced potential of horizontal gene transfer of ARGs, which was further confirmed by the correlation analysis between absolute abundances of the targeted ARGs and MGEs. The increased horizontal dissemination of ARGs may be associated with the SOS response induced by the increased ROS production, and the increased cellular membrane permeability. These findings indicate that artificial sweeteners may accelerate ARG spread through digestate disposal, thus corresponding strategies should be considered to prevent potential risks in practice.

Improving removal of combined veterinary antibiotics and mitigating their negative impacts during anaerobic digestion of swine manure using modified bentonite

This study investigated the potential of modified bentonite (MB) material in mitigating the negative effects of combined veterinary antibiotics (CVAs) on anaerobic digestion (AD) process treating swine manure. Four CVAs (i.e., Oxytetracycline (OTC), Tetracycline (TC), Norfloxacin (Norf), and Sulfadiazine (SDZ)) were selected as they are most frequently detected in swine manure; and anaerobically incubated for 30 days under mesophilic conditions (37 °C) and with addition of different MB weights (1, 5, and 10 g L−1). Results showed that 1, 5, and 10 g L−1 of MB enhanced the removal of CVAs from 61.5 (no MB addition) to 72.7, 86.4, and 91.4 %, respectively. CVAs removal was accredited to biodegradation rather than adsorption to MB. Norf was rapidly transferred to solids causing an adsorption competition and decreasing co-antibiotics removal, while it was fast removed when MB was added. When 10 g L−1 of MB were added, the CVAs' adsorption competition diminished and their inhibition on CH4 production decreased from 27 % to 1.7 %. MB addition lowered the impact of CVAs significantly by maintaining pH stability, enhanced COD removal, decreased the VFAs accumulation, and improved the activity of bacteria and archaeal communities. The cost analysis showed that MB additions to AD would reduce cost by 52 % than applied methods for animal slurry pre-treatment or post-digestive treatment for reducing antibiotic residues. These findings suggests that using MB as an environmentally-friendly and commercial additive holds promise for reducing CVAs and eradicating their negative impacts with safe digestate disposal to land applications.

An ecological and economic approach to enhancing the agronomic quality of anaerobic digestate: Effects of adding agricultural Jiaosu on metabolism and the microbial community

Anaerobic digestate disposal is challenging, hampering the development of large-scale biogas projects. Currently, digestate is primarily stabilized naturally and subsequently applied to farmland. However, during this process, the number of beneficial microorganisms decreases, free ammonia nitrogen increases, and pH rises, decreasing the benefits of digestate to soil and plants. In this study, digestate was treated by adding agricultural Jiaosu (AJ). The agronomic quality of the digestate was explored by conducting a pot experiment. Subsequently, the mechanisms of the changes in digestate properties were investigated based on chemical and microbial parameters. The results showed that the digestate with a 10% AJ supplement significantly improved the plant characteristics such as plant height, fresh weight, and leaf area. Regarding chemical properties, the addition of 10% AJ decreased the total ammonia nitrogen and free ammonia nitrogen in the digestate to below the toxicity threshold. With respect to microorganisms, the addition of AJ improved the microbial diversity of the digestate and increased the relative abundances of Advenella, Trichococcus, and Comamonas spp., which are beneficial to both soil and plants. Moreover, AJ decreased the abundance of potentially threatening microorganisms such as Thiopseudomonas and Papillibacter spp. Collaborative analysis showed that the improvement in digestate agronomic quality was closely related to its effects on microorganisms. Based on these results, the present study suggests an approach to the post-treatment of anaerobic digestate that can improve its fertilizer value while reducing its phytotoxicity. Furthermore, this study provides a model for a more comprehensive evaluation of the agronomic quality of digestate.

Synergistic effects of paper mill sludge and sulfonated graphene catalyst for maximizing bio-hydrogen harvesting from sugarcane bagasse de-polymerization

In this study, hydrogen harvesting from fermentation of sugarcane bagasse (SCB) was promoted by maintaining synergism between sulfonated graphene (SGR) catalyst and paper mill sludge (PMS). The sulfonic acid (–SO3H) groups in the catalyst played a major role in destructing the β-1,4 glycosidic bonds of sugarcane bagasse, releasing readily biodegradable sugars into the fermentation medium. The cellulose, hemicellulose, and lignin conversion efficiency were improved by 127.5%, 495.0%, and 109.2%, respectively with 20 mgSGR/gVS catalyst addition, compared with the control samples. These values were also higher than those obtained by non-sulfonated graphene catalyst. The hydrogenation of sugarcane bagasse was maximized at a sulfonated graphene catalyst dosage of 60 mgSGR/gVS, providing the highest hydrogen harvesting of 4104 ± 321 mL. This was associated with an increase of the Proteobacteria phyla up to 52.0%, Firmicutes phyla to 13.9%, and Acinetobacter sp. to 39.8% compared with only 37.0%, 11.3% and 11.1% in the control assay respectively. Moreover, sulfonated graphene catalyst supplementation promoted the acetate fermentation reaction pathway by increasing the acetate/butyrate ratio up to 4.1. Nevertheless, elevating the catalyst dosage up to 120 mgSGR/gVS reduced the hydrogen harvesting (1190 ± 92 mL) due to the release of furfural (1.76 ± 0.02 g/L) in the fermentation cultures, deteriorating the microbes’ internal composition and metabolism bioactivities. Finally maximizing the hydrogen productivity from sugarcane bagasse is feasible by incorporation of paper mill sludge and sulfonated graphene catalyst at dosage not exceeding 60 mgSGR/gVS. However, investigating the recyclability and disposal of digestate containing sulfonated graphene catalyst and the associated economic feasibility needs more attention in the future.

Current and prognostic overview on the strategic exploitation of anaerobic digestion and digestate: A review

The depletion of fossil fuels and increasing demand for energy are encountered by generating renewable biogas. Anaerobic digestion (AD) produces not only biogas, also other value-added products from the digestate using various organic, municipal and industrial wastes which have several benefits like remediating waste, reduces greenhouse gas emissions, renewable energy generation and securing socio-economic status of bio-based industries. This review work critically analyzes the biorefinery approaches on AD process for the production of biogas and digestate, and their direct and indirect utilization. The left-out residue obtained from AD is called ‘digestate’ which enriched with organic matter, nitrogen, heavy metals and other valuable micronutrients. However, the direct disposal of digestate to the land as fertilizer/landfills creates various environmental issues. Keeping this view, the digestate should be upgraded or transformed into high valued products such as biofertilizer, pyrochar, biodiesel, syngas and soil conditioner that can aid to enrich the soil nutrients and ensures the safe environment as well. In this context, the present review focused to illustrate the current techniques and different strategic exploitations on AD proper management of digestate products for storage and further applications. Such a technology transfer provides a proven strategic mechanism towards the enhancement of the sustainability of bio-based industries, attaining the energy demand, safest waste management, protection of environment and reduces the socio-economic issues of the industrial sector.

Biorefinery of anaerobic digestate in a circular bioeconomy: Opportunities, challenges and perspectives

With the ever-increasing size of anaerobic digesters (AD), the management and disposal of digestate have become a challenging task for AD operators. Anaerobic digestate is rich in nutrients and contaminants; thus, a suitable treatment is required to meet environmental legislation and protect the receiving environment. There has been a thrust among the research efforts in anaerobic digestate management in the last decade. Volarization of digestate into high-value products is necessary to make the AD process more cost-effective. Moreover, digestate utilization helps in recycling the already mined resources. Efforts have been made to use digestate as a feedstock to recover energy and value-added products such as nutrients (N, P), biochar, biofuels, polyhydroxyalkanoates (PHAs), and algal cultivation, which can arguably help to enable the circular economy in modern communities. This communication thoroughly examines the anaerobic digestate-based biorefinery concept and its linkages with the circular bio-economy. This review comprehensively summarized digestate management practices; recovery of renewable fuels and other value-added products from digestate, including bottlenecks and perspectives altogether in digestate management and treatment. The state-of-the-art of commercialization of anaerobic digestate valorization technologies has also been provided. Overall, this review could support decision-makers in identifying environmentally sound and sustainable solutions ahead of time.

Producing insect protein from food waste digestate via black soldier fly larvae cultivation: A promising choice for digestate disposal

The treatment of food waste digestate with high salinity is a big challenge. This paper evaluated the possibility of using black soldier fly larvae for food waste digestate disposal and insect protein production. Results showed that both digestates from hydrogen and methane fermentations were rich in protein and lipid contents, which benefited the BSFL cultivation. The BSFL reared on digestates from hydrogen and methane fermentations of food waste performed better in pre-pupal weight (19.12% and 41.13% higher, respectively), body length (3.62% and 18.21% higher, respectively) and crude protein contents (7.85% and 39.05% higher, respectively) than that reared on raw food waste. In addition, the maximum body weight growth rate (Rm) of BSFL cultivated on both digestates were 28.28% and 47.10% higher than that of BSFL cultivated on raw food waste, respectively. During BSFL cultivation, organic matter reduction between 40.97% and 46.07% were achieved. Digestates from hydrogen and methane fermentations represent favorable feeding substrates for BSFL cultivation. Using BSFL to treat AD digestate not only provides a digestate disposal approach, but also produces insect biomass and organic fertilizer as value-added byproducts, which shows tremendous potential in digestate disposal.

Mechanism insights into hydrothermal dewatering of food waste digestate for products valorization

Poor dewaterability is a bottleneck of the disposal of digestate from food waste (DFW). However, the dewatering mechanism remains unclear due to the complex composition of DFW. Understanding the dewatering mechanism, as well as the transformation of organic/inorganic matters is essential for the DFW management and valorization. In this study, the distribution, transformation, and complex interplay of organic and inorganic matters at different Hydrothermal treatment (HTT) temperatures were comprehensively analyzed to explore the hydrothermal dewatering mechanism of DFW. When HTT was conducted in the temperature range of 120–180 °C, the interstitial water was released as surface or free water because of membrane breaking and size reduction of the solid substrate. Releasing divalent cations increased the Zeta potential of the bulk solution. The weaker electrostatic repulsion between suspended particles made them easier to settle as the centrifugation cake. When the temperature of HTT was above 180 °C, polymerization and aromatization reactions took place gradually for organic matters, and the bound water was further removed. The generated humic substances were more hydrophobic than the raw material. In addition, the humic substance could combine with cationic metals, which decreased the zeta potential of the bulk solution but promoted the aggregation of nanoparticles and enhance the dewaterability of DFW.

Industrial symbiosis of anaerobic digestion and pyrolysis: Performances and agricultural interest of coupling biochar and liquid digestate

The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH4/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 °C, 1 h, and 10 °C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm3, respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates.

Evaluation on energetic and economic benefits of the coupling anaerobic digestion and gasification from agricultural wastes

The sustainability of the anaerobic digestion (AD) plant was closely related to the disposal of digestate and enhancement of energy recovery. Aiming to promote this, coupling AD and digestate gasification (AD-gasification) was proposed and evaluated for a large-scale AD plant. Firstly, characterization of the solid digestate was measured. Secondly, air gasification of the solid digestate was performed. Finally, two scenarios aiming at enhancing energy recovery as electricity or gas were investigated.Superior C content (50.14 wt%), H/C (1.57) and O/C (0.62) molar ratios and lower heating value (LHV) of solid digestate (18.01 MJ/kg) made it propitious to gasification. Air gasification of digestate at 800 °C with ER = 0.26 resulted in the optimal LHV of producer gas (6.35 MJ/Nm3) and cold gas efficiency (CGE, 66.99%). In the biomass-to-electricity scenario, the excess of heat from the CHP system in the AD plant was sufficient to dry the solid digestate. Compared with the stand-alone AD plant, the total electricity from the coupling system increased about 11%. In the biomass-to-gas scenario, the gas income increased by 14% when the initial solid digestate was naturally air-dried to a water content of 50%. This research would provide technical guidance for the sustainability of the AD industry.

An integrated strategy to enhance performance of anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) is an essential process in wastewater treatment plants as it can reduce the amount of waste activated sludge (WAS) for disposal, and also enables the recovery of bioenergy (i.e. methane). Here, a new pretreatment method to enhance anaerobic digestion was achieved by treating thickened WAS (TWAS) with ferric (as FeCl3) and nitrite simultaneously for 24-hour at room temperature. Biochemical methane potential tests showed markedly improved degradability in the pretreated TWAS, with a relative increase in hydrolysis rate by 30%. A comparative experiment with the operation of two continuous-flow anaerobic digesters further demonstrated the improvement in biogas quantity and quality, digestate disposal, and phosphorus recovery in the experimental digester. The dosed FeCl3 (i.e. ~6 mM) decreased the pH of TWAS to ~5, which led to the formation of free nitrous acid (FNA, HNO2) at parts per million levels (i.e. ~6 mg N/L), after dosing nitrite at 250 mg NO2−–N/L. This FNA treatment caused a 26% increase in methane yield and volatile solids destruction, 55% reduction in the viscosity of sludge in digester, and 24% less polymer required in further digestate dewatering. In addition, the dosed Fe(III) was reduced to Fe(II) which precipitated sulfide and phosphorus, leading to decreased hydrogen sulfide concentration in biogas, and increased percentage of vivianite in the total crystalline iron species in digested sludge. Our study experimentally demonstrated that combined dosing of FeCl3 and nitrite is a useful pretreatment strategy for improving anaerobic digestion of WAS.

Solid digestate disposal strategies to reduce the environmental impact and energy consumption of food waste-based biogas systems

This study examined the environmental impacts and energy consumption of three solid digestate treatment scenarios to quantify their impacts on the entire food waste (FW)-based biogas system: (1) incineration; (2) composting, and; (3) landfill. The results showed that composting had the largest net energy consumption, but least total environmental impact of 57.3 kWh and 8.75 E-03, respectively, whereas landfill showed the opposite pattern. Moreover, there were significant differences (p < 0.05) and relatively high contributions between the digestate treatment subunits among the three scenarios. The most significant contributions of digestate subunits in methods 1–3 to the 100-year global warming potential (GWP100) were 70.5%, 52.5%, and 103.4%, respectively. The results indicated that solid digestate treatment had a significant impact, and reasonable disposal of solid digestate could significantly reduce the environmental impacts and energy consumption of the entire FW-based biogas system.

Food waste anaerobic digestion in Umbria region (Italy): scenario analysis on the use of digestate through LCA

The project irexfo LIFE16 deals mainly with food waste and expired food prevention and reduction, but also with its valorization in biogas plants. Due to legal aspects the cycle of food waste needs to be closed returning the anaerobic digestate to the soil and so providing fertilizer for the cultivation and production of new crops. This is not possible at the moment in Italy because of the Decree of the 25th February 2016 on the disposal of digestate produced from raw materials which are not considered biomasses. The EU Regulation of 2019/1009 of the European Parliament and of the council of the 5th of June 2019, identifies some Component Materials Categories (CMCs), which can be considered as fertilizers; among them we find digestate other than fresh crop digestate, which includes digestate produced from bio-waste and another category on food industry wastes. For this reason, it is meaningful to compare the two possible alternatives: use of food waste digestate as it is in the field and use of food waste digestate after composting it (as currently required by the Italian law).

Anaerobic digestion disposal of sewage sludge pyrolysis liquid in cow dung matrix and the enhancing effect of sewage sludge char

Abstract Sewage sludge pyrolysis liquid (SSPL) is a mixture of various toxic organic compounds and moisture, its disposal or valorization are crucial for the sustainability of any pyrolysis plant of sewage sludge (SS). As SSPL showed strong inhibition on anaerobic digestion (AD), in order to fulfill its clean disposal, the study investigates its AD in cow dung matrix under thermophilic condition with sewage sludge char (SSC) addition. Three SSCs produced at different temperatures and two biochars were added into the AD system for comparison. Batch experiments (55 °C, 26 days) reveal that addition of SSCs/biochars could increase cumulative methane yield by 57.5–128.7%/120.7–133.7% compared with the group without char addition. Among three SSCs, the one produced at 550 °C (550SSC) shows the best effect and has similar promotion effects to those of conventional biochars. The mechanism involved is explained by the following facts: SSCs/biochars addition alleviated microbial inhibition effect of SSPL by adsorbing the toxic organic compounds in the liquid at the early stage, hosting microbes to grow, improving the reaction rate and stabilizing the pH of AD system at around 8, finally helping to obtain an earlier occurrence of daily methane yield peak and contributing to higher methane yields. The rich trace elements contained in SSCs, especially in 550SSC, help to promote the growth of microbes and contribute to the decomposition of toxic organic compounds. GC-MS analyses of digestates reveal that SSPL can be well degraded with help of SSCs/biochars addition after AD process. The obtained results suggest that AD of SSPL in cow dung matrix with 550SSC addition is a reliable and economy alternative for its treatment and valorization.

Biomethane production potential of slaughterhouse waste in the United States

Anaerobic Digestion (AD) is a promising technology to treat slaughterhouse waste (SHW) for the bioenergy production, nutrient recovery, and pathogen reduction. Three scenarios of estimating the biomethane potential from SHW of the US and the individual States have been conducted in this study. The US meat producers discharged 18.4 million metric ton (MT) SHW in 2016, which can potentially generate 22.7 × 109 kWh of biomethane. In Texas State, up to 2.3 × 109 kWh year−1 of energy can be potentially produced from AD of SHW and up to 106.3% of natural gas currently used in the Nebraska State for electricity generation can potentially be replaced with biomethane produced from the AD of its SHW. The technical challenges using SHW as the feedstock of AD process in the US have been summarized, including nitrogen and sulfur inhibition, foaming, sterilization, digestate disposal, supply chain etc. In addition, case studies were conducted by proposing an AD plant treating SHW from a typical slaughterhouse in a U.S. State that mostly processes the broiler, swine, and bovine. In our case studies, a net energy of 17,009–85,278 kWh d−1 is estimated to be generated from such AD plant. Therefore, producing biomethane from SHW can significantly promote bioenergy production in the US, thus enhancing the quick reach of bioenergy development targets set at the Federal and State levels, while overcoming the technical and management barriers of using SHW.

Removal of inorganics from sludge and digestate: the BiAR process

Abstract This conference contribution will present a novel technology for renewable ash-free fuel production from low-value ash-containing feedstocks such as sludge digestate, wood bark or rice husks that cannot be utilized directly as a heating fuel, because of the high (low melting point) ash content. Biomass Ash Removal (BiAR) process introduces the low-temperature solvolysis in cheap solvents to transform the organic matter into a liquid state, allowing its separation from the solid ash by a simple filtration or sedimentation. After the BiAR process, all tested feedstocks reduced their ash content below threshold admitted for heating biomass set by UNI EN ISO 17225:2014 standard. As anaerobic digestion is capable to recover about 50% of the carbon in form of methane (according with COD balance), BiAR could be used to ‘retrofit’ those installation to recovery the remaining 50% organic carbon leading to a potential 100% carbon, thus energy, recovery. A potential complete compensation of costs associated to dehydration and disposal of digestate could be achieved. The PCT application has been recently filed for the BiAR process (PCT/IT2016/000140).

Anaerobic co-digestion of pig manure and food waste; effects on digestate biosafety, dewaterability, and microbial community dynamics

This study assessed the effect of varying pig manure (PM)/food waste (FW) mixing ratio and hydraulic retention time (HRT) on methane yields, digestate dewaterability, enteric indicator bacteria and microbial communities during anaerobic co-digestion. Three 10 L digesters were operated at 39 °C, each with a PM/FW feedstock composition of 85%/15%, 63%/37% and 40%/60% (volatile solids basis). While the PM/FW ratio was different among reactors, the organic loading rate applied was equal, and increased stepwise with reducing HRT. The effects of three different HRTs were studied: 41, 29, and 21 days. Increasing the proportion of FW in the feedstock significantly increased methane yields, but had no significant effect on counts of enteric indicator bacteria in the digestate or specific resistance to filtration, suggesting that varying the PM/FW feedstock composition at the mixing ratios studied should not have major consequences for digestate disposal. Decreasing HRT significantly increased volumetric methane yields, increased digestate volatile solids concentrations and increased the proportion of particles >500 µm in the digestate, indicating that decreasing HRT to 21 days reduced methane conversion efficiency High throughput 16S rRNA sequencing data revealed that microbial communities were just slightly affected by changes in digester operating conditions. These results would provide information useful when optimizing the start-up and operation of biogas plants treating these substrates.