Combination Of Anaerobic Digestion Research Articles

PROSPECTS FOR THE IMPLEMENTATION OF BIOLOGICAL METHANATION TECHNOLOGIES IN UKRAINE

The search and development of alternative energy sources as a substitute for scarce natural gas is an extremely important task for the Ukrainian economy. Methanation, that is, the reaction of converting carbon dioxide and hydrogen to produce synthetic renewable methane, is one way to solve this problem. The directions and features of methanation technologies implemented today in the world are considered. The structural diagram and production of components of biological methanation technology as the most promising for Ukraine are described. Two concepts of biomethanation are considered: in-situ and ex-situ. In-situ methanation is a combination of anaerobic digestion and biological methanation processes in a single digester. However, when implementing such methanation, difficulties arise due to differences in the optimal conditions for the occurrence of these processes. Ex-situ methanation occurs in separate reactors, where it is possible to autonomously establish optimal conditions for acetogenesis and methanogenesis. Thus, the in-situ concept, compared to the ex-situ concept, is much cheaper and easier to implement, but is still much more difficult to implement the methanation process. The relevance of introducing methanation technologies in Ukraine is due to the active development and implementation of bioenergy technologies using large bioresources existing in the country. A promising direction for the implementation of methanation technologies in Ukraine is the use of biological methanation technologies for the production of biomethane and synthetic renewable methane. Establishing the production of biomethane and synthetic renewable methane will also help solve such pressing problems as accumulating unstable electricity from solar and wind power plants, which can become a powerful stimulator for the development of these areas of alternative energy. In addition, methanation protects the environment from CO2, converting it from a greenhouse gas into a fuel. Bibl. 18, Fig. 2.

Cheese whey and dairy manure anaerobic co-digestion at psychrophilic conditions: Technical and environmental evaluation

Cheese whey (CW) and dairy manure (DM) are the main residues from the dairy industry, both of which can led to significant negative environment impacts if not properly managed. However, their combined anaerobic digestion represents an opportunity to obtain bioenergy and a stabilised material as a soil improver on the farm. Biochemical potential of methane (BMP) assays were carried out at psychrophilic conditions (20 °C) to analyse the influence on biomethane production of different CW:DM mixtures (% w/w) at different of inoculum-to-substrate ratios (ISR). Based on the BMP results, a life cycle assessment (LCA) of the cheese manufacturing process was carried out considering two scenarios (i) considering the current process, where propane gas and electricity are used for cheese production (ii) the incorporation of the biogas generated in the cheese production process in the company. BMP results showed that the best mixture between CW and DM was 65:35 (weight basis) at an organic load of 0.6 gVS/L (ISR of X). The LCA showed that CW and DM anaerobic digestion allowed to reduce the cheese manufacturing carbon footprint from through the substitution of propane by the biogas produced, changing from 5.5 to 3.1 kg CO2-eq/kg cheese produced, which indicates that according to the monthly production (633.6 kg) it would stop emitting about 1519 kg CO2-eq, i.e. a saving in terms of emissions of approximately 43,6% of the total currently generated.

Biomethane and Compost Production by Anaerobic Digestion of Organic Waste: Suggestions for Rural Communities in Southern Italy

The sharp increase in rural tourism brings, on the one side, economic and social benefits among rural communities but, on the other, contributes to environmental challenges, specifically waste generation and natural resource consumption. From the ecological perspective, several pathways have been developed from local and global communities, such as prevention, reuse, recycling and energy recovery. The present research, by considering the need to boost separate collection and valorize organic waste among rural communities, evaluates the performance of a combined anaerobic digestion and composting plant in Southern Italy. The purpose is to investigate the advantages and disadvantages of collecting organic waste in rural areas and recovering it into biomethane, digestate and compost. First, the research develops the material flow analysis of a real, accessible and available anaerobic digestion and composting plant in Southern Italy. Secondly, on the basis of the results obtained, the research calculates the biomethane, digestate and compost potential in Southern Italy, considering the amount of organic waste produced in 14 rural communities identified as the most beautiful villages in Italy. Last, the research compares the advantages and disadvantages of producing biomethane through anaerobic digestion or resorting to community composting in rural areas. It results that the biomethane and compost potential through anaerobic digestion is 423,854 kg and 954,896 kg, respectively, but significant financial investments must be allocated in order to allow the municipalities to enhance the logistics and the separate collection facilities. The research highlights possible strategies under the circular economy lens to boost sustainability in rural areas, focusing on biomethane and compost production and providing policy implications in light of the National Recovery and Resilience Plan (NRRP) and the Common Agricultural Policy (CAP).

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment, Sewage Sludge Digestion and Biogas Upgrading: A Review

Anaerobic membrane bioreactors (AnMBRs) are formed through the combination of anaerobic digestion and membrane technology. The upgraded technology separates SRT from HRT in the anaerobic digester, shortening the treatment period, reducing the digester’s volume and improving effluent quality. Furthermore, AnMBRs have a strong tolerance for the existing forms of objects and can handle liquids, high-solid materials and gases. Up to now, AnMBRs have been utilized in the treatment of various types of industrial and municipal wastewater, organic solid waste and also biogas upgrading, and they have achieved excellent performance. However, there are few studies which have discussed their multiple utilization, especially following the flow of wastewater treatment. This study summarizes the application of AnMBRs in their diverse roles in the municipal wastewater treatment process. The discussion revolves around energy generation and the fouling issue of AnMBRs in the treatment of municipal wastewater, the digestion of sewage sludge generated in conventional municipal wastewater treatment and the upgrading of biogas after anaerobic digestion. In addition to controlling operating parameters, strategies used to improve the treatment effectiveness are also introduced. Lastly, online methods for preventing membrane fouling, which is the main operational obstacle to AnMBRs’ wider spread, are also discussed. This review aims to provide a fresh perspective on how AnMBRs are utilized in waste treatment.

Quantification of – And determining factors affecting – Methane emissions from composting plants

Methane is a potent greenhouse gas contributing to climate change. Reliable data for methane emissions from the waste management sector are paramount in terms of providing national methane budgets and developing climate mitigation efforts. This study quantified total methane emissions and characterised temporal as well as operational emission patterns at five commercial composting plants in Denmark. Methane emissions were measured over a one-year period, using the tracer gas dispersion method. The results show that methane emission rates ranged from 8.0 ± 0.1 to 42.5 ± 1.5 kg CH4 h−1 and were significantly affected by factors including the type of feedstock and composting technology, treated feedstock mass, operational patterns and season. The results indicate that the highest methane emission factors were obtained at the combined anaerobic digestion and open windrow composting plant (4.51–5.21 kg CH4 Mg−1 wet garden/park waste (GPW) and food waste), followed by open windrow plants co-composting GPW, sewage sludge and straw (3.49–3.76 kg CH4 Mg−1 wet feedstock). The lowest methane emission factors were found at open windrow composting plants treating GPW (1.56–3.24 kg CH4 Mg−1 wet feedstock). Emissions tended to be higher when measurements were performed during working hours, in comparison to when they were measured after the plant closed for the day. At one plant, emissions were measured monthly over one year, and emissions were about 50% higher in spring and summer in comparison to autumn and winter.

Net zero greenhouse emissions and energy recovery from food waste: manifestation from modelling a city-wide food waste management plan

Food waste (FW) being a major solid waste component and of degradable nature is the most challenging to manage and mitigate greenhouse gas emissions (GHEs). Policymakers seek innovative approaches to achieve net zero objectives and recover resources from the FW which requires a comparative and holistic investigation of contemporary treatment methods. This study assessed the lifecycle of six alternative scenarios for reducing net GHEs and energy use potential from FW management in a metropolis, taking Hong Kong as a reference. In both impact categories, the business-as-usual (landfilling) was the worst-case scenario. The combined anaerobic digestion and composting (ADC) technique was ranked best in the global warming impact but was more energy intensive than anaerobic digestion with sludge landfilling (ADL). Incineration ranked second in net GHEs but less favourable for energy recovery from FW alone. The proposed integration of FW and biological wastewater treatment represented an enticing alternative. Integration by co-disposal and treatment with wastewater (CoDT-WW) performed above average in both categories, while anaerobic co-digestion with sewage sludge (AnCoD-SS) ranked fourth. The sensitivity analysis further identified critical parameters inherent to individual scenarios along with biogenic carbon emission and sequestration, revealing their significance on the magnitude of GHEs and scenarios’ ranking. Capacity assessment of the studied treatment facilities showed a FW diversion potential of ∼60% while reducing the net GHEs by ∼70% compared to the base-case, indicating potential of net zero carbon emissions and energy footprint by increasing treatment capacity. From this study, policymakers can gain insights and guidelines for low-carbon urban infrastructure development worldwide.

Valorization of livestock waste through combined anaerobic digestion and microalgae-based treatment in México: A techno-economic analysis for distributed biogas generation, animal feed production, and carbon credits trading

A large percentage of world’s eutrophication is attributed to the livestock industry, which is responsible for producing over 14% of the global anthropogenic greenhouse gasses emissions (GHG). In Mexico, very few livestock producers have the necessary infrastructure to treat their livestock waste (LW) and most fail to comply with environmental regulations. The treatment of LW through a circular bioeconomy approach can mitigate these negative environmental impacts, while simultaneously producing value-added products. The present work aimed to characterize the spatial variation of the LW generated in cattle, swine, and poultry farms in Jalisco, México. Total nitrogen (TN), phosphorus (TP), and organic matter released from these production units were estimated, along with the associated GHG, considering the standard practice of uncontrolled release. An alternative management scenario using anaerobic digestion (AD) combined with microalgae-based wastewater treatment (MbWT) was evaluated by developing a software-based techno-economic analysis, showing that a centralized LW treatment system could represent a feasible solution to comply the legislation while generating high-protein biomass for animal feed. Besides, the reduction in GHG represents an opportunity for carbon credits trading in voluntary markets for livestock producers in México. Insights are provided regarding the economical, technical, and sociocultural challenges that must be overcome to transition towards more sustainable livestock production practices in Jalisco, México, and other developing regions around the globe.

Comparative study of energetic potential from anaerobic digestion and direct combustion of date palm wastes

Abstract This work aims to evaluate the technical and environmental feasibility of converting date palm waste from a Moroccan oasis into energy. In this study, two different scenarios were analysed. The first proposed scenario is the valorization of the date palm substrates using direct combustion (thermochemical conversion) to produce energy. The second proposed scenario is the valorization of the substrates using combined anaerobic digestion of the substrate and direct combustion of the digestate. In this study, two different date palm wastes are: empty fruit bunch (EFB) and palm leaflet (PL). The experimental lower heating values of the digestates studied are 12.93 and 12.71 MJ/kg, respectively. The results show that using Scenario 1, the estimated output energies for the EFB and PL waste were 1.13 and 1.17 MWh, respectively. Using Scenario 2, the EFB and PL output energies were 1.27 and 1.39 MWh, respectively. The study revealed that the combined process is possible as an alternative way to produce energy. Furthermore, combining anaerobic digestion and direct combustion of lignocellulosic waste can contribute to reducing greenhouse gas emissions.

Life cycle assessment of municipal biowaste management - a Czech case study

As part of coming targets to transition to a sustainable society and actively set a circular economy, one of the EU objectives is to decrease the amount of municipal solid waste and initiate the separation of its organic fraction, i.e., biowaste. Consequently, the question of how to best manage biowaste at the municipal level is of high importance, and previous research has shown the strong influence of local factors on the most sustainable treatment option. Life Cycle Assessment is a valuable tool for comparison of waste management impacts and was used to assess environmental impacts of the current biowaste management in Prague and give insight for improvements. Different scenarios were created regarding EU and Czech biowaste targets for separated collection. Results show the significant influence of the source of energy that is substituted. Consequently, in the current situation of an energy mix highly based on fossil fuels, incineration is the most sustainable option in most impact categories. However, community composting was found to have a better potential to reduce ecotoxicity and resource use of minerals and metals. Furthermore, it could supply a significant proportion of the minerals need of the region while increasing the autonomy of the Czech Republic regarding mineral fertilisers. To meet targets of EU directives for separated collection of biowaste, a combination of anaerobic digestion, to avoid use of fossil fuels, and composting, to increase circular economy, is most likely the best option. The outputs of this project would be of great significance for municipalities.

The Combination of Anaerobic Digestion and Electro-Oxidation for Efficient COD Removal in Beverage Wastewater: Investigation of Electrolytic Cells

The world’s ever-growing population is driving an increased demand for clean water, which makes treating and reusing wastewater an essential practice. In recent years, biological and physicochemical methods have been preferred for wastewater treatment, with combined systems proving particularly effective. In this study, the combination of anaerobic digestion (AD) and electro-oxidation (EO) was investigated as a process for removing chemical oxygen demand (COD) from actual beverage wastewater. The effect of hydraulic retention time (HRT) on AD, electrolysis time, sodium chloride (NaCl) dosage, initial pH, and electro-properties on EO was investigated. At optimum conditions, namely an HRT of 2 days for AD, NaCl concentration of 3 g L−1, 80 min of EO time, natural pH (7.45), and applied voltage of 20 V for EO, the removal efficiency for COD was an impressive 96.47%, with energy consumption and specific energy consumption calculating 177.33 kWh m−3 and 33.79 kWh kgCOD−1, respectively. The amount of by-product gases (CH4 and H2) were also meagerly determined in this study. The results confirm that combining the AD and EO methods is an effective COD removal solution that can benefit the industry, while also offering a sustainable solution to combat water scarcity and meet the growing demand for clean water.

Combining Geobacter spp. Dominated Biofilms and Anaerobic Digestion Effluents─The Effect of Effluent Composition and Electrode Potential on Biofilm Activity and Stability.

The combination of anaerobic digestion (AD) and microbial electrochemical technologies (METs) offers different opportunities to increase the efficiency and sustainability of AD processes. However, methanogenic archaea and/or particles may partially hinder combining MET and AD processes. Furthermore, it is unclear if the applied anode potential affects the activity and efficiency of electroactive microorganisms in AD-MET combinations as it is described for more controlled experimental conditions. In this study, we confirm that 6-week-old Geobacter spp. dominated biofilms are by far more active and stable in AD-effluents than 3-week-old Geobacter spp. dominated biofilms. Furthermore, we show that the biofilms are twice as active at -0.2 V compared to 0.4 V, even under challenging conditions occurring in AD-MET systems. Paired-end amplicon sequencing at the DNA level using 16S-rRNA and mcrA gene shows that hydrogenotrophic methanogens incorporate into biofilms immersed in AD-effluent without any negative effect on biofilm stability and electrochemical activity.

Combined anaerobic digestion of chicken manure and corn straw: study on methanogenic potential and microbial diversity

PurposeTo explore the methane production potential and microbial community changes of combined anaerobic digestion of chicken manure and corn straw. Increase methane production, reduce the environmental pollution caused by the burning of livestock manure and straw, and provide some theoretical references for the construction and operation of actual biogas projects.MethodsDifferent proportions (3%, 5%, 10%) of corn straw were added to the anaerobic digestion systems of chicken manure in order to improve the C/N ratio and to evaluate the feasibility and potential synergistic effect on the co-digestion. The key point was to use 16S rDNA sequencing to analyze the relationship between the microbial diversity and the hydrolase activity during the anaerobic digestion.ResultThe results showed that the volumetric gas production of methane in the 3% straw addition group was 227.66 ml/gVS, which was 18% higher than the cumulative methane production in the pure chicken manure experimental group. However, with the increase of straw concentration, methane production and the utilization rate of the raw materials continued to decrease. The change in activity of each hydrolase was in agreement with changes in hydrolytic acidifying bacteria, and the activity of the main hydrolase also increased with the addition of straw; the correlation coefficient was 0.9943. Sequencing results showed that the dominant strains of methanogenic archaea were Methanosarcina, Methanosaeta, Methanobacterium, and Methanospirillum. Mainly for hydrogen-eating, acetic acid-eating methanogens, its role is to use H2, methanol and acetic acid, and other substances to metabolize methane, and convert it into CH4 and CO2.ConclusionThe addition of a small amount of straw enhanced the production capacity of hydrogen-nutritive methane to some extent, and the species richness and evenness were also improved, reducing the pollution caused by livestock manure to the environment while controlling the pollution caused by straw burning.Graphical

Opportunities and Challenges from Symbiosis of Agro-Industrial Residue Anaerobic Digestion with Microalgae Cultivation

During the last few years, many studies have tested microalgal systems for nitrogen removal from the digestate. However, most of these studies were carried out using pure culture microalgal strains, which require aseptic conditions and thus cannot be used in full-scale applications. The aim of the present study was to explore opportunities in and challenges of the industrial symbiosis of anaerobic digestion and microalgae cultivation to enhance agro-industrial residue management. Batch tests were carried out to investigate the use of a mixed (open) microalgal consortium to treat the liquid fraction of the digestate for nitrogen removal. Preliminary experiments were performed to choose the carbon supply condition optimizing the growth of the open mixed consortium. In detail, the investigated carbon sources were bicarbonate, under two different carbon to nitrogen ratios, CO2 via the free surface and CO2 via air flushing. Further tests were conducted to compare the use of ammoniacal and nitric nitrogen sources. Then, the effectiveness of the liquid fraction of the digestate as nitrogen source was assessed. The highest biomass concentration of 1.6 g L−1 was obtained using CO2 as carbon source via air flushing as feeding strategy and ammoniacal nitrogen. Biomass production was lower (0.6 g L−1) under the digestate. Nonetheless, due to a probable symbiosis between microalgae and bacteria, a total nitrogen removal of 98.5% was achieved, which was the highest obtained in the present study. Such experimental results address the identification of the steps needed for larger-scale application of combined anaerobic digestion and mixed microalgal systems.

Feasibility of a Novel (SHEFROL) Technology in Pre-Treating Eatery Wastewater at Pilot Scale

The wastewater ensuing from public eateries is higher in its chemical and biological oxygen demand (COD and BOD) as also its oil, grease, and protein content than sewage. For this reason such wastewater is much harder to treat; its content of fats, proteinaceous material, and xenobiotics mounting major challenges. But in most of the developing world about 80% of such wastewater is discharged untreated and the remaining is mixed with sewage going to the treatment plants. This happens due to the prohibitively high cost of treatment that is entailed if these wastewaters are to be treated by conventional activated sludge processes (ASPs) or a combination of anaerobic digestion and ASPs. The practice of allowing eatery wastewater to join sewage en route sewage treatment plants increases the load on the latter, especially due to the high fat and protein content of the former. The present work describes attempts to use the recently developed and patented SHEFROL® technology in affecting treatment of wastewater coming from a typical eatery. After establishing feasibility at bench scale, the process was tested in a case study at pilot plant scale for treating 12,000 litres/day (LPD) of wastewater being generated by the eateries situated in the campus of Pondicherry University, India. The capacity of the pilot plant was then expanded to 30,000 LPD. Despite operating the units at a very low hydraulic retention time (HRT) of 2 ± 0.5 h, due to the limitations of land availability, which translates to a rate about three times faster than a typical ASP, over 50% removal of COD and BOD, and similarly substantial removal of other pollutants was consistently achieved. Given that the SHEFROL units can be set up at a negligible cost, the findings indicate that SHEFROL technology can be used to significantly yet inexpensively pre-treat eatery wastewaters before either sending them for further treatment to conventional sewage treatment plants, higher-end SHEFROL units, or discharging them directly if neither of the other two options is available.

Optimization of a renewable hydrogen production system from food waste: A combination of anaerobic digestion and biogas reforming

In this study, hydrogen production using food waste was optimized by investigating the effect of agitator types in anaerobic digestion reactors and catalysts for biogas reforming. The applied agitators were pitched blade and hydrofoil, and their effect on homogeneity was estimated using computational fluid dynamics. Reactors with different agitators were operated for 60 days for biogas production. Increased biogas production was observed in the reactor equipped with a hydrofoil agitator owing to its high homogeneity. In addition, Ni-CeZrO2 catalysts promoted with La2O3, CaO, or MgO were investigated for stable hydrogen production during the biogas reforming reaction using simulated gas based on biogas from the anaerobic digestion equipped the hydrofoil. Among the promoted catalysts, the MgO-promoted Ni-CeZrO2 catalyst displayed the best results for hydrogen production without significant deactivation. The stable catalytic performance of the MgO-promoted catalyst resulted from the close interaction between Ni and MgO, and its high oxygen storage capacity. Thus, 1216 L hydrogen and 646 L carbon monoxide were produced per kilogram volatile solid via the hydrogen production system that included anaerobic digestion and biogas reforming.

A multi-objective optimization approach for clean treatment of food waste from an economic-environmental-social perspective: A case study from China

The combination of anaerobic digestion and transesterification technologies to treat food waste avoids the environmental problems associated with other treatment methods and effectively utilizes food waste to produce valuable products for society. However, as the anaerobic mono-digestion of food waste is not as efficient as anaerobic co-digestion of food waste with other substrates, this needs to be considered in food waste treatment system planning. Few studies on the mixed treatment of food waste with other substrates have considered the system from the economic, environmental, and social perspectives. Therefore, this paper comprehensively considered the economic, environmental, and social objectives of food waste treatment systems and developed a multi-objective optimization model to investigate the optimal systems operational strategy for food waste mixed treatment with other substrates by anaerobic co-digestion and transesterification. Uncertainties regarding the source quantities of food waste and substrates are solved in the proposed model using trapezoidal fuzzy numbers, and a case study in China is given to assess the validity and practicality of the proposed model. It was found that different substrate types and different mixing proportions affected the optimal system decisions, environmental and economic objectives were mutually constraining, and there was a positive relationship between the social objectives and the economic and environmental objectives.

The influence of bio-plastics for food packaging on combined anaerobic digestion and composting treatment of organic municipal waste

The use of bio-plastic-based packaging as an alternative to conventional plastic packaging is increasing. Among the plethora of different bio-based plastics, the most relevant ones are those that, at the end of their life, can be treated with the organic fraction of municipal solid waste. Even in these cases, their impact on the waste processing and recycling is not always positive. This study aim to assess on a laboratory scale the influence on combined anaerobic digestion and composting industrial processes of a bio-based plastic film, namely cellulose acetate (CA), in pure and modified (additions of additive) forms. CA films were mixed with organic waste and subjected to: (i) anaerobic digestion; (ii) active composting and (iii) two stages of curing composting. Anaerobic digestion and composting were monitored through methane yield and oxygen uptake respectively; additionally, the bio-plastics degree of disintegration was assessed during all the processes. The final disintegration of pure and modified CA was 73.82% and 54.66%, respectively. Anaerobic digestion contributes to the disintegration of the material, while aerobic treatment appears to be nearly ineffective, especially for modified CA. The presence of cellulose acetate during anaerobic digestion of food waste increased the methane yield by about 4.5%. Bioassay confirmed the absence of possible toxic effects on the final compost from the bio-plastic treatment. Although bio-based materials are not the only solution to plastic pollution, the findings confirm the need to upgrade the organic waste treatment plants and the necessity to revise the requirements for the use of compost in agriculture.

Novel insights from lignocellulosic waste to biogas through regulated dry-wet combined anaerobic digestion: Focusing on mining key microbes

Dry-wet combined anaerobic digestion is a novel approach for treating lignocellulosic waste by increasing the organic load of reactor while accelerating the conversion of organic acids. Here, we investigated the effect of regulated substrate ratios and initial pH in the dry acidogenesis stage on the bioconversion efficiency of dry-wet combined anaerobic digestion. Our data revealed microbial interactions and further identified key microbes based on microbial co-occurrence network analysis. On day three of acidification, the kinetic hydrolysis rate and acidification yield reached 1.66 and 60.07%, respectively; this was attributed to enhancement of the synergistic effect between Clostridiales and Methanosaeta, which increased the proportion of corn straw in the substrate or lowered the initial spray slurry pH to 5.5–6.5. With increased acidification capacity, acetoclastic methanogens were enriched in the wet methanogenesis stage; the syntrophic effect of Syntrophomonadales, Syntrophobacterales and Methanospirillum, meanwhile, was enhanced, leading to an overall improvement in biogas production.

Olive Mill Waste-Based Anaerobic Digestion as a Source of Local Renewable Energy and Nutrients

This study focused on what combination of anaerobic digestion (AD) temperature (ambient, mesophilic, and thermophilic) and olive mill waste (OMW) to dairy manure (DM) ratio mixture delivers the desired renewable energy and digestate qualities when using AD as olive mill waste treatment. OMW is widespread in the local environment in the North Sinai region, Egypt, which causes many environmental hazards if left without proper treatment. Three different mixtures consisting of OMW, dairy manure (DM), and inoculum (IN) were incubated under ambient, mesophilic, and thermophilic conditions for 45 days. The results showed that mixture B (2:1:2, OMW:DM:IN) at 55 °C produced more methane than at 35 °C and ambient temperature by 40% and 252%, respectively. Another aim of this study was to investigate the effects of the different concentrations of the digestate taken from each mixture on faba bean growth. The results showed that the maximum fresh weight values of the shoot system were observed at 10% and 15% for mixture B at ambient temperature. The best concentration value for the highest root elongation rate is a 5% addition of digestate mixture A at 55 °C, compared with other treatments.

A combined anaerobic digestion system for energetic brewery spent grain application in co-digestion with a sewage sludge.

In the present study, a combined technology for energetic brewery spent grain (BSG) use in co-digestion with sewage sludge (SS) was presented. A holistic approach that includes the impact of co-substrates and their carriers on the anaerobic digestion (AD) process, and the energetic aspects, was involved. Prior to AD, BSG was pretreated involving the hydrodynamic cavitation (HC); two different carriers were applied: MPW (municipal pre-settled wastewater) and mature landfill leachate (MLL). An orifice plate with a conical concentric hole of 3/10mm (inlet/outlet diameter) was applied as cavitation device. The initial pressure was 7bar and the number of recirculation passes through the cavitation zone was 30. The AD experiments were performed in semi-flow reactors, under mesophilic conditions at HRT of 20 and 21 d. In both co-digestion series, the constant co-substrate dose of 6% v/v was adopted. In the presence of cavitated BSG and MPW, a significant increase in biogas/methane production was provided as compared to SS mono-digestion, with the related improvement in kinetic constant by 3.5%. The average biogas yield was 0.48±0.03m3 kg-1 VS added, while in the control run 0.41±0.03m3 kg-1 VS added. Using cavitated BSG and MLL, such a beneficial effect was not observed. In both co-digestion series, slightly lower VS removal (as for the control) and stable process performance occurred. Moreover, the improved energy balance was provided. Due to the technological aspects, only co-digestion of cavitated BSG and MPW with SS is recommended for implementation into a full-scale.