Batch Anaerobic Digestion Research Articles

Bioenergy Potential and Kinetic of Biogas Production in Anaerobic Digestion of Slaughterhouse Effluent

Many studies have investigated the technology of anaerobic digestion for waste treatment and its benefits. However, most of those studies have reported on solid waste. So, there are few articles on the anaerobic digestion of effluent, especially anaerobic digestion of slaughterhouse effluent and its bioenergy potential. The purpose of this study is to evaluate the bioenergy potential in slaughterhouse wastewater treatment. Then, anaerobic digestion (AD) was used in this study to assess the bio-energy potential and kinetics of biogas production during processing. The slaughterhouse wastewater collected was characterized before the experiments using french standard method “AFNOR”. pH, Temperature, turbidity, dissolved oxygen (O_2dis.), oxidation-reduction potential (ORP), Conductivity, Chemical Oxygen Demand (COD), biochemical oxygen demand in five days (BOD₅), total Kjeldahl nitrogen (TKN) and total phosphorus (P_tot) were analyzed and the ratio BOD₅/COD was calculated to evaluate the biodegradability of the biomass. Laboratory-scale anaerobic batch digesters consisting of a 1 L plastic container were used in all the experiments and the biogas produced in the digesters was measured daily by the water displacement method. The wastewater produced by slaughterhouses is biodegradable with a ratio between biological oxygen demand and chemical oxygen demand (BOD₅/COD) > 0.5. An effective AD design shows that over 90% of organic matter was removed when inoculation and the carbon/nitrogen (C/N) ratio were adjusted. The cumulative volume of biogas increased from 415 mL to 2,150 mL as the substrate/inoculum (S/I) ratio has decreased from 2.028 to 0.337 and increased from 1,140 mL to 5,250 mL as the C/N ratio increased from 6 to 22. The biogas produced has a high calorific value, as the methane content is 74%. Among the three kinetic models used to describe biogas production, a modified Gompertz model was found to be the best with R² between 0.983 and 0.993. This study points out energy potential of slaughterhouse wastewater and its benefit as it is managed efficiently.

Effects of Pretreatment with a Ball Mill on Methane Yield of Horse Manure

Lignocellulosic biomass is an abundant organic material, which can be utilised in biogas plants for sustainable production of biogas. Since these substrates usually have high lignin contents and consist of rather elongated particles, a special pretreatment is required for an economical and process-stable utilisation in the biogas plant. The mechanical pretreatment of horse manure was carried out with the prototype of a ball mill at different speeds. The aim of ball milling is to comminute the substrate and disintegrate the lignocellulosic bond. Mechanical pretreatment in the ball mill resulted in a significant increase in specific methane yield of more than 37% in anaerobic batch digestion (up to 243 LCH4 kgVS−1) of horse manure. The kinetics of the methane gas formation process was analysed by a modified Gompertz model fitting and showed a higher methane production potential and maximum daily methane production rate as well as a lower duration of the lag phase after pretreatment at 6 rpm. This was further confirmed by sieve analyses, which showed a significant reduction of particle size compared to the untreated variant. Thus, the use of the ball mill increases the specific methane yield and improves the fermentation of lignocellulosic substrates such as horse manure.Graphical

Effects and mechanisms of foam suppression in food waste anaerobic digester using defoaming agents

The defoaming effects of organic silicone defoamer S-559 (OSD), polyether defoamer S-717 (PD), polyether-polysiloxane defoamer S-722 (PPD), high-carbon alcohol defoamer S-714 (HCD), corn oil (CO), and biochar derived from biogas residue (BBR) were investigated based on the foaming potential test, biotoxicity test, and long-term semi-continuous test. Foaming potential experiments showed that the OSD, PD, PPD, and CO had the best initial and continuous defoaming efficiency. However, PD was biotoxic. The cumulative methane production of food waste from the batch anaerobic digesters decreased by 18.4% and 22.6% after adding 0.1% (v/v) and 0.5% (v/v) PD, respectively. After the OSD was used several times in semi-continuous experiments, the foam reduction efficiency of the OSD increased to more than 98% and the foam recurrence efficiency of the reactor decreased to <21%. In contrast, the foam reduction efficiency of the CO decreased to<18% after long-term use, and the foam recurrence efficiency increased to more than 120%. The reason for the difference in defoaming performance is that the OSD was composed of solid hydrophobic particles with sharp edges, and the liquid phase had good spread ability and low surface tension. Thus, OSD relied on the bridging-stretching mechanism, the bridging-dewetting mechanism, and the spreading effect for defoaming. CO is a liquid defoamer with low surface tension, which may only rely on the bridging-stretching mechanism for defoaming. These results provide a reference for selecting a defoamer for a food waste anaerobic digestion system, and provide insight for the development of new defoamers.

Effect of Ammonia–Autoclave Pretreatment on the Performance of Corn Straw and Cow Manure Batch Anaerobic Digestion

Biomass pretreatment is a critical method for improving the anaerobic digestion (AD) performance of lignocellulosic feedstocks. In this study, an effective combined ammonia–autoclave pretreatment method was selected for the pretreatment of corn straw at 90 °C using four ammonia concentrations (7%, 9%, 11%, and 13%). The results showed that the combined pretreatment improved the substrate’s degradation efficiency and the system’s buffer capacity, and significantly improved the hydrolysis and biogas production performance of corn straw. After pretreatment, the lignin removal rate increased by 11.28–39.69%, and the hemicellulose degradation rate increased from 10.12% to 21.23%. Pretreatment of corn straw with 9% ammonia and an autoclave gave the highest methane yield of 257.11 mL/gVS, which was 2.32-fold higher than that of untreated corn straw, making it the optimal pretreatment condition for corn straw. Therefore, the combined ammonia–autoclave pretreatment technology can further improve the AD performance of corn straw.

Pretreatment of Slaughterhouse Effluent Treatment Plant Sludge Using Electro-Fenton Process for Anaerobic Digestion

Sludge management is an integral process of an effluent treatment plant (ETP). This study aimed at using the electro-Fenton (EF) process for pretreatment of a cattle-based slaughterhouse ETP sludge to enhance biogas production from anaerobic digestion. EF-oxidation experiments were conducted in 0.5 L beakers with mild-steel electrodes, to study the effect of factors, viz., H2O2 concentration, current density and reaction time on soluble chemical oxygen demand (sCOD) concentration, soluble extracellular polymeric substances (sEPS) concentration and volatile suspended solids (VSS) removal efficiency. This was followed by the quantification of biogas production from the raw and pretreated sludge in anaerobic digestion (AD). Experimental conditions for the EF process were optimized using response surface methodology (RSM). At optimized experimental conditions, EF pretreatment resulted in an increase in sCOD and sEPS concentrations, from 0.91 g/L to 6.1 g/L and 0.18 g/L to 1.4 g/L, respectively. VSS removal efficiency was 68.1%. Batch anaerobic digestion studies demonstrated an enhancement in the specific biogas yield, from 110 NmL/g-VS to 460 NmL/g-VS.

Feasibility of successive hydrogen and methane production in a single-reactor configuration of batch anaerobic digestion through bioaugmentation and stimulation of hydrogenase activity and direct interspecies electron transfer

Two-stage anaerobic digestion is a promising way to increase the efficiency of decomposition of organic waste. However, spatial separation of stages makes this technology less economically attractive. In this work, we studied a model of two-stage anaerobic digestion with stages separated in time in one reactor. To implement this model, we used a combination of (1) bioaugmentation with a hydrogen-producing Thermoanaerobacterium thermosaccharolyticum SP-H2, resistant to low pH, (2) setting a low initial pH (5.5) to reduce the activity of hydrogenotrophic methanogens, (3) supplementing additives in the form of soluble iron (II) and granular activated carbon (GAC) to stimulate hydrogenase activity and direct interspecies electron transfer (DIET), respectively. For comparison, two methanogenic inoculums with different dominant microbial groups and initial iron concentrations were used. With the simultaneous addition of GAC and iron (II), sequential production of hydrogen and methane was observed for both methanogenic inoculums. Without the addition of GAC, methane formation was practically not observed, which, apparently, indicated the impossibility of syntrophic degradation of acidogenesis products due to the high partial pressure of hydrogen and the absence of conductive material for activation of DIET. Significant differences in hydrogenase activity and the kinetics of hydrogen and methane formation according to the modified Gompertz equation depending on the iron content in the system may indicate the importance of this additive. Further studies should be aimed at determining the optimal initial pH, concentrations of stimulating additives, bioaugmentation and methanogenic cultures, as well as confirming the stability of the proposed single-reactor two-stage anaerobic digestion system in semi-continuous mode.

Enhancing methane yield from duck waste by co-digestion with Xyris capensis

This study examined the possibilities of enhancing methane yield from anaerobic digestion of Xyris capensis and duck wastes based on improved feeding composition and the C/N ratio. Batch anaerobic digestion of Xyris capensis and duck wastes was conducted at mesophilic temperature (37 ± 2 °C) with the mixing ratios of 100:0, 75:25, 50:50, 25:75, and 0:100% of duck wastes: Xyris capensis. The highest methane yield of 301.17 mL CH4/ gVSadded was recorded when the mixing ratio of 50:50% (duck wastes: Xyris capensis) and C/N ratio of 19.26 was digested. The biodegradability (BD) of duck wastes and Xyris capensis were 86.60 and 58.57%, respectively. The BD of duck wastes increases with the addition of Xyris capensis, and it started to decline after a 50:50% mixing ratio. A stronger synergistic influence of co-digestion was noticed compared to monodigestion of the individual of each feedstock. This study showed a better performance of anaerobic co-digestion and can be used to enhance feeding composition and the C/N ratio. In general, methane production from duck wastes co-digested with Xyris capensis is a good strategy to generate renewable energy and minimize waste management challenges.

Employing micro-aeration in anaerobic digestion of poultry litter and wheat straw: Batch kinetics and continuous performance

In this study, different micro-aeration (MA) strategies for anaerobic digestion (AD) of poultry litter (PL) and wheat straw (WS) were examined. MA at different stages (pretreatment, middle, pretreatment plus middle, and daily) in batch AD of WS showed that daily MA had the highest increase (16.5 %) of the cumulative methane yield (CMY) compared to the control. Batch co-digestion (Co-AD) of WS and PL with daily MA obtained a furtherly improved (15.1 %) CMY of 225.44 N mL CH4/g vS added. The modified Gompertz model and Cone model were good in fitting the methane yield kinetics of MA engaged AD process (R2 greater than 0.99). Daily MA shortened the lag phase of Co-AD by 3.4 %. The sequencing batch reactor for the Co-AD of WS and PL showed an increased (21.5 %) daily methane yield when 0.5-h/d MA was employed. The results provided support for the application of micro-aeration in the AD of agricultural wastes.

Enhancement of biomethane recovery from batch anaerobic digestion by exogenously adding an N-acyl homoserine lactone cocktail

Biomethane recovered through anaerobic digestion (AD) is a renewable, sustainable, and cost-effective alternative energy source that has the potential to help address rising energy demands. Efficient bioconversion during AD depends on the symbiotic relationship between hydrolytic bacteria and methanogenic archaea. Interactions between microorganisms occur in every biological system via a phenomenon known as quorum sensing (QS), in which signaling molecules are simultaneously transmitted and detected as a mode of cell-to-cell communication. However, there's still a lack of understanding on how QS works in the AD system, where diverse bacteria and archaea interact in a complex manner. In this study, different concentrations (0.5 and 5 μM) of signaling molecules in the form of an N-acyl homoserine lactone cocktail (C6-, C8-, C10-, and 3-oxo-C6-HSL) were prepared and introduced into anaerobic batch reactors to clearly assess how QS affects AD systems. It was observed that the methane yield increased with the addition of AHLs: a 5 μM AHL cocktail improved the methane yield (341.9 mL/g-COD) compared to the control without AHLs addition (285.9 mL/g-COD). Meanwhile, evidence of improved microbial growth and cell aggregation was noticed in AHLs-supplemented systems. Our findings also show that exogenously adding AHLs alters the microbial community structure by increasing the overall bacterial and archaeal population counts while favoring the growth of the methanogenic archaea group, which is essential in biomethane synthesis.

Fates of intracellular and extracellular antibiotic resistance genes during sludge anaerobic digestion with different pretreatments

Intracellular and extracellular antibiotic resistance genes (iARGs and eARGs) together constitute the resistome in sludge. However, the respective fates of iARGs and eARGs during sludge anaerobic digestion (AD) with pretreatments are unclear. In this study, the removal effects of three kinds of pretreatment methods including alkaline pretreatments (ALP), thermal pretreatments (THP), and enzymatic pretreatments (ENP) on iARGs and eARGs removal in sludge were first compared. Then the variations and mechanisms of iARGs and eARGs during the subsequent 30-day batch AD were investigated. Quantification PCR was adopted to determine the intracellular and extracellular absolute abundances of seven ARGs (tet(A), tet(O), tet(X), sul1, sul2, blaSHV, and blaTEM). THP showed the most potent removal effects for iARGs and eARGs (1.3–5.1 log), followed by ALP (0.3–1.0 log), while ENP had a minor impact on their removal (0.05 log by protease pretreatment). In the subsequent AD, the absolute abundances of iARGs and eARGs rebounded during AD with THP. Intracellular tet(O) increased its abundances while the absolute abundances of other iARGs and all eARGs decreased during AD with ALP and ENP and without pretreatments. The removal amounts of eARGs were higher than those of iARGs. From the perspective of the whole pretreatment-AD process, no advantages were observed in the removal of both iARGs and eARGs than AD without pretreatments. Redundancy analysis and partial least squares path modelling results revealed that bacterial community composition directly influenced the iARGs variations. The variations in iARGs and sludge physicochemical properties together directly influenced the eARGs variations.

The effect of heat pre-treatment on the anaerobic digestion of high-solid pig manure under high organic loading level.

Since more and more large-scale farms appear in China and changes in fecal sewage source disposal, the production of high-concentration solid manure waste is also increasing, and its conversion and utilization are gaining attention. This study investigated the effect of heat pre-treatment (HPT) on the thermophilic anaerobic digestion (AD) of high-solid manure (HSM). Pig manure (PM) feed with a total solids of 13% was used for the HPT and subsequent anaerobic digestion (AD) test. The HPT was carried out at 60°C, 80°C, and 100°C, respectively, for 15min after the heating reached the set temperature. The results show that HPT led to PM feed COD solubilization, observing a maximum increase of 24.57% after pretreated at 100°C, and the treated PM feed under this condition received the maximum methane production potential of 264.64 mL·g-1 VS in batch AD test, which was 28.76% higher than that of the untreated group. Another semi-continuous AD test explored the maximum volume biogas production rate (VBPR). It involves two organic loading rates (OLR) of 13.4 and 17.8g VSadded·L-1·d-1. The continuous test exhibited that all the HPT groups could produce biogas normally when the OLR increased to the high level, while the digester fed with untreated PM showed failure. The maximum VBPR of 4.71LL-1·d-1 was observed from PM feed after pre-treated at 100°C and running at the high OLR. This reveals that thermal treatment can weaken the impact of a larger volume of feed on the AD system. Energy balance analysis demonstrates that it is necessary to use a heat exchanger to reuse energy in the HPT process to reduce the amount of energy input. In this case, the energy input to energy output (E i /E o ) ranged from 0.34 to 0.55, which was much less than one, suggesting that biogas increment due to heat treatment can reasonably cover the energy consumption of the pre-treatment itself. Thus combining HPT and high-load anaerobic digestion of PM was suitable.

Promoting the overall energy profit through using the liquid hydrolysate during microwave hydrothermal pretreatment of wheat straw as co-substrate for anaerobic digestion

Liquid hydrolysate (LH) derived from the microwave hydrothermal pretreatment (MHP) of wheat straw (WS) was anaerobically digested together with the solid residual to promote the overall energy profit. Different MHP temperatures (90, 120, 150, 180 °C) and retention times (10, 20, 40 min) were investigated. Increased MHP intensity generated plenty of VFAs (mainly acetate) and phenols in the LH, implying the double-side effect of LH on AD. The highest methane production of 227.92 mL CH4·gVS-1 Raw was obtained with MHP at 120 °C for 10 min, 21.53 % higher than the control. While, MHP at 180 °C for 40 min exhibited 29.02 % lower methane production (113.13 mL CH4·gVS-1 Raw) and 115.86 % longer lag phase (3.13 days) than the control. Butyrate fermentation endowed the treatment groups of 180 °C with resilience from the overload and inhibition. Methanosarcina was largely enriched by the abundant acetate in LH on the early stage of anaerobic digestion (AD), especially when with high MHP intensity. Increased abundance of Methanosaeta and Methanobacterium played a crucial role in maintaining methane production at the middle and later stage. The high number of species and evenness in methanogens community were beneficial for the startup of batch AD. Although negative net energy was obtained, the lower ratio of energy input and output compared with the most researches using the solid residual after MHP as the sole substrate for AD demonstrated the contribution of LH to the overall energy profit.

Biodigestion of Mixed Substrates of Cow Manure-Delignified Spent Coffee Ground (DSCG) using Microorganism Enhancer for Biogas Production and Its Kinetic Study

Environmentally benign energy strategies have been implemented to cope with the rapidly increased global energy needs. Indonesia’s coffee consumption has triggered an increase in the generation of spent coffee ground (SCG) that can be used as a biogas raw material. The novelty that we offer in this research effort is to reduce the premature formation of biogas, so that we can extend the biogas production period during the digestion of spent coffee ground by adjusting the right pH and digestion time. This study aimed to produce biogas from an organic substrate mixture containing cow manure and SCG with a 25:1 C/N ratio by employing effective microorganisms-4 (EM-4). The process began with delignification of SCG using sodium hydroxide solution to obtain delignified SCG (DSCG). The biodegradation of the substrate was performed in an anaerobic batch digestion (AD) system at ambient temperature by varying pH (5, 7, and 9) and EM-4 concentration (6%, 9%, and 12%). The biogas product and chemical oxygen demand measurements were carried out every two days for 60 days of digestion. The results showed that the increase in EM-4 concentration induced earlier initial biogas production enhanced the volume, and extended the production time. The pH 7 level and 9% EM-4 loading gave the ideal digestion substrate condition containing cow manure and SCG with a 25:1 C/N ratio to obtain 11.28 mL of biogas/g COD with 100.2% production enhancement. The modified Gompertz equation fitted the experimental data very well as indicated by a high value of the coefficient of determination (R2 &gt; 0.95).

The Impact of Self-Agitating Anaerobic Batch Digester Design on Biogas Production of Cattle Manure Co-Digested with Lemna minor

The Impact of Self-Agitating Anaerobic Batch Digester Design on Biogas Production of Cattle Manure Co-Digested with Lemna minor

Bioaugmentation with methanogenic culture to improve methane production from chicken manure in batch anaerobic digestion.

This study sought to investigate the effect of bioaugmentation on batch anaerobic digestion of chicken manure. The digestion performance with and without bioaugmentation and bioaugmented efficiency under different dosages were compared. The results demonstrated that bioaugmentation increased the methane yield and shortened the methane production time in batch reactors. Compared to the un-bioaugmented control, the methane yield of bioaugmented digesters was increased by 1.2-, 1.7-, 2.2-, 3.4-, and 3.6-fold at addition ratios of 0.07, 0.14, 0.21, 0.27, and 0.34g VS bioaugmentation seed (BS)/g VSCM, respectively. However, higher bioaugmentation doses (0.34g VSBS/g VSCM) did not exhibit significantly improved bioaugmentation efficiency, thus, the recommended dose is 0.27g VSBS/g VSCM for biomethane conversion of CM. Moreover, whole genome pyrosequencing revealed that Methanoculleus and Methanobrevibacter predominated the non-bioaugmentation digesters, whereas Methanothrix, Methanobacterium, and Methanomassiliicoccus were the dominant methanogens in bioaugmentation digesters. The increased methane may be explained by an increase in the Methanothrix population, which accelerated acetic acid degradation. With bioaugmentation the mainly methanogenic pathways have become more diverse. From gene function perspective, bioaugmentation enhanced metabolic activities in digestor which function better in metabolism.

Biogas production from thermochemically pretreated sweet potato root waste

This paper presents the results of batch anaerobic digestion (AD) of thermochemically pre-treated sweet potato root waste (SPW). This agricultural waste is available in massive quantities yet it has remained an unexploited resource amid the ever-increasing need for clean energy and waste disposal challenges. Therefore, the waste can be considered for energy production through AD. However, SPW has a complex amylopectin structure that is resistant to digestive enzymes during hydrolysis which could lead to a longer retention time in the digester. In this sense, the effect of thermochemical pre-treatment on biogas production from SPW was investigated by pre-treating the substrate with sodium hydroxide (NaOH) at (0.6 g/L–3.5 g/L), temperature (50 °C–90 °C) and pretreatment time (30–120 min). The central composite design was used to design the number of experiments. SPW was milled to a small size. The physicochemical characteristics of materials were determined using standard methods. The quality of biogas produced in terms of methane content was analysed. The results from the study revealed that thermochemical pre-treatment on SPW improved biogas and methane yields. The pre-treated SPW had superior results to the untreated one. It represented a 33.88% improvement from 28.23 mL/gSPW biogas yield for the untreated SPW to 37.8 mL/gSPW for the treated SPW at optimal conditions. The optimum conditions for biogas production were found at a NaOH concentration of 2.9 g/L, a heating temperature of 82 °C, and a pre-treatment time of 102 min. Methane content in the biogas also improved from 42% to 64% (22% increase). The digester retention time was also reduced from 22 to 16 days. It can therefore be concluded that thermochemical pre-treatment of SPW improves both biogas yield and methane content as well as improves the kinetics of AD.

Mechanism of microbial involvement in nitrogen conversion affecting methane production in dry anaerobic digestion

Nitrogen conversion is driven by different microorganisms, which plays a crucial role in methane (CH4) production during dry anaerobic digestion (AD). However, the effect of nitrogen conversion on the metabolic mechanisms of methanogens network remains unclear. Batch AD experiments were carried out using chicken manure and rice husk as substrates. Biogas slurry was added as the inoculum. In a 40-day AD experiment, the initial operating conditions of the AD system: the temperature was 37 °C, C/N ratio was 20 ± 2.5, total solid was 25 ± 0.2%. After AD, total organic nitrogen relative content varied from 1.35% to 2.05%, ammonia nitrogen content varied from 600.31 to 1028.88 mg/kg, nitrate nitrogen content varied from 649.83 to 86.51 mg/kg and nitrite nitrogen content varied from 33.63 to 11.61 mg/kg. High-throughput sequencing results showed that partial Clostridiales promoted the dissimilatory nitrate reduction to ammonia, increased ammonia nitrogen content, and further increased the abundance of partial Methanomicrobiaceae by 310%, leading to an increase in CH4 yield (0–22.03 std m3 kg−1 VS (Volatile Solids) added). This study explored the relationship between nitrogen conversion and microorganisms in the three stages of AD to propose possible mechanisms affecting CH4 yield. The results provide a theoretical basis for the identification of key microorganisms that nitrogen conversion affects methanogenesis during dry AD.

Estimation of the Energy Potential by Anaerobic Digestion of Food Waste at Nangui Abrogoua University : Codigestion of Food Waste With Cow Dung

The food wastes of the Nangui Abrogoua University are rich in organic matter that can promote the production of biogas through anaerobic digestion. These wastes are favorable for the anaerobic digestion process. This study aims at estimating the energy potential of the food wastes of the University Nangui Abrogoua by the production of biogas following the process of anaerobic digestion batch. The biogas from this food waste is estimated to be 10.79 m3 or 10790000 mL over a period of 30 days. This is equivalent to an energy potential of 75.58 kWh. These results obtained indicate that the food waste of the University Nangui Abrogoua is an important source of renewable energy.

Diversity of novel archaeal viruses infecting methanogens discovered through coupling of stable isotope probing and metagenomics.

Diversity of viruses infecting non-extremophilic archaea has been grossly understudied. This is particularly the case for viruses infecting methanogenic archaea, key players in the global carbon biogeochemical cycle. Only a dozen of methanogenic archaeal viruses have been isolated so far. In the present study, we implemented an original coupling between stable isotope probing and complementary shotgun metagenomic analyses to identify viruses of methanogens involved in the bioconversion of formate, which was used as the sole carbon source in batch anaerobic digestion microcosms. Under our experimental conditions, the microcosms were dominated by methanogens belonging to the order Methanobacteriales (Methanobacterium and Methanobrevibacter genera). Metagenomic analyses yielded several previously uncharacterized viral genomes, including a complete genome of a head-tailed virus (class Caudoviricetes, proposed family Speroviridae, Methanobacterium host) and several near-complete genomes of spindle-shaped viruses. The two groups of viruses are predicted to infect methanogens of the Methanobacterium and Methanosarcina genera and represent two new virus families. The metagenomics results are in good agreement with the electron microscopy observations, which revealed the dominance of head-tailed virus-like particles and the presence of spindle-shaped particles. The present study significantly expands the knowledge on the viral diversity of viruses of methanogens.

Integration of sludge ozonation with anaerobic digestion: From batch testing to scenario analysis with energy, economic and environmental assessment

A methodological procedure, based on results from batch experiments, is proposed and applied to a selected wastewater treatment plant generating a poorly degradable sludge, to identify the best configuration and ozone dosage for full-scale application of sludge ozonation. Samples of pre-thickened and digested sludge were collected, tested at different ozone dosages and characterized to gather useful data for energy, economic and carbon footprint balances. The most viable scenario was found to be sludge pre-treatment at the lowest tested dosage (20 mg O3/g VS), yielding energy, cost and GHG emission net savings of 177 MWh/y, 57.8 k€/y and 6.38 Mg CO2-eq./y, respectively. Sensitivity analyses, conducted by varying the specific energy required for ozone generation and the unit costs for sludge disposal and resource supply, confirmed the stability of this scenario, whereas a field pilot-scale testing is advisable to verify modified process conditions for a safe and efficient application of sludge ozonation. The proposed methodology, including laboratory batch anaerobic digestion tests, scenario definition and energy/economic/environmental balances, could be preliminary applicable to all situations to broadly analyze all involved aspects and give a useful overview about the effective applicability of sludge ozonation.