Application of a simplified ADM1 for full-scale anaerobic co-digestion of cattle slurry and grass silage:assessment of input variability

Mathematical modeling of anaerobic digestion is a powerful tool to predict gas yields and optimize the process.The Anaerobic Digestion Model No.1(ADM1)is a widely implemented model for this purpose.However,modeling full-scale biogas plants is challenging due to the extensive substrate and parameter characterization required.This study describes the modification of the ADM1 through a simplification of individual process phases,characteristic components and required parameters.Consequently,the ability of the simplified model to simulate the co-digestion of grass silage and cattle slurry was evaluated using data from a full-scale biogas plant.The impacts of substrate composition(crude carbohydrate,protein and lipid concentration)and variability of carbohydrate degradability on simulation results were assessed to identify the most influential parameters.Results indicated that the simplified version was able to depict biogas and biomethane production with average model efficiencies,according to the Nash-Sutcliffe efficiency(NSE)coefficient,of 0.70 and 0.67,respectively,and was comparable to the original ADM1(average model efficiencies of 0.71 and 0.63,respectively).The variability of crude carbohydrate,protein and lipid concentration did not significantly impact biogas and biomethane output for the data sets explored.In contrast,carbohydrate degradability seemed to explain much more of the variability in the biogas and methane production.Thus,the application of simplified models provides a reliable basis for the process simulation and optimization of full-scale agricultural biogas plants.

Nitrifying population dynamics in a redox stratified membrane biofilm reactor(RSMBR)for treating ammonium-rich wastewater

Nitrogen removal performance and nitrifyingpopulation dynamics were investigated in a redox stratifiedmembrane biofilm reactor(RSMBR)under oxygen limitedcondition to treat ammonium-rich wastewater.When theNH_(4)^(+)-N loading rate increased from 11.1±1.0 to 37:2±3:2 gNH_(4)^(+)-N·m^(-2)·d^(-1),the nitrogen removal inthe RSMBR system increased from 18.0±9.6 mgN·d^(-1)to 128.9±61.7 mgN·d^(-1).Shortcut nitrogen removal wasachieved with nitrite accumulation of about22:3±5:3 mgNO_(2)^(-)-N·L-1.Confocal micrographsshowed the stratified distributions of nitrifiers anddenitrifiers in the membrane aerated biofilms(MABs)atday 120,i.e.,ammonia and nitrite oxidizing bacteria(AOBand NOB)were dominant in the region adjacent to themembrane,while heterotrophic bacteria propagated at thetop of the biofilm.Real-time qPCR results showed that theabundance of amoA gene was two orders of magnitudehigher than the abundance of nxrA gene in the MABs.However,the nxrA gene was always detected during theoperation time,which indicates the difficulty of completewashout of NOB in MABs.The growth of heterotrophicbacteria compromised the dominance of nitrifiers inbiofilm communities,but it enhanced the denitrificationperformance of the RSMBR system.Applying a highammonia loading together with oxygen limitation wasfound to be an effective way to start nitrite accumulation inMABs,but other approaches were needed to sustain orimprove the extent of nitritation in nitrogen conversion inMABs.

Greenhouse gas emissions from different pig manure management techniques： a critical analysis

Manure management is the primary source of greenhouse gas （GHG） emissions from pig farming, which in turn accounts for 18% of the total global GHG emissions from the livestock industry. In this review, GHG emissions （N20 and CH4 emissions in particular） from individual pig manure （PGM） management practices （European practises in particular） are systematically analyzed and discussed. These manure management practices include manure storage, land application, solid/liquid separation, anaerobic digestion, composting and aerobic wastewater treatment. The potential reduction in net GHG emissions by changing and optimising these techniques is assessed. This review also identifies key research gaps in the literature including the effect of straw covering of liquid PGM storages, the effect of solid/liquid separation, and the effect of dry anaerobic digestion on net GHG emissions from PGM management. In addition to identifying these research gaps, several recommendations including the need to standardize units used to report GHG emissions, to account ~br indirect N20 emissions, and to include a broader research scope by conducting detailed life cycle assessment are also discussed. Overall, anaerobic digestion and compositing to liquid and solid fractions are best PGM management practices with respect to their high GHG mitigation potential.

N2O emission from a sequencing batch reactor for biological N and P removal from wastewater

Nitrous oxide （N2O） is a greenhouse gas that can be released during biological nitrogen removal from wastewater. N2O emission from a sequencing batch reactor （SBR） for biological nitrogen and phosphorus removal from wastewater was investigated, and the aims were to examine which process, nitrification or denitrification, would contribute more to N2Oemission and to study the effects of heterotrophic activities on N2O emission during nitrification. The results showed that N2O emission was mainly attributed to nitrification rather than to denitrification. N2O emission during denitrification mainly occurred with stored organic carbon as the electron donor. During nitrification, NaO emission was increased with increasing initial ammonium or nitrite concentrations. The ratio of N2O emission to the removed ammonium nitrogen （N2O- N/NH4-N） was 2.5% in the SBR system with high heterotrophic activities, while this ratio was in the range from 0.14% to 1.06% in batch nitrification experiments with limited heterotrophic activities.

Process stability and microbial community composition in pig manure and food waste anaerobic co-digesters operated at low HRTs

This study assessed the effects of reducing hydraulic retention times （HRTs） from 21 days to 10.5 days when anaerobically co-digesting pig manure and food waste. Continuously stirred tank reactors of 3.75 L working volume were operated in triplicate at 42℃. Digester HRT was progressively decreased from 21 to 15 days to 10.5 days, with an associated increase in organic loading rate （OLR） from 3.1 kg volatile solids （VS）·m^-3.day^-1 to 5.1 kg VS·m^3.day-1 to 7.25 kg VS.m^-3·day^-1. Reducing HRT from 21 days to 15 days caused a decrease in specific methane yields and VS removal rates. Operation at a HRT of 10.5 days initially resulted in the accumulation of isobutyric acid in each reactor. High throughput 16S rRNA gene sequencing revealed that this increase coincided with a shift in acidogenic bacterial populations, which most likely resulted in the increased isobutyric acid concentrations. This may in turn have caused the increase in relative abundance of Clocamonaceae bacteria, which syntrophically degrade non-acetate volatile fatty acids （VFAs） into H2 and CO2. This, along with the increase in abundance of other syntrophic VFA oxidizers, such as Spiorchatetes, suggests that VFA oxidation plays a role in digester operation at low HRTs. Reducing the HRT to below 21 days compromised the ability of the anaerobic digestion system to reduce enteric indicator organism counts below regulatory limits.

Impact of roxarsone on the UASB reactor performance and its degradation

Roxarsone （3-nitro-4-hydroxyphenylarsonic acid, ROX） has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most of the ROX is excreted into the manure, causing arsenic contamination in wastewater. The arsenic compounds are toxic to microorganisms, but the influence of continuous ROX loading on upflow anaerobic sludge blanket （UASB） reactor is still unknown. In this study, the impact of ROX and its degradation products on the performance of the UASB reactor and the degradation and speciation of ROX in the reactor were investigated. The UASB reactor （hydraulic retention time： 1.75 d） was operated using synthetic wastewater supplemented with ROX for a period of 260 days. With continuous ROX addition at 25.0 mg.L-1, severe inhibition to methanogenic activity occurred after 87 days operation accompanied with an accumulation of volatile fatty acids （VFAs） and a decline in pH. The decrease of added ROX concentration to 13.2 mg.L-1 did not mediate the inhibition. As（III）, As （V）, MMA（V）, DMA（V）, HAPA and an unknown arsenic compound were detected in the reactor, and a possible biotransformation pathway of ROX was proposed. Mass balance analysis of arsenic indicated that 60%-70% of the arsenic was discharged into the effluent, and 30%-40% was precipitated in the reactor. The results from this study suggest that we need to pay attention to the stability in the UASB reactors treating organoarsenic-contaminated manure and wastewater, and the effluent and sludge from the reactor tO avoid diffusion of arsenic contamination.

LivestockWaste 2016- International Conference on Recent Advances in Pollution Control and Resource Recovery for the Livestock Sector

Globally, more than 55 billion tonnes of manure are generated every year from the livestock sector. However, livestock manure management systems, consisting of storage, processing, transportation, and disposal, are often inadequate, both in developed and developing countries.

Global warming potential associated with Irish milk powder production

Climate change is an ever growing issue and a major concem worldwide. Both producers and processors need to address the issue now by reducing, their carbon footprint. Additionally, if Ireland is to meet their climate and energy targets, as outlined in Food Harvest 2020, which outlines a range ot objectives for the Irish agricultural sector, the efficient use of resources and fuels within the industry will need to be increased. In Ireland, agriculture accounts for 29.2% of the total greenhouse gas powder, is examined in order to estimate the global warming potential （GWP） associated with its manufacture using life cycle assessment. A cradle-to-processing factory gate analysis, which includes raw milk production, raw milk transportation to the processmg tactory, its processing into eacla product and product packaging, is assessed in this study using data collected circa 2013. The factories surveyed processed approximately 24% of the total raw milk processed in the Republic of Ireland in 2013, which was 5.83 billion liter. The average total GWP associated with the manufacture of milk powder is 9.731 kg CO2eq·kg^-1 milk powder, which has a standard deviation of 2.26 kg CO2eq·kg^-1 milk powder, for the life cycle stages analyzed in this study. The most significant contributor to GWP is raw milk production （84%）, followed by dairy processing （14%）, with the remainder of the life cycle stages contributing approximately 2%.

Thermochemical pretreatment of meat and bone meal and its effect on methane production

Since the solubilization of meat and bone meal(MBM)is a prerequisite in many MBM disposal approaches,enhancement of the solubilization by means of thermochemical pretreatment was investigated in this study at two temperatures(55℃and 131℃)and six sodium hydroxide(NaOH)concentrations(0,1.25,2.5,5,10 and 20 g/L).The MBM volatile solid(VS)reduction ratio was up to 66%and 70%at 55℃and 131℃,respectively.At the same temperature,the VS reduction ratio increased with the increase in the dosage of NaOH.The study on the methane(CH4)production potential of pretreated MBM shows that the addition of NaOH at 55℃did not cause the inhibition of the succeeding CH4 production process.However,CH4 production was inhibited by the addition of NaOH at 131℃.The CH4 production potential was in the range of 389 to 503 mL CH4/g VS MBM and 464 to 555 mL CH4/g VS MBM at 55℃and 131℃,respectively.