Daniel I. Massé

A critical review on inhibition of anaerobic digestion process by excess ammonia

Ammonia plays a vital role in the performance and stability of anaerobic digestion (AD) of N-rich organic-feedstock. Several research works were carried-out to study the effect of ammonia on the efficiency of AD of agro-food, industrial and livestock wastes/wastewater. However, excess ammonia remains a critical hitch in AD process. The mechanism of ammonia-inhibition has also been studied and there is no simple strategy available to mitigate ammonia-toxicity, when it exceeds threshold inhibition-level. For successful operation of AD systems at higher ammonia-level, adequate choice of temperature, control of pH and C/N ratio, and utilization of acclimatized-microflora to higher ammonia concentrations may ensure a stable and undisturbed digestion. This review provides a critical summary of earlier and recent research conducted on ammonia-inhibition during the anaerobic degradation of organic substrates, especially, at high ammonia concentrations. This article emphasizes that more profound knowledge on parameters influencing ammonia-inhibition is needed to apply appropriate control strategies.

Comprehensive model of anaerobic digestion of swine manure slurry in a sequencing batch reactor.

An improved mathematical model of anaerobic digestion in a sequencing batch reactor (SBR) process is developed. The model simulates the interactions between the biological, liquid (physicochemical) and gas phases. These phenomena are supported by experimental data. The advanced model assumes: (1) six populations of bacteria, including two populations of acetoclastic bacteria, are present in the bioreactor; (2) hydrogen in the gaseous phase is not in equilibrium with dissolved hydrogen; (3) production of volatile fatty acids (VFA) is regulated by the concentration of hydrogen in the liquid phase; and (4) the process is not affected by large concentrations of VFA and ammonia. The model contains a large number of kinetic constants and has the capability to predict the pH and methane production, as well as the concentrations of acetic (Ac), propionic (Pr) and butyric (Bu) acids; dissolved and gaseous hydrogen and soluble chemical oxygen demand (SCOD) in the SBR as a function of time. The model coefficients were determined for data, gathered from pilot scale digesters operated under psychrophilic conditions. The calibrated model was able to simulate methane production, SCOD, Ac and Pr acid concentrations in the dynamic conditions of an SBR, operated over a range of operating conditions.

The effect of temperature on slaughterhouse wastewater treatment in anaerobic sequencing batch reactors

High strength slaughterhouse wastewater was treated in four 42 l anaerobic sequencing batch reactors (ASBRs) operated at 30 degrees C, 25 degrees C and 20 degrees C. The wastewater contained between 30% and 53% of its chemical oxygen demand (COD) as suspended solids (SS). The ASBRs could easily support volumetric organic loading rates (OLRs) of 4.93, 2.94 and 2.75 kg/m3/d (biomass OLRs of 0.44, 0.42 and 0.14 g/g volatile SS (VSS)/d) at 30 degrees C, 25 degrees C, and 20 degrees C, respectively. At all operating temperatures, the total COD (TCOD) and soluble COD (SCOD) were reduced by over 92%, while average SS removal varied between 80% and 96%. Over the experimental period, 90.8%, 88.7% and 84.2% of the COD removed was transformed into methane at 30 degrees C, 25 degrees C and 20 degrees C, respectively. The decrease in the conversion of the COD removed into methane as operating temperature was lowered, may be partly explained by a lower degradation of influent SS as temperature was reduced. The reactors showed a high average methanogenic activity of 0.37, 0.34 and 0.12 g CH4-COD/gVSS/d (22.4, 12.7 and 11.8 l/d) at 30 degrees C, 25 degrees C and 20 degrees C, respectively. The average methane content in the biogas increased from 74.7% to 78.2% as temperature was lowered from 30 degrees C to 20 degrees C.

Methane Emissions from Manure Storages

The objectives of this study were to measure methane emissions from liquid manure stored on two farms (farm A and farm B) in eastern Canada and to evaluate the effect of various mitigation strategies on methane emissions. Manure from the two farms was kept at 10°C and 20°C for a 370-day period in storage pilots. The temperature profile in the storage tanks of both farms was also monitored during the experimental period. Manure from farm B (manure B) emitted methane soon after it was loaded to the storage pilots at 10°C and 20°C. It produced twice as much methane at 20°C as at 10°C. Frequent removal in the summer would significantly reduce methane emissions from manure stored on farm B, since an average manure temperature of 22°C was measured during the summer storage period. Manure from farm A (manure A) produced 3% and 54% of the methane emitted by manure B at 10°C and 20°C, respectively, over the 370-day monitoring period. Additionally, manure A produced methane after a lag phase of about 250 days at 20°C, which, on most farms, is longer than the storage period between land applications. Methane production from manure stored on farm A should then be minimal. Results were used to simulate the impact of mitigation practices on methane production from the full-scale storage structures on both farms. Increasing manure removal from 2 to 3 times a year and leaving the cows outside during summer nights decreased methane emissions by averages of 9% and 12%, respectively. Reducing the depth of residual manure left in the tank after land application from 60 to 30 cm reduced methane emissions by an average of 26%. The manure remaining in the storage structure becomes an important source of adapted inoculum that can readily produce methane. In every scenario, manure A produced about 3% of the methane emitted by manure B per kg of milk produced. The important difference between the two farms shows the large error that would arise from estimating methane production using a single emission factor for all farms within a region.

The effect of temperature fluctuations on psychrophilic anaerobic sequencing batch reactors treating swine manure

Under northern climatic conditions, a temporary decrease in the temperature of anaerobic reactors treating swine manure is likely to happen at the farm. The objective of this study was to evaluate the impact of temperature fluctuations, between 10 and 20 degrees C, on the stability and performance of psychrophilic anaerobic sequencing batch reactors (ASBRs) treating swine manure. Methane yield decreased from 0.266+/-0.014 l/g of total chemical oxygen demand (TCOD) fed to the ASBRs at 20 degrees C to 0.218+/-0.022 and 0.080+/-0.002 l/g TCOD (fed) at 15 and 10 degrees C, respectively. Soluble chemical oxygen demand (SCOD) reduction decreased from 94.2+/-1.1% at 20 degrees C to 78.8+/-3.0% at 15 degrees C and 60.4+/-6.4% at 10 degrees C. Total COD removal also tended to decrease as temperature was lowered, but difference between operating temperatures was not as pronounced. A lower methanogenic activity in the ASBRs operated at 10 degrees C probably favoured quiescent conditions during the settling period, thereby increasing physical removal of the TCOD through sedimentation of the solids with the biomass. When the operating temperature was increased back to 15 and 20 degrees C, methane yield and SCOD reduction improved, but reactor performance remained significantly (P<0.05) lower than that achieved before the cycles at 10 degrees C. Results from this experiment nevertheless suggested that fluctuation in the operating temperature of psychrophilic ASBRs should only have temporary effects on the performance and stability of the process.

Pathogen removal in farm-scale psychrophilic anaerobic digesters processing swine manure.

This study assessed the efficiency of commercial-scale psychrophilic anaerobic digestion in sequencing batch reactors (PADSBRs) for pathogen removal from pig manure. The impact of treatment cycle length and of hydraulic flow regimes on pathogen removal efficiency was investigated. Two conventionally operated SBRs (BR1 and BR2) and two SBRs simultaneously fed during the draw step (BR3 and BR4) were monitored over a two-year period. PADSBRs significantly decreased the concentration of coliforms, Salmonella, Campylobacter spp., and Y. enterocolitica, respectively from about 10(6), 10(3) CFU g(-1), 10(3), and 10(4) CFU g(-1) to undetectable levels in most samples. Densities of the gram-positive Clostridium perfringens and Enterococcus spp. remained high (10(5) CFU g(-1)) in the digesters throughout treatment. The PADSBRs maintained the same level of pathogen removal when the treatment cycle length was reduced from 2 to 1 week. Mass balances on volatile fatty acids (VFAs) revealed short-circuits of inlet flow respectively averaging 6.3% and 6.4% for BR3 and BR4, significantly reducing the overall performance of these reactors regarding pathogens removal. The results obtained in this study show the ability of low temperature anaerobic digestion to remove or significantly reduce indicator and pathogen concentration from raw pig manure.

Detection of Airborne Lactococcal Bacteriophages in Cheese Manufacturing Plants

ABSTRACT The dairy industry adds starter bacterial cultures to heat-treated milk to control the fermentation process during the manufacture of many cheeses. These highly concentrated bacterial populations are susceptible to virulent phages that are ubiquitous in cheese factories. In this study, the dissemination of these phages by the airborne route and their presence on working surfaces were investigated in a cheese factory. Several surfaces were swabbed, and five air samplers (polytetrafluoroethylene filter, polycarbonate filter, BioSampler, Coriolis cyclone sampler, and NIOSH two-stage cyclone bioaerosol personal sampler) were tested. Samples were then analyzed for the presence of two Lactococcus lactis phage groups (936 and c2), and quantification was done by quantitative PCR (qPCR). Both lactococcal phage groups were found on most swabbed surfaces, while airborne phages were detected at concentrations of at least 103 genomes/m3 of air. The NIOSH sampler had the highest rate of air samples with detectable levels of lactococcal phages. This study demonstrates that virulent phages can circulate through the air and that they are ubiquitous in cheese manufacturing facilities.

Methane yield from switchgrass harvested at different stages of development in Eastern Canada.

Mesophilic methane yield of ensiled switchgrass grown in Eastern Canada was assessed. Switchgrass was harvested at three stages of development, corresponding to mid-summer, late summer and early fall in 2007. The regrowth of plots harvested in mid-summer was also harvested in early fall as a two-cut strategy. Specific methane yields decreased significantly with crop maturity from 0.266 to 0.309 (N)L CH(4)g(-1) VS in mid-summer to 0.191-0.250 (N)L CH(4)g(-1) VS in early fall; values were similar for the first harvest in late July and the second harvest (regrowth) in October. Approximately 25% more methane was produced by hectare for the two-cut strategy (2.90-3.44 x 10(6)(N)L CH(4)ha(-1)) compared to the one-cut strategy with a harvest in late summer (2.28-2.77 x 10(6)(N)L CH(4)ha(-1)). Methane yields from switchgrass grown under the cool humid climate of Eastern Canada suggest that this crop remains an interesting renewable alternative energy source.

Potential of Biological Processes to Eliminate Antibiotics in Livestock Manure: An Overview

Simple Summary Beside their use to treat infections, antibiotics are used excessively as growth promoting factors in livestock industry. Animals discharge in their feces and urine between 70%–90% of the antibiotic administrated unchanged or in active metabolites. Because livestock manure is re-applied to land as a fertilizer, concerns are growing over spread of antibiotics in water and soil. Development of antibiotic resistant bacteria is a major risk. This paper reviewed the potential of anaerobic digestion to degrade antibiotics in livestock manure. Anaerobic digestion can degrade manure-laden antibiotic to various extents depending on the concentration and class of antibiotic, bioreactor operating conditions, type of feedstock and inoculum sources. Abstract Degrading antibiotics discharged in the livestock manure in a well-controlled bioprocess contributes to a more sustainable and environment-friendly livestock breeding. Although most antibiotics remain stable during manure storage, anaerobic digestion can degrade and remove them to various extents depending on the concentration and class of antibiotic, bioreactor operating conditions, type of feedstock and inoculum sources. Generally, antibiotics are degraded during composting > anaerobic digestion > manure storage > soil. Manure matrix variation influences extraction, quantification, and degradation of antibiotics, but it has not been well investigated. Fractioning of manure-laden antibiotics into liquid and solid phases and its effects on their anaerobic degradation and the contribution of abiotic (physical and chemical) versus biotic degradation mechanisms need to be quantified for various manures, antibiotics types, reactor designs and temperature of operations. More research is required to determine the kinetics of antibiotics’ metabolites degradation during anaerobic digestion. Further investigations are required to assess the degradation of antibiotics during psychrophilic anaerobic digestion.

Human pathogens and tetracycline-resistant bacteria in bioaerosols of swine confinement buildings and in nasal flora of hog producers

Swine confinement buildings in eastern Canada are enclosed and equipped with modern production systems to manage waste. Bioaerosols of these swine confinement buildings could be contaminated by human pathogens and antimicrobial resistant bacteria which could colonize exposed workers. We therefore wanted to analyze bioaerosols of swine confinement buildings and nasal flora of Canadian hog producers to evaluate possible colonization with human pathogens and tetracycline-resistant bacteria. Culturable and non-culturable human pathogens and tet genes were investigated in the bioaerosols of 18 barns. The nasal passages of 35 hog producers were sampled and total DNA was extracted from the calcium-alginate swabs to detect, by PCR, Campylobacter, C. perfringens, Enterococcus, E. coli, Y. enterocolitica, tetA/tetC, tetG and ribosomal protection protein genes. Airborne culturable C. perfringens, Enterococcus, E. coli, and Y. enterocolitica were present in the bioaerosols of 16, 17, 11 and 6 of the 18 facilities. Aerosolized total (culturable/non culturable) Campylobacter, C. perfringens, Enterococcus, E. coli and Y. enterocolitica were detected in 10, 6, 15, 18 and 2 barns, respectively. Tet genes were found in isolates of culturable human pathogens. TetA/tetC, tetG and ribosomal protection protein genes were detected in the bioaerosols of all 18 studied buildings. Campylobacter, C. perfringens, Enterococcus, E. coli, and Y. enterocolitica were found respectively in 4, 9, 17, 14 and one nasal flora of workers. One and 10 workers were positive for tetA/tetC and tetG genes, respectively. In swine confinement buildings, hog producers are exposed to aerosolized human pathogens and tetracycline-resistant bacteria that can contaminate the nasal flora.