The Potential of Bioelectrochemical Sensor for Monitoring of Acetate During Anaerobic Digestion: Focusing on Novel Reactor Design

Acetate as the dominant fraction of volatile fatty acids (VFAs) is an important intermediate in metabolic pathways of methanogenesis, which could reflect the stability status of anaerobic digestion (AD) process. Bioelectrochemical sensors for environmental or bioprocess monitoring have become increasingly attractive in recent years. Although it was more favorable, several challenges still need to be addressed for acetate detection, including large electrode spacing, low stability, biofouling at the cathode and low detection range. In this study, an innovative biosensor on the basis of a three-chamber microbial electrochemical system was proposed to monitor the acetate during the AD process. In such a system, acetate was first transferred from sample chamber through the anion exchange membrane (AEM) to anode due to the driven force of concentration difference and then oxidized by anodic biofilm as a substrate for the current generation. With such design, the influence of waste properties fluctuation in the cathodic reaction could be avoided. The response of current density to different acetate concentrations was investigated. The selectivity, the influence of the sample temperature and the external resistance were also evaluated. The correlation (R2 > 0.99) between the current densities and acetate concentrations (up to 160 mM) was established at specific reaction time (from 2 to 5 h). Current densities after 5 h reaction were improving about 20% when the sample temperature was high (e.g., 37 and 55°C). The detection range increased along with the decrease of external resistance. The acetate concentrations of AD effluents as determined by the biosensor where within 24.2% of the ones determined by gas chromatography. Nevertheless, the application of the biosensor for monitoring acetate in environmental samples could still be promising

Metabolism of Energy and Implementation of Net Energy System in Laying Hens

Dietary energy is an expensive component of poultry diet formulations and may be as high as 60% of diets costs in certain situations. Different energy evaluation systems have been used for poultry diets formulations. The apparent metabolizable energy system (AME) is widely accepted and has been applied in the industry for 50 years in most world areas. The system compares the total gross energy of the diet to that present in excreta to determine what is retained. Development of energetic measurement techniques such as open and closed circuit calorimetry have enabled researchers to measure the wasted heat energy to determine the true available amount of energy for different body functions as net energy (NE). While the NE system has been proposed as a more accurate system for expressing feed energy and birds energy requirements compared to the AME system some difficulties remain in the poultry area with respect to the effect of age, environmental conditions and lack of data. Net energy based feeding systems are in successful use for pig and cattle feed formulation. For laying hens most nutritionists use the same AME values used for broilers. While this may be adequate, the use of broiler NE values for laying hens would not likely be acceptable as broilers are growing at a much higher rate than layers. This thesis examined the application of the NE system in laying hens. Chapter 1 provides general information about energy metabolism in body with more focus on the objectives of this study experiments. Chapter 2 is the literature review that provides the scientific background for the comparison of different feed energy evaluation systems and their limitations in practice. Included is a discussion on the metabolism of energy in chickens, partitioning of energy for different metabolic activities (maintenance, growth, and production) and dietary energy utilization for various body functions. The effect of the dietary profile, age, genotype, physiological status and environment on the energy metabolism, specifically on the net energy of the diets are considered and discussed.Chapter 3 studies the application of the bioassay method for measuring the AME, AMEn (AME adjusted for zero nitrogen retention) and AMEs (AME adjusted to 50% nitrogen retention) values of common dietary ingredients in layers feed as specific ingredients AME values are rarely available for laying hens. The bioassay evaluation used the reference diet substitution method and compared the data with the regression estimation method. The results confirmed that the in vivo measured AME values of ingredients using laying hens were close to those calculated from proximate composition using the European prediction equation and tabulated values based on adult cockerels. The results showed a good agreement between the reference diet substitution and regression methods to estimate ingredients AME content. In conclusion, the AMEn values are not representative of production conditions, in particular for the high-protein ingredients. In addition, AME values as obtained from the difference method should be interpreted with caution as it is affected by the CP content of the test diet. AMEs would then be the most representative of productive conditions.Chapter 4 evaluates the energy efficiency and net energy prediction of feed in laying hens. Using closed-circuit calorimetry chambers by feeding different diets with various nutrient contents to the laying hens in different ages in the production phase enabled the measurement of gas exchange, heat production, AME and NE of diets. Then AME and NE equations were generated based on diets and applied to or ingredients. The equations were further validated in calorimetry chambers. It was confirmed that the NE of diets can be predicted from AME or AMEn, crude protein and ether extract levels in laying hen diets.Chapter 5 describes two production experiments that were conducted to investigate the influence of different energy ratios (NE/ AMEn) by increasing dietary ether extract (EE) levels on birds performance and egg quality parameters. This chapter examined the effect of formulating diets based on the NE system compared to the default system (AME) and is intended to provide recommendations for nutritionists serving the layer industry. The results indicate that higher NE/AMEn diets with added EE improved hen performance and egg quality with higher albumen and Haugh units and darker yolk color score.Chapter 6 examines the energy metabolism at the molecular level. The effect of dietary NE/AME levels on messenger RNA (mRNA) expression of genes involved in energy metabolism and lipogenesis in laying hens was examined. Feeding laying hens diets with different NE/AME and levels of EE over time increased mRNA expression of peroxisome proliferator-activated receptor gamma (PPARG) a gene involved in fatty acid storage and glucose metabolism, in jejunal mitochondria. The different dietary treatments did not alter the mRNA expression of genes involved in cellular energy metabolism, oxidative phosphorylation or fatty acid synthesis. Furthermore, mitochondrial content per cell remained unchanged as a result of changes in dietary NE/AME ratio.This studies conducted in this thesis have provided the data necessary for nutritionists to begin implementation of an NE based formulation system for layer feed. An NE database of ingredients has been provided along with equations that can be applied to ingredients not present in the database so the NE value can be generated. The system gives higher NE values to ingredients with higher EE levels and lower NE values to ingredients with high protein levels relative to the AME system. This should give nutritionists operating in the layer industry to formulate diets more efficiently than before with improved performance and lower dietary costs. Further study is warranted to further confirm the benefits of the NE system with the existing AMEn system for layer

Impacts of Repeated High Temperature Exposure and Nutrition Change on Thermal Tolerance, Metabolism and Metabolite Profiles in Green Peach Aphid ('Myzus persicae')

Insects are ectotherms and have limited ability to regulate body temperature above or below ambient, and as such they consequently greatly affected by temperature variation particularly heat stress. Since most insects will be exposed to increased heat stress with global warming it is important that we understand responses to an increasingly warm environment: especially the underlying changes in physiology and biochemistry. The few studies have assessed links between physiological mechanisms and impacts of repeated high temperature; identification of different recovery times and the role of nutrition in heat tolerance in aphids. The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphidae) is one of the major aphid pests infesting canola in Australia and is distributed widely across the globe, making it an ideal species for assessing the impacts of biotic and abiotic stress on its biology. The overall aim of this thesis was to use the model organism M. persicae to identify the roles of repeated high temperature exposure, nutrition and recovery time in thermal adaptation, and to asses this in a physiological context which included measuring key metabolite and metabolic rate, a postulated underlying process. In chapter 2, I examined the physiological consequences of repeated high temperature exposure with recovery periods between these stress events in Myzus persicae. Aphids exposed to repeated pulses of high temperatures had more body glucose and higher expression of proteins and osmolyte compounds compared to the prolonged exposure group. However, aphids exposed to the repeated high temperature treatment had reduced sources of energy such as trehalose and triglyceride compounds than the prolonged exposure group. In addition, recovery time had more costs (based on production of more protein and consumption of more trehalose and triglyceride) and benefits (based on production of more osmolytes) in repeated high temperature treatments. In chapter 3, in the nutritional exhibited I carried out, aphids reared on the high amino acids medium increased heat tolerance and respiration rates compared to aphids reared on the low amino acid medium. Aphids reared on the diet with high amino acids and sucrose concentration had more glucose and higher expression of proteins and osmolyte compounds compared to those reared on a lower amino acid and sucrose diet. However, aphids reared on lower amino acids diets had reduced sources of energy such as trehalose and triglyceride compounds compared to high amino acid diets. These results indicate that aphid nutrition has a strong impact on the ability and plays a critical role in environmental stress responses. In chapter 4, I demonstrated that trehalose and triglyceride are the most important sources of energy compared to glycogen in adult aphids when exposed to high temperatures. My findings indicate that adult aphids need different recovery time for different metabolite types. Overall the findings from the research carried out as part of my thesis make a significant contribution to understanding the physiological mechanisms under high thermal tolerance; to the cellular process and key nutrition that facilitate thermal adaptation; and to the impacts of a changing and more variable climate on aphids

Biochemical and Transcriptional Responses to n-3 Fatty Acids in Two Breeds of Dogs

Polyunsaturated fatty acids (PUFA), which include n-3 and n-6 fatty acids, are essential for the health of both humans and dogs. Consequently, the need to include n-3 fatty acids in commercial dog foods is gaining increasing recognition. Fish is a natural source of n-3 fatty acids; however, with the reduction in the global fish stock, alternate sources of n-3 fatty acids are gaining importance, and one such example is flaxseed oil. Besides the inclusion of PUFA in canine food, the need to cater to breed-specific dietary requirements is also recognised. In the light of this knowledge, the current research project investigated the breed differences in the biochemical (changes to plasma fatty acid composition) and transcriptional (changes to white blood cell inflammatory-related gene expression) responses to n-3 fatty acids from two dietary sources in two different breeds of dogs. Beagles and greyhounds were chosen for their differences in morphology and propensity to obesity

Revealing the link between evolution of electron transfer capacity of humic acid and key enzyme activities during anaerobic digestion

Humic acid (HA) is an important active compound formed during anaerobic digestion process, with a complex structure and dynamic electron transfer capacity (ETC). However, the mechanisms by which these macromolecular organic compounds dynamically interact with the microbial anaerobic digestion process at different operating temperatures are still unclear. In this study, the link between the evolution of the ETC of HAs and the microbial community under mesophilic and thermophilic conditions was investigated. The results showed an increasing trend in the ETC of HAs in both mesophilic (671–1479 μmol gHA−1) and thermophilic (774–1506 μmol gHA−1) anaerobic digestion (AD) until day 25. The ETC was positively correlated with the bacterial community of hydrolytic and acidogenic phases, but negatively correlated with the archaeal community of the methanogenic phase. Furthermore, the relationship between ETC and key enzyme activity was explored using a co-occurrence network analysis. HAs revealed a high potential to promote key enzyme activities during hydrolysis (amylase and protease) and acidification (acetate kinase, butyrate kinase, and phosphotransacetylase) while inhibiting the key enzyme activity in the methanogenic phase during the anaerobic digestion process. Moreover, HAs formed under thermophilic conditions had a greater influence on key enzyme activities than those formed under mesophilic conditions. This study advances our understanding of the mechanisms underlying the influence of HAs on anaerobic digestion performance

Weed species in tomato production and their role as alternate hosts of 'Tomato spotted wilt virus' and its vector 'Frankliniella occidentalis'

'Tomato spotted wilt virus' (TSWV) is an important plant virus that infects a wide range of hosts including weeds making its management difficult. A survey was undertaken to establish the occurrence of weed species in tomato production systems in Kenya and their role as hosts of TSWV and its vectors. Selected weed species were further evaluated for their reaction to TSWV, transmission efficiency by 'Frankliniella occidentalis' and ability to support thrips reproduction. Of the 43 weed species identified in the field, 29 species had been reported as hosts of TSWV, twowere non-hosts and 11 had no record of their status. Among the more common species, 'Amaranthus hybridus', 'Solanum nigrum', 'Tagetes minuta' and 'Datura stramonium' were susceptible to the virus and supported high levels of thrips reproduction. The TSWV could not be transmitted to 'Galinsoga parviflora' and 'Sonchus oleraceus' by 'F. occidentalis' despite them being highly susceptible in mechanical transmission tests. There was a significant correlation between feeding damage and number of larvae of 'F. occidentalis' on different weeds. Occurrence of weeds that support thrips reproduction and are good hosts of TSWV is a clear indicator of their role in epidemiology and the importance of their management for disease control

Nutritional value of canola meal for broiler chickens as affected by processing conditions, microbial enzymes and essential amino acids

Four experiments were conducted to assess the effects of processing conditions on nutritional value of expeller-extracted canola meal (ECM) and the replacement value of expeller and cold-pressed canola meals in broiler chicken diets. The first two experiments evaluated and characterized the effect of processing conditions such as conditioning temperature (90, 95 or 100 °C) and screw torque (high or low) during oil extraction process on apparent metabolizable energy (AME), apparent and standardised ileal digestibility of amino acids of ECM for broiler chickens. The values obtained in these two experiments were used to formulate diets with high inclusion of ECM to investigate the effect of a microbial multi-carbohydrase obtained by fermentation from 'Aspergillus aculeatus' (Ronozyme® VP), and a microbial mono-component protease (Ronozyme® ProAct), in diets on productive traits, nutrient digestibility and partitioning of energy in broiler chickens. The fourth experiment was designed to determine if reduced feed intake of birds fed CM-based diets, per se accounts for growth depression and if this retarded growth rate can be attenuated by increasing dietary digestible amino acid levels of the diet

Dynamic evolution of humic acids during anaerobic digestion: exploring an effective auxiliary agent for heavy metal remediation

Information on the dynamic evolution of humic acid (HA) from anaerobic digestate and the potential of HA serving as an effective agent for remedying heavy metals is rather scarce. This study monitored the evolution of the structure and functional groups and metal-binding abilities of HA during chicken manure and corn stover anaerobic digestion (AD) processes. Higher increases in aromatic (41-66%) and oxygen-containing functional groups (37-45%) were observed in HA from the AD of corn stover, resulting in higher metal-binding abilities for Cu(II), Co(II), and Ni(II) than those of chicken manure AD. Moreover, HA extracted from fast (before day 12 for chicken manure and day 16 for corn stover), and slow (day 40) methane production stages performed different complexation capacities for the heavy metals. These results reveal the mechanisms of HA and heavy metal interactions, and confirm the potential of HA extracted from AD process for the remediation of heavy metals

Nanobubble aeration enhanced wastewater treatment and bioenergy generation in constructed wetlands coupled with microbial fuel cells

Artificial aeration is a widely used approach in wastewater treatment to enhance the removal of pollutants, however, traditional aeration techniques have been challenging due to the low oxygen transfer rate (OTR). Nanobubble aeration has emerged as a promising technology that utilise nano-scale bubbles to achieve higher OTRs owing to their large surface area and unique properties such as longevity and reactive oxygen species generation. This study, for the first time, investigated the feasibility of coupling nanobubble technology with constructed wetlands (CWs) for treating livestock wastewater. The results demonstrated that nanobubble-aerated CWs achieved significantly higher removal efficiencies of total organic carbon (TOC) and ammonia (NH4+-N), at 49 % and 65 %, respectively, compared to traditional aeration treatment (36 % and 48 %) and the control group (27 % and 22 %). The enhanced performance of the nanobubble-aerated CWs can be attributed to the nearly three times higher amount of nanobubbles (Ø < 1 μm) generated from the nanobubble pump (3.68 × 108 particles/mL) compared to the normal aeration pump. Moreover, the microbial fuel cells (MFCs) embedded in the nanobubble-aerated CWs harvested 5.5 times higher electricity energy (29 mW/m2) compared to the other groups. The results suggested that nanobubble technology has the potential to trigger the innovation of CWs by enhancing their capacity for water treatment and energy recovery. Further research needs are proposed to optimise the generation of nanobubbles, allowing them to be effectively coupled with different technologies for engineering implementation