Anaerobic digestion of cellulose and hemicellulose in the presence of humic acids

Research on the hydrolysis step of the AD became more important with the increased use of recalcitrant waste products such as manure, sewage sludge and agricultural biomass for biogas production. Hydrolysis is often the rate limiting step of the overall AD. Hydrolysis enhancement is one of the required steps to optimise biogas production. Despite the progress to overcome the limitations of hydrolysis, inhibition of hydrolysis is still poorly researched. Humic acid-like molecules (HA) are one of the inhibitors of the anaerobic hydrolysis and their effect on the overall AD process is generally overlooked. In this thesis, the HA inhibition on anaerobic digestion of cellulosic material and mitigation strategies, using cation and enzyme addition, to overcome the inhibition were investigated. In addition, the microbial community dynamics during AD in the presence and absence of HA were examined. In this scope, in Chapter 2, we reviewed the literature and pinpointed the urgent need for comprehensive studies on the role of hydrolytic microorganisms and environmental factors that effects their abundance within biogas plants. Consequently, the hydrolysis mechanism and involved hydrolytic enzymes were discussed. The overall discussion showed that a holistic approach, including microbiological and engineering studies should be chosen to disclose the role of hydrolytic microbes within biogas reactors. In Chapter 3 and, Chapter 4 the effect of HA on anaerobic cellulose hydrolysis and methanogenesis, in batch wise incubations is reported, respectively. Our results showed that pulse addition of 5 g L-1 HA caused a 50 % decrease in hydrolysis rate of anaerobic cellulose degradation (Chapter 3). Moreover, VFA accumulation was observed in the presence of HA during the anaerobic cellulose degradation, which indicated the possible inhibition of HA on methanogenesis. Based on the results of Chapter 3, pure cultures of methanogens and a mixed culture were tested to study the vulnerability of methanogenesis to HA inhibition. Hydrogenotrophic methanogenesis in pure cultures was inhibited by more than 75% in the presence of 1 g L-1 HA whereas, acetoclastic methanogenesis by Methanosaeta concilii was only slightly affected by HA up to 3 g L-1. When methanogenic granular sludge was incubated with HA, the specific methanogenic activity tests showed less inhibition, when compared to the pure cultures of methanogens. HA inhibition was also observed during long-term CSTR operation at an HRT of 20 days, 35°C and a mixture of cellulose and xylan as a subtrate (Chapter 6). 8 g L-1 HA inhibited the hydrolysis efficiency of the cellulose and xylan digestion by 40 % and concomitantly reduced the methane yields. Mitigation of the HA inhibition is required to increase the hydrolysis efficiency and methane yields of cellulosic biomass digestion. Therefore, two different strategies were tested for their potential use as mitigation agents, viz. addition of cations such as, calcium magnesium and iron (Chapter 3 and Chapter 6) and addition of hydrolytic enzymes (Chapter 6). Addition of magnesium, calcium and iron salts mitigated the HA inhibition and hydrolysis efficiencies reached up to 75, 65 and 72%, respectively, compared to the control groups in the batch wise incubations (Chapter 3). However, in long term CSTR operations, calcium addition did not show a positive effect on hydrolysis inhibition. On the other hand, enzyme addition helped to reverse the negative effect of HA. The microbial communities involved in AD were also studied. Chapter 5 and Chapter 6 dealt with microbial community analyses with 16S rRNA next generation sequencing. In Chapter 5, five replicate reactors were monitored during the start-up period. Transient feeding strategy was used to acclimatise anaerobic sludge to efficient cellulose and xylan degradation. During the experiment, Bacteriodales, Clostridiales and Anaerolineales became dominant bacterial populations while, Methanobacteriaceae and Methanospirillaceae were the dominant archaeal populations within the reactors. In Chapter 6, the microbial population dynamics in the presence and absence of HA were monitored. Microbiological analyses showed that the abundance of hydrolytic/fermentative bacterial groups such as Clostridiales, Bacteroidales and Anaerolineales was significantly lowered by the presence of HA. HA also affected the archaeal populations. Mostly hydrogenotrophic methanogens were negatively affected by HA. In conclusion, this thesis confirms that HA inhibit the hydrolysis and methanogenesis within both batch incubations and CSTR systems. Microbial populations were also affected by HA. Therefore, hydrolytic enzyme addition can be an option to mitigate HA inhibition and enhance hydrolysis and methanogenesis during conversion of biomass to biogas.</p

Determination of Anaerobic and Anoxic Biodegradation Capacity of Sulfamethoxasole and the Effects on Mixed Microbial Culture

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Blow-up of solutions to parabolic inequalities in the Heisenberg group

We establish a Fujita-type theorem for the blow-up of nonnegative solutions to a certain class of parabolic inequalities in the Heisenberg group. Our proof is based on a duality argument

Nonexistence of global solutions for fractional temporal Schrodinger equations and systems

We, first, consider the nonlinear Schrodinger equation $$i^\alpha {}_0^C D_t^\alpha u+\Delta u= \lambda |u|^p+\mu a(x)\cdot\nabla |u|^q, \quad t>0,\; x\in \mathbb{R}^N,$$ where 0<\alpha lt;1, $i^\alpha$ is the principal value of $i^\alpha$, ${}_0^C D_t^\alpha$ is the Caputo fractional derivative of order $\alpha$, $\lambda\in \mathbb{C}\backslash\{0\}$, $\mu\in \mathbb{C}$, $p>q>1$, $u(t,x)$ is a complex-valued function, and $a: \mathbb{R}^N\to \mathbb{R}^N$ is a given vector function. We provide sufficient conditions for the nonexistence of global weak solution under suitable initial data. Next, we extend our study to the system of nonlinear coupled equations \displaylines{ i^\alpha {}_0^C D_t^\alpha u+\Delta u = \lambda |v|^p+\mu a(x)\cdot\nabla |v|^q, \quad t>0,\;x\in \mathbb{R}^N,\cr i^\beta {}_0^C D_t^\beta v+\Delta v = \lambda |u|^\kappa+\mu b(x)\cdot\nabla |u|^\sigma, \quad t>0,\; x\in \mathbb{R}^N, } where $0<\beta\leq \alpha<1$, $\lambda\in \mathbb{C}\backslash\{0\}$, $\mu\in \mathbb{C}$, $p>q>1$, $\kappa>\sigma>1$, and $a,b: \mathbb{R}^N\to \mathbb{R}^N$ are two given vector functions. Our approach is based on the test function method

Ammonia Recovery from Organic Waste Digestate via Gas&ndash;Liquid Stripping: Application of the Factorial Design of Experiments and Comparison of the Influence of the Stripping Gas

The effects of temperature, pH, and gas-to-liquid-volume-ratio on ammonia recovery via gas&ndash;liquid stripping have been widely studied. However, there is a lack of a structured approach towards characterising the stripping process. Furthermore, limited information is available on the effect of the composition of the stripping gas on ammonia recovery. This study includes the application of a factorial design of experiments to ammonia stripping. The outcome is a mathematical relationship for ammonia recovery as a function of process conditions. The temperature was found to have the highest influence on ammonia recovery. With respect to the influence of the stripping gas, similar ammonia recoveries were reported when using air, CH4, and N2 (96, 92, and 95%, respectively). This was attributed to their similar influences on the pH of the digestate, and subsequently, on the free ammonia equilibrium. In addition, the presence of CO2 in the stripping gas had a critical effect on ammonia recovery due to its influence on the total ammonia equilibrium in the digestate. These results showed the possibility of using different stripping gases interchangeably to obtain similar ammonia recoveries, with a critical emphasis on their CO2 content

Ammonia Recovery from Organic Waste Digestate via Gas–Liquid Stripping: Application of the Factorial Design of Experiments and Comparison of the Influence of the Stripping Gas

The effects of temperature, pH, and gas-to-liquid-volume-ratio on ammonia recovery via gas–liquid stripping have been widely studied. However, there is a lack of a structured approach towards characterising the stripping process. Furthermore, limited information is available on the effect of the composition of the stripping gas on ammonia recovery. This study includes the application of a factorial design of experiments to ammonia stripping. The outcome is a mathematical relationship for ammonia recovery as a function of process conditions. The temperature was found to have the highest influence on ammonia recovery. With respect to the influence of the stripping gas, similar ammonia recoveries were reported when using air, CH4, and N2 (96, 92, and 95%, respectively). This was attributed to their similar influences on the pH of the digestate, and subsequently, on the free ammonia equilibrium. In addition, the presence of CO2 in the stripping gas had a critical effect on ammonia recovery due to its influence on the total ammonia equilibrium in the digestate. These results showed the possibility of using different stripping gases interchangeably to obtain similar ammonia recoveries, with a critical emphasis on their CO2 content

Nonexistence of global solutions for fractional temporal schrödinger equations and systems

We, first, consider the nonlinear Schrödinger equation (Formula Presented)where 0 &lt; α &lt; 1, iα is the principal value of (Formula Presented) is the Caputo fractional derivative of order (Formula Presented) is a complex-valued function, and a: ℝN→ ℝN is a given vector function. We provide suffcient conditions for the nonexistence of global weak solution under suitable initial data. Next, we extend our study to the system of nonlinear coupled equations (Formula Presented) where (Formula Presented), and a; b: ℝN → ℝ N are two given vector functions. Our approach is based on the test function method. ©2017 Texas State University

Dairy Manure Digestate Age Increases Ultrasound Disintegration Efficiency at Low Specific Energies

Substantial insight into the effect of ultrasound disintegration on the changes in biochemical parameters of manure digestate and digestate age is needed to understand the potential of digestate treatment. To address this knowledge gap, in this study, the effect of digestate age on the efficiency of ultrasound (US) disintegration was investigated. In this scope, dairy manure digestate samples were incubated in an oven at 37 °C for a predetermined amount of time to obtain simulated digestate ages of 15, 22, 29, 36 and 43 days. The results showed that US disintegration efficiency significantly affected the initial biochemical characteristics of digestate and that the digestate age had a significant effect on the US disintegration efficiency. This effect diminished when the applied specific energy (SE) was higher than 3000 kJ/kg total solids (TS). A numerical partial least squares (PLS) model was constructed to investigate the relative influences of the initial biochemical parameters on the soluble chemical oxygen demand (sCOD) and soluble carbohydrates (sCARB) solubilization. The results of the high-quality (R2 = 0.8) model indicated that the most influential parameters for the efficiency of US disintegration were the SE, the initial sCARB0, the TS, the initial sCOD0 and the volatile solids (VS)

Nonexistence of global solutions for fractional temporal schrödinger equations and systems

We, first, consider the nonlinear Schrödinger equation (Formula Presented)where 0 &lt; α &lt; 1, iα is the principal value of (Formula Presented) is the Caputo fractional derivative of order (Formula Presented) is a complex-valued function, and a: ℝN→ ℝN is a given vector function. We provide suffcient conditions for the nonexistence of global weak solution under suitable initial data. Next, we extend our study to the system of nonlinear coupled equations (Formula Presented) where (Formula Presented), and a; b: ℝN → ℝ N are two given vector functions. Our approach is based on the test function method. ©2017 Texas State University

Mitigation of Humic Acid Inhibition in Anaerobic Digestion of Cellulose by Addition of Various Salts

Humic compounds are inhibitory to the anaerobic hydrolysis of cellulosic biomass. In this study, the impact of salt addition to mitigate the inhibitory effects of humic compounds was investigated. The experiment was conducted using batch tests to monitor the anaerobic hydrolysis of cellulose in the presence of humic acid. Sodium, potassium, calcium, magnesium and iron salts were tested separately for their efficiency to mitigate humic acid inhibition. All experiments were done under mesophilic conditions (30 °C) and at pH 7. Methane production was monitored online, using the Automatic Methane Potential Test System. Methane production, soluble chemical oxygen demand and volatile fatty acid content of the samples were measured to calculate the hydrolysis efficiencies. Addition of magnesium, calcium and iron salts clearly mitigated the inhibitory effects of humic acid and hydrolysis efficiencies reached up to 75%, 65% and 72%, respectively, which were similar to control experiments. Conversely, potassium and sodium salts addition did not mitigate the inhibition and hydrolysis efficiencies were found to be less than 40%. Mitigation of humic acid inhibition via salt addition was also validated by inductively coupled plasma atomic emission spectroscopy analyses, which showed the binding capacity of different cations to humic acid.status: publishe