Enhanced Process Stability Research Articles

Enhanced methane production from anaerobic co-digestion of rice straw and hydrilla verticillata and its kinetic analysis

Rice straw is a widely existing lignocellulosic waste with high potential for methane production. However, high carbon/nitrogen (C/N) ratio of rice straw causes the poor process stability for mono-digestion. This study investigated the co-digestion of rice straw and hydrilla verticillata (nitrogen rich co-substrate) at different C/N ratios to enhance biomass degradation. Different C/N ratios revealed notably enhanced process stability and higher volumetric methane yields than mono-digestion (control). C/N-25 (Co-digestion) showed the highest methane productivity with an increase of 40% than the control. This increase was caused by the improvement of the metabolic pathway due to proper nutritional structure (C/N). C/N-15 obtained the lowest methane yield due to ammonia inhibition (315 mg/L). Biodegradation reaction kinetics parameters were also calculated during the digestion process and it showed reasonably good agreement between the experimental and predicted value (R2 > 0.98) for modified gompertz model. The average Rmax of C/N-25 was 2.78% less than Rmax observed in control. The favourable reducing environment established during the degradation stage was represented by low oxidation-reduction potential (−312.8 mV) values. Since no added energy inputs are required for this process, it is highly practicable on farm-scale in contrast to pretreatment.

Co-digestion of organic and mineral wastes for enhanced biogas production: Reactor performance and evolution of microbial community and function

Mineral wastes (MWs) from municipal solid waste incineration plants and construction demolition sites are rich in minerals, heavy metals and have acid neutralising capacity. This renders such MWs a promising source of bulk and trace elements to enhance and stabilize biogas production in anaerobic processes. However, finding a MW with typical heavy metal concentrations, which promotes anaerobic digestion (AD) without adverse effects on the microbial community of the reactor is of major importance. To investigate the impact of several MW additives (1. incineration bottom ash; 2. fly ash; 3. boiler ash; 4. cement-based waste) as AD co-substrates, six 5 L single stage mesophilic, continuously stirred tank reactors (CSTR) were setup. Two different feeding regimes were employed including: (a) a liquid-recycled feeding method (LRFM); (b) a draw-and-fill feeding method (DFFM). Under the LRFM regime, one gram MW per gram organic waste enhanced process stability (pH), increased methane production (25–45% increase), and yielded (450–520 mL CH4/g VS); DFFM enhanced digestibility to a lesser degree. Illumina HiSeq 16S rRNA community sequencing of reactors showed that the microbial community compositions were unaffected by the presence of MW additives in comparison to unamended controls, but MW amendment accelerated bacterial growth (determined by qPCR). In contrast, different feeding regimes altered the microbial communities; Methanoculleus (hydrogenotrophic) and Methanosaeta (acetoclastic) were the most abundant methanogenic genera in the LRFM reactors, and the more metabolically versatile Methanosarcina genus dominated under DFFM.

Impact of biochar-supported zerovalent iron nanocomposite on the anaerobic digestion of sewage sludge

Anaerobic digestion (AD) is an attractive technology for sludge treatment as it stabilizes sludge and produce renewable energy. However, problems such as low organic matter content and high heavy metals level are often encountered which severely limits the effectiveness of AD. In this study, the biochar-supported nanoscale zerovalent iron (nZVI-BC) was synthesized and used as additives during AD of sewage sludge to investigate the enhancement effects for methane production and its impacts on microbial structure at mesophilic temperature. nZVI-BC addition enhanced process stability by improving the generation and degradation of intermediate organic acids, but inhibitory effects were observed at high dosage. The methane content and cumulative methane yields were increased by 29.56% and 115.39%, respectively. Compared with AD without nZVI-BC, the application of nZVI-BC showed positive effect on improvement of metals (Cu, Cd, Ni, Cr, and Zn) stabilization in the digestate. Microbial community analysis illustrated that nZVI-BC addition could significantly increase the Shannon diversity index and Chao1 richness index of archaea, and meanwhile archaea were more diverse in nZVI-BC amended digesters than in control. It was notable that Methanosaeta dominated in all the digesters at genera level, while the relative abundance of hydrogenotrophic methanogens (Methanobacterium and methanospirillum) increased 35.39% in nZVI-BC amended digesters compared to the control, resulting in higher methane production. The results will guide development of microbial management methods to enhance the stability of AD process.

Mechanism of process imbalance of long-term anaerobic digestion of food waste and role of trace elements in maintaining anaerobic process stability

This study investigated mechanism of process imbalance of long-term anaerobic digestion (AD) of food waste (FW) and role of trace elements (TEs) in maintaining process stability. AD of FW was strongly inhibited by volatile fatty acids (VFA, mainly propionate). The deficiency of essential TEs in FW was the fundamental reason. TEs contents in digester gradually decreased with regular substrate feeding and digestate discharge, which greatly limited growth and metabolism of hydrogenotrophic methanogens and Methanosarcina. Finally, Methanosaeta replaced Methanosarcina and became dominant methanogen and hydrogenotrophic methanogens almost disappeared accompanied by declining methanogenic community diversity, which greatly suppressed ecological functions of methanogens and led to propionate inhibition. TEs supplementation eliminated all factors causing process imbalance and significantly enhanced process stability by maintaining strong ecological functions of methanogens via stimulating dominant growth of Methanosarcina (relative abundance between 67.2% and 87.5%), sustaining stable relative abundances of hydrogenotrophic methanogens (about 10%) and enhancing methanogenic community diversity.

Influence of Surface State in Micro-Welding of Copper by Nd:YAG Laser

Laser welding of copper is characterized by low and unstable light absorption around 1000 nm wavelength. Combination of high thermal conductivity and low melting point makes it difficult to obtain good welding quality and leads to low energy utilization. To improve efficiency and welding quality, a technique to enhance process stability using 1064 nm wavelength Nd:YAG laser has been proposed, and absorption rate and molten volume in laser micro-welding were discussed. Since the surface state of specimen affects absorption phenomena, effects of surface shape and surface roughness were investigated. Absorption rate and molten volume were increased by creating appropriate concave holes and by controlled surface roughness. Stable micro-welding process with deep penetration and good surface quality was achieved for transitional processing condition between heat conduction and keyhole welding, by enhanced absorption rate.

Correlation between wire feed speed and external mechanical constraint for enhanced process stability in underwater wet flux-cored arc welding

It is a great challenge to improve the process stability in conventional underwater wet welding due to the formation of unstable bubble. In this study, mechanical constraint method was employed to interfere the bubble generated by underwater wet welding, and the new method was named as mechanical constraint assisted underwater wet welding. The aim of the study was to quantify the combined effect of wire feed speed and condition of mechanical constraint on the process stability in mechanical constraint assisted underwater wet welding. Experimental results demonstrated that the introduction of mechanical constraint not only suppressed the bubble without floating but also stabilized the arc burning process. The degree of influence of mechanical constraint, which changed with wire feed speed, played an important role during the mechanical constraint assisted underwater wet welding process. For all wire feed speeds, the fluctuations of welding electrical signal were decreased through introduction of mechanical constraint. The difference in the proportion of arc extinction process between underwater wet welding and mechanical constraint assisted underwater wet welding became less with increasing wire feed speed. At wire feed speed lower than 7.5 m/min, the improvement of process stability was very significant by mechanical constraint. However, the further improvement produced limited effect when the wire feed speed was greater than 7.5 m/min. The observation results showed that a better weld appearance was afforded at a large wire feed speed, corresponding to a lower variation coefficient.

Enhanced process stability for the low temperature sputter deposition of aluminium nitride thin films

MEMS (micro electro-mechanical systems) operated in resonance and excited piezoelectrically are nowadays used for a broad range of different application scenarios. To enhance the process stability and hence, the reproducibility of key film parameters of sputter-deposited aluminium nitride such as the film stress, the piezoelectric coefficient d33 and low leakage current levels, a novel aluminium clamped substrate holder is reported. Compared to the standard molybdenum based solution, where the thermal contact between the wafer and substrate holder varies during deposition, as the wafer can move freely, the substrate temperature variations are substantially reduced due to clamped configuration. Independent of AlN film thickness ranging between 0.5 μm and 2.0 μm the scatter in piezoelectric constant d33 and leakage current characteristics represented by the barrier height and the activation energy is reduced up to a factor of 3. These results demonstrate the importance to control carefully the temperature conditions during low-temperature AlN deposition to ensure a high reproducibility in film properties.

(Invited) Advanced Components Development for Electrochemical Ammonia Synthesis

Ammonia is an essential industrial chemical for agricultural fertilizer, medical intermediates, and energy storage. For fuel cell electric vehicle applications, it can be used as a fuel directly or as a means of hydrogen storage due to its high energy density in the liquid state. Conventional ammonia production using Haber-Bosch processes require high pressure and temperature, which is energy intensive. In addition, approximately 1.9 tons of carbon dioxide is released per ton of ammonia produced, because fossil fuels are used as the energy source in the ammonia industry. Meanwhile, renewable energy sources like solar and wind have significantly penetrated into the energy market in the past decade. During off-peak times, a large portion of this renewable energy cannot be utilized and an economically viable technology has to be used to store this surplus, “stranded” energy. The strong need to store off-peak renewable energy provides an unprecedented opportunity to utilize electrochemically synthesized ammonia as a means of accumulating hydrogen equivalents and stranded energy. Our work aims to design and implement advanced components (e.g. catalyst and membrane) to transform electrochemical synthesis of ammonia (EAS) 1-2 and to integrate this process with off-peak renewable energy. The reactants are nitrogen and water that are immediately available and abundant. Novel metal oxide and metal nitride catalysts for the nitrogen reduction reaction (NRR) have been designed and synthesized, which may boost the ammonia production rate by at least an order of magnitude; the developed catalyst can also effectively suppress competing hydrogen evolution reaction. Second, high temperature anion exchange polymer membrane and composite ceramics electrolyte have been explored to further enhance process stability and ammonia production rate; they also enable the EAS at a wide temperature range, from 80 ℃ to 350 ℃. Techno-economic analysis (TEA) of the EAS system integrated with renewable energy will be analyzed to evaluate the cost feasibility. Faradic efficiency and overall electrical efficiency in the context of capital cost and operations cost will also evaluated. Acknowledgement: ARPA-E REFUL Program under award # DE_AR000814 Reference: Marnellos, G., and M. Stoukides, “Ammonia synthesis at atmospheric pressure,” Science, 282(2), 98-100 (1998). Licht, S, Cui, B., Wang, B., Li, F-F, Lau, J., and Liu, S., “Ammonia syhthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3”, Science, 345, 637-640 (2014)

Addition of a foaming agent to improve N2 gas permeability of PVA/alginate carriers for deammonification process

Long term use of anammox carriers immobilized in PVA/alginate has always faced problem due to expansion and bursting due to dense surface. The physical and morphological characteristics were investigated by adding foaming agent to 0, 0.15, 0.3, 0.6 and 1.2 w/v% to increase the gas permeability. Maximum real and bulk density, minimum specific surface area and swelling ratio were found at 0.3 w/v% foaming agent. The gas permeability increased continuously up to 1.2 w/v% foaming agent, as found in the break point test. The 0.3 w/v% foaming agent gave optimum bacteria retention capacity of 98.9%. With 0 w/v% foaming agent, non-porous outer layer was burst due to pressure of produced nitrogen gas as confirmed by morphology test. Addition of foaming agent caused porous structure and the anammox bacteria grew deep inside the carrier. Therefore, the optimum foaming agent content of 0.3% can greatly enhance process stability in the deammonification system.

Effect of viscoelastic relaxation modes on stability of extrusion film casting process modeled using multi-mode Phan-Thien-Tanner constitutive equation

• Linear stability analysis of film casting using multimode PTT model. • Addition of faster moving modes to a slower one enhances stability of the process. • Stability regions of multimodes to not match well with the corresponding averaged ones. Extrusion film casting (EFC) is a commercially important process that is used to produce a significant quantity of polymer films, sheets and coatings for both industrial and household applications. Recently, we have demonstrated the influence of polymer chain architecture on the extent of necking under isothermal as well as non-isothermal film casting operation for commercially relevant polyolefin based materials [1] , [2] , [3] , [4] . In the present research, we focus on another instability that frequently occurs in high-speed EFC process called as draw resonance. Draw resonance manifests itself as an instability that causes periodic fluctuations in both the width as well as thickness of the extruded molten film above a critical draw ratio (DR). In this work, we have carried out a linear stability analysis of the isothermal EFC process using a multi-mode Phan-Thien-Tanner (PTT) constitutive equation to determine the onset of draw resonance. We show that as the number of relaxation modes is increased there is a dramatic change in the stability regions. In particular, there is a marked variation in the stability regions obtained by simulating the multi-mode model and those obtained by taking averaged relaxation time of the modes. Additionally, as the number of faster-relaxing modes in a multi-mode spectrum is progressively increased, the process becomes increasingly stable as the level of elasticity in the melt decreases. Finally, the addition of a long relaxation mode in a multi-mode spectrum is akin to adding a long chain branch to a linear polymer that leads to a reduction in film necking and in many cases to enhanced process stability.

Surface quality in micro milling: Influences of spindle and cutting parameters

Micro milling is a competitive process to manufacture small parts and to structure surfaces in high quality with low set-up costs. However, the micro milling process poses many challenges and basic mechanisms are still to be researched. In addition, process-machine interactions are much more pronounced in micro than in macro machining. In this paper, the influence of the tilt angle of the spindle on the generated surface quality is investigated by kinematic simulations and experiments. Single edge micro end mills with an effective milling cutter diameter of 50μm are applied. Recommendations are given to enhance process stability and surface quality.

Evaluation of tool steel alloy performance in a milling operation through operational dynamic parameters

Dynamic characteristics of machine tools and cutting tools have gained much attention from researchers and industry as it is one of the major factors limiting productivity due to excessive vibrations such as chatter during the cutting process. Numerous factors have to be taken into consideration when selecting material of the cutter body. This paper presents a comparison between two cutter bodies with the same geometry but made out of different alloys. Pre-hardened steel and conventional tool steel were investigated in order to highlight the advantages of selecting correct material to achieve high performance tools with respect of chatter resistance. The experimental part of this paper consists of impact testing, machining tests and surface integrity measurements. Operational dynamic parameters obtained through auto-regressive moving average model estimates from machining tests under stable and unstable conditions was used to characterise the performance. The findings are in correlation with material damping research and chatter analysis, thus giving a strong coupling to material selection in tool holders for enhanced process stability. The research also shows that operational dynamic properties obtained through indirect measurements is a valuable tool for process stability characterisation.

Towards a sustainable paradigm of waste-to-energy process: Enhanced anaerobic digestion of sludge with woody biochar

This study presents an integrated waste-to-energy process, using two waste streams, sludge generated from the municipal wastewater treatment plants (WWTPs) and biochar generated from the biomass gasification systems, to produce fungible biomethane and nutrient-rich digestate with fertilizer value. Two woody biochar, namely pinewood (PBC) and white oak biochar (WOBC) were used as additives during anaerobic digestion (AD) of WWTP sludge to enhance methane production at mesophilic and thermophilic temperatures. The PBC and WOBC have porous structure, large surface area and desirable chemical properties to be used as AD amendment material to sequester CO2 from biogas in the digester. The biochar-amended digesters achieved average methane content in biogas of up to 92.3% and 79.0%, corresponding to CO2 sequestration by up to 66.2% and 32.4% during mesophilic and thermophilic AD, respectively. Biochar addition enhanced process stability by increasing the alkalinity, but inhibitory effects were observed at high dosage. It also alleviated free ammonia inhibition by up to 10.5%. The biochar-amended digesters generated digestate rich in macro- and micronutrients including K (up to 300 m/L), Ca (up to 750 mg/L), Mg (up to 1800 mg/L) and Fe (up to 390 mg/L), making biochar-amended digestate a potential alternative used as agricultural lime fertilizer.

Enhancing biogas production from vinasse in sugarcane biorefineries: Effects of urea and trace elements supplementation on process performance and stability

In this study, the effects of nitrogen, phosphate and trace elements supplementation were investigated in a semi-continuously operated upflow anaerobic sludge blanket system to enhance process stability and biogas production from sugarcane vinasse. Phosphate in form of KH2PO4 induced volatile fatty acids accumulation possibly due to potassium inhibition of the methanogenesis. Although nitrogen in form of urea increased the reactor’s alkalinity, the process was overloaded with an organic loading rate of 6.1gCODL−1d−1 and a hydraulic retention time of 3.6days. However, by supplementing urea and trace elements a stable operation even at an organic loading rate of 9.6gCODL−1d−1 and a hydraulic retention time of 2.5days was possible, resulting in 79% higher methane production rate with a stable specific methane production of 239mLgCOD−1.

Generalized multi-attribute failure mode analysis

Modern technology products are becoming more advanced, complex, and expensive, necessitating the use of failure mode and effects analysis (FMEA) to stabilize production and enhance market competitiveness. Traditional FMEA adopts the risk priority number (RPN) to stabilize production and monitor risks of failure. The RPN has 3 parameters—severity (S), occurrence (O), and detection (D)—which are used to assess and prioritize potential risks in production. Although the traditional RPN is efficient, it has several shortcomings. For example, it assumes that weighting factors have equal weight, it fails to examine the nature of problems stepwise and structurally, available information can be lost easily, and priority orders are assessed identically with high frequency. Thus, to improve the RPN, we propose an integrated method, combining multiattribute failure mode analysis (MAFMA) and 2-tuple representation, called generalized multiattribute failure mode analysis (GMAFMA). This study uses a TFT-LCD product of a technology company in Taiwan as an actual case study and compares the RPN, MAFMA, and GMAFMA by numerical verification, demonstrating that the disadvantages above are improved and obtaining a more reasonable assessment of risk priority. This method provides references that enhance process stability and reduce the risk of failure for managers.

Toward sustainable dairy waste utilization: enhanced VFA and biogas synthesis via upcycling algal biomass cultured on waste effluent

AbstractBACKGROUNDIn 2012, 9.3 million head of dairy cows in the USA produced an estimated 20 million metric tons of manure solids, but little value was gained from this manure. There is a pressing need to enhance manure resource recovery efforts, as dairy manure has potentially significant environmental impacts. This study evaluated components of an integrated suite of biological processes designed to maximize resource recovery from dairy manure, in which algae grown on polyhydroxyalkanoate (PHA) production effluent (PHA‐algae) were fermented and anaerobically digested to determine process impacts.RESULTSA 10% PHA‐algae supplement produced 11% more volatile fatty acids (VFA) during fermentation and 11% more methane during anaerobic digestion (AD) (vs. dairy manure); the PHA‐algae biogas also contained a higher percentage (62.7 vs. 59.1%) of methane than manure biogas. Algal augmentation exhibited no negative effect on fermenter or AD operation. Quantitative polymerase chain reaction (PCR) showed that the ADs contained substantial populations of both acetoclastic and hydrogenotrophic methanogens, which, given the heterogeneous substrate, enhanced process stability. There were significant differences between PHA‐algae batches, and large quantities of COD were released during algae freezing.CONCLUSIONPHA‐algae yielded more VFA during fermentation, and a more methane‐rich biogas following AD than dairy manure. A 10% PHA‐algae supplement caused no process disturbance in normal manure flora. © 2015 Society of Chemical Industry

Using the properties of soil to speed up the start-up process, enhance process stability, and improve the methane content and yield of solid-state anaerobic digestion of alkaline-pretreated poplar processing residues.

BackgroundSolid-state anaerobic digestion (SS-AD) was initially adopted for the treatment of municipal solid waste. Recently, SS-AD has been increasingly applied to treat lignocellulosic biomass, such as agricultural and forestry residues. However, studies on the SS-AD process are few. In this study, the process performance and methane yield from SS-AD of alkaline-pretreated poplar processing residues (PPRs) were investigated using the properties of soil, such as buffering capacity and nutritional requirements.ResultsThe results showed that the lignocellulosic structures of the poplar sample were effectively changed by NaOH pretreatment, as indicated by scanning electron microscopy and Fourier transform infrared spectra analysis. The start-up was markedly hastened, and the process stability was enhanced. After NaOH pretreatment, the maximum methane yield (96.1 L/kg volatile solids (VS)) was obtained under a poplar processing residues-to-soil sample (P-to-S) ratio of 2.5:1, which was 29.9% and 36.1% higher than that of PPRs (74.0 L/kg VS) and that of experiments without NaOH pretreatment (70.6 L/kg VS), respectively. During steady state, the increase in the methane content of the experiment with a P-to-S ratio of 2.5:1 was 4.4 to 50.9% higher than that of the PPRs. Degradation of total solids and volatile solids ranged from 19.3 to 33.0% and from 34.9 to 45.9%, respectively. The maximum reductions of cellulose and hemicellulose were 52.6% and 42.9%, respectively, which were in accordance with the maximal methane yield. T80 for the maximum methane yield for the experiments with NaOH pretreatment was 11.1% shorter than that for the PPRs.ConclusionsPretreatment with NaOH and addition of soil led to a significant improvement in the process performance and the methane yield of SS-AD of PPRs. The changes in lignocellulosic structures induced by NaOH pretreatment led to an increase in methane yield. For the purpose of practical applications, SS-AD with soil addition is a convenient, economical, and practical technique.

The Research of Coated Product Quality Control System Based on PAT

This article describes the current quality control method during hot coating process. To improve the current quality control method during hot coating process, this article also elaborates the advanced coated product quality control system based on process analytical technology (PAT), the concept of which is “Quality by Design”, the targets of which are to enhance process stability and to improve the technological and economic index.

Anaerobic co-digestion of the marine microalga Nannochloropsis salina with energy crops

Anaerobic co-digestion of corn silage with the marine microalga Nannochloropsis salina was investigated under batch and semi-continuous conditions. Under batch conditions process stability and biogas yields significantly increased by microalgae addition. During semi-continuous long-term experiments anaerobic digestion was stable in corn silage mono- and co-digestion with the algal biomass for more than 200 days. At higher organic loading rates (4.7 kg volatile solids m(-3)d(-1)) inhibition and finally process failure occurred in corn silage mono-digestion, whereas acid and methane formation remained balanced in co-digestion. The positive influences in co-digestion can be attributed to an adjusted carbon to nitrogen ratio, enhanced alkalinity, essential trace elements and a balanced nutrient composition. The results suggest that N. salina biomass is a suitable feedstock for anaerobic co-digestion of energy crops, especially for regions with manure scarcity. Enhanced process stability may result in higher organic loading rates or lower digester volumes.

Enhancing pIFN-α Production and Process Stability in Fed-Batch Culture of Pichia pastoris by Controlling the Methanol Concentration and Monitoring the Responses of OUR/DO Levels

Effective expression of porcine interferon-α (pIFN-α) with recombinant Pichia pastoris was conducted in a bench-scale fermentor using an in situ methanol electrode-based feeding process with the control level of methanol concentration linearly increased to 10 g l⁻¹ for the first 20 h and maintained at 10 g l⁻¹ for the rest of expression phase. With this two-stage control process, the highest pIFN-α concentration reached a level of 1.81 g l⁻¹, which was 1.5-fold of that in the previous constant 10 g l⁻¹ induction experiments. There is an improvement of the pIFN-α productivity from more distribution of carbon flux to protein expression. The pIFN-α expression stability could be further enhanced by a simple on-line fault diagnosis method for methanol overfeeding based on oxygen uptake rate changing patterns. By implementing corrective action of feeding glycerol after fault detection, the production yield increased to twice the amount it would have been without the diagnosis.