Non-enclosure methods for non-suspended microalgae cultivation: literature review and research needs

Microalgae are getting more interests from industry and science communities. Applications of these small, unicellular microorganisms are countless: from fourth generation biofuels, through fish feed to pharmaceuticals. Ordinary methods of cultivation may be associated with many problems such as high costs, high energy consumption, and low product yield. It is difficult to control contaminations in open ponds while photobioreactors are mainly at laboratory scale and expensive to scale-up. Scientists are investigating various methods of microalgae cultivation and processing to overcome those problems. One of the novel approaches is the non-suspended method for microalgae culturing, where microalgae are grown on attached surfaces. Growing microalgae on surfaces is an attractive option and showing promising results. In comparison with ordinary suspended photobioreactors, the attached systems offer higher biomass yields, easy to scale-up with better light distribution within the reactor and better control of contamination. Moreover, the consumption of water can be drastically reduced. So far, there is not enough research for this method. Limited studies have been reported on enclosure mode of this approach with algae encapsulation into matrix. It is found that this mode would be difficult to scale up due to high costs of the enclosure material and difficulty of separating microalgae from matrix. Non-enclosure mode is more promising way of non-suspended cultivation. So far, no work has been carried out to conduct non-suspended culturing with the use of aeroterrestrial microalgae. They are species growing on the surfaces at highly humid environments. Using them in attached cultivation systems could potentially lower the water consumption to minimum. Studies have shown that the biomass of lower water content can be produced if compared to non-suspended cultivation methods. In addition, mechanization of the cultivation and harvesting processes would be less complex, as the product will not be immersed in the liquid. There would be no need for glass reactors, as lights can be placed in the spaces between surfaces. The light distribution is predicted to be the highest among all existing methods, as there would be no free floating particles absorbing and reflecting light. It will only need humid conditions, rich in CO2 between attachment surfaces. To evaluate potential advantages for non-suspended culturing of aeroterrestrial microalgae in non-enclosure way, proper experiments need to be conducted. In this review, basic concepts of attached cultivation system are discussed, focusing on the studies of biofilm formation including factors affecting deposition and systems. The detailed description of aeroterrestrial microalgae is included to give insight into potential applications of the species into attached cultivation systems

New direction in electrode design for electrochemical energy storage

With the electrification of transport, the increase in cordless appliances, and the intention of many countries to switch to renewable energy production, the demand in energy storage, especially in batteries, is rapidly increasing. At present, lithium-ion batteries are used to power most electric cars and portable devices.[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] However, lithium is a rare material with an appearance in the upper earth crust of less than 70 ppm and its primary resources in China and Bolivia.[12] Sodium-ion batteries are discussed as a potential alternative to replace lithium-ion batteries partly.[13, 14, 15, 16, 17, 18] Like lithium-ion batteries, sodium-ion batteries contain transition metal materials on the cathode side, e.g., layered oxide or phosphates, paired with a carbon comprising anode. Graphite cannot be reversibly cycled in sodium-ion batteries when carbonated electrolytes are used, so amorphous hard carbon is the anode of choice for sodium-ion batteries.[13, 19, 20] But improvements in the observed charge rate are required for many potential applications such as power tools, e-mobility and stationary energy storage. An improvement in electrode design is required to enable fast charging of sodium-ion batteries and eliminate metallic dendrite growth on the electrodes. In this work, fundamental research is undertaken to understand the limitations in cell testing design and the influence of testing parameters to build up a reliable and repeatable test regime. The then tested composite electrodes are determined in terms of electrochemical performance and physical properties with the aim to link manufacturing parameters to performance and implement those findings to improve the overall battery performance. The results emphasize the importance and limitations of ionic transport within hard carbon electrodes, and the required optimization between electronic and ionic conductivity for sodium-ion transport in these electrodes. By adding the ionic conductor zeolite to the composite electrode, better rate performance and improved ageing characteristics were observed, which may enable faster charging of sodium-ion batteries

The moderating impact of supply network topology on the effectiveness of risk management

While supply chain risk management offers a rich toolset for dealing with risk at the dyadic level, less attention has been given to the effectiveness of risk management in complex supply networks. We bridge this gap by building an agent based model to explore the relationship between topological characteristics of complex supply networks and their ability to recover through inventory mitigation and contingent rerouting. We simulate upstream supply networks, where each agent represents a supplier. Suppliers’ connectivity patterns are generated through random and preferential attachment models. Each supplier manages its inventory using an anchor-and-adjust ordering policy. We then randomly disrupt suppliers and observe how different topologies recover when risk management strategies are applied. Our results show that topology has a moderating effect on the effectiveness of risk management strategies. Scale-free supply networks generate lower costs, have higher fill-rates, and need less inventory to recover when exposed to random disruptions than random networks. Random networks need significantly more inventory distributed across the network to achieve the same fill rates as scale-free networks. Inventory mitigation improves fill-rate more than contingent rerouting regardless of network topology. Contingent rerouting is not effective for scale-free networks due to the low number of alternative suppliers, particularly for short-lasting disruptions. We also find that applying inventory mitigation to the most disrupted suppliers is only effective when the network is exposed to frequent disruptions; and not cost effective otherwise. Our work contributes to the emerging field of research on the relationship between complex supply network topology and resilience

Can Combined Priority Bus Lanes, as a Preparatory Step of Bus Rapid Transit (BRT) Implementation, Improve Public Transport Service Performance? Assessing two Bus Route and Layout Options for the City of Chisinau/Moldova

This study assesses the performance impacts of a projected exclusive Combined Priority Lane (CPL) network for the use of all scheduled public transport systems (trolleybuses, conventional diesel buses and minibuses) in the City of Chisinau. For the assessment, two in terms of network extent different route layout options were compared to the current public transport situation. The CPL design enables a subsequent Bus Rapid Transit Systems (BRT) upgrade. In a multi-layered approach a utility analysis was conducted, evaluating 15 performance indicators describing transport and economical efficiency, as well as societal and environmental impacts. Furthermore cost-utility estimations were made for the investment costs of the two layout options. The results were benchmarked with best practice development alternatives. For the procedure a set of empirical methodologies mainly from transport, social, and economic sciences as well as urbanism were used. The results point out that especially transport users and the local economy benefit from extensive travel time savings. In regard to the enhanced travel time competitiveness the measure entails a notable shift of trips from motorized to public transport, which proves to have a positive impact on local environment and energy consumption schemes. Accordingly, the overall rating of the CPL impact on Chisinau public transport performance was positive. However, comparing the CPL model with other development alternatives, it must be clear that it could only be the first step on the pathway to an efficient, equitable, attractive, and sustainable public transport

Topological robustness of the global automotive industry

The manufacturing industry is characterized by large-scale interdependent networks as companies buy goods from one another, but do not control or design the overall flow of materials. The result is a complex emergent structure with which companies connect to each other. The topology of this structure impacts the industry’s robustness to disruptions in companies, countries, and regions. In this work, we propose an analysis framework for examining robustness in the manufacturing industry and validate it using an empirical dataset. Focusing on two key angles, suppliers and products, we highlight macroscopic and microscopic characteristics of the network and shed light on vulnerabilities of the system. It is shown that large-scale data on structural interdependencies can be examined with measures based on network science

Resilence of complex supply networks

During recent decades supply chains have grown, and became increasingly interconnected due to globalisation and outsourcing. Empirical and theoretical studies now characterise supply chains as complex networks rather than the hierarchical, linear chain structures often theorised in classical literature. Increased topological complexity resulted in an increased exposure to risk, however existing supply chain risk management methodologies are designed based on the linear structure assumption rather than interdependent network structures. There is a growing need to better understand the complexities of supply networks, and how to identify, measure and mitigate risks more efficiently. The aim of this thesis is to identify how supply network topology influences resilience. More specifically, how applying well-established supply chain risk management strategies can decrease disruption impact in different supply network topologies. The influence of supply network topology on resilience is captured using a dynamic agent-based model based on empirical and theoretical supply network structures, without a single entity controlling the whole system where each supplier is an independent decision-maker. These suppliers are then disrupted using various disruption scenarios. Suppliers in the network then apply inventory mitigation and contingent rerouting to decrease impact of disruptions on the rest of the network. To the best of author’s knowledge, this is the first time the impact of random disruptions and its reduction through risk management strategies in different supply network topologies have been assessed in a fully dynamic, interconnected environment. The main lessons from this work are as follows: It has been observed that the supply network topology plays a crucial role in reducing impact of disruptions. Some supply network topologies are more resilient to random disruptions as they better fulfil customer demand under perturbations. Under random disruptions, inventory mitigation is a well-performing shock absorption mechanism. Contingent rerouting, on the other hand, is a strategy that needs specific conditions to work well. Firstly, the strategy must be applied by companies in supply topologies where the majority of supply chain members have alternative suppliers. Secondly, contingent rerouting is only efficient in cases when the reaction time to supplier’s disruption is shorter than the duration of the disruption. It has also been observed that the topological position of the individual company who applies specific risk management strategy heavily impacts costs and fill-rates of the overall system. This property is moderated by other variables such as disruption duration, disruption frequency and the chosen risk management strategy. An additional, important lesson here is that, choosing the supplier that suffered the most from disruptions or have specific topological position in a network to apply a risk management strategy might not always decrease the costs incurred by the whole system. In contrast, it might increase it if not applied appropriately. This thesis underpins the significance of topology in supply network resilience. The results from this work are foundational to the claim that it is possible to design an extended supply network that will be able reduce the impact of certain disruption types. However, the design must consider topological properties as well as moderating variables.PhD in Manufacturin

Aeroterrestrial and freshwater microalgae biofilms: deposition and growth in aqueous and non-aqueous systems.

Non-suspended microalgal cultivation methods have gained an interest over the last decade. In contrast to traditional cultivation systems, where microalgae are grown in highly diluted suspensions, microalgae grow concentrated in biofilms over a particular substrate. Growth in biofilms gives higher biomass concentrations of end products and decreases overall water and energy consumption. However, there are research gaps in the field of biofilm formation and growth. The studies on material and strain properties and their effects on microbial attachment are very limited. So far, a small number of strains and materials have been tested, leading to many contradictory conclusions. In this thesis the primary colonisation of 36 material-strain pairings was tested and related to topographical and physicochemical properties of substrates. Experimental data was also confronted against properties of microalgal strains. Further microalgal biofilm development in aerial conditions, and its relation to substrate properties, was analysed for the first time. To address some of the sustainability issues associated with microalgal cultivation, a novel Humid Biofilm-Based Reactor (HBBR) was also proposed. This novel method focused on growing microalgae in a humid atmosphere enriched with nutrients. The natural phenomenon of biofilm development in aerial humid conditions was a working principle of the system, resulting in higher biomass concentrations than in other non-suspended reactors proposed so far. Using mist instead of a liquid medium significantly minimised the water consumption. No presence of a liquid medium in the reactor enabled easier maintenance of the system and improved light distribution. Growth trial in this novel reactor and its comparison to reference systems showed that HBBR was a promising way of culturing microalgae with higher growth rates, lower water and nutrient consumption, more effective light distribution and easier maintenance of the system.PhD in Energy and Powe

Artificial dry surface biofilm (DSB) models for testing the efficacy of cleaning and disinfection

Dry surface biofilms (DSB) harbouring pathogens are widespread in healthcare settings, difficult to detect and resistant to cleaning and disinfection interventions. Here, we describe a practical test protocol to palliate the lack of standard efficacy test methods for DSB. Staphylococcus aureus DSB were produced over a 12‐day period, grown with or without the presence of organic matter, and their composition and viability were evaluated. Disinfectant treatment was conducted with a modified ASTM2967‐15 test and reduction in viability, transferability, and biofilm regrowth post treatment were measured. Dry surface biofilms produced over a 12‐day period had a similar carbohydrates, proteins and DNA content, regardless the presence or absence of organic matter. The combination of sodium hypochlorite (1,000 ppm) and a microfiber cloth was only effective against DSB in the absence of organic load. With the increasing concerns of the uncontrolled presence of DSB in healthcare settings, the development of effective interventions is paramount. We propose that our DSB model in the presence of organic load is appropriate for the testing of biocidal products, while the use of three parameters, log10 reduction, transferability and regrowth, provides an accurate and practical measurement of product efficacy

It's a trap! The development of a versatile drain biofilm model and its susceptibility to disinfection

Background Pathogens in drain biofilms pose a significant risk for hospital-acquired infection. However, the evidence of product effectiveness in controlling drain biofilm and pathogen dissemination are scarce. A novel in-vitro biofilm model was developed to address the need for a robust, reproduceable and simple testing methodology for disinfection efficacy against a complex drain biofilm. Methods Identical complex drain biofilms were established simultaneously over 8 days, mimicking a sink trap. Reproducibility of their composition was confirmed by next-generation sequencing. The efficacy of sodium hypochlorite 1000 ppm (NaOCl), sodium dichloroisocyanurate 1000 ppm (NaDCC), non-ionic surfactant (NIS) and peracetic acid 4000 ppm (PAA) was explored, simulating normal sink usage conditions. Bacterial viability and recovery following a series of 15-min treatments were measured in three distinct parts of the drain. Results The drain biofilm consisted of 119 mixed species of Gram-positive and -negative bacteria. NaOCl produced a >4 log10 reduction in viability in the drain front section alone, while PAA achieved a >4 log10 reduction in viability in all of the drain sections following three 15-min doses and prevented biofilm regrowth for >4 days. NIS and NaDCC failed to control the biofilm in any drain sections. Conclusions Drains are one source of microbial pathogens in healthcare settings. Microbial biofilms are notoriously difficult to eradicate with conventional chemical biocidal products. The development of this reproducible in-vitro drain biofilm model enabled understanding of the impact of biocidal products on biofilm spatial composition and viability in different parts of the drain. Keyword

Candida auris dry surface biofilm (DSB) for disinfectant efficacy testing

Candida auris is an emerging pathogen that needs to be controlled effectively due to its association with a high mortality rate. The presence of biofilms on dry surfaces has been shown to be widespread in healthcare settings. We produced a C. auris dry surface biofilm (DSB) on stainless steel surfaces following sequential hydration and desiccation cycles for 12 days. The ASTM2967-15 was used to measure the reduction in viability of 12 commercially wipe-based disinfectants and sodium hypochlorite (1000 ppm) against C. auris DSB. We also evaluated C. auris transferability and biofilm regrowth post-treatment. A peracetic acid (3500 ppm) product and two chlorine-based products (1000 ppm available chlorine) were successful in reducing C. auris viability and delaying DSB regrowth. However, 50% of the products tested failed to decrease C. auris viability, 58% failed to prevent its transferability, and 75% did not delay biofilm regrowth. Using three different parameters to measure product efficacy provided a practical evaluation of product effectiveness against C. auris DSB. Although log10 reduction in viability is traditionally measured, transferability is an important factor to consider from an infection control and prevention point of view as it allows for determination of whether the surface is safe to touch by patients and hospital staff post-treatmen