About the development of advanced membrane process control systems

This paper focuses on the design and development of advanced control systems to use on either batch or continuous, new or existing membrane process plants. In the last decade, membrane technologies resulted to be very appealing and shows positive market trends. One main drawback is membrane fouling, which affects productivity, selectivity and longevity of the process, which leads to both technical and economical failures: proper membrane process design and control is a difficult task to accomplish. This leads to overdesign the plant capacities by process engineers, making this technology less reliable and convenient. Nowadays membrane processes are controlled by a constant permeate flow rate or constant applied operating pressure. These simple control strategy approaches are sufficient to operate the processes, but do not distinguish different fouling operating regions, and therefore do not avoid process failures due to fouling. Fouling may be described by the boundary flux theory in a convenient way, separating low-fouling operations from high-fouling ones. The paper reports about the development of an advanced membrane process control system based on the boundary flux concept. The developed advanced control strategy by the use of a simulation software, capable to predict boundary flux values by measurement of some key parameters, provides suitable set-point values to the feedback controllers in order to work at or below the boundary flux. As a consequence, the membrane process is always operated far from irreversible fouling issues. The developed approach was then successfully validated by experiments on lab scale

Chitin and lignin. Natural ingredients from waste materials to make innovative and healthy products for humans and plant

In a globalized world, plants are continually cut to obtain free land for intensive farming without remembering their important function in the planet ecosystem. They produce oxygen eliminating the carbon dioxide excess, contributing to reduce the pollution thus giving a great support to our health. According to the World Health Organization (WHO), air pollution -both outdoor and indoor- is nowadays "the biggest environmental risk to health carrying responsibility for about one in every nine deaths" (WHO, 2016). Outdoor pollution alone, in fact, kills around 3 million people each year. At this purpose however, it is necessary to remember that indoor emission of nanoparticles (NP) represent 50-80% of human exposure, calculated from 10.000 to 249.000 NP/mL air-while in polluted air NP are from ~10.000 to 50.000 NP/mL (Nohynek, 2011). Thus, there is a strict necessity "to consider air pollution as a global health priority in the sustainable development agenda" (WHO, 2016). Moreover, plants, multicellular organisms, as well as humans have evolved several mechanisms of defense and sensor systems to detect danger and prevent entry of most foreign material (Janeway et al, 2001). The sensors can direct and assist the host defenses by the use of specialized cells that ingest and digest foreign material. This protective non-specific method is called innate immune system, also connected with certain specific molecular patterns recognition associated with invading microbes or tissue damage (Nurnberger et al., 2004). In addition to innate immunity, vertebrates have evolved an adaptive immune system that relies on many antigen receptors, expressed by specialized immune cells. Unlike vertebrates, plants lack mobile defender cells and respond to infection by a two-branched immune system (Jones et al., 2006). The first branch recognizes and responds to all the common microbial molecules, while the second responds to pathogen virulence factors only. However, both plants and mammals have as first-line defense a barrier that, separating and shielding the interior of the body from the surrounding environment, represents the initial obstacle to be overcame from any pathogenic microorganisms. This barrier not only provides a physical separation, but releases also substances with antimicrobial properties. Moreover, when the first-line barrier has been breached, sensor systems are activated to give information to other components of the host defenses. Thus, while mammals activate, for example, the toll-like receptors capable to recognize families of compounds unique to microbes, plants release specialized compounds known as elicitors, signaling molecules able to induce their defense systems (Trouvelot et al., 2014). Examples of common ingredients, used from both plant and mammal as elicitors and defense-related compounds, are chitin and lignin. In this work, these materials will be briefly reviewed and results of chitin nanofibrils production and usage is reported. Finally, possible usage of combined chitin-lignin nanofibrils in commercial products will be pointed out

Description of the biofouling phenomena affecting membranes by the boundary flux concept

Membrane fouling, showing up with a significant reduction of process productivity and membrane lifetime, is one of the main issues in membrane technologies and has been successfully described by the boundary flux concept. Although the concept was applied for both organic and inorganic fouling, biofouling enjoys partial treatises in literature. In this work, a model extending the boundary flux concept to biofouling issues was developed. A population dynamics-based model considering the development of a fouling layer originated by attached growing biomass on the surface of the membrane using nutrients and substrates available in the processed feed has been developed. The manuscript highlights the critical aspects of the developed model and the possible connection points between it and the boundary flux concept

A novel approach for the production of nitrogen doped TiO2 nanoparticles

In this study a visible light active nitrogen doped nanostructure titanium dioxide was synthesized by a simple mixing of Degussa P25 and Urea powder and further thermal treatment under the adequate conditions. Photocatalytic activity of produced nanoparticles was verified by providing of photocatalytic degradation of phenol aqueous solution. Mainly this work was focused on the investigation of the following effects: urea concentration, temperature treatment, catalyst loading and initial phenol concentration. Kinetics study was also carried out. The approach appears to be successful and may be applied for example during the photocatalytic treatment of wastewater streams without or with a limited aid of UV lamps. Copyright © 2015, AIDIC Servizi S.r.l

Mass transfer, light pulsing and hydrodynamic stress effects in photobioreactor development

Photobioreactor scalability involves multiple different interacting aspects including mass transfer, light pulsing and hydrodynamic stress. An efficient carbon dioxide supply and a frequent displacement of cells from poorly to highly illuminated zones is desired to maximise the achieveable specific growth rate. However, a strong mixing is energy consuming and may reduce the specific growth rate because of induced cell damage. The current work examines mass transfer effects in photobioreactor development and estimates their relationship to light pulsing and hydrodynamic stress effects with a special reference to the novel inclined, thinlayer, wavy-bottomed cascading photobioreactor

Optimal design of membrane processes. A problem of choices between process layout, operating conditions and adopted control system

The development of membrane processes as a technology for environmental treatment applications and in particular for the purification of wastewater streams has significantly increased in the last decades. Fouling on membranes appears to be one of the main technical limit of this technology. This phenomenon causes the unavoidable deposition of particles on the membrane surface, building a resistive growing layer to permeability. Sensible fouling of the membrane leads to a significant reduction of the performances, a decrease of the operating life and, as a consequence, the increase of the operational costs due to the replacement or cleaning of the exhausted membrane modules. The presence of the fouling phenomena makes the proper design and control of membrane systems a difficult task. Optimal design of the membrane processes will be here discussed. The procedure requires to determine the optimal process layout given the input data and target requirements. At the end, the required membrane area is calculated. This latter property is strictly dependant of the adopted operating conditions, most importantly by the adopted value of transmembrane pressure (TMP). Moreover, it depends if the value of TMP remain fixed as a function of time or is variable (as in case of fixed permeate flow rates). Therefore, the optimal design of the system may occur only if the adopted control strategy is defined a priori. As a consequence, design choices of the membrane process layout, operating condition and adopted control system are strictly dependant, and connections between these different aspects should not be neglected during the engineering and P & I development stage of membrane systems. This paper will start from the theory of the boundary flux, in order to describe a novel design approach to membrane systems. Parallel to this, the development of an advanced control system, that allows to limit fouling formation during operation, is presented. The advanced control system relies on a suitable simulation software capable to predict the boundary flux, that changes the controller's set-points accordingly. Finally, the paper will merge all elements together, and report about the optimal design of membrane processes equipped with the advanced membrane process control system; validation of the proposed approach will be based on the use of a custom simulation model in ASPEN HYSYS and by experiments on lab scale

About the validation of advanced membrane process control systems in wastewater treatment applications

This paper focuses on the validation of advanced control systems to use on either batch or continuous, new or existing membrane process plants, by use of a simulation software (Aspen Hysys). In the last decade, membrane technologies resulted to be very appealing and shows positive market trends. One main drawback is membrane fouling, which affects productivity, selectivity and longevity of the process, which leads to both technical and economical failures: proper membrane process design and control is a difficult task to accomplish. This leads to overdesign the plant capacities by process engineers, making this technology less reliable and convenient. Nowadays membrane processes are controlled by a constant permeate flow rate or constant applied operating pressure. These simple control strategy approaches are sufficient to operate the processes, but do not distinguish different fouling operating regions, and therefore do not avoid process failures due to fouling. Fouling may be described by the boundary flux theory in a convenient way, separating low-fouling operations from high-fouling ones. The paper reports about the validation of an previously developed advanced membrane process control system based on the boundary flux concept on different wastewater feedstocks. The advanced control strategy by the use of a simulation software by Aspen Hysys, capable to predict boundary flux values by measurement of some key parameters, was validated and capable to set suitable set-point values to the feedback controllers in order to work at or below the boundary flux. As a consequence, the membrane process is always operated far from irreversible fouling issues. The developed approach was then successfully validated by experiments on lab scale

Production and characterization of silver nanoparticles in cultures of the cyanobacterium A. platensis (Spirulina)

The increasing application of Silver nanoparticles in biologically-relevant areas (including production of textiles, cosmetics, and biomedical devices), where their presence provides a continuous release of silver ions to provide protection against bacteria and other unwanted microbial contaminants urges adoption of intrinsically biologically safe production processes. Various species of cyanobacteria and algae have been known to absorb and take up heavy metal ions. This capability is shown also by Arthrospira platensis (Spirulina), a cyanobacterium that enjoys the Generally Recognised as Safe (GRAS) status and has been declared by WHO one among the greatest superfood. The present study aims at investigating the coupling between the recognised beneficial effects of Spirulina biomass to the antimicrobial activity of Ag nanoparticles (SNPs). In this work, Spirulina was grown in sequential cultures targeting biomass production and nanoparticle formation. The cultures were conditioned during their lifetime in order to assess the effect of pH and added polysaccharides on the size and on the stability of the obtained SNPs. The synthesized SNPs were characterized as to their size and stability (Nanosizer), composition (XRD) and structural aspect (Scanning Electron Microscope)

Production of nano zero valent iron particles by means of a spinning disk reactor

Nitrates are considered hazard compounds for human health due to their tendency to be reduced to nitrites, in particular in reducing environment. Nano zero valent iron (nZVI) represents an efficient and low-cost adsorbent/reductive agent for nitrate removal from groundwater. In this work, nZVI particles were produced by means of two different equipment types based on the same chemical synthesis method: a batch stirred tank reactor (BSTR) and a spinning disk reactor (SDR). This latter apparatus is capable to strongly promote micromixing at a steady-state, continuous condition, and such as qualifies to subsist in the framework of process intensification. Particle size distribution (PSD) of the obtained nZVI particles were measured by a DLS technique. The removal efficiency of the produced nVI particles were checked by using two NO3-solutions (1.6 and 6.4 mM) and by monitoring nitrate concentration reduction rates at selected time intervals. Results showed that the nZVI particles produced by SDR have a narrow PSD with a mean diameter of 65nm; on the contrary, particles produced by BSTR shows bimodal PSD with modal sizes of 105 nm and 400 nm, respectively. Experimental tests of nitrates reduction in water have been performed, using both the particles produced by the above mentioned techniques. Results of batch tests showed that the highest removal efficiency of nitrates was observed by using the nZVI particles produced by means of SDR, as a consequence of the higher average specific surface. Since nitrate removal process involves both reduction and adsorption processes, the removal mechanism has been investigated, and the pseudo-first-order reduction kinetic model was successfully tested and reported in both cases

Study on fouling behaviour of ultrafiltration and nanofiltration during purification of different organic matter polluted wastewaters

The boundary flux concept is a profitable tool to analyse fouling issues in membrane processes. The boundary flux value separates an operating region characterized by reversible fouling formation from irreversible one. Boundary flux values are not constant, but function of time, as calculated by the sub-boundary fouling rate value. The knowledge of both parameters may fully describe the membrane performances in sub-boundary operating regimes. Many times, for wastewater purification purposes, ultrafiltration and nanofiltration membranes are employed to treat different wastewater streams. This appears to be feasible from both technical and economical point of view many times. Whereas initial productivity and selectivity to reach the desired purification targets are generally guaranteed, key to reach process feasibility is that the membrane must resist to fouling issues, with a limited reduction of the performances as a function of time. In other words, longevity of the membranes must be that high to minimise their substitution and, consequently, operating (consumable) costs for the replacement. In this work, after a brief introduction to the boundary flux concept, for many different wastewater, the boundary flux and sub-boundary fouling rate values of different microfiltration and ultrafiltration membranes will be discussed and compared. By this approach, it will be possible to separate those systems where the use membranes for their treatment results successfully from those that represent a challenge (from a technical and/or economic point of view). This will depend sensibly of the feedstock characteristics and, in detail, on the particle size of the suspended matter and guidelines for process designers will be discussed. In most cases, it will be shown that membranes appear to perform very well, making this technology very interesting for many case studies