Vasile Lavric

Regeneration of internal streams as an effective tool for wastewater network optimisation

Abstract A significant decrease of water disposal to treatment section from a wastewater network (WWN) can be achieved rising internal water reuse through regeneration, i.e. lowering the concentration of one or more contaminants. Zero discharge is the limit case of complete regeneration, although economic considerations may hamper its full application. In this paper the mathematical model of the WWN is extended to consider partial/total stream regeneration. An improved variant of genetic algorithms is used to solve it. Several concepts are formulated, pinpointing which contaminant is better to be removed for decreasing supply water consumption. A case study with six unit operations, four contaminants, one water source and one regeneration unit is analysed. Four regeneration scenarios are investigated, considering (a) the critical contaminant, (b) the contaminants from the bottleneck island, (c) three contaminants—one being outside the bottleneck island and (d) all the contaminants, according to the zero discharge theory. The results obtained are compared against the base case (without regeneration) to highlight the relationship between supply water reduction and internal regeneration. Increased water reuse is related as well to WWN topology optimisation.

Dual-objective optimization of integrated water/wastewater networks

Abstract The dual-objective optimization of an integrated water/wastewater network (IWWN) is addressed by targeting for minimum fresh water consumption at the same time with operating costs reduction. An IWWN is a recycle system composed of two oriented graphs, the first encoding the water-using units (WUs) and the second, the treatment units (TUs). Although internal recycles are forbidden ab initio for the WUs graph, external recycles from the appropriate TU to the WU whose inlet restrictions are met by the partially treated water are encouraged. The corresponding mathematical model was written. A synthetic example is proposed and analyzed under several scenarios with respect to the fresh water consumption, the magnitude of internal and treated water reuse and the investment/operating costs related to the active pipes network. A comparison is made regarding the differences in network topology and fresh water consumption implied by different points from the Pareto front (PF).

A sensitivity analysis of the fed‐batch animal‐cell bioreactor with respect to some control parameters

Animal cell culture is widely used in the manufacture of valuable products, and this process is nowadays seeing a rapid expansion. The growth of animal cells is a complex process, because the cells are very sensitive to environmental changes (in, for example, nutrients, pH, temperature, oxygen and osmolarity) during this phase and to the toxic compounds produced by the cell itself. Ammonia and lactate are the two major waste materials of cell culture. They can have inhibitory effects on cell growth and product (monoclonal antibodies among others) formation. In order to model the behaviour of a fed‐batch animal cell bioreactor producing monoclonal antibodies, it is necessary to use a complex kinetic model with optimal operating patterns ensuring high productivities. Good knowledge of such domains of operating parameters, together with the understanding of the response of this rather complex system to small modifications in the working conditions, are essential for on‐line control to improve the quality of product and the yield of an animal cell culture. The present study focuses on the sensitivity analysis of a fed‐batch animal cell bioreactor with respect to some candidate control parameters (substrate set‐point concentrations, feeding time‐step patterns and concentration of feeding solutions), emphasizing the influence of these on the overall performance of the system.

Determination of bioactive, free isothiocyanates from a glucosinolate-containing phytotherapeutic agent: a pilot study with in vitro models and human intervention.

Isothiocyanates (ITCs) derived from plants of the order Brassicales are known for their antibacterial, anti-inflammatory or anticarcinogenic potential. Although only the free ITCs exert bioactivity, quantification in vivo is almost exclusively performed on total ITC/metabolite content. We therefore investigated in a pilot study the amount of free ITC at different steps critical for therapeutic efficacy. A sensitive and specific GC-MS/MS method for the simultaneous quantification of individual free ITC after solid-phase extraction (SPE) was developed. We show here that release of biologically active ITC from plants occurs at not only alkaline but also acidic pH. Furthermore, in human urine conversion of the ultimate, inactive mercapturic acid conjugate back into its corresponding bioactive form is increased at alkaline as compared to neutral pH. This was also observed in the urine of human volunteers, where - in correlation with the pH value - a mean of 0.16 to 1.03 μmol ITC was detected after oral application of a phytotherapeutic agent containing 30.4 μmol of the initial pro-drugs. The amounts of free ITC being necessary for bioactivity in vitro were found to be indeed achieved in vivo. These data might be helpful to better understand the beneficial effects of ITC observed in vivo.

Topological impact of regeneration unit constraints upon water and wastewater network

Abstract Optimization of water use/reuse gained an increasing attention during the last years based on four major driving forces: higher water demands, supply water cost increase, such as the wastewater treatment cost and more stringent regulatory limits for the disposal of the used water. This means a drastic reduction of the contaminants level of wastewater discharge, which itself has to be reduced continuously. A significant decrease of water disposal can be achieved rising internal water reuse/recycle through regeneration; the concept of “zero discharge” being the limit, although economic considerations are a major impediment in its full application. The topological impact of regeneration unit upon water and wastewater network is studied for three cases: critical component regeneration, partial regeneration and total regeneration (zero discharge concept) . Every case is compared against the optimal water network topology obtained using as objective function the total supply water flow rate.

Process Design, Integration and Optimisation: Advantages, Challenges and Drivers

Abstract: This chapter begins with a short history of process design, and then presents a hierarchical approach to the main currents: heuristic approach, phenomena-driven design, conflict-based approach, case-based reasoning, driving force method and axiomatic design. The main similarities and differences between design and retrofit are emphasised. Process Integration definitions and main tools are introduced, the integration techniques are detailed, and the distinction between integration and intensification is clarified. The main optimisation techniques are shown, emphasising that different scalar/vector objective functions applied to the same mathematical model give different topologies. Lastly, simultaneous integration and control is advocated.

Continuous hybridoma bioreactor: sensitivity analysis and optimal control

Animal cell culture has already established itself as a mature technology able to make a wide range of valuable products, the actual focus being to find the competitive bioreactor design and operating conditions for increasing production. A complex analysis, implying sensitivity calculus and optimal control computation, is done for a system composed of a continuous perfectly mixed bioreactor, with cell recirculation, a cell separator, a mixer and a purge. The bioreactors sensitivity to the control parameters is measured by a new concept, entropic density, developed from the notion of Shannon entropy. An optimization procedure based on a genetic‐algorithms approach is applied for the computation of the inlet flow profile in time, which guarantees optimum monoclonal‐antibody production. Our studies, including the present one, proved that the best approach to obtain high production is to use a hybrid operating sequence: fed‐batch mode followed by the continuous mode.

Optimal control of a continuous perfectly mixed hybridoma bioreactor

Abstract Production of industrial scale quantities of monoclonal antibodies (MAbs) is an expensive task and the current focus is on cutting down the operating costs. One of the pertinent challenges is reducing the formation of large amount of lactate and ammonia (secondary metabolic products of the cellular metabolism of glucose and glutamine), which are waste materials that have also inhibitory effects on cell growth and production rates. It is therefore important to maintain the cells in a physiological state characterized by a minimal production of waste metabolites and a maximum production of biomass and hence antibodies. This goal implies the development of an optimal nutrients supplying strategy which modifies the growth medium in such a way that the cells alter their metabolism to produce as much MAbs as possible, with minimal waste. In the present study, the optimal control of a continous perfectly mixed hybridoma bioreactor with cell recirculation from a separator was sought, using genetic algorithms. The results were compared against the optimal control of a fed batch animal cell bioreactor in order to establish which of the two performs better in similar conditions. An improved result can be obtain by combining the two ways of operating, thus reducing the drawbacks of both methods and increasing the performance of the system.

Simultaneous production of oil enriched in ω-3 polyunsaturated fatty acids and biodiesel from fish wastes

The waste resulted from fish processing industries are discarded into the environment around the world, causing environmental pollution. The main problem of fish oil extracted from waste is the high content in free fatty acids (FFA) which decrease the yield in fatty acids esters during transesterification reactions. Therefore, to correct the fish-oil properties, a new environmentally friendly heterogeneous superacid catalyst (SO42-/SnO2-ZrO2) was tested in the esterification reaction of FFA with ethanol. The catalyst was characterized by different techniques (XRD, FT-IR, FT-IR of adsorbed pyridine, BET, SEM-EDX, TGA and acidity measurements). The reaction was found to follow a Langmuir-Hinshelwood (L-H) dual-site mechanism with the novelty that both Brönsted and Lewis acid centers participate equally in the esterification reaction. The pre-treated oil was subjected to transesterification reaction with ethanol over a heterogeneous base catalyst and then, the saturated and unsaturated fractions of fatty acid ethyl esters (FAEE) were separated using a vacuum rectification unit with falling film. The saturated content can be used as biofuel, while the unsaturated FAEE are further transesterified with glycerol in order to obtain oil with high content in polyunsaturated fatty acids (PUFA). A detailed study of the intrinsic kinetic process at the surface of the superacid catalyst and a thorough mathematical model of the fixed bed reactor were written and validated by an experimental program, designed according to the D-optimal methodology.

Late transition metal recovery from a silver nitrate electrolyte using a phosphine-oxide bearing scavenger

Silver is one of the eight precious metals, along with gold and the six platinum-group metals (PGM). Most silver is obtained as a by-product of mining and refining of other metals. Fine silver is produced in electrolytic processes, using silver anodes (electrolytic refining) or inert ones (electrowinning) and an acidified silver nitrate electrolyte. Because the standards for refined silver are very high, it is necessary to control the behaviour of the impurities. Depending on the refining process parameters, it is not uncommon to find precious metals, such as palladium, platinum or even gold, dissolved in the electrolyte. In particular, palladium is very challenging because of its standard oxidation–reduction potential similar to the one of silver . The recovery of palladium and platinum from the silver refining processes is important for two reasons: to produce high quality silver and to recover the valuable precious metals. In this work, Pd and to a lesser extent Pt recovery from a silver nitrate effluent was investigated using a phosphine oxide – bearing coordinating resin (MPX-310). Laboratory scale studies, in batch and continuous modes, have shown the ability of MPX-310 to capture Pd and Pt from a matrix highly concentrated in Ag (up to 131 g l−1) and Cu (up to 70 g l−1) from industrial effluents. Moreover, adiabatic calorimetry studies were performed in order to determine the reactivity of the resin in the silver nitrate effluent and the optimal conditions where this resin can be safely used in an industrial process. Pilot scale experiments were done and the results obtained in the laboratory were confirmed.