Horst Chmiel

Membrane processes for water reuse in the food industry

By using low-contaminated process water from the food industry, a new water treatment technology, capable of producing water which can be reused (e.g. water for cleaning and cooling, boiler feed water) was developed. The treated water fulfills the requirements specified in drinking water regulations. At present, this water treatment technology is undergoing authorisation procedure.

Microbial acetate conversion to methane: kinetics, yields and pathways in a two-step digestion process

SummaryOrganic waste is converted in a two-stage process to methane and carbon dioxide by mixed cultures of microorganisms. Acetate, a product of acidogenic and acetogenic bacteria and the main substrate for methanogenic bacteria, is an important intermediate of the anaerobic degradation process, which results in the generation of methane. It was shown by labelling experiments using (U-14C) acetate that as much as 65%–96% of the total methane produced came from the acetate. The first order utilization rate for acetate in the methanogenic stages of a two-stage digestion process was between 0.17 h-1 and 0.5 h-1. The kinetics as well as the mass flow and yields of acetate and the methyl group of acetate were determined by pulse-labelling experiments with (U-14C) acetate and (2-14C) acetate without a significant rise of the total concentrations. Up to 58% of the acetate carbon was transformed to methane, and about 30% to carbon dioxide; only 4%–15% was incorporated into the biomass. There are at least two parallel degradation mechanisms in the metabolic transformation of acetate to methane: acetate is cleaved either to form methane and carbon dioxide or to form hydrogen and carbon dioxide, which can be transformed by an additional reaction to methane. Labelling experiments with (2-14C) acetate show that both mechanisms took place at similar order.

Treatment of low-contaminated waste water from the food industry to produce water of drinking quality for reuse

Abstract The treatment of low-contaminated waste water from the meat processing industry was studied with the objective of producing water of drinking quality for reuse. A demonstration plant with a capacity of up to 2 m3/h was built based on our experiments to compare different treatment processes for the removal of suspended particles, dissolved inorganics, undissolved and dissolved organics and micro-organisms contained in the waste water and which exceed the limit for drinking water. The demonstration plant consists of water pretreatment (sedimentation with fat skimming, cartridge filtration and UV disinfection), nanofiltration and post-treatment (UV oxidation and UV disinfection). The experimental results from an operating period of over 4 months showed that treated water with drinking water quality, according to the German drinking water regulations, can be produced. The applied waste water technology is now undergoing authorization procedure with the German authorities.

Rejection and Continuous Regeneration of the Native Coenzyme NAD(P)H in a Charged Ultrafiltration Membrane Enzyme Reactora

Coenzyme-dependent enzymatic transformations on a process scale are of increasing interest for industry because a wide variety of products can be synthesized by oxidoreductases that require a cofactor. During the last six years, various transformations of carbohydrates with NAD(P)(H)-dependent enzymes have been studied.’.* In these processes, it is necessary to regenerate the expensive coenzymes for economical reasons. Cofactor regeneration can be achieved by a coupled enzyme system (FIGURE la) or by the coupled substrate approach (FIGURE lb). A method has been developed that allows use of dehydrogenases in continuous processes. Results on two of these systems are presented here. In one, mannitol is produced from fructose by mannitol dehydrogenase (MDH) and NADH is regenerated simultaneously by glucose dehydrogenase (GDH) from Bacillus megaterium, which converts glucose to gluconic acid.3 Both products are used in the food industry. In the other process, the enantiomeric alcohol S-sulcatol, a pheromone of a bark beetle, is produced together with a ketone by using alcohol dehydrogenase from Thermoanaerobium brockii (TBADH) .4*5

Efficient design and optimisation of two-stage NF processes by simplified process simulation

The modelling of membrane filtration processes is often conducted by applying black-box models or short-cut methods because of its complexity due to molecular interactions on and inside the membrane. The assumptions made for the short-cut-methods are applicable for reverse osmosis, whereas the simulation of nanofiltration processes can lead to unreliable results, which sometimes deviate greatly from real conditions. A steady-state process simulation NF-PROJECT, which is based on input information from membrane characterisation, was developed (isothermal operation). The individual separation characteristics of every membrane element are calculated in iteration, which leads to reduction of permeability and rejection for every further element arranged in series inside the pressure vessel. The simulation provides information on the increasing feed concentration and osmotic pressure, the hydraulic pressure loss, the deterioration of the flow conditions along the feed side in the vessel and the combined performance of the membrane elements to be analysed. Serving as an example from practical applications, a two-stage nanofiltration pilot plant was simulated, the results of which will be presented. Examples of design and optimisation potentials will be illustrated for the target criteria of economic efficiency (specific energy costs), permeate quality and flow.

Choice of reactor to minimize enzyme requirement: 1. Mathematical model for one-substrate Michaelis-Menten type kinetics in continuous reactors

In order to establish the theoretically ideal conditions necessary to minimize enzyme requirement for a given process, a computer simulation of the ideal stirred tank reactor (CSTR), the ideal plug flow reactor (PFR) and the ideal laminar flow reactor (LFR) is presented. The reaction is assumed to follow Michaelis-Menten kinetics and the effects of competitive substrate and product inhibition are considered. The magnitude of the initial reactant concentration strongly influences the result. At low initial substrate concentrations (S0/Km<2) both tube reactors require less enzyme than the tank reactor for a given conversion and inhibition effects are negligible. At higher initial reactant concentrations, the CSTR yields better results for substrate inhibited reactions. However, when product inhibition occurs the PFR and the LFR perform superiorly. Conversion in the LFR is always less than in the PFR.

Characteristics and Application of Ceramic Nanofiltration Membranes

Abstract: In this paper we report on the characteristic and filtration behavior of a newly developed ceramic nanofiltration membrane and compare it with other commercial ceramic nanofiltration membranes currently available. It is shown that it is possible to produce a ceramic membrane with separation properties in the nanofiltration range and with permeability rates that are clearly superior to those of polymer nanofiltration membranes. The ceramic membrane was used in tests involving the treatment of textile wastewater, alkaline solutions from bottle washing machines, and pickling bath solutions.

Application of the process simulation tool NF-PROJECT for efficient process development optimization of two-stage NF processes for the treatment of spent process water

In recent years, nanofiltration has increasingly gained in significance. To increase efficiency in process development, particularly for new fields of application, it has become essential to use calculation tools in conjunction with the process in question. The tool NF-PROJECT for the simulation of two-stage NF processes at industrial scale has already been developed and presented. Its suitability for practical application in process simulation was examined as an additional aid for process development, the results of which will be discussed in this paper. To this end, the simulation tool was applied in the treatment of spent process water from the food industry. In this case, NF-PROJECT was conducive to the selection of suitable nanofiltration membranes and to process optimization while significantly reducing the time span of process development.

Modeling of Impurity Concentrations in the Cleaning Zones of Bottle Washing Machines in the Treatment of Alkaline Cleaning Solutions and Rinsing Water

While demands on the quality of alkaline cleaning solutions and rinsing water are increasing, the current technical possibilities for saving water and other materials in modern bottle washing machines in the food industry have been more or less exhausted. By treating these alkaline solutions and rinsing water by membrane filtration processes, the increasing concentration of impurities carried by bottles and conveyor belts into the individual cleaning stages, can be reduced. The waste load in the alkaline solution and in the rinsing water zones of the bottle washing machines can be calculated by a simulation program while taking membrane separation treatment into account. Thus, saving potential resulting from the treatment of alkaline cleaning solutions and rinsing water from bottle washing machines in the beverage industry as well as the costs of a treatment plant can be assessed by using this model.

Computer-aided simulation for optimizing nanofiltration processes

The modeling of membrane filtration processes is only possible by applying black-box models or short-cut methods, because of its complexity due to molecular interactions on and inside the membrane. The assumptions made for the short-cut methods are applicable for reverse osmosis, whereas the simulation of nanofiltration processes leads to unreliable results, which sometimes deviate highly from real conditions. A steady-state process simulation NF-PROJECT, which is based on input information from membrane characterization, was developed. The individual separation characteristics of every membrane element are calculated in iteration, which leads to a reduction in the permeability and retention of the elements inside the pressure vessel. The simulation provides information on the increasing feed concentration and osmotic pressure, the hydraulic pressure loss, the deterioration of the flow conditions in the vessel and the combined performance of the membrane elements to be analyzed. As an example, the simulation was applied in a two-stage nanofiltration pilot plant, the results of which are presented.