Inventory control for a perishable product with non-stationary demand
Pauls-Worm, K.G.J. - \ 2016
Wageningen University. Promotor(en): Jack van der Vorst, co-promotor(en): Eligius Hendrix; Rene Haijema. - Wageningen : Wageningen University - ISBN 9789462578500 - 142
logistics - food products - supply chain management - food wastes - industrial wastes - inventories - logistiek - voedselproducten - ketenmanagement - voedselafval - industrieel afval - inventarisaties
Globally, around one-third of the edible parts of perishable food products is wasted every year. Adequate logistics management of the food supply chain is of importance. Inventory control of processed fresh food with a best-before or use-by date deals with the questions how much to order and how often, and how to review the inventory position. For perishable products, there exists a trade-off between desired product-availability and waste. A high order quantity or frequent ordering may result in high product-availability but also waste. A small order quantity or less frequent ordering results in lower inventory levels, but may cause out-of-stock. For the inventory control of a perishable product the age-distribution of the items should be considered. This is influenced by order picking at a food producer or warehouse, or consumer behaviour at a supermarket, picking First In First Out (FIFO), where first the oldest items are used, or Last In First Out (LIFO), where first the freshest items of the product are used. This thesis investigates periodic review order policies for a food producer and a retailer for a perishable product with a fixed lifetime and a non-stationary demand. For a food producer as well as a retailer, it is not always economically feasible to reorder in every period. For planning purposes it is desirable to set the timing of the orders in advance.
The aim of this thesis is to contribute to better decision making regarding inventory control in the food supply chain from food producer to supermarket, in the trade-off between product-availability and waste. Methods are designed to generate practical order policies using commercial solvers for business rather than custom made solution procedures, where at least the timing of ordering or production is set beforehand. The practical inventory control problems discussed in this thesis are characterised by a perishable product with a fixed lifetime, non-stationary stochastic demand, a single-echelon production/inventory situation in a finite time horizon. The product has a service level requirement to ensure a certain product-availability. The decision problems deal with fixed setup or ordering cost, holding cost and disposal cost for wasted items. The age-distribution of the items in stock is considered in specific theoretical Stochastic Programming (SP) problems that deal with the service level requirement as a chance constraint or fill rate constraint. The studied problems vary in planning characteristics.
Fluctuations in demand combined with fixed setup or ordering costs imply that regular production or ordering is probably not optimal. This situation requires a strategy to deal with the fluctuations. In inventory literature, non-stationary demand for a perishable product with a fixed lifetime is hardly studied, and consequently also strategies to deal with it are little investigated. In this thesis, methods have been designed to generate practical order policies using commercial solvers, where at least the timing of ordering or production is set beforehand. The practical order policies have been benchmarked with custom made solution procedures. The developed practical policies are applicable in the practice of fresh food producers and in retail organisations, on the level of the store, as well as on the level of the distribution centre. An interesting conclusion is that the policies with fixed order timing are hardly more costly than the investigated policy with flexible order timing. The fixed order timing increases the ease of planning.
The studied cost functions in the models comprise disposal cost for which the value of the disposal cost in the experiments was varied. The results show that in the models with fixed order timing and corresponding order-up-to levels, increasing the disposal cost can reduce the percentage of waste, maintaining the service level. In setting a (fictitious) value for the disposal cost, one can steer the percentage of waste in determining the order policy, and thus contribute to better decision making in the food supply chain from food producer to supermarket in the trade-off between product-availability and waste.
Brewing with fractionated barley
Donkelaar, L.H.G. van - \ 2016
Wageningen University. Promotor(en): Remko Boom; Atze Jan van der Goot. - Wageningen : Wageningen University - ISBN 9789462577343 - 152
brewing - brewing quality - barley - fractionation - endosperm - beers - malt - filtration - industrial wastes - process optimization - food process engineering - bierbereiding - brouwkwaliteit - gerst - fractionering - endosperm - bieren - mout - filtratie - industrieel afval - procesoptimalisatie - levensmiddelenproceskunde
Brewing with fractionated barley
Beer is a globally consumed beverage, which is produced from malted barley, water, hops and yeast. In recent years, the use of unmalted barley and exogenous enzymes have become more popular because they enable simpler processing and reduced environmental impact. Raw barley, however, contains less endogenous enzymes and more undesired components for the use of beer brewing, compared to malted barley.
The overall aim of this thesis is to investigate how barley can be fractionated to optimize the use of resources for the beer brewing process, while maintaining the quality of the brewed beer. A resource use efficiency analysis was performed to verify the presumed benefits on the environmental sustainability of the proposed process change. The work was based on the hypothesis that fractionation of the unprocessed barley will reduce the amount of undesired components, which leads to improvements in the brewing process based on partial or no malting. Fractionation can be performed by milling and separation, which requires physical disentanglement of the components. This fractionation can be influenced by properties of the components of the material, such as the glass transition temperature (Stuart et al.). Fractionation by abrasive milling, also known as pearling, is another possibility: here one makes use of the spatial distribution of components in the kernels. In case of barley for brewing this technique is especially promising as most of the undesired components are in the outer layer of the kernel. In addition, the removal of bran from the barley reduces the amount of water needed in the process. It will also reduce the volume of spent grains, hence reducing wastes and energy required for drying the spent grains. A disadvantage of pearling is however that it lowers the ability of the barley kernel to produce enzymes. This leads to the need of the addition of exogenous enzymes, as is the case when the malting step is omitted.
Chapter 2 describes the glass-to-rubber transition of protein and starch isolated from the barley endosperm, for different moisture levels. The hypothesis for this chapter is that dry fractionation by milling is facilitated by milling conditions in which the protein is in a rubbery state and the starch in a glassy state. Two methods were used to measure the Tg; differential scanning calorimetry (DSC) and thermo-mechanical compression tests (TMCT). The methods gave different results due to the differences in moisture content range, and heating rates, which may lead to conformational changes of the protein. The value of the Tg of partially crystalline materials, such as starch in barley, was not unambiguous when using TMCT because the mechanical effect of expansion of these materials was smaller. For both results, the Tg lines were modelled using the Gordon-Taylor equation. Based on sorption isotherms, it was concluded that moisture does not distribute evenly over the protein and starch in the kernel. Starch absorbs more moisture than protein at given water activities. This required a correction of the Tg lines. After this correction, the glass transition lines of starch and protein were closer together. The expectation is therefore that achieving good separation between the components based on having one glassy component and one rubbery component is challenging.
For this reason, another dry fractionation technique, pearling, was considered. Chapter 3 describes the chemical composition of the barley and of fractions removed by pearling. Pearling was shown to selectively remove insoluble fibre, ash, protein and polyphenols, while the β-amylase activity and starch content of the remaining kernel was hardly affected. For example, removing the outer 5% of the kernel reduced insoluble arabinoxylans (15%), insoluble fibres (23%), ash (19%), polyphenols (11%) and water holding capacity of the non-starch components (25%), while only lowering starch content by 0.20%. The water holding capacity of the barley fractions was strongly related to the fibre content. This indicates that when the fibre content in the mash was reduced by pearling, the spent grains will take up less water, leading to less wort and sugar losses in this waste stream, and hence better use of the raw materials and less wastes.
Chapter 4 compares a traditional brewing process to an enzyme-assisted brewing process with respect to their resource use efficiency, which is one aspect of the sustainability of the processes. The use of exogenous enzymes is found to be more efficient than producing enzymes through the malting process. The exergetic efficiency of the conventional malting process was 77%. The main losses stem from the use of natural gas for removal of moisture from the barley in the kilning process, and from the loss of starch in the germination process. In case of the use of exogenous enzymes, it was concluded that the chemical exergy content of the enzymes was not a good measure for the exergy content of the enzymes. Instead, we proposed to use the cumulative exergetic consumption in the enzyme production rather than just the chemical exergy content of the enzymes. This cumulative exergetic consumption in the production of the enzymes was ± 30 times higher than their standard chemical exergy. This shows that the cumulative exergetic costs of minor components should be taken into account if a process uses them in significant quantities. This can be done by extending the system boundaries to include the production process of the purified components. The exergy efficiency of the enzyme formulation production process ranges between 20% and 42% depending on whether the by-product of the fermentation broth was considered as useful as the enzyme product. Even though the cumulative exergy consumption of the process was 30 times the standard chemical exergy of the dry enzyme, the total exergy input (i.e. both wasted and destroyed) for the production of 100 kg of beer was still larger for the conventional malting process (441 MJ) than for the enzyme-assisted process (354 MJ). In addition, beer produced using exogenous enzymes reduces the use of water by 7%, of raw materials by 14%, and of natural gas by 78%. Thus, the exergy loss of the enzyme production process is more than compensated by the prevention of exergy loss in the total beer brewing process.
Chapter 5 describes brewing tests using malted, unmalted and pearled, unmalted barley kernels. Brewing with unmalted barley saves material, energy and water in the malting stage but may result in complications during processing. Pearling mitigates these problems. Exogenous enzymes were used to compensate for the low enzyme activity in unmalted barley. Lautertun filtration and mash filtration were considered as filtration methods. Principle component analysis was performed on the chemical composition of the wort and the various spent grains, to investigate the effect of the malt-to-barley ratio, the degree of pearling and the filter method. A mash filter is optimal for this type of process, and we identified a window of operation in which optimal use is made of the raw materials while maintaining the end product quality, judged on basis of 4 quality parameters.
The concluding chapter 6 presents a general discussion of all results described in this thesis. In addition, the benefits of pearling over that of milling and fractionation, and the effect of pearling on milling properties were discussed. Furthermore, it explores the advantages in environmental sustainability that can be achieved by pearling. Pearling as a pre-treatment for malting reduces the enzyme activity of germinating barley, and therefore the mash quality.
This thesis provides insights in how pre-treatment of barley can make beer brewing more efficient in the use of resources. It stresses the need to optimally use all material streams in a process, to be able to design an environmentally sustainable process, and it shows that efficient resource use is key for achieving this. Additionally the value of enzymes as processing aids was discussed. A clear result is that one needs to include the resource use in the production of enzymes or other processing aids, when analyzing the environmental sustainability of a process, since this can be significant in the overall process.
Cradle 2 cradle - 3 stappen terug, 1 vooruit
Bos, H.L. ; Rabbinge, R. - \ 2010
Milieu dossier 2010 (2010)2. - p. 17 - 20.
recycling - afvalbeheer - milieubeheer - industrieel afval - duurzaamheid (sustainability) - duurzaamheid (durability) - inventarisaties - cradle to cradle - waste management - environmental management - industrial wastes - sustainability - durability - inventories
Het boek en de ontwerpfilosofie Cradle to Cradle van de Amerikaan William McDonough en de Duitser Michael Braungart mogen zich verheugen in een zeer brede belangstelling. Steden proberen nieuwe wijken volgens het C2C-concept te bouwen, de rijksoverheid vraagt zich af hoe C2C in het beleid kan worden ingepast en de beide auteurs krijgen van diverse universiteiten eredoctoraten aangeboden. Maar wat is de 'Van wieg tot wieg' filosofie nu eigenlijk precies? En wat kan het betekenen in het kader van een ontwikkeling naar een meer duurzame samenleving?
High rate sulfate reduction at pH 6 in a Ph-auxostat submerged membrane bioreactor fed with formate
Bijmans, M.F.M. ; Peeters, T.W.T. ; Lens, P.N.L. ; Buisman, C.J.N. - \ 2008
Water Research 42 (2008)10-11. - ISSN 0043-1354 - p. 2439 - 2448.
afvalwaterbehandeling - industrieel afval - bioreactoren - membranen - filtratie - sulfaat reducerende bacteriën - sulfaatreductie - waste water treatment - industrial wastes - bioreactors - membranes - filtration - sulfate reducing bacteria - sulfate reduction - gas-lift reactor - reducing bacteria - hydrogen-sulfide - carbon-dioxide - growth - methanogenesis - conversion - removal - sludge - water
Many industrial waste and process waters contain high concentrations of sulfate, which can be removed by sulfate-reducing bacteria (SRB). This paper reports on mesophilic (30 °C) sulfate reduction at pH 6 with formate as electron donor in a membrane bioreactor with a pH-auxostat dosing system. A mixed microbial community from full-scale industrial wastewater treatment bioreactors operated at pH 7 was used as inoculum. The pH-auxostat enabled the bacteria to convert sulfate at a volumetric activity of 302 mmol sulfate reduced per liter per day and a specific activity of 110 mmol sulfate reduced per gram volatile suspended solids per day. Biomass grew in 15 days from 0.2 to 4 g volatile suspended solids per liter. This study shows that it is possible to reduce sulfate at pH 6 with formate as electron donor at a high volumetric and specific activity with inocula from full-scale industrial wastewater treatment bioreactors operated at neutral pH. The combination of a membrane bioreactor and a pH-auxostat is a useful research tool to study processes with unknown growth rates at maximum activities.
Anaerobic microbial LCFA degradation in bioreactors
Sousa, D.Z. ; Pereira, M.A. ; Alves, J.I. ; Smidt, H. ; Stams, A.J.M. ; Alves, M.M. - \ 2008
Water Science and Technology 57 (2008)3. - ISSN 0273-1223 - p. 439 - 444.
afvalwater - industrieel afval - vetzuren met een lange keten - voedselindustrie - anaërobe afbraak - bioreactoren - clostridiaceae - methanobacterium - palmitaten - waste water - industrial wastes - long chain fatty acids - food industry - anaerobic digestion - bioreactors - clostridiaceae - methanobacterium - palmitates - chain fatty-acids - sludge - nov. - methanogenesis - inhibition - bacterium - digestion - coculture - acetate
This paper reviews recent results obtained on long-chain fatty acids (LCFA) anaerobic degradation. Two LCFA were used as model substrates: oleate, a mono-unsaturated LCFA, and palmitate, a saturated LCFA, both abundant in LCFA-rich wastewaters. 16S rRNA gene analysis of sludge samples submitted to continuous oleate- and palmitate-feeding followed by batch degradation of the accumulated LCFA demonstrated that bacterial communities were dominated by members of the Clostridiaceae and Syntrophomonadaceae families. Archaeal populations were mainly comprised of hydrogen-consuming microorganisms belonging to the genus Methanobacterium, and acetate-utilizers from the genera Methanosaeta and Methanosarcina. Enrichment cultures growing on oleate and palmitate, in the absence or presence of sulfate, gave more insight into the major players involved in the degradation of unsaturated and saturated LCFA. Syntrophomonas-related species were identified as predominant microorganisms in all the enrichment cultures. Microorganisms clustering within the family Syntrophobacteraceae were identified in the methanogenic and sulfate-reducing enrichments growing on palmitate. Distinct bacterial consortia were developed in oleate and palmitate enrichments, and observed differences might be related to the different degrees of saturation of these two LCFA. A new obligately syntrophic bacterium, Syntrophomonas zehnderi, was isolated from an oleate-degrading culture and its presence in oleate-degrading sludges detected by 16S rRNA gene cloning and sequencing
Bondt, N. ; Meeusen-van Onna, M.J.G. - \ 2008
Den Haag : LEI (Rapport / LEI : Domein 3, Natuurlijke hulpbronnen en milieu ) - ISBN 9789086152032 - 43
residuen - industrieel afval - afval - organisch afval - bijproducten - agrarische afvalstoffen - agro-industriële bijproducten - brandstoffen - vetten - technologie - plantaardige vetten - voedselindustrie - drankenindustrie - nederland - economische haalbaarheid - economische evaluatie - rentabiliteit - biobrandstoffen - bioethanol - biobased economy - residues - industrial wastes - wastes - organic wastes - byproducts - agricultural wastes - agroindustrial byproducts - fuels - fats - technology - plant fats - food industry - beverage industry - netherlands - economic viability - economic evaluation - profitability - biofuels - bioethanol - biobased economy
Dit rapport beschrijft de markt van reststromen uit de Nederlandse voedings- en genotmiddelenindustrie, en de aantrekkelijkheid van deze reststromen voor de productie van bioethanol en biodiesel. De eerstegeneratietechnologie kan slechts 29% van de 7,5 miljoen ton reststromen goed omzetten in biobrandstoffen. Als bovendien rekening wordt gehouden met niet-technische criteria blijken er voor bio-ethanol niet of nauwelijks reststromen interessant te zijn. Voor biodiesel kan wel gebruik worden gemaakt van de plantaardige en dierlijke vetten. De economische gevolgen voor onder meer de diervoedersector zijn beperkt. This report examines the market for residues from the Dutch food and beverage industry, and the appeal of these residues for the production of bio-ethanol and biodiesel. The firstgeneration technology is readily suited to the conversion of no more than 29% of the 7.5 million tonnes of residues into biofuels. Moreover, when non-technological criteria are also taken into account virtually none of the residues are of interest for conversion into bioethanol, although vegetable and animal fats can be used to produce biodiesel. The economic consequences for sectors such as the animal-feed sector are limited.
Carbon dioxide sequestration by mineral carbonation
Huijgen, W.J.J. - \ 2007
Wageningen University. Promotor(en): Rob Comans; G.J. Witkamp. - [S.l.] : S.n. - ISBN 9789085045731 - 232
kooldioxide - koolstofvastlegging - koolzuurgastoediening - verwering - wollastoniet - mineralen - industrieel afval - haalbaarheidsstudies - carbon dioxide - carbon sequestration - carbonation - weathering - wollastonite - minerals - industrial wastes - feasibility studies
The increasing atmospheric carbon dioxide (CO2) concentration, mainly caused by fossil fuel combustion, has lead to concerns about global warming. A possible technology that can contribute to the reduction of carbon dioxide emissions is CO2 sequestration by mineral carbonation. The basic concept behind mineral CO2 sequestration is the mimicking of natural weathering processes in which calcium or magnesium containing minerals react with gaseous CO2 and form solid calcium or magnesium carbonates: (Ca,Mg)SiO3 (s} + CO2 (g) ->(Ca,Mg)CO3 (s) + SiO2 (s)
Potential advantages of mineral CO2 sequestration compared to, e.g., geological CO2 storage include (1) the permanent and inherently safe sequestration of CO2, due to the thermodynamic stability of the carbonate product formed and (2) the vast potential sequestration capacity, because of the widespread and abundant occurrence of suitable feedstock. In addition, carbonation is an exothermic process, which potentially limits the overall energy consumption and costs of CO2 emission reduction. However, weathering processes are slow, with timescales at natural conditions of thousands to millions of years. For industrial implementation, a reduction of the reaction time to the order of minutes has to be achieved by developing alternative process routes.
The aim of this thesis is an investigation of the technical, energetic, and economic feasibility of CO2 sequestration by mineral carbonation.
In Chapter 1 the literature published on CO2 sequestration by mineral carbonation is reviewed. Among the potentially suitable mineral feedstock for mineral CO2 sequestration, Ca-silicates, more particularly wollastonite (CaSiO3), a mineral ore, and steel slag, an industrial alkaline solid residue, are selected for further research. Alkaline Ca-rich residues seem particularly promising, since these materials are inexpensive and available near large industrial point sources of CO2. In addition, residues tend to react relatively rapidly with CO2 due to their (geo)chemical instability.
Various process routes have been proposed for mineral carbonation, which often include a pre-treatment of the solid feedstock (e.g., size reduction and/or thermal activation). The only available pre-treatment option that has proven to be energetically and potentially economically feasible is conventional grinding.
Two main types of process routes can be distinguished; (1) direct routes in which carbonation takes place in a single step process, either in a gas-solid or a gas-liquid-solid process, and (2) indirect routes in which the Ca is first extracted from the silicate matrix and subsequently carbonated in a separate process step. The aqueous route in which Ca-silicates are directly carbonated in an aqueous suspension at elevated temperature and CO2 pressure is selected as the most promising process route for further investigation. The following key issues for further research are identified: the reaction rates and mechanisms of mineral carbonation as well as its energy consumption and sequestration costs. Another important aspect of mineral carbonation is the destination of the carbonated products.
In Chapter 2 the mechanisms of aqueous steel s!ag carbonation are studied experimentally. Process variables, such as particle size, temperature, and carbon dioxide pressure are systematically varied and their influence on the carbonation rate is investigated. The maximum carbonation degree reached is 74% of the Ca content in 30 minutes at 19 bar CO2 pressure, 100 0C, and a particle size of<38 prn. The two most important factors determining the reaction rate are particle size (<2 mm to<38 pm) and reaction temperature (25-225 0C). The carbonation reaction is found to occur in two steps: (1) leaching of calcium from the steel slag particles into the solution and (2) precipitation of calcite on the surface of these particles. The first step and, more in particular, the diffusion of calcium through the solid matrix towards the surface, appears to be the rate-determining reaction step. The Ca-diffusion is found to be hindered by the formation of a CaCO3-coating and a Ca-depleted silicate zone during the carbonation process.
In Chapter 3 the mechanisms of aqueous steel slag carbonation are further investigated, together with the environmental properties of the (carbonated) steel slag. Steel slag samples are carbonated to a varying extent and leaching experiments and geochemical modelling are used to identify solubility-controlling processes of both major and minor elements that are present in the slag. Carbonation is shown to reduce the leaching of alkaline earth metals (except Mg) by conversion of Ca-phases, such as portlandite, ettringite, and Ca-(Fe)-silicates into calcite, possibly containing traces of Ba and Sr. The leaching of vanadium increases substantially upon carbonation, probably due to the dissolution of a Ca-vanadate. The increased reactive surface area of AI- and Fe-(hydr)oxides after carbonation tends to reduce the leaching of sorption-controlled trace elements. Sorption on Mn-(hydr)oxides is found to be also required to adequately model the leaching of divalent cations, but is not influenced by carbonation, Consideration of these three distinct reactive surfaces and possible (surface) precipitation reactions resulted in adequate modelling predictions of oxyanion and trace metal leaching from (carbonated) steel slag. Hence, these surfaces exert a major influence on the environmental properties of both fresh and carbonated steel slag.
In Chapter 4, the mechanisms of aqueous wollastonite carbonation as a possible carbon dioxide sequestration process are investigated experimentally by systematic variation of the reaction temperature, CO2 pressure, particle size, reaction time, liquid-to-solid ratio, and agitation power. The carbonation reaction is observed to occur via the aqueous phase in two steps: (1) Ca leaching from the CaSiO3 matrix and (2) CaCO3 nucleation and growth. Leaching is hindered by a Ca-depleted silicate rim resulting from incongruent Ca-dissolution. Two temperature regimes are identified in the overall carbonation process. At temperatures below an optimum reaction temperature, the overall reaction rate is probably limited by the leaching rate of Ca. At higher temperatures, nucleation and growth of calcium carbonate is probably limiting the carbonation rate, due to a reduced (bi)carbonate activity. The mechanisms for the aqueous carbonation of wollastonite are shown to be similar to those of steel slag (Chapter 2) and of the Mg-silicate olivine. The carbonation of wollastonite proceeds rapidly relative to Mg-silicates, with a maximum conversion of 70% in 15 min at 200 0C, 20 bar CO2 partial pressure, and a particle size of<38 um.
The obtained insight in the reaction mechanisms in Chapter 2 - 4 is used as the (experimental) basis for the energetic and economic assessment of CO2 sequestration by mineral carbonation in Chapters 5 & 6.
The energy consumption of a mineral carbonation plant causes extra CO2 emssions and, thereby, reduces the net amount of CO2 sequestered by the process. Chapter 5 studies the energetic CO2 sequestration efficiency (i.e., the fraction of CO2 that is sequestered effectively) of the aqueous mineral carbonation in dependence of various process variables using either wollastonite or steel slag as feedstock. A flowsheet of a mineral carbonation plant is designed and the process is simulated to determine the properties of streams as well as the power and heat consumption of the process equipment. For woliastonite, the maximum energetic efficiency within the ranges of process conditions studied is 75% at 200 0C, 20 bar CO2, and a particle size of<38 ?m. The main energy-consuming process steps are the grinding of the feedstock and the compression of the CO2 feed. At these conditions, a significantly lower efficiency is determined for steel slag (69%), mainly due to the lower Ca content of the feedstock. The CO2 sequestration efficiency might be improved substantially for both types of feedstock by e.g. reducing the amount of process water applied and further grinding of the feedstock, In Chapter 6 a cost evaluation of CO2 sequestration by aqueous mineral carbonation is presented, using either wollastonite or steel slag as feedstock. On the basis of a basic design of the major process equipment, the total investment costs are estimated with the help of pubiic!y available literature and a factorial cost estimation method. Subsequently, the sequestration costs are determined on the basis of the depreciation of investments and variable and fixed operating costs. Estimated costs are 102 and 77 /ton CO2 net avoided for wollastonite and steel slag, respectively. For wollastonite, major costs are associated with the feedstock and the electricity consumption for grinding and compression (54 and 26 /ton CO2 avoided, respectively). The sequestration costs for steel slag are significantly lower due to the absence of costs for the feedstock. A sensitivity analysis shows that additional influential parameters in the sequestration costs include the liquid-to-solid ratio in the carbonation reactor and the possible value of the carbonated product. In the Epilogue the main conclusions of this thesis are summarised and recommendations for further research are given.
This thesis shows that CO2 sequestration by carbonation of Ca-silicates is possible at technically feasible process conditions. Altough the energy consumption of current mineral carbonation processes is substantial, the identified possibilities to reduce the energy demands of the process suggest that mineral carbonation may become energetically feasible after further technology development. Finally, the costs of CO2 sequestration by mineral ore carbonation processes are relatively high compared to other CO2 storage technologies and (current) CO2 market prices. (Niche) applications of mineral carbonation based on the use of a solid residue as feedstock and/or the production of a carbonation product with positive value, hold significantly better prospects for an economically feasible process.Overall, mineral CO2 sequestration is (still) a longer-term option compared to other 'carbon capture & storage'-technologies and probably has limited potential in the short term. However, the possibilities identified for further process improvement, the permanent and inherently safe character of the CO2 sequestration, and the large sequestration potential warrant further research on mineral CO2 sequestration. This research should primarily focus on cost reduction, which is a prerequisite for mineral CO2 sequestration to become part of a broad portfolio of employable CO2 mitigation options.
An environmental systems analysis of the Kraft pulp industry in Thailand
Warit, J. - \ 2006
Wageningen University. Promotor(en): L. Hordijk, co-promotor(en): Carolien Kroeze; W. Soontaranun. - [S.l.] : S.n. - ISBN 9789085045106 - 203
pulp- en papierwarenindustrie - pulpfabrieksafvalwater - verzuring - eutrofiëring - industrieel afval - papierfabrieksslib - eucalyptus - thailand - pulp and paper industry - pulp mill effluent - acidification - eutrophication - industrial wastes - paper mill sludge - eucalyptus - thailand
The pulp industry in
Greening Food Processing Industry in Vietnam: Putting Industrial Ecology to Work
Tran Thi My Dieu, - \ 2003
Wageningen University. Promotor(en): Arthur Mol; Wim Rulkens. - [S.l.] : S.n. - ISBN 9789058088253 - 290
industrieel afval - chemische ecologie - voedselindustrie - verontreinigingsbeheersing - ecosystemen - tapioca - suikerindustrie - zoetwarenindustrie - cacao- en chocolade-industrie - zuivelindustrie - vietnam - industrial wastes - chemical ecology - food industry - pollution control - ecosystems - tapioca - sugar industry - confectionery industry - cocoa industry - dairy industry - vietnam
The significant contribution to Vietnam's gross domestic product over the years give evidence of the important role of food processing industry in the economic and industrial development of the country. This is even more relevant from now onwards, as it is Vietnam's development strategy to become one of the top agricultural countries in the world by the year 2010. However, it is not difficult to recognize that the rapid growth of food processing industry in Vietnam goes together with environmental deterioration and puts stress on natural resources. So far, most efforts in environmental management of (food processing) industry in Vietnam have mainly been focussing on dealing with wastes and emissions after they have been generated. While to some extent, this end-of-pipe approach helps to reduce or eliminate adverse environmental impacts from the generated wastes and emissions, in most cases, the isolated implementation of this approach shows several disadvantages, shortcomings and inefficiencies. Thus, it should not surprise us that environmental quality in Vietnam is still poor, although the end-of-pipe approach has been implemented from the early 1990s onwards.
In order to reduce present and future threats to human health and the environment, industrialized countries have developed and introduced alternative approaches, which can overcome some of the weaknesses of end-of-pipe treatment solutions and are more (economic and environmentally) effective and efficient in reducing the generation of wastes. From existing literature and the experiences of industrialized countries we can clearly envision various advantages of environmental protection strategies that are based on cleaner production, waste exchange (offsite reuse and recycling) or industrial ecology approach instead of end-of-pipe treatment solely. Certainly, each of these approaches can only be applied successfully in some circumstances and is limited in others. Therefore the combination and integration of some or all these approaches is often seen as the best or only strategy to overcome the continuing environmental deterioration. This potential is investigated in this study. The core objective of this research is to analyze and assess the possibilities and the potency for greening food processing industries in Vietnam, based on the combination and integration of existing pollution treatment and prevention approaches. More specifically, this study seeks to fulfil the questions on: how to apply and adapt the existing experiences of industrial ecosystem from highly industrialized Western countries to develop an (agro)-food processing industrial ecosystem with the existing institutions, technological and socio-economic conditions of Vietnam? Whether it is possible to apply these ideas for large stand-alone firms as well as small (household) and medium sized (agro)- food processing companies? What would be core features of a zero waste industrial ecosystem model of food processing industry in Vietnam? Which actors, institutions and relations are crucial or potentially crucial to introduce the proposed model in practice?
Dealing with these questions, a methodology to analyze and design pollution prevention models for (agro-food processing) industries, integrating the physical-technological and socio-institutional models is developed. Using various theoretical ideas of cleaner production/waste minimization, waste exchange and industrial ecology, a methodology towards physical-technological models of a zero waste industrial ecosystem is established having four basic steps. The methodology starts with analyzing the material and energy flows that run through the industrial systems and partly end up in wastes, followed by analyzing various possibilities to prevent the generation of wastes in the second step. The third step concentrates on identifying, analyzing and designing potential offsite recovery and reuse options. The last step entails the identification of remaining wastes that need to be treated properly before discharging into the environment. Together, these four steps form a systematic methodology that leads us towards (close to) a physical-technological model for a zero waste industrial ecosystems. In addition, taking into account complex political, economic and social relations between the industrial system and actors outside, the triad-network model developed by Mol (1995) is applied to complement the physical-technological model with an actor and institutional analysis. The roles of actors and the interrelations between them and industrial systems are investigated in three networks: economic, policy and societal network.
The applicability of the developed methodology is assessed by applying it on different cases of the Vietnamese food industrial sector. Three case studies (at tapioca producing households in Tra Co Village, a large-scale tapioca processing plant of Tan Chau-Singapore Company, and food processing companies in Bien Hoa 1 IZ) represent differences between: (1) small/household-scale enterprises and large-scale companies; (2) one enterprise and a group of enterprises; (3) a group of enterprises from one industrial sector and a group of enterprises from different industrial sectors (but still within the broad category of agro-food industries); (4) enterprises located within and outside industrial zones, as industrial zones have specific advantages in industrial ecology design.
In general, these case studies illustrate that excessive generation of non-products (including reusable/valuable materials, wastes and air pollutant emission) arises due to: inefficient technology, inadequate processing, inadequate onsite and offsite reuse and recycling, cheap natural resources, financial limitations, no strict enforcement and lack of incentives on pollution prevention.
Experiences from the three case studies have made clear that failures in current environmental management due to improper performance of the existing actors and institutions can be indicated in the following five points. First, state environmental management authorities, especially provincial DOSTEs, face difficulties of high workload, lack of expertise, and scare resources for monitoring and enforcement. Second, specific regulations and incentives for producers to make their production processes more ecologically sound and to reuse and recycle wastes are completely lacking at the moment. Third, influences from economic agencies do not seem to encourage producers to improve their production efficiencies and environmental performances. Fourth, there is hardly any enduring relation between research institutes and the producers in neither production nor environmental protection. Finally, civil society is not actively involved in environmental issues.
Seeking possibilities to overcome the causes of excessive generation of non-products, these case studies have revealed that cleaner production, waste exchanges and ideas of industrial ecology are valuable in greening food processing industry, though the feasible technical options and organizational schemes are different in the different cases. The diversity of industrial system situations in Vietnam in terms of scale, size, industrial sector and location causes a number of dissimilarities in the proposed options and implementations to approach a zero waste (food processing) industrial ecosystems. Therefore, this study concludes that any general or national approach to green food processing industry is doomed to fail in practice if in its operationalization these differences are not taken into account. Though several constraints (in terms of technical dimensions, environmental policy, economic aspects and public participation) hampering the implementation of the proposed physical technological models of zero waste industrial ecosystems were found from the case studies, there also appear several opportunities to overcome these constraints.
The possibilities and approaches for greening food processing industry in Vietnam learned by experiences from these case studies can be generalized in a physical-technological model, in which (food processing) industry and agriculture cooperate. This model consists of food processing enterprises and all or some of the following components: other enterprises, which use products from food processing enterprises as raw materials, livestock feed production enterprise, fish culture households, livestock breeding households, composting plant, biogas production plant, agricultural fields and wastewater treatment plant. Though operationalization of this physical-technological model will vary due to the diversity of (food processing) industrial systems, this generalized model is the foundation for governmental authorities, planers, policy makers and environmentalists in reforming existing industrial systems and establishing new industrial systems as well.
Though several similarities and dissimilarities arose from the three case studies, it is possible to draw two general conclusions on the proposed methodology. First, the methodology to design a physical-technological model of a zero waste industrial ecosystem following four basic steps proved feasible to apply to any industrial system. Second, the case studies show that without an analysis of actor and institutions, any physical-technological model remains a theoretical possibility at best. An analysis of actors and institutions following a triad-network model proved useful in all studied industrial systems.
At last, this study specifies five crucial points, which reflect the very Western ideas of Industrial Ecology Concept when applied in Vietnam. First, the industrial ecology concept has been applied especially in Europe and USA market economics with advanced technological systems, while Vietnam is a less technological development country. Therefore, with the same kind of industrial sector, the application of industrial ecology in Vietnam will differ from European and American ones. Second, in Vietnam, the organizational and institutional structures around industry and industrial systems are in general simpler than what we see in Western countries. This means that an operationalisation of industrial ecology can rely less on all kinds of advanced organizational models. Third, a number of socio-institutional conditions that are crucial for advancing and implementing industrial ecology models in practice as present in advanced industrialized societies are absent or less developed in Vietnam. Thus, developing feasible options that have a high chance to be implemented and succeed in Vietnam will be different from those developed in advanced industrialized countries. Fourth, Vietnam still has a large number of reuse and recycling practices that are not so much motivated by environmental considerations but rather by economic ones. With further development of the economy in Vietnam, these existing recycling and reuse practice might come under pressures and need to be 'protected': that is an active industrial ecology policy needs to be developed to continue these practices. Finally, the large agricultural sector together with the large proportion of the land used for agricultural production opens favorable conditions for agro-industrial ecology models and practices in Vietnam.
|Water Recycling and Resource Recovery in Industry : analysis, technologies and implementation
Lens, P.N.L. ; Hulshoff Pol, L.W. ; Wilderer, P. ; Asano, T. - \ 2002
London : IWA - ISBN 9781843390053 - 677
hergebruik van water - industrieel afval - watervoorraden - afvalwaterbehandeling - milieutechnologie - water reuse - industrial wastes - water resources - waste water treatment - environmental technology
Anaerobic hydrolysis during digestion of complex substrates
Sanders, W.T.M. - \ 2001
Wageningen University. Promotor(en): G. Lettinga; G. Zeeman. - S.l. : S.n. - ISBN 9789058083753 - 101
hydrolyse - organische verbindingen - afvalwater - rioolwater - kinetica - industrieel afval - aardappelfabrieksafvalwater - slachthuisafval - mest - hydrolysis - organic compounds - waste water - sewage - kinetics - industrial wastes - potato factory effluent - slaughterhouse waste - manures
Complex waste(water) such as, raw sewage, dairy wastewater, slaughterhouse wastewater, fish processing wastewater, primary sludge and the organic fraction of municipal solid waste have been proven to be degradable under anaerobic conditions. However, during the digestion process the conversion of the complex organic molecules into mono- and dimer components, also called the hydrolysis, is often the rate-limiting step. For design and optimization of the anaerobic conversion of complex waste(water) a good knowledge of the hydrolysis kinetics is therefore essential. The scope of this thesis was therefore to clarify the hydrolysis kinetics during the anaerobic digestion of complex waste(water), with emphasis on the hydrolysis of particles, dissolved macromolecules and lipids in coherence with the process conditions during the digestion. The mechanisms of the hydrolysis were elucidated by lab experiments and simulations with mechanistic hydrolysis models. For the hydrolysis of particulate substrates the results presented in this thesis revealed that, at constant pH and digestion temperature, the amount of surface available for the hydrolysis is the most important parameter for the hydrolysis rate and all other parameters are of minor importance.
With respect to dissolved polymers, such as gelatine and dissolved starch, the results indicate that the mechanism of the enzymatic hydrolysis in batch experiments can be described as a random polymerisation process. Moreover, the hydrolysis rate of dissolved components is linearly related to the sludge concentration in the batch experiment. The hydrolysis of neutral lipids under acidogenic conditions is slower as compared to the hydrolysis under methanogenic conditions. Based on the results presented in this thesis it was hypothesised that this is due to positive effect of the methane production on maintaining the lipid-water interface and subsequent higher volumetric hydrolysis rate.
In practice the hydrolysis rate is most commonly described by an empirical first order relation, in which the hydrolysis rate is linearly related to the amount of biodegradable substrate that is available (Eastman and Ferguson, 1981).
The identification of the essential parameters of the hydrolysis mechanisms in this thesis made it possible to evaluate the first order approach and designate the limitations of the relation. The evaluation revealed that the hydrolysis only proceeds according to first order kinetics if no changes in the rate limiting step or the biodegradability occur during the degradation of a substrate. Moreover, the first order hydrolysis constant seems system and substrate specific and the use of literature values for the hydrolysis constant is therefore not advised.
For assessment of a hydrolysis constant in a lab experiment the following guidelines were presented: (1) For waste(water) containing mainly protein and carbohydrates, first order kinetics can be established under acidic and methanogenic conditions in batch or completely stirred tank reactor (CSTR) system. (2) For waste(water) that contains high concentrations of lipids the assessment of the hydrolysis constant for neutral lipids under acid conditions is impossible due to coagulation of the lipid. Under methanogenic conditions the hydrolysis constant can be assessed in a 'multiple flask' batch system. However as (gas) mixing can differ between a laboratory batch and a full-scale CSTR-system, the subsequent effect on the lipid-water interface might cause a difference in the prevailing k h value of the two systems.
Thermophilic sulfate and sulfite reduction with methanol in a high rate anaerobic reactor
Weijma, J. ; Haerkens, J. ; Stams, A.J.M. ; Hulshoff Pol, L.W. ; Lettinga, G. - \ 2000
Water Science and Technology 42 (2000). - ISSN 0273-1223 - p. 251 - 258.
afvalwaterbehandeling - industrieel afval - ontzwaveling - methanol - anaërobe behandeling - waste water treatment - industrial wastes - desulfurization - methanol - anaerobic treatment
Appropriate technologies for effective management of industrial and domestic waste waters : the decentralised approach
Lier, J.B. van; Lettinga, G. - \ 1999
Water Science and Technology 40 (1999)7. - ISSN 0273-1223 - p. 171 - 183.
afvalwaterbehandeling - anaërobe behandeling - milieubescherming - hergebruik van water - vuilnis - industrieel afval - waste water treatment - anaerobic treatment - environmental protection - water reuse - refuse - industrial wastes
Mogelijkheden van natte bijproducten voor rose vleeskalveren
Heeres, J. - \ 1998
Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 11 (1998)1. - ISSN 1386-8470 - p. 31 - 33.
industrieel afval - bijproducten - kalveren - vleesproductie - voer - samenstelling - droge stof - groei - ontwikkeling - productiviteit - rentabiliteit - dierhouderij - vloeibare voedering - industrial wastes - byproducts - calves - meat production - feeds - composition - dry matter - growth - development - productivity - profitability - animal husbandry - liquid feeding
Om in de roze vleeskalverhouderij een redelijk arbeidsinkomen te behalen is een lage kostprijs van essentieel belang. De voerkosten bedragen ca. 45% van de totale kosten en zijn dus een belangrijke kostenpost. De meeste praktijkrantsoenen bestaan uit krachtvoer en snijmais. Vanwege de kosten kan het aantrekkelijk zijn een deel van het krachtvoer te vervangen door natte bijproducten. De vraag is dan in welke mate dat de technische resultaten beonvloedt.
Sequenced anaerobic - aerobic treatment of hemp pulping wastewaters
Kortekaas, S. - \ 1998
Agricultural University. Promotor(en): G. Lettinga; J.A. Field. - S.l. : S.n. - ISBN 9789054859505 - 145
industrieel afval - hennep - afvalwaterbehandeling - anaërobe behandeling - aërobe behandeling - industrial wastes - hemp - waste water treatment - anaerobic treatment - aerobic treatment
Biological treatment is an indispensable instrument for water management of non-wood pulp mills, either as internal measure to enable progressive closure of water cycles, or as end of pipe treatment. In this thesis, the sequenced anaerobic-aerobic treatment of hemp ( Cannabis sativa L. ) pulping wastewaters is described, with a focus on the treatability of thermomechanical pulping (TMP) effluents and soda pulping black liquors. The research was performed within the framework of the Dutch Hemp Programme, which aimed to develop environmentally safe and economically feasible pulping processes as a measure to explore non-food markets for arable farming.
Pulp and paper industry wastewaters are highly heterogeneous, depending on the feedstock and the pulping processes utilized. Hemp TMP wastewaters were found to be non-toxic to methanogens and highly suitable for sequenced anaerobic-aerobic treatment, which enabled 63-66% COD removal at loading rates up to 27 g COD/ lUASBd. Hemp black liquors on the other hand, were somewhat more problematic, due to the high methanogenic toxicity, causing 50% inhibition of acetoclastic methanogenic activity (50% IC) at concentrations ranging from 2-6 g COD/ l , which is 10 to 100 times lower than the black liquor concentrations in industry and comparable to the methanogenic inhibition of wood pulping wastewaters.
Apolar hemp extractives (resinous compounds) were observed to be the main source of inhibitory substances in hemp black liquors. Lignin derivatives on the other hand, were less important for methanogenic inhibition, since the main share of lignin in hemp black liquors was non-toxic. Despite the high methanogenic toxicity of hemp black liquors, anaerobic treatment was feasible, provided that adequate dilution was applied. Anaerobic treatment of diluted hemp stem wood black liquor (HSWBL) facilitated recovery of methane and high treatment efficiencies at high organic loading rates. Subsequent aerobic post-treatment provided almost complete removal of BOD, however COD-removal was limited due to the presence of recalcitrant lignin. Additionally, substantial detoxification was obtained after anaerobic-aerobic treatment. The major removal of inhibitory compounds was accomplished in the aerobic step.
The effective reduction of methanogenic toxicity during sequenced anaerobic-aerobic treatment of hemp black liquors was used as a detoxification strategy denominated upfront dilution, recirculating the aerobic effluent to dilute the incoming influent to sub-toxic concentrations. The feasibility of the upfront dilution method was demonstrated in an experiment, in which direct anaerobic treatment and sequenced anaerobic-aerobic treatment with upfront dilution were compared. Direct anaerobic treatment of 12 g COD/ l HSWBL led to almost complete inhibition of the methanogenic activity within 14 days. While recirculation of 75% of the aerobic post-treatment effluent for upfront dilution of the toxic HSWBL, enabled anaerobic treatment at loading rates up to 21.5 g COD/ lUASBd without noticeable inhibition of methanogenesis. Extensive detoxification was confirmed during anaerobic-aerobic treatment of 20 g COD/ l HSWBL recirculating 86% of the aerobic effluent. COD and BOD removal was 47% and 68%, respectively, after anaerobic treatment; and 74% and 97%, respectively, after anaerobic-aerobic treatment at an overall loading rate of 3.6 g COD/ l d, while 30-35% of the incoming COD was recovered as methane.
Lignin removal during anaerobic-aerobic treatment of hemp pulping wastewaters was remarkably high and ranged up to 44%, of which globally half was obtained anaerobically. Studies on hemp TMP wastewater revealed that lignin removal during anaerobic treatment corresponded to the lowest molecular weight derivatives, indicating that biodegradation was the major removal mechanism. Subsequently, aerobic post-treatment of hemp pulping wastewaters caused extensive polymerization of lignin to molecular weights in excess of 34 kD, which was associated with strong increases in wastewater color. Autoxidative polymerization of polyphenols formed out of lignin by anaerobic bioconversion is proposed as a mechanism for the observed increase in lignin molecular weight and color. Apart from the highly stable high molecular weight lignin-derived humic COD, biologically treated pulping effluents are relatively clean, which offers benefits for lignin removal during tertiary treatment, such as reduced fouling of ultrafiltration membranes and improved precipitation with divalent salts.
Comparison of anaerobic-aerobic treatment and aerobic treatment shows that treatment efficiencies and detoxification were similar. The anaerobic-aerobic treatment system however, provided 50% lower surplus sludge production, production of methane as an energy source (0.16 m 3/kg COD removed ), less nutrient dosage and substantial reductions in aeration costs.
The results of this research demonstrate that sequenced anaerobic-aerobic treatment is a suitable technology for the treatment of hemp pulping wastewaters. Upfront dilution effectively reduced inhibition of methanogenesis by extractive compounds during anaerobic treatment, whereas the observed increase in lignin molecular weight after biological treatment offers benefits for lignin removal during optional tertiary treatment.
Natte en droge bijproducten in rantsoenen rose-vleeskalveren
Bikker, P. ; Heeres-van der Tol, J.J. - \ 1997
Lelystad : Praktijkonderzoek Rundvee, Schapen en Paarden (Publicatie / Praktijkonderzoek Rundvee, Schapen en Paarden (PR) 126) - 24
voer - droge stof - water - vleesvee - kalveren - voedingswaarde - industrieel afval - bijproducten - feeds - dry matter - water - beef cattle - calves - nutritive value - industrial wastes - byproducts
Natte bijproducten kunnen zeer goed in het rantsoen van roze-vleeskalveren worden opgenomen. Door het dalen van de totale voerkosten en een iets betere voederconversie-karkas dalen de voerkosten per kg groei ten opzichte van het rantsoen met maos en krachtvoer.
Varkens en bijproducten: een combinatie met perspectief
Scholten, R. ; Hoofs, A. ; Loo, D. van de - \ 1997
Praktijkonderzoek varkenshouderij 11 (1997)6. - ISSN 1382-0346 - p. 19 - 24.
industrieel afval - bijproducten - varkens - biggen - spenen - voer - groei - ontwikkeling - karkassamenstelling - vloeibare voedering - industrial wastes - byproducts - pigs - piglets - weaning - feeds - growth - development - carcass composition - liquid feeding
Op het Varkensproefbedrijf te Sterksel is een eerste reeks proeven afgerond waarbij vloeibare bijproducten werden verstrekt aan vleesvarkens en gespeende biggen. De algemene conclusie is dat het verstrekken van drie gangbare vloeibare bijproducten aanvleesvarkens een voordeel biedt ten aanzien van technische resultaten en voerkosten. Het mager-vleespercentage behoeft echter extra aandacht.
Membranes as separators of dispersed emulsion phases
Lefferts, A.G. - \ 1997
Agricultural University. Promotor(en): K. van 't Riet; M.A. Cohen Stuart; A. van der Padt. - S.l. : Lefferts - ISBN 9789054857099 - 157
membranen - omgekeerde osmose - ultrafiltratie - waterzuivering - afvalwaterbehandeling - filters - zand - rioolwater - afvalwater - industrie - industrieel afval - membranes - reverse osmosis - ultrafiltration - water treatment - waste water treatment - filters - sand - sewage - waste water - industry - industrial wastes
The reuse or discharge of industrial waste waters, containing small fractions of dispersed oil, requires a purification treatment for which membranes can be used. If only little oil is present, removal of the dispersed phase might be preferable to the more commonly applied removal of the continuous phase. For this purpose dispersed phase separators can be applied, which combine the features of conventional coalescers and membrane filtration. The membrane surface promotes coalescence (similar to a coalescer) but in the mean time the coalesced phase is separated and transferred in a continuous oil permeate phase.
In the present thesis the possibility to use sheets of polypropylene membrane (with a pore diameter of 0. 1 μm) as dispersed phase separators for treatment of secondary (bromo-) hexadecane-in-water emulsions stabilized by Tween-40 is investigated. The weight fraction of the dispersed phase is always lower than 0.06 and the volume to surface averaged diameter of the oil droplets is generally smaller than 10 μm. The research focuses on understanding the mechanisms controlling the permeation behavior of the oil droplets. The process can be described in two stages: firstly the droplets have to be transported form the bulk of the emulsion towards the membrane and secondly they have to coalesce and permeate.
In chapter 2 and 3 the transport mechanisms are determined both experimentally and theoretically. It is shown that the theories developed for collectors of solid particles, based on the convective diffusion equation, can be used to describe the transport behavior of the oil droplets in membrane modules. The main transport mechanisms are diffusion, gravity and interception. The latter occurs if the location of the stream lines and the droplet size results in contact between droplet and membrane. The influence of several parameters, such as droplet size, density of the dispersed phase, flow rate and module design can be explained using the convective diffusion theory, assuming the membrane to be a perfect sink. This means that as soon as a droplet reaches the membrane it coalesces and permeates. Since theory and experimental results agree qualitatively, it can be concluded that the system is transport limited in most cases.
In chapter 4, the coalescence mechanism is discussed. Only if the contact time between droplet and membrane becomes smaller than the time needed for coalescence, the system will be coalescence limited. The coalescence time, t c [s], is determined by the drainage of the aqueous film between droplet and membrane. Calculations show that t c for the small droplets under investigation against a liquid interface is smaller than I second while in case of the presence of a membrane t c will be even smaller. As the contact times are at least a few seconds, coalescence will occur which is in agreement with the perfect sink assumption. Only in case of a dead end module at high flow velocities the system becomes coalescence limited because of short contact times. Finally, at high surfactant concentrations coalescence is not detected.
As oil droplets are slightly negatively charged, the transport can be enhanced by electrophoresis. Therefor, in chapter 5 possibilities to apply an electric field over the emulsion are investigated. If the anode is placed at the feed side of the membrane the transport velocity is increased significantly. However, not all droplets permeate and a cream layer is formed in front of the membrane. If the anode is placed at the permeate side of the membrane, problems are encountered because of the large resistance of the continuous oil permeate phase. The electric field is situated mainly over this phase, at the cost of the electric field over the emulsion. The resistance of the permeate phase can be successfully decreased by addition of an apolar electrolyte (TBAI). Also, it is possible to circulate an aqueous phase at the permeate side. In this case, oil droplets with a diameter of several millimeters are detected in the permeate. Here, the membrane acts as a conventional coalescer. All systems show indeed an enhanced extraction in the presence of an electric field. However, we think that only the first and the last are scaleable.
Finally, in the general discussion the dispersed phase separator is compared to conventional emulsion separation methods. The dispersed phase separator becomes advantageous at low oil concentrations. Feasibility will increase if the remaining oil fraction in the retentate can be decreased further. Ideas for optimization in case of transport limitation are introduced, such as adjusting the flow profile to increase the interception mechanism. Problems are encountered in practice because of the presence of all kinds of impurities in industrial waste waters which will hinder the coalescence. In that case, research should focus on coalescence enhancing parameters of the membrane material such as surface potential and surface roughness. Preliminary experiments using a reflectometer indicate the importance of surface roughness, which is explained theoretically.
Economische evaluatie van het voeren van natte bijproducten aan vleesvarkens
Brakel, C.E.P. van; Scholten, R.H.J. ; Backus, G.B.C. - \ 1996
Rosmalen : Praktijkonderzoek varkenshouderij (Proefverslag / Praktijkonderzoek Varkenshouderij P1.147) - 36
bijproducten - boekhouding van landbouwbedrijf - rekeningen van landbouwbedrijf - industrieel afval - varkens - byproducts - farm accounting - farm accounts - industrial wastes - pigs
Natte bijproducten voeren aan vleesvarkens
Brakel, C. van; Scholten, R. ; Backus, G. - \ 1996
Praktijkonderzoek varkenshouderij 10 (1996)3. - ISSN 1382-0346 - p. 12 - 13.
dierhouderij - bijproducten - kostenanalyse - drinkbakken - voerverdelers - voer - industrieel afval - varkens - productiviteit - rentabiliteit - vloeibare voedering - animal husbandry - byproducts - cost analysis - drinkers - feed dispensers - feeds - industrial wastes - pigs - productivity - profitability - liquid feeding
Door de lage prijs van natte bijproducten in relatie tot hun voedingswaarde leveren bijproducten een bijdrage aan de verlaging van de voerkosten.