Anforderungen an umweltfreundliche Holzfeuerungsanlagen

An ecological combustion of wood and wood residues requires an efficient barn out of the combustible gases and an efficient precipitation of the particles. To reach a complete burn out the combustion is divided in the gasfication with primary air and the burn out of the gases with secondary air. If these conditions are met the emission of carbon monoxide and hydrocarbons can be diminued effectively. On the contrary the emissions of nitric oxides cannot be diminued since they origin mainly from the fuel bound nitrogen. It is necessary to develop low NO_x wood firings due to staged combustion or other new technologies. For large scale plants the use of processes to reduce nutric oxides in the flue gas have to be exammed.     

Arsen im Holzschutz

Arsenic compounds used in wood preservation are classified as dangerous substances for which a cancerogenic effect to man has clearly been shown. Occupational exposure is possible by working up the preservatives and the impregnated wood. In the area of preservation plants in part a tremendously high contamination of soil by arsenic has been measured. By modern technology the environmental input in the area of the preservation plant could be reduced to a large extent. Although wood impregnated with arsenicals is thought to be relatively safe during its use, considerable proportions of the arsenic from CCA-treated wood can be loaded onto the environment under severe leaching conditions. By burning treated wood without flue gas cleaning 20% to 80% of the arsenic will be emitted to the air. There the arsenic is again present in a form for which a cancerogenic potential has been shown. Waste management problems of treated wood are discussed from a legal, practical and environmental policy point of view, and other sources of emission of arsenic are referred to comparison.     

Arsen im Holzschutz

Arsenic compounds used in wood preservation are classified as dangerous substances for which a cancerogenic effect to man has clearly been shown. Occupational exposure is possible by working up the preservatives and the impregnated wood. In the area of preservation plants in part a tremendously high contamination of soil by arsenic has been measured. By modern technology the environmental input in the area of the preservation plant could be reduced to a large extent. Although wood impregnated with arsenicals is thought to be relatively safe during its use, considerable proportions of the arsenic from CCA-treated wood can be loaded onto the environment under severe leaching conditions. By burning treated wood without flue gas cleaning 20% to 80% of the arsenic will be emitted to the air. There the arsenic is again present in a form for which a cancerogenic potential has been shown. Waste management problems of treated wood are discussed from a legal, practical and environmental policy point of view, and other sources of emission of arsenic are referred to comparison.     

Sorption studies on hygroscopic materials,utilizing a MP-based differential environmental control chamber

In certain cases, a knowledge of the sorption rates of wood is of importance, as c.g. for wood which has been treated with water repellent agents. To study the sorptional behaviour of treated and also of untreated wood, particularly when it is abruptly exposed to different climatic conditions (different temperatures and relative humidities of the surrounding air), the so-called differential environmental control chamber (DECC) was designed and built by the authors. Constructive details and the function of the DECC are dealt with.     

Development of a new rapid method for mould testing in a climate chamber: preliminary tests

The purpose of this study was to develop fast, simple and robust solid wood mould testing methods for the use in small-scale laboratory tests. The objective was to investigate mould susceptibility of different wood materials within the batches. The proposed method is based on natural contamination of non-sterile surfaces in climates conducive to mould growth. For this purpose, a climate chamber with regulated temperature and relative humidity was used. The conditioning chamber was divided into upper and lower chamber by a thin layer of stainless steel placed horizontally above the fan to minimise air circulation to the sample in the upper compartment. Mould-infected samples from outdoor tests were used as a source of mould inocula, and test trials were conducted on Scots pine (Pinus sylvestris L.) sapwood. Samples were suspended from the top of the upper chamber, and the chamber was exposed to different temperature and humidity levels. Severe mould infestation was observed after 12–14 days of incubation. Visual mould rating was then performed. Regardless of some constraints, this test method was very simple, fast, and effective. More importantly, unlike other test methods, it closely models mould infestation as it would occur under natural condition.     

Arsen im Holzschutz

Arsenic in wood preservation is used all over the world mainly in Copper-Chrome-Arsenic (CCA) wood preservatives by pressure treatment. In the Federal Republic of Germany this use for outdoor wood is not yet forbidden as an exception of a comprehensive ban of the use of arsenical compounds. This regulation originates primarily from an EEC directive. Arsenic content of the CCA salts varies between 11% and 29%, the most common retention is 6 kg salt per m³ of the total volume of treated wood. In the FRG CCA salts are not produced anymore and are used to a relative low extent yet. Although there seems to be a declining trend towards the import of wood treated with arsenicals, in 1988 still approximately 100–200 t of arsenic were introduced to the FRG by this way.     

Holzfeuchteminderung und -ausgleich durch Wechseldruckvortrocknung von schwachem Buchenstammholz

The objective of this study was to assess, whether it is possible to reduce and to level out cross sectional wood moisture contents in thin beech timber through mechanical wood demoistening, i. e. a regime of alternating atmospheric high and ambient pressure. For this purpose, 25 pieces of beech timber of up to 30 cm mid diameter and 2.80 m length were treated in a pressure chamber. Their wood moisture content and cross sectional wood moisture distribution were compared to 26 untreated controls. The treated beech timber had significantly lower wood moisture contents as compared to untreated controls. Furthermore, wood moisture was significantly more evenly distributed across the trunks. Neither untreated controls nor treated samples had noticeable wood moisture gradients from the stem periphery to the centre. Instead, wood moisture was distributed irregularly across the trunks.     

Holzfeuchteminderung und -ausgleich durch Wechseldruckvortrocknung von schwachem Buchenstammholz

The objective of this study was to assess, whether it is possible to reduce and to level out cross sectional wood moisture contents in thin beech timber through mechanical wood demoistening, i. e. a regime of alternating atmospheric high and ambient pressure. For this purpose, 25 pieces of beech timber of up to 30 cm mid diameter and 2.80 m length were treated in a pressure chamber. Their wood moisture content and cross sectional wood moisture distribution were compared to 26 untreated controls. The treated beech timber had significantly lower wood moisture contents as compared to untreated controls. Furthermore, wood moisture was significantly more evenly distributed across the trunks. Neither untreated controls nor treated samples had noticeable wood moisture gradients from the stem periphery to the centre. Instead, wood moisture was distributed irregularly across the trunks.     

生物膜的形成与控制

生物膜对食品工厂的危害极大,可使微生物残存增加,加工车间设备无法适当清洗、清毒;产品受到污染,甚至危害产品的安全。食品加工厂欲控制生物膜的形成,应从设计、生产环节着手,设计出良好的生产环境,注意清洗频率,使用正确的清洗、消毒方法,严格控制生物膜的形成,才能保障产品的卫生安全。     

Wo steht der Holzschutz heute?

Starting from a draft survey of the general socialpolitical situation in Germany the position of the various groups envolved in wood preservation is illustrated from the authors point of view. Non chemical measures have preferance to chemical measures, which are reduced. This tendency will expand in future. Most urgent problems are presented, being the need of detailed knowledge regarding possible harm to environment by the use of treated wood, the possibilities for disposal of treated wood by giving preferance to environmental aspects, and the question of prophylactic treatment of round wood and sawn timber.     

Emissions of chromium, copper, arsenic, and PCDDs/Fs from open burning of CCA-treated wood

Aged and weathered chromated copper arsenate (CCA) treated wood was burned in an open burn research facility to characterize the air emissions and residual ash. The objectives were to simulate, to the extent possible, the combustion of such waste wood as might occur in an open field or someone's backyard; to characterize the composition and particle size distribution (PSD) of the emitted fly ash; to determine the partitioning of arsenic, chromium, and copper between the fly ash and residual ash; and to examine the speciation of the CCA elements. This work reports preliminary air emission concentrations and estimated emission factors for total particulate matter, arsenic (As), chromium (Cr), copper (Cu), and polychlorinated dibenzodioxins/dibenzofurans (PCDD/F) totals and toxic equivalents (TEQs). The partitioning of As, Cr, and Cu between the emitted fly ash and residual ash is examined and thermochemical predictions from the literature are used to explain the observed behavior. Results indicate a unimodal fly ash PSD between 0.1 and 1.0 microm diameter. In addition to a large carbonaceous component, between 11 and 14% of the As present in the burned CCA treated wood was emitted with the air emissions, with the remainder present in the residual ash. In contrast, less than 1% of both the Cr and Cu present in the wood was emitted with the air emissions. PCDD/F levels were unremarkable, averaging 1.7 ng TEQ/kg of treated wood burned, a value typical for wood combustion. Scanning electron microscopy (SEM) was unable to resolve inorganic particles consisting of Cu, Cr, or As in the wood samples, but X-ray absorption fine structure (XAFS) spectroscopy confirmed that the oxidation states of the CCA elements in the wood were Cu2+, Cr3+, and As5+. SEM examination of the fly ash samples revealed some inorganic microcrystals within the mostly carbonaceous fly ash, while XAFS spectroscopy of the same samples showed that the oxidation states after combustion were mixed Cu+ and Cu2+, Cr3+, and mixed As3+ and As5+. Estimates of the ratios of the mixed oxidation states based on the XAFS spectra were As3+/(total As) = 0.8-0.9 and Cu+/(total Cu) = 0.65-0.7. The Cu and Cr present in the fly ash were determined to coexist predominantly in the two oxide phases CuCrO2 and CuCr2O4. These results indicate that the open burning of CCA-treated wood can lead to significant air emissions of the more toxic trivalent form of As in particle sizes that are most respirable.     

Sensory effects of hexanal vapor on fresh-cut slices of golden delicious apples

Hexanal is a natural antimicrobial molecule that characterizes apples aroma. In this paper, the sensory effects of hexanal, as a component of packaging atmosphere, on fresh sliced Golden Delicious apples after storage at 4 °C for 8 d were evaluated. In particular, a colorimetric analysis of slices treated with different concentrations of hexanal vapor (coming from 3.040 to 0.076 mmol of liquid aldehyde per liter of air) fixed at 0.076 mmol/L the amount of hexanal in evaluating sensory effects in the subsequent analysis. Color and texture evaluation of slices by Two-out-of-Five method did not highlight any significant difference between treatment and control. The results from olfactory evaluation showed instead that treated samples had an intense odor compared with those untreated (P < 0.001). A significant difference between treatment and control was also highlighted during the flavor evaluation (P < 0.01); however, from the panelists' observations it emerged that such an effect would work negatively. The positive effect of the tested dose of hexanal on the odor of Golden Delicious slices and its flavor acceptability were verified by using regular apple consumers. A significant preference (P < 0.001) for the odor of treated apple slices came out, so the small dose of hexanal intensifies the odor of apples pleasantly. The different flavor of treated samples was not identified by the consumers, who altogether expressed positive judgments about it. This suggests the nicety of this difference that in the absence of an untreated reference sample is very difficult to detect.     

Effect of heat treatment on the wettability of white ash and soft maple by water

Heat treatment of wood has attracted a lot of attention both in Europe and recently in North America as an environmentally-friendly wood-protection method. The untreated wood is hydrophilic (high affinity for water). During the heat treatment, wood becomes more and more hydrophobic (low affinity for water) with increasing heat treatment temperature. As a result, it becomes more resistant to biological attacks. Furthermore, it becomes dimensionally more stable compared to untreated wood. Its hardness increases. As the wood becomes more hydrophobic, its wettability by water decreases. The effect of heat treatment is different for each species. Studying the wetting characteristics of heat treated wood gives a good indication of the heat treatment effects on certain wood properties which are related to its degree of hydrophobic character. The aim of this work was to study the characteristics of dynamic wetting process for two different heat-treated North American wood species white ash (Fraxinus americana) and soft maple (Acer rubrum). Contact angle measurements before and after heat treatment showed a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases higher for heat-treated wood than for untreated wood.     

Characterization of Listeria monocytogenes isolates from the meat, poultry and seafood industries by automated ribotyping

A total of 564 Listeria monocytogenes isolates were characterized by automated ribotyping. The samples were taken from equipment, personnel and the environment after cleaning procedures and during food processing, as well as from raw materials and products from six meat, two poultry and five seafood processing plants located in the Faroe Islands, Finland, Iceland, Norway and Sweden. Altogether, 25 different ribotypes (RTs) were generated. Two RTs occurred in the samples from all three food sectors--meat, poultry and seafood. Four RTs occurred in meat and poultry plant samples and other four RTs occurred in meat and seafood plant samples. Five RTs occurred only in meat plant samples, five only in poultry plant samples and five only in seafood plant samples. Eight of the thirteen plants had their own in-house L. monocytogenes ribotype. There was geographical differences between the RTs, but no correlation between RTs and food sectors was detected. The discrimination power of automated ribotyping was satisfactory to trace the contamination sources in the food processing plants clearly indicating the sites at which improved cleaning procedures were necessary. In addition, it was possible to screen a large number of isolates with two instruments located at different institutes and to make a reliable combination of the results.     

多种浆粕混用制备粘胶的探讨

浆粕是制造粘胶纤维的重要原料。由于国内棉浆供应能力不足,在生产中全部使用优质棉浆是不现实的,必须采取木浆混用。该文就多种浆粕混用而采取的工艺措施、设备改进方面进行探讨。     

Application of copper monoethanolamine solutions as primers for semitransparent exterior wood stains

The effects of copper monoethanolamine (CuA) treatment of wood surfaces on the surface weathering and durability of a semitransparent penetrating stain were compared with those of chromic acid (CrA) treatment which is known as a photoprotective primer, using artificial weathering trials. Chemical changes in chemically treated and untreated wood surfaces during artificial weathering were investigated using Fourier transform infrared (FTIR) spectroscopy. Surface roughness, water contact angle measurements and scanning electron microscopy observations were performed to assess stain durability. Results of FTIR analyses indicated that lignin losses following CuA and CrA treatment were less than those of the untreated wood surfaces during the initial stage of artificial weathering. CuA pretreatment prior to staining also retarded the increase in the average surface roughness compared with that observed for the CrA-pretreated surface and untreated control (only stained) during artificial weathering. Furthermore, CuA pretreatment retarded the decrease in the contact angle compared with that observed for the untreated control, although the use of a highly concentrated CuA solution led to a decrease in the water repellency of the stained wood surface. These results indicated that CuA solution could be used for the pretreatment of wood surfaces to enhance the durability of semitransparent penetrating stains, as long as excessive CuA concentrations are avoided.     

Bonding performance of heat treated wood with structural adhesives

Bonding of untreated, intermediate (hydro-thermolysed) and heat treated wood with melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF) and polyurethane (PUR) adhesives was studied. An industrial heat treatment process (Plato ^®) was used, which included two separate heat treatment stages and a drying stage in-between. Laminated beams having four lamellas were prepared from untreated and treated timber for mechanical testing of the bond lines. The results of the tests showed that heat treatment affected the shear strength and the delamination of the laminated wood depending on the adhesive system used for bonding. The PUR and MUF adhesives performed in a rather similar way, and better than the PRF adhesive. The shear strength of laminated wood bonded with the waterborne MUF and PRF adhesives decreased for the specimens made of hydro-thermolysed timber and decreased further for the specimens made of fully heat treated timber. The difference in adhesive bond shear strength between untreated, intermediate and fully treated wood was less obvious in the case of the PUR adhesive. Delamination of the PRF bond line decreased drastically for all the specimens made of heat treated timber.     

脱臭系统清洗实践

在油脂精炼过程中设备触油表面会产生油垢,导致传热传质效果下降,而提高脱臭温度会造成油脂质量下降,因此需要对脱臭系统进行清洗。从清洗机制、清洗剂种类、清洗程序等方面介绍了脱臭系统的清洗实践。油脂精炼厂清洗脱臭系统可先采用碱液和高压水冲洗,再请专业公司采用溶解性清洗剂进行清洗,清洗效果要求被清洗的金属表面除垢率大于95%、无点蚀及过洗现象、腐蚀率小于或等于1.0 g/(m²·h)。在油脂精炼生产中需按照操作规程进行操作和维护,设置好预防清洗的工艺控制参数。     

Untersuchungen über Emissionen bei der thermischen Verwertung von holzschutzmittelhaltigen Holzresten

Since the introduction of strict legal conditions, the disposal of used wood and wood residues treated with wood preservatives became subject of many and diverse discussions. An alternative to disposal and recycling in principle is the thermal utilization, the application of which, however, is ruled by the emission behaviour of the individual fuel components during the combustion process. Due to the fact that up to now only few experimental findings on emissions of organic and inorganic substances during the combustion of wood treated with wood preservatives were known, the combustion behaviour of wood residues and used wood containing wood preservatives, after mixing with untreated wood in a ratio of 1∶4, was investigated in several test series. The presented results for organic solvents, creosote, Cu-HDO and CCB show that the concentrations of the harmful chemicals occuring in the exhaust gas correspond approximately to those registered for untreated wood. Even properties decreasing the emissions were found for Cu-HDO and CCB. The fixed limit values for polychlorinated dibenzodioxins and dibenzofurans also can be observed provided there exist good combustion conditions.     

Evaluation of the direct epifluorescent filter technique for assessing the hygienic condition of milking equipment

The hygienic condition of 6 milking installations, 3 sanitized by circulation cleaning (CC) with chlorine-based chemicals and 3 by flushing with acidified boiling water (ABW), was tested using rinses of quarter strength Ringer's solution. The bacterial content of the rinses was determined using both colony counts and the direct epifluorescent filter technique (DEFT). A comparison of testing methods gave correlation coefficients between colony count and DEFT of 0.82 for plants using CC and 0.46 for plants using ABW. Five strains of bacteria belonging to different genera and commonly found on milking equipment were exposed to various degrees of heat and to various concentrations of chlorine. The effects of such treatments on the staining characteristics of the organisms were studied. It was observed that Staphylococcus aureus and Streptococcus lactis, although killed by heat treatment, stained a bright orange when treated with acridine orange dye. Pseudomonas fluorescens, Escherichia coli and vegetative cells of Bacillus cereus did not take up the orange stain after heat treatment, nor did any of the 5 strains stain orange after treatment with NaOCl. It is suggested that the DEFT is a useful and rapid means of counting bacteria in rinses of equipment where sterilization is due primarily to chlorination, but in the absence of a stain which can differentiate more accurately between dead and living organisms its use is limited where sterilization is carried out solely by heat.