Determination of orifice diameter for horizontal pipelines in layers for composing windrows via variation of pressure losses

Compressed air plays an important role in forced aeration composting systems; the lateral outlet orifices on the main pipeline must be properly sized to maintain a pressure drop of less than 5% at the output of each orifice. Organic matter (OM) was aerated at a rate of 0.557 m³ air·d^-1·kg^-1, as determined by dry weight (DW), and the internal temperature and humidity of the windrows were monitored. The calculated variation of the pressure loss for the pipelines in the experimental windrow was between 1.53% and 2.56% at a maximum internal temperature of 70.8°C, unlike the conventional windrow, which reached a maximum temperature of 47.1°C. In both systems, the humidity was greater than 50%. The cost per metre for commercial scale implementation is equivalent to US$21.22, considering the use of alternative materials with the necessary mechanical and thermal resistance values.     

Ambient volatile organic compound (VOC) concentrations around a petrochemical complex and a petroleum refinery

Air samples were collected between September 2000 and September 2001 in Izmir, Turkey at three sampling sites located around a petrochemical complex and an oil refinery to measure ambient volatile organic compound (VOC) concentrations. VOC concentrations were 4-20-fold higher than those measured at a suburban site in Izmir, Turkey. Ethylene dichloride, a leaded gasoline additive used in petroleum refining and an intermediate product of the vinyl chloride process in the petrochemical complex, was the most abundant volatile organic compound, followed by ethyl alcohol and acetone. Evaluations based on wind direction clearly indicated that ambient VOC concentrations measured were affected by the refinery and petrochemical complex emissions. VOC concentrations showed seasonal variations at all sampling sites. Concentrations were highest in summer, followed by autumn, probably due to increased evaporation of VOCs from fugitive sources as a result of higher temperatures. VOC concentrations generally increased with temperature and wind speed. Temperature and wind speed together explained 1-60% of the variability in VOC concentrations. The variability in ambient VOC concentrations that could not be explained by temperature and wind speed can be attributed to the effect of other factors (i.e. wind direction, other VOC sources).     

Emission of volatile organic compounds during composting of municipal solid wastes

The objective of this study was to identify and quantify volatile and semi-volatile organic compounds (VOCs) produced during composting of the organic fraction of municipal solid wastes (MSW). A laboratory experiment was conducted using organic components of MSW that were decomposed under controlled aerobic conditions. Mixed paper primarily produced alkylated benzenes, alcohols and alkanes. Yard wastes primarily produced terpenes, alkylated benzenes, ketones and alkanes, while food wastes primarily produced sulfides, acids and alcohols. Among 13 aromatic VOCs found in MSW composting facilities, toluene, ethylbenzene, 1,4-dichlorobenzene, p-isopropyl toluene, and naphthalene were in the largest amounts. Unseeded mixed paper, seeded mixed paper, seeded yard wastes, unseeded yard wastes, seeded food wastes and unseeded food wastes produced approximately 6.5, 6.1, 2.1, 0.83, 2.5 and 0.33 mg of 13 volatile and semi-volatile aromatic organic compounds combined, respectively, per dry kg. All VOCs were emitted early during the composting process and their production rates decreased with time at thermophilic temperatures.     

The effects of power plant condenser cooling water entrainment on the amphipod. Gammarus sp.

The abundant Hudson River amphipod Gammarus sp. was examined for viability before and during entrainment in the Indian Point cooling water system. The mean per cent survivial of Gammarus sp. sampled during ΔT's of 7.1–8.3°C and ambient temperatures of 24.9–26.0°C was 98.5 and 97.4 per cent for the two intake stations and 90.1 and 96.8 per cent for the discharge canal stations D-1 and D-2 respectively. A statistically significant (α = 0.05) difference was detected between the survival of Gammarus sp. at the intake stations and discharge station D-1. located near the upper end of the discharge canal. Entrained Gammarus sp. experience increased initial and latent mortalities during periods of condenser chlorination. Comparison of the abundances of entrained Gammarus sp. during day and night sampling periods reveals a significantly higher occurrence during darkness. Temperature bioassays indicate that the thermal tolerance of Gammarus sp. is dependent on exposure time and ambient temperature. The temperature resulting in a 50 per cent mortality of Gammarus sp. for 30 min exposure times increased approximately 11 C as ambient temperatures increased from 2.5 to 25.8°C. Consequently, Gammarus sp. was capable of surviving ΔT's of greater magnitude as the ambient temperature to which they were acclimated decreased. Temperature bioassays indicated that Gammarus sp. should be able to tolerate all projected time-temperature exposure combinations encountered during entrainment through the cooling water system.     

温度变化对风压疲劳载荷作用下动车组车窗应力的影响

研究了不同环境温度下,动车组车窗各部位受风压疲劳载荷作用后的应力变化。结果表明,影响动车组车窗不同部位应力的主要因素各不相同。玻璃几何中心的应力受风压疲劳载荷作用的影响比受环境温度影响更大,铝合金窗框长边中点的应力同时受环境温度和风压疲劳载荷的影响,玻璃长边中点和玻璃角点的应力则受环境温度和风压疲劳载荷的影响都较小。     

The effect of the wind speed velocity on the stack pressure in medium-rise buildings in cold region of China

This paper presents the numerical simulation results of the stack effect in medium-rise buildings in Harbin, a typical city in the severe cold region of China. The simulation was carried out using the multizone ventilation model COMIS. The effect of the wind speed velocity and the temperature of the stairwell on the pressure difference curves shape have been investigated. The pressure difference between the stairwell and the outside shows a linear variation with the height. However, the wind speed velocity may have a strong effect on the pressure difference. The results of the simulation show that at high wind speed velocity the curve of the pressure difference is not linear in shape. It has been also shown that the air total change cannot be provided by only infiltration due to leakage particularly for such air-tight residential building in windy cold climate. Therefore, mechanical ventilation is required to compensate for the lack of it. A quantitative evaluation of IAQ based on the total volatile organic compounds (TVOCs) concentration has been done. The effect of the wind speed velocity and the temperature of the stairwell on the VOTCs concentration at each floor have been also presented.     

Critical components of odors in evaluating the performance of food waste composting plants

The current Taiwan government policy toward food waste management encourages composting for resource recovery. This study used olfactometry, gas chromatography-mass spectrometry (GC-MS) and gas detector tubes to evaluate the ambient air at three of the largest food waste composting plants in Taiwan. Ambient air inside the plants, at exhaust outlets and plant boundaries was examined to determine the comprehensive odor performance, critical components, and odor elimination efficiencies of various odor control engineering. Analytical results identified 29 compounds, including ammonia, amines, acetic acid, and multiple volatile organic compounds (VOCs) (hydrocarbons, ketones, esters, terpenes and S-compounds) in the odor from food waste composting plants. Concentrations of six components--ammonia, amines, dimethyl sulfide, acetic acid, ethyl benzene and p-Cymene--exceeded human olfactory thresholds. Ammonia, amines, dimethyl sulfide and acetic acid accounted for most odors compared to numerous VOCs. The results also show that the biotrickling filter was better at eliminating the concentrations of odor, NH(3), amines, S-compounds and VOCs than the chemical scrubber and biofilters. All levels measured by olfactometry at the boundaries of food waste composting plants (range, 74-115 Odor Concentration (OC)) exceeded Taiwan's EPA standard of 50 OC. This study indicated that the malodor problem continued to be a significant problem for food waste recovery.     

Comparative process stability and efficiency of anaerobic digestion; mesophilic vs. thermophilic

The comparative process stability and efficiency of mesophilic (35 degrees C) and thermophilic anaerobic digestion (55 degrees C) has been evaluated for four different reactor configurations, which are: daily batch-fed single-stage continuously stirred tank reactor (CSTR), continuously fed single-stage CSTR, daily batch-fed two-phase CSTR, and daily batch-fed non-mixed single-stage reactor. The results are discussed for three periods: (1) start-up, (2) steady state, and (3) organic loading rate (OLR) increase until reactor failure (pH below 5.5). During the start-up, the single-stage CSTRs at both temperatures showed the least stability, while the non-mixed single-stage reactors reached steady state in the shortest time with relatively stable pH and low volatile fatty acid (VFA). In the case of the thermophilic non-mixed reactor, efficient removal of propionate occurred but supplementation of nutrients (Ca, Fe, Ni, and Co) was required when VFA increased. The results imply the importance of inorganic nutrients bioavailability. The comparative results of the reactor performance at steady state clearly showed the superior performance of the thermophilic non-mixed reactor with respect to lower VFA, higher gas production and volatile solids removal implying that microbial consortia proximity can alleviate the problem of poor effluent quality in thermophilic system. During the OLR increase until reactor failure, all thermophilic reactors except the thermophilic non-mixed reactor showed increases in propionate concentrations as the OLR increased, while all mesophilic reactors except the mesophilic two-phase system showed little increase in VFA concentrations. When all reactors had the same conditions with OLR increase, the continuously fed reactors showed the lowest gas production, while the non-mixed reactors showed the highest gas production at both temperatures. It is hypothesized that the non-mixing reactor configuration has closer microbial consortia proximity than others. Therefore, the results in this study indicated the importance of microbial consortia proximity. A proposed model for the effect of the distance between two syntrophic bacteria reasonably matched the data in this study.     

Degradation of yew, ragwort and rhododendron toxins during composting

Recent concerns have been raised that plants such as ragwort (Senecio jacobaea), yew (Taxus baccata) and rhododendron (Rhododendron ponticum) that are toxic to livestock may be included in compost windrows but may not be fully detoxified by the composting process. This study investigates the decomposition during composting of toxic pyrrolizidine alkaloids present in ragwort, taxines (A and B) present in yew, and grayanotoxins (GTX I, II, and III) present in rhododendron during composting. Plant samples were contained within microporous bags either towards the edge or within the centre of a pilot-scale compost heap. They were destructively harvested at regular intervals over 1200 °C cumulative temperature (about three months). Samples were analysed for levels of toxins by liquid chromatography time of flight mass spectrometry (LC-TOF-MS). Pyrrolizidine alkaloids and taxines were shown to degrade completely during the composting process. While GTX I showed significant reductions, concentrations of GTX III remained unchanged after 1200 °C cumulative temperature. However, estimates of exposure to grazing livestock coming into contact with source-segregated green waste compost containing up to 7% rhododendron suggest that GTX III poses no appreciable risk.     

Anaerobic batch digestion of sheep tallow

Anaerobic batch digestion reactors were operated at mesophilic (35°C) and thermophilic (50°C) temperatures with sheep tallow at levels up to 59% of the volatile solids. Tallow was rapidly fermented to long-chain fatty acids (LCFA) and volatile fatty acids (VFA) at 35°C, but was refractory at 50°C. Oleic acid was fermented to palmitic, stearic and acetic acid. Methanogenesis was delayed by characteristic adaptation periods before LCFA and VFA were completely degraded. This demonstrated that wastes with high lipid contents are amenable to stabilization by mesophilic batch digestion.     

Mesophilic and thermophilic temperature co-phase anaerobic digestion compared with single-stage mesophilic- and thermophilic digestion of sewage sludge

The performance of thermophilic and mesophilic temperature co-phase anaerobic digestions for sewage sludge, using the exchange process of the digesting sludge between spatially separated mesophilic and thermophilic digesters, was examined, and compared to single-stage mesophilic and thermophilic anaerobic digestions. The reduction of volatile solids from the temperature co-phase anaerobic digestion system was dependent on the sludge exchange rate, but was 50.7-58.8%, which was much higher than 46.8% of single-stage thermophilic digestion, as well as 43.5% of the mesophilic digestion. The specific methane yield was 424-468 mL CH(4) per gram volatile solids removed, which was as good as that of single-stage mesophilic anaerobic digestion. The process stability and the effluent quality in terms of volatile fatty acids and soluble chemical oxygen demand of the temperature co-phase anaerobic digestion system were considerably better than those of the single-stage mesophilic anaerobic processes. The destruction of total coliform in the temperature co-phase system was 98.5-99.6%, which was similar to the single-stage thermophilic digestion. The higher performances on the volatile solid and pathogen reduction, and stable operation of the temperature co-phase anaerobic system might be attributable to the well-functioned thermophilic digester, sharing nutrients and intermediates for anaerobic microorganisms, and selection of higher substrate affinity anaerobic microorganisms in the co-phase system, as a result of the sludge exchange between the mesophilic and thermophilic digesters.     

喷雾降温效果影响因素的数值模拟分析

采用计算流体力学软件(Fluent)对室外空间喷雾降温过程进行了数值模拟,在不同环境风速、喷雾压力、喷嘴流量工况下,模拟模型区域的温度场、速度场、相对湿度分布。环境风速较小时,局部区域降温幅度大,范围窄,温度梯度大;环境风速增大使液滴飘散效果更好,虽然降温幅度减小,但降温区域分布更广,温度分布更均匀。环境风速较小的地区,可以减小单个喷嘴流量,缩短喷嘴布置间距,使喷嘴作用范围内温度分布更加均匀。环境风速较大的地区,宜适当增加单个喷嘴流量并增大下游喷嘴间距,利用环境风速使液滴飘散。此外,在环境风速较大的情况下还可以适当降低喷嘴高度使人员可感知区域的温降增大。在相同环境风速下,喷雾压力对降温范围与降温幅度的影响较小,可适当降低喷雾压力,以提高喷雾系统运行的经济性。     

Wind tunnel tests on compartment fires with crossflow ventilation

When a fire occurs in a room at ground level or a compartment located in the higher floors of a very tall building , the strong ambient wind will play an important role in fire spreading and smoke movement behavior. However, wind effect on compartment fire in cross ventilation condition has not been fully studied so far. In the present study, an effort has been made to study the wind effect on compartment fire in cross ventilation condition through experimental investigations. The experimental fire was generated by 250 ml n-heptane on the floor center of a cube enclosure with two opposite vents on the walls. The inside and outside gas temperature profiles at different vertical and horizontal locations were recorded by two thermocouple matrixes. The ambient wind velocity was set to 0, 1.5 and 3 m s⁻¹. It is observed that the ambient wind would enhance the fire severity by increasing the compartment fire temperature and reducing the time to flashover. The spilled-out flame/plume would extend horizontally farther with the increase of wind speed. Simple theoretical analysis shows that there is a critical wind velocity, or a dimensional number, to differentiate whether the gas flow across the vents is bidirectional or unidirectional, which is believed to influence enclosure fire behavior greatly.     

堆肥过程中臭气的产生和释放过程研究进展

堆肥过程中产生的臭气容易导致恶臭污染问题.总结了堆肥过程中主要臭气物质的产生机理、物理化学性质、影响因素及调控措施.堆肥过程中产生的臭气物质主要包括NH<,3>、H<,2>S和部分挥发性有机物;H<,2>S是堆肥过程产生的恶臭潜力最高的臭气;NH<,3>的最大释放浓度可达6 000 mg/m<'3>.堆肥原料的C/N值、调理剂种类、通风条件是影响氨气挥发的重要因素.指出过程控制是解决臭气问题的根本措施.     

Influence of high gas production during thermophilic anaerobic digestion in pilot-scale and lab-scale reactors on survival of the thermotolerant pathogens Clostridium perfringens and Campylobacter jejuni in piggery wastewater

Safe reuse of animal wastes to capture energy and nutrients, through anaerobic digestion processes, is becoming an increasingly desirable solution to environmental pollution. Pathogen decay is the most important safety consideration and is in general, improved at elevated temperatures and longer hydraulic residence times. During routine sampling to assess pathogen decay in thermophilic digestion, an inversely proportional relationship between levels of Clostridium perfringens and gas production was observed. Further samples were collected from pilot-scale, bench-scale thermophilic reactors and batch scale vials to assess whether gas production (predominantly methane) could be a useful indicator of decay of the thermotolerant pathogens C. perfringens and Campylobacter jejuni. Pathogen levels did appear to be lower where gas production and levels of methanogens were higher. This was evident at each operating temperature (50, 57, 65 °C) in the pilot-scale thermophilic digesters, although higher temperatures also reduced the numbers of pathogens detected. When methane production was higher, either when feed rate was increased, or pH was lowered from 8.2 (piggery wastewater) to 6.5, lower numbers of pathogens were detected. Although a number of related factors are known to influence the amount and rate of methane production, it may be a useful indicator of the removal of the pathogens C. perfringens and C. jejuni.     

堆肥过程中挥发性有机物的产生与释放

总结了堆肥过程中挥发性有机物(VOCs)的产生及其影响因素.堆肥产生的VOCs中,氮化物、硫化物及挥发性脂肪酸属于臭味物质,但大部分VOCs不产生臭味,其中甲胺、二甲胺、甲硫醇、乙硫醇、2-甲基呋喃和甲醛应作为堆肥厂职业健康安全评价时的参考指标.温度、通气状况是影响堆肥过程中VOCs释放的重要因素,温度升高可促使VOCs产生,适当通风可减少VOCs释放.     

生物可降解度判定生活垃圾堆肥处理的稳定性

准确判定城市生活垃圾（MSW）堆肥化处理的生物降解稳定性具有重要的环境、社会和经济意义，然而现有判定指标受垃圾组成不均匀性的影响，表现出一定的波动性。针对堆肥过程中微生物降解的主要对象——生物可降解物质进行研究，测定了接种1％高温菌、小风量连续通风静态好氧堆肥试验过程中生物可降解物质和有机质含量的变化。结果表明，堆肥过程中生物可降解度（BDM）受垃圾组分的影响较小，可较好地反映垃圾生物降解的规律，优于其他从有机成分变化角度判定MSW生物降解稳定性的指标。从动力学的角度，运用Matlab软件分段拟合出了整个堆肥过程中BDM变化曲线的表达式，验证了两段拟舍的可行性。     

Waste activated sludge hydrolysis and short-chain fatty acids accumulation under mesophilic and thermophilic conditions: Effect of pH

The effect of pH (4.0–11.0) on waste activated sludge (WAS) hydrolysis and short-chain fatty acids (SCFAs) accumulation under mesophilic and thermophilic conditions were investigated. The WAS hydrolysis increased markedly in thermophilic fermentation compared to mesophilic fermentation at any pH investigated. The hydrolysis at alkaline pHs (8.0–11.0) was greater than that at acidic pHs, but both of the acidic and alkaline hydrolysis was higher than that pH uncontrolled under either mesophilic or thermophilic conditions. No matter in mesophilic or thermophilic fermentation, the accumulation of SCFAs at alkaline pHs was greater than at acidic or uncontrolled pHs. The optimum SCFAs accumulation was 0.298 g COD/g volatile suspended solids (VSS) with mesophilic fermentation, and 0.368 with thermophilic fermentation, which was observed respectively at pH 9.0 and fermentation time 5 d and pH 8.0 and time 9 d. The maximum SCFAs productions reported in this study were much greater than that in the literature. The analysis of the SCFAs composition showed that acetic acid was the prevalent acid in the accumulated SCFAs at any pH investigated under both temperatures, followed by propionic acid and n-valeric acid. Nevertheless, during the entire mesophilic and thermophilic fermentation the activity of methanogens was inhibited severely at acid or alkaline pHs, and the highest methane concentration was obtained at pH 7.0 in most cases. The studies of carbon mass balance showed that during WAS fermentation the reduction of VSS decreased with the increase of pH, and the thermophilic VSS reduction was greater than the mesophilic one. Further investigation indicated that most of the reduced VSS was converted to soluble protein and carbohydrate and SCFAs in two fermentations systems, while little formed methane and carbon dioxide.     

障碍物对氯乙烯气体泄漏扩散影响的模拟研究

针对化工企业气柜泄漏造成人员伤亡等问题,利用Fluent 软件对3 种障碍物情况下气体扩散进行数值模拟研究。结果表明,障碍物对泄漏源上风侧气体浓度的影响远远小于下风侧。泄漏初期,障碍物、泄漏速率为下风侧氯乙烯气体浓度的主导因素;泄漏中期,下风侧氯乙烯气体在重力、初速度、风速的共同作用下,浓度维持短暂稳定;泄漏后期,环境风速替代泄漏速率成为下风侧氯乙烯气体浓度的主导因素,由于障碍物对环境风速有较强的阻碍作用,因此下风侧气体浓度表现为,障碍物越多,浓度降低越缓慢。