Anaerobic digestion of the organic fraction of municipal solid waste: influence of co-digestion with manure

Anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was investigated in two thermophilic (55 degrees C) wet digestion treatment systems R1 and R2. Initially OFMSW was co-digested with manure with a successively higher concentration of OFMSW, at a hydraulic retention time (HRT) of 14-18 d and an organic loading rate (OLR) of 3.3-4.0 g-VS/l/d. Adaptation of the co-digestion process to a OFMSW:manure ratio of 50% (VS/VS) was established over a period of 6 weeks. This co-digestion ratio was maintained in reactor R2 while the ratio of OFMSW to manure was slowly increased to 100% in reactor R1 over a period of 8 weeks. Use of recirculated process liquid to adjust the organic loading to R1 was found to have a beneficial stabilization effect. The pH rose to a value of 8 and the reactor showed stable performance with high biogas yield and low VFA levels. The biogas yield from source-sorted OFMSW was 0.63-0.71 l/g-VS both in the co-digestion configuration and in the treatment of 100% OFMSW with process liquid recirculation. This yield is corresponding to 180-220 m3 biogas per ton OFMSW. VS reduction of 69-74% was achieved when treating 100% OFMSW. None of the processes showed signs of inhibition at the free ammonia concentration of 0.45-0.62 g-N/l.     

Effect of settling on performance of the upflow anaerobic sludge bed reactors

The effects of settler volume on the start-up and steady-state performance of 41. laboratory upflow sludge bed reactors treating bean blanching waste of 10,000 mg COD l⁻¹ were determined. The rate of start-up, as well as the maximum loading rate, increased with increased settler volume and performance. A loading rate of 30 kg COD m⁻³ day⁻¹ (based on reactor volume alone) and a COD removal of 95% was obtained with a 21. settling flask and a 4 to 1 recirculation rate. Without a settler, the maximum loading rate was 10 kg COD m⁻³ day⁻¹. The sludge was flocculent rather than granular. Sludge profiles and characteristics in the reactors and settlers were determined.     

Waste activated sludge fermentation: Effect of solids retention time and biomass concentration

Laboratory scale, room temperature, semi-continuous reactors were set-up to investigate the effect of solids retention time (SRT, equal to HRT hydraulic retention time) and biomass concentration on generation of volatile fatty acids (VFA) from the non-methanogenic fermentation of waste activated sludge (WAS) originating from an enhanced biological phosphorus removal process. It was found that VFA yields increased with SRT. At the longest SRT (10 d), improved biomass degradation resulted in the highest soluble to total COD ratio and the highest VFA yield from the influent COD (0.14 g VFA-COD/g TCOD). It was also observed that under the same SRT, VFA yields increased when the biomass concentration decreased. At a 10 d SRT the VFA yield increased by 46%, when the biomass concentration decreased from 13 g/L to 4.8 g/L. Relatively high nutrient release was observed during fermentation. The average phosphorus release was 17.3 mg PO₄-P/g TCOD and nitrogen release was 25.8 mg NH₄-N/g TCOD.     

Effect of high temperatures on antioxidant depletion from different HDPE geomembranes

The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.     

Characterization of barley straw biochar produced in various temperatures and its effect on lead and cadmium removal from aqueous solutions

Conversion of agricultural wastes into a carbon rich material (i.e. biochar) using pyrolysis process could be an appropriate approach for their management. This study was carried out to convert barley straw to biochar in different temperatures (300, 400 and 500°C) and to investigate the potential of the produced biochar as a sorbent of heavy metals (Pb and Cd). Considering the pretest results of Pb and Cd sorption, the biochar produced at 500°C (BS500) was selected to find effect of pH, the sorbent dose, the initial concentration of Pb and Cd and the contact time on metal removal efficiency. The results showed that the optimum conditions of adsorption were pH = 6, the sorbent dose 1 g/L and the contact time of 45 min. The adsorption kinetics and isotherms had the best fit to the pseudo‐second order and Langmuir models, respectively.     

Effect of gas empty bed contact time on performances of various types of rotating drum biofilters for removal of VOCs

The effects of gas empty bed contact time (EBCT), biofilter configuration, and types of volatile organic compounds (VOCs) were evaluated to assess the performance of rotating drum biofilters (RDBs), especially at low EBCT values. Three types of pilot-scale RDBs, a single-layer RDB, a multi-layer RDB, and a hybrid RDB, were examined at various gas EBCTs but at a constant VOC loading rate. Diethyl ether, toluene, and hexane were used separately as model VOC. When EBCT increased from 5.0 to 60s at a constant VOC loading rate of 2.0kgCOD/(m(3)day), ether removal efficiency increased from 73.1% to 97.6%, from 81.6% to 99.9%, and from 84.0% to 99.9% for the single-layer RDB, the multi-layer RDB, and the hybrid RDB, respectively, and toluene removal efficiency increased from 76.4% to 99.9% and from 84.8% to 99.9% for the multi-layer RDB and the hybrid RDB, respectively. When hexane was used as the model VOC at a constant loading rate of 0.25kgCOD/(m(3)day), hexane removal efficiency increased from 31.1% to 57.0% and from 29.5% to 50.0% for the multi-layer RDB and hybrid RDB, respectively. The single-layer, multi-layer, and hybrid RDBs exhibited, respectively, the lowest, middle, and highest removal efficiencies, when operated under similar operational loading conditions. Hexane exhibited the lowest removal efficiency, while diethyl ether displayed the highest removal efficiency. The data collected at the various EBCT values correlated reasonably well with a saturation model. The sensitivity of removal efficiency to EBCT varied significantly with EBCT values, VOC properties, and biofilter configurations. Process selection and design for RDB processes should consider these factors.     

街道峡谷中垂直绿化的滞尘效应及应用——以武汉市为例

【目的】城市街道中人群活动密集,其空气质量问题值得关注。为解决街道峡谷内颗粒污染物难以扩散的问题,探究垂直绿化净化街道峡谷空气的能力和策略。【方法】以垂直绿化的滞尘效应为研究对象,通过现场调研与实测、正交实验结合计算机软件数值模拟等方法,定量探讨垂直绿化在街道峡谷形态、相对风向、布局方式等多种因素共同作用下的滞尘效应,并比较各因素的影响强弱。【结果】1）街道峡谷宽度、布局方式与水平向布置密度对垂直绿化滞尘效应影响最强。2）垂直绿化更适宜布置在道路较窄的城市支路以及迎风时长较多的建筑立面。【结论】得出滞尘效应最优的因素水平组合,总结出垂直绿化滞尘效应最佳的设计策略与滞尘能力模型,并评估垂直绿化在武汉市的滞尘潜力,为垂直绿化在街道峡谷中的应用提供理论依据。     

环境岩土工程研究进展

该文总结了近年来国内外环境岩土工程领域的研究进展,主要包括：①环境岩土工程调查与评价方法。重点介绍了电阻率静力触探探头、与静力触探结合的传感器薄膜界面探头、光纤光学化学传感器、X荧光分析仪等在场地污染物分布和污染程度识别技术;综述了土工离心技术应用于土体及地下水中污染物运移,及污染场地修复的研究现状;总结了污染场地分类方法和风险评价模型。②城市固体废物填埋技术。介绍了固废填埋场多场相互作用的主要耦合模型理论,总结了固废生化反应-骨架变形-水气运移-溶质迁移模型及应用;提出了填埋场污防污屏障服役寿命的定量评价方法。③工业固体废弃物资源化再利用技术。介绍了废弃电石渣和木质素加固过湿土、粉土路基的性能和工程应用;总结了固化污泥和淤泥技术的研究现状。④工业污染地基处理技术。总结了工业污染场地主要修复技术;介绍了固化污染土稳定技术、新型固化剂和稳定剂的研发进展;总结了常见竖向隔离墙技术,介绍了土-膨润土系竖向隔离墙长期防渗防污性能的研究进展;介绍了曝气法处理有机污染地下水技术的研究进展。     

Trajectories in geographical space out of communication in acquaintance space: An agent‐based model of a textile industrial district

This paper presents an agent‐based model of an Italian textile district where thousands of small firms specialize in particular phases of fabrics production. It reconstructs the web of communication between firms as they arrange production chains. In turn, production chains result in road traffic between the geographical areas on which the district extends. The reconstructed traffic exhibits a pattern that has been observed, but not foreseen, by policy‐makers.     

Natural attenuation and characterization of contaminants composition in landfill leachate under different disposing ages

Chemical Oxygen Demand (COD) composition in landfill leachate would vary as the disposal time extended. Leachates with different ages were collected from Laogang Refuse Landfill of Shanghai, the largest landfill in China with a placement scale of 7600 t refuse per day. To characterize COD composition in leachate, samples were size-fractioned into suspended fractions (> 0.45 μm), colloid fraction (0.45 μm < fraction < 1 K Da MW) and dissolved fractions (< 1 KDa MW) based on the molecular weight distribution. The fractions < 0.45 μm (including colloid fraction and dissolved fractions) in leachate were further divided into 6 fractions, i.e. hydrophobic bases (Ho-base), hydrophobic acids (Ho-acid), hydrophobic neutral (Ho-neutral), hydrophilic bases (Hi-base), hydrophilic acids (Hi-acid) and hydrophilic neutral (Hi-neutral). It was found that the ratio of TOC/TC in leachate decreased over time, indicating that the percentage of organic matters in leachate decreased as the disposal time extended. It was also observed that the hydrophobic fraction accounted to about 50% of the total matters presented in the fraction < 0.45 μm of all leachate samples. The main components in < 0.45  μm fraction were the Ho-acid, Hi-acid and Hi-base fractions. The percentage of Ho-acid in leachate decreased from 60.8% (2 a) to 43.2% (12 a). In addition, leachate with different ages was categorized into 3 phases according to the results of Principle component analysis (PCA). TOC/COD ranges of leachate in periods I, II and III were 40-54.6%, 16.9-41.3% and 10-38.9%, respectively, indicating that the COD contribution of non-carbon reduction substances increased over time in leachate. Hence, the corresponding landfill leachate treatment process should be modified according to the leachate characterization. The results obtained in this study might provide the important information for modeling, design, and operation of landfill leachate treatment systems.     

Dosing free nitrous acid for sulfide control in sewers: Results of field trials in Australia

Intermittent dosing of free nitrous acid (FNA), with or without the simultaneous dosing of hydrogen peroxide, is a new strategy developed recently for the control of sulfide production in sewers. Six-month field trials have been carried out in a rising main sewer in Australia (150 mm in diameter and 1080 m in length) to evaluate the performance of the strategy that was previously demonstrated in laboratory studies. In each trial, FNA was dosed at a pumping station for a period of 8 or 24 h, some with simultaneous hydrogen peroxide dosing. The sulfide control effectiveness was monitored by measuring, on-line, the dissolved sulfide concentration at a downstream location of the pipeline (828 m from the pumping station) and the gaseous H₂S concentration at the discharge manhole. Effective sulfide control was achieved in all nine consecutive trials, with sulfide production reduced by more than 80% in 10 days following each dose. Later trials achieved better control efficiency than the first few trials possibly due to the disrupting effects of FNA on sewer biofilms. This suggests that an initial strong dose (more chemical consumption) followed by maintenance dosing (less chemical consumption) could be a very cost-effective way to achieve consistent control efficiency. It was also found that heavy rainfall slowed the recovery of sulfide production after dosing, likely due to the dilution effects and reduced retention time. Overall, intermittent dose of FNA or FNA in combination with H₂O₂ was successfully demonstrated to be a cost-effective method for sulfide control in rising main sewers.