Development of an enzymatic assay for the determination of cellulose bioavailability in municipal solid waste

As there is a constant need to assess the biodegradation potential of refuse disposed of in landfills, we have developed a method to evaluate the biodegradability of cellulosic compounds (cellulose and hemicellulose) in municipal solid waste. This test is based on the quantification of monosaccharides released after the hydrolysis of solid waste samples with an optimised enzyme preparation containing commercially available cellulases and hemicellulases. We show that the amounts of monosaccharides could be related to the biodegradability of the cellulosic material contained in the samples. This enzymatic cellulose degradation test was assayed on 37 samples originating from three Belgian landfills and collected at different depths. As results correlated well with those obtained with a classical biochemical methane potential assay, this new and rapid test is sufficiently reliable to evaluate cellulose bioavailability in waste samples.     

生命周期评价方法在城市生活垃圾管理中的应用研究述评

结合城市生活垃圾管理系统特征,系统归纳基于生命周期评价(Life cycle assessment,LCA)方法的城市生活垃圾管理模型的发展现状,并对LCA方法在城市生活垃圾管理中的实践以及在我国开展城市生活垃圾管理LCA研究的应用前景进行评述。分析表明,LCA是城市生活垃圾管理领域的重要工具之一,基于LCA方法的城市生活垃圾管理模型在全生命周期环境影响评价与识别、处置工艺选择与改进、可持续生活垃圾管理决策支持等方面具有十分重要的应用价值。中国在本地化生活垃圾管理系统LCA模型开发、清单数据库和评价指标体系构建以及与其他研究方法集成等方面面临挑战。     

草坪植物对生活垃圾堆肥基质的生理生态响应

以生活垃圾堆肥和土壤(对照)为基质,采用不同播种方式进行草坪建植,研究了堆肥基质对草坪植物光合特性和保护酶系统的影响.结果表明:堆肥能明显地提高草坪植物的净光合速率,第一峰值出现在9:00,在单播方式下,堆肥基质黑麦草、高羊茅分别比各自对照高出12.7%、11.4%;黑麦草与早熟禾混播、高羊茅与早熟禾混播分别比对照高出33.0%、29.6%.堆肥基质黑麦草单播、黑麦草与早熟禾混播表现出比对照较低的日平均蒸腾速率和较高的水分利用效率;而高羊茅单播、高羊茅与早熟禾混播,则呈现比对照较高的日平均蒸腾速率和相似的水分利用效率.以垃圾堆肥为草坪基质,黑麦草表现出高光合、低蒸腾的节水对策;而高羊茅则表现出高光合、高蒸腾的代谢特点.另外,堆肥基质也显著地提高了草坪植物叶片叶绿素含量,单播黑麦草和高羊茅叶片的叶绿素含量显著高于对照(P<0.05).堆肥基质还能显著增强草坪植物叶片POD、SOD和CAT活性,与对照相比差异均达到显著(P<0.05)或极显著水平(P<0.01),表明堆肥基质中草坪植物的抗逆境能力显著增强.     

Anaerobic solubilisation of nitrogen from municipal solid waste (MSW)

This paper reviews anaerobic solubilisation of nitrogen municipal solid waste (MSW) and the effect of current waste management practises on nitrogen release. The production and use of synthetically fixed nitrogen fertiliser in food production has more than doubled the flow of excessive nitrogenous material into the community and hence into the waste disposal system. This imbalance in the global nitrogen cycle has led to uncontrolled nitrogen emissions into the atmosphere and water systems. The nitrogen content of MSW is up to4.0% of total solids (TS) and the proteins in MSW have a lower rate of degradation than cellulose. The proteins are hydrolysed through multiple stages into amino acids that are further fermented into volatile fatty acids, carbon dioxides, hydrogen gas, ammonium and reduced sulphur. Anaerobic digestion of MSW putrescibles could solubilise around 50% of the nitrogen. Thus, the anaerobic digestion of putrescibles may become an important method of increasing the rate of nitrogen recycling back to the ecosystem. A large proportion of the nitrogen in MSW continues to end up inland fills; for example, in the EU countries around 2 million tonnes of nitrogen is disposed of annually this way. Nitrogen concentration in the leachates of existing landfills are likely to remain at a high level for decades to come. Under present waste management practices with a relatively low level of efficiency in the source segregation or mechanical sorting of putrescibles from grey waste and with a low level of control over landfill operating procedures, nitrogen solubilisation from landfilled waste will take at least a century. This revised version was published online in June 2006 with corrections to the Cover Date.     

Steam pressure disruption of municipal solid waste enhances anaerobic digestion kinetics and biogas yield.

Biomass waste, including municipal solid waste (MSW), contains lignocellulosic-containing fiber components that are not readily available as substrates for anaerobic digestion due to the physical shielding of cellulose imparted by the nondigestible lignin. Consequently, a substantial portion of the potentially available carbon is not converted to methane and the incompletely digested residues from anaerobic digestion generally require additional processing prior to their return to the environment. We investigated and developed steam pressure disruption as a treatment step to render lignocellulosic-rich biomass more digestible and as a means for increasing methane energy recovery. The rapid depressurization after steam heating (240 degrees C, 5 min.) of the nondigested residues following a 30-day primary digestion of MSW caused a visible disruption of fibers and release of soluble organic components. The disrupted material, after reinoculation, provided a rapid burst in methane production at rates double those observed in the initial digestion. This secondary digestion proceeded without a lag phase in gas production, provided approximately 40% additional methane yields, and was accompanied by a approximately 40% increase in volatile solids reduction. The secondary digestate was found to be enriched in lignin and significantly depleted in cellulose and hemi-cellulose components when compared to primary digestate. Thus, steam pressure disruption treatment rendered lignocellulosic substrates readily accessible to anaerobic digestion bacteria and improved both the kinetics of biogas production and the overall methane yield from MSW. Steam pressure disruption is central to a new anaerobic digestion process approach including sequential digestion stages and integrated energy recovery, to improve process yields, provide cogenerated energy for process needs, and to provide effective reuse and recycling of waste biomass materials.     

生活垃圾堆肥淋洗液培植无土草皮的生态特征

以生活垃圾堆肥淋洗液培植无土草皮,结果表明,垃圾堆肥淋洗液中有机质、全氮、有效磷及其它营养元素含量显著高于对照土壤淋洗液,能够充分满足草坪植物生长需要。高浓度淋洗液使黑麦草和高羊茅种子萌发高峰期推迟出现,但不影响发芽率,到萌发第11天,种子发芽率分别达到94％和92％以上。对黑麦草而言,80％的淋洗液可显著提高植株高度、地上生物量和叶绿素含量;对高羊茅,60％的淋洗液则为最佳浓度。当淋洗液培植的无土草皮进行田间铺坪90d时,黑麦草和高羊茅草皮地上生物量分别达到5．38g／块和7．89g／块,并显著高于对照草皮（P〈0．05）,而地下生物量和根长差异不显著。垃圾堆肥淋洗液改变了黑麦草和高羊茅植株地上／地下生物量的分配格局,使其根冠比降低,其分别为4．60和3．71,并明显低于对照。从坪用性状上看,铺坪后垃圾堆肥淋洗液培养的草皮叶色深绿,质地柔软光滑,明显优于土壤淋洗液培养的对照草皮。     

The effects of spent mushroom compost and municipal solid waste compost on Phytophthora drechsleri in vivo and in vitro

Leached spent mushroom compost (SMC), municipal solid waste compost (MSWC) and their extracts, were tested to suppress Phytophthora drechsleri in cucumber plants. The composts were mixed with sand-loam soil in sterile and non-sterile types and were used to assess suppressiveness against P. drechselri in greenhouse experiments. The extracts of composts, in both sterile and non-sterile types, were applied to evaluate their effect in suppression of pathogen in vitro. The results of the experiments showed that all applications rate of non-sterile SMC were significantly effective in the control of the pathogen. However the sterile SMC amendments did not have a positive effect on the pathogen suppression in vitro or in vivo, as it was expected. In greenhouse experiments, both composts were effective in controlling pathogen at the rate of 15%, but the treatments amended with higher rate of MSWC did not show a positive effect. The treatments amended with MSWC (15%) and SMC (25%) showed the most suppressive effect in controlling the pathogen. The extract of leached-SMC could inhibit P. drechselri in petri dish.     

基于混合生命周期评价的生活垃圾处理系统生态效率分析

基于混合生命周期评价(Hybrid life cycle assessment,HLCA)提出一种改进生态效率模型,系统评价卫生填埋、卫生填埋⁃填埋气利用、焚烧发电、堆肥+卫生填埋和堆肥+焚烧发电5种我国典型生活垃圾处理情景的生态效率,并探究可持续性包含的环境、经济和社会多维权衡关系。结果表明,具有最大生态效率的生活垃圾处理情景因可持续性维度选取不同而异,如考虑人体健康损害影响,焚烧发电情景具有最大经济生态效率,而卫生填埋⁃填埋气利用情景具有最大社会生态效率。生活垃圾处理系统的可持续性评价维度之间具有显著的权衡关系,忽略某些影响类型可能带来问题转移。5种生活垃圾处理情景的环境影响各异,非焚烧情景气候变化影响和焚烧情景人体毒性影响突出。机器设备和燃料使用对资源消耗影响贡献最大,而生活垃圾处理过程对经济效益和其他环境影响贡献最大。本文提出的改进生态效率模型可以定量评价生活垃圾管理系统生态效率及权衡关系,为有效制定生活垃圾管理政策提供全面的信息支持。     

城市生活垃圾综合管理决策研究进展

城市生活垃圾综合管理主要是指选择合适的方案、政策手段等来实现特定的管理目标。选择适宜的研究方法是开展城市生活垃圾管理科学决策的重要基础和保障。综述了近年来该领域常用的相关研究方法和研究进展,总结分析了以统计分析、多准则决策分析、全生命周期分析、费用效益分析等为代表的传统数学模型方法和以系统动力学、基于Agent的建模等为代表的复杂系统模拟方法两大类方法的适用场景、优缺点和研究进展,分析了未来该领域研究的趋势和需重点关注的方向。研究发现：传统的数学模型方法被广泛应用于生活垃圾管理决策领域,成为支撑决策的重要研究工具,但这类方法通常大多以单一主体为研究对象,难以解释各种因素对其它主体及整个生活垃圾管理系统的作用,且大多为静态的或对某个或某几个时间点进行分析,容易忽略系统性和系统中各主体间的非线性关系、行为的交互作用及随时空的动态变化等。未来研究需充分关注城市生活垃圾管理系统的复杂性和系统不同主体间的行为交互作用,加强系统模拟模型开发,开展系统性政策评估分析等,为城市生活垃圾精细化管理决策提供科学支撑。     

垃圾填埋场氧化亚氮排放控制研究进展

填埋是国内外城市生活垃圾处理的一种主要方式.垃圾填埋场是温室气体氧化亚氮(N2O)和甲烷(CH4)的重要排放源.作为一种高效痕量的温室气体,N2O具有极高的潜在增温效应,其每分子潜在的增温作用是二氧化碳(CO2)的296倍.而且N2O能在大气中长期稳定存在,对臭氧层具有较强的破坏作用.本文针对垃圾填埋场N2O排放的控制研究,概述了垃圾填埋处理过程中主要排放源的N2O排放及其影响因素,提出了现阶段适应我国垃圾填埋场N2O排放控制的一系列措施,并展望了垃圾填埋场温室气体N2O排放控制理论和技术的研究方向.     

Stoichiometry of the aerobic biodegradation of the organic fraction of municipal solid waste (MSW)

An elemental analysis was applied to describe the composition ofthe organic fraction of municipal solid waste (MSW). The initial elemental composition was constant at₅H_8.5O₄N_0.2. The changes of the composition during the biodegradation process and the final waste composition were strictly dependent on the process conditions. The decrease in carbon content due to biodegradation increased with temperature at which the experiments were conducted, from 20% at20 °C to about 40% at 37–42 °C after 96 hours. It was correlatedwith the amount of oxygen that was utilised in the investigated processes of aerobicbiodegradation of the waste suspension. The amount of oxygen required for biodegradation of organic fraction of MSW was estimated on the basis of stoichiometric equations and increased from 0.92 moles per 1 mole of waste at 20 °C to 1.6 moles at 42 °C within 96 hours of the experiments.     

Organic compounds in re-circulated leachates of aerobic biological treated municipal solid waste

Biodegradation of organic matter is required to reduce the potential of municipal solid waste for producing gaseous emissions and leaching contaminants. Therefore, we studied leachates of an aerobic-treated waste from municipal solids and a sewage sludge mixture that were re-circulated to decrease the concentration of biodegradable organic matter in laboratory-scale reactors. After 12 months, the total organic C and biological and chemical oxygen demands were reduced, indicating the biodegradation of organic compounds in the leachates. Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS) revealed that phenols, alkylaromatic compounds, N-containing compounds and carbohydrates were the predominate compounds in the leachates and solid waste. Leachate re-circulation led to a higher thermal stability of the residual organic matter as indicated by temperature-resolved Py-FIMS. Admixture of sewage sludge to solid waste was less effective in removing organic compounds from the leachates. It resulted in drastic higher and more bio-resistant loads of organic matter in the leachates and revealed increased proportions of alkylaromatic compounds. The biodegradation of organic matter in leachates, re-circulated through municipal solid waste, offers the potential for improved aerobic waste treatments and should be investigated on a larger scale.     

RNA assay as a method of viable biomass determination in the organic fraction of municipal solid waste suspension

A method of RNA determination by means of alkaline hydrolysis and UV detection was applied to evaluate the amount of viable biomass during the aerobic biodegradation of the organic fraction of the municipal solid waste suspension. The relative standard deviation of this determination was from 0.7 to 4%. The viable biomass constituted only 9% of the volatile suspended solids in the activated sludge.     

Leachates from municipal solid waste disposal sites harbor similar, novel nitrogen-cycling bacterial communities

High emissions of nitrous oxide (N(2)O) have recently been documented at municipal solid waste (MSW) landfills. However, the biodiversity of the bacterial populations involved remains unexplored. In this study, we investigated communities of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria associated with the leachates from three MSW disposal sites by examining the diversity of the ammonia monooxygenase structural gene amoA and the nitrous oxide reductase gene nosZ, respectively. Cloning and phylogenetic analysis of the functional genes revealed novel and similar groups of prokaryotes involved in nitrogen cycling in the leachates with different chemical compositions. All amoA sequences recovered grouped within the Nitrosomonas europaea cluster in the Betaproteobacteria, with the vast majority showed only relatively moderate sequence similarities to known AOB but were exclusively most similar to environmental clones previously retrieved from wastewater treatment plants. All nosZ sequences retrieved did not cluster with any hitherto reported nosZ genes and were only remotely related to recognized denitrifiers from the Gammaproteobacteria and thus could not be affiliated. Significant overlap was found for the three denitrifying nosZ leachate communities. Our study suggests a significant selection of the novel N-cycling groups by the unique environment at these MSW disposal sites.     

基于生命周期方法的生活垃圾资源化利用系统生态效率分析

我国生活垃圾产量大但处理能力不足,产生多种环境危害,对其资源化利用能够缓解环境压力并回收资源。为探讨生活垃圾资源化利用策略,综合生命周期评价与生命周期成本分析方法,建立生态效率模型。以天津市为例,分析和比较焚烧发电、卫生填埋-填埋气发电、与堆肥+卫生填埋3种典型生活垃圾资源化利用情景的生态效率。结果表明,堆肥+卫生填埋情景具有潜在最优生态效率;全球变暖对总环境影响贡献最大,而投资成本对经济影响贡献最大。考虑天津市生活垃圾管理现状,建议鼓励发展生活垃圾干湿组分分离及厨余垃圾堆肥的资源化利用策略。     

Bioconversion of municipal solid waste to glucose for bio-ethanol production

Selected biodegradable municipal solid waste fractions were subjected to fifteen different pre-hydrolysis treatments to obtain the highest glucose yield for bio-ethanol production. Pre-hydrolysis treatments consisted of dilute acid (H₂SO₄, HNO₃ or HCl, 1 and 4%, 180 min, 60°C), steam treatment (121 and 134°C, 15 min), microwave treatment (700 W, 2 min) or a combination of two of them. Enzymatic hydrolysis was carried out with Trichoderma reesei and Trichoderma viride (10 and 60 FPU g⁻¹ substrate). Glucose yields were compared using a factorial experimental design. The highest glucose yield (72.80%) was obtained with a pre-hydrolysis treatment consisting of H₂SO₄ at 1% concentration, followed by steam treatment at 121°C, and enzymatic hydrolysis with Trichoderma viride at 60 FPU g⁻¹ substrate. The contribution of enzyme loading and acid concentration was significantly higher (49.39 and 47.70%, respectively), than the contribution of temperature during steam treatment (0.13%) to the glucose yield.     

Solid-state 13C NMR spectroscopic, chemolytic and biological assessment of pretreated municipal solid waste

In Central Europe, composting and anaerobic digestion of municipal solid waste (MSW) is used as pretreatment before landfilling to reduce landfill emissions. MSW samples were analyzed before, during, and after pretreatment to assess the stability of the organic matter. Chemolytic, nuclear magnetic resonance (NMR) spectroscopic, and respiration parameters were correlated to evaluate a substitution of the time-consuming respiration analysis by chemical parameters. ¹³C cross polarization magic angle spinning (CPMAS) NMR spectroscopy showed a preferential biodegradation of O-alkyl carbon (carbohydrates) and a selective accumulation of plastics during all pretreatments, confirming findings from chemolytic analyses. Principal component analysis exhibited a strong association between the respiration rate, the carbohydrate content, and the O-alkyl C content, corroborating that carbohydrates are the most important compounds of MSW with regard to the emission potential. Rank correlation (Spearman) also showed strong relationships between the respiration rate and the content of carbohydrates (r=0.75) and of O-alkyl C (r=0.72). Journal of Industrial Microbiology & Biotechnology (2001) 26, 83–89. Received 20 April 2000/ Accepted in revised form 21 July 2000     

Microbial characterization during composting of municipal solid waste

This study investigates the prevailing physico-chemical conditions and microbial community; mesophilic bacteria, yeasts and filamentous fungi, bacterial spores, Salmonella and Shigella as well as faecal indicator bacteria: total coliforms, faecal coliforms and faecal Streptococci, present in a compost of municipal solid waste. Investigations were conducted in a semi-industrial pilot plant using a moderate aeration during the composting process. Our results showed that: (i) auto-sterilization induced by relatively high temperatures (60–55°C) caused a significant change in bacterial communities. For instance, Escherichia coli and faecal Streptococci populations decreased, respectively, from 2×10⁷ to 3.1×10³ and 10⁷ to 1.5×10³ cells/g waste dry weight (WDW); yeasts and filamentous fungi decreased from 4.5×10⁶ to 2.6×10³ cells/g WDW and mesophilic bacteria were reduced from 5.8×10⁹ to 1.8×10⁷ bacteria/g WDW. On the other hand, the number of bacterial spores increased at the beginning of the composting process, but after the third week their number decreased notably; (ii) Salmonella disappeared completely from compost by the 25th day as soon as the temperature reached 60°C; and (iii) the bacterial population increased gradually during the cooling phase. While Staphylococci seemed to be the dominant bacteria during the mesophilic phase and at the beginning of the thermophilic phase, bacilli predominated during the remainder of the composting cycle. The appearance of gram-negative rods (opportunistic pathogens) during the cooling phase may represent a serious risk for the sanitary quality of the finished product intended for agronomic reuse. Compost sonication for about 3 min induced the inactivation of delicate bacteria, in particular gram-negatives. By contrast, gram-positive bacteria, especially micrococcus, spores of bacilli, and fungal propagules survived, and reached high concentrations in the compost.     

Comparative life cycle assessment of two landfill technologies for the treatment of municipal solid waste

Goal and Scope  The potential environmental impacts associated with two landfill technologies for the treatment of municipal solid waste (MSW), the engineered landfill and the bioreactor landfill, were assessed using the life cycle assessment (LCA) tool. The system boundaries were expanded to include an external energy production function since the landfill gas collected from the bioreactor landfill can be energetically valorized into either electricity or heat; the functional unit was then defined as the stabilization of 600 000 tonnes of MSW and the production of 2.56x10⁸ MJ of electricity and 7.81x10⁸ MJ of heat. Methods  Only the life cycle stages that presented differences between the two compared options were considered in the study. The four life cycle stages considered in the study cover the landfill cell construction, the daily and closure operations, the leachate and landfill gas associated emissions and the external energy production. The temporal boundary corresponded to the stabilization of the waste and was represented by the time to produce 95% of the calculated landfill gas volume. The potential impacts were evaluated using the EDIP97 method, stopping after the characterization step. Results and Discussion  The inventory phase of the LCA showed that the engineered landfill uses 26% more natural resources and generates 81% more solid wastes throughout its life cycle than the bioreactor landfill. The evaluated impacts, essentially associated with the external energy production and the landfill gas related emissions, are on average 91% higher for the engineered landfill, since for this option 1) no energy is recovered from the landfill gas and 2) more landfill gas is released untreated after the end of the post-closure monitoring period. The valorization of the landfill gas to electricity or heat showed similar environmental profiles (1% more raw materials and 7% more solid waste for the heat option but 13% more impacts for the electricity option). Conclusion and Recommendations  The methodological choices made during this study, e.g. simplification of the systems by the exclusion of the identical life cycle stages, limit the use of the results to the comparison of the two considered options. The validity of this comparison could however be improved if the systems were placed in the larger context of municipal solid waste management and include activities such as recycling, composting and incineration.     

Environmental risk assessment of the municipal solid waste in a city-state: A case study of Macao

The article is the evaluation in the practice of risk assessment for city-states. The Pressure-State-Response (PSR) model was applied to the establishment of an environmental risk assessment indicator system. Environmental risk index (ERI) and each subsystem index were calculated through an analytic hierarchy process. It takes the municipal solid waste (MSW) in Macao as a case study to execute. The risk grading and the potential risk for the MSW in Macao were determined. The results showed that the ERI of the Macao's MSW remained at a medium level (Level III, 0.4–0.6) from 2000 to 2015, respectively, and increased gradually. Meanwhile, the future trend of the environmental risk of the MSW was predicted for Macao and the causes were analyzed. The environmental risk of the MSW in 2019 will achieve a high level (Level IV, 0.6–0.8), and the environment risk in 2041 will achieve an extremely high level (>0.8). For the first time, the research applied to the PSR model into the environmental risk assessment of MSW, this method is reasonable and feasible. Further research can provide a scientific basis for risk prevention management in city-states and can be of reference for other urbanized areas.