Use of pruning waste compost as a component in soilless growing media

The objective of this work was to study the use of pruning wastes compost (PWC) as a growing media component for ornamental plants. The main physical, chemical and biological characteristics of PWC were analysed in order to evaluate its suitability for use in soil-less cultivation. Six growth substrates were prepared by mixing PWC with peat (P), ground leaves (GL), sand (S) and spent mushroom compost (SMC) in different proportions. Two different pot experiments were carried out to test its characteristics of production using perennial ryegrass (Lolium perenne L.) and cypress (Cupressus sempervirens L.) as indicators and the different media as treatments. The growth experiments showed that PWC required mixing with a nutrient-richer material to produce higher results. Therefore, substrates containing SMC (PWC+P+SMC and PWC+SMC) seems to be the most adequate growing media. After the statistical analysis, we concluded that the PWC could be used as a growing media component.     

城市垃圾堆肥对Cr污染土壤的修复效应

通过模拟土培试验和盆栽试验 ,研究垃圾堆肥对Cr污染土壤的修复效应 .结果表明 ,垃圾堆肥对于土壤中有效Cr含量的影响是通过有机质含量、Eh、pH、<0 0 1mm粘粒含量等理化因子的变化来实现的 ;有机质含量变化和Eh变化分别是旱地土壤和淹水土壤中的主要影响因素 ,对有效Cr的效应分别占贡献的 73 4 %、5 5 5 %;垃圾堆肥施入土壤后 ,土壤渗透性得到改善 ,土壤中的Cr因被还原、吸附而固定 ,迁移量减少 ;垃圾堆肥施入可以减少植株对Cr的吸收 ,旱地土壤中 ,施加垃圾肥可使生物产量增加 35 9%,植株体内Cr含量下降 48 9%,在淹水土壤中 ,这种效应更加显著 ,生物产量比旱地土壤高 86 3%,Cr含量低 2 3 8%;垃圾堆肥施入后 ,植株体内的其他重金属含量未超标 ,垃圾肥可以安全用于Cr污染土壤的修复 .     

Critical evaluation of municipal solid waste composting and potential compost markets

Mechanical biological treatment (MBT) of mixed waste streams is becoming increasingly popular as a method for treating municipal solid waste (MSW). Whilst this process can separate many recyclates from mixed waste, the resultant organic residue can contain high levels of heavy metals and physical and biological contaminants. This review assesses the potential end uses and sustainable markets for this organic residue. Critical evaluation reveals that the best option for using this organic resource is in land remediation and restoration schemes. For example, application of MSW-derived composts at acidic heavy metal contaminated sites has ameliorated soil pollution with minimal risk. We conclude that although MSW-derived composts are of low value, they still represent a valuable resource particularly for use in post-industrial environments. A holistic view should be taken when regulating the use of such composts, taking into account the specific situation of application and the environmental pitfalls of alternative disposal routes.     

Improving the quality of municipal organic waste compost

The effects of different municipal organic waste (MOW) management practices (shredding, addition of carbon-rich materials and inoculation with earthworms) on organic matter stabilization and compost quality were studied. Four static piles were prepared with: (i) shredded MOW; (ii) shredded MOW+woodshavings; (iii) non-shredded MOW; and (iv) non-shredded MOW+woodshavings. After 50 days, a part of each pile was separated for vermistabilization, while the rest continued as traditional thermophilic composting piles. At different sampling dates, and in the finished products, the following parameters were measured: pH, electrical conductivity, carbon dioxide evolution, and concentrations of organic matter, total nitrogen, water-soluble carbon, nitrate nitrogen, ammonium nitrogen, and extractable phosphorus. Shredded treatments exhibited faster organic matter stabilization than non-shredded treatments, evidenced specially by earlier stabilization of carbon dioxide production and shorter thermophilic phases. Woodshavings addition greatly increased quality of final products in terms of organic matter concentration, and pH and electrical conductivity values, but decreased total nitrogen and available nutrient concentrations. Vermicomposting of previously composted material led to products richer in organic matter, total nitrogen, and available nutrient concentrations than composting only, probably due to the coupled effect of earthworm activity and a shorter thermophilic phase.     

Environmental assessment of energy production from municipal solid waste incineration

Background, Aims and Scope During the combustion of municipal solid waste (MSW), energy is produced which can be utilized to generate electricity. However, electricity production from incineration has to be evaluated from the point view of the environmental performance. In this study, environmental impacts of electricity production from waste incineration plant in Thailand are compared with those from Thai conventional power plants. Methods The evaluation is based on a life cycle perspective using life cycle assessment (LCA) as the evaluation tool. Since MSW incineration provides two services, viz., waste management and electricity production, the conventional power production system is expanded to include landfilling without energy recovery, which is the most commonly used waste management system in Thailand, to provide the equivalent function of waste management. Results The study shows that the incineration performs better than conventional power plants vis-à-vis global warming and photochemical ozone formation, but not for acidification and nutrient enrichment. Discussion There are some aspects which may influence this result. If landfilling with gas collection and flaring systems is included in the analysis along with conventional power production instead of landfilling without energy recovery, the expanded system could become more favorable than the incineration in the global warming point of view. In addition, if the installation of deNO_x process is employed in the MSW incineration process, nitrogen dioxide can be reduced with a consequent reduction of acidification and nutrient enrichment potentials. However, the conventional power plants still have lower acidification and nutrient enrichment potentials. Conclusions The study shows that incineration could not play the major role for electricity production, but in addition to being a waste management option, could be considered as a complement to conventional power production. To promote incineration as a benign waste management option, appropriate deNO_x and dioxin removal processes should be provided. Separation of high moisture content waste fractions from the waste to be incinerated and improvement of the operation efficiency of the incineration plant must be considered to improve the environmental performance of MSW incineration. Recommendations This study provides an overall picture and impacts, and hence, can support a decision-making process for implementation of MSW incineration. The results obtained in this study could provide valuable information to implement incineration. But it should be noted that the results show the characteristics only from some viewpoints. Outlook Further analysis is required to evaluate the electricity production of the incineration plant from other environmental aspects such as toxicity and land-use.     

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.     

Application of municipal solid waste compost reduces the negative effects of saline water in Hordeum maritimum L

The efficiency of composted municipal solid wastes (MSW) to reduce the adverse effects of salinity was investigated in Hordeum maritimum under greenhouse conditions. Plants were cultivated in pots filled with soil added with 0 and 40tha(-1) of MSW compost, and irrigated twice a week with tap water at two salinities (0 and 4gl(-1) NaCl). Harvests were achieved at 70 (shoots) and 130 (shoots and roots) days after sowing. At each cutting, dry weight (DW), NPK nutrition, chlorophyll, leaf protein content, Rubisco (ribulose-bisphosphate carboxylase/oxygenase) capacity, and contents of potential toxic elements were determined. Results showed that compost supply increased significantly the biomass production of non salt-treated plants (+80%). This was associated with higher N and P uptake in both shoots (+61% and +80%, respectively) and roots (+48% and +25%, respectively), while lesser impact was observed for K+. In addition, chlorophyll and protein contents as well as Rubisco capacity were significantly improved by the organic amendment. MSW compost mitigated the deleterious effect of salt stress on the plant growth, partly due to improved chlorophyll and protein contents and Rubisco capacity (-15%, -27% and -14%, respectively, in combined treatment, against -45%, -84% and -25%, respectively, in salt-stressed plants without compost addition), which presumably favoured photosynthesis and alleviated salt affect on biomass production by 21%. In addition, plants grown on amended soil showed a general improvement in their heavy metals contents Cu2+, Pb2+, Cd2+, and Zn2+ (in combined treatment: 190%, 53%, 168% and 174% in shoots and 183%, 42%, 42% and 114% in roots, respectively) but remained lower than phytotoxic values. Taken together, these findings suggest that municipal waste compost may be safely applied to salt-affected soils without adverse effects on plant physiology.     

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.     

Anaerobic digestion of municipal solid waste as a treatment prior to landfill

Anaerobic digestion of organic fraction of municipal solid waste was conducted in pilot-scale reactor based on high-solid combined anaerobic digestion process. This study was performed in two runs. In Run 1 and Run 2, pre-stage flushing and micro-aeration were conducted to determine their effect in terms of enhancing hydrolysis and acidification in ambient condition. In Run 2, after pre-stage, the methane phase (methanogenesis) was started-up after pH adjustment and inoculum addition in mesophilic condition. Acidified leachate produced in pre-stage was used for percolation during active methane phase. At the end of methane phase, air flushing was conducted before unloading the digesters. Hydrolysis and acidification yield of 140 g C/kg TS and 180 g VFA/kg TS were achieved, respectively in pre-stage. Micro-aeration exhibited an equivocal result in terms of enhancing hydrolysis/acidification; however it showed a positive effect in methane phase performance and this needed further investigation. Leachate percolation during methane phase showed an enhanced methanization when compared to the reactors without leachate percolation. After 60 days, 260 l CH(4)/kg VS was obtained. Based on the waste methane potential, 75% biogas conversion and 61% VS degradation were achieved.     

Microbial dynamics and enzyme activities during rapid composting of municipal solid waste - a compost maturity analysis perspective

An investigation was carried out in the laboratory to find out the microbial dynamics and enzyme activities during rapid composting of municipal solid waste (MSW). Various treatments such as aeration (A), addition of chemical agents (glucose (G) and acetic acid (AA) and application of cellulolytic microbial (M) inoculum (Phanerochaete chrysosporium and Trichoderma reesei) were used to facilitate the decomposition of MSW. The result of the present investigation revealed that the degradation of organic substrates were quick (within 9-12 days) in case of rapid composting as indicated by the reduction (below 20) in C/N ratio. Whereas, normal composting took more than 20 days to attain C/N ratio of below 20. Estimation of selected enzymes (amylase, protease, phosphatase and cellulase) provided information on the substrate specific degradation profiles of various labile substrates contained in organic waste.     

生活垃圾填埋场不同封场期场地植物抗氧化酶活性

比较了湖南省某城市生活垃圾填埋场2个不同封场期场地优势植物超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性,发现在环境较恶劣的场地A(封场3年)齿果酸模、酸模叶蓼、水莎草SOD活性较高,分别为408.35、298.56和219.97U·mg-1 prot;稗、野菊花、女菀CAT活性较高,分别为20.72、18.10和16.42U·mg-1 prot,而臭荠的CAT活性最低,仅为3.54U·mg-1 prot。通过对各植物酶活性及相对幅度R/Q值之和进行综合比较,初步推断齿果酸模、酸模叶蓼、稗、野菊花、女菀具有较强的抵抗环境胁迫的能力,为封场初期优势植物种。场地B(封场8年)SOD活性最高的5种植物依次是:臭荠小苜蓿小飞蓬齿果酸模飞廉,而CAT活性由高到低是:朝天委陵菜飞廉棒头草女菀齿果酸模,R/Q值之和的变化范围是0.17～0.61,臭荠、朝天委陵菜、飞廉、棒头草、齿果酸模适应性较强。不同封场阶段优势物种存在着自然演替的现象,为填埋场植被恢复提供依据。     

Airborne microorganisms in a municipal solid waste recovery system

The types of bacteria and fungi present in the air of a municipal solid waste recovery system have been characterized and the population densities estimated. Conventional methods were successful in enumerating coagulase-positive staphylococci, Klebsiella spp., gram-negative bacteria, fungi, and common indicator organisms. Selective and enrichment media, however, did not yield Salmonella isolates. Salmonella and Shigella were recovered at a frequency of 3% or less on trypticase soy agar. A broad spectrum of bacteria and fungi were isolated. No evidence has been found that indicates that these organisms have produced adverse health effects.     

Bacterial community diversity assessment in municipal solid waste compost amended soil using DGGE and ARISA fingerprinting methods

Bacterial community structure and diversity of Tunisian agricultural soil treated with different amounts of municipal solid waste compost (MSWC) and other fertilizers were studied using DGGE and ARISA fingerprinting methods. Sequence analysis of dominant DGGE bands revealed the presence of three major clusters, Cytophaga/Flexibacter/Bacteroides (CFB) group, Proteobacteria and Acidobacteria group. Using ARISA profiles, dominant populations were assigned to low and high GC Gram positive bacteria, Cyanobacteria, Spirochetes and Cytophagales. The two methods revealed the absence of significant bacterial community shifts related to the different MSWC applications. Moreover, indigenous bacterial population of the used loam-clayey soil was observed to limit proliferation and survival of Proteobacteria, initially dominant in MSWC and farmyard manure. Effectiveness of the two methods for soil bacterial community studying was shown. While DGGE was more accurate for bacterial identification, ARISA was more practical for handling and rapid estimation of dominant bacteria.     

Environmental impact and cost assessment of incineration and ethanol production as municipal solid waste management strategies

Purpose

Municipal solid waste (MSW) can be handled with several traditional management strategies, including landfilling, incineration, and recycling. Ethanol production from MSW is a novel strategy that has been proposed and researched for practical use; however, MSW ethanol plants are not widely applied in practice. Thus, this study has been conducted to analyze and compare the environmental and economic performance of incineration and ethanol production as alternatives to landfilling MSW.

Methods

The ISO 14040 life cycle assessment framework is employed to conduct the environmental impact assessment of three different scenarios for the two MSW management strategies based on processing 1 ton of MSW as the functional unit. The first scenario models the process of incinerating MSW and recovering energy in the form of process heat; the second scenario also includes the process of incinerating MSW but yields in the recovery of energy in the form of electricity; and the third scenario models the process of converting MSW into ethanol. The economic impacts of each scenario are then assessed by performing benefit-to-cost ratio (BCR) and net present value (NPV) analyses.

Results and discussion

The results from the environmental impact assessment of each scenario reveal that scenario 2 has the highest benefits for resource availability while scenario 3 is shown to be the best alternative to avoid human health and ecosystems diversity impacts. Scenario 1 has the worst environmental performance with respect to each of these environmental endpoint indicators and has net environmental impacts. The results of the economic analysis indicate that the third scenario is the best option with respect to BCR and NPV, followed by scenarios 2 and 1, respectively. Furthermore, environmental and economic analysis results are shown to be sensitive to MSW composition.

Conclusions

It appears municipalities should prefer MSW incineration with electricity generation or MSW-to-ethanol conversion over MSW incineration with heat recovery as an alternative to landfilling. The contradiction between the environmental impact assessment results and economic analysis results demonstrates that the decision-making process is sensitive to a broad set of variables. Decisions for a specific MSW management system are subject to facility location and size, MSW composition, energy prices, and governmental policies.     

Anaerobic digestion of solid slaughterhouse waste (SHW) at laboratory scale: Influence of co-digestion with the organic fraction of municipal solid waste (OFMSW)

Mesophilic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been evaluated. These processes were carried out in a laboratory plant semi-continuously operated and two set-ups were run. The first set-up, with a hydraulic retention time (HRT) of 25 days and organic loading rate (OLR) of 1.70 kg VS m⁻³ day⁻¹ for digestion, and 3.70 kg VS m⁻³ day⁻¹ for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m⁻³ day⁻¹ for digestion and 1.85 kg VS m⁻³ day⁻¹ for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammonia content, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 days and OLRs of 1.70 and 3.70 kg VS m⁻³ day⁻¹, for digestion and co-digestion, respectively (the same conditions of the digesters failures previously). These digesters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) were undetected or only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus found to be a suitable technology for efficiently treating lipid and protein waste.     

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.