Degradation of diesel oil in soil using a food waste composting process

We investigated the simultaneous degradation of diesel oil in soil and the organic matter in food waste by composting in 8 l reactors. Using a 0.5 l/min air flow rate, and 0.5-1% diesel oil concentrations together with 20% food waste, high composting temperatures (above 60°C) were attained due to the efficient degradation of the food waste. Petroleum hydrocarbons were degraded by 80% after only 15 days composting in the presence of food waste. In a 28 l reactor scale-up experiment using 1% oil, 20% food waste and 79% soil, removal efficiencies of petroleum hydrocarbons and food waste after 15 days were 79% and 77%, respectively.     

Low pH as an inhibiting factor in the transition from mesophilic to thermophilic phase in composting

During composting of household waste, the acidity of the material affects the process during the initial phase of rising temperature. In this study, the effects of temperature (36-46 degrees C) and pH (4.6-9.2) on the respiration rate during the early phase of composting were investigated in two different composts. A respiration method where small compost samples were incubated at constant temperature was used. The respiration rate was strongly reduced at 46 degrees C and pH below 6, compared to composts with a higher pH or lower temperature. The combination of high temperature and low pH is a possible adverse factor in large-scale composting of food waste.     

Composting of spent mushroom compost, carnation wastes, chicken and cattle manures

This study has purposed to determine the optimum mixture ratio of used mushroom compost, chicken manure, cattle manure and carnation waste for composting. For this purpose, these materials have been mixed in seven various ratios (R1-R7) and composted in the experimental composting reactors. The highest dry material losses and temperature values have been obtained by the R4 which contains 50% carnation waste, 25% chicken manure and 25% spent mushroom compost. Beside R4, mixtures of R2, R5 and R6 have also provided high process temperature and dry material loss values. The lowest dry material loss and temperature values have been obtained in the R7 which contains only carnation wastes. In the study, it has also seen that FAS (free air space) parameter is effective on the process and must be in the interval of 24-32%.     

Effects of compositions on food waste composting

The objective of this work was to provide a method of predicting important parameters (composting time, highest temperature, final and lowest pH values, cumulative CO(2) evolution, and percentages of material losses) that characterized the composting process of synthetic food waste in terms of weight fractions of protein and fat. Experimental results showed that final products of all 12 experimental runs passed multiple maturity tests. Quadratic equations obtained by the multi-regression analysis were also developed for quick estimation. The models were tested for real kitchen waste and the agreements between experimental and predicted results were fair.     

Design and application of a pre-composting test step to determine the effect of high fat food wastes on an industrial scale in-vessel composting system

The high fat content in food wastes was suspected to inhibit an industrial in-vessel composting process from reaching the European Union Animal By-Product Regulation (composting temperature >70 °C for 1 h). The aim of this study was to design a test step to guide the mixing ratio of food waste to green waste to meet the regulation. A 15-compartment composting unit was designed to contain the compost mixes. Sausage and cheese wastes were mixed with green waste at 1:1; 1:2; 1:3 and 1:4 ratios by wet weight volume. Only the sausage waste mix ratio of 1:4 gave an average temperature of 70 °C for at least 1 h after 2 days of composting (fat content - 17%; C: N ratio - 8.6). All the cheese waste mixes did not reach 70 °C after 15 days of composting. This study demonstrated that using a simple pre-composting test step could reduce the chances of process failure during industrial composting. Although both sausage and cheese wastes are high in fat, they performed very differently in the composting process. Two linear equations were fitted to model the impact of these wastes on the maximum composting temperature.     

Process inhibition due to organic acids in fed-batch composting of food waste – influence of starting culture

Inhibition of the degradation during low pH conditions has been observed in fed-batch composting systems. To analyse this phenomenon, fed-batch composting of food waste with different amounts of starting culture was examined in laboratory reactor experiments. Changes in temperature, carbon dioxide evolution, pH, solids, ash and short chain organic acids were measured. In reactors with a daily feed rate of 24% or less of the starting culture, thermophilic temperatures occurred and the pH and carbon dioxide evolution were high and stable after a starting period of 4–5 days. In reactors with a daily feed rate of 48% or more of the starting culture the composting process failed, as the pH dropped below 6 and remained there and the temperature and carbon dioxide evolution were low. It was concluded that the use of adequate amounts of starting culture consisting of active compost can efficiently prevent low pH conditions and process inhibition in fed-batch composting of food waste.     

Coal fly ash and lime addition enhances the rate and efficiency of decomposition of food waste during composting

To evaluate the use of coal fly ash (CFA) on the decomposition efficiency of food waste, synthetic food waste was mixed with lime at 1.5% and 3% (equivalent to 0.94% and 1.88% CaCO₃, respectively), CFA at 5%, 10% and 15% with lime so as to achieve CaCO₃ equivalent of 1.88% and composted for 42 days in a thermophilic 20 l composter with two replicates each. Alkaline materials at 1.88% CaCO₃ equivalent successfully buffered the pH during the composting and enhanced the decomposition efficiency. When these buffering was achieved with CFA + lime, the composting period could be shortened to ∼28 days compared with ∼42 days in 3% lime. Organic decomposition in terms of CO₂ loss, carbon turnover and nitrogen transformation were significantly higher for treatments with 1.88% CaCO₃ equivalent. Nutrient transformations and compost maturity parameters indicated that addition of CFA (5–10%) with lime at 1.88% CaCO₃ equivalent enhances the decomposition efficiency and shortens the composting period by 35%.     

Fungal Communities Associated with the Biodegradation of Polyester Polyurethane Buried under Compost at Different Temperatures

Plastics play an essential role in the modern world due to their low cost and durability. However, accumulation of plastic waste in the environment causes wide-scale pollution with long-lasting effects, making plastic waste management expensive and problematic. Polyurethanes (PUs) are heteropolymers that made up ca. 7% of the total plastic production in Europe in 2011. Polyester PUs in particular have been extensively reported as susceptible to microbial biodegradation in the environment, particularly by fungi. In this study, we investigated the impact of composting on PUs, as composting is a microbially rich process that is increasingly being used for the processing of green waste and food waste as an economically viable alternative to landfill disposal. PU coupons were incubated for 12 weeks in fresh compost at 25°C, 45°C, and 50°C to emulate the thermophilic and maturation stages of the composting process. Incubation at all temperatures caused significant physical deterioration of the polyester PU coupons and was associated with extensive fungal colonization. Terminal restriction fragment length polymorphism (TRFLP) analysis and pyrosequencing of the fungal communities on the PU surface and in the surrounding compost revealed that the population on the surface of PU was different from the surrounding compost community, suggesting enrichment and selection. The most dominant fungi identified from the surfaces of PU coupons by pyrosequencing was Fusarium solani at 25°C, while at both 45°C and 50°C, Candida ethanolica was the dominant species. The results of this preliminary study suggest that the composting process has the potential to biodegrade PU waste if optimized further in the future.     

Characterisation of source-separated household waste intended for composting

Large-scale composting of source-separated household waste has expanded in recent years in the Nordic countries. One problem can be low pH at the start of the process. Incoming biowaste at four composting plants was characterised chemically, physically and microbiologically. The pH of food waste ranged from 4.7 to 6.1 and organic acid concentration from 24 to 81 mmol kg(-1). The bacterial diversity in the waste samples was high, with all samples dominated by Gammaproteobacteria, particularly Pseudomonas and Enterobacteria (Escherichia coli, Klebsiella, Enterobacter). Lactic acid bacteria were also numerically important and are known to negatively affect the composting process because the lactic acid they produce lowers the pH, inhibiting other bacteria. The bacterial groups needed for efficient composting, i.e. Bacillales and Actinobacteria, were present in appreciable amounts. The results indicated that start-up problems in the composting process can be prevented by recycling bulk material and compost.     

有机固体废弃物堆肥的物质变化及腐熟度评价

堆肥是资源化处理有机固体废弃物的有效途径之一．有机固体废弃物的种类繁多,物科的性质差异很大,另外,由于堆肥条件的不同,也会引起堆肥的物质变化有很大差异．堆肥的稳定度和腐熟度是衡量堆肥产品质量的尺度,其评价对于安全农用有着重要意义．稳定度则重于堆肥施用对周围环境的影响,而腐熟度则重于堆肥施用对植物生长的影响,它们受堆肥物料,堆肥条件等诸多因素的综合影响,其评价指标因而多种多样．堆肥稳定度主要从堆肥的温度、颜色、CO2是最为简便的稳定度评价指标,当其趋于环境温度时,表明堆肥达到稳定．堆肥腐熟度的评价指标很多,包括化学指标、生物活性指标以及植物毒性指标3类,其中种子发芽系数作为植物毒性指标被认为是最可靠的评价指标之一。     

Life-cycle greenhouse gas inventory analysis of household waste management and food waste reduction activities in Kyoto, Japan

Purpose

Source-separated collection of food waste has been reported to reduce the amount of household waste in several cities including Kyoto, Japan. Food waste can be reduced by various activities including preventing edible food loss, draining moisture, and home composting. These activities have different potentials for greenhouse gas (GHG) reduction. Therefore, we conducted a life-cycle inventory analysis of household waste management scenarios for Kyoto with a special emphasis on food waste reduction activities.

Methods

The primary functional unit of our study was ??annual management of household combustible waste in Kyoto, Japan.?? Although some life-cycle assessment scenarios included food waste reduction measures, all of the scenarios had an identical secondary functional unit, ??annual food ingestion (mass and composition) by the residents of Kyoto, Japan.?? We analyzed a typical incineration scenario (Inc) and two anaerobic digestion (dry thermophilic facilities) scenarios involving either source-separated collection (SepBio) or nonseparated collection followed by mechanical sorting (MecBio). We assumed that the biogas from anaerobic digestion was used for power generation. In addition, to evaluate the effects of waste reduction combined with separate collection, three food waste reduction cases were considered in the SepBio scenario: (1) preventing loss of edible food (PrevLoss); (2) draining moisture contents (ReducDrain); and (3) home composting (ReducHcom). In these three cases, we assumed that the household waste was reduced by 5%.

Results and discussion

The GHG emissions from the Inc, MecBio, and SepBio scenarios were 123.3, 119.5, and 118.6 Gg CO₂-eq/year, respectively. Compared with the SepBio scenario without food waste reduction, the PrevLoss and ReducDrain cases reduced the GHG emissions by 17.1 and 0.5 Gg CO₂-eq/year. In contrast, the ReducHcom case increased the GHG emissions by 2.1 Gg CO₂-eq/year. This is because the biogas power production decreased due to the reduction in food waste, while the electricity consumption increased in response to home composting. Sensitivity analyses revealed that a reduction of only 1% of the household waste by food loss prevention has the same GHG reduction effect as a 31-point increase (from 50% to 81%) in the food waste separation rate.

Conclusions

We found that prevention of food losses enhanced by separate collection led to a significant reduction in GHG emissions. These findings will be useful in future studies designed to develop strategies for further reductions in GHG emissions.     

Biodrying for mechanical–biological treatment of wastes: A review of process science and engineering

Biodrying is a variation of aerobic decomposition, used within mechanical–biological treatment (MBT) plants to dry and partially stabilise residual municipal waste. Biodrying MBT plants can produce a high quality solid recovered fuel (SRF), high in biomass content. Here, process objectives, operating principles, reactor designs, parameters for process monitoring and control, and their effect on biodried output quality are critically examined. Within the biodrying reactors, waste is dried by air convection, the necessary heat provided by exothermic decomposition of the readily decomposable waste fraction. Biodrying is distinct from composting in attempting to dry and preserve most of biomass content of the waste matrix, rather than fully stabilise it. Commercial process cycles are completed within 7–15 days, with mostly H₂O_(g) and CO₂ loses of ca. 25–30% w/w, leading to moisture contents of <20% w/w. High airflow rate and dehumidifying of re-circulated process air provides for effective drying. We anticipate this review will be of value to MBT process operators, regulators and end-users of SRF.     

In situ filtration of Anchusa officinalis culture in a cell-retention stirred tank bioreactor

Summary The effect of agitation and aeration on filtration of Anchusa officinalis culture in a stirred tank bioreactor integrated with an internal filter unit was investigated. Increases in suction head of the pump that drove the filtration process were measured at impeller speeds of 100 and 200 rpm. Surprisingly, suction head attained at 200 rpm was about 40% higher than at 100 rpm. Direct observation of the cake deposition process in the reactor using a dilute cell suspension revealed that the filter cake formed at 100 rpm was thicker, but less compact. Aeration at 0.4 vvm was shown to have little effect on the filtration rate, since the bulk fluid flow was dominated by the impeller hydrodynamics. The initial flux can be recovered by filter backwashing with compressed air at a flow rate of 0.6 vvm for a duration of 5 minutes.     

The impact of cage ventilation on rats housed in IVC systems

Today the use of individually ventilated cage systems (IVC systems) is common, especially for housing transgenic rodents. Typically, in each cage a ventilation rate of 40 to 50 air changes per hour is applied, but in some systems even up to 120 air changes per hour is applied. To reach this rate, the air is blown into the cage at a relatively high speed. However, at the animal's level most systems ventilate with an air speed of approximately 0.2 m/s. In the present paper, two studies were conducted, one analysing whether an air speed below 0.2 m/s or just above 0.5 m/s affects the rats, and another study analysing whether air changes of 50, 80 and 120 times per hour affect the rats. In both studies, monitoring of preferences as well as physiological parameters such as heart rate and blood pressure, was used to show the ability of the animals to register the different parameters and to avoid them if possible. Air speeds inside the cage of as high as 0.5 m/s could not be shown to affect the rats, while the number of air changes in each cage should be kept below 80 times per hour to avoid impacts on physiology (heart rate and systolic blood pressure). Also the rats prefer cages with air changes below 80 times per hour if they have the opportunity of choosing, as shown in the preference test.     

Life cycle environmental and economic impact of a food waste recycling-farming system: a case study of organic vegetable farming in Japan

Purpose

Bio-based recycling systems and agricultural production using recycled materials are often evaluated separately. This study performs an environmental and socio-economic life cycle assessment (LCA) of a food waste treatment and spinach farming system in Japan. The environmental and economic tradeoffs of introducing a recycling system and the net environmental benefit of the substitution of market fertilizer considering operation changes are also examined.

Methods

Three scenarios were developed and compared. In the conventional (CV) scenario, food waste is collected, incinerated, and disposed of in landfill, and the farmer uses market organic fertilizer. The on-site composting (OC) scenario processes food waste using an on-site garbage disposer and transports compost to a nearby spinach farmer. Food waste in the centralized composting (CC) scenario is transported to a centralized composting facility and resultant compost is sent to the farm. Primary data were obtained from field experiments and interviews. Non-greenhouse gas (GHG) emissions from the field and nitrogen leaching to water systems were simulated using the denitrification–decomposition (DNDC) model.

The environmental LCA targeted climate change, eutrophication, and waste landfill. An input–output analysis estimated socio-economic indicators, namely gross added value and employment inducement effect.

Results and discussion

The scenario with the lowest impact is the CC scenario. Climate change and eutrophication impacts are highest in the OC scenario and waste landfill impacts are most significant in the CV scenario. The weighted impact by LIME2 can be reduced by 47% in the CC scenario and 17% in the OC scenario due to the recycling of food waste instead of dumping in the landfill. The difference in socio-economic indicators between the scenarios was relatively small, although the CV scenario encouraged more employment. The substitution effect of composting, as well as the environmental impact reduction of replacing market organic fertilizer with compost, will result in 28.7% of the avoided impacts in GHG emissions.

Conclusions

Both composting scenarios are feasible from an environmental and socio-economic perspective when compared with conventional organic production, although there is a tradeoff between waste landfill and GHG emissions for the on-site composting system. However, the OC scenario needs to save electricity to improve its environmental competitiveness with the CV scenario. When considering the substitution effect of composting, it is recommended to take into account that agricultural operation also changes.

     

Dynamics of pruning waste and spent horse litter co-composting as determined by chemical parameters

Co-composting of pruning waste and horse manure was monitored by different parameters. A windrow composting pile, having the dimensions 2.5m (height) x 30m (length) was established. The maturation of pruning waste and horse manure compost was accompanied by a decline in NH(4)(+)-N concentration, water soluble C and an increase in NO(3)(-)-N content. Organic matter (OM) content during composting followed a first-order kinetic equation. This result was in agreement with the microbiological activity measured by the CO(2) respiration during the process. The correlation at a high level of probability found between the OM loss and CO(2) evolution showed that both parameters could be used to indicate the degree of OM degradation that is the maturity and stability phases of the compost studied. Humification parameters data from the organic matter fractionation did not show a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.     

湿度对堆肥理化性质的影响

水分是堆肥微生物生命活动的基础 ,也是堆肥中重要的工艺控制参数。弄清湿度对堆肥微生物及理化性质的影响 ,对于优化堆肥工艺参数、提高堆肥效率、降低投资和运行成本具有重要意义。综述了堆肥湿度研究的动态 ,指出了当前研究中存在的问题 ,并提出了未来的研究方向。大量的研究表明 ,湿度低于 4 5 %或高于 6 5 %都不利于堆肥处理。湿度太高会导致堆料的压实度增加、FAS减少、透气性能降低 ,从而导致堆体内氧气供应不足、堆肥升温困难、有机物降解速率降低、堆肥周期延长。湿度过低 ,水分会限制堆肥微生物的新陈代谢 ,导致微生物活性下降、堆肥腐熟困难。由于鼓风、散热、水蒸发等会使堆体内存在湿度的空间变异 ,也会降低堆肥效率和堆肥产品的质量。另外 ,堆肥湿度还影响堆肥的保肥能力。由各文献得出结论 ,堆肥的最佳湿度范围一般为 5 0 %～ 6 0 %左右     

Nitrogen transformation during organic waste composting by the Rutgers system and its effects on pH, EC and maturity of the composting mixtures

The evolution of the different forms of nitrogen during the composting of several wastes was studied, as well as its relation to the pH, electrical conductivity and parameters of maturity of the composts obtained. Four mixtures were prepared from different organic materials: sewage sludge, municipal solid waste, brewery sludge, sorghum bagasse, cotton waste and pine bark. The evolution of the different forms of nitrogen during composting depended on the material which supplied the nitrogen to the mixtures and the organic matter (OM) degradation rate during composting. The greatest concentration of ammonium was observed during the first weeks of composting, coinciding with the most intense period of OM degradation, and ammonium then decreased gradually to reach final values of below 0.04%. The use of urea as a nitrogen source in the mixtures led to high ammonium levels during the first weeks as a result of its rapid hydrolysis. The nitrification process began only when the temperature of the mixtures had dropped below 40 degrees C and its intensity depended on the quantity of ammonium present when the process began. The highest concentrations of NO3-N were always produced at the end of maturation, reaching values of 0.52%, 0.53%, 0.12% and 0.20% in the four mixtures studied. Nitrogen losses during composting depended on the materials used and on the pH values of the mixtures. Mixtures with the highest lignocellulose content showed the lowest losses (below 25%), while those containing municipal solid waste lost more than 40% of the initial content. Statistically significant correlations at a high probability level were found between the NO3-N concentration and pH and electrical conductivity. confirming that nitrification was responsible for the falling pH values and increasing electrical conductivity. The ratio of NH4-N and NO3-N concentrations was shown to be a clear indicator of the maturity of the mixtures during composting, the final values of 0.08, 0.04, 0,16 and 0.11 for the four mixtures being equal to, or below the maximum value established as a maturity index in other materials.     

The fulvic acid fraction as it changes in the mature phase of vegetable oil-mill sludge and domestic waste composting

Sludge resulting from the treatment of effluent from a vegetable oil mill, was composted mixed with domestic waste in a pile for five months. Different proportions of sludge and dry waste were mixed: M1 (1v/2v) and M2 (1v/1v). Monitoring different physical-chemical parameters showed the effect of the substrate on the microbiological activity and on the formation of fulvic acids, affecting the maturity of the final compost. Elemental analysis revealed that the fulvic acids of mixes M1 and M2 presented very low concentrations of carbon, hydrogen, and oxygen and a high level of nitrogen. The FTIR spectroscopy results showed a decrease during composting of the intensity of absorbance of the easily assimilable compounds that are predominant in the initial mixtures i.e. the carbohydrates (1170-1080 cm(-1)) in M1 and long aliphatic chains (2920 cm(-1)) in M2. For mix M1 there was enrichment in compounds bearing oxygen-containing moieties. In M2 it was the nitrogen-containing compounds (in the form of stable amides) which predominated at the end of composting. The first component of PCA analysis, PC1, accounted for 83% of the difference between two distinct groups of parameters governing degradation and restructuration of the fulvic acids during composting. PC2 (17%) explained the variance due to the level of free or less polycondensed compounds in the two mixtures. Oxidised polyphenolic and polysaccharide structures were the least free, or most polycondensed, in the fulvic structures of M1. In M2 fulvic acids however, it was the polyphenols and peptide structures that were involved in the bonding, most likely of the polyphenol-peptide type.     

翻堆频率对堆肥减量化、腐殖化和稳定化的影响

好氧堆肥是有机固体废弃物处理处置的有效手段之一,堆肥还田也是贫瘠土壤改良的常用措施。但好氧堆肥是一个典型的CO_2等温室气体的释放过程。如何减少堆肥过程中的CO_2释放,强化堆肥的腐殖化过程对于实现有机固体废弃物的低碳化堆肥、提高作为优良土壤改良剂的腐殖质产量具有重要意义。本文选取农林秸秆和餐厨垃圾作为堆肥原料,研究不同翻堆频率对堆肥过程中的物料减量化、腐殖化和稳定化的影响,以期发现一个较低碳的堆肥工艺,并从微生物角度初步探索了其影响机制。研究结果显示,不同的翻堆频率(分别为每2 d、4 d和6 d翻堆一次),堆料的减量化和腐殖化程度有一定差异,翻堆频率为4 d的堆肥工艺物料减量率最高为50.5%,但碳减量率最低为77.4%;而翻堆频率为2 d的堆肥工艺腐殖质产量最高;3种堆肥工艺经62 d堆肥都达到了腐熟程度,翻堆频率为4 d的堆肥工艺腐熟化程度最高。不同的翻堆频率可能通过影响堆肥过程中堆料的温度、含氧量等因素从而改变堆料中活性微生物量、种类和生物酶活性,进而影响堆料的矿化和腐殖化进程。