Compostaje de residuos sólidos orgánicos : aplicación de técnicas respirométricas en el seguimiento del proceso /

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Aroma a fruita a partir de residus orgànics

El Grup de Recerca de Compostatge (GICOM) del Departament d'Enginyeria Química, Biològica i Ambiental de la UAB ha desenvolupat un procés productiu d'aromes fruiteres mitjançant la fermentació en estat sòlid (FES) per un llevat de residus de la indústria sucrera. Aquest procés és més net i econòmic que els tradicionals, a més, modificant les condicions en les quals ocorre la fermentació, es pot modular el tipus d'aroma produïdaEl Grupo de Investigación en Compostaje (GICOM) del Departamento de Ingeniería Química, Biológica y Ambiental de la UAB ha desarrollado un proceso productivo de aromas frutales mediante fermentación en estado sólido (FES) por una levadura de residuos de la industria azucarera. Este proceso es más limpio y económico que los tradicionales, además, modificando las condiciones en las que ocurre la fermentación, se puede modular el tipo de aroma producido.The Composting Research Group (GICOM) from the Chemical, Biological and Environmental Engineering Departament at UAB has developed an aroma producing process by yeast solid state fermentation (SSF) of organic waste from the sugar industry. This process is cleaner and more economic than the traditional ones, besides, by modifying the fermentation conditions the aroma profile can be modified too

The use of respiration indices in the composting process : a review

Respiration is directly related to the metabolic activity of a microbial population. Micro-organisms respire at higher rates in the presence of large amounts of bioavailable organic matter while respiration rate is slower if this type of material is scarce. In the composting process respiration activity has become an important parameter for the determination of the stability of compost. It is also used for the monitoring of the composting process and it is considered an important factor for the estimation of the maturity of the material. A wide range of respirometric protocols has been reported based either on CO₂ production, O₂ uptake or release of heat. The most common methods are those based on O₂ uptake. Respirometric assays are affected by a number of parameters including temperature, humidity, and both incubation and pre-incubation conditions. Results from respirometries are generally expressed as 'respiration indices', most of them with their own units and basis. In consequence, some confusion exists when referring and comparing respiration indices. This is particularly important because current and future legislations define and measure the biological stability of waste on the basis of respiration activity of the material. This paper discusses and compares most common respiration indices currently used

Dehydrogenase activity as a method for monitoring the composting process

Dehydrogenase enzymatic activity was determined to monitor the biological activity in a composting process of organic fraction of municipal solid waste. Dehydrogenase activity is proposed as a method to describe the biological activity of the thermophilic and mesophilic stages of composting. The maximum dehydrogenase activity was detected at the end of the thermophilic stage of composting, with values within 0.5-0.7 mg g dry matter−1 h−1. Also, dehydrogenase activity can be correlated to static respiration index during the maturation mesophilic stage

A complete mass balance of a complex combined anaerobic/aerobic municipal source-separated waste treatment plant

In this study a combined anaerobic/aerobic full-scale treatment plant designed for the treatment of the source-separated organic fraction of municipal solid waste (OFMSW) was monitored over a period of one year. During this period, full information was collected about the waste input material, the biogas production, the main rejects and the compost characteristics. The plant includes mechanical pre-treatment, dry thermophilic anaerobic digestion, tunnel composting system and a curing phase to produce compost. To perform the monitoring of the entire plant and the individual steps, traditional chemical methods were used but they present important limitations in determining the critical points and the efficiency of the stabilization of the organic matter. Respiration indices (dynamic and cumulative) allowed for the quantitative calculation of the efficiency of each treatment unit. The mass balance was calculated and expressed in terms of Mg y⁻¹ of wet (total) matter, carbon, nitrogen and phosphorus. Results show that during the pre-treatment step about 32% of the initial wet matter is rejected without any treatment. This also reduces the biodegradability of the organic matter that continues to the treatment process. About 50% of the initial nitrogen and 86.4% of the initial phosphorus are found in the final compost. The final compost also achieves a high level of stabilization with a dynamic respiration index of 0.3 ± 0.1 g O₂ per kg of total solids per hour, which implies a reduction of 93% from that of the raw OFMSW, without considering the losses of biodegradable organic matter in the refuse (32% of the total input). The anaerobic digestion process is the main contributor to this stabilization

Effect of freezing on the conservation of the biological activity of organic solid wastes

To assess the effect of freezing on the indigenous biological activity of an organic waste, five types of organic wastes (raw sludge [RS], municipal solid waste [MSW], partially processed municipal solid waste [MSWpp], digested sludge [DS] and composted organic fraction of municipal solid waste [OFMSWc]) were frozen and stored during different times to identify if the interruption of the native biological activity was recovered. Respiration indices (DRI₂₄h and AT₄) were used to determine the biological activity expressed as oxygen consumption. ANOVA analysis was used to compare the results. Respiration indices of RS, DS, MSWpp and OFMSWc were not affected by freezing storage during 1 year. Contrarily, respiration indices of MSW samples were statistically different after 52 and 20 weeks of freezing storage (DRI₂₄h and AT₄, respectively). Regarding the lag phase and the time to reach maximum respiration activity, frozen samples induced a significant change in the organic samples analyzed except for OFMSWc

Optimal bulking agent particle size and usage for heat retention and disinfection in domestic wastewater sludge composting

Composting of two types of sludge produced in wastewater treatment plants, raw sludge (RS) and anaerobically digested sludge (ADS), has been systematically studied by means of the experimental design technique. The results have been analyzed using a full factorial experimental design in order to determine the optimal conditions for composting such sludges in terms of bulking agent particle size and bulking agent:sludge volumetric ratio, two of the key parameters to ensure an optimal performance of the composting process. The objective function selected was a simulated death kinetics of Salmonella, which was chosen as a model pathogen microorganism to represent the disinfection of the material. For both types of sludge, optimal values were found at 5 mm bulking agent particle size and 1:1 bulking agent:sludge volumetric ratio when a Gaussian function was fitted to the experimental data. Pilot scale experiments using optimal values obtained were successfully undertaken and confirmed a full disinfection of the sludge by means of the composting process. A mathematical model to simulate the disinfection performance of a composting material is presented. The model can be applied to simulate the disinfection performance of a given pathogen

Monitoring the biological activity of the composting process : oxygen uptake rate (OUR), respirometric index (RI) and respiratory quotient (RQ)

Composting of several organic wastes of different chemical composition (source-separated organic fraction of municipal solid waste, dewatered raw sludge, dewatered anaerobically digested sludge and paper sludge) was carried out under controlled conditions to study the suitability of different biological indexes (oxygen uptake rate, respirometric index, and respiratory quotient) to monitor the biological activity of the composting process. Among the indexes tested, oxygen uptake rate (also referred to as dynamic respirometric index) provided the most reliable values of microbial activity in a compost environment. On the other hand, values of the static respirometric index measured at process temperature, especially in the early stages of the composting process, were significantly lower than those of the dynamic index, which was probably due to oxygen diffusion limitations present in static systems. Both static and dynamic indexes were similar during the maturation phase. Static respirometric index measured at 37°C should not be used with samples obtained during the thermophilic phase, since it resulted in an underestimation of the respiration values. Respiratory quotient presented only slight variations when changing the process temperature or the waste considered, and its use should be restricted to ensure aerobic conditions in the composting matrix

Ammonia emissions from the composting of different organic wastes : dependency on process temperature

Ammonia emissions were quantified for the laboratory-scale composting of three typical organic wastes with medium nitrogen content: organic fraction of municipal solid wastes, raw sludge and anaerobically digested sludge; and the composting of two wastes with high nitrogen content: animal by-products from slaughterhouses and partially hydrolysed hair from the leather industry. All the wastes were mixed with the proper amount of bulking agent. Ammonia emitted in the composting of the five wastes investigated revealed a strong dependence on temperature, with a distinct pattern found in ammonia emissions for each waste in the thermophilic first stage of composting (exponential increase of ammonia emitted when increasing temperature) than that of the mesophilic final stage (linear increase of ammonia emissions when increasing temperature). As composting needs high temperatures to ensure the sanitisation of compost and ammonia emissions are one of the main environmental impacts associated to composting and responsible for obtaining compost with a low agronomical quality, it is proposed that sanitisation is conducted after the first stage in large-scale composting facilities by a proper temperature control

Prediction of temperature and thermal inertia effect in the maturation stage and stockpiling of a large composting mass

A macroscopic non-steady state energy balance was developed and solved for a composting pile of source-selected organic fraction of municipal solid waste during the maturation stage (13,500 kg of compost). Simulated temperature profiles correlated well with temperature experimental data (ranging from 50 to 70 °C) obtained during the maturation process for more than 50 days at full scale. Thermal inertia effect usually found in composting plants and associated to the stockpiling of large composting masses could be predicted by means of this simplified energy balance, which takes into account terms of convective, conductive and radiation heat dissipation. Heat losses in a large composting mass are not significant due to the similar temperatures found at the surroundings and at the surface of the pile (ranging from 15 to 40 °C). In contrast, thermophilic temperature in the core of the pile was maintained during the whole maturation process. Heat generation was estimated with the static respiration index, a parameter that is typically used to monitor the biological activity and stability of composting processes. In this study, the static respiration index is presented as a parameter to estimate the metabolic heat that can be generated according to the biodegradable organic matter content of a compost sample, which can be useful in predicting the temperature of the composting process