Residus més biodegradables

El tractament de residus sòlids orgànics per obtenir compost -esmena orgànica estable i aplicable al sòl- és un procés d'àmplia aplicació, però complex. Aconseguir que un residu sigui compostat amb èxit, dependrà de que aquest tingui certes característiques químiques i biològiques. Per això, quan aquestes no hi són, existeix la possibilitat de compensar-les mitjançant el cocompostatge. Aquest es basa en l'addició de cosubstrats al residu original, per tal que aquest superi les seves deficiències de partida i pugui ser tractat posteriorment. Seguint aquesta línia, s'han dut a terme una sèrie de proves en el laboratori afegint proteïna, greix i cel·lulosa per separat a fangs de depuradora d'aigües residuals urbanes. Els resultats han estat força positius, tant pel que fa al desenvolupament del procés, com per la conservació del nitrogen en el producte final. Els cosubstrats utilitzats es troben en un nombre important de residus orgànics, especialment aquells que provenen de la indústria agroalimentària. El seu tractament mitjançant compostatge obre una excel·lent via de valorització.El tratamiento de residuos sólidos orgánicos para obtener compuesto - enmienda orgánica estable y aplicable al suelo- es un proceso de amplia aplicación, pero complejo. Conseguir que un residuo sea compostado con éxito, dependerá de que éste tenga ciertas características químicas y biológicas. Por eso, cuando éstas no están, existe la posibilidad de compensarlas mediante el cocompostaje. Éste se basa en la adición de cosustratos en el residuo original, a fin de que éste supere sus deficiencias de partida y pueda ser tratado posteriormente. Siguiendo esta línea, se han llevado a cabo una serie de pruebas en el laboratorio añadiendo proteína, grasa y celulosa por separado a barros de depuradora de aguas residuales urbanas. Los resultados han sido bastante positivos, tanto con respecto al desarrollo del proceso, como por la conservación del nitrógeno en el producto final. Los cosustratos utilizados se encuentran en un número importante de residuos orgánicos, especialmente aquéllos que provienen de la industria agroalimentaria. Su tratamiento mediante compostaje abre una excelente vía de valorización.The treatment of organic solid waste to obtain compost - which can be used as soil conditioner or fertilizer - is a complex process. However, certain physico-chemical and biological characteristics are required in a waste to be successfully composted. When these characteristics are not present, there is the possibility of compensating them through cocomposting. This technique consists in adding a cosubstrate to the original waste to make up for its original deficiencies and facilitate its treatment by composting. Cocomposting was tested with a series of laboratory trials in which protein, fats and cellulose were added to sewage sludge separately. The results were quite positive not only due to enhancement of the composting process evolution but also for the increase in nitrogen conservation in the final product. The cosubstrates used can be found in different organic wastes specially those from the food industry. The treatment of these wastes though composting offers an excellent opportunity for their valorization

Biodegradation of animal fats in a co-composting process with wastewater sludge

A composting process was proposed as an effective technology for the biodegradation of fats in a proportion of 40-50%. Anaerobically digested sludge was used as co-substrate for animal fats to balance the C/N ratio of the composting mixture and to provide additional biodegradable organic matter and active biomass. Two different strategies were studied: static pile and dynamic turned pile. Air-filled porosity was initially adjusted to 40% for both experiments. It was observed that non-turned strategy increases the formation of material agglomerates which derived in a non-homogeneous fat distribution, the development of filamentous fungi, and a considerable increase in the amount of leachate generated. Turning the composting material resulted in the best results for composting fat-enriched wastes, preventing the formation of agglomerates. An effective biodegradation up to 92% of the fats was observed under these conditions. Besides, the addition of fats increased significantly the duration of the thermophilic period of the composting process

Factors affecting air pycnometer performance for its use in the composting process

Air filled porosity (AFP) is a crucial factor in composting to guarantee aerobic conditions inside the composting matrix. Among the different methods proposed to measure AFP in composting processes, air pycnometry is defined as the most adequate. There is a lack of a standard methodology for air pycnometry utilization for AFP determination in heterogeneous samples as those from composting materials. Air pycnometers currently used for this purpose are custom made instruments operating under different conditions (sample volume, initial pressure, etc.). All factors affecting air pycnometry accuracy in the composting process are related to the proper maintenance and handling of the air pycnometer and the composting sample. In this study, AFP measurements have been performed in more than 50 samples of a wide range of composting materials using two different custom made pycnometers, one of them coupled to a composting reactor allowing in situ AFP measurement. While temperature variation during AFP measurement has been discarded as an error source, the determination of the sample volume has been found to be a significant factor affecting the air filled porosity calculation. Regarding the initial pressure to use, a compromise between accuracy and practicality has to be established for each pycnometer design as AFP values obtained with diverse initial pressures (from 200 to 500 kPa gauge pressure) were found to present no statistical differences. An initial pressure in the range of 300-500 kPa (gauge pressure) is recommended. In conclusion, there is a need for a standard methodology for AFP determination or prediction at industrial scale. A complete procedure for air filled porosity determination by air pycnometry is also presented in this work

Influence of different co-substrates biochemical composition on raw sludge co-composting

The influence of biochemical composition of different co-substrates added to raw sludge during co-composting process was studied. The physical properties of the composting mass and their influence on the biological activity were also investigated. Three treatments composed of mixtures of raw sludge and co-substrate (commercial fats, protein, and cellulose) were carried out and compared to a control composed of raw sludge. Mixture conditioning was performed on the basis on air filled porosity (40%). The results obtained in the co-composting processes reflected a higher biological activity and higher degradation percentages of dry and organic matter when compared with control. Higher temperatures (60, 67 and 62°C for fats, protein and cellulose, respectively) were also achieved in all co-composting experiments as compared to the control test (55°C). Biological activity was measured using both Static and Dynamic Respiration Indices obtaining higher values in co-composting experiments compared to the control test. Fats content reduction was higher (66%) at higher fats content in the initial mixture (10.6%). The addition of fats seems also to promote the degradation of cellulose and lignin. Co-composting experiments with fats and cellulose presented higher initial C/N ratio and lower nitrogen losses, 27.5 and 34.2% compared to 40% for raw sludge. It has been demonstrated that the addition of an adequate co-substrate to raw sludge leads to a higher degradation percentages of the different biochemical fractions and higher nitrogen conservation

Performance of different systems for the composting of the source-selected organic fraction of municipal solid waste

Performance of three pile composting systems at field-scale were studied and compared in the composting of source-selected organic fraction of municipal solid waste (OFMSW): turned pile (TP), static forced-aerated pile (SAP) and turned forced-aerated pile (TAP). Routine parameters such as temperature, oxygen content, moisture and porosity were monitored. Temperature was found to be higher in turned systems whereas oxygen content was higher in forced-aerated systems. Although the initial air-filled porosity (AFP) for all mixtures was high, around 70%, the material tended to compact in the static system. A high degree of heterogeneity was found in the non-turned system. Extent of biodegradation was measured by respiration techniques (from 5.3 to 1.1 mg [O2] g [organic matter {OM}]−1 h−1 in TP and from 4.7 to 0.7 mg [O2] g [OM]−1 h−1 in turned forced-aerated pile). The non-turned compost showed a low level of stability (3.6 mg [O2] g [OM]−1 h−1) and the lowest maturity grade (I) measured by the self-heating test. In forced-aerated systems a low intermittent aeration rate of 1 l kg [volatile solids {VS}]−1 min−1 (5 min on, 30 min off) proved to be excessive, causing major water losses and hampering moisture control. Comparison of the results obtained for TP and TAP demonstrated that the investment cost in a forced-aeration system is not necessary for this waste. Hence, turned systems are recommended for OFMSW pile composting

Possibilities of composting disposable diapers with municipal solid wastes

The possibilities for the management of disposable diapers in municipal solid waste have been studied. An in-depth revision of literature about generation, composition and current treatment options for disposable diapers showed that the situation for these wastes is not clearly defined in developed recycling societies. As a promising technology, composting of diapers with source-separated organic fraction of municipal solid waste (OFMSW) was studied at full scale to understand the process performance and the characteristics of the compost obtained when compared with that of composting OFMSW without diapers. The experiments demonstrated that the composting process presented similar trends in terms of evolution of routine parameters (temperature, oxygen content, moisture and organic matter content) and biological activity (measured as respiration index). In relation to the quality of both composts, it can be concluded that both materials were identical in terms of stability, maturity and phytotoxicity and showed no presence of pathogenic micro-organisms. However, compost coming from OFMSW with a 3% of disposable diapers presented a slightly higher level of zinc, which can prevent the use of large amounts of diapers mixed with OFMSW

Categorizing raw organic material biodegradability via respiration activity measurement : a review

A massive characterization in terms of respiration activity for the most common types of organic solid wastes is presented in this compilation. Respiration activity for a solid waste is a crucial parameter to understand the behaviour of the waste in the environment and for waste management aspects such as the definition of a suitable biological treatment and the determination of the potential rate of microbial self-heating if organic wastes are to be used as solid recovered fuels. The respiration data compiled in this work are the result of five years of research focused on the determination of the biological activity of organic wastes. A compilation of respiration data found in the literature is also presented. The main groups of organic wastes analyzed are: municipal solid wastes (including mixed wastes and source-selected organic fraction), wastewater sludge (including digested and nondigested sludge from primary and secondary operations in municipal and industrial wastewater treatment plants), different types of manure (of different origin), other particular wastes (animal by-products, hair waste, fats, etc.) and some mixtures of different wastes. Results suggest that respiration activity can be used to classify the biodegradability of organic wastes into three main categories: i) highly biodegradable wastes (respiration activity higher than 5 mg O₂ g Organic Matter⁻¹ h⁻¹), which includes source-selected organic fraction of municipal solid waste, nondigested municipal wastewater sludge and animal by-products; ii) moderately biodegradable wastes (respiration activity within 2 to 5 mg O₂ g Organic Matter⁻¹ h⁻¹), including mixed municipal solid waste, digested municipal wastewater sludge and several types of manure; iii) wastes of low biodegradability (respiration activity lower than 2 mg O₂ g Organic Matter⁻¹ h⁻¹), which includes few organic wastes such as some particular wastes from the food industry

Recovery of organic wastes in the Spanish wine industry : technical, economic and environmental analyses of the composting process

The main organic wastes produced in modern wine industries include grape pomace (62%), lees (14%), stalk (12%) and dewatered sludge (12%). Some of these wastes are being used as by-products (grape pomace and lees) whereas the rest of organic wastes (stalk and wastewater sludge) has been traditionally incinerated or disposed in landfill. In this work, composting is proposed for the recovery of stalk and wastewater sludge to produce a sanitized organic amendment for application in the vineyard, closing the organic matter cycle. The environmental and economical analyses of the different alternatives to manage organic wastes from the wine industry are also presented. Composting costs are almost negligible when compared to other management options. From the environmental point of view, in-situ composting presents the best performance in 8 of the 10 impact categories analysed. Finally, the energy balance shows that the 4 composting systems involved less energy than the systems based on Mineral Fertilizer consumption

Desenvolupament d’un simulador numèric del procés de compostatge i aplicació a l’optimització del compostatge de llots i mescles amb altres residuos orgànics

L’objectiu principal del present projecte és l’obtenció d’un simulador, basat en un model estructurat, que permeti optimitzar les condicions del procés de compostatge de llots de depuradora, així com predir-ne l’evolució. L’esmentat simulador i el model associat hauran de ser aplicables al compostatge d’altres residus orgànics com la fracció orgànica de residus municipals, els residus ramaders i, en general, les mescles de residus de composició coneguda (cocompostatge).Postprint (published version