Luz Ruggieri

Air filled porosity measurements by air pycnometry in the composting process: a review and a correlation analysis.

Air filled porosity (AFP) appears as the best measure to determine the available porosity in a composting material or, in general, in an organic matrix. Several methodologies, including theoretical and empirical approaches have been developed to estimate AFP. Among them, air pycnometry has been considered the most suitable and accurate technique to obtain reliable measures of AFP. In this review, the published methodologies to determine AFP by air pycnometry are explained in detail, and the main advantages and disadvantages of such methodologies are discussed. Also, a massive sampling of several organic wastes and mixtures intended for composting has been characterized by air pycnometry, and the theoretical and empirical correlations proposed in literature are compared in terms of accuracy in AFP measurement. Results obtained show that some theoretical correlations are suitable for estimating AFP in the majority of organic wastes studied. However, some waste samples need an experimental determination to obtain a realistic value of AFP.

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.

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.

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.

A study on Air Filled Porosity evolution in sludge composting

Air Filled Porosity (AFP) is a key parameter in the composting process, conditioning oxygen availability and heat accumulation. Air pycnometry is considered the most adequate methodology for AFP determination. This technique requires withdrawing a sample of material from the composting mass for AFP measurement, which may alter its physical characteristics. A novel strategy that permits to measure AFP in situ during the composting process is presented in this study. Raw and Anaerobically Digested Sludges (ADS) have been used as substrates. A common trend in AFP evolution during the composting process has been observed in most of the cases.

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.