Marco de Bertoldi

Composting Management: a New Process Control Through O2 Feedback

A new strategy for composting has been developed, based on O2 feedback control. Experiments were carried out on composting the biodegradable fraction of municipal solid waste in a closed bioreactor, aerated by pressure ventilation. Ventilation was controlled in order to maintain the O2 level in the internal atmosphere of the composting mass between 15 and 20%. The new strategy seems to give satisfactory results in terms of process control, quality of end-product, low energy consumption, and hygienization of compost. These results were supported by analyses of: (1) the variation of the main microbial groups during composting; (2) the balance of material; (3) the gas present in the internal atmosphere (O2, NH3, CO2, H 2S); (4) phytotoxicity; and (5) pathogenic and indicator micro-organisms. The importance of carrying out these analyses to guarantee the quality of the end-product and to control the process is discussed. Finally, the new system for controlling composting is compared with the existing strategies (Beltsville and Rutgers systems).

The influence of Lactobacillus plantarum culture inoculation on the fate of Staphylococcus aureus and Salmonella typhimurium in Montasio cheese

The growth and survival of Staphylococcus aureus and Salmonella typhimurium were investigated during the manufacturing and ripening of raw milk Montasio cheese. Initial inoculated populations in the cheese milk were about 10(5) cfu/ml for S. aureus and 10(6) cfu/ml for S. typhimurium. Samples of curds and cheeses were taken during manufacturing and storage and analysed for pH and microbial populations. S. aureus increased slightly in number during the early period of ripening and attained a population of about 10(6) cfu/ml during the remaining period of storage. S. typhimurium decreased during cheesemaking and storage but persisted through 90 days. The addition of Lactobacillus plantarum culture (0.2% v/v) produced a marked reduction in populations of the test strains in 10 days of storage. Enterotoxin A was not detected in Montasio cheese even with a S. aureus population of 1.1 X 10(7) cfu/ml. L. plantarum strains were also tested by the spot method and the associative growth approach for their antagonistic activity against S. aureus and S. typhimurium. The compound excreted by L. plantarum was active only toward S. aureus. Furthermore, its activity was destroyed by protease treatment. These results indicated that while the growth of S. typhimurium is reduced by the acid production, S. aureus inhibition can be ascribed to bacteriocin production.

Production and Utilization of Suppressive Compost: Environmental, Food and Health Benefits

Since many centuries, compost has been utilized in agriculture to replace organic matter and nutrients for different crops. Only in recent decades, particular composts, produced with selected starting material and with controlled processes, have been applied to suppress phytopathogenic agents. Such composts can be used to control soil-borne or air-borne pathogens. This has been tested, to control diseases, both in the field and laboratory on many different crops and conditions: greenhouse, horticulture, floriculture, apple, grapes, container systems, pot culture, turf grass, plant nursery, etc. The mechanisms of disease suppression are still not fully understood and include a complex interplay of abiotic (pH, temperature, C/N, organic matter quality, etc.) and biotic (predators, antagonists, competition for nutrients, antibiosis, production of lytic enzymes, microbial metabolites like siderophores, etc.) factors. In this chapter, compost characteristics related to disease suppression, the use of suppressive compost and economical benefits are discussed, in particular the possible reduction of pesticide use.

ADAPTATION OF A SACCHAROMYCES-CEREVISIAE STRAIN TO HIGH COPPER CONCENTRATIONS

A strain of Saccharomyces cerevisiae has been adapted to increasing concentrations of copper at two different pH values. The growth curve at pH 5.5 is characterized by a time generation increasing with the amount of added copper. A significant decrease of cell volume as compared with the control is also observed. At pH 3 the cells grow faster than at pH 5.5 and resist higher copper concentrations (3.8 against 1.2 mm). Experimental evidence indicates that, after copper treatment, the metal is not bound to the cell wall, but is localized intracellularly. A significant precipitation of copper salts in the medium was observed only at pH 5.5. Increased levels of superoxide dismutase (SOD) activity were observed in copper-treated cells and which persisted after 20 subsequent inocula in a medium without added metal. On the contrary, catalase activity was not stimulated by copper treatment and, hence, not correlated with SOD levels. The mechanism of copper resistance, therefore, probably involves a persistent induction of SOD, but not of catalase, and it is strongly pH-dependent.

Yard Waste Composting with Heat Recovery

▪ The feasibility of yard waste composting in a closed continuous reactor with heat recovery has been investigated. Results obtained in this research are reported and discussed. In the system, the recovered energy (heat) can be transformed by a heat pump in hot water both for domestic and for residential heating. The organic fertilizer produced can be used in horticulture.

High Rate Composting with Innovative Process Control

Despite the variety of composting plants present on the market, the design and operation of composting systems to improve the rate of the process and quality of end products are still an objective that has not been achieved. The composting process evolves through a thermophilic phase followed by a mesophilic one. The metabolism of microorganisms involved in the process is deeply disturbed by environmental changes like temperature, oxygen level and moisture. The aim of this study was to carry out a composting process in two separate reactors: the first, only in the thermophilic phase, with the purpose of pathogen destruction and decomposition by selected thermophilic microorganisms; the second, only in the mesophilic phase, to perform the main microbial transformations with a higher rate of volatile solids destruction. The results confirmed that maintaining constant the main parameters which affect the process, the microbial activity is enhanced. In the two-phase process, the evolution of parameters like moisture, organic carbon, humified organic matter, organic N, C/N and germination index (phytotoxicity) is more rapid relative to the single phase process. Also pathogen destruction is improved with the complete elimination of Faecal coliforms and Enterobacteriaceae and with a stronger reduction of Faecal streptococci.

Composting Food Processing Waste in the European Economic Community

For more than half a century, large food processing companies, faced with mounting solid waste disposal problems, have opted for landfilling. Other options, concentrating on utilization, are now being increasingly explored. Energy recovery (ethanol and methanol) and fodder production from food processing residuals in some cases are valid solutions. Of the many alternatives to food recovery waste disposal, composting seems to be an effective method. Managed properly, research has shown that composting can produce a nutrient-rich soil amendment; odors can be controlled during the transformation process and in the final product. The process is competitive and cost-effective environmentally, completes the biological chain and returns to the soil what has been taken from it. For these reasons, composting seems to be the best candidate to solve problems connected with food factory waste disposal.

Biological wastewater treatments for metallurgical industries

Variable contents of nitrite (NO2−)- and nitrate (NO3−)-nitrogen are present in wastewater of metallurgical cylinder-producing industries after treatment in a physical-chemical plant. Biological denitrification and oxidation treatments to reduce the oxidized nitrogen forms to within legal limits were evaluated. Wastewater streams were characterized and quantified in order to build a pilot plant, improve strategies to reduce environmental impact and increase water recycling. Initial sedimentation of raw mixed streams reduced iron and zinc contents by 87% and 71%, respectively. The resulting COD was refractory to be used in biological phases and an added carbon source was necessary to optimise the denitrification process. The biological treatment gave good results even without subsequent physical-chemical treatments, lowering NO2− and NO3− values to below the 0.6 and 20 mg L−1 limits respectively.