Abstracts 01/03 back to overview Editorial DESIGNING COMPOST MATURATION FACILITIES BASED ON MAINTAINING AEROBIC CONDITIONS D.D. Cabanas-Vargas, E. I. Stentiford School of Civil Engineering, The University of Leeds. Leeds, United Kingdom. 1. ABSTRACT The paper works on the basis that successful maturation depends on maintaining aerobic conditions throughout the pile mass to avoid anaerobic odours and maximise the maturation rate. A series of columns was used with varying cross-sections up to 300 mm in diameter and with heights up to 2 m. Sampling points were set at different points in the column to allow the temperature, O2 and CO2 profiles to be monitored throughout the vertical section. The columns were filled with composts of different ages using biowaste and sewage sludge as raw materials. The composts were characterised based on respiration rate (Specific Oxygen Uptake Rate — SOUR), volatile solids content, particle size distribution and porosity. The results show that the O2 and temperature profiles were both related to the SOUR with higher SOUR values correlating with higher temperatures and a greater O2 depletion. The composts used were relatively stable (maximum SOUR 2.28 mgO2/gVS/hr) but the pattern of results obtained allowed a family of curves to be developed from the laboratory work which will be validated for full scale operations. SEWAGE SLUDGE PRE-TREATMENTS FOR ENHANCING ITS ANAEROBIC BIODEGRADABILITY S. Mace, J. Costa and J. Mata-Alvarez, Dept. Chem. Engineering. Univesity of Barcelona. Marti i Franques 1, pta 6 08028 Barcelona. 1. ABSTRACT Several tests at laboratory scale were carried out to study different pre-treatments for centrifuged sewage sludge (SS) prior to its anaerobic fermentation. Results show that digestability is improved by means of these pre-treatments. The concentrations achieved show a considerable improvement, although it is not very high due to the dilute nature of the sewage sludge. Concentrations of VFA of more than 6300 mg/L can be obtained with an aerobic thermophilic pre-treatment of 24 h, followed by a fermentation of 5 days at mesophilic temperatures, which represents an improvement of 21.5% with respect to the control fermenter without pre-treatment. Concentrations of VFA of around 7500 mg/L can be obtained with an alkaline pre-treatment of 24 h, followed by a fermentation of 5 days at mesophilic temperatures, which represents an improvement of around 45 % with respect to the control fermenter without pre-treatment This pre-treatment introduces a foreign anion into the system. A review of some pretreatments is also carried out. TREND OF HEAVY METAL CONCENTRATION IN COMPOST PRODUCED IN VENETO REGION Paolo Giandon, Lorena Franz, Federica Germani ARPAV Centro Agroambientale, Castelfranco Veneto (TV) - Italy 1. ABSTRACT Since 1994 the Agroenvironmental Centre of Regional Protection Agency is dealing with the control of the chemical composition of composts produced in Veneto Region. During last years composting plants were required to reduce the risks of heavy metal contamination of compost; the new regulation, stated in march 2000, confirmed this requirement in order to give enough assurance to farmers that are going to use it. Data obtained from samples collected between 1996 and 1999 were examined to point out if any improvement was achieved in order to reduce concentration of heavy metals, such as cadmium, chromium, copper, mercury, nichel, lead and zinc, in composts; results, grouped by type of composted materials, showed a significant reduction in many cases, confirming the efforts made by compost producers of Veneto Region. Not always a positive trend take place, highlighting that there is still a need of increase the knowledge about the carachteristics of compostable materials and the process control. CORRELATION AMONG PLANT DESIGN, PROCESS CONTROL AND QUALITY OF COMPOST Marco de Bertoldi1 and Ulrike Schnappinger2 1 Department of Industrial Microbiology, University of Udine, Italy 2 Architektur + Umvelttechnik, Munich, Germany 1. ABSTRACT Composting is a microbial process that occurs inside plants or reactors; these reactors are designed and built by architects or engineers, which in their work are conditioned by the biological process that occurs in these plants. When discussing composting, a careful distinction must be made between questions regarding the plant and those concerning the process and its control. By plant it is meant the system of machinery, buildings and equipment for composting. By process we mean the correct application and control of the microbial transformation of organic matter, with the optimisation of all parameters and conditioning factors. Industrial microbiologists, who devise and perform the process, and architects or civil engineers who design and construct the plants have been working independently and separately. As a consequence, most of the existing plants have been built without taking into considerations the simplest requirements of microbial metabolism. Closer collaboration would certainly improve the practical results. A correct application of these principles will result in: (1) a better control of the process with high quality end-product; (2) lower retention times and consequently smaller reactors; (3) reduced building, operating and maintenance costs; and (4) reduced energy consumption. The quality of compost is today the most important prerogative in order to recycle organic waste, to market and utilize the product in agriculture. Besides a good correlation between the process, the design and the building of a composting plant, the quality of the end-product is conditioned by the quality of the starting material, its conditioning (physical and chemical), the type of microbial process chosen (continuous or discontinuous), the composting system, the feed back control used, the biological stabilization and hygienization of compost. When quality is guaranteed, compost will have no problem to be used as an organic fertilizer in our soils. In modern agriculture, monoculture of cereals, absence of rotations and of green manure, extensive and intensive crop production, in particular in greenhouses, have depleted our soils. The availability of alternative sources of organic matter as compost, will be very important to maintain biological fertility of soils. In Europe, where agricultural soils have been depleted since 2000 years (see Mediterranean areas), the organic matter content in some cases is very low; when this value drops below 1%, the irreversible effect of desertification can occur. COMPOST AS A PRODUCT AND ITS MARKET Martínez Orgado, Carlos. Spanish Waste Club, Madrid, Spain 1. ABSTRACT At present, approximately 10 million tonnes out of the total biowaste that could potentially be recovered are composted in homes or processed through selective collection and later treatment, giving an approximate production of 5.5 million tonnes of compost in the EU as a whole. In order to encourage the use of this product, it is necessary to create a much more consolidated market in which compost is seen as not as a hard to eliminate waste problem but as a quality product with numerous applications and, therefore, a wide range of commercial outlets. This article analyzes the strengths and weaknesses of compost as a quality product, the traditional and more innovative outlets, its main competitors and barriers. In addition, at the same time as it studies the current situation and the future prospects of the compost market, it also highlights the importance, when it comes to fostering this market, of developing a Community Directive and creating associations of compost consumers and producers that can work to ensure the production and distribution of a high-quality product. Establishing quality standards within the scope of the European Union is an essential measure to ensure and harmonize the quality of compost as a product, to generate a climate of confidence among consumers and, of course, to encourage the development of the compost market.