Abstracts 02/01 back to overview Editorial EVALUATING THE POTENTIAL OF AN ELECTRONIC NOSE FOR DETECTING THE ONSET OF ANAEROBIC CONDITIONS DURING COMPOSTING Figueiredo S. A. B. and Stentiford E. I. School of Civil Engineering, University of Leeds, UK 1. ABSTRACT Most bad odours in composting plants are formed under anaerobic conditions and often they could be avoided if detected early enough. In this project an electronic nose was used to evaluate the odours produced during a composting process at bench scale. The electronic nose consists of an array of electronic chemical sensors with partial specificity and an appropriate pattern recognition system capable of recognising simple or complex odours. Their advantage is their rapid response rate and simplicity of operation. Closed reactors were set up in water baths in the laboratory to enable their operating temperature to be changed. In the experiment described in this paper the temperature was kept at 40ºC and the waste used was the vegetable fraction of food waste. Each reactor was fitted with an aeration system which could maintain aerobic conditions inside the reactors when needed. Samples of the headspace gas were analysed and the odour was assessed during the biodegradiation process. Oxygen was measured in the headspace gas, and parameters such as the oxidation reduction potential (redox) were measured in the solid material. The reactors were initially operated aerobically and then the air was turned off. The changes in headspace gases and redox were then monitored as the conditions became anaerobic and the results compared to those of the electronic nose. The initial results from the trials indicate that the electronic nose can detect an early transition from aerobic to anaerobic conditions, but at this stage more work is needed in the laboratory. Further trials are taking place in the field METHODS FOR DETERMINING PHYSICAL, PARTICLE-RELATED CHARACTERISTICS RELEVANT TO FLUID FLOW PHENOMENA IN BIOWASTE Eckhard Kraft Bauhaus-Universität Weimar, Germany 1. ABSTRACT The characterisation of biowaste and its influence on the fluid flow in packed beds of biowaste has been researched. For the first time, a considerable number of experiments have been conducted to measure particle density. The particle density can be used to estimate the amount of pores in the biowaste. Particle size distributions have been examined for the organic material. Possibilities have been tested to specify characteristic classification numbers and effective particle diameters in order to study the properties of the material. Using the knowledge of the specific surface, conclusions can be drawn about interaction of Newton`s fluids in porous media. Certainly there has been an interdependence between viscosity, current properties, biodegradation and adsorption processes. At the moment, it is difficult to determine specific surfaces of packed columns by using proven methods. Although this could help to improve process engineering in a range of technical fields. This study provides a statistical basis to estimate specific surfaces of packed columns. The results of a test of this method executed on defined materials and on organic waste are presented. Based on these results the accuracy of the method is discussed. PROCESSING OF SEWAGE SLUDGE FOR ENERGETIC PURPOSES-A CHALLENGE FOR PROCESS TECHNOLOGY Arlt A., Leible L., Seifert H., Nieke E. and Fürniss B. Forschungszentrum Karlsruhe GmbH (FZK), Institute for Technology Assessment and Systems Analysis (ITAS), Karlsruhe, Germany 1. ABSTRACT The process chains used in Germany and other European countries for the processing of sewage sludge from municipal sewage treatment plants to biofuel are investigated. The goal of the study is to show which technological, energetic and economic issues have to be faced in order to produce a storable, microbiologically inert biofuel with a water content of less than 10 % compared to the original sludge. The process chains existing in German sewage treatment plants were investigated, which mainly consist of the following components: mechanical draining, stabilisation, mechanical dewatering, and drying. For each step of the process, cost estimates from the leading companies were gathered and analysed. The information gained in this way was compared with data given by the operators of the process technologies at the treatment plants. First results showed that the processing of biogenic sludge is a very expensive business because of the high technological effort involved. However, the energy balance of the whole process chain can be positive, at least if heat reutilization within the drying plant is realised and the sludge is not transported over long distances. The utilisation of sewage sludge as a biofuel can make a contribution, albeit small, to the national energy supply. Furthermore, the processing of sewage sludge into a biofuel fits well with the precautionary principle for the protection of soil and natural resources. MECHANICAL-BIOLOGICAL PRETREATMENT OF MSW Damiecki R. RWE Umwelt Services International GmbH, Essen, Germany 1.ABSTRACT The process of mechanical-biological pretreatment (MBP) of municipal solid waste (MSW) was developed and optimized by the engineering team of the Trienekens group in close cooperation with the German Federal Environmental Agency. It is based on experience from similar treatment plants, which have been operated by Trienekens since the early 1980s. Mechanical-biological pretreatment can be used first, in combination with a landfill, and second, in combination with an incinerator. Pretreatment of MSW prior to landfilling substantially enhances the quality of the landfill material (leachate quality, gas potential, stability) and significantly reduces the required landfill space. Pretreatment prior to incineration has other advantages: MBP makes it easy to separate recyclable material (metal, paper, plastic, RDF, etc.), reduces incinerator input and homogenizes the waste material in terms of water content, calorific value and particle size. The two methods cannot only be used alternatively, but can also be developed on a step-by-step basis. You can start with MBP on a small scale to improve your landfill. To comply with tightening environmental protection standards, MBP can later be developed into a full-scale pretreatment facility. Trienekens AG and its subsidiaries are now running three large-scale MBP plants in Germany. An MBP pilot plant is being planned abroad. DETERMINING THE DEGREE OF AEROBIOSIS IN COMPOSTING MATERIAL Matthias Klauß (1), Efstathios K. Papadimitriou (2), (3) (1) Weimar Bauhaus University, Chair of Waste Management, Coudraystraße 7, 99425 Weimar, Germany (2) Leeds University, School of Civil Engineering, LS2 9JT Leeds, UK (3) CalRecovery Europe Ltd., CRe House, Home Croft, Threshfield BD23 5HW, UK 1. ABSTRACT A laboratory test rig was constructed to investigate the possible use of exhaust gas 02 concentration, the microbial respiratory quotient, and oxygen consumption rate, in evaluating the degree of aerobiosis of a composting matrix. This laboratory study involved trials with two batches of source-separated household organic waste, including yard waste, incubated at 50°C and 65°C, and at variable forced-aeration rates to achieve exhaust gas 02 concentrations in the range of 1-17 % (v/v). The outcomes of this study indicated that any of the aforementioned parameters would not, in isolation, be sufficient for evaluating the degree of aerobiosis of a composting matrix. Comparatively speaking, the oxygen consumption rate was found to be the most useful for this purpose. A more extensive degree of aerobiosis was observed at RQ values less than 0.8.