Session

Session- Developments in Composting Systems

Development of Rapid, Contained Composting Technique to Manage Municipal Solid Wastes in the Philippines

CUEVAS, VIRGINIA C. (1), Resurrecion, Arsenio N.(2) and Malayang, Ben S. (3)

(1) Institute of Biological Sciences, (2) College of Engineering and AgroIndustrial Technology, and (3) School of Environmental Science and Management, The Philippines

A technique for composting market biodegradable wastes in contained bins was described. Composting was rapid and accomplished in 11 days. Favorable conditions for rapid composting were provided. Fresh market wastes collected from Los Banos, Poblacion Public Market, Laguna, Philippines, were first shredded. Compost activator was introduced into the shredded wastes as they were placed in the bins. Air was forced into each container from a 0.5 hp motor. Aeration was provided for 8 hours every day. Ripe compost had a C:N ratio of 14:1, with 2.0% N, black color and soily appearance. Mean pH was 8.4. There was no foul smell. The system may still be improved by incorporating controlled heating to further shorten composting period. Wastes in the Control bins on the 11th day have 4.75 pH, foul smell and numerous larvae of fruit flies. The prototype developed in this study can be replicated and adapted to apartments in urban areas or for a block of houses in a residential area. It can also be upgraded for restaurants or small market area where daily wastes generated is less than 0.5 tons/day. It can be part of an integrated solid waste management system. The development of the bin is a demonstration of the integration of disciplines such as policy advocacy, biology and engineering to address an environmental problem. Ripe compost had a C:N ratio of 14:1, with 2.0% N, black color and soily appearance. Mean pH was 8.4. There was no foul smell. The system may still be improved by incorporating controlled heating to further shorten composting period. Wastes in the Control bins on the 11th day have 4.75 pH, foul smell and numerous larvae of fruit flies. The prototype developed in this study can be replicated and adapted to apartments in urban areas or for a block of houses in a residential area. It can also be upgraded for restaurant use.

Composting in A New Two-Phase Continuous Reactor

Marco de Bertoldi

Department of Industrial Microbiology, University of Udine, Udine, Italy

At industrial level composting must be a controlled process. Many different composting systems have been performed up to now to obtain valid and rapid processes, but all the composting systems have used discontinuous processes (batch culture) which present the typical growth curve with lag, exponential, stationary and death phases. This because during the process there is a continuous change of environmental conditions like temperature, pH, moisture, oxygen concentration and C/N ratio. Consequently the microbial activity never is at the highest levels, specially because of the variation of temperature, which causes an alternation of microbial populations (mesophilic, thermophilic, mesophilic). Low rate processes need longer time to reach biological stabilization and humification of compost. Longer times involve longer retention times in the reactors and therefore bigger plants, higher building, running and maintenance costs. The only possibility to overtake these disadvantages is to pass to continuous culture systems, maintaining the microorganisms always in the exponential growth phase. Practically, this can only be realized using a two-phase reactor with thermophilic and mesophilic phases separated. In the primary reactor, continuously feeded and unloded, temperature is constantly mantained at 70 C with a retention time of 4 days. In this primary thermophilic reactor the main function is hygenization of the starting materials ans the starting of metabolization of easy degradable molecules. From the first reactor, the composting material automatically pass in the second reactor and it is immediately cooled by an air flow. This reactor is feed-back temperature controlled (45 C) and ventilated from the top to the bottom with a downstream air flow, which intensity is regulated by a computer in order to maintain oxygen and temperature to the desired levels. In this second mesophilic reactor the retention time is 14-21 days, according to the composition of the starting material. The advantages of this new continuous composting system are reported in detail in the paper.

Successful planning of a composting plant considers not only the choice of the technical equipment, but the architectural concept of the plant as well. The design must consider the relationship of the buildings to the existing surroundings, local infrastructure, and their integration into the urban space or the rural context. The modelling of the shapes of the buildings and the integration of ecological aspects including the use of sustainable materials, the micro-climate, water and natural ventilation-systems and the recuperation of energy are other important considerations. Corrosion caused by leachate and composting process condensates is a further aspect that must be addressed. The management of a plant depends on the successful integration of technical equipment and building construction. This requires concerted efforts by many disciplines including civil engineering, microbiology

State of the Art Treatment of Source Separated Organics in the European Union

LUIS F. DIAZ (1), Linda L. Eggerth (1), George M. Savage (1), Edward I. Stentiford (2) and Efstathios K. Papadimitriou (2)

Several EU member states have made substantial advances in the management and beneficial use of organic residues. Some of these countries are utilizing sophisticated strategies and state-of-the-art facilities. This paper will provide both technical and non-technical information on the latest strategies and the type of facilities used to treat the source separated organic fraction.