https://doi.org/10.15255/KUI.2002.001
Published: Kem. Ind. 52 (3) (2003) 95–102
Paper reference number: KUI-01/2002
Paper type: Original scientific paper
Download paper:  PDF

Aerobic Composting of Fruit and Vegetable Leftovers: Modeling the Process

F. Briški, Z. Gomzi, A. Hublin and M. Vuković Domanovac

Abstract

Laboratory scale composting tests of mixture of fruit and vegetable leftovers is conducted under different air flow rates and particle sizes of the substrate. Rich soil was added to composting material as a source of microorganisms and for adjustment of moisture content, while PVC filings as a bulging agent. The moisture of initial waste mixture was 64.4 % and C/N ratio was 30.6 : 1. The experiments were carried out in the adiabatic continuous column reactors. Continuous up-flow aeration was provided by a membrane pump. The temperature during the composting process was continuously monitored by means of the four thermocouples which were connected to a datalogger. They were placed at the inlet and outlet of a reactor, in the middle and near the surface of composting mass. At the beginning and at the end of each composting test analysed were parameters such as moisture content in percentage of wet weight, total solids, volatile solids and volume of the waste mixture and compost, respectively. Furthermore, for the first five days the change in number and groups of microorganisms in the composting mass, was closely monitored. Evolution rate of carbon dioxide was measured daily because it indicates the degradation rate of selected substrate. The obtained results showed that the adequate biodegadation of selected mixture of fruit and vegetables is achieved at air flow rate 10 dm3 h-1 and particle size of 3 × 5 × 10mm(Fig. 3 ). The changes in number of mesophilic and thermophilic populations in mixed microbial culture are observed at different stages of composting process (Fig. 5). During the first three days in substrate dominated mesophilic bacteria and after that the intensive growth of thermophilic bacteria was observed. Similar results were obtained for thermophilic fungi though they appeared a little bit later because they are slower to initiate growth. After 14 days substrate was biodegraded and as a result 40 % of carbon dioxide evolved (Fig. 4), while the initial volume of waste mixture containing a soil was reduced to about 50 %. For the biodegradation of solid waste in continuous column reactor a mathematical model is proposed. A simple empirical and Michaelis-Menten kinetic model is selected to describe the biodegradation rate of organic waste. Better agreement (Fig. 6) is achieved by empirical kinetic model rs= kwns . Percentage of substrate conversion during 14 days was also calculated by empirical model. It could be seen that during the first three days 60 % of substrate (Fig. 6) was degraded, what is in accordance with the mass of evolved carbon dioxide in that period. These results suggest that selected model describes well the process of aerobic composting of selected substrate and confirms the assumption that released heat is proportional to the progress of biodegradation.

This work is licensed under a Creative Commons Attribution 4.0 International License

Keywords

aerobic composting, food leftover, adiabatic continuous column reactor, process modelling