Anaerobic treatment of organic waste – example from Brazil
Fermenting organic residues is one alternative for waste recycling which produces biogas – a valuable energy carrier. Although biowaste fermentation plants are widespread in Germany, this technology is not used in Brazil. In Brazil, household waste is usually collected with other waste and used for landfill. Up to two thirds of Brazilian household waste consists of organic material. The energy content is not currently utilized by converting the valuable organic component of waste to biogas.
Biogas and fertilizer from kitchen waste
Fraunhofer IGB has built a bioreactor plant for the fermentation of organic waste as part of the BMBF (German Federal Ministry for Education and Research) funded research project "Decentralized Water Supply and Disposal in Association with Energy Recovery, Taking into Consideration Aspects of Hygiene for the Region of Piracicaba" at the Departamento de Água e Esgoto (DAE) in Americana, a town in the state of São Paulo.
This is being used for teaching and training purposes as well as for determining fundamental data. The plant is used for the anaerobic fermentation of kitchen waste produced by the canteen at the waterworks at DAE. During anaerobic conversion, the quantity of remaining organic material is considerably reduced. Since phosphorous, nitrogen and mineral salts survive the anaerobic conversion process, the plant outputs valuable fertilizers. The biogas produced is a regenerative energy carrier which can be used in almost exactly the same way as natural gas.
Operation principle of biowaste fermentation plant
Figure 1 shows the schematic representation of a biowaste fermentation plant. To operate, water is added to the fermentation material to about 10% solids, mixed using a mixer and stored in a storage tank B01. The agitator mixes the contents of the tank before and while it is conveyed to the reactor. The feed pump P01 (single screw pump) periodically charges the bioreactor with the mixed organic waste several times a day. The charge in the bioreactor B02 is mixed by injecting gas. The hydraulic residence time in the bioreactor is about 10 days. The temperature in the bioreactor is thermostatically controlled at approximately 30 to 37°C using a heating/cooling thermostat since this is the optimum temperature range for an anaerobic mixed population of micro-organisms to work. The quantity of biogas formed is recorded by a gas meter. Overall control of the bioreactor plant is maintained using a programmable logic controller (PLC).
The plant has been installed directly next to the environmental training center of DAE. An excursion to the biodigestor (Figure 2) took place 18 October during the "1O Seminário Internacional de Biotecnologia" arranged by the Universidade Metodista de Piracicaba and Fraunhofer IGB.
The "Decentralized Water Supply and Disposal in Association with Energy Recovery, Taking into Consideration Aspects of Hygiene for the Region of Piracicaba" research project is funded by the Federal Ministry of Education and Research.