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Batch Dry Fermentation

Batch Dry Fermentation


Dry fermentation is in comparison to wet fermentation designed for the recovery of biogas from dry and wastes, containing contaminants.
 
The dry fermentation has been proven for the anaerobic treatment of organic wastes such as the organic fraction of household waste, separately collected organic and green wastes or dry agricultural residues. The biogas produced from the waste can be converted in a CHP to electrical and thermal energy or fed as processed bio-methane into the natural gas grid or used as fuel (CNG).
 
 


Figure 1: Batch dry fermentation according to the BEKON process. Source: BEKON Energy Technologies GmbH & Co. KG

 
The fermenters are sealed with a gas-tight door and after a residence time of 3 - 4 weeks, the fermenter is emptied with the wheel loader. In order to obtain a uniform biogas production, at least 3 fermenter modules are necessary in the batch process. The batch processes are characterized by a very high tolerance of contaminants. In these methods, no agitators or pumps are in contact with the material and the process is therefore extremely robust and reliable in operation. No special pretreatment of the waste is necessary because the process is not affected by contaminants. The robustness of the process leads to low maintenance costs and operating expenses.
 
To inoculate the process, a part of the digestate is recirculated and brings the necessary microorganisms back to the fermenter. During the residence time of 3 – 4 weeks, the mixture of waste and digestate is slightly percolated, which accelerates the biogas production by transporting organic compounds and microorganisms. The percolate is stored in a percolate tank and pumped to the batch fermenter, which then flows through the waste before being pumped back to the percolate tank.
 
For dry batch fermenter a special safety flushing with exhaust air (CHP or CO2 derived from gas cleaning) is necessary to avoid explosive atmospheres while opening or closing the fermenter door. By using exhaust air to replace biogas or the air inside the fermenter, an explosive atmosphere is prevented.
 
Batch dry fermentation can be operated under mesophilic (38°C - 40°C) and thermophilic (50°C – 55°C) conditions. A heating system is integrated in the floor and walls of each fermenter and secures the required temperature for the process. The thermophilic operation ensures a higher biogas yield due to faster degradation of the organic matter. Through thermophilic operation the waste can be sanitized inside the batch digester.
 
The digestate has a dry matter content of 35 – 40 % and is suitable without further mechanical treatment for subsequent composting. Contaminants such as stones and plastics can be easily removed after composting by using a drum screen.
 
Dry batch fermentation has been successfully proved for many years in different countries. Through the treatment of waste, the production of renewable energy and the production of high quality compost, these methods make an important contribution to climate and environmental protection.


 


Figure 2: Filling a batch fermenter. Source: BEKON Energy Technologies GmbH & Co. KG

 

References:

  • Chynoweth, D., Jose R. Sifontes, Arthur A. Teixeira. 2003: Sequential Batch Anaerobic Composting of Municipal and Space Mission Wastes and Bioenergy Crops. Presented at ORBIT Conference, Perth Australia, 2003.
  • Vandevivere, P., De Baere, L., Verstraete, W. (1999) unpublished manuscript. Found at: Verma, S., 2002: Anaerobic Digestion Of Biodegradable Organics In Municipal Solid Wastes. Department of Earth & Environmental Engineering (Henry Krumb School of Mines) Fu Foundation School of Engineering & Applied Science Columbia University
  • Verma, S., 2002: Anaerobic Digestion Of Biodegradable Organics In Municipal Solid Wastes. Department of Earth & Environmental Engineering (Henry Krumb School of Mines) Fu Foundation School of Engineering & Applied Science Columbia University

Created by Dr. Rolf Liebeneiner (BEKON Energy Technologies GmbH & Co. KG), (), last modified by ()




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