Abstract
A persistent topic of the anaerobic digestion of biowaste is the efficient use of co-substrates. According to Renewable Energy Sources Act the co-substrate input is limited to 10 percent of the average daily substrate feed in Germany. In this concern, the primary focus of this paper is to understand the suitability of crude glycerol in anaerobic digestion of biowaste. Two identical lab-scale anaerobic digester units were added with crude glycerol, and each unit was equipped with four identical fermenters. Unit A was fed with an average organic loading rate of 4.5 kg VS m−3 d−1, and the average organic loading rate of unit B was set at 5.5 kg VS m−3 d−1. The share of crude glycerol in the total feed was 0.77 percent of the fresh matter. The abort criterion is a ratio of the volatile organic acids and buffer capacity (FOS/TAC) in the fermenter above 1.2. The abort criterion was reached after 16 days. In summary, the results lead us to the conclusion crude glycerol is not suitable as a co-substrate for anaerobic digestion for several reasons.
Highlights
Anaerobic digestion of biowaste is an established process for treating biowaste in Germany and is most common in other regions of the world
The results of the present study demonstrate that the co-digestion of crude glycerol together with biowaste does not work
long-chain fatty acids (LCFA) are dissolved in the crude glycerol and can inhibit acetogenic bacteria, acetoclastic methanogenic archaea, and hydrogenotrophic methanogenic archaea
Summary
Anaerobic digestion of biowaste is an established process for treating biowaste in Germany and is most common in other regions of the world. The benefits of anaerobic digestion compared to aerobic treatment (composting) are the additional production of biogas and the consequent conversion in electricity and heat by combined heat and power modules. To increase the biogas yield in a fermentation plant and to strengthen the biocenosis, several modifications in the process are feasible such as the use of biochar and the co-digestion of suitable co-substrates. Biochar can catalyze anaerobic digestion by alleviating mild ammonia inhibition, support archaeal growth, and methanize labile carbon present in the biochar [6]. Mumme et al (2016) investigated the influence of utilizing pyrochar (biochar from pyrolysis) and hydrochar (biochar from hydrothermal carbonization) in anaerobic digestion and their effects on biogas yield and ammonia inhibition. The investigation results showed that there is no clear effect from utilizing pyrochar on methane production; hydrochar utilization increased the methane yield by 32%
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