Abstract
This article describes the use of the electrical conductivity for measuring bed expansion in a continuous anaerobic biofilm reactor in order to prevent the exit of support material from the reactor with the consequent loss of biomass. The substrate used for the tests is obtained from a two-stage anaerobic digestion (AD) process at the pilot scale that treats the liquid fraction of fruit and vegetable waste (FVW). Tests were performed with the raw substrate before anaerobic treatment (S1), the effluent from the hydrolysis reactor (S2), and the effluent from the methanogenic reactor (S3) to evaluate its effect on the electrical conductivity values and its interaction with colonized support material. The tests were carried out in a 32 L anaerobic inverse fluidized bed reactor (IFBR), which was inoculated with colonized support material and using two industrial electrodes at different column positions. The results with the previously digested samples (S2 and S3) were satisfactory to detect the presence of support material at the points where the electrodes were placed since the electrical conductivity values showed significant changes of up to 0.5 V, while with substrate S1 no significant voltage differences were appreciated. These results demonstrate that electrical conductivity can be used as an economic and simple mean for monitoring the support material expansion in order to avoid over expansion in the IFBR. It was also demonstrated that the conditions of the substrate in the methanogenic stage (pH and presence of volatile fatty acids) do not affect the operation of the electrical conductivity detection system.
Highlights
Anaerobic digestion (AD) is a biochemical technological process where complex organic substrates are degraded by a consortium of microorganisms through four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis producing intermediary products, mainly volatile fatty acids (VFAs) and biogas as the final product, which consists mostly of methane (CH4 ) and carbon dioxide (CO2 ) [1,2,3].The anaerobic process has received increasing attention in recent years and has been widely used for the treatment of organic substrates such as sewage, industrial effluents, animal manure, and organic solid substrates, both at laboratory and pilot scales [4,5,6,7]
Electrical conductivity tests were performed with the substrate at different conditions in combination with the support material already colonized
From the analysis of the experimental results obtained in this study, the following conclusions obtained: the variations in electrical conductivity were analyzed with the expansion of the support are obtained: the variations in electrical conductivity were analyzed with the expansion of the material using three substrate conditions, which represent three points in the two-stage anaerobic digestion (AD) process: support material using three substrate conditions, which represent three points in the two-stage AD
Summary
Anaerobic digestion (AD) is a biochemical technological process where complex organic substrates are degraded by a consortium of microorganisms through four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis producing intermediary products, mainly volatile fatty acids (VFAs) and biogas as the final product, which consists mostly of methane (CH4 ) and carbon dioxide (CO2 ) [1,2,3].The anaerobic process has received increasing attention in recent years and has been widely used for the treatment of organic substrates such as sewage, industrial effluents, animal manure, and organic solid substrates, both at laboratory and pilot scales [4,5,6,7]. The anaerobic inverse fluidized bed reactor (IFBR) has the advantage of operating in continuous with high organic load effluents, using low density support particles that are downward fluidized by the liquid flow, requiring lower. The inlet for the reactor feed is at the top, while the effluent outlet at the bottom This system has a recirculation flow which takes advantage of the downward force exerted by the liquid by expanding the support towards the bottom of the reactor in a reverse fluidization. The use of support particles in IFBRs solves the problems that occur during conventional fluidization [13] These particles require low flow rate for expansion, it can be controlled [11,14]. To operate the bioreactor efficiently, the biofilm thickness should be approximately 100 μm [15]
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