Electrical Conductivity for Monitoring the Expansion of the Support Material in an Anaerobic Biofilm Reactor

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.

Anaerobic Co-digestion of Organic Fraction of Municipal Solid waste and Septage for Sustainable Waste Treatment: A Case Study from Goa, India

“…The study conducted by Marín-Peña et al showed the effect of conductivity on biogas generation concluded that conductivity above 14 mS/cm is ideal for the reactors. In the present study, conductivity gradually increased to an average of 15 to 30 µS/cm after 16 th day and was remained constant for the rest of the process [24].…”

“…The results thus obtained reflect the proposed aim of the study. Studies carried out by Klein et al, and Marín-Peña et al showed that the conductivity of more than 30 mS/cm has shown an adverse effect on the biogas system [24], [29]. However, in this study, it was seen that the conductivity never exceeded the threshold value making the system efficient and also proving the fact that the OFMSW and SS can be mixed at 5: 1 ratio.…”

“…VFA was seen to be varying from 1000±922.45 to 5000±956.98 ppm, and the VFA/TA ratio was between 0.5 to 0.6, which indicates slight system overloading as stated in work carried out by Lin et al, and Gao et al The pH was between 7 to 8, indicating healthy conditions for allowing optimum microbial growth. The maximum conductivity was found to be 18±4.5 mS/cm, which is less than the threshold for any inhibitory action to take place by the changing electron transport pathways [21], [24].…”

Batch and Semi-Continuous Anaerobic Digestion of Industrial Solid Citrus Waste for the Production of Bioenergy

“…Lee et al [41] reported that methanogenesis occurs efficiently in an anaerobic reactor at pH values between 6.5 and 8.2. Marín-Peña et al [42] also reported that pH values in the range of 7.0-7.5 favor the methanogenic stage of anaerobic digestion. In addition, during the anaerobic co-digestion of 50% orange peel with 50% catering waste, Anjum et al [23] observed that the pH was in the range of 6.38-7.01 between days 39 and 42, which is the optimum range for methanogenesis.…”

Evaluation of the Effect of the Application of Combined Pretreatments and Inoculum with High Alkalinity on Food Residues Through BMP Tests

“…Most of the EU, except for EU 7, 8, and 9 (inoculum blank), present values below 0.5, indicating the consumption of buffer capacity within the system; the total alkalinity (Table 6) in all the systems presented a low value compared to the recommended levels (13 -15 g CaCO 3 •L -1 ) [ 33]. The electrical conductivity was found to be within normal values for anaerobic processes [34,35]. It is possible to distinguish two groups: those with values below 8 mS •cm -1 (concentration of 7g TVS •L -1 ) and those with values above 8 mS •cm -1 (Concentration of 14 g TVS •L -1 ), indicating that the fed concentration has a direct effect on the electrical conductivity, which may be associated with the salts and seasoning implemented during the cooking processes of the food [36].…”