Abstract
The application of cationic polymers to enhance membrane fluxes in anaerobic membrane bioreactors has been proposed by several authors. However, literature shows contradictory results on the influence of those chemicals on the biological activity. In this research, we studied the effect of a cationic polymer on the production of methane from acetate by acetoclastic methanogens. We assessed the effect of polymer concentration on the accumulated methane production (AMP) and the specific methanogenic activity (SMA) in batch tests. Batch tests results showed lower SMA values at higher concentrations of polymer and no effect on the final AMP. Different inhibition models were calibrated and compared to find the best fit and to hypothesize the prevailing inhibition mechanisms. The assessed inhibition models were: competitive (M1a), non-competitive (M2a), un-competitive (M3a), biocide-linear (M4a), and biocide-exponential (M5a). The parameters in the model related to the polymer characteristics were adjusted to fit the experimental data. M2a and M3a were the only models that fitted both experimental SMA and AMP. Although M1a and M4a adequately fitted the experimental SMA, M1a simulations slightly deviated from the experimental AMP, and M4a considerably underpredicted the AMP at concentrations of polymer above 0.23 gCOD L−1. M5a did not adequately fit either experimental SMA and AMP results. We compared models a (M1a to M5a), which consider the inhibition by the concentration of polymer in the bulk liquid, with models b (M1b to M5b) considering the inhibition being caused by the total concentration of polymer in the reactor. Results showed that the difference between a and b models' simulations were negligible for all kinetic models considered (M1, M2, M3, M4, and M5). Therefore, the models that better predicted the experimental data were the non-competitive (M2a and M2b) and un-competitive (M3a and M3b) inhibition models, which are biostatic inhibition models. Consequently, the decreased methanogenic activity caused by polymer additions is presumably a reversible process
Highlights
Anaerobic membrane bioreactor (AnMBR) is an innovative technology for municipal wastewater treatment (Smith et al, 2012) and an established technology for industrial wastewater treatment with several full-scale AnMBRs already treating wastewater from food processing industries (Dereli et al, 2012)
A 50 % specific methanogenic activity (SMA) inhibition was obtained at 0.27 gCOD L−1 of polymer, the value was obtained by linear interpolation
The cationic polymer showed a negative effect on the biological activity of the anaerobic sludge
Summary
Anaerobic membrane bioreactor (AnMBR) is an innovative technology for municipal wastewater treatment (Smith et al, 2012) and an established technology for industrial wastewater treatment with several full-scale AnMBRs already treating wastewater from food processing industries (Dereli et al, 2012). The deposition and accumulation of particles on the surface and in the membrane pores, generally designated as “fouling,” causes a reduction in the permeate flux. Lower fluxes translate into higher membrane surface requirements, which leads to increased construction costs, taking into account that membranes represent a significant amount in the total cost of an AnMBR (Lin et al, 2013). Several papers report the use of adsorbents, coagulants, and flocculants, usually called flux enhancers, to decrease membrane fouling and to increase the operational flux in membrane bioreactors. Cationic polymers, such as commercial synthetic polymers composed of Polydiallyldimethylammonium chloride (polyDADMAC), have been successfully used as flux enhancers in both aerobic and anaerobic membrane bioreactors. The effect of flux enhancers on the biological activity in anaerobic conditions needed further study
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