Effects of pretreatments on thickened waste activated sludge and rice straw co-digestion: Experimental and modeling study

Abstract In order to maximize the biogas production from thickened waste activated sludge (TWAS), co-digestion of TWAS and rice straw (RS) was studied and the application of thermal/thermo-alkaline and NaOH/H 2 O 2 to TWAS and RS, respectively, was evaluated. The batch experiments were conducted at three different TWAS/RS (volume basis) ratios of 1:3, 1:1 and 3:1, respectively. Furthermore, the modified Gompertz model was introduced to predict the biogas yield and evaluate the kinetic parameters. The highest biogas production (409.2 L/kg VS added ) was achieved from co-digestion of TWAS thermo-alkaline and RS NaOH at mixing ratio of 1:1, which is greater by 42.2% and 5.9% than that of digesting TWAS thermo-alkaline , and RS NaOH alone, respectively. The highest VS removal rate was obtained from the co-digestion of TWAS thermo-alkaline and RS NaOH at mixing ratio of 1:3, which is greater by 55.8% and 14.0% than those of mono-digestion. The modified Gompertz model (R 2 : 0.993–0.998 and 0.993–0.999 for mono- and co-digestions, respectively) showed a good fit to the experimental results and the estimated parameters indicating that the pretreatments and co-digestion of substrates markedly improved the biogas production rate.