Abstract
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•Effect of different substrate ratios of SS and IS was investigated on AD and ACoD.•The highest biogas production was achieved with the ACoD of 25%SS−75%IS.•Biogas increased by 29% and 493% compared to 100% SS and 100% IS, respectively.•Increasing the SS ratio in the mixture decreased the biogas production.•In general, after ACoD, the concentration of carbohydrates decreased but the sCOD increased.
Today, with the increase in industrialization, the disposal of organic sludge formed after industrial activities has started to pose a serious problem. For this reason, biogas production from such organic wastes under anaerobic conditions is very valuable in terms of both sustainable environmental policy and renewable energy recovery. In this study, the effects of mono-digestion and co-digestion of starch sludge (SS), industrial sewage sludge (IS), and wastewater (CIWW) from the cardboard manufacturing industry on the biogas production potential and the changes in parameters such as dissolved COD, carbohydrates and pH were presented. In addition, a pH-controlled study was carried out with the sample with the lowest final pH level (100% SS) after anaerobic fermentation. The mixtures were prepared to contain 100%SS, 100%IS, 100%CIWW, 75%SS-25IS, 66%SS-33IS, 50%SS-50%IS, 33%SS-66IS, and 25%SS-75%IS on a dry weight basis. The amount of biogas produced by 100%SS (257 mL) was almost 5 times greater than 100%IS (56 mL). The utilization of the CIWW together with SS and IS increased the biogas production potential approximately 10 times and 2 times, respectively. The highest biogas production was achieved with the anaerobic co-digestion (ACoD) of 25%SS and 75%IS as 332 mL. Under these conditions, biogas production increased by 29% and 493%, respectively, compared to mono-digestion of the substrates. As the SS ratio in the mixture increased, the pH value decreased due to VFA accumulation in the medium. In addition, there was a decrease of approximately 11% in biogas production. The soluble COD concentration of all mixtures increased after anaerobic fermentation except 100%IS. On the contrary, carbohydrate removal was observed in all reactors except 50%SS-50%IS mixture.