Effects of the incorporation of drinking water sludge on the anaerobic digestion of domestic wastewater sludge for methane production Available to Purchase

Water purification and wastewater treatment generate sludge, which must be adequately handled to prevent detrimental effects to the environment and public health. In this study, we examined the influence of the application of settled sludge from a drinking water treatment plant (S_DWTP) on the anaerobic digestion (AD) of the thickened primary sludge from a municipal wastewater treatment plant (S_WWTP) which uses chemically assisted primary treatment (CAPT). On both plants the primary coagulant is ferric chloride. The study was performed at laboratory scale using specific methanogenic activity (SMA) tests, in which mixtures of S_WWTP–S_DWTP with the ratios 100:00, 80:20, 75:25, 70:30 and 00:100 were evaluated. Methane detection was also performed by gas chromatography for a period of 30 days. Our results show that all evaluated ratios that incorporate S_DWTP, produce an inhibitory effect on the production of methane. The reduction in methane production ranged from 26% for the smallest concentration of S_DWTP (20%) to more than 70% for concentrations higher than 25%. The results indicated that the hydrolytic stage was significantly affected, with the hydrolysis constant K_h also reduced by approximately 70% (0.24–0.26 day⁻¹ for the different ratios compared with 0.34 day⁻¹ for the S_WWTP alone). This finding demonstrates that the best mixtures to be considered for anaerobic co-digestion must contain a fraction of S_DWTP below 20%.