(Source: Andreoli et al., 2007)
+++: Significant importance; ++: Moderate importance; +: Little or non-existent importance
↑: Volume increase
To generate pathogen-free sludge, operators must ensure that Salmonella, enteroviruses, and viable helminth eggs concentrations are below the present analytical methodology’s detection criteria. Other species are likely to be below the permissible limits if the quantities of these indicator organisms are kept under control (Bergwerff, & Debast, 2021). Viruses and helminths cannot reappear in the sludge after being inactivated, unless in the case of external recontamination, and if the sludge is sufficiently stabilized, ambient parameters (temperature and pH) are controlled, and there is no cross-contamination.
Assessment of sludge treatment and disposal alternatives
Sludge final disposal is influenced by the plant’s conceptual design, which influences sludge amount and characteristics, as well as unit activities such as sludge stabilization, dewatering, pathogen removal, storage, and handling. Due to poor planning, a lot of treatment facilities lack the basic infrastructure required for such operations, necessitating retrofitting in order to effectively operate the generated sludge (Spinosa & Doshi, 2021). Sludge processing and final technologies are selected based on the type, size, and location of the treatment facility (Wu et al., 2019). For the selection of processing and/or final disposal choices, there can be no fixed rule, but rather a careful analysis on a case-by-case basis to pick the best available option in terms of operational and economic issues. A flow chart of proper sludge disposal is shown in figure 4.