Issues of Sustainable Sludge Handling and Management in the Wastewater Sector: A Review

The activated sludge contains various types of contaminants in the form of pathogens, heavy metals, and different kinds of organic pollutants, which poses a potential threat to human health and produces various gases that directly or indirectly deplete the environment. The increment in this sludge production has taken place in every sector, as in domestic and industrial sectors. This study discusses various methods of treating, handling and managing wastewater sludge in the domestic and industrial sectors. Sludge handling is quite a hard task for management purposes. So, in this review, we are comparing different sludge handling techniques which include Filter press, Dissolved Air Flotation (DAF), Centrifuging process, etc. In this process, Sludge characteristics varies from domestic and industrial sludge. Suitable treatment methods need to be considered for domestic sewage as well as industrial sewage. Because of its less calorific value, domestic sewage is used for biogas production, landfilling for agricultural applications, composting and cap of landfill process at last. For industrial sludge, because of its high calorific value, toxicity and ignitability, it can be used as co-fuels for boilers, or it is used for the incineration process. The impact of these issues is decided by the level of global warming and various acidic and eutrophic consequences. Moreover, handling of sludge is challenging as it requires ample space, materials and energy, which is generally unavailable in urban areas. Besides this, biogas recirculation is also an option for the treatment of sludge, which boosts the production of Methane gas. As CPCB 2015, India was generating over 62,000 MLD of sewage. For the 20,120 MLD of sewage that was treated, 3157 MLD of sewage is now being treated at certain proposed and under construction facilities, and 38 722 MLD of sewage is not being treated at all. Around 3955,000 metric tonnes of dry sewage sludge would be produced annually after comprehensive sludge treatment. Therefore, it is important to handle this sludge carefully. Most of the generated sludge is dumped at landfills. In India, there are not enough facilities for managing or treating sludge. While some WWTPs have anaerobic digesters for sludge, most of them flare the biogas generated.