Substantiating the water demand in anaerobic digestion using sewage: a study using Ageratum conyzoides and Parthenium hysterophorus—an Indian perspective

Anaerobic digestion (AD) is a highly beneficial technique for managing organic solid waste and generating biogas as a by-product of energy production. However, preparing slurry from organic waste requires additional water, which can be challenging in regions with limited water resources, such as India. In this study, the use of domestic sewage as a substitute for water in the production of feedstock slurry for AD was explored. This approach addresses two crucial issues in developing countries: limited water resources and lack of sewage treatment, often resulting in untreated discharge into water bodies. This study employed cow dung as a source of inoculum and Ageratum conyzoides (AC) and Parthenium hysterophorus (PH) as the substrates. It was observed that a significant biogas yield of 3712 ± 34 mL for AC and 3900 ± 15 mL for PH was observed. Sequencing microbial composition in cow dung and sewage samples provided valuable information for further studies. The microbes in the cow dung were very diverse, whereas nearly 85% of the microbes in sewage are hydrolytic. The additional hydrolytic bacteria from domestic sewage help reduce the digestion period. It was observed that lignin degradation accelerated when sewage was used instead of water. The field emission scanning electron microscopy data shows higher structural degradation of organic matter when sewage is used in place of water. Overall, this study investigated the use of domestic sewage as a substitute for water in AD, and its findings on biogas production and microbial composition provided valuable insights into the field.