Due to rapid population growth and urbanization, ensuring adequate water availability and managing the generated wastewater is a significant challenge in developing countries with limited resources. Skewed distribution of freshwater sources, climate change-induced water scarcity and anthropogenic pollution are viewed as the key factors contributing to water scarcity. Reuse of wastewater and adherence to discharge standards in water bodies is crucial to ensure water security. However, effective and sustainable reuse is restricted by the limitations of the conventional centralized treatment plants, which are cost and energy-intensive, cause net positive greenhouse gas emissions and are vulnerable to the impacts of climate change. Additionally, they have limited serviced area, and the treated water quality with respect to nutrients and emerging contaminants is poor, resulting in health impacts and ecosystem imbalances. Inadequacy in treatment infrastructure, therefore, leads to a considerable amount of sewage getting discharged untreated into drainage channels, polluting water bodies and endangering future water availability. In this context, in-stream treatment within drains using nature-based engineered systems is an attractive option. This study proposes a hybrid sequential treatment involving anoxic biofilm, aerobic biofilm and hydroponic floating wetlands, followed by tertiary electrochemical treatment. Each stage was optimized for operational parameters through batch and continuous flow studies. Attached growth processes were studied in terms of support material, biofilm growth and pollutant removal under anoxic and aerobic conditions. Native microbial communities in wastewater form biofilms and the need for external aeration in the aerobic system was overcome by adopting passive photosynthetic aeration of algae-bacteria consortia. Hydroponic floating wetland was configured using a local plant species and was self-adaptive to the fluctuations in the water depth in drains. Tertiary treatment for the removal of pathogens and emerging contaminants will be done by electrocatalysis. Finally, the results from these lab-scale optimization studies will be integrated to evaluate the field-scale efficiency of the proposed in-situ treatment system.