Wastewater Treatment Systems for City-Based Municipal Drains for Achieving Sustainability

Currently, drains in several cities carry both rainwater and untreated greywater with black water from settlements nearby. In emerging economies, cities often become hubs of illegal and unauthorised colonies which thrive in the vicinity of stormwater drains. These create a unique pressure on the infrastructure and pose a challenge for civic bodies for ensuring adequate outflow quality as per environmental discharge norms. The flow characteristics (variable, seasonal, minimum or continuous flow) and structural constraints (the bed and site complexity) in the design of these drains restrict the options for implementing large wastewater treatment plants. In addition to the above, the techniques that rely heavily on structural, mechanical and energy inputs are economically not feasible and demand more maintenance, which acts as hindrances in these harsh environments. In these scenarios, human health is a critical factor, as frequent exposure to sewage without any protective equipment during maintenance could lead to health hazards and high-stress levels. The utilisation of decentralised and distributed wastewater treatment systems offers an in situ choice for achieving the desired result in quality and nutrient removal in the influent. These systems enable the water to be safely discharged to rivers or channelised for agriculture or industrial purposes. Furthermore, the solid fraction in the sewage is extracted as manure or composted after curing. The selection, design and implementation with maintenance are essential for improved efficiency and productivity of the system. Therefore, an investigation into such processes presently utilised, and a few other possibilities are discussed in this paper. This paper aims to establish various concepts and schemes that municipal corporations could adopt sustainably for efficient treatment within the limited spatial and temporal boundaries offered by city drains.