Introduction
The underground world of sewers is often out of sight and out of mind, yet it plays a critical role in the maintenance of public health and environmental quality. Many sewer systems around the globe have been in operation for decades, if not centuries, and are in desperate need of rehabilitation. Successfully renovating these systems can lead to improved efficiency, reduced pollution, and better service for a growing population. This article will explore various case studies where sewer makeovers have resulted in significant successes.

Case Study 1: London’s Victorian Sewers
Historical Challenge
London’s sewer system, designed by Sir Joseph Bazalgette in the mid-19th century, was an engineering marvel of its time. However, with the exponential growth of the city, these Victorian sewers became overburdened, leading to inefficiency and environmental hazards.

Rehabilitative Strategy
The solution came in the form of the Thames Tideway Tunnel, a massive project aimed at preventing sewage overflow into the River Thames. Using tunnel-boring machines, a 25 kilometer ‘super sewer’ was constructed, significantly increasing capacity.

Impact and Outcome
Since its completion, the project has been praised for drastically reducing pollution in the Thames and enabling the Victorian sewers to cope with modern demands, preserving this historical infrastructure.

Case Study 2: The Milwaukee Metropolitan Sewerage District
Flooding Fiascos
In Milwaukee, antiquated sewers were prone to overflows, flooding homes and streets while also polluting Lake Michigan.

Innovative Response
The district invested in the ambitious Milwaukee Metropolitan Sewerage District’s Water Quality Initiative. This initiative included the construction of an 18-mile-long underground storage tunnel and the implementation of green infrastructure.

The Results
The efforts have drastically reduced the amount of untreated sewage discharge into natural water bodies and have cut down on flood events, proving the effectiveness of combining traditional and green infrastructure in sewer system rehabilitation.

Case Study 3: Singapore’s Deep Tunnel Sewerage System
Facing Space Constraints
Singapore’s limited land area posed unique challenges for sewer system expansion. Traditional methods were no longer viable in the island-city.

Innovative Underground Engineering
Singapore’s answer to this problem was the creation of the Deep Tunnel Sewerage System (DTSS), an integrated project with deep tunnel sewers linking to centralized water reclamation plants.

Transformative Effects
The DTSS has conserved valuable above-ground space, supported water recycling efforts, and provided a scalable solution to Singapore’s sewerage needs.

Case Study 4: The Los Angeles Sewer Rehabilitation
Aging Infrastructure
Los Angeles faced a dire situation with its aging and deteriorating sewer infrastructure, which put the city at risk of major spills and environmental damage.

Focused Rehabilitation Program
Over a period of decades, the city committed to an aggressive sewer rehabilitation program that utilized cutting-edge technologies such as cured-in-place pipe (CIPP) lining and trenchless replacements to modernize its sewer system.

A Model for Others
The program not only extended the life of the existing pipes but also served as a model for other municipalities on managing large-scale infrastructure updates in a cost-effective and minimally disruptive manner.

Conclusion
Sewer makeovers are complex, expensive, and require long-term planning, but as these case studies illustrate, the successes they yield can provide monumental benefits for urban environments and ecological systems. By adopting innovative solutions and best practices from around the world, cities can effectively manage their sewer rehabilitation projects and ensure that their infrastructures meet the needs of future generations.