Ann: Fluence awarded first Aspiral Project in the Philippines, page-34

Robert Baffrey is head of Manila Water's wastewater operations. You can read about the difficulties of a private company trying to build new pipe infrastructure in a built up city where there was none previously.
https://www.adb.org/features/robert-baffrey-dealing-manilas-dirty-water

Highlights:
The first and most ideal strategy is the establishment of separate systems, with dedicated pipes connecting households and our Sewage Treatment Plants (STPs). This is a very difficult undertaking, as it requires very large lengths and depths for pipes-making construction, and subsequently customer resistance, a hindrance to implementation.
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Our third strategy is the combined sewer-drainage system. Since pipe-laying for separate sewer systems is prohibitive, the most viable method to stop wastewater from entering the river systems is to intercept existing drainage canals.
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The separate system is the most ideal and highest form of wastewater treatment. But as I said, in a mega-city where development and urbanization has severely outpaced the provision of sewer infrastructure, innovative yet effective methods need to be employed to have an immediate impact in providing service.
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As we are moving into full-scale implementation of sewerage and sanitation services, we are learning a lot about how to effectively deliver these types of services in a highly urbanized yet developing city. One of the main issues is basically land acquisition for STPs. It is very difficult to find an open area of land, especially for sewage treatment, in Metro Manila. Pipe-laying is also very difficult. Sewer pipes rely on gravity, which means they have to be laid at much deeper depths. Trenches should be much wider. Unlike water supply pipes that are pressurized, sewer pipes need to maximize gravity flow to reduce operational costs.
Apart from this, acquiring customer acceptance and local government support is also a key challenge in implementing sewerage projects. As such, we've endeavoured to have an effective interaction and discourse with the local governments and agencies. We've found this to be the key to almost every successful project, which we of course combine with a good information-education campaign with the surrounding residents.
From an operational perspective, another challenge is solid waste, which enters our combined systems through drainage canals. We're not actually mandated to haul and treat solid waste as part of our concession, so we have to rely on cooperation with local governments to address this issue as well. Another aspect we find difficult, which is common for all sewer systems but is even more difficult in combined sewer systems, is the variability of influent to our STPs. We have to closely monitor our processes and make sure our personnel have the best training available in order to make sure our treatment plants continue to comply with effluent standards.
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In terms of New York/Paris/etc, hopefully they go with the simple option of dropping a SUBRE unit into their existing WWTPs to increase existing capacity and efficiency, before they give up on maintaining old infrastructure and put in new government mandates that all new buildings need to install their own on-site treatment facilities.