What are all the different sewage treatments?
Secondary:
Settlement and filtration and microorganisms to remove solids and break down dissolved organic waste in sewage.
Tertiary:
Additional physical and chemical processes usually to target specific nutrients eg nitrates and phosphorus, fine particles, and incidentally (not by design) sometimes some microbes are reduced; Disinfection may be used but rarely is.
Quaternary(enhanced):
Adds advanced processes to remove contaminants (like PFAS and micropollutants eg medicine residues, microplastics) and, with disinfection, can eliminate remaining pathogens (microbes). Disinfection is very likely to be added.
Advanced wastewater treatment:
A set of enhanced treatment processes that cleans wastewater beyond conventional methods, removes difficult contaminants and produces high quality water that can be reused as drinking water.
Disinfection – a note – disinfection is how microbes/pathogens are removed from sewage. It is very rarely used in the UK at a tertiary level. It is something that must be part of any new sewage infrastructure.
And why do we care?
We care because it is more evident that even at tiny levels micropollutants can harm aquatic life, interfere with fish hormones, and build up in the environment over time.
We should also care because by not building improved sewage treatment we are wasting a potential source of drinking water for the future.
The sewage of today is not the same as the sewage of yesterday. We cannot continue to build to older standards.
At a glance: Tertiary vs Quaternary (enhanced) sewage treatment
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NOTE: We recognise that, as with all industrial type processes, there are issues with these enhanced and advanced processes: more chemicals are used, more carbon, more energy. Removing the full range of contaminants that are in sewage requires action at a wider level than sewage treatment works, starting with controlling at source; eg limiting the production of some PFAs in the first place and implementing the “polluter pays” principal to help pay for the cleanup.
There are solutions, but planning to build infrastructure that will dump more and more sewage containing more and more contaminants into waterbodies is not a solution.
Enhanced sewage treatment is not the only way to remove these contaminants but bearing in mind that it brings cleaner water to waterbodies and can make sewage water reusable, it must be part of the future package of improvements to sewage infrastructure.