Author – Ben Howard (Engineering Designer)
Wastewater is vitally important to us all. Unfortunately wastewater treatment is in a sad state of affairs with only around 20% of the world’s wastewater currently being treated. For countries with limited infrastructure treating wastewater is too expensive and for others it may also be culturally embarrassing to process human waste. This article will focus on the following aspects:
- Wastewater and H2S (Hydrogen Sulfate)
- Wastewater and the Environment
WasteWater and H2S
When Wastewater is subject to anaerobic conditions (not enough oxygen) wastewater becomes septic and produces hydrogen sulfate gas (H2S), giving off a “rotten egg” smell. Usually, a manhole (concrete structure) is only partially filled with wastewater, the damp surface above the wastewater line contains bacteria that oxidize the H2S thus producing sulfuric Acid (H2SO4), sulfuric acid is really bad for concrete because it dissolves the calcium carbonate that’s key in the concretes strength, the corrosion on the concrete pipes usually near the crown ( Top of pipe) can make the concrete brittle eventually causing the pipe or manhole to collapse.
Engineers use coatings to protect the concrete from sulfuric acid. My colleague recently used a PE ( poly-ethylene) coating to prevent corrosion of a manhole.
Wastewater and the environment
Before wastewater can safely be released into the ecosystem the bulk of the harmful compounds need to removed to make the wastewater safe for the environment. the main two measures of wastewater quality are BOD (biological oxygen demand) and TSS ( total suspended solids) in New Zealand we require BOD to be no more than 20 Mg/L and TSS be no more then 30Mg/L, some systems produce much better results than others, for instance, a membrane filtration system ( A film that filters the wastewater as it passes)
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Sources : https://www.wwdmag.com/