Domestic wastewater is a complex mixture of organic and synthetic compounds.
Its overall strength is typically assessed using indicators like BODโ
(Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), and TOC (Total Organic Carbon). Within this mix are readily biodegradable substances such as sugars, starches, and proteins. Although FOG components degrade more slowly due to their low solubility, microbial communities can break them down over time. In contrast, a smaller fraction of the influent consists of persistent, recalcitrant chemicals that resist biological treatment. These include pharmaceuticals, pesticides, surfactants, and other synthetic compounds that often bypass conventional processes and enter receiving waters, posing long-term environmental risks.
Chemical Categories & Why They Persist
| ๐งด Category | ๐ก Examples | ๐งฌ Why They Resist |
|---|---|---|
| Pharmaceuticals | Ibuprofen, antibiotics, hormones | Complex molecular structures |
| PFAS | Non-stick coatings, waterproof sprays | Strong carbon-fluorine bonds |
| Pesticides & Herbicides | Glyphosate, atrazine | Low biodegradability |
| Personal Care Products | Triclosan, synthetic musks | Stable chemical structures |
| Plasticizers | Phthalates in cosmetics, detergents | Recalcitrant, accumulate in sludge |
| Flame Retardants | PBDEs in furniture, electronics | Chemical stability, low solubility |
| Surfactants | Nonylphenol ethoxylates in cleaners | Resist microbial degradation |
| Siloxanes | Cyclic siloxanes (e.g., D5) in shampoos, deodorants | Volatile, slow to biodegrade |