Sewage and Industrial Wastewater Treatment
Preliminary treatment - screens for large objects
Primary treatment - allow solids to settle
Secondary treatment - biological - microorganisms to eat organic contaminants dissolved in water.
Disinfection = kill microorganisms with chlorine / UV light
Tertiary treatment - advanced treatment. Filtration of fine particles, etc.
Industrial Strength Treatment
Industrial wastewater treatment is harder than municipal wastewater treatment.
Physical treatment: sedimentation, flotation, filtering, stripping, ion exchange, adsorption.
Chemical treatment: precipitation, oxidation with chemicals, reduction with chemicals, stripping.
Secondary treatment is usually biological
Some industrial wastewater rich in organics, other deficient.
Total dissolved solids = TDS = can be higher than levels in sewage.
Is waste always the same over time? Not if campaign manufacturing.
BOD = biochemical oxygen demand = biological oxygen demand = Amount of O2 needed for organisms to break down organic matter. Units = mg O2 / liter in 5 days of incubation at 20 degrees C
COD - chemical oxygen demand . Units = mg O2 / liter
Sometimes called mechanical treatment. remove colloidal solids, emulsified oil and a small portion of BOD and COD
1) Equalization tank. Acts as buffer. Smooths variations in flowrates and contamination loads. Concrete tank with coating.
2) Screening. Sedementation by gravity. Neutralization (i.e., pH adjustment), coagulation, flocculation and dissolved air flotation (DAF).
3) Coagulation and flocculation. Wastewater from the neutralization tank usually flows by gravity into coagulation tanks for removal of colloidal solids.
Uses microbes to destroy remaining dissolved organic material.
The water then goes to additional settling tanks (clarifiers) to remove more of the suspended solids.
The activated sludge process is the most common process. Trickling filters (which use moss or sludge) and artificial ponds enabling biological treatment are often part of the design.
Water quality can sound nebulous, but we try to articulate it in terms of measurable characteristics. We compare physical, chemical, biological, and radiological measurements to a set of standards and criteria. Water quality is context-specific; it depends on the intended use, and different people have different criteria. A public health official might be concerned about the pathogens in the water; fishermen might be concerned about whether water provides a habitat for fish.
Water quality is not just a consequence of what human technology has done to the water. Water quality is affected by natural causes, too.