Course TEN-702 Industrial waste management unit-2 Lecture -8 & 9

Physical unit operations Treatment methods in which the application of physical forces predominates are known as physical unit operations. Because most of these methods evolved directly from man’s first observations of nature, they were the first to be used for wastewater treatment.  Screening,  mixing,  flocculation,  sedimentation,  flotation,  filtration, and  gas transfer are typical unit operations.

Screening Bar racks and screens of various description Grit Removal Removal of inorganic suspended solids Grit chamber Removal of large floating, suspended and settleable solids

Chemical Unit Processes Treatment methods in which the removal or conversion of contaminants is brought about by the addition of chemicals or by other chemical reactions are known as chemical unit processes.  Precipitation,  adsorption, and  disinfection are the most common examples used in wastewater treatment. In chemical precipitation, treatment is accomplished by producing a chemical precipitate that will settle. In most cases, the settled precipitate will contain both the constituents that may have reacted with the added chemicals and the constituents that were swept out of the wastewater as the precipitate settled. Adsorption involves the removal of specific compounds from the wastewater on solid surfaces using the forces of attraction between bodies.

Biological Processes Treatment methods in which the removal of contaminants is brought about by biological activity are known as biological unit processes. Biological treatment is used primarily to remove the biodegradable organic substances (colloidal or dissolved) from wastewater. Basically, these substances are converted into gases that can escape to the atmosphere and into biological cell tissue that can be removed by settling. Biological treatment is also used to remove nutrients (nitrogen & phosphorus) from wastewater. With proper environmental control, wastewater can be treated biologically in most cases.

Pretreatment Goal is to prepare raw influent wastewater for treatment Pretreatment can involve: –Removal of large solids and rags –Removal of grit –Equalization of high flow and loads (important) –Odor control –Chemical Addition

Pretreatment Removal of large solids and rags –Why would this be important? –Can plug downstream equipment –Decreases cleaning effort

Types of pretreatment include: –pH neutralization –Temp regulations –Solids separation –Toxic metal removal –Oil and grease Pretreatment Program Implementation

Pretreatment - Screens Screens are used to remove solids and rags Simplest is manual, coarse bar screen Used at smaller plants Often outdoors Screen opening of 1” to 2”

Pretreatment - Screens Mechanical fine screens are used at larger plants Need to install inside building Common screen opening size is ¼” (6 mm) – Membrane biological reactors (MBRs) can require 0.06” openings (1.5 mm) Includes motors, controls Many types Typically includes a washer and compactor

Pretreatment - Screens Basket type mechanical fine screen, 4.6 MGD Compactor is integral with screen Note manual coarse bar screen in background

Pretreatment - Screens Large mechanical fine screen, 9 MGD Influent flow channel is on floor below Note “plug” of screenings going into green basket

Pretreatment - Screens Other screens –Static screen on left –Rotary drum screen on right Compactor in between

Assignment-1 Discuss the philosophy behind industrial wastewater treatment with reference to wastewater quality characteristics, standards, unit processes and process train.

Assignment-2 Write a short note to clearly bring out the difference between disposal, reuse and recycling of industrial wastewater.

Thanks! In next lecture we will discuss grit removal, equalization, odour control