A World for Recycling

Technologies employed include the activated sludge process, which is the most commonly used method, as well as variants of pond and constructed wetland systems, trickling filters and other forms of treatment that rely on biological activity to break down organic matter.

An activated-sludge train usually is divided into an aeration section for BOD removal and nitrification, and an anoxic section for denitrification. In the aeration section, compressed air passes through the wastewater. Dissolved oxygen from the compressed air acts as a respiratory source for aerobic bacteria present in wastewater that decompose the organic load (expressed as BOD and COD) and ammonia to carbon dioxide and nitrates, respectively. In the anoxic section, bacteria use the oxygen in nitrates as a respiratory source, thus converting the nitrates to nitrogen gas.

Denitrified wastewater from the anoxic tank flows downstream to the aeration (or BOD-removal) tank where aerobic bacteria decompose the organic load and ammonia present using dissolved oxygen supplied by air blower(s).

The treated effluent from the aeration tank usually flows by gravity to a secondary clarifier, which most often is a gravity clarifier. Here, sludge is removed from the treated effluent, which then passes to tertiary treatment.

Tertiary treatment

Tertiary treatment usually involves filtration systems such as disc filters, reverse osmosis (RO) units

The Fenton process can remove non-biodegradable COD. The Fenton section usually consists of dosing systems for hydrogen peroxide and ferrous sulfate.

A coagulant solution (typically polymer based) usually is injected automatically by dosing pumps ("1+1" configuration)

Coagulation is a quick process, requiring a relatively low retention time of 2–5 min.

Wastewater from coagulation tanks most often flows by gravity into the flocculation system (tanks) where agglomeration of flocculent formed during coagulation process takes place. Anionic polymer usually serves as flocculent.

Wastewater from flocculation passes by gravity into a DAF clarifier system.

Disinfection

Liquid disinfectants like phenolic compounds, hydrogen peroxide liquid, quaternary ammonium compounds, formaldehyde, glutaraldehyde, iodophor, blend of peracetic acid and hydrogen peroxide, bleach and sodium hypochlorite enlisted by EPA(Environmental Protection Agency), FDA (Food and Drug Administration) and WHO are used in industrial, commercial and medical facilities to eradicate microbial pathogens. Some disinfectants e.g. glutaraldehyde are broad-spectrum and kill a variety of microorganism. A liquid sterilant like ethylene oxide can kill or destroy all microbial pathogens including spores. Disinfectants played an integral role in the outdoor environments to control microbial pathogens.