Wastewater Treatment Practice Flashcards

These flashcards cover the vocabulary and core concepts of wastewater treatment stages, including preliminary, primary, secondary, and tertiary processes as discussed in ENVENG 200.

Preliminary Treatment

The initial stage of wastewater treatment involving screening and grit removal to remove large debris and abrasive materials to protect downstream equipment.

Primary Treatment

The second stage of treatment focused on the sedimentation of suspended solids (SS) under gravity, typically removing approximately $60\%$ SS and $30 \text{--} 35\%$ BOD.

Secondary Treatment

A biological treatment stage used to remove organic pollutants (BOD) and excess microorganisms through aerobic oxidation and sedimentation.

Tertiary Treatment

Advanced treatment processes such as nutrient removal (nitrogen and phosphorus) and disinfection, used to meet strict consent limits or enable water reuse.

Bar Screens

Manual or mechanical devices used in preliminary treatment to remove items like rags, plastics, wood, and trash.

Grit

Dense, inorganic inert material such as sand, gravel, cinders, or other heavy solids that can cause abrasive wear to pumps and accumulate in pipelines.

Equalization Basin

A tank designed to provide flow and waste strength stability, dampen pH fluctuations, and dilute toxic substrates to improve downstream process reliability.

Primary Clarifiers

Large tanks where wastewater flow slows down to allow heavier solids to settle as primary sludge and floating matter to be skimmed off as scum.

Suspended Growth Systems

Biological treatment processes, such as activated sludge systems, that use microbes kept in suspension to oxidize organics.

Attached Growth Systems

Treatment processes like trickling filters where a biofilm develops on a media surface (rocks or plastic) to degrade organic matter.

Activated Sludge Process

A system where wastewater, return sludge, and air are mixed in an aeration tank so microbes can oxidize BOD, followed by settling in a secondary clarifier.

RAS (Return Activated Sludge)

Microbes that are settled in the secondary clarifier and recycled back into the aeration tank to maintain the biological process.

WAS (Waste Activated Sludge)

Excess biomass removed from the secondary treatment process to be sent for sludge handling and disposal.

Nitrification

The aerobic biological process of converting ammonia to nitrate via the sequence ${NH_4}^+ \rightarrow {NO_2}^- \rightarrow {NO_3}^-$.

Denitrification

The anoxic biological process where nitrate (${NO_3}^-$) is converted into $N_2$ gas, requiring a carbon source.

Phosphorus Accumulating Organisms (PAOs)

Special bacteria used in biological phosphorus removal that store phosphorus within their cells.

Chemical Precipitation

A phosphorus removal method involving the addition of $Al^{3+}$ or $Fe^{3+}$ salts to form insoluble phosphate compounds.

Chlorination

A common disinfection method that is effective and leaves a residual, but may involve chemical handling concerns.

UV Disinfection

A disinfection method using shortwave light (typically $253.7\,nm$) to dissociate DNA within living cells, preventing reproduction without leaving chemical residues.

Ozonation

A strong oxidant method for disinfection that is complex and costly but effectively protects public health.

Hydrogen Sulphide ($H_2S$)

A gas produced in anaerobic zones and sludge handling that causes a characteristic rotten egg smell.

Sludge Handling

The process of stabilization, dewatering, and disposal or reuse of solids removed during wastewater treatment.