Infiltration. The quantity of groundwater which enters a sewer pipe through faulty joints, porous walls
Inflow. Includes storm flows and non-contaminated flows such as cooling water which are diverted to a
separate sanitary sewer. Can cause sewer overflows and overloading of treatment facilities.
Ion Exchange. The reciprocal transfer of ions between a solid and a solution surrounding the solid.
Ionization. The process by which, at the molecular level, atoms or groups of atoms acquire a charge by
the loss or gain of one or more electrons.
Land Application (Land Spreading or Land Treatment). Disposal of wastewater by discharge to the land
(such as irrigation) or disposal of waste sludge by spreading on the land.
Life Cycle Costs. All cost applicable to a facility over the period of its useful life. Such costs include
fixed charges such as depreciation, interest, taxes, and insurance as well as operating expenses, labor,
maintenance and supplies.
Vitrification (Nitrogen Conversion). The conversion of nitrogenous matter into nitrates.
Nitrogen, Ammonia (NH3-N). A measure of the amount of nitrogen which is in the form of ammonia.
Expressed in mg/L as N.
Nitrogen, Kjeldahl (Total Kjeldahl Nitrogen or TKN). A measure of nitrogen combined in organic and
ammonia forms. Expressed in mg/L as N.
Nitrogen, Nitrate (N03-N). A measure of the amount of nitrogen which is in the form of nitrate.
Expressed in mg/L as N.
Nitrogen Removal. Unit operations and unit processes required to remove different forms of nitrogen
from a water. This may be accomplished partially in a biological process used in secondary treatment;
however, normally it entails subsequent aerobic and anaerobic processes, ammonia stripping, chlorination
or other similar steps.
Package Plant. A treatment plant, pumping station or major functional part thereof which has been
pre-assembled prior to delivery for installation.
pH. A measure of the intensity of acid or alkaline condition of the solution. The logarithm of the
reciprocal of the hydrogen ion concentration. In an aqueous solution, neutral pH is 7.0, alkaline pH
greater than 7.0, and acid pH less than 7.0. pH differs from alkalinity and acidity which measure the
capacity of a solution to provide hydrogen or hydroxylions.
Phosphatizing. Application of a phosphate-bearing coating to a metal part as a corrosion inhibitor and/or
as a base for other coatings.
Phosphorus Removal. The process of removing phosphorus from the wastewater by precipitation,
adsorption or biological means.
Physical-Chemical Treatment (PCT). A combination of unit operations arranged to achieve treatment
equivalent to conventional secondary biological treatment. Basically suspended solids are removed by
addition or a coagulant and coagulant aid followed with a clarification step achieved by settling. The
effluent may be filtered to ensure essentially complete suspended solids removal. Dissolved organic
pollutants are removed in a subsequent activated carbon unit.
Pickling. The treatment of a metallic material or part with acid to remove surface oxide.
Pond. An engineered impoundment containing raw or partially treated wastewater in which aerobic
and/or anaerobic stabilization occurs. Sometimes referred to as a lagoon.
Preliminary Treatment. Treatment operations such as screening, grit removal, comminution and
Pretreatment. Those treatment operations used at a point source or upstream from the wastewater
collection system. This is particularly applicable to industrial process wastewaters to eliminate
constituents such as grease or toxic materials which may adversely affect the collection system or
subsequent treatment processes.
Primary Treatment. Removal of waste constituents (suspended solids and BOD associated with the
settleable solids removed) by settling, usually without addition of coagulant or coagulant aids.
Raw Waste. Waste entering a treatment facility.
Reverse Osmosis. A process whereby water is forced to pass through semi-permeable membranes under
high pressures. Water passing through the membrane is relatively free of dissolved solids; solids are
retained in concentrated form on the feed side of the membrane and are wasted.
Secondary Treatment. A stage of treatment to perform additional waste constituent removal beyond that
provided by primary treatment. The most common form of secondary treatment is a biological process