Glossary

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Term	Definition
Alkalinity	The ability of a water sample to react with and neutralize an input of acid; also referred to as acid neutralizing capacity (ANC).
Backwash	The process of pumping water upward through a filter to flush captured particles out of the filter media.
Baffles	Obstructions in the channel of a flocculator that restrain flow in a particular direction.
Buffer	A solution containing a weak acid-base pair that resists pH change by maintaining its hydrogen ion concentration.
Capture Velocity	The velocity of the slowest settling particle that a clarifier can reliably capture.
Chlorination	The process of disinfection in water treatment that uses chlorine compounds to kill bacteria, viruses, and microbes.
Coagulant	A sticky substance added to water to enable particle to attach to each other.
Collision Potential	A measure of the potential for particles in a fluid to hit each other, serving as a performance metric for flocculators with higher values representing better flocculation; the dimensionless product of velocity gradient and residence time.
Constant Head Tank	A container that uses set differences in elevation and a float valve to ensure constant flow.
Control Volume	An imaginary 3-dimensional space with fixed boundaries that remain at steady state.
Diffusion	The net movement of a fluid from an area of higher concentration to an area of lower concentration.
Dose	The concentration of a chemical being added to water undergoing treatment.
Driving Head	An elevation difference that causes a fluid to flow.
Eddy	The swirling of a fluid in turbulent flow that moves in a direction different from the surrounding flow.
Energy Dissipation Rate	The amount of energy lost from viscous forces in turbulent flow; equivalent to head loss in a reactor.
Floc	A cluster of colloidal particles formed through collision and adhesion in the processes of coagulation and flocculation.
Floc Filter	A fluidized layer of flocs that is maintained in the bottom of an upflow clarifier.
Floc Hopper	The collection area in a clarifier where flocs accumulate after overflowing from the floc filter.
Fractal	A geometric structure in which each part shares the characteristics of the whole, forming the same pattern at any scale.
Friction Factor	A dimensionless quantity approximating the magnitude of friction between a fluid and pipe wall, for use in the Darcy-Weisbach equation of major head loss.
Head Loss	Reduction in the energy of a fluid as it flows through a system, including major and minor losses.
Hydraulic Head	The energy of an incompressible fluid expressed as a unit of length representing the height of the fluid in an equivalent static column; the sum of the pressure and elevation terms in the energy equation.
Inner Viscous Length Scale	The order of magnitude where the kinetic energy of small eddies is dissipated by the fluid’s resistance to deformation.
Kolmogorov Length Scale	The order of magnitude where the kinetic energy of turbulence is dominated by viscosity.
Laminar Flow	Fluid particles moving in smooth and highly ordered layers with minimal lateral mixing; flow with a Reynold’s number less than 2,100.
Linearity Error Ratio	The amount of acceptable error in the linear relationship between head and flow.
Major Loss	Energy lost through friction between a fluid and material surfaces.
Minor Loss	Energy lost through the expansion of flow, often pipe fittings.
Obstacles	Obstructions formed by half-pipes that were created by AguaClara to add extra head loss between baffles in a flocculator channel, which makes it possible to design smaller flocculators without compromising efficiency.
Organic Matter	Carbon-based compounds found in the environment.
pH	A measure of the acidity and basicity of a solution, ranging from 0 (acid) to 14 (basic), with neutrality at 7.
Piezometric Head	See Hydraulic Head.
Plate Settlers	A series of inclined plastic sheets that provide a large effective area for particles to accumulate in a clarifier.
Porosity	The ratio of empty volume between individual particles and the total volume of a material.
Precipitation	The process by which a dissolved substance in an aqueous solution forms an insoluble solid.
Residence Time	The amount of time that a fluid spends in a control volume.
Reynolds Number	The ratio of inertial to viscous forces acting on a fluid, indicating that the fluid’s movement is dominated by laminar flow (low Re) or turbulent flow (high Re).
Settling Velocity	The speed of a particle falling at terminal velocity in a still fluid.
Shear	A type of fluid flow where parallel layers move at different speeds.
Streamline	A line that is parallel to the local velocity vector at all points; the path that a particle would take if it could be placed in the fluid without changing the original flow.
Suspension	A heterogeneous fluid mixture containing particles.
Sutro Weir	A rectangular overflow dam sides that curve parabolically outward at the base causing discharge flow to be proportional to head; also referred to as a proportional weir.
Terminal Velocity	The maximum velocity of a particle falling through fluid, achieved when the drag and buoyancy forces equal gravity.
Turbidity	The optical clarity of water, measured by light scattering off suspended solid particles; turbidity is low in clear water and high in cloudy water.
Turbulent Flow	Fluid particles moving in disordered paths due to chaotic changes in velocity and pressure that lead to mixing; flow with a Reynold’s number greater than 2,100.
Velocity Gradient	A measure of fluid deformation defined by how quickly one point of water along one streamline moves in comparison to another point on another streamline, taking into account the distance between the streamlines.
Vena Contracta	A point of contracting flow with the minimum cross sectional area and maximum velocity.
Viscosity	The resistance of a fluid to flow or deformation, also referred to as the “thickness” of liquid, related to the force applied (dynamic viscosity) or velocity of movement (kinematic viscosity).