Water Quality Monitoring
Dissolved oxygen (DO) refers to the level of free, noncompound oxygen present in water, and is a critical factor in the capacity of an aquatic ecosystem to support living organisms. Two methods are used for the in-situ measurement of DO in surface waters: Winkler titration, membrane-covered electrochemical sensors (polarographic or galvanic cell), and luminescent-based optical sensors. Optical technology has quickly become
a preferred method for measurement of DO, due to accuracy advantages over electrochemical sensors when it comes to fouling and long-term drift.
pH and Redox Potential
The pH value describes the activity of hydrogen ions in aqueous solutions typically on a scale of 0 to 14, from which liquids are characterized as being acidic, alkaline or neutral. In environmental sampling and monitoring, high or low pH values can be indicative of pollution.
Oxidation-reduction potential (ORP) measures the ability of an aquatic environment to break down waste products, such as contaminants and dead plants and animals. The potentiometric method for measuring pH is used by most major sensors manufacturers.
Electrical conductivity can be used to determine concentration of solutions, detect contaminants and determine the purity of water. There are two types of conductivity
measurement: contacting and inductive. The choice of which to use depends on the amount
of conductivity, the corrosiveness of the liquid, and the quantity of suspended solids. The inductive method is generally better when the conductivity is high, the liquid is corrosive, or suspended solids are present. Conductivity, along with temperature, also allow for salinity values to be calculated through algorithms.
Turbidity is the measurement of water clarity. Suspended sediments, such as particles silt, clay and sand frequently enter the water from disturbed soils and can contain pollutants such as phosphorus, pesticides, or heavy metals which adversely affect the aquatic ecosystem. Turbidity sensors measure in either Nephelometric Turbidity Units (NTU) or Formazin Nephelometric Units (FNU). Due to the different light sources used in each of these measurements results are not directly comparable.