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Water Quality

Citation

Modified from: Kenimer, Ann L., J. Villeneuve and S. Shelden. 2005. Fundamental Concepts: Water Quality - Power Point Presentation. in (M.A. Gross and N.E. Deal, eds.) University Curriculum Development for Decentralized Wastewater Management. National Decentralized Water Resources Capacity Development Project. University of Arkansas, Fayetteville, AR.

  • Standard Methods for the Analysis of Water and Wastewater. American Water Works Association and the American Public Health Association.
  • EPA Methods and Guidance for the Analysis of Water. US Environmental Protection Agency.

Water Pollution

  • Water Pollution: any condition that adversely affects the quality of streams, lakes, oceans, or groundwater
  • Unpolluted water has a wide diversity of aquatic organisms and contains enough dissolved oxygen
  • Polluted water inhibits the growth of aquatic organisms

Water Quality Terms

  • Water resource uses
  • Swimming
  • Boating
  • Fishing / fish consumption
  • Shellfish harvesting
  • Aquatic habitat
  • Water supply
  • Humans
  • Animals

  • Water use impairment- the inability of a resource to meet it’s intended uses
  • For example, an estuary is impaired when high levels of bacteria ban the harvesting of oysters.

Importance of Organic Matter

  • Organic material consumes oxygen in water during decomposition
  • Organic material can cause taste and odor problems in recreational and drinking water
  • Some material may be hazardous

Dissolved Oxygen

  • Dissolved oxygen is oxygen that has been incorporated into water
  • Many aquatic animals require it for their survival < 2 mg/L most fish cannot survive, 4+ mg/L is ok
  • Often measured in-situ with field meters and loggers

Dissolved Oxygen

There are two important factors that can influence the amount of dissolved oxygen present

  • Water temperature
  • Greater temperature  Lower saturated DO
  • Lower temperature  Greater saturated DO
  • Organic matter
  • If oxygen is available, organic material requires oxygen to decompose
  • Organic material may also decompose in the absence of oxygen
  • More organic material requires more DO, and will tend to deplete water of DO

Biochemical Oxygen Demand

  • Biochemical oxygen demand, or BOD is the amount of oxygen used by organisms during the breakdown of organic material
  • BOD is considered an indirect measure of the organic content of a sample
  • BOD analysis is done under these conditions:
  • Must be in the dark
  • Must be at 20ºC
  • Must have an excess of nutrients

BOD5 Procedure

  • Collect sample in a bottle, once in lab add nutrients, maybe seed (microorganisms), and oxygenated distilled water
  • Measure initial DO
  • Incubate sample for 5 days at 20o C in dark
  • Measure final DO
  • The BOD5 is directly related to the amount of DO used up over the 5-day period

BOD

  • BODt = BOD at t days (mg/L)
  • DOi = Initial DO (mg/L)
  • DOf = Final DO (mg/L)
  • Vs = Volume of sample (L)
  • Vb = Volume of BOD bottle (L)

Chemical Oxygen Demand (COD)

  • COD is the equivalent amount of oxygen needed to break down organic matter and oxidize nitrogen compounds using strong oxidizing agents
  • Another means of measuring oxygen demand needed to oxidize organics and reduced nitrogenous compounds
  • Faster than BOD
  • Always higher than BOD
  • COD is much higher than BOD in raw wastewaters
  • COD:BOD ratio is usually less than 2:1 in treated effluents
  • COD:BOD ratio is dependent on circumstances and reduces with treatment

Total Organic Carbon

  • Total organic carbon, or TOC, is the amount of organic carbon bound in a sample.

Fats, Oil, and Grease

  • Generally listed under one heading called FOG (fats, oils, and grease) as it is often not important to know the exact make-up of this group of components

Solids

Cause many problems:

  • May clog distribution systems, pipes, tanks, causing wastewater back-up in home
  • Fill storage areas in trenches
  • Reduce infiltrate rate of soil, and may cause surfacing of wastewater

Total Solid (TS)

  • Total solids of a sample is the matter left behind after drying a sample of water at 105ºC

There are two ways that solid materials may be classified

  • Suspended solids and dissolved solids (size)
  • Volatile solids and fixed solids (organic or mineral)

Solids

  • Total suspended solids are the part of the sample that may be caught with a 0.45 µm filter
  • Total dissolved solids are the part of the sample that will pass through the filter

  • Total volatile solids is the portion of the sample lost after the sample has been heated to 550ºC. It is an approximation of the organic material present
  • Total fixed solids is the portion that still remains after heating. It is an approximation of the mineral matter present

Solids

  • These categories may be combined:
  • Volatile dissolved solids (VDS) (small, organic)
  • Volatile suspended solids (VSS) (large, organic)
  • Fixed dissolved solids (FDS) (small, mineral)
  • Fixed suspended solids (FSS) (larger, mineral)

Nutrients

Problems associated with excess nutrients:

  • Causes an increase in productivity of aquatic plants (organic matter), leading to depleted DO levels
  • May cause odor problems
  • Extra vegetation near surface may inhibit penetration of light into water

Nutrients

  • Nitrogen
  • Phosphorus
  • Required for plant life
  • In excess can promote too much plant life (algal blooms)
  • Brackish waters : usually N limited (0.1 to 1 mg/L mg/L or greater may stimulate blooms)
  • River in-stream processes reduce and transform N before reaching estuary, denitrification and plant uptake in marshes reduces N
  • Fresh waters: usually P limited (0.02 mg/L or greater may stimulate blooms)
  • P often bound to soil particles and not available in fresh water systems, but P released when mixing with

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Chemistry of Nitrogen

  Nitrogen can exist in nine various forms in the environment due to seven possible oxidation states:

  • Nitrogen Compound Formula Oxidation State
  • Organic nitrogen Organic-N -3
  • Ammonia NH3 -3
  • Ammonium ion NH4+ -3
  • Nitrogen gas N2 0
  • Nitrous oxide N2O +1
  • Nitric oxide NO +2
  • Nitrite ion NO2- +3
  • Nitrogen dioxide NO2 +4
  • Nitrate ion NO3- +5

Nitrogen Dynamics

  • Nitrogen can undergo several transformations

  • Adsorption of NH4+-N in the soil
  • Volatilization of NH3-N in alkaline soils at a pH above 8.0
  • Nitrification and subsequent movement of NO3- -N towards the groundwater
  • Biological uptake of both NH3-N/NH4+-N and NO3- -N
  • Denitrification if the environmental conditions are appropriate

Phosphorus

  • Originates from weathering of igneous rock, soil leaching, and organic matter.
  • Also anthropogenic sources include wastewater, fertilizer, and detergent (phosphate detergent has been banned)
  • Commonly transported with sediment via erosion, but OSWS may contribute phosphorus to ground and surface waters if P-index of soil is high, and/or if P was bound by Fe oxides, and anaerobic and saturated conditions cause Fe3+ to become reduced to Fe2+ and leach, thus leaching P
  • Fresh waters usually phosphorus limited- may cause eutrophication

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Microbial Organism

  • Serve many important purposes including degrading waste materials
  • Some of them may be dangerous to human health and must be removed from water

Microbial Organisms

  • Aerobic-perform best when waters are well aerated and contain relatively high concentrations of dissolved molecular oxygen
  • Anaerobic- perform best in conditions with little or no molecular oxygen
  • Obtain needed oxygen from molecules that contain oxygen such as NO3, Fe(OH)3
  • Prefer aerobic conditions but easily adapt to low oxygen circumstances

Testing for Microbial Organisms

  • Fecal coliform, E. coli, Enterococcus, total coliform counts are used as an indicator organisms
  • The samples are typically filtered, nutrient broths are added, the samples incubate for 24 hours
  • The number of colonies that form are counted – colonies are proportional to how many microbial organisms are present in a sample

Salts

Problems associated with excess salt:

  • High salt concentrations detrimental to plant growth and can damage crops
  • Salt can damage equipment, especially some materials which react with the salts
  • Electrical conductivity (US/cm) often used to infer salt content (very conductive)

Specific Conductance/Electrical Conductivity

  • uSiemens/cm at 25 C

  • Measures electrical conductance due to dissolved substances in water per 1 cm path length at 25C

  • Ranges uSiemens/cm at 25C
  • Distilled water 0-2
  • Rainfall 2-117 (average = 13 at Lewiston, NC)
  • Sandstone headwater stream 50-70
  • Limestone stream 300-600
  • Wastewater 1100+
  • Salt water 35,000+

  • Can provide an indication of how long water has spent underground with minerals- more dissolved- higher SpC

Metals

Problems associated with excess metals:

  • High metal content in wastewater or biosolids that are applied to agricultural fields can reduce crop growth
  • Metals in high enough concentrations are pollutants and can be serious health risks.

Turbidity

  • Turbidity is a measure of the clarity of water.
  • Turbidity is influenced by the number of insoluble particles present
  • Sediment and organics often cloud surface waters after storms
  • Often used to estimate suspended sediments (with calibration)
  • Need many suspended sediment samples to relate to turbidity for a given river
  • Turbidimeter
  • Units - Nephelometric turbidity units (NTU)

pH

  • pH is the negative log of the hydrogen ion concentration
  • It can have a major impact on biological and chemical reactions
  • There is an inverse proportion of H+ and OH- ions, and the pH scale is logarithmic.
  • pH of 6 has 10x more H+ ions in solution than pH 7, 100x more than pH 8, etc.,
  • pH of natural waters may vary widely (6-9) due to organic acids (e.g. humic acids) or alkaline mineral deposits (e.g., limestone).
  • Rainfall less than pH of 5 is considered “acid rain”
  • Often measured with field meters

Alkalinity

  • Alkalinity is the capacity of water to absorb hydrogen ions without significant pH change
  • Bicarbonates, carbonates, and hydroxides are the three chemical forms that contribute to alkalinity
  • Lack of alkalinity can limit the nitrification rate of effluent, because when NH4 converts to NO3, the H is released and can lower pH unless there is sufficient buffering capacity (alkalinity). If the pH is too low, microbes will not nitrify the NH4.

Major Pollutants Causing
Stream Use Impairment

Source: USEPA

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Sediment, as mentioned before, is the major pollutant of concern in freshwater streams.

Source: USEPA

Major Pollutants Causing Estuary Use Impairment

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Nutrients and bacteria are the major pollutants of concern in estuaries.

Treatment Efficiency

Treatment Efficiency (Concentration Reduction)

Efficiency = [(C in - Cout)/Cin ] 100

Where: Cin = Influent concentration (typically mg/L)

Cout = Effluent concentration (typically mg/L)

And Efficiency is expressed as a percentage (%)

Concentration = mass/volume (mg/L)

Treatment Efficiency (Load Reduction)

Efficiency = [(L in - Lout)/Lin ] 100

Where: Lin = Influent load (typically kg/yr)

Lout = Effluent load (typically kg/yr)

and Efficiency is expressed as a percentage (%)

Treatment Efficiency

Load = concentration*flow (mg/day)

mg/L * L/day

b

V

s

V

f

DO

i

DO

t

BOD

-

=

0500100015002000250030003500

Impaired Stream Miles

Turbidity

Low Dissolved Oxygen

Fecal

Sediment

Pollutant

NC: 37,563 Stream Miles

010002000300040005000

Impaired Estuary Square Miles

Low Dissolved Oxygen

Bacteria

Nutrients

Pollutant

USA: 26,847 Square Miles Survey