Surface Waters Module II D' Orvos

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Surface Waters Module IID. Orvos
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Phosphorous

• In contrast to nitrogen, phosphorus in aquatic
  systems has no gaseous form and only one charged
  form (PO4-3). However, the water chemistry of
  phosphorus is complicated by its tendency to
  adsorb onto inorganic particulate matter and its
  incorporation into organisms to form organic
  phosphorus.

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Phosphorous

• Phosphorus is not needed large quantities like
  carbon, hydrogen, and nitrogen, but it is often
  the limiting factor for primary production in
  both terrestrial and aquatic environments. This
  occurs for 3 reasons
• 1. phosphorus containing rocks are often scarce
  so the supply from rock breakdown may be poor.
• 2. there is no gaseous stage of phosphorus so
  there is no equivalent to nitrogen fixation
• 3. phosphorus is sufficiently reactive to be
  bound to many types of soil

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Total P and Lake Productivity

• lake productivity total P ug/L
• ultra oligotrophic lt 5
• oligotrophic 5-10
• mesotrophic 10-30
• eutrophic 30-300
• hypereutrophic gt 300

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Forms of P

• 1. dissolved phosphate (PO4 -3)
  orthophosphate, reactive P
• 2. dissolved total phosphorus orthophosphate
  DOP (see below)
• 3. particulate phosphorus bacterial, plant and
  animal phosphorus and phosphorus absorbed to
  suspended inorganic particles

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Forms of P
0.45 u filter
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Phosphorous

• Dissolved total P and particulate P must first be
  mineralized by an acid to reactive P before
  measurement.
• Total phosphorus can be divided into particulate
  (filterable) and dissolved (filtrate) phosphorus.
  The filters are 0.45 µ polymer.
• Only the orthophosphate can be used directly for
  algal growth, so it is often called reactive
  phosphorus.

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Phosphorous

• Relative to total soluble phosphorus there is
  usually much more particulate phosphorus.
  Particulate phosphorus includes phosphorus bound
  in bacteria, plants, and animals as well as
  phosphorus adsorbed to suspended inorganic
  particles such as clays.
• Sources
• weathering of rocks
• particles in air
• pollution (detergents, fertilizers) leads to
  cultural eutrophication
• Losses
• water effluents
• organisms settle to bottom
• insect hatches - fish removal
• precipitates FePO4, MnPO4, Ca3(PO4)2

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Phosphorous in Surface Water

• Orthophosphate is lost from the open water by a
  variety of mechanisms but most involve
  precipitation of inorganic solid phosphate phases
  formed by direct precipitation with calcium,
  iron, etc. or sorption onto clay particles.
• Phosphorus does not normally accumulate in lake
  waters because of rapid loss to the sediments,
  followed by little return of phosphorus in
  oligotrophic lakes and only more or less seasonal
  returns in eutrophic lakes.

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Measurement of P

• Phosphate is measured colormetrically with
  ascorbic acid. Total P must be digested via acid
  to convert it to orthophosphate, which is then
  quantified. Ion chromatography is also used.

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Chlorine

• Chlorine is a common disinfectant used in
  automated watering systems. At lower
  concentrations it is used to disinfect animal
  drinking water. At higher concentrations,
  chlorine is used to sanitize rack manifolds and
  room distribution piping. A chlorine test kit or
  titrator must be used to measure the
  concentration of chlorine in water.

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Forms of Chlorine

• Free Chlorine
• Combined Chlorine
• Total Chlorine

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Free Chlorine

• Chemistry important in disinfection
• Free chlorine is defined as the concentration of
  residual chlorine in water present as dissolved
  gas (Cl2), hypochlorous acid (HOCl), and/or
  hypochlorite ion (OCl-). The three forms of free
  chlorine exist together in equilibrium.
• Cl2 H2O ? HOCl H Cl-
• HOCl ? H OCl-
• As the pH falls below 2, the predominant form is
  Cl2. Between pH 2 and 7 the equilibrium is in
  favor of HOCl. At pH 7.4 HOCl and OCl- are about
  equal, while above this increasing proportions of
  OCl- are present.

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Combined Chlorine

• Combined chlorine is defined as the residual
  chlorine existing in water in chemical
  combination with ammonia or organic amines which
  can be found in natural or polluted waters.
  Ammonia is sometimes deliberately added to
  chlorinated public water supplies to provide
  inorganic chloramines.
• Chloramines in presence of organic matter can
  form trihalomethanes. Importance?

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Total Chlorine

• Total chlorine is the sum of free and combined
  chlorine. When chlorinating most potable water
  supplies, total chlorine is essentially equal to
  free chlorine since the concentration of ammonia
  or organic nitrogen compounds (needed to form
  combined chlorine) will be very low. When
  chloramines are present in the municipal water
  supply, then total chlorine will be higher than
  free chlorine.

Germicidal strength of different forms of
chlorine in water are ranked as follows HOCl gt
OCl- gt inorganic chloramines gt organic chloramines
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Biochemical Oxygen Demand

• Often called biological oxygen demand, although
  that is technically incorrect
• Abbreviated BOD
• BOD refers to the amount of oxygen that would be
  consumed if all the organic material in 1 L of
  water (or wastewater or industrial effluent) were
  oxidized by microbes

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Measuring BOD

• The first step in measuring BOD is to obtain
  equal volumes of water (or wastewater or
  industrial waste) from the area to be tested and
  dilute each specimen with a known volume of
  buffered distilled water that has been thoroughly
  shaken to insure oxygen saturation. The greater
  the sample BOD, the larger the dilution.

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Measuring BOD

• After this, an oxygen meter is used to determine
  the concentration of oxygen within one of the BOD
  bottles. The remaining vial is than sealed and
  placed in darkness and tested five days later.
  BOD is then determined by subtracting the second
  meter reading from the first. Why five days?
• The range of possible readings can vary
  considerably water from an exceptionally clear
  lake might show a BOD of less than 2 mg/L of
  water. Raw sewage may give readings in the
  hundreds and food processing wastes may be in the
  thousands of mg of BOD
• Engineers likes pounds of BOD!

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CBOD and BODu

• BODu is the ultimate BOD, i.e., the BOD with no
  time restriction placed on the test (although it
  is usually a 30-day test)
• CBOD or Carbonaceous BOD represents the BOD from
  organic compounds and oxidation of inorganic
  compounds such as ferrous iron and sulfide. Any
  BOD from nitrifying organisms, which consume
  oxygen in the nitrification process of converting
  ammonia to nitrate, is removed by adding a
  nitrification inhibitor. Usually, CBOD BODu in
  most effluents

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BOD Measurement Use
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Chemical Oxygen Demand

• The quantity of oxygen used in biological and
  non-biological oxidation of materials in water a
  measure of water quality. Acid heat are used
  to oxidize the sample.
• The determination of chemical oxygen demand (COD)
  is used in municipal and industrial laboratories
  to measure the overall level of organic
  contamination in wastewater. The contamination
  level is determined by measuring the equivalent
  amount of oxygen required to oxidize organic
  matter in the sample.
• BOD/COD ratio the greater the ratio, the more
  oxidizable (biologically treatable) the waste.
  Ratios rarely exceed 0.8-0.9.

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Oxygen-Reduction Potential

• The redox potential or oxidation-reduction
  potential (Eh) is the electrical voltage which
  exists between two electrodes, one made of
  hydrogen and the other made of the material under
  study.
• When oxygen combines with a material chemical
  oxidation has occurred when oxygen is removed
  from a substance chemical reduction has occurred
• Changes in the redox potential are important only
  in eutrophic conditions or in special limnologic
  environments such as highly reducing acidic bogs.
• The oxidation state of many metal ions and some
  nutrient compounds are controlled by the amount
  of oxygen present and the associated redox
  potential.

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Chlorophyll
Seasonal concentrations of chlorphyll a in a New
York lake Orvos et al., 2000.
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Trace Metals

• Many metals are present in small amounts. Often
  these are of concern because of source and
  potential effects to humans, plants, and animals.
  Common trace metals include Cu, As, Cd, Hg,
  and Pb. Metals are usually detected with atomic
  absorption spectrometry or ICP.

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Trace Organics

• Pesticides, volatile organic compounds (VOCs),
  PCBs, and a multitude of other compounds are
  found in surface waters. Its a whole other
  course of material.