pH
An example of a strong base is drain cleaner or oven cleaner. Both strong acids and strong bases can be very harmful to your skin and tissues. Distilled water has a pH of 7, which is neutral.
pH meter
pH is typically measured using a pH meter, so this is one of the simplest tests performed in the water and wastewater laboratory.
The electrode is the portion of the pH meter which senses the pH. It is a very sensitive and fragile instrument which is susceptible to scratches. It’s the reason why you have to blot the electrode dry carefully when cleaning it. Light and temperature can also harm the electrode, so it should be stored in a buffer solution at 10-25°C and protected from light.
Using a pH Meter
Remove the electrode(s) from the storage solution.
Rinse with distilled water and then carefully dry the electrode(s) with a high quality laboratory tissue.
Place the electrode(s) in the sample.
Continue stirring the sample as the pH is measured by the meter.
Record the sample's pH in the Data section.
Place the instrument in standby mode and remove the electrode(s) from the sample.
Rinse the electrode(s) thoroughly with distilled water and carefully blot dry.
CHEMICAL OXYGEN DEMAND (COD)
COD is used to gauge the short-term impact wastewater effluents will have on the oxygen levels of receiving waters. High COD values imply a high level of pollution.
The COD limit value for the Serpis River is 125 mg/l.
The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent (potassium dichromate) under acidic conditions. In the process of oxidizing the organic substances found in the water sample, potassium dichromate is reduced, forming Cr3+. The amount of Cr3+ is determined after the complete oxidization, and is used as an indirect measure of the organic contents of the water sample.
Presence of nitrates
Nitrates are a form of nitrogen, which is found in several different forms in terrestrial and aquatic ecosystems. These forms of nitrogen include ammonia (NH3), nitrates (NO3-), and nitrites (NO2-). Nitrates are essential plant nutrients, but in excess amounts they can cause significant water quality problems. Together with phosphorus, nitrates in excess amounts can accelerate eutrophication.
The natural level of ammonia or nitrate in surface water is typically low (less than 1 mg/l); in the effluent of wastewater treatment plants, it can range up to 30 mg/l.
Sources of nitrates include wastewater treatment plants, runoff from fertilized lawns and cropland, failing on-site septic systems, runoff from animal manure storage areas, and industrial discharges that contain corrosion inhibitors.
Presence of nitrogen
Total nitrogen is the sum of all forms of nitrogen present in water, including ammonia and organically bound nitrogen, nitrite and nitrate.
Presence of phosphates
Phosphorus is vital within our freshwater ecosystems because it is the limiting nutrient for algae. Eutrophication, or excess nutrients within a body of water, can be harmful due to the potential for an explosion of plant life. This excessive algae growth, called "algal blooms", can deplete oxygen within a water body, causing fish kills. Also some algae can produce toxins that can be harmful to humans and animals.
There are several sources of phosphorus in our aquatic ecosystems. Non-point sources, such as fertilizer runoff, are the most significant contributor. However, municipal and industrial wastewater facilities (point sources) are another significant contributor of phosphorus. These facilities remove organics and solids from wastewater but, more recently, are required to remove nutrients like phosphorus and nitrogen. Phosphorus removal has become an essential priority for facilities discharging to freshwater systems or other at-risk environments. In the US, effluent limits for total phosphorus (TP) are commonly below 1 mg P/L, with critical regions implementing "ultra-low" limits below 0.1 mg P/L.
https://www.ysi.com/parameters/phosphorus
Natural waters normally contain amounts of phosphate below 1 mg/l.
PHOSPHORUS
Phosphorus occurs naturally in rocks and other mineral deposits. During the natural process of weathering, the rocks gradually release the phosphorus as phosphate ions, which are soluble in water, as the mineralized phosphate compounds break down. Phosphates PO⁻³ are formed from phosphorus.
Phosphorus is one of the key elements necessary for the growth of plants and animals and in lake ecosystems it tends to be the growth-limiting nutrient.
Eutrophication (from the Greek - meaning "well nourished") is enhanced production of primary producers resulting in a reduced stability of the ecosystem. This overproduction can lead to a variety of problems ranging from anoxic waters to toxic algal blooms, a decrease in diversity and food supply, and habitat destruction.
A recommended limit of 0.05 mg/L has been established for total phosphates in streams and 0.1 mg/L for total phosphorus in flowing waters.
For the determination of total phosphorus, the photometric method with molybdenum blue is used after acid hydrolysis and oxidation at 120ºC for 30 minutes.
This method consists of two parts. In the first, all the organic and inorganic substances that contain phosphorus are oxidized in an acid medium to obtain phosphate. The decomposition reagent contains sodium peroxodisulfate. In the second part, by reaction in acid medium (with sulfuric acid) of ammonium molybdate with the present phosphate, phosphomolybdic acid is formed, which is reduced to molybdenum blue, a compound that colors the sample directly proportional to the concentration of phosphates. Assay results are measured at 690 nm.
WATER HARDNESS (CALCIUM AND MAGNESIUM)
According to the amount of salts it contains dissolved, water can be classified as soft (little amount) or hard (a lot). Distilled water is an example of soft water.
A very simple way to determine the hardness of the water is to use detergent. Hard water produces little foam compared to the amount of foam that distilled water can produce. You can analyze the tap water at home to see the degree of hardness.
How is the hardness of water determined?
Total hardness determination reaction (Mg +2 + Ca+2):
Ca2+ + Mg2+ + Buffer (pH 10) + NET --> [ Ca-Mg-NET] (purple complex)
[ Ca-Mg-NET] + EDTA --> [ Ca-Mg-EDTA] (blue color) + NET
Material
Volumetric pipette, graduated pipette, Pasteur pipette, watch glass, beaker, Erlenmeyer flask and burette.
Reagents
NH3 – Concentrated ammonia
NH4Cl – Ammonium chloride
Na2 EDTA – Disodium salt of ethylenediaminetetraacetic acid
Preparation of reagents
NET at 1% in NaCl: 0.5g of NET in 45.50 g of NaCl (mix well and pulverize with a mortar)
Murexida (Indicator). Grind 0.2 g of murexida with 100 g of pulverize NaCl.
Preparation of 250 mL of NaOH 1M
Preparation of 500 mL of EDTA 0,01M
Preparation of 500mL of buffer pH=10 of NH4Cl/NH3: 21,7gr of NH4Cl with 175mL of NH3 concentrate and screed to 500 mL
Operating procedure
Fill and bring to the level the burette with EDTA 0.01M.
Measure 25 mL or 50 mL with a volumetric pipette and transfer it to an Erlenmeyer flask.
Add drop by drop, with the pasteur pipette, buffer solution up to pH 10 (approx. 1 mL)
Check that the pH of the solution is 10. Use the indicator paper and watch glass.
Add a little powder (NET), a spatula tip. The solution will turn purple-red.
Gradually add EDTA solution from the burette.
The solution starts to turn blue before the end point. This point is the point at which all traces of purple fade, leaving a pure blue color. The last portions of reagent should be added slowly since the reaction is quite slow. (Maintain pH 10 throughout the titration.
Criteria of acceptance
Water classification according to its hardness
Category | Germany | France | USA |
Very soft | 0-4 | 0-7 | 0-70 |
Soft | 4-8 | 7-14 | 70-140 |
Medium hard | 8-12 | 14-21 | 140-210 |
Pretty hard | 12-18 | 21-32 | 210-320 |
Hard | 18-30 | 32-54 | 320-540 |
Very hard | > 30 | > 54 | > 540 |
DISOLVED OXIGEN (DO)
Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water and therefore, the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality.
Although water molecules contain an oxygen atom, this oxygen is not used by aquatic living things in natural waters. They actually use a small amount of molecular oxygen ( ten molecules of oxygen per million water) which is found dissolved in the water.
DO is measured in ppm. This unit stands for parts per million and is equivalent to milligrams per liter (mg/L). That is the amount of oxygen in a liter of water.
And how does this oxygen get into the water?
An aquatic system produces and consumes oxygen. On the one hand, it obtains oxygen from the atmosphere and from plants as a result of photosynthesis. On the other hand, the respiration of aquatic animals and other living things, decomposition and various chemical reactions that take place in different aquatic ecosystems, consume oxygen.
Meter and Probe
A dissolved oxygen meter is an electronic device that converts signals from a probe that is placed in the water into units of DO in milligrams per liter.
We are going to use the oxygen meter in the field and in the laboratory. The reason is that dissolved oxygen levels in a sample bottle change rapidly due to the decomposition of organic material by microorganisms or the production of oxygen by algae and other plants in the sample.
Using a DO Meter
If you are using a dissolved oxygen meter, be sure that it is calibrated.
Record the dissolved oxygen level on the field data sheet.
Analyze data
Analyze your field data samples. Then discuss with your classmates the quality of the water sampled.
Water quality standards
If we have a concentration between 1 and 9 ppm, it is harmful to the ecosystem. The ecosystem experiences hypoxia.
Less than 2 ppm, it is fatal for most species. The ecosystem suffers from anoxia.
TEMPERATURE
The incidence and problems associated with odors and flavors in water is marked by two factors: pH and temperature.
The measurement of water temperature in a field site is essential for the collection of water quality data since it directly influences other parameters such as dissolved oxygen concentration, conductivity, pH, velocity and equilibrium of the water-chemical reactions...
Accurate water-temperature data are essential to document thermal alterations to the environment caused by natural phenomena and by human activities.
Under normal conditions, temperature variations are due to: time of day, season, depth of water...
High temperatures imply the acceleration of putrefaction and therefore the decrease in the concentration of dissolved oxygen in the water (increased growth of decomposing organisms).
Temperatures above 15ºC favor the development of microorganisms and intensify odors and flavors. And temperatures above 25 ºC mark the beginning of thermal pollution.
Measurement
Water temperature must always be measured in situ and in a manner that ensures that the measurement accurately represents the intended sample conditions. We will use a portable digital thermometer with a stainless steel probe.
Record the temperature on the field data sheet.
Analyze data
Analyze your data and discuss with your classmates the quality of the water.
Redox potential
Geochemists, soil scientists, and limnologists have used redox potential (Eh) measurements to characterize oxidation–reduction status of surface environments. The redox potential of soil, water, and marine systems is a measure of electrochemical potential or electron availability within these systems. Electrons are essential to all inorganic and organic chemical reactions. Redox potential measurements allow for rapid characterization of the degree of reduction and for predicting stability of various compounds that regulate nutrients and metal availability in soil and sediment. Redox potential is diagnostic for determining whether an area is functioning as wetland or nonwetland.
Oxidation and reduction reactions regulate many of the biogeochemical reactions in surface environments. Redox potential (Eh) is determined from the concentration of oxidants and reductants in the environment. The inorganic oxidants include oxygen, nitrate, nitrite, manganese, iron, sulfate, and CO2, while the reductants include various organic substrates and reduced inorganic compounds.
The redox potential is measured in millivolts (mV) relative to a standard hydrogen electrode and is commonly measured using a platinum electrode with a saturated calomel electrode as reference. In well-oxidized water, as long as oxygen concentrations stay above ∼1 mg O2 l−1, the redox potential will be highly positive (above 300–650 mV). In reduced environments, such as in the deep water of stratified lakes or the sediment of eutrophic lakes, the redox potential will be low (below 100 mV or even negative). Microbial-mediated redox processes can decrease the redox potential to a level as low as −300 mV. Higher measurements (850mV) mean better environmental conditions.
Measurement
A portable potentiometer is used, previously calibrated with a pattern of 220 mV.
Conductivity
Conductivity is an integrated measure of ionic substances (salts) present in water. It can be stated, therefore, that the more conductive the water, the more mineralized it is, the more salts it contains.
In rivers without human alteration, the conductivity depends on the geology of the basin due to the different solubility of the materials that make up the soil; The river basin of our region is of calcareous geology and has high conductivities. It also varies with the distance to the head of the river, due to the different variation of the surface of the basin that has been washed. Thus, in the lower reaches of the rivers the conductivity is naturally higher than in the headwaters. Our rivers are near the headwaters.
Conductivity, then, is the measure of the amount of ions in water, and is determined by the concentration of dissolved salts it contains. The major ions in river water are chlorides, bicarbonates, sulfates, calcium, magnesium, sodium, and potassium. The magnitude of the conductivity therefore depends on their concentration and degree of dissociation.
We measure the capacity a solution has for conducting an electrical current.
It is used in a wide variety of industries. For instance, measuring conductivity in waste water o industrial effluents helps provide readings on their total ionic strength. Generally speaking, measuring conductivity is a quick and easy way of determining the ionic strength of a solution.
However, the value of conductivity is also influenced by human activity. In more or less humanized places, it is related to land use or the presence of wastewater discharges, which provide chlorides and other salts to the river. The units of measurements which are normally used are µS/cm. 1,000 µS/cm is considered the limit above which water is difficult to drink for human consumption. For organisms adapted to living in inland freshwater, where salts should not exceed 1 ‰, high conductivities pose a risk of toxicity due to the osmotic regulation problems that this entails.
The conductivitymeter measures the electrical conductivity of the ions in a solution. To do this, it applies an electrical field between two electrodes and measures the electrical resistance of the solution. To prevent changes occurring in the substances, or the deposit of a layer on the electrodes alternating current is used.
Other alternative forms of expressing the conductivity are Salinity and Total Dissolved Solids (TDS). TDS conductivity can be used as an indicator of the quantity of materials dissolved in a solution. It is expressed in ppm or g/l of CaCO3.
The effect of temperature the conductivity of a solution is very dependent on temperature. This has a dual effect on electrolytes: it affects how far they dissolve and ion mobility. The conductivity of a solution increases with temperature.
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