Water and Wastewater Analysis Lecture 5 PDF

WATER AND WASTEWATER ANALYSIS ENVIRONMENTAL CHEMISTRY LECTURE 5 Water and Wastewater Analysis in Chemistry Water and wastewater analysis is a crucial aspect of environmental chemistry and public health. It involves determining the physical, chemical, and biologi...

WATER AND WASTEWATER ANALYSIS ENVIRONMENTAL CHEMISTRY LECTURE 5 Water and Wastewater Analysis in Chemistry Water and wastewater analysis is a crucial aspect of environmental chemistry and public health. It involves determining the physical, chemical, and biological characteristics of water samples to ensure their safety for consumption, discharge into the environment, or reuse in various applications. Methods of Analysis Standard Methods of Water and Wastewater Analysis published by the American Public Health Association in collaboration with the American Water Works Association and the Water Environment Federation. Expression of Results For water and wastewater – mg/L or ppm For sludges, soil and semisolid samples – ppm Water Quality Parameters ❑ Turbidity ❑ pH ❑ Dissolved oxygen ❑ Biological oxygen demand (BOD) ❑ Chemical oxygen demand (COD) ❑ Nutrients (e.g., nitrogen, phosphorus) ❑ Heavy metals Water Sampling Techniques 1. Grab samples Those taken instantaneously and analyzed separately Most samples in environmental engineering practice is grab sampling Problem of frequency of sampling – may vary from one to hundreds per day Application: - For deep well water that has been in service for some time – single grab sample is representative - Large river that changes its quality slowly – once daily grab sample - Industrial waste that changes quality daily – grab sampling every 10 or 15 minutes that could be pooled into 2-, 4-, 8-, 12-, or 24-h composites Water Sampling Techniques 2. Composite Samples Used for evaluating the efficiency of wastewater treatment facilities where average results are adequate Samples are collected at regular interval usually every 1 or 2 hours pooled into 24 hours Application: - Wastewater treatment plants – 8 am to 4 pm measure the strength of daytime waste; samples collected prior to 8 am measures treatment for weak waste METHODS OF CHEMICAL ANALYSIS TO QUANTIFY A SAMPLE A. Gravimetric Analysis Analysis by weight where the final results are obtained by means of analytical balance Application: determination of total solids, suspended solids, fixed and volatile solids Time consuming Constant weight of containers that hold precipitate or residue, e.g. crucible or dish Thoroughly cleaned and heat-treated to the same actual temperature to be used Cooled in the dessicator METHODS OF CHEMICAL ANALYSIS TO QUANTIFY A SAMPLE B. Volumetric Analysis (Titrimetry) Depends upon the measurement of liquid reagent volumes of standard solutions needed to complete a particular reaction in samples Volumetric analysis involves the measurement of the volume of a solution of known concentration (the titrant) that is required to react completely with the substance being analyzed (the analyte). The endpoint of the reaction is usually indicated by a color change (using an indicator) or by reaching a certain pH. This method is commonly used for acid-base titrations, redox titrations, and complexometric titrations.  Equivalent weight of a compound is the weight of that compound which contains one-gram atom of available hydrogen or its chemical equivalent Molarity – 1 molar solution (1 M) contains 1 gram molecular weight of chemical per liter of solution. A mole is one gram molecular weight of a substance The molecular weight of a common table salt is 58.44, thus 58.44g of NaCl is 1 mole of NaCl. 2M solution of HCl (hydrochloric acid) would contain two gram molecular weights, 2 x (1+35.5) or 72.9 g HCl in 1 liter of water A molar solution of NaOH contains 58.44 grams of pure salt dissolved in a total solution of 1 liter. Molality – weight to weight relationship rather than weight-to-volume relationship. A m solution consists of1 mole of substance dissolved in 1000 g of solvent, e.g. 1 liter of water Normal solution – a solution that contains one equivalent weight of a substance per liter of solution. A 1 N solution contains one gram-equivalent weight of particular acid, base or salt per liter of water. To prepare 1 liter of normal solution of acid or base: Amount of compound to furnish ion to yield 1.008 g of H+ or 17.007 g of OH- Enough distilled water to make 1 liter Normality of solution is its relation to normal solution, N Half-normal solution is 0.5 N or N/2 Normality expresses equivalency in reactions. For example 1N (normal) solution of sodium hydroxide will exactly neutralize 1 N solution of sulfuric acid. The valence of sodium is +1 and the sulfate is –2. Formula: N/50 or 0.02N NaOH solution consists of 0.8 g (40/50 or 0.02x40) NaOH in 1 liter of water. Problem 1: If 40 ml of 0.02 N NaOH is equivalent to 30 ml of CaCO , what is the normality of the CaCO 3 3 solution? Problem 2: If 50 ml of 0.1 N HCl is equivalent to 25 ml of NaOH solution, what is the normality of the NaOH solution? C. Standard Solution Standard solution – a solution whose strength or reacting value per unit volume is known. Facilities needed for conducting volumetric analysis: 1. Equipment to measure the sample accurately, e.g. analytical balance, volumetric glassware such as pipet 2. Standard solution 3. Indicator to show stoichiometric end point 4. Calibrated buret to measure volume of standard solution Standard solutions use solutions which are equivalent to one another in strength, i.e. 1.0 ml of reagent A with react exactly with 1.0 ml of reagent B 1 g of hydrogen atomic weight or 1.008 g of hydrogen ion reacts with 1 g ionic weight or 17.007 g of hydroxyl ion. Indicators Indicators serve as signal the reaching of the completed reaction Types of indicators: electrometric, acid-base, precipitation, adsorption, oxidation – reduction Water Sampling Techniques Flow-Through Sampling Flow-through sampling is a method where water or another liquid is continuously passed through a system that allows for real-time sampling and analysis. This technique is often used in environmental monitoring, where continuous data collection is needed, such as in rivers, lakes, or industrial discharges. Flow- through systems can include sensors and other devices to measure parameters like pH, temperature, dissolved oxygen, or specific contaminants. Water Sampling Techniques Sampling Equipment 1. Samplers: Automatic Samplers: These devices are used for collecting samples at predetermined intervals or in response to specific triggers (e.g., changes in water quality). They can be programmed to collect samples at specific times or flow volumes, making them ideal for long-term monitoring projects. Grab Samplers: These are manual devices used to collect a single sample at a specific point in time. Grab samplers are typically used when an immediate snapshot of water quality is needed. They can be as simple as a container on a pole or a more complex device that can be lowered to a specific depth. Water Sampling Techniques 2. Bottles: Glass Bottles: Often used for collecting samples where chemical reactions with the container are a concern, such as in trace metal analysis. Glass is inert and doesn’t leach chemicals that could contaminate the sample. Plastic Bottles: Typically made of polyethylene or polypropylene, these are used for general sampling purposes. They are lightweight, durable, and less prone to breakage compared to glass. However, they may not be suitable for sampling certain chemicals that can interact with the plastic. Water Sampling Techniques 3. Preservatives: Chemical Preservatives: These are added to samples immediately after collection to prevent changes in the composition of the sample before analysis. For example, nitric acid is often added to water samples intended for metal analysis to preserve the metal ions in solution. Refrigeration: Some samples need to be kept cool to prevent biological activity that could alter the sample's composition. For example, samples for nutrient analysis are often refrigerated or placed on ice until they can be analyzed. Equipment and Techniques Spectrophotometry a. UV-Vis spectrophotometer Equipment and Techniques Spectrophotometry b. Atomic absorption spectrophotometer Atomic absorption spectrometry (AAS) detects elements in either liquid or solid samples through the application of characteristic wavelengths of electromagnetic radiation from a light source. Individual elements will absorb wavelengths differently, and these absorbances are measured against standards. Equipment and Techniques Chromatography Liquid chromatography (LC) Gas chromatography (GC) Mass spectrometry (MS) Equipment and Techniques Titration a. Acid-base titration b. Redox titration c. Conductivity titration