Total Solids (TS) - material remaining after evaporation of sample liquid

Transcription

1 Page 1 of 8 Reference Two publications are widely used as the principal cookbooks for water and wastewater analysis: o Standard Methods for the Analysis of Water and Wastewater. American Water Works Association and the American Public Health Association. Published about every two years. o EPA Standard Methods. US Environmental Protection Agency. These references contain information regarding which analytical tests are appropriate for what types of questions or problems along with step-by-step analytical procedures. In many cases these references also provide information on how to handle and preserve samples to provide the best possible analyses. Associated problems include: Mass deposition filling of storage areas; blockage of ditches, channels, degrades fish spawning areas Increased turbidity light penetration to aquatic vegetation, feeding habits of sighthunting fish, unappealing appearance (Brazos River, Dijle River) Interference with Mechanical Systems plugs, filters & sprinkler heads, complicates water treatment, erodes equipment High TDS typically associated with high salts concentrations taste problems in public drinking water supplies (local tap water) descriptions typically include: Total (TS) - material remaining after evaporation of sample liquid Total Volatile (TVS) - material lost after total solids are ashed (organics that are burned off at 550 ºC) Total Fixed (TFS) - material (mineral basis) left after total solids are ashed TS = TVS + TFS (1) Total Suspended (TSS) - dried solids caught during filtration through a 1.5 μm filter Total Dissolved (TDS) - dried solids passing through filter TS = TSS + TDS (2) Volatile Suspended and Volatile Dissolved (VSS/VDS)

2 Page 2 of 8 Fixed Suspended and Fixed Dissolved (FSS/FDS) concentration is measured as the mass of solids per known volume of water: S mt m vol c (3) Where S = solids concentration, mg/l m t = total mass of solids and container, mg m c = mass of container, mg vol = volume of liquid sample, L Example A 100 ml sample is filtered through ash-free filter paper having a weight of g and the filter paper is dried. The resulting dried weight is g. What is the TSS concentration? mt m TSS vol c mg 0.1L 750 mg/l The filter paper containing the solids is then ashed yielding a total weight of g. What are the FSS and VSS concentrations? mg FSS 0.1L 250 mg/l VSS = TSS - FSS = 750 mg/l mg/l = 500 mg/l Description of Content in Water Sample is Dried (24 h at 100 C) Sample is Ashed 24 h at 550 C) Mineral Fraction (what remains after ashing) Volatile (Organic) Fraction (what burns off during ashing) Unfiltered Sample Total * Total Fixed Total Volatile * Filtered Sample Retained on filter paper Total Suspended * Fixed Suspended Volatile Suspended * * Analyses most commonly used in environmental science and engineering Passing through filter paper Total Dissolved * Fixed Dissolved Volatile Dissolved

3 Page 3 of 8

4 Page 4 of 8 Nutrients Generally consists of macro nutrients N-P-K, primarily N and P, naturally occurring (without human influence) in surface waters at low level concentrations N=0.3 mg/l, P=0.05 mg/l Eutrophication Excess nutrients act as fertilizer to aquatic plants increased productivity. Added organic matter eventually decays odors and decreased DO Thick vegetation also interferes with swimming and boating. Decaying matter may foul beaches. High concentrations of suspended material inhibit light penetration to submerged aquatic vegetation (just like turbidity from sediment) Limiting nutrient the least abundant in relation to plant needs. Plants will establish until one is used up when it is unavailable, development is impaired and other nutrients go unused. As P becomes more abundant, much more productivity is allowed. Nitrogen Commonly reported Nitrogen forms include: Nitrate (NO 3 -N) - most oxidized state, inorganic Nitrite (NO 2 -N) - intermediate oxidation state, inorganic Ammonia (NH 3 -N) - least oxidized state Organic N - nitrogen bound in organic compounds (proteins, urea, etc.) Total Kjeldahl Nitrogen (TKN) - total organic nitrogen and ammonia Total nitrogen - sum of all forms Ammonia concentration of 0.2 mg/l may be toxic to fish, especially trout NO 2, NO 3 may cause methemoglobinemia (blue baby), reduced oxygen carrying capacity in blood high nitrate waters should be avoided by pregnant women and children under 6 mo to 1 yr (10 mg/l) Nitrogen readily changes forms depending on ambient conditions Phosphorus Typically reported forms: orthophosphates (ortho-p) reactive phosphorus, available without prior oxidation, most available to plants condensed (poly) phosphates become reactive with preliminary oxidation or acid hydrolosis organic phosphorus bound in organic matter which must be destroyed (by digestion) before phosphorus becomes reactive total phosphorus (TP) all of the above

5 Page 5 of 8 Microbial Organisms (Pathogens) Salts Common descriptor Fecal coliform count number of colonies formed on a specific medium after filtering sample Presence of pathogenic organisms Generally considered a surface water problem but some suggest movement to groundwater is occurring. Examples: Contaminated oyster beds, Crypto sporidium problem in Milwaukee, Pfiesteria blooms in Chesapeake Bay estuaries Saline conditions may limit usefulness of water for municipal, industrial, or agricultural applications. Accumulation of Na leads to soil dispersion structure breakdown, decreased infiltration, possible toxicity, greater suspension in water Can be a particular problem in irrigated areas Metals Nontoxic taste, staining, biological growth odors Toxic bioaccumulation, population disturbance Hardness Concentration of multivalent cations (usually measured as equivalent amounts of calcium carbonate) mostly calcium, magnesium, iron, and manganese Hard water leaves scale in pots, pipes, hot-water heaters, also requires increased amounts of soap for washing and bathing Soft water has fewer multivalent cations and suds and lathers easily with soap may seem difficult to remove soap residue (soft water in Bryan/College Station, hard water in Leuven) Dissolved Oxygen (DO) Amount of molecular oxygen dissolved in water Important in sustaining aquatic life Maximum possible DO level decreases as temperature increases, so DO stress is greatest during the day in summer months Measured by meter and probe Oxygen Demand Referred to as the amount of oxygen consumed in the oxidation (breakdown) of organic substances Use of DO during breakdown of organic constituents by microorganisms depletes the DO supply available for aquatic life may result in fish kills

6 Page 6 of 8 Measurement of oxygen demand is considered an indirect measure of the amount of organic material in water changes in DO are measured instead of a direct measurement of the organic concentration Biochemical Oxygen Demand (BOD) Amount of oxygen used during the biochemical breakdown of organics Relies on microbial and natural chemical processes for breakdown similar to what happens in natural water resources Usually conducted over a 5-day period (yields BOD 5 ). A microbial seed and nutrients for bacterial growth may be added to ensure proper breakdown DO is measured at the start of the test and again after the incubation period BOD measurements detect the amount of BOD degraded over the incubation time (BOD consumed). After incubation, some BOD will remain in the sample (BOD remaining). The amount of BOD detected increases as the amount of incubation time increases until the ultimate BOD is detected (everything that will degrade naturally has broken down) BOD consumed + BOD remaining = ultimate BOD BOD is determined from laboratory measurements as: DOi DOf BOD V s Vb (4) Where BOD = biochemical oxygen demand, mg/l (BOD consumed) DO i = initial DO concentration, mg/l DO f = final DO concentration, mg/l V s = volume of sample, L V b = volume of the BOD bottle, L The term V s /V b allows for sample dilution when organic concentrations are high Example 30 ml of a wastewater are placed in a 300 ml BOD bottle. The sample is diluted to fill the bottle. The DO concentrations at the beginning and the end of the 5-day incubation period are 7.3 mg/l and 1.8 mg/l, respectively. What is the BOD?

7 Page 7 of 8 BOD DO DO mg/l 30 ml 300 ml i f 5 V V s b 55 mg/l BOD breakdown over time, in an incubated sample or elsewhere, follows first-order reaction kinetics (the rate at which it is used up is proportional to the amount present): BOD rem BOD e u kt (5) Where BOD t = BOD remaining at time t, mg/l BOD u = ultimate BOD concentration, mg/l k = reaction rate coefficient, 1/d t = time, d or, expressed in terms of BOD consumed: BOD con BOD (1 e u kt ) (6) Typical values for k at 20 C are in the range of day -1 for water with moderate amounts of organic wastes. As with most reactions, k increases as temperature increases. Example The BOD 5 of a wastewater was determined to be 250 mg/l. If the reaction coefficient was /d, what is the ultimate BOD? The BOD 5 value is BOD consumed over 5 days, so use the BOD consumed equation: BOD BOD ( 1 e kt ) t u (. )( ) 250 BOD ( u 1 e ) BOD u = mg/l What is BOD 3? BOD 3 is a measure of BOD consumed after 3 days, so use equation 6: 0.23(3) BOD (1 e ) mg/l What is the BOD remaining at 3 days? BOD rem = BOD u - BOD 3 = = mg/l

8 Page 8 of 8 Chemical Oxygen Demand The equivalent amount of oxygen needed to break down organic matter under strong oxidizing agents Breaks down more of the organic materials than a natural process would because of the strong chemicals used hence COD BOD Much faster to perform than BOD testing since an incubation period is not required Does not match as closely the behavior of the waste in a natural situation Organic Materials Indirect Measurement BOD and COD both provide an indirect measurement of organic material in water The higher the BOD or COD concentrations, the higher the concentration of organic material Total Organic Carbon (TOC) The amount of carbon bound in organic constituents Special instrumentation has been developed for this analysis organics are oxidized and the resulting CO 2 is measured Quick and easy to run if instrument is available the equipment is very expensive Oil and Grease Measurement of the oily or greasy component of water without determining the actual chemical constituency of the greasy substances Measures amount of material which can be extracted using a specific solvent Sometimes listed as fats, oils, and grease (FOG) Man-Made Organics May be toxic at high concentrations recall bioaccumulation May yield taste and odor problems