Water Treatment Miscellaneous Parameters

• Turbidity and Total Suspended Solid ( TSS )

    When we refer to Turbidity, we are looking at how clear or translucent the liquid is by looking at the water’s light scattering properties. Testing turbidity can reveal some suspended solids, algae, organic material, and any other minuscule particles that cause the liquid to become cloudy or murky resulting in a higher Nephelometric Turbidity Unit (NTU) reading. NTU’s are units that are used to describe turbidity. A low NTU reading indicates clearer liquid and higher readings indicate low water clarity. NTU readings generally range from 1 to 4000 where 1 would indicate pristine clarity and 4000 would have the transparency similar to that of milk. An NTU reading of less than 1 is generally considered quite good for tap water.

    Total Suspended Solids (TSS) refers to any particles that are suspended in the water column. These particles can include silt, algae, sediment, and other solids floating in the water (both organic and inorganic). These particles are defined as being large enough to not pass through the filter (through the filtration process) used to separate them from the water. Suspended solids absorb heat from sunlight and as a result, the water temperature increases resulting in a deprivation of dissolved oxygen in the water which can be disastrous to aquatic life if levels are too high. TSS can be measured in ppm, mg/L, g/L and %. To determine TSS, you need to run sample liquid through a filtering process where the sample is filtered, dried, and weighed. Results can be ran through the below formula to determine the TSS in mg/L.

      There are portable instruments available that do measure TSS but they can get quite expensive. The best meter we have found measures both TSS and turbidity is made by Hach. It is a portable hand-held meter complete in a carry case which measures turbidity, suspended solids, and sludge blanket level . More information on this product can be found here.

     When looking at TSS readings, it is generally considered that a reading of less than 20 mg/L is clear. Readings between 40 and 80 mg/L will begin to appear cloudy and readings over 150 mg/L will appear quite dirty. These numbers can vary depending of the type of particles present and are provided as a guide only.

      Turbidity can be measured using either an electronic turbidity meter or a turbidity tube. Both methods have advantages and disadvantages.

      The Difference of  Turbidity and TSS

    Turbidity and TSS are similar in the sense that they are both measuring clarity of liquid but they aren’t actually measuring the same thing. It is worth noting that measuring turbidity from a sample allows you to get an instantaneous reading of NTUs meaning you can take the reading directly from out in the field. Measuring TSS on the other hand, is a manual and drawn out process requiring a precise technique and measurements that often have to be conducted back in a laboratory. While portable meters are available as mentioned earlier, they are expensive and depending on the application, may or may not be worth the investment. It is worth considering the regularity of testing required and whether testing needs to be done on-site or can be taken back to a laboratory to go through the filtering process.

   Put simply, turbidity looks at how well a light passes through liquid and TSS is a quantitative expression of suspended particles. Even though turbidity and TSS compliment each other, they are both influenced differently. For example, TSS can calculate sedimentation rates, while turbidity can’t. Turbidity and TSS do overlap in the measurement of some particles as shown in the illustration below but as mentioned, they do actually differ making it extremely difficult to form any kind of correlation between the two.

• Specific Conductivity and Anion Conductivity

    There are two types of conductivity measurements: specific and cation. Specific conductivity can detect only large amounts of contaminants. Condenser tube leaks normally start out very small, and may increase over time. For example, condensate flow may be 5,000 gpm, and the “leak” 0.1 gpm. On a volumetric basis, this is 20 ppm. Specific conductance instruments may not be able to detect this small leak unless the cooling water conductivity is very high to start.

    Cation conductivity instruments pass the condensate sample through a cation (ion exchange) resin to convert cations (sodium, calcium, etc.) to the hydrogen form, producing an acidic effluent. Since acids are much more conductive than mineral salt solutions, the effective sensitivity is increased dramatically. The generally accepted lowest detection limit (LDL) is 0.05 micro siemens per centimeter (μS/cm). With such sensitivity, cation conductivity can be a very useful measurement to detect condenser tube leaks.

     Specific conductivity aims to know the number of dissolved solid which contained in water, whereas cation conductivity to know negative ion (anion) which dissolved in water. Nevertheless cation conductivity can not know the kind of anion specifically.

• Chemical Oxygen Demand (COD) , Biological Oxygen Demand (BOD) and Dissolved Oxygen (DO)

BOD or Biochemical/Biological Oxygen Demand is a characteristic that express the amount of dissolved oxygen needed by microorganism (usually bacteria) to decompose or break down the organic matter under anaerobic condition (Umaly and Cuvin, 1998; Metcalf and Eddy, 1991). Reiterated again by Boyd (1990), that organic material decomposed in BOD is organic material that is ready to decompose (readily decomposable organic matter). Mays (1996) defines BOD as a measure of the amount of oxygen used by microbial populations contained in waters in response to the entry of decomposed organic matter. From these notions it can be said that although the BOD value states the amount of oxygen, but for simplicity it can also be interpreted as a description of the amount of biodegradable organics in the waters.

Chemical Oxygen Demand (COD) is a second method of estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. test uses a strong chemical oxidizing agent (potassium dichromate or potassium permanganate) to chemically oxidize the organic material in the sample of wastewater under conditions of heat and strong acid, so that all kinds of organic materials, both those that are easy to decompose or are easily complex and difficult to decompose, will oxidize. It has the disadvantage of being completely artificial but is nevertheless considered to yield a result that may be used as the basis upon which to calculate a reasonably accurate and reproducible estimate of the oxygen-demanding properties of a wastewater.

The COD test is often used in conjunction with the BOD test to estimate the amount of nonbiodegradable organic material in a wastewater. In the case of biodegradable organics, the COD is normally in the range of 1.3 to 1.5 times the BOD, and it could be that the BOD value is the same as the COD, but the BOD cannot be greater than the COD. When the result of a COD test is more than twice that of the BOD test, there is good reason to suspect that a significant portion of the organic material in the sample is not biodegradable by ordinary microorganisms. As a side note, it is important to be aware that the sample vial resulting from a COD test can contain leachable mercury above regulatory limits. If such is the case, the sample must be managed as a toxic hazardous waste.

Dissolved Oxygen (DO) is the amount of dissolved oxygen in the solution. The illustration of relation between BOD, COD and DO are the following:

figure 1. BOD COD and DO relationship