BOD5 stands for “5-day Biochemical Oxygen Demand.” Although those words sound a bit intimidating, the concept is pretty familiar for most people. Just as we breathe, microbes also breathe, and they use oxygen when they breathe. The BOD test is a way to measure how much oxygen is used as microbes breathe as they eat the contaminants in wastewater. The more contaminants in the wastewater, the more oxygen is needed. So a high BOD indicates high concentration of contaminants in the wastewater that the microbes have eaten. The “5-day” means that the oxygen content is measured when the test starts, and again at the end of 5 days. The difference in the oxygen content on the first day and on the last day is used to calculate the Biochemical Oxygen Demand of the wastewater.  


TSS stands for “Total Suspended Solids.” TSS is essentially a measure of how “dirty” the water is in terms of solid material suspended in the water. The more solid that is suspended in the water, the higher the TSS value. TSS is measured by weighing a clean, dry filter, then pouring the sample through the filter, drying it, then weighing the dirty dry filter. The amount of weight gained is used to calculate the suspended solids concentration.