The strength of the wastewater is determined by measuring the amount of suspended material in the water and the amount of organic material in the water. The suspended, filterable solids in the waste flow are known as Suspended Solids or SS. They can be trapped on a filter, dried, and weighed to determine the concentration. The organic strength of the wastewater is determined indirectly. The microorganisms in the biological treatment processes decompose or stabilize the raw organic material in the waste flow. As they do this, they use oxygen as part of the respiration process. Instead of directly measuring the strength of the organic load as pounds of sugars and proteins, we determine the amount of oxygen that the "bugs" use as they eat it. This is known as the Biochemical Oxygen Demand or BOD. If these organics are not stabilized in the treatment process, there will be dissolved oxygen depletion from the receiving water. This oxygen depletion can result in fish kills and damage to the aquatic ecosystem.