Here are the answers to O&M Quiz No. 3.
1. T or F - Maintenance activities for a system are not affected by the hydraulic loading.
Answer: False. Generally, the higher the daily flow, the more maintenance and checking are needed to make sure all components are operating the way they should. An important part of this is to make sure the flow is not consistently exceeding the estimated daily sewage flow, and taking a close look at peak flows and how they may impact the system. For instance, if you as a maintenance provider are working off a weekly average of flows, and that average exceeds 70 percent of the estimated daily flow, you should be concerned and you should increase your frequency of looking at the system to prevent hydraulic overloading.
2. T or F - Total suspended solids is a measure of the quantity of solids that are suspended in the wastewater.
Answer: True. Suspended solids are the amount suspended in wastewater (or any water for that matter). For septic tank effluent we want to see the suspended solids be less than 60 mg/L, and the lower the better. Solids can be organic or inorganic. Inorganic solids can permanently plug soil pores in the final dispersal and soil treatment area. Typically, suspended solids are not removed or affected by an effluent screen. Effluent screens only catch and hold the larger solids that might otherwise move out of the septic tank.
3. T or F - BOD is the only indicator of the organic strength of wastewater.
Answer: False. There are other methods used, such as CBOD. BOD is the most common. The measure of fats, oils and grease (FOG) is also important, particularly for restaurants and other establishments with food preparation.
4. T or F - Graywater is relatively clean wastewater with limited amounts of contaminates.
Answer: False. I often get pushback from class attendees over this answer. But the fact is that while graywater does not contain fecal matter and the amount of organic loading is reduced, pathogen and bacteria reduction is not as much as you would think. They are reduced by an order of magnitude from millions to a million per liter, but there are plenty of organisms left in the water that can cause illness. Also, graywater still contains potentially harmful nutrients such as nitrogen and phosphorus, so graywater still needs to be treated before it is released to the environment. If the question was: Is graywater cleaner than raw wastewater? The answer would be yes.
5. T or F - Aerobic microbes use free oxygen for respiration.
Answer: True. This is true regardless of where the organisms reside, as part of an aerobic treatment unit or in the soil. For aerobic organisms to function and break down the organic waste requires oxygen just like we need oxygen to breath. So if wastewater organic loads are too high, oxygen transfer is limited. These organisms will not provide the amount of treatment we rely upon in our systems.