Here are three questions from a Grade 2 Wastewater Practice Exam.\u00a0 They’re helpful if you’re trying to obtain your Wastewater Treatment Certification.\u00a0 I included the answers at the bottom of the page.<\/span><\/p>\n

Grade 2 Wastewater Practice Exam<\/strong><\/span><\/h2>\n

PRACTICE QUESTIONS<\/strong><\/span><\/h2>\n

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1. \u00a0Which of the following is equivalent to 1 mg\/L?<\/span><\/li>\n<\/ol>\n
   \n
   1. 1 ppb<\/span><\/li>\n
   2. 10 parts per million<\/span><\/li>\n
   3. 1 lbs\/day<\/span><\/li>\n
   4. 1 ppm<\/span><\/li>\n<\/ol>\n

      2.\u00a0 What is the ideal dry solids content of primary sludge?<\/span><\/p>\n

      \n
      1. 1% dry solids<\/span><\/li>\n
      2. 2% dry solids<\/span><\/li>\n
      3. 4 to 8% dry solids<\/span><\/li>\n
      4. 2.5 to 3.4% dry solids<\/span><\/li>\n<\/ol>\n

         3.\u00a0 What is the ideal velocity in a grit channel?<\/span><\/p>\n

         \n
         1. 2 ft\/s<\/span><\/li>\n
         2. 2.5 ft\/s<\/span><\/li>\n
         3. 0.1 ft\/s<\/span><\/li>\n
         4. 1 ft\/s<\/span><\/li>\n<\/ol>\n

            Grade 2 Wastewater Practice Exam<\/strong><\/span><\/h2>\n

            ANSWERS<\/strong><\/span><\/h2>\n

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            1. \n

               d<\/span><\/h2>\n<\/li>\n<\/ol>\n

               First of all, both mg\/L and ppm are units of concentration.\u00a0 For example, mg\/L and ppm are often used to measure the concentration of chemicals, such as chlorine.<\/span><\/p>\n

               Now, let me explain why 1 mg\/L = 1 part per million (ppm) .\u00a0 Take a look at the following math conversion.<\/span><\/p>\n

               Keep in mind that 1 liter (L) of wastewater weighs 1,000,000 milligrams (mg).\u00a0 You’ll need this information to understand the first step of this conversion.\u00a0 Look at the bottom of the fraction in STEP 1.<\/span><\/p>\n

               STEP 1:<\/span><\/strong><\/span><\/p>\n

               <\/a><\/p>\n

               STEP 2:<\/span><\/strong><\/span><\/p>\n

               <\/a><\/p>\n

               Therefore, 1 mg\/L = 1 ppm.<\/span><\/p>\n

               2. c<\/span><\/h2>\n

               First of all, primary sludge is the waste that is removed from the incoming wastewater, and settles to the bottom of a primary clarifier.\u00a0 \u00a0It must be removed from the clarifier on a frequent basis.\u00a0 Otherwise, you’ll encounter septic conditions, which can lead to undesirable formation of gas bubbles.\u00a0 <\/span><\/p>\n

               Consequently, these bubbles will lift the settled sludge to the water surface.\u00a0 Obviously, you don’t want sludge to rise from the bottom.\u00a0 <\/span><\/p>\n

               T<\/span>he purpose of the clarifier is to remove the incoming waste by settling solids to the bottom using gravity.\u00a0 Therefore, it’s very important to prevent septic conditions by removing the primary sludge from the bottom on a routine basis.<\/span><\/p>\n

               Ideally, you want the primary sludge to be about 4 to 8% dry solids.\u00a0 Moreover, you should aim to have a thick sludge with minimal water content.<\/span><\/p>\n

               In order to better understand this subject, I encourage you to carefully review the following image.\u00a0 The yellow arrows show the path of the sludge.\u00a0 <\/span><\/p>\n

               Once it enters the primary clarifier, the sludge starts to settle to the bottom.\u00a0 Later, it is periodically removed with a primary sludge pump.\u00a0 By pumping frequently, you’ll avoid septic conditions, and thus, prevent rising sludge.<\/span><\/p>\n

               Incidentally, the pink arrow moving to the right, is the path of the treated sewage, which flows to the next stage for further treatment.<\/span><\/p>\n

               <\/a><\/span><\/p>\n

               3. d<\/span><\/h2>\n

               First of all, the purpose of the grit channel is to remove heavier solids, such as sand and eggshells, from the incoming wastewater.\u00a0 By using gravity, these heavier solids are allowed to settle to the bottom of the grit channel.\u00a0 <\/span><\/p>\n

               You want to remove these heavier wastes because they can cause excessive wear in mechanical equipments, such as pumps.\u00a0 Therefore, the grit channel is located in the earlier stage of the treatment process.<\/span><\/p>\n

               Ideally, you want the velocity of the wastewater to be about 1 foot\/second as it flows through the grit channel.\u00a0 This reduced velocity helps settle the heavier solids, while keeping the lighter organics suspended.\u00a0\u00a0<\/span><\/p>\n