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- A filter must be backwashed when _____________________.<\/span><\/li>\n<\/ol>\n
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- \n
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- Influent NTU decreases<\/span><\/li>\n
- Influent pH changes<\/span><\/li>\n
- Temperature increases<\/span><\/li>\n
- Head loss across the filter increases and reaches a pre-determined limit<\/span><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
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2. Which of the following is a disinfection by-product precursor?<\/span><\/p>\n
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- \n
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- \n
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- Inorganics<\/span><\/li>\n
- Arsenic<\/span><\/li>\n
- Natural organic matter<\/span><\/li>\n
- Nitrate<\/span><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
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3. What is used to regulate iron and manganese?<\/span><\/p>\n
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- \n
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- MCL<\/span><\/li>\n
- SMCL<\/span><\/li>\n
- Revised Total Coliform Rule<\/span><\/li>\n
- Lead and Copper Rule<\/span><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
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4. Which layer has the most significant temperature change in a stratified lake?<\/span><\/p>\n
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- \n
- \n
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- Epilimnion<\/span><\/li>\n
- Hypolimnion<\/span><\/li>\n
- Thermocline<\/span><\/li>\n
- Upper layer<\/span><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
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Click here for\u00a0Water Treatment Certification Practice Test<\/a><\/strong><\/h2>\n
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ANSWERS<\/strong><\/h2>\n
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1. D<\/h2>\n
A filter is backwashed periodically to remove entrapped solids and clean the filter.\u00a0 Essentially, the water flows in the reverse direction to remove the solids.\u00a0\u00a0<\/span><\/p>\n
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As the filter treats the incoming water, it gradually becomes clogged with solids.\u00a0 Eventually, it will reach a point where the filter must be cleaned or backwashed by reversing the flow of water.\u00a0\u00a0<\/span><\/p>\n
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As clogging in the filter increases, the head loss also increases.\u00a0 Head loss is the resistance to the flow caused by the solids build-up in the filter.\u00a0 Therefore, you want to clean or backwash the filter when the head loss reaches a certain point.\u00a0 You don’t want the filter to clog excessively.<\/span><\/p>\n
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To illustrate, the following drawing shows the water flowing downwards into the filter to treat the water.\u00a0 Then, it shows the water reversing direction and flowing upwards to clean or backwash the filter.<\/span><\/p>\n
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![\"WATER](\"https:\/\/www.waterandwastewatercourses.com\/wp-content\/uploads\/2018\/10\/FILTER-BACKWASH.gif\")
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![\"Water](\"https:\/\/cropaia.com\/wp-content\/uploads\/2018\/03\/Rapid-sand-filtration-e1520427763870.jpg\")
Filter at a water treatment plant.\u00a0<\/span><\/em><\/figcaption><\/figure>\n <\/p>\n
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2. C<\/h2>\n
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First of all, a disinfection by-product is an undesirable chemical that forms when chlorine reacts with natural organic matter.\u00a0 It’s undesirable because it is a health threat, and causes cancer.\u00a0 <\/span><\/p>\n
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There are various disinfection by-products.\u00a0 However, the most important disinfection by-product for the operator exam is trihalomethane.\u00a0 It’s commonly known by its acronym, THM.<\/span><\/p>\n
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A disinfection by-product precursor is the substance that reacts with chlorine to form disinfection by-products.\u00a0 Earlier, we mentioned that natural organic matter reacts with chlorine to form disinfection by-products.\u00a0 Therefore, the correct answer is “natural organic matter”.\u00a0\u00a0<\/span><\/p>\n
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![\"Water](\"https:\/\/2.bp.blogspot.com\/-Apkfc5dPTgs\/WWBf-oMbUYI\/AAAAAAABK38\/WZNQGN8c1m4d_Gv0Ir58BOl7mBMjmr0zACLcBGAs\/s1600\/1529.png\")
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\u00a0\u00a0<\/span><\/p>\n
3. B<\/h2>\n
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Iron and manganese are minerals that are naturally present in untreated water.\u00a0 <\/span>They don\u2019t pose a health threat, but they’re undesirable because they stain plumbing fixtures.\u00a0 Specifically, iron causes water to appear red, while manganese leads to black stains.\u00a0<\/span><\/p>\n
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Therefore, iron and manganese are regulated by non-mandatory water quality standards called Secondary Maximum Contaminant Levels (SMCL).\u00a0 An SMCL is not enforceable, and testing for iron and manganese is voluntary.\u00a0 The EPA established SMCLs to help water utilities manage the taste, color and odor of drinking water.\u00a0 \u00a0Again, SMCLs are for contaminants that are not a threat to human health.\u00a0 \u00a0\u00a0<\/span><\/p>\n
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In contrast, drinking water contaminants that pose a health risk fall under a more stringent set of requirements:\u00a0 <\/span>Maximum Contaminant Levels (MCL).\u00a0 <\/span>An\u00a0MCL\u00a0is the maximum allowable concentration of a drinking water contaminant.\u00a0 They are mandatory and enforceable.\u00a0 \u00a0<\/span><\/p>\n
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Furthermore, all public water systems must comply with the MCL to protect public health.\u00a0 They are not voluntary.\u00a0 <\/span>Arsenic and nitrate are examples of drinking water contaminants that are hazardous to human health, and have an MCL.\u00a0 \u00a0<\/span><\/span><\/p>\n
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Here’s a photo of water with high concentration of iron.<\/span><\/p>\n
![\"Water](\"https:\/\/www.discountwatersofteners.com\/blog\/wp-content\/media\/remove-iron-from-water-katalox-iron-filter-discount-water-softeners.jpg\")
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4. C<\/h2>\n
First of all, the water temperature of a lake differs as you move deeper in the water.\u00a0 The sun causes the upper layer to be warmer than the lower depths.\u00a0 <\/span><\/p>\n
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As the upper layer heats up, the water density decreases.\u00a0 Meanwhile, the water in the lower depths remain cold and dense.\u00a0 As a result, the difference in density minimizes the vertical mixing in the lake.<\/span><\/p>\n
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When this occurs, the lake is thermally stratified.\u00a0 The water temperature differs as you go deeper.<\/span><\/p>\n
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A lake that is thermally stratified has 3 layers.\u00a0 Most noteworthy, the middle layer has the biggest temperature decrease with depth.\u00a0 It is called “thermocline” or “metalimnion.”<\/span><\/p>\n
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Furthermore, “epilimnion” is the upper warm layer, while “hypolimnion” is the lower cold layer.<\/span><\/p>\n
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![\"Water](\"https:\/\/www.researchgate.net\/profile\/Lionel_Ho\/publication\/242740698\/figure\/fig5\/AS:650793111781409@1532172577713\/Cross-section-of-a-thermally-stratified-lake-showing-location-of-the-epilimnion-and.png\")
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The lake remains stratified until early winter, when the surface water cools, and mixing begins.\u00a0 Consequently, the water temperature during winter is fairly similar throughout the entire depth.<\/span><\/p>\n
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Water Treatment Certification Practice Test s<\/a><\/h2>\n
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- Hypolimnion<\/span><\/li>\n
- Epilimnion<\/span><\/li>\n
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- SMCL<\/span><\/li>\n
- MCL<\/span><\/li>\n
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- Arsenic<\/span><\/li>\n
- Inorganics<\/span><\/li>\n
- \n
- Influent pH changes<\/span><\/li>\n
- Influent NTU decreases<\/span><\/li>\n
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- \n