TEXAS WASTEWATER A EXAM QUESTIONS AND ANSWERS.

What is TCEQ doing to control "point source" pollution of the Texas waterways? *Permitting of domestic wastewater plants *Permitting of industrial wastewater plants Describe proper design of force main wastewater lines. Minimum two fps velocity with the smallest pump operating alone. Minimum four inch diameter pipe with 150 psi rating. What is Standard Dimension Ratio? Ratio of outside pipe diameter (OD) to wall thickness (PVC) Describe proper design of gravity wastewater lines. Designed to flow half full ,under normal conditions, at a minimum of two fps and a maximum of ten fps. Manholes should have a minimum opening of? 24 inches and be at least 4 feet wide. pH meters should be calibrated how often? What standards should be used for calibration purposes? Daily with at least two buffers. What is the standard chlorine residual and minimum contact time on Texas wastewater permits? a. 1.0 mg/L for a minimum 20 minutes detention time at peak flow b. No chlorine residual needed if detention time is greater than 21 days As the complexity of an organization increases, what management function becomes most important? Planning What is the effective chlorine disinfecting agent? Hypochlorous Acid (HOCl) Does pH affect the chlorination process? Explain your answer. When using free chlorine the disinfectant is HOCl acid. As such it is much more effective at pH's below 7.0. Above 7.0 pH the acid begins to be neutralized. What is the effluent chlorine residual in Texas that is standard on permits and the minimum detention time? What is the maximum residual allowed? Texas standard is 1.0 mg/L for a minimum 20 minutes detention time at peak flow. Maximum residual allowed is 4.0 mg/L. A treatment plant has a clarifier that is 60 feet in diameter and is 10 feet deep. The weir is 2 feet inside the outer clarifier wall. The flow is 1.0 MGD. The weir and outflow channel is 3 feet deep. a. What is the detention time in hours? Formula What activated process cannot nitrify in a single stage? Contact Stabilization What is the GPM output of a piston pump with an 8-inch diameter piston with a 10-inch stroke operating at 50 strokes per minute? Formula A treatment plant has a clarifier that is 60 feet in diameter and is 10 feet deep. The weir is 2 feet inside the outer clarifier wall. The flow is 1.0 MGD. The weir and outflow channel is 3 feet deep. a. What is the detention time in hours? b. What is the surface loading in gal/ft2/day? c. What is the weir loading in gal/linear ft/day? Formulas A primary clarifier has a flow of 3.0 MGD and has a diameter of 100 feet. It is 12 feet deep and has 24 inches of freeboard. What is the detention time in hours? Formulas Anaerobic digester gas should contain? 65-75% methane, 25-35% carbon dioxide and 1-5% nitrogen. An activated sludge plant has an average daily flow of 3.5 MG. The aeration tank capacity is 1.2 MG with a MLSS concentration of 3200 mg/L. The clarifier has a capacity of 400,000 gallons with a MLSS concentration of 6,000 mg/L. The wasting rate is 40,000 gallons per day with a MLSS concentration of 8, 000 mg/L. The effluent TSS is 18 mg/L. Assuming volatile concentrations of 70%, what is the MCRT and what type of activated sludge plant should this be? Formulas MCRT What are some of the causes of filaments in the aeration basin? a. low DO b. low organic loading c. septic wastes d. nutrient deficiencies . e. high sulfur content Good sludge quality will have a predominance of what organisms in the MLSS? Ciliated protozoa When an RBC is operating correctly, how will the slime appear on the media? Grey to brown 0.05 to 0.1 inches thick According to design criteria, what are the minimum allowable diameters for a manhole? 24 inch opening and 48 inch inside diameter What activated sludge process does not achieve complete nitrification? Contact Stabilization In the selection of forced main wastewater piping, what is the minimum working pressure? 150 psi The oxygen depletion of BOD dilution water should not exceed 0.2 mg/L. What is the minimum air gap when making water and wastewater connections? Minimum of one inch or twice the inlet pipe size whichever is greater. What is the minimum useful size pipe to prime a centrifugal pump? 1 inch An anaerobic digester must maintain an average year round temperature of 95 degrees F. How do you remove shoring from a trench? From the bottom up Which of the following methods would you use to increase the degree of nitrification in an activated sludge plant? increase dissolved oxygen levels and increase the sludge age Which of the following are considered normal operator controls on an activated sludge plant? aeration rates return and wasting rates Reducing the return sludge flow rate for an activated sludge system which has a good settling sludge will ________. increase the RAS concentration and the clarifier sludge blanket thickness An extended air activated sludge plant has a fast settling sludge and high amounts of pin floc leaving the clarifier. One way to correct this problem is to ________. * reduce the MCRT by wasting more * increase the F/M ratio by wasting more The primary causes of wastewater stoppages are ________. roots and grease The inside diameter of a manhole must be how wide? 48 inches On a construction job site, equipment booms must maintain at least how many feet of clearance from overhead electric lines? 10 feet Digester gas should contain about ________. a. 65% - 75% methane A treatment plant has two primary clarifiers. Each has a diameter of 40 feet and a depth of 12 feet. If the design flow is 1.2 mgd, find the surface loading on each clarifier in gallons/ft2/day. Assume the flow is equally split between the two clarifiers. 3.14 x 20 x 20 = 1256 1,200,000 /2 = 600,000 gallons each 600,000/ 1256 b. 478 gallons/ft2/day