Texas Basic Waste Water Operations Ch#05 The Collection System

A properly constructed and maintained wastewater system is necessary to protect public health. Its purpose is to collect and transport waste from the source to treatment. Wastewater should move through the system quickly to prevent septicity.

Benefits of the wastewater collection system include the following: • Removal of potential health hazards (most important) • Prevention of odors, flies, and mosquitoes • Cleanliness and appearance • Comfort and convenience

There are many parts of a wastewater system, listed as follows: • Wastewater lines • Manholes • Lift stations • Wastewater crossings • Inverted siphons • Cleanouts

If gasoline or solvent odors are detected in a manhole, contact supervisory and emergency personnel immediately!

Safety Rules In and Around Manholes • While working, place traffic guards around the manhole and lights (at night). • Use a proper tool to handle the cover. • §217.333. Confined Spaces. (c) A confined space entry must be conducted according to the requirements of 29 Code of Federal Regulations §1910.146. • Test the manhole for gases and sufficient oxygen with gas detectors before removing lid. • Wear a lifeline and use a portable ladder to enter the manhole (tripod is preferred). • Have two workers assisting at the surface. • Ventilate the manhole while working. • After leaving the manhole, wash to prevent infection. • Never use manhole ladder rungs. • Replace manhole lid when finished or when leaving the area.

High-Density Polyethylene (HDPE) and PVC are the most common pipe materials used, but many other materials are available, including the following: • Polyvinyl Chloride (PVC) • Vitrified tile (clay) • Asbestos Cement (AC) • Polyethylene • Concrete • Acrylonitrile-butadiene-styrene (ABS) • Ductile iron • Cast iron • High-Density Polyethylene (HDPE) Bituminous fiberboard or aluminum pipe is not acceptable in a collection system.

The grade or slope of the pipe is important. Flat-graded lines are undesirable because solids will settle in the line and cause stoppages. In addition, slow moving wastewater allows bacterial action to deplete oxygen. As oxygen depletes, anaerobic conditions cause odor, corrosion, and toxic gases.

Velocity is important in a gravity collection line. For any gravity collection line, the minimum velocity required to keep solids in suspension is 2 ft/sec. Accepted practice recommends velocities of 3 to 5 ft/sec. Where flow velocity exceeds 10 ft/sec, protection from shock or erosion should be provided.

Lay the bell end of the pipe facing upstream or uphill. Dig holes for the bells so the barrel of the pipe, not the bell, supports the pipe and backfill.

Homes, stores, restaurants, hospitals, and other community sources are waste generators. Sometimes industrial sources such as factories, refineries, food processors, or metal plating manufacturers will contribute wastes. The wastewater collection system is not intended to carry stormwater. A separate storm wastewater system will carry rainwater away.

According to TCEQ Design Criteria for Domestic Wastewater Systems, install wastewater collection lines no closer to water lines than 9 feet in all directions. Install parallel wastewater and water lines in separate trenches. Install water lines above wastewater lines. When the 9-foot separation cannot be achieved, a list of alternatives may be found in 30 TAC Chapter 217.53(d).

The Occupational Safety and Health Administration (OSHA) requires cave-in protection for trenching (29 CFR 1926). OSHA regulations apply only to private business, but political subdivisions of a state, such as cities, should use the standards as guidelines. OSHA sets standards for shoring, sloping, or trench boxes for trenches five feet or deeper. Providing shoring is the employer’s responsibility. Employees are responsible for using shoring.

If the trench is four feet or deeper, use a portable ladder or other means of exit. The ladder must extend three feet above the trench and be secured. Ladders must be within 25 feet of trench workers and not more than 50 feet apart. The excavation spoil must be at least two feet from the edge of the trench. Sloping of a trench wall may be used in place of shoring; however, the slope must meet the angle of repose or maximum allowable slope. The angle of repose refers to the angle of the trench wall where the soil will no longer slough off, thus preventing cave-in.

If the trench is four feet or deeper, use a portable ladder or other means of exit. The ladder must extend three feet above the trench and be secured. Ladders must be within 25 feet of trench workers and not more than 50 feet apart. The excavation spoil must be at least two feet from the edge of the trench. Sloping of a trench wall may be used in place of shoring; however, the slope must meet the angle of repose or maximum allowable slope. The angle of repose refers to the angle of the trench wall where the soil will no longer slough off, thus preventing cave-in.

If the trench is four feet or deeper, use a portable ladder or other means of exit. The ladder must extend three feet above the trench and be secured. Ladders must be within 25 feet of trench workers and not more than 50 feet apart. The excavation spoil must be at least two feet from the edge of the trench. Sloping of a trench wall may be used in place of shoring; however, the slope must meet the angle of repose or maximum allowable slope. The angle of repose refers to the angle of the trench wall where the soil will no longer slough off, thus preventing cave-in.

If the trench is four feet or deeper, use a portable ladder or other means of exit. The ladder must extend three feet above the trench and be secured. Ladders must be within 25 feet of trench workers and not more than 50 feet apart. The excavation spoil must be at least two feet from the edge of the trench. Sloping of a trench wall may be used in place of shoring; however, the slope must meet the angle of repose or maximum allowable slope. The angle of repose refers to the angle of the trench wall where the soil will no longer slough off, thus preventing cave-in. NOTE: might be that this paragraph is important......

The primary causes of stoppage are roots and grease. Other factors include poor construction, public abuse, flushing disposable wipes, line failure, and flat grades. To prevent line stoppages and clogging, collection lines should be cleaned regularly.

Collection line cleaning accomplishes the following: • Increases pipe capacity • Prevents septic conditions • Reduces odor • Maintains flow velocity • Reduces emergency repairs • Reduces stoppages NOTE: i know the question says "wastewater cleaning" but it really should say collection line cleaning because it isnt the waste water being cleaned but that is how it is written in the textbook.

Hydraulic cleaners (jetting units) use water under pressure forced through cleaning nozzles. When using hydraulic cleaners, the operator must not flood homes or basements. Other hydraulic equipment includes the following: • Sewer balls or pigs have ribs that create a jet action, flushing debris from lines. • Bags and kites collect water and then scour wastewater lines as they push the wastewater forward.

Maps should be as built, showing corrections made in the field during construction. It is the operators duty to ensure maps are corrected to reflect what is actually in the ground. Up-to-date maps of the system are important to do the following: • Locate mains and manholes • Determine size of mains • Determine flow direction • Note manhole and line depth

Some chemicals used with grout packers produce toxic fumes. Follow safety directions. When chemicals are used to solve line problems, consider worker and public safety!

It is more economical for wastewater to flow to treatment by use of a gravity sewer. However, when hilly terrain or deep excavation makes this impossible, a lift station is used. The wastewater flows into a holding tank and is pumped to a higher point to continue gravity flow or pumped to treatment through a force main.

There are three basic designs of lift stations: • Dry well stations • Wet well stations • Pneumatic ejectors

Dry well stations have the motors and pumps in a dry well, separated from the adjacent wet well where the wastewater collects. Dry well stations below ground must have nonslip steps, two-sump pumps, mechanical ventilation, and explosion resistant lights. In a wet well station, pumps and motors are submerged in the wastewater. A pneumatic ejector uses compressed air to move wastewater. System flow can be up to 1,000 gallons per minute (GPM).

The centrifugal pump is most often used in a lift station. It has a shaft mounted in two bearings set into a volute (discharge casing). On the end of the shaft is an impeller. An impeller transfers energy from the shaft to the water. This design is low cost, easy to maintain, and efficient if properly sized.

Foreign matter in the impeller can cause noisy operation and should be investigated. When impellers wear out, pumping costs increase.

The check valve, usually a swing type, prevents water from the pump discharge from flowing backwards when the pump is off.

The best isolation valve is the gate valve because it leaves an unrestricted path when open. The gate valve is the most commonly used valve in the collection system.

The best isolation valve is the gate valve because it leaves an unrestricted path when open. The gate valve is the most commonly used valve in the collection system.

Motors are usually three-phase alternating current induction motors. Power for a three-phase motor is supplied by three AC power sources. Electric motor speed is measured in rotations per minute (rpm).

To reduce wastewater gases, the TCEQ requires lift stations to have a ventilating system. A dry well must use mechanical ventilation. One design uses an exhaust fan to expel station air and another design forces outside air into the station. Be sure the ventilating system is working before entering a pump station. If it is not, check for gases or oxygen deficiency with a gas detector.

Hydrogen sulfide is very toxic and deadens the sense of smell at high concentrations! The presence of a hazardous atmosphere can make this a “permit required confined space.”

Do not pump the station dry because the pump may lose prime. If a pump loses prime, it can heat up and damage the seal. There should be an alarm for low wet well level as well as high wet well level. Check the control system daily.

Water level detection is necessary for pump control and alarm system operation. Common equipment used to detect liquid depths and control pumps include the following: Floats. As the water level rises or lowers, so does the float, turning a pump switch on or off. | Pneumatic Bubblers. As the water level rises or lowers, air trapped in a tube increases or decreases in pressure, causing a switch to turn on or off; to keep the tube filled with air, air is pumped into it. | Electric Probes (Electrodes). As the water level rises or lowers, an electric circuit is completed or broken between two probes, turning a pump switch on or off. | Ultrasonic Sensors (Acoustic). Sensors measure the time sound waves take to reach the water level and bounce back. Sensors also measure the water height. Controls are then used to start or stop the pump.

Sump pumps are installed in dry wells to collect packing seal leakage, as well as clean up water. NOTE: Slump, bump, and dump pumps do not exist to my knowledge this should be free points.

NOTE: while technically only "prefabricated" is incorrect based on their definitions "preventative maintenance" is a commonly used term. Preventive maintenance is the act of performing regularly scheduled maintenance activities to help prevent unexpected failures in the future. Put simply, it's about fixing things before they break.

Records are important to lift station operation and maintenance. Records include a daily checklist, sign-in log, and a procedures manual.

Records include a daily checklist, sign-in log, and a procedures manual. NOTE: the referenced paragraph for questions 37/38 is two sentences long and yet is still referenced more than once so might be worth remembering.