Texas Basic Waste Water Operations Ch#06 Prelim Treatment & Flow Meas.

Preliminary treatment is usually the first step of treatment. This process removes inorganic solids, large objects, grit, and grease from the wastewater, which prevents problems with plant piping, tanks, equipment, or later treatment.

Manually cleaned screen maintenance includes washing the area to reduce odor and cleaning the screen channel to remove grit and sand. Manually cleaning bar screens may require lifting heavy material with a rake, potentially causing back injuries. When lifting, keep your feet apart, back straight and knees bent. Protect your hands with gloves. The area is often wet; use caution to prevent slipping. Before repairing the screen, turn the power off and tag and lockout the controls.

Motor driven grinders shred or grind large objects. Debris is returned to the wastewater stream for later removal. Grinder cutting knives are damaged by hard objects. Comminutors and barminutors are the two designs of grinding units.

Grit chambers remove grit by gravity and are used prior to primary and secondary treatment. Grit removal is one process of preliminary treatment. Grit is mostly settleable inorganic solids that cause the following: • Stoppages • Pumping problems • Accumulation in aeration basins • Equipment damage • Accumulation in digesters

The following are the most common designs of grit removal units: • Manually cleaned chambers - These chambers have one or more channels. The velocity is about 1 ft/sec, which allows grit to settle. Hand-cleaned chambers have no moving parts. Maintenance involves removing and washing the grit and checking for leaks. • Mechanically cleaned chambers - Chain-powered scrapers remove the grit from the channel floor and then pull it up an incline, where it falls into a container. • Aerated chambers - Air scours gases, floats grease, and reduces the velocity of the water. Grit settles into the hopper. Pumps remove the grit from the hopper. • Cyclone separators - Wastewater pumps into a cone-shaped unit. The shape of the unit and the angle of flow cause a spiral. As the wastewater spins, grit is thrown by centrifugal force to the wall of the unit, and then falls to the bottom, where it flows into a washer. • Screw washers - The purpose of a grit washer is to remove organic material from the grit. The grit washer is composed of two primary components, the screw impeller and the screw conveyor. Screw impellers circulate the contents of the washer and float the organic particles to the surface. Screw conveyors bring grit from the bottom of the washer to a hopper for transfer to disposal.

Manually Cleaned Chambers. These chambers have one or more channels. The velocity is about 1 ft/sec, which allows grit to settle. Hand-cleaned chambers have no moving parts. Maintenance involves removing and washing the grit and checking for leaks.

Wastewater pumps into a cone-shaped unit. The shape of the unit and the angle of flow cause a spiral. As the wastewater spins, grit is thrown by centrifugal force to the wall of the unit, and then falls to the bottom, where it flows into a washer.

The purpose of a grit washer is to remove organic material from the grit. The grit washer is composed of two primary components, the screw impeller and the screw conveyor. Screw impellers circulate the contents of the washer and float the organic particles to the surface. Screw conveyors bring grit from the bottom of the washer to a hopper for transfer to disposal. NOTE: Since the reference is a single sentence in the screw washer description i will also include an explanation for understanding why we do this from the Waste Water Treatment textbook referenced in another quiz set i have made. "A grit removal unit of any type, no matter how well designed or well operated, will allow some organic matter, called detritus, to cling to and settle out with the grit." "The washed grit still contains some organic material; therefore it should be disposed of as soon as possible, usually by proper disposal in a sanitary landfill."

Grease interferes with biological treatment and causes stoppages, odor, and unsightly conditions. Remove grease at the plant or prevent it from entering the collection system by requiring appropriate businesses to use grease traps.

Some plants use grease flotation to remove grease. Diffused air causes grease to rise to the surface. Chlorine congeals grease, allowing skimming. Skimmers collect grease from sedimentation basins. NOTE: "The purpose of pre-aeration is to remove grit, reduce gases, add oxygen, and to float grease." air is the invisible gaseous substance surrounding the earth, a mixture mainly of oxygen and nitrogen, readily available, and easily gathered/used. while pure oxygen, nitrogen, or other gasses would accomplish the floatation of grease; only oxygen could satisfy the entire listed purpose. Since using pure oxygen would present its own safety and cost challenges it is easier and cheaper to simply use the atmosphere in which we reside.

Some plants use grease flotation to remove grease. Diffused air causes grease to rise to the surface. Chlorine congeals grease, allowing skimming. Skimmers collect grease from sedimentation basins. NOTE: while "float" may sound like a valid answer it is the air lifting congealed masses of grease or the relative density of grease and water that causes floatation not the chlorine. chlorine does however affect the electrostatic charge of the grease molecules causing them to coalesce/congeal.

Disposal of grit, screenings, and grease is by burial in a sanitary landfill.

The purpose of pre-aeration is to remove grit, reduce gases, add oxygen, and to float grease.

Flow equalization increases treatment capacity by controlling flow variation or shock loads, as well as helps to reduce or eliminate permit violations. A shock load is a type of flow or pollutant concentration received at a water or wastewater treatment plant in sufficient quantity or strength to momentarily exceed the normal loading ranges.

Wastewater flow varies with time of day, seasons, and weather. It is important to monitor flow to calculate plant load, as well as to determine inflow/infiltration, treatment costs, and flow trends.

Flow is the water volume passing a given point in a specified time in gallons per minute (GPM) or cubic feet per second (CFS). NOTE: i was unable to find an example of when we would specifically use cubic feet per second for water flow but the duck creek WWTP uses standard cubic feet per minute (SCFM) for air flow to the aeration basin.

A weir is an obstruction placed in a channel causing the water to back up. The depth of the water flowing over the weir determines the flow rate. Common weir designs are V-notch, rectangular, and Cipolletti.

A weir is an obstruction placed in a channel causing the water to back up. The depth of the water flowing over the weir determines the flow rate. Common weir designs are V-notch, rectangular, and Cipolletti.

A weir is an obstruction placed in a channel causing the water to back up. The depth of the water flowing over the weir determines the flow rate. Common weir designs are V-notch, rectangular, and Cipolletti. NOTE: referenced three times in a row...... might be important......

Ultrasonic flow meters work with a weir, flume, or filled pipe, and use the principle of sonar. Sound from the unit bounces off or through the water and back to the receiver. The unit measures the round-trip time or change in sound and then computes the flow rate. NOTE: radar uses radio waves which are electromagnetic and tends to detect moving conductive material such as metal or water. solar uses photons from the sun to provide the energy required to free and move electrons and at best detects day/night. Radio much like radar is electromagnetic waves that are amplitude modulated(AM) or frequency modulated(FM) to carry encoded information such as music. Radio will still return in the same way radar will however radio stations have no need of the equipment required to properly analyze the returned energy.

The magnetic meter works by the law of induction. When an electrical conductor moves through a magnetic field, friction produces voltage in the conductor. The higher the water velocity, the greater the voltage and the greater the flow rate.

Without regular maintenance, especially cleaning, meter readings can become inaccurate. In each discharge permit, the TCEQ requires annual calibration of flow meters. They must be ± 10% accurate.

Without regular maintenance, especially cleaning, meter readings can become inaccurate. In each discharge permit, the TCEQ requires annual calibration of flow meters. They must be ± 10% accurate.