Controlling Salt Buildup In Wastewater Recycling Systems · Controlling Salt Buildup In Wastewater...
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Transcript of Controlling Salt Buildup In Wastewater Recycling Systems · Controlling Salt Buildup In Wastewater...
ALABAMA COOPERATIVE EXTENSION SERVICE, AUBURN UNIVERSITY, ALABAMA 36849-5612
Controlling Salt Buildup In Wastewater Recycling Systems
Widespread use of wastewater recycling systems has im
proved waste handling from poultry layer and swine production facilities. Wastewater recycling reduces pit gases and odors and improves poultry and swine performance, flock and herd health, and in-house working environments.
However, wastewater recycling also causes buildup of a grayish-white crystalline salt on the internal surfaces of pump and piping systems used for lagoon liquid recycling. This compound is predominantly magnesium ammonium phosphate, sometimes referred to as struvite. Deposits occur most frequently on metallic surfaces but also occur in varying degrees on plastics. Among metal components, steel, cast iron, bronze, and brass appear to be about equally susceptible.
Salt buildup first occurs in the internal pump components and gradually moves outwrurd into discharge pipes. Buildup also occurs at pipe joints, elbows, valves, or imperfections because grit and manure solids tend to lodge at these points, providing a base on which salt can grow. However, predicting the occurrence of salt crystallization and deposition is difficult since exact causes are nor well defined.
Salt buildup has been extensively studied in other livestockproducing states. Based on the research and the field trials from
other states, this publication identifies design, maintenance, and management techniques to reduce salt buildup.
Pump And Piping System Design
• Choose a high-quality lowpressure, self-priming centrifugal or submersible pump for the best service.
• Avoid using a significantly oversized pump. Using a pump that is too large for the piping system will restrict the discharge and increase pipe flow velocities and pump cavity turbulence.
• Locat~: the pump as close to the high water level of the lagoon as possible to minimize suction lift.
• Consider placing pump controls on a timer.
• Ensure that the suction line is large enough to prevent pump cavitation. (A good rule of thumb is the suction pipe diameter should be one standard size larger than the discharge pipe.)
• Replace fine mesh suction intake strainers with wire screens or baskets with l-inch or larger mesh and a diameter at least 5 times the suction pipe diameter.
• Use nonmetallic pipe and fittings.
• Consult pump experts to size pipe diameters large enough to maintain flow velocities between 3 to 5 feet per second. The minimum pipe diameter at any point throughout the system, except at
CIRCULAR ANR-860
the immediate vicinity of the discharge point, should be 11/z inches.
• Minimize shrurp pipe bends such as elbows and tees. Instead use flexible plastic pipe and long sweep elbows for direction changes.
• Choose a pump and piping system with enough capacity to allow it to operate only one-half to two-thirds of the time.
• If a piping system will not be in continuous use, design it so that it can be drained between pumping events.
Electrostatic Charge Elimination
• Eliminate static charges or stray voltage that may contribute to salt buildup by directly grounding the pump housing. Drive a metal rod 10 to 12 feet into moist soil near the lagoon edge.
• Periodically check cable connections at the ground rod and pump for corrosion.
Lagoon Management • Properly size primary la
goons to provide adequate treatment capacities.
• Charge a new lagoon at least half full of water prior to startup. Bring up the liquid level to design levels as soon as possible.
• Maintain lagoon levels during weather extremes. Rainfall during normal years dilutes lagoon liquid concentrations.
Extended periods of hot, dry weather increase nutrient and salt levels and the rate of salt buildup. During these dry periods, flush with fresh water or irrigate a portion of the lagoon contents and replace with fresh water as needed to dilute lagoon salt concentrations.
Acid Cleaning • Dissolve salts from internal
pump and pipe surfaces with dilute acid treatments.
Dilute 1 gallon muriatic (hydrochloric) acid in 9 gallons of water. Muriatic acid (30 percent [20°) technical grade) can be purchased at most chemical supply houses or paint stores. (Muriatic acid costs approximately $27 for a 15-gallon drum plus a $25 drum deposit and $1 drum cleaning fee.)
NOTE: Exercise extreme caution when mixing acids with water. Never try to add water to the concentrated acid. Always partially fi.ll the tank with water; then add the acid to the water very slowly. Mixing acid and water generates heat. Wear eye protection against possible spattering. Although this dilution should not hurt metal, avoid prolonged contact of the acid solution and metal.
• To remove heavy salt buildup, install an acid recirculation loop for thorough treatment. Install a l-inch line to return acid from the end of each treated pipe section to the tank. Consider installation of a permanent return line for convenience.
Use a 150-gallon acid-resistant tank as the acid recirculation reservoir. Make sure the tank is large enough to supply enough total solution to fill the pipe length to be cleaned plus somP reserve to keep the recirculation pump primed (See table to calculate gallons needed to fill pipe).
Calculating Gallons Per Foot Of Length Based On Inside Pipe Diameter.
Inside Pipe Diameter, Inches
1.0 1.5 2.0 2.5 3.0 4.0 6.0
Gallons Per Foot Of Length
0.06 0.13 0.20 0.29 0.43 0.70 1.53
Isolate pipe line sections with valves so that acid can be circulated through only one section. Isolating pipe sections will reduce the amount of acid solution needed and, therefore, reduce tank size. Install a quick-connect coupling to switch the flush pump suction from the lagoon to the bottom of the acid tank.
If the salt buildup is heavy, recirculate the solution overnight. After it is used to dissolve a heavy salt buildup, the solution may have to be discarded. An inexpensive pH test kit can show how much strength remains. If the solution is weak, discard it. Spent acid may be dumped in the lagoon.
The
E:.."1Aiabama lil7Cooperative
Extension Service AUBURN UNIVERSITY
Circular ANR-860 This publication was prepared by Ted W. Tyson and James 0. Donald, Extension Agricultural Engineers. It was adapted from "Crystalline (Salt) Formation In Wastewater Recycling Systems," EBAE 082-81. James C. Barker. Biological, and Agricultural Engineering, North Carolina State University, Raleigh, NC.
Use chemicals only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed.
For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.
Issued In furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension Service, Auburn University, Ann E. Thompson, Director, offers educational programs and materials to all people without regard to race, color, national origin, sex, age, or handicap and is an equal opportunity employer. ACES, 3M, New 5:94, ANR-860