ALABAMA COOPERATIVE EXTENSION SERVICE, AUBURN UNIVERSITY, ALABAMA 36849-5612 Controlling Salt Buildup In Wastewater Recycling Systems W idespread use of wastewater recycling systems has im- proved waste handling from poultry layer and swine produc- tion facilities. Wastewater recy- cling reduces pit gases and odors and improves poultry and swine performance, flock and herd health, and in-house working en- vironments. However, wastewater recy- cling also causes buildup of a grayish-white crystalline salt on the internal surfaces of pump and piping systems used for la- goon liquid recycling. This com- pound is predominantly magne- sium ammonium phosphate, sometimes referred to as struvite. Deposits occur most frequently on metallic surfaces but also occur in varying degrees on plas- tics. Among metal components, steel, cast iron, bronze, and brass appear to be about equally sus- ceptible. Salt buildup first occurs in the internal pump components and gradually moves outwrurd into discharge pipes. Buildup also oc- curs 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 occur- rence of salt crystallization and deposition is difficult since exact causes are nor well defined. Salt buildup has been exten- sively studied in other livestock- producing states. Based on the re- search and the field trials from other states, this publication iden- tifies design, maintenance, and management techniques to re- duce salt buildup. Pump And Piping System Design • Choose a high-quality low- pressure, 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. • the pump as close to the high water level of the lagoon as possible to minimize suction lift. • Consider placing pump con- trols 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 larg- er than the discharge pipe.) • Replace fine mesh suction in- take 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 fit- tings. • Consult pump experts to size pipe diameters large enough to maintain flow velocities between 3 to 5 feet per second. The mini- mum pipe diameter at any point throughout the system, except at CIRCULAR ANR-860 the immediate vicinity of the dis- charge point, should be 1 1 /z inch- es. • 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 con- nections at the ground rod and pump for corrosion. Lagoon Management • Properly size primary la- goons to provide adequate treat- ment capacities. • Charge a new lagoon at least half full of water prior to start- up. Bring up the liquid level to design levels as soon as possible. • Maintain lagoon levels dur- ing weather extremes. Rainfall during normal years dilutes la- goon liquid concentrations.