Screening or settling the wastewater to remove debris and grit help prevent clogging and wear of the irrigation equipment. Suspended solids in the wastewater should be less than 1/3 the sprinkler nozzle diameter. Oil and grease can also clog pipes and nozzles. Primary treatment to remove settleable solids, oil, and grease should be considered for communities with significant industrial or commercial waste flows.
Biological treatment stabilizes and aerates wastewater. Treatment is needed to achieve a CBOD5 content of less than 25 mg/l for unrestricted access sites. For agricultural and restricted access sites, a CBOD5 content of less than 40 mg/l is sufficient.
Facultative and aerated lagoons are often used to provide biological treatment for irrigation systems. Lagoons provide much of the needed storage to maximize flexibility in managing the irrigation system. In areas where a large level area is not available for a lagoon, fixed film systems may be an option. Trickling filters and sand filters provide adequate treatment with low energy and minimal labor requirements.
Some communities currently using a mechanical treatment system before stream discharge may wish to switch to wastewater reuse. Activated sludge, extended aeration, or oxidation ditch systems already in operation can continue to be used to renovate wastewater prior to reuse. Additional storage may need to be added to existing treatment facilities to take advantage of wastewater reuse.
Disinfection is an important feature in wastewater reuse systems with unrestricted access. Tablet chlorinators are often used to disinfect wastewater. Another popular option is injecting liquid sodium hypochlorite into the wastewater. However, other chlorination systems or ultraviolet light can also be used if already available. Disinfection can occur prior to holding ponds, tanks, or application.
Leaves that fall into holding tanks can clog irrigation systems. Placing screens over holding tanks is one approach for keeping leaves out. Bar screens at the inlet of the irrigation system should also be installed to collect debris.