SPRAY AND DRIP IRRIGATION SYSTEMS
FOR DISPOSAL OF WASTEWATER EFFLUENT

Why Use Spray and Drip Irrigation?

The need for wastewater treatment is increasing due to continued development, while wastewater treatment plants in the area are facing more strict discharge standards.  Alternatives to conventional stream discharge methods must be used to help treatment plants meet the new requirements while still maintaining an environmentally sound community.  Spray and subsurface drip irrigation systems are two increasingly common alternatives.

The Pennsylvania Code classifies Pickering Creek and Marsh Creek as high quality waters.  Discharge into these streams is permitted only when all other options have been exhausted, and faces very strict effluent quality limits.  The proposed spray and subsurface drip irrigation systems provide a means of effluent disposal for Upper Uwchlan Township’s sewer systems that meet regulatory requirements, recharge groundwater supplies, and maintain the high quality of local water bodies.

How They Work?

For small community wastewater treatment facilitates utilizing spray or drip irrigation as a means of effluent disposal, the treatment plant provides the primary treatment.  The treatment plant’s effluent is not discharged into nearby streams.  Instead, the treated water flows to a pressurized unit that sends the liquid through disk or screen filters to prevent clogging of the output units.  Backwash piping connected to the unit sends the remaining particles back through the treatment process to promote further purification.  The resulting effluent is then pumped to either a sub-surface drip or spray apparatus.

The drip or spray devices discharge the treated effluent into the ground.  The drip system involves underground piping with emitters that release set amounts of water into the ground each day.  The spray systems range from a simpler sprinkler to more high tech sensory sprinklers.  Regulations concerning the water’s pre-treatment, use, and location of discharge make the process very safe and controlled.  The water discharged from both systems seeps into the ground and is further cleansed by microorganisms living in the soil.  The final product is clean water that recharges local aquifers, replenishing the area’s water supply.

Individual homes can also have spray and subsurface drip systems.  The home’s pretreatment system, consisting of a two-compartment septic tank or aerobic treatment tank followed by a secondary peat or sand filter, replaces the wastewater treatment plant.

Advantages of Spray and Subsurface Drip Irrigation

• Cover crops used to restrict effluent runoff can be harvested and sold.
• Relieves the local streams and rivers of the burden placed on it by the water discharged by treatment plants.
• Keeps nearby water sources from contamination.
• Adds water, nutrients, and minerals to the soil, which promotes plant life.
• Recharges precious ground water resources.

Advantages Specific to Subsurface Drip Irrigation

• Low-pressure system has low energy demands.

Disadvantages of Spray and Subsurface Drip Irrigation

• Large land area is required to be dedicated to spray or drip fields.
• Maintenance must be performed regularly.

Disadvantages Specific to Subsurface Drip Irrigation

• Driving vehicles over the system is likely to damage piping.

Disadvantages Specific to Spray Irrigation

• Wind obstructions may be necessary to prevent the air-transport of effluent offsite.
• Storage facilities for effluent must exist for extended periods of time when the ground is wet or frozen.

Informational Sources

• Partnership for Advancing Technology in Housing www.toolbase.org/techinv/techDetails.aspx?technologyID=169
• Pennsylvania State University Department of Agricultural and Biological Engineering www.age.psu.edu/extension/factsheets/f/F172.pdf