Spray irrigation began as a method of disposing and recycling treated wastewater from municiple systems. From a public health and environmental health perspective, spray irrigation is one of the most beneficial ways of dealing with all aspects of wastewater. When properly designed, spray irrigation places effluent where plants can take up nutrients, sunlight can provide some disinfection, soil microbes can consume remaining organic matter, ground water resources are recharged, and point source discharges are eliminated. As effective as spray irrigation is, not everyone likes it. Spray irrigation sounds like a nuisance waiting to happen and consequently it has some opponents. It appears that the concept could use a good public relations agent to make it as appealing the the public as a constructed wetlands. Properly designed and operated, spray irrigation is cost effective, beneficial and not a nuisance.
The spray irrigation photos above were taken at the spray irrigation facility serving the town of Garner, NC. The site covers approximately 277 hundred acres and disposes of 0.8 to 0.9 million gallons per day. The site can ultimately treat and dispose of 1.2 million gallons per day. The wastewater is treated and disinfected before it is sprayed on hay fields and in woodlands. The plants take up nutrients and harvesting the plants removes nutrients previously applied to the site.
What appears to be a placid lake on the left is actually one of a pair of 25 acre lagoons where the treatment process for the town of Garner begins. Lagoons have a bad reputation, too. Properly constructed and run, they are not a nuisance factor or a threat to ground water. These lagoons had very little odor (even up close), there was no apparent weed problems, and ducks were observed using the lagoons. The reason these lagoons are working well is because they were properly designed and are carefully managed. Consequently, it shouldn't be a surprise that they consistently produce secondary treatment levels. Total nitrogen output from the lagoons is 12-15 mg/l. Total retention time in lagoon is a minimum of 30 days for treatment and there is up to 60 days of storage time available. The storage allows the town to hold effluent when it wouldn't be prudent to spray a field. After periods of prolonged rainfall when runoff might be a problem or prior to harvesting hay, are examples of when they may not wish to spray.
The photo on the right shows the chlorine contact chamber. After passing the lagoon and before the effluent is sprayed, it is disinfected with chlorine.
After the effluent is chlorinated, several rather impressive turbine pumps move the effluent to the various spray fields where final treatment and dispersal into the environment occurs. These are the pumps that run the thousands of spray heads (literally)in this system.
The photo on the right show A.R. "Bob" Rubin, Ph.D., standing by one of those spray heads in a wooded part of the spray site. Dr. Rubin is a professor at NCSU and is ardent proponent of environmentally sound wastewater treatment and dispersal methods. He finds a lot to like with spray irrigation and he has been particularly helpful to us in carrying out the training aspects of our residential spray irrigation training program.
So, what does all this have to do with an onsite wastewater program that's principally directed at residental waste flows? Quite a bit actually. The Division was interested in learning if there was a way to make spray irrigation practical for the average homeowner. Wastewater storage (usually a logoon) has always been an essential element of spray irrigation. On commercial sites, lagoons make a lot of sense but on residential sites, convincing a homeowner to install a storage lagoon is neither popular nor practical. Since the soil requirements for a spray site are much less restrictive than for a conventional system the Department funded research with Virginia Tech to see if there was an alternative to lagoon storage. If an affordable alternative could be found to requiring a lagoon much land that was unsuitable for a conventional system could be safely used for a spray irrigation system. Dr. Reneau, through a research grant funded by VDH, was able to demonstrate a way to safely eliminate the lagoon. The Department, in cooperation with DEQ, then set forth to develope proceedures for permitting spray irrigation systems for residential and limited small commercial sites. From concept, through research, to policy development and through staff training and program implementation took approximately five years. The result though, appears to be well worth the time and resources invested as Virginia has a model residential spray program. Homeowners that would otherwise be denied a permit, now have a safe, sanitary, and environmentally sound option for onsite wastewater treatment and dispersal.