Using Aquaponics with Renewable Energy Resources to Create Sustainable Food Systems while Reducing Nutrient, Energy, and Water Costs

In the bigger scheme of things, lettuce production in Hawaii increased five-fold last year. This is according to the National Agriculture Statistics Service (NASS). It attributed the increases in aquaponics and hydroponics of three of this project’s producers. Tomatoes were 80% homegrown as well, and they are grown hydroponically. Using aquaponics and hydroponics production was sustainable and natural. These were shared with fellow producers and the public in a field day/workshop (Appendix 1). There is a great deal of interest in aquaponics now.

The sites and our work to assist at the sites will be described from the least successful to the most.

The first farmer was doing hydroponics. He had a relationship to Costco and, while generating good income, he was having a hard time keeping up with the needs of the store and had an energy problem. Due to the one month revocable leases in Hawaii, it is difficult to get the electric company to invest in wiring up remote areas. His electrical needs were met by a diesel generator which is very expensive.

Another farmer whose base was aquaculture also dropped out. He got started, purchased and installed solar power which he used to run his tanks, but dropped out when he found other employment and could no longer afford the time to do this project.

A third farmer is a chef by training, and his wife is a horse trainer. He built his system using plastic growbeds which added to the cost. He had to dip into his personal finances for the project. When we visited his site for the second time, we did the water scan. His pH, dissolved oxygen, ammonia and nitrite values were excellent, demonstrating chemically that he followed instructions of the how-to manual. He had not lost a fish and his nitrate values were very high. This and the log book kept on feeding were excellent. However, when we visited we immediately noticed poor, scrawny plants. He had built his system under roof and had assumed that since he could see in the day times, the plants would have enough light. We measured his light intensity at 1,600 LUX, and our research determines that an intensity of 40,000 LUX is needed for lettuce. He should be fine once he replaces the roof panels with transparent ones. He will use his vegetables at his restaurant.

Another farmer whose background was aquaculture had challenges. He had power issues and purchased a wind-powered electrical generator. As he was about to install it, he was told he needed an environmental assessment. He was also told that any money he saved using his wind turbine would have to be repaid via his land lease. Thus his wind turbine now sits idle, but he is moving forward. He built a series of eight fish tanks and four large tanks that function as grow beds. He had just begun stocking his fish. Upon our site visit, his plants did not look good. His fish tanks were not covered, and there was algae in the water. These observation immediately suggested that any plant nutrients generated by his fish was being used by the algae in the greenwater, and this would be consistent with emaciated looking plants. Water chemistry revealed excellent dissolved oxygen, pH, and ammonia but very low nitrate (2.9 mg/L). Our research has shown good results with nitrate levels of 15 mg/L or so. Once the tank water is no longer exposed to the sun and fish are being fed at higher levels, we will examine the water chemistry again and hopefully he will have better results. His will be a low nutrient system, and what we find will be new science for low nutrient systems. They may work.

A fifth farmer also just started. He is an old-fashioned vegetable farmer. He took a while to get started because he wanted to investigate the markets before he invested his time into aquaponics. He required some assistance from one of our students, who supervised his field hands in constructing his system. On our third visit after he had just started, we noticed etiolated watercress and lettuce, his fish tank water was exposed to the sun, and he fed only a little feed because his fish were mature and did not eat much. He had had them on hand as pets. Water chemistry was fine regarding dissolved oxygen, pH and ammonia. We gave him some of our fish and repeated our instructions to feed them to satiety. In the next visit his nitrate nitrogen had arisen to 65 mg/L and his watercress formed a thick lawn in his growbed. He is selling all the watercress he can grow at very good prices. We believe it is wonderful to see a farmer get such good prices for his products. In part, this is due to the fact that he had the foresight to grow an aquatic plant and this plant is of unique quality.

The sixth farmer started out with a landscaper background. He attended the first workshop and decided to get into aquaponics since the landscape business was slow due to the economy. When we were first called he had a 4 foot X 100 foot fish tank and five 4 foot X 96 foot raceways.

He said his lettuce was growing slowly. His fish tank was aerated with an aquarium pump just like our 50 gallon fish tank and dissolved oxygen levels were about 1 mg/L. This leads to denitrification (fertilizer nitrate is converted to nitrogen gas and is lost to the atmosphere). When apprised of these data he installed a 1.5 horsepower air blower and his nitrate levels rose with the increased dissolved oxygen levels. They were a satisfactory >10mg/L and he was able to sell lettuce. He chose health food stores and a high end grocery store (Whole Foods). He then undertook to obtain organic agriculture certification and parlayed profits from his five raceways to build about 20 raceways, some enclosed in net houses to exclude insects. At last visit, he harvests 15,000 heads of lettuce a month. He now grows lettuce, Japanese cucumbers, heirloom tomatoes and blueberries. He receives good prices for these products and sells his tilapia live also for good prices. He may be the biggest aquaponics farmer in the world. His website is www.marisgarden.com

He wrote a grant and purchased Solar panels. Electricity is the biggest expense of an aquaponics operation. During the daytime he is off the grid.

The Aquaponics Manual has been completed. The videographer is completing the video project. We replaced the two farm visits with virtual farm visits, as workshops.