Turning Food Waste Into Food For Plants

Tinia Pina is the founder of Re-Nuble, an innovative and award-winning company that transforms food waste into organic liquid fertilizer for hydroponic farms.

To share the story of her company and fertilizers, Tinia sat down with Patrick Flynn of Urbanvine.co:

Patrick: Can you start off by talking about Re-Nuble and how it started? What's your mission? What is Re-Nuble?

Tinia: I founded Re-Nuble in 2011, the whole premise behind it was to try to increase access to more nutritious options, primarily in cities, because I saw that as where the trend was as far as macroeconomics of people migrating towards.

We manufacture value-added organic liquid fertilizers, primarily within the hydroponic industry, because there was at the time definitely, and still is, a demand to grow with organic inputs. It has been challenging, but we've proven that you can achieve comparable grow results compared to using conventional inputs.

Patrick: Why is there more of a learning curve with organic fertilizers for hydroponics compared to conventional fertilizers?

Tinia: The challenge with organics or anything that's biologically derived is that it's natural, so you can't have the precision that you have with a synthetic fertilizer which is already in its ionic form and readily available to the plant.

With synthetic fertilizer, you know exactly to the parts per million what ionic nitrogen or phosphate or mineral is available to the plant.

With biologicals, a lot of the decomposed matter, (for example, in ours, we have organic certified produce waste), still goes through a degradation when it is subjected to a hydroponic reservoir (unlike synthetic fertilizer).

Patrick: What specifically are some of the implications of having an organic biological fertilizer in the hydroponic reservoir?

Tinia: Organic fertilizer is still decomposing when it is in a hydroponic reservoir, and that lessens the ability to have precision and know exactly how much your pH or EC will be, especially within the first 1 or 2 weeks of growing, but the readings tend to stabilize after that.

The pH and EC swing after application into the hydroponic solution happens due to microbe activity, so you're unable to say "you can expect with certainty a pH of 6.5 within the first 2 weeks” simply because biological fertilizer has to normalize.

We've shown historically that your EC swings during that two week mark, anywhere from 0.8 to 3.0. Then it tends to normalize, and that's only for hydroponic reservoirs.

In soil, because you have the soil and you have a medium that diffuses, the microbes act differently, just like they would in rockwool or similarly in coco coir. Applying organic fertilizers in those substrates or soil therefore has less effect on your EC and your pH right after application.

Patrick: For people who are looking at the unit economics, cost and benefit analysis, maybe they're thinking about starting their own urban farming hydroponic operation, what do you look at when you're looking at the cost of say, a biologic fertilizer compared a synthetic one?

Tinia: On the unit cost side, you will notice that with organic hydroponics you will typically need more applied fertilizer than with synthetic fertilizer.

This is because synthetic fertilizers already provide the nutrients in ionic form, which just means it's readily available for the plant to pick up, whereas with organics, there's still a requirement for the plant to convert (the organic waste based fertilizer) into a form that can be picked up.

This means that you will need more organic fertilizer to get to the same needed concentration, compared to synthetic fertilizer.

I typically estimate you will need 20% more of the organic fertilizer than with synthetics, but if you're selling the now organic urban farmed produce, and you can sell it at a premium, it's typically worth the cost!

Patrick: When these types of crops are grown and harvested, what do you typically see as the mark-up for the organic hydroponic produce you're typically helping your customers grow?

Tinia: We've seen to date that just organic or natural branded crops tend to command a ~44% pricing premium. That mainly pertains to metropolitan areas, we've done less testing with rural, traditional farmland areas.

(This interview was originally conducted in 2017)

Interview by Patrick Flynn. Patrick created Urbanvine.co in 2016 to help urban dwellers learn how to start urban farming without any previous experience. As the site grew, he discovered that "urban farming" was actually a general term that can include a wide variety of concepts, including: grow lights and hydroponics, both topics which the site now covers in depth.