One of the greatest challenges to sustainable agriculture is the depletion of the natural resource base on which food production depends. To sustain the natural resource base requires broad adoption of circular economy, closed loop agriculture. Closed loop agriculture is:

an economic system focused on maximizing the reuse of resources and products and minimizing their depreciation. The circular system consists of two material cycles: (i) a technical cycle, and (ii) a biological cycle. The technical cycle relies on the use of mineral resources as production inputs, where products and their parts are designed and marketed in a way that they can be maintained and reused, maximizing their quality and their economic value. Within the biological cycle, resources used as production inputs have a biological origin, allowing for products to be safely discarded into the natural system once they reach their end of life. The system is meant to be both ecologically and economically restorative (Breure, 2018; see also Nogueria, et al, 2020).

Whiskey Hill Farm ( is a 14-acre organic farm on California’s Central Coast, near Watsonville. 

It is is a pioneer in developing a systems approach to agricultural technology by recycling and reusing various inputs and outputs in farming and demonstrating the technology and best practices of a circular, closed-loop food economy (see figure below).


The Farm employs poly-cropping techniques of permaculture, creating food forests in its six football field-sized greenhouses. To mimic the natural world of multi-layered poly-culture, the Farm grows turmeric and gingers underground, with melons, heirloom peppers and basil varieties at ground level. They then plant vining fruits such as tomatoes, passion fruit and lemon cucumbers and finally fruit trees such as mango and papayas. The Farm’s cultivation techniques are steeped in regenerative agricultural practices making the richest, most vital soil possible to both repair damaged soil.

The role of soil

Regenerative, closed loop agriculture begins with the soil.  High quality soil is full of nutrients, minerals, microorganisms and water, all of which, plus sunlight, are necessary to grow food.  Prior to its current incarnation, Whiskey Hill was the site of a cut flower operation, which reduced the soil to hard clay, with virtually no topsoil and requiring frequent inputs of chemicals and pesticides.  The new operators of the farm were determined to restore and regenerate the soil cover in the greenhouses, by turning large volumes of organic and farm wastes into compost piles which decompose to produce new, rich soil.
These piles contain the materials left after crops have ceased producing, organic wastes from neighboring farms and food businesses and the residues of the distillation process.  The irrigation pipes seen in the photo serve to periodically water the piles but also to aerate the piles so they do not have to be turned.  Finally, water is circulated through the piles, warmed by the heat of decomposition and circulated through pipes underneath crops to irrigate and warm them.

Turning Organic Wastes into Ethanol

The process of turning organic farm and food processing wastes into valuable outputs begins in the biorefinery operated by Blume Distillation.  Organic wastes from the farm and outside sources are cooked and turned into a liquid in a boiler fueled by methane produced by the the Farm’s biodigester (see below).

The liquids, full of sugar, starch and nutrients, are piped into fermenting tanks, to which yeast is added.  In a few days, the mixture has fermented and contains about 10% ethanol alcohol.  That liquid is run through a steam heating column in which the ethanol is turned into vapor and separated from the liquid for further refining and conversion into various grades of alcohol.  The nutrient-rich liquids left behind in the distillation column and are piped into the farm’s methane digester (the long, plastic-covered pond), where the organic residues decompose and generate methane.

The methane is collected and returned to the biorefinery where it is burned to heat the various tanks and distillation columns. 

The digestion pond is tilted and the liquid, which still contains nutrients, is pumped into the adjacent pond to feed cattails.

Many farmers regard cattails as a nuisance plant. They grow and spread quickly wherever there is standing water and are difficult to eliminate because their seeds spread so easily.  But these cattails play an essential role in closed loop system at Whiskey Hill Farm. 

First, the leaves grow so quickly that the pond can be “mowed” four times a year.  They turn nutrients in the water protein, which can be extracted and turned into flour or animal feed (what is left behind is recycled, of course).  Second, the cattail roots, or rhizomes, are full of starch, and can be ground into animal feed. And, third, the cattails are very efficient at removing the nutrients from the water, cleaning it to a high level of purity, higher than the California standard. 

The water is put to work again, pumped into a pond full of duckweed for reoxygenation. The duckweed can also be harvested and recycled or used as animal feed.

Finally, this clean, oxygenated water is pumped into the aquaculture pond, inhabited by catfish and “fresh water” lobsters (aka, Australian crayfish).

Sustaining the greenhouses

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Breure, A.M. J.P.A. Lijzen, L. Maring, 2018. “Soil and land management in a circular economy,” Science of The Total Environment 624: 1125-1130,

Nogueira A, Ashton W, Teixeira C, Lyon E, Pereira J. Infrastructuring the Circular Economy. Energies. 2020; 13(7):1805.