Evaluating Food Digestion Effluent For Landscape Use

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Courtesy of BioCycle Magazine

Over the last year, Loyola Marymount University (LMU) has installed and studied a food waste diversion technology that converts raw food waste into a liquid effluent that is disposed through the sewer system. As an urban university located in West Los Angeles, California, LMU faces two major barriers with respect to composting food waste: on-campus space constraints and long distances to off-site composting facilities. There are neither ideal spaces for on-site composting, nor composting facilities permitted for food waste in close proximity to the campus. Faced with few options for food waste diversion in the university’s dining facilities, LMU’s dining services provider, Sodexo, purchased and installed a technology called the ORCA GreenTM Machine (ORCA).

The ORCA system is a food digester, also described as a food liquifier, which converts raw food waste into a liquid effluent through microbiological activity. This system consists of a heavy-duty stainless steel rectangular box with a rotating drum inside. Kitchen staff open the top hatch and dump raw food waste, including vegetables and meat scraps (with the exception of bones), into the machine. The ORCA runs 24-hours/day and can be fed continuously as long as space is available in the machine. Large aluminum paddles attached to a stainless steel shaft spin continuously, physically breaking up the food waste into smaller particles.

A proprietary mixture of microorganisms and enzymes are added on a weekly basis to ensure rapid decomposition. Plastic chips are put in the main chamber as a bulking agent for the food waste. Over the course of one to two days, raw food waste is broken down by various microorganisms and digested into particles that can fit through small holes in the bottom of the machine. These small food waste particles are flushed through the system, ultimately exiting as a liquid effluent with no other resulting by-product.

The company that sells the ORCA, Totally Green, Inc., claims the liquid effluent discharged from the ORCA can be “reused for irrigation, farmland, & gardens” (www.totally green.com/). Preliminary discussions by LMU faculty, students and staff resulted in a strong interest in studying the suitability of using the ORCA effluent as nutrient-laden irrigation water for landscaped areas of the LMU campus grounds. A research plan was developed to answer the following questions: What are the chemical, physical and biological properties of the ORCA effluent? Is the ORCA effluent suitable for irrigation purposes?

Methods

During the Spring semester of 2012 (February through April) a team of LMU undergraduate students and a graduate student from California State University, Northridge conducted a suite of chemical, physical and biological water quality tests on ORCA effluent. Results of these tests were compared with values typical of domestic raw sewage. It was reasoned that if constituents in the ORCA effluent, like organic matter or any harmful bacteria, were less in concentration than characteristic of domestic raw sewage, then the effluent would be suitable for irrigation given its potential high nutrient content.

Effluent samples were collected nearly weekly on seven occasions during the early afternoon. During each sampling event, three aliquots were extracted from the effluent sample and tested for a suite of water quality parameters. Chemical and physical tests performed included biological oxygen demand (BOD), total solids and nutrients (nitrate, phosphate). Table 1 includes the test methods. One sample of effluent was sent to a consulting laboratory for determination of fats, oil and grease.

Microbiological tests focused on determining concentrations of fecal indicator bacteria (FIB, including total coliforms, E. coli, enterococci), followed by species identification of cultured isolates to determine if potentially pathogenic strains were present.

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