- Spring 1996 "Update" Newsletter Article -
Industrial compost
Researchers test new method for converting winery solid waste into high-quality compost
From CATI Publication #960401
Copyright © 1996. All rights reserved.
A research team from the Viticulture and Enology Research Center at California State University, Fresno is testing new methods of converting fruit pulp and other winery waste materials into high-quality fertilizer and soil amendments.
The efforts have been prompted by recent state regulations that will require wineries, grape juice processing plants and other industries to reduce solid waste landfill deliveries by 25 percent by the year 2000.
That is a significant percentage and poses "a serious problem in the area of solid waste disposal," notes Fresno State Enology Program Director Carlos Muller, who is overseeing the composting test project. "Increasing regulation and rising costs could make landfill disposal of winery wastes prohibitive by 2000," he said.
California wine industry officials estimate wineries and juice concentrate processors generate 600,000 to 900,000 tons per year of solid waste, in the form of dried fruit pulp and other materials. Much of that goes right back onto fields and vineyards as organic soil amendment. However, because of chemical composition, a significant portion is unsuitable for "recycling" and is delivered to landfills.
With the new state laws requiring the waste reductions, wineries will have to find new ways of converting waste materials into a product suitable for the vineyard or other applications. And that's where the VERC research team comes in. Under Muller's guidance, graduate student Fran Lightly is investigating combinations of waste materials, in some cases with amendments, in an effort to produce a compost with "maximum recycle benefits."
Compost is a natural product which provides chemical, physical, and biological benefits when applied to the soil, Lightly explained. It is a stable by-product resulting from the microbial decomposition and detoxification of organic materials. Compost is typically produced from materials which would otherwise be disposed of as wastes. These include yard wastes, manures and bedding materials, sawdust and wood scraps, food wastes, even municipal sludge.
Agricultural processing operations are ideal sources of compostable material, he noted. Examples are wastes from vegetable packing, hulls from nut processing, trash from cotton gins, straw from rice harvesting, and pomace from grape concentrate and wine production. Many of these wastes need to be blended with other materials to achieve optimum conditions for composting.
According to Lightly, the main objective of the project was to compare the speed and efficiency of various composting methods. Research is being conducted at a large central valley winery and involved setting up, monitoring, maintaining and evaluating a series of trials using winery solid wastes as the feedstock.
The different materials included sweet pomace - the pressed residue of stems, skins, and seeds plus a liquid phase of approximately 50% by weight which is basically sweet grape juice (20-24% sugar); fermented pomace - post-fermentation press residue of skins, seeds, and yeast, plus a liquid phase of roughly 50% which is basically red wine (10-14% alcohol, little or no residual sugar); and filter residues - wine-soaked slurry or cake of filter powder with varying amounts of yeast cells and grape solids.
The composting methods being compared include the following:Beginning last year, the trials were initially monitored and sampled every 7-10 days to determine temperature, moisture content, pH, carbon and nitrogen. Periodic analyses were and are being conducted to determine organic acid concentrations. These will indicate whether the process is aerobic or anaerobic and will be a preliminary indicator of compost quality. As the composting trials approach completion, additional tests will be conducted to determine maturity, phytotoxicity, and nutrient content.
- turned windrow - periodic turning to provide aeration, mixing, and mechanical breakdown. This method generally uses specialized turning equipment and periodic water addition is required.
- static pile - fixed with perforated piping for air access. This trial includes both forced aeration using a mechanical blower and natural air diffusion with no blower. Periodic water additions may be required.
- Ag-Bag* vessel - modified aerated static pile housed within a tubular plastic bag. The composting material is protected from the effects of rain or wind and there is very little loss of moisture since it is a nearly closed system. Requires specialized equipment for filling of the bag as well as a blower for aeration.
- untreated pile - no provision for aeration. Serves as a control trial for comparison.
Lightly expects to complete preliminary data analysis by early summer and to continue the process through this year. Although comopsting of waste products is certain to add to the expenses of winemaking, it is something that must be done in order to reduce the the industry's waste output.
"Composting to treat winery solid wastes appears to be viable and environmentally sound solution to this waste disposal problem. It yields a product which can be recycled as a valuable and beneficial soil additive compatible with the concepts of organic farming and sustainable agriculture," he said{ page top }