GREEN WASTE AND BY SEMI-PERMEABLE MEMBRANE
Abstract:In search of cost-effective recycling of biosolids, the City of Oceanside,California, has decided to explore the feasibility of co-composting of biosolids with green waste at an existing local green waste composting facility. One of the key criteria for the feasibility of this Phase I effort was the absence of adverse odor impacts. To assess the degree to which the co-composting could affect the odors in the area surrounding the yard waste composting facility, a pilot scale test was conducted. Four green waste composting windrows were constructed with biosolids to green waste ratios of 0, 1:10, 1:6 and 1:4. In addition, an aerated static pile was constructed with a biosolids togreen waste ratio of 1:4. The pile was operated with negative aeration with the exhaust treated bya biofilter. The change in the three main odor parameters: odor concentration, intensity and character was evaluated as a function of increased biosolids content. Consistent relationships were established for all three parameters. In addition, a series of systematic odor surveys was conducted in the surrounding area to determine the “odor footprint” of the existing green waste facility, toquantify odor intensity and to document the odor character within the footprint. The results indicated that the co-composting option would not be feasible for the City of Oceanside because of the constraints imposed by the existing background odors. It was also concluded that further optimization of the aerated static pile and biofiltration would be required for that option to pass the odor emission criteria.
Phase II investigated the feasibility of controlling the odors from composting of green waste and a mixture of green waste and biosolids by enclosing two test aerated static piles with a semipermeable membrane. The ratio of biosolids to green waste in the test piles was 0 and 1:4. An open green waste windrow was constructed for a side-by-side comparison with the static piles. The semi-permeable membrane allows the air and water molecules to pass through while retaining the larger molecules, including those of many odorous compounds. In the course of the composting process the retained odorous compounds are thought to be re-incorporated into the composting mixture and metabolized in a manner similar to biofiltration. Odor emissions during active aeration of covered piles were significantly higher than during the inactive portion of the aeration cycle. Thus, overall reduction in odor emissions from a facility with a large number of composting piles could possibly be accomplished by staggering the times of the active pile aeration. Among the advantages of semi-permeable membranes in comparison with open windrows are operational benefits related to positive mechanical aeration, moisture retention and shortened processing time, as well as reduced odor emissions. The semi-permeable membrane was found to be especially effective in control of odors from green waste composting and it is thus well suited for that application. The semi-permeable membrane was found to be less effective in control of the odors from biosolids composting. The odor levels atthe surface of the covered biosolids composting pile during aeration were significantly higher than the levels typically emitted from biofilters used for biosolids composting odor control.
Document Type: Research Article
Publication date: January 1, 2006
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