Composting

In aerobic composting, an air blower distributes air under the pile and maintains most of the pile in aerobic conditions for faster degradation. The piles are turned daily to redistribute material and moisture and to maintain porosity of the pile. The mechanical stress imposed by turning the compost piles facilitates 

DOD has been evaluating composting systems to treat explosives waste 

In 1988, the Army began a series of demonstration studies at the Louisiana Army Ammunition Plant to determine the effectiveness of composting explosives-contaminated soils. In the initial study, static-pile composting required 153 days to remediate soils contaminated with just 3% explosive waste by volume. 

Based on these results, the Army determined that static-pile composting would not be cost effective for remediating large volumes of explosives waste. 

The Army conducted a second study to optimize the cost effectiveness of composting. This study used a less expensive carbon-source material, thereby cutting amendment costs from over 200/ton to less than 50/ton, and used a commercially available mechanically agitated composter rather than a static pile. These conditions led to more rapid and extensive degradation of the explosives, achieving cleanup levels of 10 to 20 ppm of TNT and RDX within twenty days. Nevertheless, this method also was determined to be economically infeasible, due to the initial cost of the commercial composter. 

Finally, the Army conducted a study to examine the effectiveness of windrow composting. This study used cow manure, sawdust, and potato waste amendments and required the construction of a concrete pad leachate collection system. Temperatures were maintained at 55°C and the compost was turned once a day. This process produced 98% reductions of explosives contamination within twenty days, and degraded HMX, 

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Bioremediation also offers options for dealing with oked material, such as seaweed, that gets stranded on shorelines composting has been shown to be effective. 

Composting by the addition of readily degradable hulking agents is also a useful option for relatively small volumes of excavated contaminated soil. 

Since efficient composting invafiably involves self-heating as biodegradation proceeds, this also offers an option for extending the bioremediation season into the winter months in cold climates. A potential drawback of composting is that it usually increases the volume of contaminated material, but if fully successful the finished compost can be returned to the site as a positive contribution to soil quaUty. 

Air. Biofilters are an effective way of dealing with air from industrial processes that use halogenated solvents such chloromethane, dichioromethane, chloroethane, 1,2-dichloroethane and vinyl chloride, that support aerobic growth (26). Both compost-based dry systems and trickling filter wet systems are in use. Similar filters could be incorporated into pump-and-treat operations. 

RDX and HMX are rather more recalcitrant, especially under aerobic conditions, but there are promising indications that biodegradation can occur under some conditions, especially composting (67). Several strains of bacteria able to use RDX (and Triazine) as a sole source of nitrogen for growth have recentiy been isolated, and this is an area where rapid progress is being made. 

Soil. Composting of soils contaminated by high explosives is being carried out at the Umatilla Army Depot near Hermiston, Oregon (70). Soil from munitions washout lagoons is being treated iadoors ia compost rows of 2,000 m, and the estimated cost is less than one-third the estimated cost of iaciaeration. If this is successful, there are 30 similar sites on the National Priority List that could be treated ia a similar way. 

The suggestion frequentiy is made that substitution of organic fertilizers, namely manures and composts, for chemical fertilizers would be of ecological benefit. The reaUty is, however, that the supply and logistics of such materials could never be adequate for the present-day level of agriculture. Furthermore, iatensive appHcation of such materials to the soil would itself present ecological problems, such as mn-off pollution and steady buildup of toxic heavy metals. 

For water-soluble polymers, there is a weU-estabUshed disposal infrastmcture, with the widely available wastewater treatment plants, whereas plastics being developed for composting require large-scale implementation of a composting infrastmcture. This fact will certainly influence the rate of their acceptance. 

There have been numerous communications on the subject of biodegradation test methods, including aerobic compost (30), anaerobic bioreactor (31), general methodology and future directions (32—34), and a fine review article (24). ASTM (22) and MITI (35) have also set forth standard testing protocols for plastics, as shown in Table 2, whereas OECD test methods (29) are more suited to water-soluble polymers. 

Fig. 3. Materials recovery, composting, combustion, and discards of municipal solid waste from 1969 to 2000 (1995—2000 estimated) as a fraction of total generation, where A represents landfill and other B, combustion C, recovery for recycling and D, recovery for composting.

Small tire chips have also been utilized as a soil amendment to improve athletic playing fields (see Recreational surfaces). A patented process marketed under the trade name Rebound (fai Tire) combines cmmb mbber from scrap tires with composted organic material to reduce soil compaction, resulting in better athletic playing surfaces (52). Installations have been made in Florida, California, Colorado, Hawaii, Maryland, Michigan, Missouri, Nevada, Virginia, and Wisconsin. 

Fig. 6. An iategrated approach to the management of municipal soHd waste (MSW), advocated by the U.S. EPA, that links source segregation, recycling, waste-to-energy (WTE), and landfilling ia a single system. Source segregation refers to the separation of compostable and recyclable components from the balance of the trash at the poiat where MSW is collected. In source reduction (not shown), another action to reduce waste to landfills, changes are made ia...

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