1a. Objectives (from AD-416)
Characterize, test, and develop an environmentally-sound containerized composting system for treating crab waste such that ammonia and odorous emissions to the atmosphere are reduced to non-nuisance levels and that the final product is beneficially useful in agriculture/horticulture.
1b. Approach (from AD-416)
ARS will conduct side-by-side comparison tests of composting using four distinct technologies described to handle highly unstable organic residuals such as crab chum: 1) Aerated Static Pile with compost blanket covers, 2) Ag-Bag (containerized) composting, 3) RCM containerized composting, and 4) Wright Environmental In-vessel composting. Input feedstock material will be the same mixture for all four systems, approximately two parts woodchips to three parts crab chum. Systems 1, 2, and 3 will use 40 cu yds. of the residuals mixture and each will be mechanically exhausted independently to biofilter piles composed of mature compost and wood chips (6 cu yd each) and operated according to the manufacturer's recommended best practice. Biofilter piles will be containerized so that all exit air can be analyzed real-time by infrared sensor technology. Residence time in the primary phase thermophilic composting is expected to range from 20-30 days and curing period is expected to range from 30-45 additional days. System 4 is smaller (600 lbs per day (1.5 cu yd)) and will be operated as the manufacturer suggests for 14 days with its own containerized biofilter. Wright compost will then subsequently be cured in an open-air non-mechanically aerated compost pile. This Wright Environmental unit accommodates for 14 days and is also biofiltered. Temperature profiles from exterior most positions to the core will be continuously measured and referenced to ambient temperatures. Exhaust gases, before and after the biofiltration units, will be collected and measured with a Jerome meter (for reduced-S compounds), GasTec for amines and ammonia, Innova (for CO2, CH4, N2O), PPBRae (for total VOCs). Field-based olfactometry tests (Scentometer) also will be conducted on biofilter exhaust. Solids and leachate samples initially and at periodic intervals will be characterized according to U.S. Composting Council, USDA, and USEPA compost quality standards. Information will be used by both ARS and the Cooperator to jointly determine which methods will provide the best option for an economically and environmentally sustainable practice for transforming currently landfilled crab waste to a beneficial horticultural planting medium.
3. Progress Report
The blue crab processing industry in Maryland generates approximately 4,000 metric tons of blue crab shells and viscera ('crab chum') seasonally, April to October. Currently, crab chum is land applied on-farms or landfilled. However, these practices results in nuisance odors and nutrient runoff into environmentally sensitive areas or filling of limited landfill space with organic material that could be used more beneficially and sustainably. In this study we compared five composting formats as alternative management approaches for the crab chum. Three different forced-aeration systems (static-aerated pile, ag-bag, and in-vessel composting) each comprising approximately 30.6 cu.m. of feedstock coupled with biofiltration (4.6 cu.m.) of exhaust air were included to manage odor emissions. Low-tech composting alternatives included a 30.6 cu.m. windrow and 8.38 cu.m. static pile, passively aerated and without biofiltration. Compost feedstocks were crab chum and shredded wood debris mixed on a 50:50 weight ratio estimated to achieve a 25:1 carbon-nitrogen ratio; moisture content was adjusted to 35-50 percent. The smaller static pile was turned twice and achieved maturity in 5.5 months and had no adverse odor or nutrient instability. The other systems reached thermal stability after 6.5 months of composting. The biofilters reached 95 percent removal efficiencies for ammonia. Results show that composting crab chum using relatively small piles and minimal energy inputs produces low odor emissions and a beneficial soil amendment. The seasonally generated quantity of chum may necessitate use of large piles at some locations and this may require forced aeration with biofiltration to meet compost quality, odor reduction, and time requirements. Hauling from dispersed production sites and associated environmental costs should be balanced against the benefit of operating large centralized composting facilities.