MICROORGANISMS AND ENDOTOXIN IN STORED BIOWASTE PERCOLATE AND AEROSOLS

Source separated biowaste was stored in containers at temperatures ran ging from 16 degrees C to 29 degrees C in a climate chamber for two we eks, simulating outdoor storage in a domestic waste collection system. Samples of exuded percolate were collected after 3, 4, 6, 8, 10, 12 a nd 14 days and analyzed for content of microorganisms and endotoxin. T hroughout the storage period, the mean concentrations (GM) of total mi croorganisms ranged from 5.0 to 12 x 10(9) cells ml(-1) and concentrat ions of endotoxin were between 0.54 and 1.5 x 10(6) EU ml(-1) (45 to 1 30 mu g ml(-1)). The maximum levels of microorganisms and endotoxin in the percolate were stable during storage and no significant differenc e was found between storage times of one or two weeks, which correspon ds to common Danish collection frequencies of biowaste. Analyses of th e microflora indicated dominance of bacteria as demonstrated by almost equal concentrations obtained by aerobic and anaerobic cultivation (2 .8 to 9.0 x 10(8) and 3.1 to 12 x 10(8) cfu ml(-1), respectively). Yea sts formed a minor part of the microflora (below 0.5% of the total num ber of microorganisms) and molds were only detected sporadically at co ncentrations close to the limit of detection. For percolate keeping a pH below 5 during the first week of storage, a tendency (p = 0.08) was observed towards lower concentrations of aerobic Gram-negative bacter ia and yeasts as compared to percolate exceeding a pH of 5. In two wee ks, a mass of 17 kg of biowaste exuded approximately 1.3 l of percolat e (range: 0.7 to 2.1 l), and handling experiments demonstrated that bi oaerosols generated from splashing percolate may cause exposure risks of endotoxin and microorganisms. Bioaerosols above stored bio waste co ntained fungal spores up to 1.8 x 10(4) cfu m(-3) but no detectable ba cteria and endotoxin. Headspace measurements of gases showed maximum e mission of hydrogen sulfide and methyl mercaptan after one week of sto rage, while concentrations of ammonia increased throughout the two wee k storage period.