Microbial succession associated with organic matter decomposition during thermophilic composting of organic waste.

Using dog food as a model of the organic waste, thermophilic composting was carried out for 14 days at a fixed temperature of 60 degrees C. The relationship between organic matter decomposition measured by CO2 evolution during the bio-stabilization process and microbial succession expressed as the changes over time in the restriction fragment length polymorphism (RFLP) patterns of 16S rDNA sequences, of micro-organisms associated with the composting material was also examined. The CO2 evolution rate peaked on day 3 and gradually decreased until it became extremely small after day 9 of composting, indicating that vigorous organic matter decomposition ceased around this time. On the other hand, the RFLP pattern changed drastically from day 0 to day 4 or 5, then remained stable until day 7 or 8, reaching its final configuration, with little variations, after day 9 of composting. RFLP analysis therefore indicates that microbial succession continued into the later stage of composting. Nevertheless, by day 9, the rate of organic matter decomposition was so low that its influence on microbial populations could be hardly recognized by conventional methods of dilution plating. Moreover, the compost produced by day 9 showed no inhibitory effect on the growth of Komatsuna (Brassica campestris L. var. rapiferafroug), indicating that the maturity of compost is sufficient for plant growth when the rate of organic matter decomposition has become extremely low and the RFLP patterns become stable.     

Remediation of soil contaminated with dioxins by subcritical water extraction

The effectiveness of subcritical water extraction (SCWE) was examined for removing dioxins from contaminated soil. Most dioxins in the soil sample were reduced at 300 degrees C or more, but decreased dioxin concentrations were also observed at 150 degrees C. After 4 h of extraction, 99.4%, 94.5% and 60% of PCDDs were removed from samples at 350, 300 and 150 degrees C, respectively. It was also determined that degradation of dioxins had occurred, since the sum of dioxins in the soil plus water extracts after the experiments had considerably decreased. This study revealed that pressurizing is not essential for the removal of dioxins. Reduction was complete within 30 min at 350 degrees C; however, it took a much longer time at lower temperatures. The results of addition experiments in which OCDDs were added to different types of soil samples have shown that dechlorination is one of the major reaction pathways. After addition of OCDD to soil samples, experiments were carried out to examine in detail the degradation pathways of PCDDs. The removal rates and congener profiles varied among soil types. Although it was previously assumed that removal rates and congener profiles depended on the chemical components in soil, nonparametric statistical analysis revealed no significant relationship between the rate of reduction and elements present in the soil. It was confirmed from isomer patterns that dechlorination of the 2,3,7,8-positions in PCDDs takes place somewhat faster than for the 1,4,6,9-positions.     

Comparison of the weight-loss degradability of various biodegradable plastics under laboratory composting conditions

Eight kinds of biodegradable plastics were compared for their degradability in controlled laboratory composting conditions. A thin film of each plastic was mixed into the composting material, and weight-loss degradability was calculated from the weight changes of the film during composting. It was found that weight-loss degradability strongly depended on the specific kind of biodegradable plastic; two were very high, four moderate, and the remaining two very slight. The most easily degradable plastic degraded by as much as 81.4% over 8 days of composting. By comparing the weight-loss degradability with ultimate degradability, which is defined as a molar ratio of carbon loss as CO₂ to the carbon contained in the biodegradable plastic, the order of the ease of degradation of the biodegradable plastics differed. Received: February 7, 2000 / Accepted April 14, 2000     

Degradation of fats during thermophilic composting of organic waste.

The degradation of fats during thermophilic composting was investigated by adding lard of four different mixing ratios (0, 33.3, 42.9 and 50% on a dry weight basis) to dog food used as a model substrate for organic waste. The lard added at the mixing ratio of 33.3% did not inhibit the decomposition of organic matter in the dog food, with lard itself beginning decomposition after decay of more easily decomposable organic compounds of the dog food, 84 h from the start of composting. The percentage of lard decomposition reached as high as 29.3% by the end of 8 days of composting. By contrast, the decomposition of organic matter in the processed dog food was apparently inhibited when the portion of lard was greater than 33.3%, especially at the earliest stage of composting. It is possible, however, that lard would decompose vigorously once decomposition has begun, even when the ratio of lard is as high as 50%. The percentages of lard decomposition in composting mixtures with 42.9 and 50% lard were 15.7 and 9.50%, respectively, thus the higher the mixing ratio of lard, the lower the percentage of lard decomposition. However, it was found that the maximum decomposition rate of the lard was similar for all of the ratios tested; that is, approximately 5.0 x 10(-3) g carbon h(-1).     

A simple numerical model for predicting organic matter decomposition in a fed-batch composting operation

Using dog food as a model of the organic waste that comprises composting raw material, the degradation pattern of organic materials was examined by continuously measuring the quantity of CO2 evolved during the composting process in both batch and fed-batch operations. A simple numerical model was made on the basis of three suppositions for describing the organic matter decomposition in the batch operation. First, a certain quantity of carbon in the dog food was assumed to be recalcitrant to degradation in the composting reactor within the retention time allowed. Second, it was assumed that the decomposition rate of carbon is proportional to the quantity of easily degradable carbon, that is, the carbon recalcitrant to degradation was subtracted from the total carbon remaining in the dog food. Third, a certain lag time is assumed to occur before the start of active decomposition of organic matter in the dog food; this lag corresponds to the time required for microorganisms to proliferate and become active. It was then ascertained that the decomposition pattern for the organic matter in the dog food during the fed-batch operation could be predicted by the numerical model with the parameters obtained from the batch operation. This numerical model was modified so that the change in dry weight of composting materials could be obtained. The modified model was found suitable for describing the organic matter decomposition pattern in an actual fed-batch composting operation of the garbage obtained from a restaurant, approximately 10 kg d(-1) loading for 60 d.     

Effects of acclimated sludge used as seeding material in the start-up of anaerobic digestion of glycerol

Methods for improving the anaerobic digestion of glycerol (propane-1,2,3-triol) were investigated, particularly the effects of using acclimated sludge as seeding material during start-up. Glycerol was supplied to the anaerobic digester at an organic loading rate of 2.5 g-COD L^?1 day^?1. Four experimental runs were carried out with varying mixing ratios of acclimated sludge to unacclimated sludge (0, 10, 20, and 33%). Calculations were performed by employing a numerical model, whose parameters were determined by experimental measurements. Methane production rate (MPR) for all runs attained similar stable values around 21.4 mmol L^?1 day^?1, though more time was required for attaining stable state of methane production with lower mixing ratios of acclimated sludge. The initial MPR calculated was proportional to the mixing ratio of acclimated sludge. Furthermore, molecular biological methods showed that the types of microorganisms observed in all runs were similar. These results indicate that the seeding with different mixing ratios of acclimated sludge did not affect the microbial consortia in the anaerobic digestion approaching stable state, but did affect the cell density of the useful microorganisms at the start of methane fermentation. Consequently, it was confirmed that at a higher mixing ratio of acclimated sludge, the start of methane production became more vigorous.     

Antibiotic removal from waste milk by electrochemical process: degradation characteristics in concentrated organic solution

Journal of Material Cycles and Waste Management - The use of antibiotics in lactating dairy cows produces waste milk containing antibiotic residues. Antibiotics have been one of the emerging...     

Predicting the degradation pattern of organic materials in the composting of a fed-batch operation as inferred from the results of a batch operation

The degradation pattern of organic materials was confirmed by continuously measuring the quantity of CO₂ evolved during the composting process in both batch and fed-batch operations. It was possible to predict the degradation pattern for organic material during a fed-batch operation from that observed during a batch operation after corrections made on the basis of two suppositions. First, it was assumed that the degradation of dog food (which degrades easily) occurred prior to the degradation of the bulking agent and seeding material that were contained in the raw compost mixture; second, it was assumed that the dog food thrown into the fed-batch operation, where the microorganisms were already proliferating, began to be actively degraded with only a short lag time. Received: June 16, 1998 / Accepted: August 7, 1999     

Study on dechlorination technology for municipal waste plastics containing polyvinyl chloride and polyethylene terephthalate

It is necessary to remove chlorine efficiently from municipal waste plastics (MWP) that contain polyvinyl chloride (PVC) and other plastics containing chlorine. In this article we consider thermal degradation liquefaction technology. In Japan, the chlorine content of reclamation oil products must be kept below 100 ppm owing to the quality standard for pyrolysis oil. Liquefaction dechlorination technology for MWP is still an important issue to study. The twin-screw extruder that has been developed as dechlorination technology for blast furnaces and coke ovens has a shorter residence time for dechlorination than other dechlorination technologies. In this article, we used a single-screw extruder for the dechlorination process because it also has a short residence time. Experiments on the dechlorination process were carried out by using a single-screw extruder to assess its dechlorination performance. Practical use of the single-screw was demonstrated by the operation of a commercial oil reclamation plant operated by Sapporo Plastic Recycle Co., Ltd. (SPR). Moreover, an investigation of cascade recycling was carried out in 2008 in which material recycle wastes were mixed with MWP and processed by chemical recycling (liquefaction). It was demonstrated that cascade recycling is an efficient recycling combination and contributes to local feedstock recycling. However, it was shown that MR wastes affect the quality of the reclamation oil when they make up more than 40% of the feed mix. If the quantity of MR wastes is kept below 40%, the reclamation oil is able to meet the quality standard. The SPR plant can be operated safely and in a stable manner.     

Bioethanol from sea lettuce with the use of crude enzymes derived from waste

The mid-gut gland of the scallop contains saccharification enzymes such as cellulase and amylase, and these enzymes have been disposed of together with the mid-gut gland after the removal of the adductor muscle, an edible part of the scallop. We used a drip from the mid-gut gland of the scallop, obtained by squeezing the gland, as an inexpensive enzyme mixture and tried to produce bioethanol from the glucans present in sea lettuce by the method of simultaneous saccharification and fermentation (SSF) with the use of baker’s yeast. The ethanol concentration attained was as high as 7.2 g/L, which corresponded to ~37% of the conversion of glucans in sea lettuce in the solid-state SSF. Furthermore, we ascertained that the drip and sea lettuce contain nutrients that are indispensable for maintaining the yeast activity, and, thus, the SSF did not require any additional nutrients, such as yeast extract or peptone, the use of which increases the cost of fermentation to a high level.