Large amounts of various organic wastes are discharged from agricultural and livestock industries. We investigated the waste treatment process using anaerobic digestion system in order to retrieve methane gas energy. Some wastes were found to be suitable for anaerobic treatment because of high Methane gas Production Ratio (MPR) . The MPR levels (Nml-CH₄/gVS) were as follows; pig manure 236, cattle manure 158, poultry manure 320, internal pig organs 705, rice straw 264 and pressed oranges 536. It was found that rice straw and pressed oranges were particularly suitable for energy recovery during the winter season. In order to asess the economic feasibility, we conducted a case study of anaerobic digestion which treated pig manure (35, 000 heads/d), cattle manure (1, 500 heads/d), internal pig organs (4.2 tons/d) and pressed oranges (30 tons/d) .
The results indicated that the total methane gas production was 8, 400 Nm³/d and excess methane gas was 6, 400 Nm³/d which were measurements available without heating the anaerobic digestion process. Other outputs from the system were supernatant liquor (300 m³/d) and digested dewatered sludge (60 tons/d) . The supernatant liquor had to be purified further by nitrification and denitrification processes due to the high concentration of ammonium. The supernatant liquor when used in part was found to be an effective liquid fertilizer. The digested sludge was also found to be useful as a fertilizer.

View full abstract

The ammonia and odorous sulfur compounds generated in aerobic composting processes were measured by the titration method and by gas chromatography, respectively. The composting temperature was set at two different points, 50°C and 60°C, and the concentrations and cumulative quantities of odorous compounds generated by these two composting processes were compared. Under both operational temperatures high concentrations of methyl melcaptan (MMC), dimethyl disulfide (DMDS), and NH₃were generated by the composting process after 50 hours had elapsed, when approximately 40% of the carbon in the raw material of compost had been converted to CO₂. In contrast, dimethyl sulfide (DMS) was generated only in the 50°C composting process. It was also confirmed that the generation pattern for the odorous compounds in the two composting processes differed with the cumulative quantities of MMC and NH₃generated at 60°C composting, the patterns of the latter being larger than those generated at 50°C composting process. However, the differences in the actual quantity of these compounds generated at the two composting temperatures were relatively small.

View full abstract

The local authorities are worried about the increase in waste generation. Therefore, our work was geared up towords a guideline for getting waste reduction and the promotion of waste recycling in all areas. At first, we surveyed the waste generation rate per capita and the resource recovery rate per capita in all elementary school districts, and mapped out the data. The characteristics of waste generation in all areas as clarified through our survey are summarized as follows:
The generation rates of incombustible wastes in residential districts, commercial areas and resort areas were high.
The resource recovery rates in the residential districts were high and the generation rates of incombustible waste were low. The highest resource recovery rate accounted for 30% of the incombustible waste generation rate. The generation rates of incombustible waste in the commercial district was 1.7 times higher than that in the residential district.
From the above mentioned results, it can be suggested that the minimization of incombustible waste generation can be achieved by the promotion of resource recovery, while the increase of it is caused by the contamination of domestic incombustible waste by commercial waste.

View full abstract

In the law for“Promotion of Sorted Collection and Recycling of Containers and Packaging”, liquefaction is outlined as one of the resource recovery methods for ‘plastic containers with the exception of PET bottles’. In this study, an evaluation method is proposed for the liquefaction of plastic wastes over a wide area involving several local governments from the stand points of energy consumption, environmental impacts, and running costs.
The northern part of Shikoku has been selected and six simulated cases with variable plastic collection ratio, locations of pretreatment and liquefaction plants were calculated. The following results were concluded: 1) approximately four times of the energy which is invested in liquefaction is yielded, 2) environmental impacts of energy consumption (CO₂, NOx and consumption of landfill space) and‘transportation costs’are considerably lower than those for‘facilities’, 3) due to scale merits the larger plant is able to save more on energy consumption and costs than the smaller plant.

View full abstract

Waste generation rates (WGRs: kg/m², m³/m²) of building demolition waste were revised by re-examining and re-evaluating the existing ones. The two points considered were as follows : 1) to evaluate data reliability by analyzing the existing WGRs and to re-examine data through additional surveys, 2) to classify WGRs by analyzing their attributes.
As a result, WGRs by building type (W, S, RC, SRC), use (Dwelling, Office, Other) and waste (combustibles, metals, concrete and total wastes) were set up with their statistical data. It was shown that WGRs of wooden building were reliable enough, but those of non-wooden buildings were not, and applications for the use of classified WGRs were outlined.

View full abstract

We have developed a separation/recovery method for papers and plastics from the mixture waste of them. This method consists of a moisturizing process that endows papers with conductivity, and an electrostatic separation process which separates the conductive papers from non-conductive plastics. In using this method, we were able to recover paper from a model waste : both paper recovery and content were more than 90 wt%.

View full abstract