The operational performances of continuous stirred tank reactors (CSTRs), using biogas reactor of conventional immobilized carrier and novel entrapped carriers containing inorganic, trace metals and vitamin B groups were compared. These reactors were operated at 25, 15 and 5°C, and innoculated with psychrophilic methanogens acclimated for 6 months from mesophilic one which was transferred from mesophilic digested reactor in a sewage plant. The novel entrapped carriers were developed and experimented for the psychrophilic biogas reactors. The novel entrapped carriers contained 100, 1, 000, 5, 000 and 10, 000 times of the conventional inorganics, trace metals and vitamin B groups concentrations in the glucomannan-gel, and these were entrapped the outlayer of the glucomannan by PVA-gel. The outer diameter of carriers were about 4-5mm. Operational conditions of these experiments were set at 1-4kg-VAm^-3d^-1 of loading organic acid, 5, 10 and 20% packing ratio of the working volume and 20 days of constant hydraulic retention time (HRT). The following optimal conditions were obtained by comparison to CSTR; 1, 000 times of the contained inorganics, trace elements and vitamin B groups, 3.5-4kg-VAm^-3d^-1 of organic acid and 10% packing ratio. From the aspect of evaluation of methanogenic activity (as shown with unit of CH₄-mLd^-1g-VSS^-1), the operation temperatures for the psychrophilic biogas reactor should be selected in the range of 15-25°C.

View full abstract

The objective of this study is to reuse CO₂ of the compost gas in the plant growth facilities which exhausted in composting process. The influence of the compost gas applying to the plants was examined. And elimination methods of the several components from the compost gas were examined.
H₂S, CH₃SH and NH₃ were unfavorable for the plants when they were cultivated in greenhouse. Especially, H₂S and CH₃SH injured the plants. The biological filter (bio-filter) was useful or effective for NH₃ contained the compost gas. But the bio-filter was less effective for CH₃SH and (CH₃)₂S. And the variation of environmental temperature influenced the availability of the bio-filter. The catalytic-filter with the activate carbon and catalyst was effective for CH₃SH, while it is not effective for NH₃. By-product such as (CH₃)₂S was produced by the catalysis activity. The compost gas which was treated by both bio-filter and catalytic-filter didn't injure the plants fatally. The SPAD value of the radish applied the compost gas treated by bi-filter and catalytic-filter was higher than that grown by the atmospheric air.

View full abstract

The ammonia concentration in exhaust gas from composting with vacuum-type aeration is higher than that of positive-pressure aeration thus requiring a new deodorization method. Experiments have been conducted on the deodorization and recovery of high concentrations of ammonia using recovery materials (adsorption materials) made from rice husks and orthophosphoric acid at mass ratios of 1:0.5, 1:1.0, 1:1.5, 1:2.0 and 1:2.5. For 1kg of recovery material, the time and quantity of ammonia adsorption were about 28 hours and 159g (1:2.0), respectively. In this case, the recovery material was filled to a heap height of 50cm in an adsorption reactor about 15cm in diameter and ammonia gas at 4000ppm was flowed through it. This was about 2.6 times and about 23 times the adsorptions of impregnated charcoal and of zeolite, respectively. In terms of pH, it is considered that diammonium phosphate and ammonia dihydrogen phosphate were coated with the rice husks of the recovery materials after adsorption. Re-emission of the ammonia from the recovery materials after absorption was observed when air temperature exceeded 30°C. Thus, further study is needed on the relationship between the re-emission of ammonia and atmospheric temperature.

View full abstract

We have been trying to evaluate dairy production systems from not only economy but also fossil energy input and nitrogen surplus.
In our previous paper the evaluation from three indexes was made on A-district having grass land dairy production. In this paper the same evaluation was also made on B-district having mixed production area of up-land crop and milk, and the comparison between A and B district are made.
As results, stocking rate is a lot higher in B-district (2.5±0.7) than A-district (1.4±0.4 [herd/ha]). Milk yield per cow per year was larger in B-district (7.8±1.0) than A-district (6.9±1.2 [t/milking cow]). B-district has more intensive farming than A-district.
Therefore, net agricultural income per unit operating area is higher in B-district (395±145) than A-district (212±84 [1, 000yen/ha]). However, net agricultural income ratio as an index of economical efficiency was lower in B-district (30±8) than A-district (36±10 [t/milking cow]).
Fossil energy input per ha was 39±14 in A-district and 91±32 [GJ/ha] in B-district. Fossil energy input output ratio as an index of energy efficiency is 2.0±0.5 in A-district and 2.4±1.5 in B-district. Nitrogen surplus per ha is 106±51 in A-district and 268±93 [GJ/ha] in B-district.
[Energy input/Net agricultural income] ratio, which means how much of fossil energy is consumed to earn 1, 000yen of net agricultural income, is higher in B-district (267±172) than A-district (210±117 [MJ/1, 000yen]).
[Nitrogen surplus/Net agricultural income] ratio which means how much of nitrogen is unutilized inside the farm to earn 1, 000yen of net agricultural income, is higher in B-district (0.8±0.5) than A-district (0.6±0.4 [kg/1, 000yen]).
B-district had higher evaluation in terms of economy. On the other hand, A-district has higher evaluation in terms of energy and nitrogen surplus. In other words, A-district seems to have higher evaluation from the environmental issues.
Although a district having higher net agricultural income had been evaluated as a better farming area for long time. It is revealed the district can be evaluated differently by applying the other evaluation indexes related to environmental issue.

View full abstract