Judul: Kajian Peningkatan Kapasitas Proses Co-Composting Blotong dan Abu Ketel
Abstrak: Co-composting at industrial scale can be applied for utilization of filter cake and boiler ash. For applying in industrial scale, study on composting performance in larger capacity was needed. The purpose of this research was to study the performance of composting process in large scale compared with laboratory scale as reference for industrial implementation. The parameters in scale increasing consist of the C/N decrease rate and the effect of aeration for 60 days of composting. Increased composting capacity was done by increasing the capacity of 5 kg to 120 kg. Constant factor in the increase in capacity is congruency geometry, aeration rate and the value of C/N beginning 40. The result showed that composting process at 120 kg scale was not different from 5 kg scale, in which the temperature formed in mesophilic phase, pH level was neutral and optimum moisture content. The rate of decrease C/N was, 1.3675 / day with yield of 68.97% and the estimated time of compost for 20 days. There was no effect of 14 aeration during compost of 120 kg at a rate of decrease C/N. B/C ratio in the analysis of business of industrial compost capacity was 1.42, that means it could be implemented.
Keyword: boiler ash, filter cake, increased capacity, co-composting

Judul: Evaluasi Kinerja Peningkatan Kapasitas Pengomposan dari Campuran Blotong, Bagas, dan Abu Ketel
Abstrak: Composted filter cake, bagasse, and boiler ash on laboratory scaled which used aerated pile method had generated an optimum initial C/N and resulted the best compost quality. Meanwhile in order to be applied directly in industrial scale, the evaluation of laboratory scaled co-composting performance was needed along with increased processing capacity. The aim of this study was to compare larger scale of co-composting performance evaluation with laboratory scale. Capacity enhancement was done by increasing the capacity process from laboratory scaled of 5 kg to 100 kg. The evaluated performance parameters in co-composting were composting rate and the effect of aeration during composting. While constant factors, as same as capacity of 5 kg’s, were reactor geometrical congruency, initial C/N and aeration treatment. Compost mixture had initial C/N value of 50 and active aeration treatment of 0.4 L/min.kg was given in for 1 hour per day in the first week. The result showed that there were no any significant differences of composting rate between 5 kg and 100 kg. Besides, active aeration did not give significant effect to process condition and the composting rate in 100 kg scaled co-composting. Financial analysis of composting was able to bring profits based on the equation of B/C ≥1.
Keyword: evaluation of capacity process, co-composting, C/N, capacity enhancement, aeration

Judul: Pemodelan Nilai Tukar Rupiah terhadap Dollar Amerika Menggunakan Deret Waktu Hidden Markov Empat Waktu Sebelumnya
Abstrak: The exchange rate of Rupiah to US Dollar fluctuates according to time in a long period. An existing exchange rate might happen again in the future. Assume that the causes of the fluctuation are not observed directly and form a Markov chain, then the exchange rate of Rupiah to US Dollar can be modeled by the hidden Markov time series. In this research, the model used to describe the exchange rate of Rupiah to US Dollar is the four previous time in hidden Markov time series. This model assumes that the exchange rate of Rupiah to US Dollar depends on Markov chain explained by the cause of occurence and the four previous exchange rates of Rupiah to US Dollar. The model parameter is estimated by using the maximum likelihood method, while the estimation itself is calculated using the expectation maximization algorithm, which is implemented using Mathematica. After estimating the parameter, the exchange rate of Rupiah to US Dollar are calculated. The results are as follows. The symmetric mean absolute percentage error (SMAPE) is 2,1%, the maximum absolute error is 19,16%, the minimum absolute error is 0,0036%, and only 1,95% of the whole absolute percentage error that is bigger than 10%. These results show that the four previous time in hidden Markov time series can describe the exchange rate of Rupiah to US Dollar very well.
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