Long-run availability of a repairable parallel system

We analyze the long-run availability of a two-unit parallel system sustained by a cold standby unit and attended by two identical repairmen. The system satisfies the usual conditions (i.i.d. random variables, perfect repair, instantaneous and perfect switch, queueing). Each operative unit has a constant failure rate and a general repair time distribution. We use Hokstad's supplementary variable method to construct a system of simultaneous partial differential equations. We present a first-order numerical scheme and an iterative algorithm for the solution of the equations. A particular but important numerical example (Weibull repair), illustrated by computer-plotted graphs, motivates the proposed approximation.     

Removal of contaminated organic acids from simulated succinic acid fermentation broth by reactive extraction process: Single- and mixed-solute solution

This work aims to study how to remove the organic acid by-products from simulated fermentation broth containing succinic acid by reactive extraction. Model solutions including single-, binary-, ternary-, and quaternary-solute solutions were used. The broths were reactively extracted using 0.25 mol TOA/kg 1-octanol under pH of 2.45-6.0. The extracted broths were then distillated under vacuum -0.017 MPa with operating temperature between 45 and 65°C. Finally, the distilled broths were crystallized at 4°C and pH of 2.0. The results showed that the purity and yield of succinic acid of 99.10% and 30.25%, respectively, were obtained.     

On-site nitrate removal of groundwater by an immobilized psychrophilic denitrifier using soluble starch as a carbon source

On-site denitrification of nitrate-contaminated groundwater was conducted at 15 degrees C using a facultative psychrophilic denitrifier (strain 47) immobilized on macro-porous cellulose carriers and utilizing soluble starch as a non-toxic carbon source. A C/N ratio of 2.5 to 3.0 and a P/N ratio of 0.05 to 0.10 were found to allow complete denitrification of the groundwater used in this study. Under these conditions, the long-term performance of the system (4 months) was examined by decreasing the HRT (hydraulic retention time) from 4 h to 0.25 h. The process was stable and 95 to 100% of the influent nitrogen (NO3-N ranging from 13.0 to 16.5 mgl(-1) was removed until an HRT of 0.75 h was reached. The maximum NO3-N removal rate was 0.46 kg-Nm(-3)d(-1) at an HRT of 0.75 h. Nitrogen removal efficiency of 99.5% at an HRT of 1 h was obtained with a C/N ratio 2.58, corresponding to 4.3 g of soluble starch per 1 g of NO3-N.