3. Results and discussion
A detailed description of the performance of the leach-bed process involving exchange of leachate between a fresh waste bed and an anaerobically stabilized waste bed can be found in Chugh et al. (1999). The performance of the experiments presented here was similar to the studies reported in Chugh et al. (1999).Hence, the focus of the discussions here will be on the generation of SCOD and its correlation to cellulolytic activity in the leachate.
Figs. 1 and 2 show the profiles of pH, methane gas content, concentration of SCOD in the leachate, methane generation rate, hydrolytic activity of the leachate and SCOD generation rate for the NEW reactors in the 50/} and 100/} experiment, respectively. Sequencing was continued for 26 and 8 days for the 50/} and 100/} experiment, respectively,before the conditions for sequencing termination were met (Figs. 1(A) and 2(A)). In the 50/} experiment, the quantity of leachate that was flushed through the bed was half of that of the 100/} experiment and, as a result, it took a longer time to initiate degradation. Chugh et al. (1998) showed that the time for initiating degradation was dependent on the quantity of leachate flushed through the bed. Furthermore, in this study, the OLD reactor used in the 50/} experiment was left dormant for more than 60 days before its leachate was sequenced with the NEW reactor. Consequently, the activities of the microorganisms within the OLD reactor of the 50/} experiment were lower than those within the OLD reactor of the 100/} experiment. This was evident as there was no methane production from the OLD reactor of the 50/} experiment until day 6. However, from the OLD reactor of the 100/} experiment, 20.3 1 of methane was produced on the first day of flushing leachate from NEW reactor and the total methane produced after 6 days of sequencing was 72.8 1.
Use of Eq. (1) to estimate SCOD generation rate required measurement of daily SCOD concentration in the leachate. Concentrations of SCOD in the leachates of NEW reactor of the 50/} and 100/} experiments are shown in Figs. 1(B) and 2(B). Since the SCOD concentrations were not measured daily, an approximation of SCOD
concentrations in the intervening days was made by fitting a curve to the measured SCOD data. From concentration values predicted by the curve, an estimate of the SCOD inventory during the course of the 50/} and 100/} experiments were made.TheSCOD inventory throughout the 50/} and 100/} experiments was plotted along with methane generation from the NEW reactors in Figs. 1(B) and 2(B).
Significant production of SCOD during start up was observed for both experiments. The SCOD generation in the NEW reactors was very high initially and it continued to drop thereafter (Figs. 1(C) and 2(C)).
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