RESULTS AND DISCUSSION
The competency of the uncharacterized microbial consortia was evaluated in continuous cultures supplemented with phenol as carbon source. Figure 1 shows the acclimatization stage that resulted in nearly complete reduction of phenol (93%) within 14 days of degradation. This result is comparable with result found by Gonzalez et al. [4] with complete reduction of phenol after 10 days of degradation with initial concentration of 1000 mg/L by using pure cultures of Pseudomonas putida ATCC 17484. This result proved that, robust mixed culture from residential wastewater have comparable performances as defined pure culture. This acclimatized consortia then was used in continuous biodegradation with shock loading of phenol as shown in Figure 2 and successfully reduced 61% of phenol concentration. The OD decreased as dilution rate is increased. Previous study also obtained that cell concentration decreased with incremental in dilution rate (D) during continuous biodegradation of phenol [6]. As a comparison, an experiment has been performed to study continuous biodegradation without acclimatization stage and the result is shown in Figure 3. These non-acclimatized consortia have resulted in 67% of phenol reduction. Incremental loading rate has apparently decreased the stability of the continuous culture for both experiments. Microbes managed to degrade phenol at low dilution rates, namely 0.02 h-1 and 0.04 h-1. Further increase of dilution rate at 0.056 h-1 has resulted in a washout, and consequently increased the phenol level up to 200 ppm. Hensel and Straube [8] also observed that the stability of the system decreased with increasing dilution rate.