A new rotating biological contactor-packed media technology (RBC-PMT) is locally innovated using light polyethylene Amazon screen material as disc media. A single-stage co-current fed of this type, which is connected with a series of equalization tanks as an integrated wastewater treatment system (IWWTS), showed good carbonnitrogen-phosphorus (C-N-P) removal and unveiled biofilm growth characteristics noteworthy for treating pollutants in wastewater.The equalization tanks approached facultative anaerobic conditions while the RBC-PMT exhibited a completely aerated system, both with a slightly alkaline pH, whose temperatures are ranging from 21 to 24• C, and both performed as biological nutrient removal systems. The combined nutrient removal efficiency at high organic loading rate (HOLR) and low organic loading rate (LOLR) showed fair chemical oxygen demand (COD) removal at 65.68 and 67.89%, respectively. Nitrate-nitrogen removal demonstrated good removal at 79.17% at HOLR and 83.43% at LOLR. There was excellent phosphate-phosphorus removal determined at 91.64 and 94.35% at high and low OLRs, respectively. This indicates that increasing the organic loading rate decreases the C-N-P removal in the IWWTS.Biofilm growth was characterized by the selection and survival of microorganisms present under aerobic environmental conditions in the RBC-PMT system and their respective metabolism in removing C-N-P substrates. Yeasts, coliform bacteria particularly E. coli, Cyanobacteria, and benthic diatoms were dominant microorganisms found upon oil-immersion microscopy. Protozoans and algae including Chlorococcum, Chlorella, Diatoma, Tribonema, Oscillatoria, Euglena, and other motile rotifiers were also dominantly found in the biofilm samples. Biofilm growth is observed and its average thickness was measured to be 7.71 µm at HOLR and 2.81 µm at LOLR. Thicker biofilm at HOLR has caused the reduced rate of diffusion of the microorganisms and their metabolic products as manifested by the low C-N-P removal during HOLR.
The effect of the substrate feeding pattern on sludge settleability in denitrifying systems was investigated. The feeding pattern was simulated in two sequencing batch reactors (SBR). SBR1 simulates a system with a limiting substrate (acetate) and a non-limiting electron acceptor (nitrate), while SBR2 simulates the opposite condition. Sludge volume index (SVI) was the main observed parameter. The stoichiometry, substrate uptake rate, storage capacity as well as sludge morphology and mixed culture population dynamics were also determined. Results show that independent of the feeding pattern, the settleability of the sludge remained good (SVI approximately 50 mL/g) and stable. Neither the concentration of the acetate nor of the nitrate offered any limitations on sludge settleability, assuring that a good bio-P activity is present in nitrate limiting systems. Filamentous bacteria belonging to the TM group were usually present, although in low numbers. Despite the diffused, irregularly shaped and open floc structure, good settleability was observed. The results obtained were in line with the hypothesis on diffusion based selection.
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