POLYETHYLENE TEREPHTHALATE (PET) AS CARRIER MEDIA ON FIXED BED REACTOR IN DOMESTIC WASTEWATER TREATMENT AND ITS OCCURRENCE IN THE REACTOR AS MICROPLASTICS

• Main Author: Nur, Ansiha
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik saniter dan perkotaan; teknik perlindungan lingkungan
• Online Access: https://digilib.itb.ac.id/gdl/view/67718
• Institution: Institut Teknologi Bandung

Polyethylene terephthalate (PET) plastic bottle waste has been widely used as the carrier for residential WWTPs in Indonesia, because of its advantages. This study investigates aspects of novelty in scientific development in the field of domestic wastewater treatment technology, such as the wettability of PET material, PET design criteria, and the potential for secondary microplastics from its use. The study was carried out both in the field and in the laboratory. The wastewater characterization of residential WWTPs was conducted out at the field scale and provides the basis for laboratory scale experiments. Laboratory experiments were classified as batch and continuous Batch conditions for analyzing the ability of microorganisms to adhere and grow on the PET surface, as well as PET design criteria based on Specific Surface Area (SSA) parameters. The batch method gave the PET form was the best performance in organic and nutrient removal, which was then applied under continuous conditions. In continuous condition, the reactor was operated at different Hydraulic Retention Time (HRT), Recirculation Ratio (RR) and organic loading rate. The occurrence of PET as a secondary microplastic was identified in order to assess the potential for fragmentation of PET as carrier in the reactor during the research. In order to support this information, the research was supplemented by a batch study of the possibility of PET fragmentation as a microplastic. Wastewater characterization was performed on eight residential WWTPs in Bandung City, including four types of Anaerobic Upflow Filter (AUF) using PET as the carrier and four types of Anaerobic Baffled Reactor (ABR). The two types were chosen to compare the potential for microplastics in the WWTP due to the use of PET media. The characterization results show that this wastewater typically ranges from 370.67 ± 44.06 mgCOD/L (low strength) to 624.00 ± 32.00 mgCOD/L (medium-high strength), with an average of 435.17 mgCOD/L. The biodegradability of wastewater was demonstrated by a BOD/COD ratio of 0.51 - 0.58, indicating that wastewater is easily biodegradable, and an average C:N:P ratio of 100:11:1,32. Although it did not meet the quality standard of PermenLHK No. 68 of 2016, AUF type WWTP performs better than ABR in terms of removing organics and nutrients. The provision for COD, BOD and NH4-N was 42.74 – 86.11%, 69.19 - 87.20%, 20.72 – 28% at AUF and 12.04 - 58.99%, 37, 52 - 78.22%, 1.39 - 20.21% in ABR. This demonstrates that using PET as an adhesive medium can improve AUF WWTP performance. This phenomenon was supported by laboratory-scale studies that show PET is hydrophilic. PET has a water contact angle of 70.670 ± 0.15 (hydrophilic) or good wettability, allowing microorganisms to adhere to and grow on the PET surface. The growth of biomass on the PET surface was seen from the increase in the value of Total Attached Solid (TAS) and the thickness of the biofilm during observations. The increase was observed gravimetrically and microscopically using SEM and Confocal Laser Scanning Microscopy (CLSM). The thickness of the biofilm at the end of the observation was 342.47 ± 0.05 m under anoxic conditions and 428.85 ± 0.07 m under aerobic conditions. The fastest biofilm growth rate was 0.0146 ± 0.006 mg/cm2.day from day 20 to day 50 under anoxic conditions and 0.0429 ± 0.011 mg/cm2.day from day 10 to day 25 under aerobic conditions. The PET arrangement in the form of a flower created the highest SSA (490.63 m2/m3) and outperformed the zigzag (SSA = 392.50 m2/m3) and round (SSA = 294.38 m2/m3) shapes in terms of performance. The best PET form performs well in terms of removal efficiency, substrate removal kinetics, and bacterial growth kinetics. This flower-shaped PET was then applied to a continuous anoxic-anoxic-aerobic fixed-bed reactor (FBR). This series of continuous FBR with PET as the bio carrier (SSA 490.63 m2/m3) can remove organic and nutrients from medium-strength domestic wastewater at an optimum level (meeting the quality standard of the Minister of Environment and Forestry Regulation No. 68 of 2016) at 36 hours HRT operational conditions and a recirculation ratio (RR) 200%. The second-order model of Grau and Stover-Kincannon showed the most suitable estimation model for COD, N, and P removal in continuous FBR. The addition of a recirculation system improved the removal of ammonia, nitrate, nitrite, and phosphate significantly (p < 0.05). This study considers an environmentally friendly wastewater treatment approach by observing the fragmentation of PET as a secondary microplastic from field research to laboratory scale. The occurrence of PET as carrier for AUF WWTP (field scale) did not contribute to the addition of secondary microplastics in the reactor; in fact, AUF WWTP can remove microplastics by 78.90 - 90.34%, which was better than ABR, which can remove 70.12 - 82.74%. The ATR-FTIR results revealed no PET spectra from the bottle type, but rather from another type. The occurrence of microplastics in WWTP was found in the influent, which ranged from 434.67 ± 22.68 MP/L to 973.33 ± 37.87 MP/L. The removed microplastics were found in the sludge, which was 6256.25 ± 823.94 MP/kg (wet weight) and the biofilm attached to PET was 65.72 ± 15.80 MP/g (dry weight). Similarly, the laboratory scale reactor did not demonstrate the possibility of adding microplastics from the use of PET. The FBR configuration can remove microplastics up to 99.18% from domestic wastewater. The microplastics removed from the FBR were found to accumulate and settle with the sludge, adsorbed and trapped in the biofilm.