Optimasi Laju Transfer Oksigen Terhadap Kinerja Moving Bed Biofilm Reactor Kombinasi Membran Nanofiltrasi pada Sistem Resirkulasi Akuakultur

Abstract

Akumulasi amonia (0,72 mg/L) dan nitrit (0,53 mg/L) dari metabolisme ikan koi memicu penurunan pH media hingga 5,0, melampaui ambang batas baku mutu akuakultur. Tesis ini mengevaluasi kinerja sistem resirkulasi akuakultur (RAS) terintegrasi yang menggabungkan reaktor moving bed biofilm reactor (MBBR) bermedia Kaldnes K5 (pengisian 60%) dan filtrasi fisik membran nanofiltrasi (NF90-4040), yang didukung oleh pengembangan Integrated Hybrid Model berbasis unsteady-state. Reaktor berskala laboratorium ini dioperasikan pada debit sirkulasi konstan 40 L/min dengan tiga variasi debit aerasi (100, 150, dan 190 L/min). Hasil menunjukkan sistem mencapai efisiensi penyisihan amonia 23,32–97,01%. Kondisi operasional terbaik tercapai pada debit aerasi 150 L/min dengan konsentrasi amonia permeat rata-rata terendah (0,03 mg/L), efisiensi penyisihan nitrit tertinggi (87,19%), serta kerapatan biomassa melekat (TAS) maksimal sebesar 8,4 g/m². Sebaliknya, peningkatan aerasi hingga 190 L/min memicu fluid shear stress yang merontokkan biofilm (TAS turun menjadi 7,8 g/m²) dan menurunkan penyisihan nitrit hingga 43,67% akibat hilangnya keseimbangan populasi AOB dan NOB. Fenomena membrane fouling paling masif terjadi pada debit 150 L/min dengan laju fouling harian sebesar 0,11 bar/hari, pemicunya adalah pelepasan Soluble Microbial Products (SMP) akibat mekanisme kelaparan (starvation) saat beban substrat amonia sangat rendah. Validasi Integrated Hybrid Model menunjukkan presisi tinggi pada parameter amonia permeat (??2 = 0,895; ?? = 0,946) dan fluks membran (??2 = 0,930; ?? = 0,964), serta terbukti valid secara statistik (?? > 0,05) . Secara keseluruhan, konfigurasi MBBR–NF efektif menyisihkan nitrogen terlarut, namun pengendalian alkalinitas dan laju aerasi wajib dijaga secara ketat untuk mencegah pH crash di bawah 5,5 serta meminimalkan irreversible fouling akibat akumulasi SMP.

Accumulation of ammonia (0.72 mg/L) and nitrite (0.53 mg/L) from koi fish metabolism triggers a drop in water pH to 5.0, exceeding aquaculture water quality standards. This thesis evaluates the performance of an integrated recirculating aquaculture system (RAS) combining a moving bed biofilm reactor (MBBR) with Kaldnes K5 media (60% filling ratio) and a nanofiltration membrane (NF90-4040), supported by the development of an unsteady-state Integrated Hybrid Model. The bench-scale reactor was operated at a constant circulation rate of 40 L/min under three aeration rates (100, 150, and 190 L/min). Results demonstrated ammonia removal efficiencies ranging from 23.32% to 97.01%. Optimal performance was achieved at an aeration rate of 150 L/min, yielding the lowest average permeate ammonia concentration (0.03 mg/L), highest nitrite removal efficiency (87.19%), and maximum attached biomass density (TAS = 8.4 g/m²). Conversely, increasing aeration to 190 L/min induced fluid shear stress that detached the biofilm (TAS dropped to 7.8 g/m²) and reduced nitrite removal to 43.67% due to the disruption of AOB and NOB population balance. Severe membrane fouling occurred at 150 L/min with a daily fouling rate of 0.11 bar/day, driven by the release of Soluble Microbial Products (SMP) under substrate starvation at low ammonia loads. Validation of the Integrated Hybrid Model demonstrated high predictive accuracy for permeate ammonia (??2 = 0.895; ?? = 0.946) and membrane flux (??2 = 0.930; ?? = 0.964), and was statistically proven valid (?? > 0.05). Overall, the MBBR–NF configuration effectively removes dissolved nitrogen; however, strict control of alkalinity and aeration rate is required to prevent pH crash below 5.5 and minimize irreversible fouling from SMP accumulation.