Biokinetic Optimization of Adsorption–Modified Biofilm Reactor for Pollutant Removal and n-Propanol Production from Palm Oil Mill Effluent

Abstract

n-Propanol is a promising value-added chemical with broad industrial applications, while its biological production from renewable organic wastes offers an opportunity for resource recovery and circular bioeconomy development. Palm oil mill effluent (POME) is a promising renewable carbon source for n-propanol production due to its high biodegradable organic content, but its high pollutant load requires effective treatment. Therefore, this research developed an coupled system consisting of oil palm empty fruit bunch (OPEFB) adsorption-modified Anaerobic Rotating Biological Contactor (modified AnRBC)-Moving Bed Biofilm Reactor (MBBR)-sedimentation to enhance pollutant removal and n-propanol production. An integrated Anaerobic Digestion Model No. 1 (ADM1)–Activated Sludge Model No. 1 (ASM1) was also developed to predict reactor performance and support process optimization. Laboratory-scale experiments were conducted at HRT of 1, 2, and 3 d. Modified OPEFB fibers prepared using the sol–gel method were used as adsorbents for O&G removal before biological treatment. Reactor performance was evaluated based on pH, total chemical oxygen demand (TCOD), biochemical oxygen demand (BOD), total suspended solids (TSS), oil and Grease (O&G), total nitrogen (TN), and n-propanol production. The modified ADM1 and ASM1 models were calibrated to predict n-propanol production and TCOD removal, respectively, and evaluated using the coefficient of determination (R²), Pearson correlation coefficient, and root mean square error (RMSE). The coupled modified OPEFB adsorption–modified AnRBC–MBBR system achieved average removal of 95.38% BOD, 96.97% TCOD, 94.58% TSS, 93.35% O&G, and 81.78% TN, with an effluent pH of 8.18 and average n-propanol production of 9.81 mg/L. However, only the final pH complied with the Indonesian wastewater discharge standard, indicating that additional polishing treatment is required before discharge. HRT significantly affected both pollutant removal and n-propanol production. Increasing HRT significantly improved treatment performance, with HRT 3 achieving the highest removal, while maintaining the effluent pH at 8.09. Although the highest n-propanol concentration (37.35 mg/L) occurred at HRT 2, HRT 3 achieved a higher average production and the best overall treatment performance. The integrated ADM1–ASM1 biokinetic model was successfully developed to predict n-propanol production in the modified AnRBC and TCOD removal in the MBBR. The optimized ADM1 parameters (KS = 0.50 kgCOD/m3, km,c3 = 60 /d, and DprOH = 8 × 10-10 m2/s) achieved satisfactory performance (R2 = 0.84, Pearson correlation = 0.89, RMSE = 1.09 mg/L). The optimized ASM1 parameters (YH = 0.75, µH,max = 0.10 /d, KS = 25 mgCOD/L, and DS = 9.77 × 10-9 m2/s) showed excellent prediction of TCOD effluent (R2 = 0.91, Pearson correlation = 0.95, RMSE = 466.88 mg/L).

n-Propanol merupakan bahan kimia bernilai tambah yang memiliki berbagai aplikasi industri, dan produksinya secara biologis dari limbah organik terbarukan mendukung pemulihan sumber daya dan ekonomi sirkular berbasis hayati. Limbah cair pabrik kelapa sawit (LCKS) merupakan sumber karbon terbarukan yang potensial untuk produksi n-propanol karena kandungan bahan organik biodegradable yang tinggi, tetapi beban pencemarnya yang tinggi memerlukan pengolahan yang efektif. Oleh karena itu, penelitian ini mengembangkan sistem terintegrasi yang terdiri atas adsorpsi tandan kosong kelapa sawit (TKKS) termodifikasi-Anaerobic Rotating Biological Contactor termodifikasi (AnRBC)Moving Bed Biofilm Reactor (MBBR)-sedimentasi untuk meningkatkan penyisihan pencemar dan produksi n-propanol. Model terintegrasi Anaerobic Digestion Model No. 1 (ADM1)-Activated Sludge Model No. 1 (ASM1) juga dikembangkan untuk memprediksi kinerja reaktor dan mendukung optimasi proses. Percobaan skala laboratorium dilakukan pada HRT 1, 2, dan 3 hari. Serat TKKS termodifikasi yang disiapkan menggunakan metode sol–gel digunakan sebagai adsorben untuk menyisihkanO&G sebelum proses biologis. Kinerja reaktor dievaluasi berdasarkan pH, kebutuhan oksigen kimia total (TCOD), kebutuhan oksigen biokimia (BOD), total padatan tersuspensi (TSS), minyak dan lemak (O&G), dan nitrogen total (TN). Model ADM1 dan ASM1 yang dimodifikasi dikalibrasi untuk memprediksi produksi n-propanol dan penyisihan TCOD, kemudian dievaluasi menggunakan koefisien determinasi (R²), koefisien korelasi Pearson, dan galat akar kuadrat rata-rata (RMSE). Sistem terintegrasi adsorpsi TKKS termodifikasi–AnRBC termodifikasi–MBBR mencapai efisiensi penyisihan rata-rata sebesar 95,38% BOD, 96,97% TCOD, 94,58% TSS, 93,35% O&G, dan 81,78% TN, dengan pH efluen sebesar 8,18 dan produksi n-propanol rata-rata sebesar 9,81 mg/L. Namun, hanya pH akhir memenuhi baku mutu. HRT berpengaruh signifikan terhadap penyisihan polutan dan produksi n-propanol. Peningkatan HRT meningkatkan kinerja pengolahan, dengan HRT 3 menghasilkan penyisihan tertinggi serta mempertahankan pH efluen 8,09. Meskipun konsentrasi n-propanol tertinggi (37,35 mg/L) diperoleh pada HRT 2, HRT 3 menghasilkan produksi n-propanol rata-rata yang lebih tinggi serta kinerja pengolahan keseluruhan yang terbaik. Model biokinetik terintegrasi ADM1–ASM1 berhasil dikembangkan untuk memprediksi produksi n-propanol pada AnRBC termodifikasi dan penyisihan TCOD pada MBBR. Parameter ADM1 optimum (KS = 0.50 kgCOD/m3, km,c3 = 60 /d, dan DprOH = 8 × 10-10 m2/s) menghasilkan kinerja yang baik (R2 = 0.84, korelasi Pearson = 0.89, RMSE = 1.09 mg/L). Sementara itu, parameter ASM1 (YH = 0.75, µH,max = 0.10 /d, KS = 25 mgCOD/L, dan DS = 9.77 × 10-9 m2/s) memberikan prediksi TCOD efluen yang sangat baik (R2 = 0.91, korelasi Pearson = 0.95, RMSE = 466.88 mg/L)