Enhancement of Stabilization/Solidification Method with Bioaugmentation for Sludge Remediation

Abstract

The Stabilization/Solidification (S/S) method encapsulates heavy metals in sludge, while bioaugmentation can degrade organic contaminants. However, each method is limited in its ability to address both contaminants simultaneously. This study aims to enhance the S/S method by integrating bioaugmentation, using either immediate or pre-inoculation of bio-agents. Ordinary Portland Cement (OPC) served as the binder in the S/S process, with the bacteria Sphingobacterium spiritivorum and the fungi Aspergillus brasiliensis acting as bio-agents. Before testing, chemical oxygen demand (COD) and heavy metals in sludge and cement were measured. COD and heavy metal concentrations' leaching behavior were tested using TCLP after 14 and 28 days. The result shows 23.39% of organic contaminants were in the fibreboard sludge. The TOC results for Portland cement were negligible. All heavy metal elements (Cr, Cu, Zn, As, and Pb) in the Portland cement and fibreboard sludge exceeded the standard USEPA limit. COD reduction was evaluated for immediate versus pre-inoculation of fungi and bacteria over 14 and 28 days. Pre-inoculation consistently yielded lower COD levels than immediate inoculation, with fungi pre-inoculation achieving the greatest reduction (579 mg/L at 14 days; 544.7 mg/L at 28 days) and bacteria pre-inoculation showing moderate improvement (579.3 mg/L at 14 days; 570.3 mg/L at 28 days). Concentrations of heavy metal reductions followed a similar trend: after 28 days, pre-inoculated samples contained 0.01 mg/L (Cr), 0.22 mg/L (Cu), 0.06 mg/L (Zn), and 0 mg/L for both As and Pb, whereas immediate-inoculated samples showed 0.04 mg/L (Cr), 0.22 mg/L (Cu), 0.01 mg/L (Zn), and 0 mg/L for As and Pb. Statistical comparison shows significant differences between immediate-inoculation and pre-inoculation, but not between the bio-agents used in this study. To improve the findings, a co-culture method that combines both bio-agents is recommended, offering a viable strategy for industrial sludge management, with future studies needed to scale up the method for practical, sustainable waste treatment applications.

ABSTRAK: Kaedah Pengukuhan dan Penstabilan (S/S) bertujuan mengkapsulkan logam berat dalam enap cemar, manakala bioaugmentasi digunakan bagi mengurai bahan pencemar organik. Walau bagaimanapun, setiap kaedah mempunyai keterbatasan dalam menangani kedua-dua jenis pencemar secara serentak. Kajian ini bertujuan menambah baik kaedah S/S dengan menggabungkan bioaugmentasi, sama ada melalui inokulasi segera atau pra-inokulasi mikrob. Simen Portland Biasa digunakan sebagai agen pengikat dalam proses S/S, manakala bakteria Sphingobacterium spiritivorum dan kulat Aspergillus brasiliensis bertindak sebagai agen bio. Sebelum kajian dijalankan, Permintaan Oksigen Kimia (COD) dan logam berat dalam enap cemar serta simen ditentukan. Tingkah laku larut lesap COD dan kepekatan logam berat diuji menggunakan kaedah TCLP selepas 14 dan 28 hari. Dapatan kajian menunjukkan sebanyak 23.39% bahan pencemar organik terdapat dalam enap cemar papan gentian. Kandungan TOC dalam simen Portland didapati sangat rendah dan tidak memberi kesan ketara. Semua unsur logam berat (Cr, Cu, Zn, As dan Pb) dalam Simen Portland Biasa dan enap cemar papan gentian melebihi had piawaian yang ditetapkan oleh USEPA. Pengurangan COD dinilai bagi inokulasi segera berbanding prainokulasi dengan kulat dan bakteria selama 14 dan 28 hari. Prainokulasi secara konsisten menghasilkan tahap COD lebih rendah berbanding inokulasi segera, dan prainokulasi kulat menunjukkan pengurangan paling ketara (579 mg/L pada 14 hari; 544.7 mg/L pada 28 hari) manakala prainokulasi bakteria menunjukkan peningkatan sederhana (579.3 mg/L pada 14 hari; 570.3 mg/L pada 28 hari). Kepekatan pengurangan logam berat mengikuti corak serupa: selepas 28 hari, sampel prainokulasi mengandungi 0.01 mg/L (Cr), 0.22 mg/L (Cu), 0.06 mg/L (Zn), dan 0 mg/L bagi As dan Pb, manakala sampel inokulasi segera menunjukkan 0.04 mg/L (Cr), 0.22 mg/L (Cu), 0.01 mg/L (Zn), dan 0 mg/L bagi As dan Pb. Perbandingan statistik menunjukkan terdapat perbezaan signifikan antara kaedah inokulasi segera dan prainokulasi, namun tiada perbezaan signifikan antara jenis agen bio yang digunakan dalam kajian ini. Bagi meningkatkan keberkesanan rawatan, kaedah ko-kultur menggabungkan kedua-dua bioagen dicadangkan, menawarkan potensi terbaik bagi pengurusan sisa industri. Kajian lanjut diperlukan untuk penskalaan bagi aplikasi praktikal dan rawatan sisa lestari.