An Evaluation of Soft-drink Wastewater Treatment by Anaerobic Digestion Process

Series of batch operations were conducted for testing the suitability of anaerobic process for the treatment of soft-drink wastewater. No buffering control substances and biomass growth enhancer were added during the experiment although the wastewater used lacked those substances. Each batch operation resulted in the normal methane yield which was between 0.28 to 0.34 m per kg COD removed. Nevertheless, with the increments of hydraulic loading up to one-third of the working volume, the treatment operation has unable to further remove the carbonaceous components. This failure was also shown by the cessation of CH4 production. The final organic mass loading per working volume was at 1.33 kg/m, which was relatively low to cause failure. Further investigation showed that operation failed because of the methanogenesis process has been subjugated. Impediment of methanogenesis was caused by losses of its alkalinity during effluent withdrawal and addition of influent with low pH. VFAs were found to be as high as 1500 mg/L. Lack of nitrogen source was also the cause of the subjugation when reduction of biomass concentration were also had been observed. Treatment of such wastewater with low nitrogeneous substances and low levels of pH and alkalinity requires additional controlling measures to avoid operational failure. ABSTRAK Beberapa siri operasi berkelompok telah dijalankan untuk menguji kesesuaian penggunaan proses anaerobik untuk rawatan air sisa minuman-ringan. Tidak ada bahan kawalan penimbal and penambah tumbesaran biojisim digunakan semasa eksperimen walaupun kedua-dua bahan ini adalah berkurangan dalam air sisa yang digunakan. Setiap operasi berkelompok telah menjanakan jumlah gas metana yang normal, iaitu diantara 0.28 hingga 0.34 m per kg COD disingkirkan. Walaubagaimanapun apabila kenaikan muatan hidraulik meningkat sehingga satu per tiga dari jumlah isipadu kerja, operasi rawatan telah menunjukkan kegagalan untuk menyingkir komponen berkarbon. Kegagalan ini ditunjukkan oleh pengurangan penghasilan gas metana. Muatan organik per isipadu kerja yang terakhir adalah setinggi 1.33 kg/m, yang mana secara relatifnya adalah rendah untuk menyebabkan kegagalan operasi. Kajian seterusnya menunjukkan kegagalan operasi adalah disebabkan proses metanogenesis telah berhenti. Halangan proses ini adalah disebabkan oleh kehilangan alkaliniti semasa pemindahan keluar effluen dan penambahan influen yang mempunyai nilai pH yang rendah. Kehadiran VFA dengan kepekaran 1500 mg/L juga telah dicerap. Kekurangan sumber nitrogen juga menjadi penyebab kegagalan operasi apabila berlakunya pengurangan jumlah biojisim. Rawatan untuk air sisa yang kepekatan bahan bernitrogen, pH dan alkaliniti yang rendah memerlukan langkah kawalan tambahan bagi mengelakkan kegagalan operasi. (Anaerobic process, soft drink wastewater, alkalinity, nitrogen sources, operation failures, volatile fatty acids) ____________________________________________________________________________________ Malaysian Journal of Science 26 (1): 23 – 34 (2007)