Effect Of The Hydrothermal Pretreatment On The Anaerobic Digestion Of The Sludge And Variation Of The Organic Matters

Hydrolysis of the sludge solids was the limited step of the anaerobic digestion, andthe hydrothermal pretreatment was an effective way to break the sludge. It adjusted thereaction temperature from110°C to210°C for15min to90min while maintaining theNaOH dose from0g/g-VS to0.25g/g-VS at the hydrothermal treatment. Afterpretreatment for hydrolysis, the sludge supernatant fluid came into the anaerobicdigestive for the anaerobic digestion at35°C directly. The effects of the alkaline thermalhydrolysis treatment on the characteristics of the excessive sludge were investigatedunder the different treatment temperature, the treatment time and the alkali addition. Theeffects of the anaerobic digestion and the variation of the organic matters duringpretreatment were investigated simultaneously. They concluded as follows.(1) The concentration of SCOD in the sludge supernatant was increased, the solidsubstances dissolved in the sludge and the amount of the sludge reduced with theincrease of the temperature, time and the alkali dose. After treating at170°C for30min,the dissolution ration of SCOD was43.6%, VSS/TSS reached32.0%and the moisturecontent of sludge decreased to77.4%; while adding0.10gNaOH/g-VS, those parameterswere69.1%,24.1%and69.7%respectively. At the same time, the structures of thesludge flocs were changed obviously after heat treatment, the sludge particles becamesmaller and smaller.(2) In the process of the anaerobic digestion, the removal rations of SCOD and thesolid organic matters were increased with the increase of temperature and the dose ofalkaline, the lowest removal ration of SCOD was67.1%, and the removal rations of thesolid organic matters were above58%. After the hydrothermal pretreatment, theperformances of the anaerobic digestion were improved. However, the intermediateproducts which generated during the hydrothermal reaction of the sludge might inhibitanaerobic digestion at the high temperature or with the excessive alkali. After treating at170°C for30min, a gas production was570ml (each100ml of the sludge supernatantfluid), while adding0.10gNaOH/g-VS, the gas production was1080ml (each100ml ofthe sludge supernatant fluid).(3) The Fourier transform infrared spectroscopy and the3DEEM fluorescencespectra showed that lipids, polysaccharides, proteins and humic acid were existed in thesludge supernatant.3DEEM fluorescence spectra also showed that mainly protein-like,fulvic-like and humic-like peaks were existed in the supernatant. There were mainly protein-like fluorescence peaks at90°C and130°C for30min. As the rise of thetemperature, the proteins were hydrolyzed gradually; fulvic-like and humic-like peakswere occurred simultaneously. With hydrothermal treatment, sludge organic matters weredissolved and further hydrolyzed; the proteins and humic acid substances were dissolvedout; the maillard reaction was taken place between the proteins and the polysaccharides.It produced humic-like substances.(4) The concentrations of the proteins and the polysaccharides were both increasedfirstly and then decreased with the increase of temperature. At130°C for30min, themaximum concentration of the proteins was726mg/L and at110°C for30min, themaximum concentration of the polysaccharides was1315mg/L. After alkaline thermalhydrolysis, the concentrations of the proteins and the polysaccharides were increasedwith the increase of NaOH. The concentration of the humic acids increased after thesludge heat treatment. Using the conditions of170°C, the treatment duration of30minand NaOH/VS of0.2, the content of the humic acids in the sludge supernatant fluid was6.3g/L.