CHARACTERIZATION OF ENHANCED ANAEROBIC DEGRADATION OF DIGESTED SLUDGE MIXTURES AFTER THERMO - CHEMICAL AND ENZYMATIC TREATMENT

摘要

Anaerobic stabilization of sludge is the most common treatment technique with plenty of benefits such as reduction of the volatile suspended solids, biogas production, sanitation of the treated effluent and improvement of the dewaterability. Nevertheless, only ca. 55% of the primary and 35% of the secondary sludge is converted anaerobically. Different mechanical, thermo-chemical, etc. methods have been proposed for further improvement of the degradation. The presented investigation focuses on the influence of different methods (thermal, thermal-acidic, thermal-alkaline and enzymatic) on the extended anaerobic degradability of sludge mixtures, which have been already treated anaerobically using a two stage process, in order to define the optimal operation mode in the pilot plant. Batch experiments were carried out in spherical, pressure resistant, glass autoclaves. The autoclaves with the reaction mixture and the appropriate inoculum are incubated at 38°C and darkness for ca. 15 days. The progress of the degradation process is followed by periodical pressure measurement. Produced biogas volume was calculated using the measured pressure increase. To determine the most appropriate operating conditions, the most significant parameters were monitored to assess the influence of: 1) the kind of chemical treatment, 2) temperature and 3) pH. All results were compared to the equivalent results from a blanc-untreated sludge sample. Enhancement of biodegradability was evaluated by measuring and comparing the produced biogas volume, NH_4~+ concentration (protein destruction), COD solubilisation and degradation, acetic and propionic acid production. Comparison of the pre-treatment investigations results confirm that a substantial reduction of the anaerobic degraded sludge mixtures was achieved, when a thermal-alkaline pre-treatment was applied. All pre-treatments allowed a biogas production equal to or higher than the one for untreated sludge experiments. COD in the supernatant increased for thermal, thermal-acidic and thermal-alkaline pre-treatment respectively. Gas-chromatographic analysis of acetic and propionic acid clearly showed that further biodegradation of anaerobic treated sludge is achieved. Increase of ammonium production after the hydrolysis treatments implied protein molecules degradation.