ABSTRACT
RESUMO Esta pesquisa comparou o desempenho de um digestor anaeróbio de lodo sob diferentes estratégias operacionais. Foi avaliada a influência do aumento da carga orgânica volumétrica (COV) (OP I) e o efeito da redução do tempo de detenção hidráulica (TDH) (OP II e OP III) no processo anaeróbio. As cargas aplicadas variaram entre 0,5 e 4,5 kgSV.m-3.d-1 e o TDH foi reduzido de 15 a 5 dias. Produção de gás metano, degradação do material orgânico e a diversidade microbiana foram utilizadas para medição e comparação do desempenho do processo. Foram necessários períodos de aclimatação a cada nova COV aplicada o que levou às instabilidades na remoção de SV e DQO do lodo. A operação com TDH entre 7 e 5 dias apresentou as maiores eficiências de remoção de SV, superiores a 70%, o que influenciou positivamente na estabilidade do processo. As COV aplicadas de 2,5 e 3,5 kgSV.m-3.d-1 resultaram nas maiores produções de metano durante a OP I. Para TDH inferiores a sete dias a produção de CH4 foi prejudicada apesar da existência de microorganismos metanogênicos atuantes no digestor. Comparativamente, a estratégia de redução do TDH resultou em um melhor desempenho do sistema que a fixação da COV. Quanto menor o TDH aplicado, melhor os resultados obtidos na operação do digestor, sugerindo que a eficiência do processo é otimizada em sistemas de alta carga com operação em baixos tempos de detenção hidráulica.
ABSTRACT This study compared the performance of a pilot anaerobic sludge digester under different operating strategies. The influence of increasing organic loading rate - OLR (OP I) and the effect of hydraulic retention time - HRT reduction (OP II and OP III) in anaerobic process were evaluated. The applied loads ranged between 0.5 and 4.5 kgSV.m-3.d-1; HRT was reduced from 15 to 5 days. Production of methane, organic matter degradation and microbial diversity were used to measure and compare the system´s performance. Acclimation periods were taken for each new OLR applied, leading to instabilities in sludge VS and COD removals. The experimental time with HRT between 7 and 5 days showed the highest VS efficiency removals (higher than 70%), which positively influenced process stability. The applied OLR of 2.5 and 3.5 kgVS.m-3.d-1 resulted in higher yields of methane during OP I. CH4 production showed impaired with HRT lower than 7 days, although it was observed active methanogenic microorganisms in the digester. Comparatively, HRT reduction resulted in a better system performance than the increasing OLR approach. The lower HRT applied, the better the results obtained in the operation of the digester, suggesting that the process efficiency is optimized with high load operation at low hydraulic retention times.
ABSTRACT
Short-chain fatty acids (SCFAs) are the most important intermediate in the waste activated sludge (WAS) fermentation process. This work explored a novel approach to improve the SCFAs production from WAS. Experimental results showed that the disintegration and acidification of WAS were enhanced markedly by using bi-frequency (28+40 kHz) ultrasonic pretreatment compared with mono-frequency (28 kHz and 40 kHz) ultrasonic pretreatments. After 28+40 kHz ultrasonic pretreatment, the SCOD concentration increased from original 363 mg COD l-1 to 10810 mg COD l-1 which was 1.53-fold and 1.44-fold of the values obtained with 28kHz and 40kHz ultrasonic pretreatments, respectively. The maximum SCFAs production reached 7587 mg COD l-1 in the 28+40 kHz test which was respectively 1.25-fold and 1.31-fold of that in the 28kHz (6053 mg COD l-1) and 40 kHz (5809 mg COD l-1) tests. This was the highest SCFAs production obtained so far using WAS, pretreated by ultrasonic technology, as the renewable carbon source. SCFAs composition analysis revealed there was more acetic acid (3992 mg COD l-1, accounted for 52.6% of the total SCFAs) for the 28+40 kHz ultrasonic pretreatment which was beneficial to many subsequent bioprocesses.