Enzymatic pre-hydrolysis of high fat content dairy wastewater as a pretreatment for anaerobic digestion

Enzymatic extract preparation from Psendomonas aeruginosa KM110 under accession No. HQ730879 with lipase activity [0.3 U/ml], was used to perform enzymatic hydrolysis pretreatment of a synthetic dairy wastewater with 1000 mg/L total fat content. The pretreatment was optimized for 48 h hydrolysis time, at 45[ae%] C with 10% v/v enzymatic extract. The biological treatment of synthetic dairy wastewater was investigated using a batch bioreactor. Both raw and prehydrolyzed wastewater was digested in a batch bioreactor. Enhanced anaerobic digestion efficiency compare to raw wastewater was achieved [chemical oxygen demand [COD], removal efficiency of 90% vs. 66% and biogas production of 4710 ml vs. 2330 ml after 13days]. The results obtained in this study illustrated that the application of a pretreatment process to hydrolyze and dissolve fats may improve the biological degradation of fatty wastewaters, accelerating the process and reducing time of anaerobic digestion. Moreover, the pretreatment of wastewater from several sources is a new and promising application for Upases

Study of syntrophic anaerobic digestion of volatile fatty acids using enriched cultures at mesophilic conditions

Volatile fatty acids are the most important intermediates in anaerobic digestion, and their degradations are extremely complicated thermodynamically. In this research, syntrophic anaerobic digestion of volatile fatty acids using enriched acetogenic and methanogenic cultures in a batch reactor at mesophilic conditions was investigated. Interactive effects of key microbiological and operating variables [propionic, butyric and acetic acids, retention time and methanogen to acetogen populations ratio] on the anaerobic degradation of volatile fatty acids were analyzed. Acetogenic and methanogenic anaerobes in the granular sludge from an up-flow anaerobic sludge blanket reactor were enriched at mesophilic conditions within a period of four weeks, separately. Enriched cultures were mixed with known proportions and then used in the bioreactor. Experiments were carried out based on central composite design and analyzed using response surface methodology. Four parameters [final concentrations of propionic, butyric and acetic acids and biogas production] were directly measured as response. Also, the optimum conditions for volatile fatty acid degradation were found to be 937.5 mg/L, 3275.5 mg/L, 2319.5 mg/L, 45 h and 2.2 proportions for propionic acid, butyric acid, acetic acid, retention time and methanogen to acetogen populations ratio, respectively [corresponding to maximum volatile fatty acid removal efficiencies and biogas production]. The results of the verification experiment and the predicted values from the fitted correlations at the optimum conditions were in close agreement at a 95% confidence interval. The present study provides valuable information about the interrelations of quality and process parameters at different values of microbiological and operating variables

precise experimental study on key dissimilarities between mesophilic and thermophilic anaerobic digestion of waste activated sludge

Key dissimilarities between thermophilic and mesophilic anaerobic digestion of waste activated sludge [WAS] were experimentally studied in this research. Typical WAS with total solids [TS] concentrations of 30 and 60 g/L were digested anaerobically in a batch digester at mesophilic and thermophilic temperatures. Solids reduction, total COD changes, the production of different volatile fatty acids [VFAs], pH variation, the quality and quantity of the produced biogas, an energy audit, pathogen inactivation and sludge dewaterability during anaerobic digestion were investigated and compared for mesophilic and thermophilic processes in this research. Only the thickest sludge [TS concentration 60 /L] provided auto-thermality under mesophilic conditions. The mesophilic digestion took place after 32 to 36 days with slightly more methane production and removal of organics than thermophilic digestion. The results showed that there was no significant difference between thermophilic and mesophilic digestion with respect to the gas composition. Among the VFAs [key intermediates], only propionate accumulated during sludge anaerobic digestion at both the mesophilic and thermophilic temperatures. Thermophilic anaerobic digestion imparts improved dewaterability. The required time for sludge pathogen inactivation under mesophilic conditions was more than one month