Ultrasonic Intensification of Methane Fermentation Process

The investigation studies presented in the paper involve the search for favourable conditions for the disintegration process which prepares the excess sludge for fermentation. The disintegration of sludge involves the application of ultrasounds of narrow frequency (15-50 kHz) and high intensity. The cavitation excited by the acoustic wave passing through the sludge brings about number mechanical and sonochemical effects. The obtained effects dependent on parameters of the reactor, on the ultrasonic field as well as on physicochemical parameters of the sludge which are directly related with the dose of ultrasonic radiation emitted to the disintegration area. A disintegration effect could be defined by the indexes of disintegration ratio or by the concentration of desires products obtained during sonochemical degradation of organic compounds in the sludge as e.g. volatile fatty acid (VFA) or biogas. In the present investigation was measured the concentration changes of COD before and after disintegration as well as the changes of concentration VFA obtained (after some days of digestion) in sonificated and non-sonificated sludge. The influence of sludge layer hight over the emitter on VFA recovery and biogas production effect was controlled. The efficiency of ultrasonic disintegration we obtained where layer over emitter is not higher then 10 cm and concentration of dray mass in sludge is lower than 4,5%. For this parameters we obtained 1,6- times increment of VFA (in two days shorter time of fermentation) and about 30% higher biogas production. Key words: cavitation, ultrasonic disintegration of sewage sludge, dispersion and dissipation of floculles, destruction of cells.