Sedimentation and prefermentation of domestic wastewater in a fixed bed biofilm reactor.

This investigation was undertaken with the aim of developing a new wastewater prefermentator reactor in order to increase the percentages of sedimentation, hydrolysis and prefermentation of all the organic matter present in the raw wastewater, using only one unit of pre-treatment. The study was carried out using a pilot fixed bed biofilm reactor of 43.3 L in net volume. HRT of 0.5, 1, 2 and 4 h were applied. The reactor has been operating for 403 days during which it has been fed on raw wastewater from the city of Santander, in Spain. The results showed that it is possible to carry out the sedimentation and prefermentation of the organic matter contained in the raw wastewater in this reactor. The TSS average elimination percentage was higher than 50% during the whole testing period. The highest percentage of TSS retained in the reactor was 70% with a HRT of 4 hours and a flow rate of 0.3 m/h. The maximum COD(Total) elimination percentage was 30% for any of the four OL tried. The COD(Particulate) average solubility was greater than 40%. About 44% of the COD(Dissolved) in the effluent consisted of VFA. The highest concentration of VFA measured in the effluent was 44 mg COD/L, applying a HRT of 1 h. The average acidising was slightly higher than 30%. The acetic, propionic, butyric and valeric acids were the species of VFA detected, the acetic acid being the one present in a larger amount (> 50%). The production rate of VFA increases as the HRT decreases.