ATTACHED-FILM MEDIA PERFORMANCE IN PSYCHROPHILIC ANAEROBIC TREATMENT OF DAIRY-CATTLE WASTE-WATER

Retention of microorganisms in anaerobic digesters by providing an att achment medium can potentially increase their productivity at lower op erating temperatures. The objective of this work was to investigate th e effectiveness of attached-film bioreactors for psychrophilic anaerob ic digestion of daily manure. Eight digesters were maintained in an en vironmental chamber, with the temperature varied between 37 and 10 deg rees C. Two digesters were packed with limestone gravel, two with piec es cut from non-woven polyester matting two with a combination of lime stone gravel and polyester pieces, and two had no packing. Digester op eration was initiated at a temperature of 37 degrees C. After the dige sters reached stable operation at the initial temperature, the tempera ture was lowered slowly to 10 degrees C. The temperature was held at 1 0 degrees C for 5 weeks after stabilizing. The polyester medium with i ts high porosity and surface to volume ratio had the best overall perf ormance for methane productivity at both 37 and 10 degrees C. The biog as production (ml/d) and methane production (ml/d) were significantly higher for the polyester medium when compared to the limestone and com bination media reactors (p<0.0001 and 0.0002, respectively). At 10 deg rees C, the polyester medium reactors performed significantly better t han all others for biogas (ml/d) and methane (ml/d) production (p<0.00 01). The polyester medium also yielded the maximum reductions in volat ile solids (VS) and chemical oxygen demand (COD) at 37 degrees C. (C) 1997 Published by Elsevier Science Ltd.