Drastic reduction of sludge in wastewater treatment plants: co-digestion of sewage sludge and aqueous waste in a thermophilic membrane reactor.

Sewage sludge and aqueous wastes are usually treated in separate facilities. Both may pose specific issues, mainly related to the uncertainty of the recovery/disposal route and costs, for the sludge, and to the extremely variable quantitative and qualitative properties, for the aqueous waste. In the present work, the co-digestion of thickened sludge and aqueous wastes in a Thermophilic Aerobic Membrane Reactor (TAMR) was studied in order to allow the almost complete reduction of sludge directly in wastewater treatment plants (WWTPs). Different conditions (aerobic and alternate aeration) were tested in a pilot plant, at the semi-industrial scale. The TAMR plant was operated at 48°C with constant organic load rate (5 kgCOD m-3 d-1) and hydraulic retention time (5 days). The main results obtained are the following: (I) high overall COD (78-97%) and total phosphorus (>60%) removal rate under both the studied aeration conditions; (II) increase of ammonia concentration due to the effective ammonification of organic nitrogen; (III) low specific sludge production (0.04[Formula: see text]) in the thermophilic reactor.

Experimental treatment of a refinery waste air stream, for BTEX removal, by water scrubbing and biotrickling on a bed of Mitilus edulis shells.

The paper presents the results of a two-stage pilot plant for the removal of benzene, toluene, ethylbenzene and xylene (BTEX) from a waste air stream of a refinery wastewater treatment plant (WWTP). The pilot plant consisted of a water scrubber followed by a biotrickling filter (BTF). The exhausted air was drawn from the main works of the WWTP in order to prevent the free migration to the atmosphere of these volatile hazardous contaminants. Concentrations were detected at average values of 12.4 mg Nm(-3) for benzene, 11.1 mg Nm(-3) for toluene, 2.7 mg Nm(-3) for ethylbenzene and 9.5 mg Nm(-3) for xylene, with considerable fluctuation mainly for benzene and toluene (peak concentrations of 56.8 and 55.0 mg Nm(-3), respectively). The two treatment stages proved to play an effective complementary task: the water scrubber demonstrated the ability to remove the concentration peaks, whereas the BTF was effective as a polishing stage. The overall average removal efficiency achieved was 94.8% while the scrubber and BTF elimination capacity were 37.8 and 15.6 g BTEX d(-1) m(-3), respectively. This result has led to outlet average concentrations of 1.02, 0.25, 0.32 and 0.26 mg Nm(-3) for benzene, toluene, ethylbenzene and xylene, respectively. The paper also compares these final concentrations with toxic and odour threshold concentrations.