A STUDY OF THE POTENTIAL CONTRIBUTION OF SEDIMENTATION TO AEROBIC TREATMENT PROCESSES FOR PIG SLURRY

The technique of aeration can only partly treat pig slurry because of its limited effect on much of the undissolved matter present. Further reduction in the environmental impact of the effluent, thus requires s ome form of physical clarification. Centrifugation tests showed the ex tent to which physical separation could concentrate a range of insolub le slurry components into a sludge, leaving a clarified supernatant ef fluent. These insoluble components included suspended solids (TSS), Ch emical Oxygen Demand (GOD), copper, zinc, and manganese; the effect of separation on the Total Solids concentration (TS) was less owing to i ts partial solubility. Batchwise gravitational sedimentation revealed that aerobic treatment enhanced the settling characteristics of slurri es. However, the total solids (TS) concentration of the whole slurry w as a more significant factor: sedimentation was most effective in dilu te slurries (<25 kg/m(2) TS) but the effect of aerobic treatment was t hen less pronounced. Very concentrated slurries (>40 kg m(3) TS) did n ot separate effectively. An overall mass balance indicated that sedime ntation could only be used for slurries up to 25 kg/m(3) TS if excessi ve sludge fractions (>50%) were to be avoided. Continuous sedimentatio n was satisfactorily demonstrated at pilot scale and performance compa red well with batch sedimentation. A novel sedimentation factor was de fined to aid the evaluation performance. This combined the traditional separation efficiency with a correction factor to allow for the volum es of sludge produced.