Initial Study On Bio-augmentation Technology Of Recycled Sludge

Aiming at the problems of current activated sludge process, taking the activatedsludge--the main body of activated sludge process as the research object, thispaper makes a initial exploration of bio-augmentation techonology of recycled sludge. Both static and dynamic experiments on activated sludge are taken mainlyusing a special kind of soil material--humus soil. Function of humus soil onactivated sludge is inspected through static test of the sludge, and through a long period of dynamic test of continuous operation of the activated sludge process systems, the influence on water quality of the humus soil reactor are inspected. Following are the main conclusions:(1) Based on the analysis of humus soil, SS and VSS of humus soil changes little after it dissolves in the water.The average percentage of VSS is 29%, which is slightly smaller than organic matter content of humus soil itself of 32%, while the average percentage of SS is 86%, which is slightly less than the SS percentage of humus soil itself of 90%. It indicates that when humus soil contacts with water, only small part of organic matter and suspended solids dissove in the solution. So in the following research on humus soil,it can be considered that the input of humus soil will not cause changes of organic matter content in water. Humus soil contains a high proportion of Ca, Mg, Al, Fe element contents, 2.171,1.330,45.729,29.047 g / kg respectively. The contents of these elements in the sludge in the dynamic system 2# are also much higher than those in non-humus soil reactor in system 1#. These elements are important ingredients of coagulant which in a certain extent, explained the effect of humus soil on sludge sedimentation and dehydration.(2) It is indicated from static tests that, the zone settling velocity(ZSV) and sludge volume index (SVI) of sludge decrease with the increase of sludge concentration, which means that with the same dosage of humus soil, the settlement ability become better with the increase of sludge concentration. And under the condition of different dosage of humus soil, the zone settling velocity (ZSV) and sludge volume index (SVI) of sludge decrease with the increase of the dosage of humus soil, which means that settlement ability of sludge improves with the increase of the dosage of humus soil.(3) It is indicated from static tests that, the sludge specific resistances decline when adding humus soil, and sludge specific resistances decline with the increasment of dosage of humus soil. But all the values are in the order of magnitude of l0¹²m/kg.(4) It is indicated from the treatment effect of the dynamic test that:The effect of COD removal of the two systems are almost the same. The average COD removal of working condition 1 is about 83%, while that of working condition 2 is about 50%. The reason of the low COD removal may have something to do with the low inflow COD concentration and low temperature. In the removal of N, the NH3-N removal of system 2# is generally better than that of system 1#. In working condition 1, the difference of NH₃-N removal is more obvious with 71.07% of system 2# which is 11.12% higher than that of system 1# of 59.95%. In working condition 2, there is little difference with the average NH3-N removal of about 50%. The situation of TN removal is similar with that of NH₃-N removal. The TN removal of system 2# is generally better than that of system 1#. In working condition 1, the difference of TN removal is more obvious with 52.67% of system 2# which is 7.94% higher than that of system 1# of 44.73%. In working condition 2, neither of TN removal of the two systems are high, with 9.31% of system 2# which is 5.65% higher than that of system 1# of 3.66%. In the removal of P, system 2# shows an obvious P removal effect. In working condition 1, average TP removal of system 2# is 58.26%, which is 27.26% higher than system 1# of 31.00%. In working condition 2, average TP removal of system 2# is 78.76%, which is 70.66% higher than system 1# of 8.10%. In working condition 2, the TP removal effect of system 2# is much more obvious, which has something to do with the increase of retention time in the humus soil reactor.(5) It can be seen from the operation of humus soil reactor that, the recycled sludge ratio should not be too small, and that it is better to use mechanical agitation instead of aeration. DO is the main controlling factor in the reactor, the value of which shoul within the range of 0.3～0.8mg/L. (6) After dynamic systems be running seven months, the TP concentration of the inflow sludge of humus soil is 32.29 g/kg, while that of the outflow sludge is 32.76 g/kg, which shows little difference. The TP concentration of system 1# is much smaller, 22.40 g/kg, which is close to that of traditional activated sludge process in literature reference (20 g/kg). It indicates that system 2# with humus soil reactor has stronger TP absorption ability, which in some extent explains why system 2# has a higher TP removal rate.