UNIT PROSES ACTIVATED SLUDGE PROCESS PROGRAM STUDI TEKNIK LINGKUNGAN FAKULTAS TEKNIK UNIVERSITAS LAMBUNG MANGKURAT Chairul Abdi, S.T., M.T.

FIGURE 1 PLUG-FLOW (PF) and DISPERSED PLUG FLOW REACTORS (DPF) 2 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

PLUG-FLOW and DISPERSED PLUG FLOW REACTORS Figure 1 shows as schematic profile through a plug-flow or dispersed plug-flow reactor basin, along with its final clarifier and recycle pumps. In the plug-flow reactor there negligible diffusion along the flow path through the reactor, whereas in the dispersed plug-flow reactor is significant diffusion along the flow path through the reactor. The conventional activated sludge process and the tapered aeration activated sludge process both use plug- flow and dispersed plug-flow reactor basins. 3 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

FIGURE 2 Conventional Activated Sludge Process 4 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

TABLE 1 Design and Operational Parameters for Activated Sludge Treatment of Municipal Wastewaters 5 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

ACTIVATED SLUDGE PROCESS The wastewaters preliminary treated to remove screened materials and grit, such as sand and silt; then the wastewater is primary treated to remove as much settleable suspended solids as possible. The primary sludge must be treated by some method such as anaerobic digestion to bio-oxidize the organic solids and thus stabilize the primary sludge solids. The clarified wastewater, Q, is mixed with the return activated sludge flow, R, to inoculate the wastewater with active biological solids, and the mixed liquor, Q+R, enters the biological reactor. 6 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

ACTIVATED SLUDGE PROCESS As the mixed liquor passes through the reactor, the activated sludge solids sorb the organic matter, both the insoluble and soluble portions, and bio-oxidize the materials to produce carbon dioxide, water, and other end products and to synthesize new cells. As the bio-oxidation proceeds in the reactor, endogenous degradation is occurring simultaneously. Aerobic conditions are maintained by compressed air or mechanical aeration devices, space uniformly along the length of the reactor, and the minimum operating DO level is 2,0 mg/l. 7 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

THE RECYCLE RATIO (R/Q) and SLUDGE DENSITY INDEX (SDI) The mixed liquor passes from the reactor to the final clarifier (solid-liquid separator), where the activated sludge solids settle by gravity. The effluent spills over the clarifier weirs and is ussualy disinfected by chlorine prior to discharge. The settled activated sludge is pumped by recycle pumps, and the major portion, R, of the recycled sludge is mixed with the feed wastewater to inoculate the flow, Q, to the reactor. The recycle ratio, R/Q, is from 25 to 100%, depending on the desired MLSS and the sludge density index (SDI) 8 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

ACTIVATED SLUDGE PROCESS A portion of the activated sludge, Qw, is wasted to remove the net mass synthesized in the system. In plants having a capacity less than several million gallons a day (million liters a day), the wasted activated sludge, Qw, is ussualy mixed with the feed to the primary clarifier. It is subsequently settled and removed with the primary sludge, PS. In this manner, the sludge is thickened and a large portion of its water is removed prior to sludge treatment. 9 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

ACTIVATED SLUDGE PROCESS In large plants, the waste activated sludge flow, Qw, is usually thickened by separate sludge thickeners. The primary sludge and waste activated sludge solids must be oxidize or stabilized, ussualy by anaerobic or aerobic digestion, prior to disposal. Ussualy the waste activated sludge flow is from 1 to 6% of Q by volumetric flow. 10 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

FIGURE 3 Tapered Aeration Activated Sludge Process 11 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

TAPERED AERATION ACTIVATED SLUDGE PROCESS The tapered aeration activated sludge process, Figure 3, is only modification of the conventional process. It is identical with the conventional process except that the aeration devices are spaced along the length of the reactor in accordance to the oxygen demand. 12 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

FIGURE 4 Relative Oxygen Demand for the Conventional or Tapered Aeration Activated Sludge Process (Municipal Watewater) 13 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

THE TAPERED AERATION At the upstream end of the reactor, Figure 4, the oxygen demand is high because the BOD5 is the maximum in the reactor. As the mixed liquor passes through the reactor, the BOD5 gradually declines; thus, the oxygen demand also gradually declines. Both the BOD5 and the oxygen demand become minimum at the downstream end. The oxygen required for each quarter for treating municipal wastewater with a reaction time less than 8 hr. 14 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

TABLE 2 Oxygen Demand versus Reactor Length for Municipal Watewaters 15 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

FLOW REGIME The flow regime in biological reactors used in the conventional or tapered aeration process is dispersed plug flow; however, it may approach plug flow in some cases. In plug flow reactor, there is negligible induced mixing between elements of the fluid along the axial direction of flow. Actually, in the conventional or tapered aeration reactor, thre is some longitudinal or axial mixing, but in long, narrow tanks, the flow regime may approach plug flow. 16 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

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PLUG-FLOW 18 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

DISPERSED PLUG-FLOW 19 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

FIGURE 5 20 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

DISPERSED PLUG-FLOW 21 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF

EXAMPLE 22 PROGRAM STUDI TEKNIK LINGKUNGAN UNIT PROSES/LUMPUR AKTIF