Activated sludge processes

Process Va.ria.tlons, There are many variations of the activated sludge process which have been developed in response to different wastewater... 

In the activated sludge process, performance is related to the food-to-microorganism ratio (F/M), which is the kg BOD appHed/d/kg volatile suspended soHds (VSS). 

Fig. 13. Types of activated sludge processes (a) plug flow (b) complete mix (c) selector-activated sludge.

Chemica.1 Remova.1. Phosphoms can be precipitated with lime to form Ca2(P0 2- The actual composition of the precipitate is a complex compound called apitate. Achieving minimum phosphoms concentrations requires a pH in excess of 10.5. Alum or iron will precipitate phosphoms as AIPO4 or FePO. This procedure is generally employed in conjunction with the activated sludge process, in which the coagulant is added at the end of the aeration basin or between the aeration basin and the final clarifier. 

Activated Sludge. There are several generic activated sludge processes presendy available. Complete Mix (CMAS) is appHcable to refractory-type wastewaters in which filamentous bulking is not a problem. This process has the advantage of dampening ductuations of induent wastewater quaUty. 

The BPT is defined as the level of treatment that has been proven to be successful for a specific industrial category and that is currendy in fuU-scale operation. Sufficient data exist for this level of treatment so that it can be designed and operated to achieve a level of treatment consistendy and with rehabUity. For example, in the pulp and paper industry, BPT has been defined as biological treatment using the aerated lagoon or the activated sludge process with appropriate pretreatment. 

Fig. 2. Typical flow sheet for a domestic wastewater treatment plant utilizing the activated-sludge process.

Fig. 3. Process components for the activated-sludge process, with aerobic digestion at plants <473.1 m /h and two-stage anaerobic digestion at plants...

Table 5. Design Parameters for the Activated-Sludge Process ...

Fig. 4. Contact stabilization plant. Conventional activated-sludge process. The reaeration and contact tanks can be replaced by an aeration tank (21).

Trickling Filters. The so-called trickling filter is not a filter but a bed of stones or other coarse material (packing) over which the sewage flows. In terms of the total number of installations, it is the most widely used biological treatment process. However, the greatest total volume of waste is treated by the activity-sludge process (12). 

G. M. Shaul, R. J. Lieberman, C. R. Dempsey, and K. A. Dostal, "Eate of Azo Dyes in the Activated Sludge Process," presented at the 41st Annual Purdue Industrial Waste Conference, Purdue University, West Lafayette, Ind., May 13—15, 1986. 

FIG. 25-54 Schematic diagrams of various modifications of the activated-sludge process, a) Conventional activated sludge. (h) Step aeration, (c) Contact stabilization, (d) Complete mixing, (e) Pure o gen. (f ) Activated hiofiltration (ABF), (g) Oxidation ditch. 

Figure 1. Simplified process flow sheet of activated sludge process.

Comminution Shredding. A mechanical treatment process which cuts large pieces of waste into smaller pieces so that they won t plug pipes or damage equipment. Contact stabilization Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are used. One tank is for separate reaeration of the return sludge for at least four hours before it is permitted to flow into the other aeration tank to be mixed with the primary effluent requiring treatment. 

F/M A ratio of the amount of food to the amount of organisms. Used to control an activated sludge process. 

MCRT Mean Cell Retention Time - days. An expression of the average time that a microorganism will spend in an activated sludge process. 

Sludge age A measure of the length of time a particle of suspended solids has been retained in the activated sludge process. 

Aerobic Treatment. The activated sludge process depends on aerobic biological action. In this case the microorganisms, in searching for food, break down the complex organic substances into simple stable substances. This process results in the removal of soluble and suspended organic matter from wastewater. 

The activated sludge process usually must be preceded by neutralization and some metal removal, and possibly by solids removal. The process is normally followed up by a separation step, usually sedimentation, to remove the biological sludge from the waste liquid stream. 

The activated sludge process for domestic wastewater treatment was introduced to the world in 1914.1 Since then, many studies have been conducted to improve the oxygen transfer efficiency. Among the aeration devices introduced have been a porous diffuser, a filter type diffuser, a mechanical aeration device, an orifice type diffuser and a fine-pore air diffuser. The aeration market is in a substantial state of flux in the USA today. Emphasis on high efficiency has led many intensive research programmes to aim at the evaluation of the design, operation and control processes to improve overall system performance. 

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