Conventional 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).

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. 

A partial listing of design criteria for the conventional activated sludge process is summarized as follows ... 

Process-Specific Kinetics of the Conventional Activated Sludge Process Systems with Sludge Recycle... 

In the conventional activated sludge process with biological sludge recycled from the final sedimentation clarifier, shown in Figure 27.11, the mean cell residence time or sludge retention time is... 

There are a number of full-scale activated sludge plants that are in operation in countries such as the United States, Canada, and Finland, which treat effluents from Kraft, sulfite, TMP, CTMP, and newsprint mills [22]. SchneU et al. [70] reported the effectiveness of a conventional activated sludge process operating at an alkaline-peroxide mechanical pulping (APMP) plant at Malette Quebec, Canada. The full-scale plant achieved 74% reduction in filterable COD and nearly complete elimination of BOD5, resin acids, and fatty acids in the whole mill effluent. The treated effluent tested nontoxic as measured by a Microtox assay. Saunamaki [71] reported... 

In looking for greater organic material removal and a lower sludge production, specialists have developed several modifications to the conventional activated sludge process. Some of them are indicated in Table 11.2. 

This system is used for the treatment of high strength wastes and is operated at much higher BOD loadings than those in the conventional activated sludge process. There is a shorter hydraulic retention time and shorter aeration periods. 

Chin and Wong (74) attempted to treat palm oil refinery effluent by conventional activated sludge process with limited success. The treated effluent was highly colored with over 800 Hazen units. 

The first suspended growth process, now called the conventional activated sludge process, was developed to achieve carbonaceous BOD removal. However, since its inception, many modifications to the basic process have taken place. The variations in the activated sludge process are too numerous to be discussed in detail here. However, some of these are step aeration, contact stabilization, aerated lagoon, deep-tank aeration, and pure oxygen aeration. 

The factor 1.42 represents the oxygen equivalent of cell mass produced. For only BOD removal, the oxygen requirements can vary from 0.8 to 1.3 kg 02/kg BOD removed for most conventional activated sludge processes. 

Conventional activated sludge process loading rate in terms of F/M ratio (mass loading g BOD/g MLVSS day) varies from 0.2 to 0.6. In some instances, the loading rate is based on the tank volume. The volumetric loading rate in terms of BOD applied per unit tank volume varies from 0.3 to 0.6 kg BOD/m day. The hydraulic residence time (V/Q) varies from 4 to 8 hr. 

Over the years, the conventional activated sludge process has been modified to improve or to suit a specific operational condition. Some of the more common modifications are extended aeration process, contact... 

Fig. 4.27. Schematic diagram of conventional activated sludge process. 1 — wastewater, 2 — air supply, 3 — sludge return, 4 — clarified effluent, 5 — waste sludge, A — aeration basin, B primary sedimentation tank, C — secondary sedimentation (thickening) tank... 

Among several techniques used, the advantages offered by membrane bioreactor (MBR) technology have been recognized for some time. An MBR comprises a conventional activated sludge process coupled with membrane separation to retain the biomass. Since the effective pore size is generally below 0.1 pm, the MBR effectively produces a clarified and substantially disinfected effluent. In addition, it concentrates up the biomass and, in doing so, reduces the necessary tank size and also increases the efficiency of the biotreatment process [1]. 

Conventional activated sludge process including basin, aeration system, recycle pumping and secondary clarifier. PM cost 8 150000 for design flow rate = 120 L/s with n = 0.71 for the range 0.5-4400 L/s. 

Munz et al. (2009) evaluated the role of tannins in both conventional activated sludge processes (ASP) and MBR. They found similar values in the removal of natural and synthetic tannins by comparing the two treatments. Further, in both processes the nitrification process presented extremely reduced kinetics. Finally, the inhibition of the nitrifying biomass was attributed to the whole wastewater rather than the non-biodegradable fraction. 

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