Activated sludge processes, wastewater

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

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. 

Fig. 2. Typical flow sheet for a domestic wastewater treatment plant utilizing 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 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. 

The activated sludge process for wastewater treatment uses recycle of live cells. The goal is to oxidize organics without generating too much sludge (i.e., biomass). 

This process is similar to the activated sludge process however, it requires a large surface area to cause more temperature effects than that experience in the activated sludge process. The aeration process in this system supplies oxygen to the influent wastewater and the turbulent generated keeps the contents of the basin in suspension. The suspended solids are then removed in a settling tank where the wastewater may further be treated before discharge.23... 

The activated sludge process for meat processing wastewater treatment was reported by Annachhatre and Bhamidimarri.37 When a model reactor was operated at an HRT of 5-15 h, a COD removal of more than 85% was achieved. The COD loading for the above performance was 3.2kg COD/(m3d). An SRT of 13 d resulted in almost complete nitrification. El-Gohary et al.30 reported that the activated sludge process reduced the BOD and COD of a potato-chips factory wastewater by 86% and 84%, respectively. The organic loading rate and HRT were reported as 8.9 kg BOD/ (m3d) and 6h, respectively. 

For waste treatment rather than fermentation for product formation, again few examples of process economics exist in the literature. Those that do, favor fluidization. Badot et al. (1994) described an industrial prototype fluidized bed reactor that competed favorably on an economical basis with activated sludge processes for treating carbon pollution and was estimated to be economically comparable to fixed bed processes for denitrification. Schneeberg (1994) described the successful and economically-sound implementation of fluidization as an upgrade to an existing wastewater treatment plant. The restricted space available for extension of the wastewater plant made fluidization particularly advantageous in this case. 

Panswad T, Iamsamer K, Anotai J (2001) Comparison of dye wastewater treatment by normal and anoxic+anaerobic-aerobic SBR activated sludge process. Water Sci Technol 43 355-362... 

From the very beginning, it is important to notice that activated sludge and wastewater, as they occur in sewer networks, are different matrices for microbial activity. The concepts developed when dealing with sewer processes may be different from what is known for activated sludge in a wastewater treatment system. 

Microbial processes in terms of sludge (biomass) production, BOD and nutrient removal have been focused on when dealing with biological wastewater treatment. Therefore, and because the sewer is the system for input to the wastewater treatment plant, there is a basis as well as a perspective to establish a process concept for the sewer that can be integrated with the activated sludge processes. 

Sollfrank, U. and W. Gujer (1991), Characterisation of domestic wastewater for mathematical modelling of the activated sludge process, Water Science and Technology, 23(4-6), 1057—1066. 

A methodology for OUR measurements in wastewater systems was originally developed for the characterization of activated sludge in terms of COD components and process parameters (Ekama and Marais, 1978 Dold et al 1980). It included OUR measurements of the activated sludge under substrate-limited and substrate-nonlimited growth conditions, typically performed by discontinuous addition of wastewater. Development of respirometry principles and techniques has taken place, e.g., motivated for the control of the activated sludge processes (Spanjers et al., 1998). 

Brenes, M., Garcia, P., Romero, C., and Garrido, A. 2000. Treatment of green table olive wastewaters by an activated-sludge process. J. Chem. Technol. Biotechnol. 75, 459-463. 

Secondary treatments are accomplished either by an activated sludge process or a trickling filter, in which organic components of the wastewater are subjected to aerobic degradation by microbial biocoe-nosis [52]. Surfactants can be metabolised by adapted micro-organisms... 

Lee. S.E., Shin, H.S., and Paik, B.C. Treatment of Cr(VI)-containing wastewater by addition of powdered activated carbon to the activated sludge process, imvzro/ . 5d. Technol, 23(ll) 67-72, 1989b. 

Depending on the wastewater treatment, removal rates can differ [46 9]. Moreover, for compounds of the same pharmacotherapeutic group, such as p-blockers, highly variable removal rates were obtained when the same treatment procedure was used. Activated sludge process lead to a significative removal efficiency for betaxolol, bisprolol, carazolol and metoprolol (65-90%) [49, 50],... 

The activated sludge process has been found to be the most efficient treatment for various categories of pharmaceutical wastewater [14,15,19,42-46]. It has also been reported that this process can be successfully employed for the removal of tert-butanol, a common solvent in pharmaceutical wastewater that cannot be degraded by anaerobic treatment [44]. At a volumetric loading rate of 1.05 kg COD/m day, HRT (hydraulic retention time) of 17 hours, and mixed liquor dissolved oxygen concentration of 1 mg/dm, the tert-butanol can be completely removed by the activated sludge process. 

The activated sludge process has been successfully employed for the treatment of a wide variety of pharmaceutical wastewaters. The American Cynamid Company operated an activated sludge treatment plant to treat wastewater generated from the manufacture of a large variety of... 

The performance of the activated sludge process for the treatment of wastewater from a synthetic drug factory, has been reported [14,15,45]. One of the biggest plants of its kind in Asia, M/S Indian Drugs and Pharmaceutical Ltd., Hyderabad, went into production in 1966 to make sulfa drugs such as sulfanilamides antipyretics (phenacetin), B-group vitamins, antimbercular drugs (isonicotinic acid hydrazide) and antihelminthics, and so on. 

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