Performance evaluation of biosimulator for treating domestic wastewater using activated sludge treatment system

This research investigation was aimed at demonstrating the performance evaluation of pilot activated sludge treatment system (biosimulator; model MF-114). An intensive analytical program was followed for evaluating the performance efficiency of the biosimulator by maintaining the dissolved oxygen (DO) concentration at 4.0 mg/L throughout the study period. Biosimulator performance was evaluated after every 2 hours and analyzed for pH, DO, COD, ammonia-nitrogen (NH3-N), nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N). In all ten experimental replicates were performed and the mean figures are taken for discussion. Although no significant variation in the pH was observed during the study period but the mean pH values of the samples during the treatment process gradually increased and it ranged from 6.81-7.52. The removal of COD was found to be in direct relationship with retention time and the mean COD of the raw wastewater samples ranged from 164-1160 mg/L whereas it got reduced considerably during the treatment process and the mean removal efficiency was found to be 86%. The COD and NO2-N removal efficiency was better than NH3-N and NO3-N this is considered to be satisfactory especially with respect to organic loading and retention time. Similarly, the mean NH3-N values of wastewater after 29 hours of treatment were found to be fluctuating between 14.52-20.54 mg/L whereas the mean NO3-N level of the raw wastewater ranged from 0.106-0.279 mg/L. The overall conditions were very much favorable even at high organic loading and minimum retention time. It is therefore concluded that the system is practically feasible for the treatment of wastewater containing high content of organic matter. @JASEM Environmental pollution develops and deepens whenever the volume of wastewater flow exceeds combined capacity of natural and manmade facilities organized to control, capture, convoy and decompose the generated waste. The industrial or domestic wastewater discharged untreated into aquatic environment results in serious water pollution, causing deterioration of marine environment (WRIR, 1990; Nicholas, 1989). The ecology of the activated sludge system is very complex and dynamic. It represents a very complicated and variable biological activity depending upon temperature, pH, DO level, etc. Heterotrophs and autotrophs influence nitrogen and carbon removal during the wastewater treatment. The activated sludge process has been utilized since long time for the treatment of domestic and industrial wastewater; it is quite efficient in decreasing the concentration of many priority pollutants to concentrations below detection and permissible limits (Ramalho, 1997; Robert, 1998). The principle of the system is based upon the aeration of the wastewater, which reduces the organic matter and finally produces a flocculent sludge. The sludge contains some inert solids, but the main components making up its loose, flocculent structure are living or active bacteria and protozoa, hence the name activated sludge (Mara, 1978). Muller et al., (1980) observed the removal of volatile non-biodegradable organic compounds from wastewater during the activated sludge treatment. One of the reliable and accurate estimates of these biodegradable organic compounds is the chemical oxygen demand. The COD method is a rigorous, high temperature, acidic, chemical digestion process in which oxygen demanding materials are consumed by a powerful oxidizing agent (Standard Methods, 1985). The treatment of domestic wastewater during the treatment produced the water of good quality and there is an interest in its potential for drinking water supply (McCartey et al., 1984). The domestic wastewater contains readily biodegradable organic matter which is mainly composed of volatile fatty acids and low molecular weight carbohydrates that can pass through the cell membrane and be metabolized within minutes by the bacteria (Henze et al., 1987). It has been reported that microorganisms that bring about the decomposition of organic matter in wastewater can perform their activity efficiently in the activated sludge system (Barker and Dold, 1995). Eliosov and Argaman (1995) observed the hydrolysis of particulate organic matter in activated sludge system and reported that the degradation rate of the particulate matter in raw domestic wastewater was slower than that of nonsettleable particulate matter, which was due to the physical characteristics of two types of particles. Filamentous microorganisms affect the sludge settling. It is reported that a high filament length concentration, zone settling velocity reaches a maximum value and the decrease with increasing suspended solid concentration (Sezgin, 1980). The sludge age together with mixed liquor suspended solids in the aeration tank generates the dynamic stability of the overall process. An under loaded and over loaded system can lead the whole process dynamically unstable (Cakici and Bayramoglu, 1995). Figure 1 shows the arrangements of the Performance evaluation of biosimulator...