 Let us see in this module about some aerobic process that is used in the effluent treatment as we have seen in our previous module that is the trickling filters. So, as concerned the trickling filter the term filter in this operation is a misnomer. As the action of the trickling filter is not one of the filtration, but rather it is fixed film bioreactor settled effluent to be treated is passed down through a packed bed counter current to flow of air. The microorganisms adhering to the packing matrix adsorb oxygen from the up flow air and the organic matter from the down flowing effluent the later is then metabolized and the effluent streams BOD reduced. So, this is the principle on which the trickling factor act. So, the effluent trickles gradually through the bed and a slime layer of biological active material including bacteria, fungi, algae, protozoa and nematodes forms on the surface of the sport material. So, you can see in the next slide the trickling filter. So, you can see the effluent is here and then there is a retorting arm and then there is a packing material. So, you can see that. So, this is the effluent spray and the rotating drum and this is the packing matrix. So, because of the trickling filter do not have both the high specific area and the high widest there are less suitable for the treatment of large volume of the strong industrial effluent. So, this trickling filters is mostly used a small quantity or a small industries effluent treatment. So, as concerned then the other is that is the biologically aerated filters BAFs. So, as concerned the BAFs the biological aerated filters are the relatively recent development based on the trickling filters. They consist of a packed bed which provide the sides for the microbial growth through which air is passed out, but unlike the trickling filters the reactor volume is flooded with the effluent to be treated with the past upward or downward through the reactor. So, the combination of the aeration and the filtration allows a high rate of BOD and ammonia removal together with the solid capture. So that the sedimentation tank may not be required. So, this is the basically the improved version of the trickling filters. So, as concerned the third possible techniques that is activated sludge process. So, as concerned the activated sludge processes the basic activated sludge process you can see the whole diagram in the next slide consists of the aerating and the agitating the effluent in the presence of the fluctuated suspension of the microorganisms on a particular organic matter which we called as activated sludge. So, in this whole story is what is activated sludge. So, activated sludge is basically the fluctuated suspension of the microorganism on any particular organic matter. So, this process is mostly widely used for the blurgical treatment process for both domestic and industrial wastewater treatment. So, a number of modification of this basic process can be used to improve the treatment efficiency for the more specific purpose such as denitrification tapered aeration and stepped feed aeration are used to balance the oxygen demand with the amount of oxygen supplied. So, here you can see that the simplified cross section of activated sludge. So, you can see that it is aeration basin and effluent comes from this side and then it goes to the settlement basin and this you can collect here the treatment effluent and then there is a return of the sludge back to that and that is the waste sludge. So, this is basically the cross section of the activated sludge process. So, as concerned the contact stabilization exploits the biosorption process and thereby allows the considerable reduction in the basin capacity up to 50 percent for a given water through pump. The need identification can be accomplished in an activated sludge plant when the first part of the basin is not aerated. So, in advanced activated sludge treatment plant the amount of dissolved oxygen available for the biological activity is increased to improve the treatment rate. So, the activated sludge treatment is actually the biological treatment and the sludge activated is basically the micro-ioskinism that is very active in conditioning the effluent.