 As we have seen in our previous module of affluent treatment about some aerobic process, but in this module we will talk about some available anaerobic processes. As concerned the anaerobic treatments of the waste organic material that is originated with the use of the septic tank, which have now been replaced by the variety of high rate digesters. Law 1968 has listed the following reasons for using the anaerobic process for the waste treatment. Number one, the high yielding loading rate can be achieved through, achieved then and possible for aerobic treatment techniques. Lower power requirement that may be needed per unit BOD treated. Stable and products such as digested sludge are combustible gases that may be produced, that may be methane, that may be hydrogen. Organic matter is metabolized to the stable form. Fifth one, there is an alteration of water binding characteristics to permit the rapid sludge dewatering. The reduced amount of microbial biomass leads to easier handling of the sludge. As concerned the seven that is the low level of microbial growth will decrease the possible need for supplementary treatment. So as concerned the large volumes of the wet sludge which are produced in primary and scented sedimentation tanks may have to be reduced in volume before disposal. The volume of the sludge can be reduced by anaerobic digestion. So in sludge containing 20,000 to 60,000 milligram per later solid matter and 80% of the degradable matter may be digested which will reduce the solid content by 50%. So during this anaerobic digestion the acid fermenting bacteria degrade the waste to free volatile fatty acids mainly acetic acid and propionic acids which are then converted to methane and carbon dioxide which mostly called as the biogas. So this gas produced which we called as biogas is very useful by product and can be burnt as a heating fuel fed to gas engines to generate electricity or the use of vehicle fuel. So as well as being used in the sludge digestion and conditioning anaerobic digesters are also used directly in the treatment of many high strength wastewater for example from the food and agricultural industries. So as concerned the activator sludge you can see that aeration and mixing mechanical devices that also having aid of this whole treatment. You can say that the anaerobic treatment of the plant as we say that there is a biogas is produced during this whole process of anaerobic process of treatment that is the fuel which we called as the alternated fuel that can reduce the pressure on the fossil fuels. In order to reduce the fossil fuels we can save a lot of energy by using the effluent treatment as an example you can see if we are going have a fermentation industry of alcohol fermentation industry. So as the effluent of the alcohol fermentation industry that can be very useful for the ethanol production. So as in Pakistan we can see that there are the different industries as an unique example is shakargan sugar mill that is producing the ethanol as a byproduct of the sugar cane industry. So as the effluent of the ethanol industry they produce the biogas and the biogas effluent they are used for the bio fertilizers. So that is the possible way of the effluent treatment. So that can overall decrease the burden of the fossil fuels. On other there are different examples if we are dealing with the baker yeast industry then we can also use that baker yeast effluent for in any animal feed and others processes.