Methane fermentation method
It is the basic, biological method of pre-treatment of industrial wastewater to parameters similar to those of municipal wastewater, enabling its further purification using the activated sludge method. As a result of this process, 85% – 95% reduction of organic compounds and 20% – 30% reduction of biogenic compounds is obtained and it is treated as the first stage of biological purification.
The process of methane fermentation carried out by anaerobic bacteria is ideally suited to the decomposition of complex organic compounds, because it proceeds in four basic phases, in which they are gradually reduced to the final products, which are biogas (a mixture of methane and carbon dioxide) and water.
The first stage of methane fermentation is the hydrolysis of complex organic compounds contained in wastewater in dissolved form and in suspensions. Hydrolytic bacteria break down proteins into amino acids, complex carbohydrates into simple sugars, and fats into higher fatty acids. The products of hydrolytic decomposition are used as a substrate for acidogenic bacteria, which in the second stage of biodegradation carry out acidogenesis, resulting in simple organic acids. In the third stage of decomposition, acetateogenesis, these acids are reduced to acetic acid, from which methane, carbon dioxide and water are obtained in the methanogenesis stage. Methane is also obtained, but in a much smaller amount, by reducing carbon dioxide with previously produced hydrogen. The conditions necessary for the proper conduct of the process are the appropriate biological quality of the anaerobic sludge, the process temperature in the range of 36⁰C – 38⁰C and the reaction at the level of 6.8 to 7.6 pH.
Activated sludge method
It is a widely used method of wastewater treatment in municipal wastewater treatment plants. Activated sludge is a complex biocenosis of many groups of microorganisms, from bacteria, through protozoa and worms, to nematodes. They all exist only in the presence of oxygen, so aeration is necessary. Unlike anaerobic sludge used in methane fermentation, aerobic activated sludge is adapted to the decomposition of relatively simple organic compounds that are quickly biodegradable. For this reason, industrial wastewater treatment plants use activated sludge reactors for the final treatment of wastewater in order to obtain the parameters of treated wastewater that allow it to be discharged to the surface water receiver.
A very important issue regarding the technological system in which the oxygen reactor operates is the issue of removing biogenic compounds of nitrogen and phosphorus in it. While the removal of phosphorus compounds from wastewater can be carried out both by biological and chemical methods through precipitation in the form of insoluble phosphates, in the case of biogenic nitrogen compounds, only biological methods are available, consisting in the oxidation of ammonium ion to nitrate ion, which in turn is decomposed under appropriate conditions. to gaseous nitrogen in the denitrification process and thus removed from wastewater. Removal of nitrogen compounds is possible in a system of at least two activated sludge chambers with optimal conditions for this process, i.e. aeration in the nitrification chamber and hypoxic conditions in the denitrification chamber. The effectiveness of the denitrification process also depends on the proper ratio of the concentration of organic compounds defined as COD to the concentration of nitrogen compounds in the wastewater flowing into the denitrification chamber.