Biogas Production From Wastes: Biogas Technologies

Biogas Production Technologies

In anaerobic treatment plants or biogas production plants it must be provided that microbial community/biomass should have the optimum conditions (temperature, pH, OLR, HRT) to keep producing biogas stable and effectively and descharging effluent parameters such as COD, BOD, and TS, etc. at desired low concentrations. The key point of ensuring these expectations is designing the reactors according to the desired conditions and lower costs. One thing that determines the significant percentage of the cost of biogas plants is the reactor volume. As higher the volume of reactors gets as higher the construction cost of the plant is. To avoid large reactor volume requirements that cause higher costs and maintanence difficulties, biomass retention time/solid retention time which is described as the time that anaerobic biomass spends in the reactor until washout, was increased by many kinds of engineering technics such as using new packing materials and introducing design parameters. This is why it is importan to increase the SRT of an anaerobic process.

Slowly growing anaerobic bacteria require longer SRT in anaerobic reactors. Loading rates are therefore, primarily dictated by the concentration of active biomass in anaerobic reactors. Consequently, maintenance of a high SRT is the major point of interest in practical application of AD process.

High rate anaerobic treatment could be achieved by employing efficient biomass retention methods.

In anaerobic reactors to maintain higher biomass densities, SRT has to be in excess of HRT (hydraulic retention time). SRT>>HRT

High biomass densities also provide greater resistance to any inhibitory substances in the influent.

To accomplish the higher treatment efficiency and reliability associated with a long SRT, a number of anaerobic reactor configurations have been developed. All of these studies are being conducted to maintain sufficient retention time to allow for hydrolysis of particulate substrates and provide beneficial conditions for methanogenesis.

Anaerobic treatment plants (ATP) are divided into two groups: low rate and high rate ATP according to their loading rates. The figure below compares the HRTs of low rate and high rate anaerobic reactors as well as the HRTs of batch, plug flow and mixed reactors. As seen in the figure HRTs of low rate reactors vary between 10 and 100 days fed with extended feed concentrations from 1 to 100% TS. On the other hand HRTs of high rate reactors vary from hours to couple of days with feed concentrations not more than 1 0r 2 % TS.