Optimization of mixing in a Chinese dome digester for tropical regions

Abstract

ReferencesAdeoti O. (1998). Engineering economy studies of biogas as renewable energy source at household level in Nigeria. M.Sc.

Development of an Optimised Chinese Dome Digester Enables Smaller Reactor Volumes; Pilot Scale Performance

“…The large difference in methane production and therefor hydrolysis at a theoretical HRT of 40 days between the optimised and blank CDD digester suggests a very large difference in real SRT. The blank reactor might suffer from extensive dead zones, as shown in laboratory experiments by Jegede [6]. It is not clear why these differences are less distinct when operating the CDDs at a theoretical HRT of 30 days.…”

“…Domestic biogas plants can serve as an energy solution to meet the cooking needs of rural households. Various governments and international funders support this system, and if managed well [6], it is a cost-effective way of mitigating greenhouse gas emissions from animal dung [7]. This is accomplished by replacing fossil fuels with biogas and reducing methane emissions during manure management, starting from its production to the final application on agricultural lands [8].…”

“…During gas use, pressure is released, and the slurry flows back into the main reactor, creating a mixing regime or cycle (Figure 1a,b). Therefore, CDD depends on the hydraulic variation, i.e., the change of slurry level in the digester and extension chamber during gas use and could be regarded as intermittent natural mixing [6]. Mixing is an important process in anaerobic digestion for establishing contact between micro-organisms and feed for homogenisation of temperature throughout the digester and prevention of settling and floating layers [11].…”

“…In addition, Chinese dome digesters are generally operated at long hydraulic retention times (>70 days) and low influent total solid (TS) concentrations (≤7%) when compared to mixed reactors (intermittently or continuously). Mixing is limited, leading to a large reactor volume and higher cost [6].…”

“…Applying this approach to CDD could help in the reduction of both the water required for dilution and the reactor size; however, the mixing in CDDs that can be achieved during feeding, biogas production and use would be limited. In addition, Jegede [6] investigated the impact of different influent TS (3-15%) concentrations and the related volumetric biogas production on mixing in lab-scale CDDs. The results revealed that mixing in CDDs, due to biogas production and reactor feeding, is not sufficient at high (>10%) TS concentrations.…”