Abstract:
Anaerobic treatment has gained wide acceptance as a sustainable technology for
treatment of solid wastes and waste water. But in the local context this technology is
not rapidly advancing due to process failures and poor technology management.
Most of the failures are reported in the anaerobic solid waste treatment than waste
water treatment. Recently, novel plug flow reactor system has been installed in few
local institutions to treat semi solid wastes with improved efficiency. However lack
of understanding of operational parameters and functional units of this reactor system
has led to suboptimal operation and thereby low gas production and methane yield.
Objective of this study is to develop dynamic mathematical model for plug flow
reactor system and propose new strategies to enhance the methane yield and
stability of the process. The anaerobic digestion model No. 1 (ADM 1) developed by
the international water association (IWA) task group for mathematical modeling of
anaerobic digestion process is the most sophisticated model established for full- scale
industrial applications. In this work ADM1 was implemented in the simulation
software package called AQUASIM 2.1f and advective diffusive reactor
compartment was initially used to model the plug flow reactor. To be able to model
the actual plug flow reactor system as installed two scenarios are introduced i.e.
advective diffusive reactor compartment followed by two continuous stirred tank
reactors for collection of slurry and gas. The simulation was done for the different
hydraulic retention times and feed flow rates for the substrate of food waste. As
second scenario, series of CSTR reactors was used to model plug flow reactor and
simulated as before. Simulation results on advective-diffusive reactor model reveal
that accumulation of gasses in the slurry cause an inhibition in methane production.
In series of CSTR model, when the food waste alone was used at low hydraulic
retention times, pH decreases drastically and cause to process inhibition in the first
reactor. This inhibition radiates towards the other connected CSTR reactors and after
a certain periods of time total methane production terminates.
Keywords: Anaerobic digestion, Plug flow reactor, ADM 1
