Inversion-Based and Optimal Feedforward Control for Population Dynamics with Input Constraints and Self-Competition in Chemostat Reactor Applications

Through chemostat reactors, organisms can be observed under laboratory conditions. Hereby, the reactor contains the biomass, whose growth can be controlled via the dilution rate respectively the speed of a pump. Due to physical limitations, input constraints need to be considered. The population density in the reactor can be described by a hyperbolic nonlinear integro partial differential equation of first order. The steady-states and generalized eigenvalues and -modes of these integro partial differential equation are determined. In order to track a desired reference trajectory an optimal and an inversion-based feedforward control are designed. For the optimal feedforward control, the singular arc of the control is calculated and a switching strategy is stated, which explicitly considers the input constraints. For the inversion-based feedforward control, the integro partial differential equation is first linearized around the steady-state. To comply with the input constraints a control system simulator is designed. For the simulation model, the integro partial differential equation is approximated using Galerkin's method. Simulations show the functionality of the designed controls and provide the basis for comparison. The inversion-based feedforward control operates well near the steady-state, whereas the performance of the optimal feedforward control is not bounded to the proximity to the steady-state.

A benchmark simulation to verify an inhibition model on decay stage for nitrification

Activated Sludge Models (ASMs) are widely used for biological wastewater treatment plant design, optimisation and operation. In commonly used ASMs, the nitrification process is modelled as a one-step process. However, in some process configurations, it is desirable to model the concentration of nitrite nitrogen through a two-step nitrification process. In this study, the benchmark datasets published by the Water Environment Research Foundation (WERF) were used to develop a two-step nitrification model considering the kinetics of Ammonium Oxidising Bacteria (AOB) and Nitrite Oxidising Bacteria (NOB). The WERF datasets were collected from a chemostat reactor fed about 1,000 mg-NH3-N/L synthetic influent with at different sludge retention times of 20, 10 and 5-d, whereas the pH in the reactor varied in the range of 5.8 and 8.8. Supplemental laboratory batch experiments were conducted to assess the toxicity of nitrite-N on nitrifying bacteria. These tests suggested that 500 mg-N/L of nitrite at pH 7.3 was toxic to NOB and resulted in continuous decrease in bulk oxygen uptake rate. To model this phenomenon, a poisoning model was used instead of the traditional Haldane-type inhibition model. The poisoning model for NOB and AOB with different threshold poisonings for unionised NO2-N and NH3-N concentrations could successfully reproduce the three WERF datasets.

Influences of pH and hydraulic retention time on anaerobes converting beer processing wastes into hydrogen

To convert high-solids organic wastes (3% w./w.) to high-value hydrogen, a full factorial experimental design was employed in planning the experiments for learning the effects of pH and hydraulic retention time (HRT) on the hydrogen production in a chemostat reactor using waste yeast obtained from beer processing wastes. For determining which experimental variable settings affect hydrogen production, predictive polynomial quadratic equation and response surface methodology were employed to determine and explain the conditions required for high-value hydrogen production. Experimental results indicate that a maximum hydrogen production rate of 460 mL/gVSS/d was obtained at pH=5.8 and HRT=32 hours. Moreover, hydrogenase targeted RT-PCR results indicate that Clostridium thermocellum and Klebsiella pneumoniae predominated.

The characteristics of the biofilm fixed inside porous medium by sequencing batch reactor

The fixed biomass inside porous medium has two layers where biomass yield constants are different from each other when it is cultivated in the chemostat reactor. The biomass fixed inside porous medium is tested to see whether the operation type affected the structure of it. Two kinds of operation method of the reactor were used for the biofilm cultivation. One is the batch reactor. Another is the chemostat reactor. From the kinetic test, it is found that the biofilm fixed in the batch reactor does not have two layers that were observed in the biofilm from the chemostat reactor. Within the experimental conditions for type-1, the result of kinetic tests show homogeneous biofilm characteristics. It can be concluded that the reactor type (batch type or chemostat type) affects the structure of biomass fixed inside porous medium.

Biological sulfate removal in an acidogenic bioreactor with an ultrafiltration membrane system

The biological sulfate removal in the acidogenic bioreactor with an ultrafiltration membrane system was investigated at 35°C. Sucrose was used as the sole organic substrate. The sulfate concentration in the substrate ranged from 0 to 600mgS·1−1. The chemostat reactor was operated to compare with the membrane bioreactor. The fouling phenomenon caused by FeS precipitate was observed at higher concentration of sulfate. However, it was possible to continuously operate the membrane bioreactor by cleaning the membrane. The efficiency of sulfate removal by sulfate reduction reached about 100% in the membrane bioreactor, and 55 to 87% of sulfide was removed from the permeate by the membrane filtration. The composition of the metabolite was remarkably changed by the change in sulfate concentration. When the sulfate concentration increased, acetate and 2-proponol significantly increased while n-butyrate and 3-pentanol decreased. The sulfate-reducing bacteria play the role as acetogenic bacteria consuming volatile fatty acids and alcohols as electron donors under sulfate-rich conditions. The results show that the acidogenesis and sulfate reduction simultaneously proceed in the membrane bioreactor.