**3. Application of Tabu search for inverse modeling of anaerobic fixed bed biofilm reactor**

Tabu search is applied to determine the parameters of kinetic and film thickness models through the validation of the mathematical models of the process with the help of measured data acquired from an experimental fixed bed anaerobic biofilm reactor used in the treatment of pharmaceutical industry wastewater.

#### **3.1 Experimental biofilm reactor and its description**

The schematic of a laboratory scale fixed bed biofilm reactor setup used for industry waste water treatment is shown in **Figure 4**. The description of the experimental unit, its auxiliary items and the packing specifications are given as follows.

The reactor consists of a QVF glass column of 1 m height and 0.1016 m internal diameter. A Teflon perforated plate of thickness 3 mm is provided at the base of the column to support the packing material. Two openings fitted with valves made of Teflon are provided at the bottom of the reactor so that one valve is used to control the flow rate of influent pumped into the reactor and the other valve is used to discharge the excess sludge accumulated. The top of the column has a provision to place a thermometer to measure the temperature. Three sampling ports are placed at equal distances along the side of the column to withdraw samples. The temperature of the column is maintained by varying the voltage through the 0.2 kW heating tape connected to a dimmer-stat. The column is insulated with 1.0 in. asbestos rope. The entire setup is supported by a 1.0 in. M.S. pipeline structure. The column and the packing specifications are given elsewhere [27].

#### **3.2 Experiments and data generation**

The experimental setup shown in **Figure 4** is used to conduct experiments for anaerobic treatment of pharmaceutical industry wastewater involving different packing materials with varying organic loading rates and feed rates, and different hydraulic retention times. The influent kept in a 2 *l* capacity vessel is fed to the column through an inlet connection located at the bottom using a peristaltic pump made of Watson Marlow. The effluent sample is collected from an outlet located at the top of the column. The column and the packing specifications are given

*A Metaheuristic Tabu Search Optimization Algorithm: Applications to Chemical… DOI: http://dx.doi.org/10.5772/intechopen.98240*

#### **Figure 4.**

*Experimental biofilm reactor setup.*

elsewhere [27]. The reactor is filled with the packing material and then seeded with 1.0 *l* of active anaerobic sludge brought from M/s. Alkabir, Hyderabad, India. To maintain the initial growth of microorganisms, the reactor is further added with 2.6 *l* of very dilute solution of synthetic glucose medium (1000 mg/l) with nutrients such as total nitrogen as urea (125 mg/l), total phosphorous as KH2PO4 (50 mg/l), NaCl (50 mg/l), KCl (40 mg/l), CaCl2 (15 mg/l), MgCl2 (10 mg/l) and FeCl3 (2 mg/l). The pH of the solution is maintained at 7.2 by adding 0.1 N NaOH. The reactor is made biologically active by keeping it undisturbed for about 20 days. The gas (CH4 + CO2) evolved at the top of the column confirms the biological activity of microorganisms.

The wastewater procured from a typical pharmaceutical industry is a complex medium and its composition is reported elsewhere [28]. Substrates of varying COD concentrations are prepared using the wastewater in order to use them as feed solutions for biofilm reactor experiments. Once the biological activity of the bed is detected, the diluted industry wastewater solution equivalent to three bed volumes is sent to the reactor by an electronic dosing pump. NaHCO3 is added to maintain the pH of the feeding solution at 7.2. Different experiments are conducted for treating the pharmaceutical industry wastewater using the feed solutions having the COD concentrations of 4,980 mg/l, 11,860 mg/l, 23,460 mg/l and 40,720 mg/l. The hydraulic retention time (HRT) of each experiment is varied from 2 to 12 days based on the substrate concentration of the feed solution. Each experimental run subsequent to attainment of its HRT is allowed to continue for 13 days so as the operation reaches stable state condition by that time.

Thirteen experiments are conducted using the different feed solutions prepared from the pharmaceutical industry wastewater. The reactor is provided with the sampling ports to withdraw samples at bed heights of 0.25 m, 0.5 m and 0.75 m

from the bottom. Samples collected from the three sampling ports of the column as well as from the effluent water are analyzed for COD, BOD, TVA, TA, pH etc. The stable state condition of each experiment is observed with respect to the minimal variation in reactor effluent pH, alkalinity and COD concentrations. Thus 13 experiments are conducted under different feed stream conditions. The data corresponding to the influent and effluent COD concentrations, HRT and OLR of all experiments are given elsewhere [28].
