Question

Discuss the kinetics of biodegradation of pollutants in subsurface environments.

Answer 1

Biodegradable substances include food scarps, cotton, wool, wood, human and animal waste, manufactured products based on natural materials.

In the 1990s, biological processes were used for the removal of heavy metal due to the reactive ability of microorganisms with a variety of pollutants that include organic and inorganic species. It was recognized that the microorganisms influence the mobility of the metal by modifying the chemical and physical characteristics of the metals . Recently, Lu et al. investigated a novel biological filter with bacterial strain of P. putida immobilized in Ca-alginate granules for removal of formaldehyde in the gas phase . The effects of inlet concentration, empty bed residence time, and nutrient feeding rate on the performance of the system were examined in their study. It was found that the removal efficiency of the dripping biofilter system increased from 68.6% to 93.5%, when the inlet formaldehyde concentration was in the range of 0.2 to 1.34 mg/m³. Among the various technologies, such as adsorption, chemisorption, photocatalytic oxidation and botanical filtration, that have been tried for the removal of formaldehyde, the complete removal is still a challenging problem due to low kinetics, byproduct formation, and low efficiency using any of the above-mentioned methods. However, biological degradation technology with high removal efficiency has been successfully applied in industries for effluents and waste gas treatments. Even though biological processes have been used for several applications that include heavy metal ion removal and indoor air purification, its application has not been intensely investigated for numerous reasons. Thus, researchers have combined biological process with other techniques such as chemical processes, photocatalysis , and AOP.

Combined biological and chemical degradation methods were carried out to evaluate the effectiveness of mature municipal landfill leachate in laboratory scale by Di Iaconi and coworkers. The biological treatment was followed by chemical oxidation for further removal of COD . Higher removal efficiency was obtained due to the use of chemical treatment. In another study, a combined AOP and biological process was carried out to remove pesticides in aqueous solution .

It was found that O₃ and O₃/UV oxidation treatment was able to achieve 90 and 100% removal of the pesticide deltamethrin, in a period of 210 min. Utilization of ozone with UV irradiation was found to enhance the degradation of pesticides. It has been well documented elsewhere that the rate of pesticide removal mainly depends on both the chemical nature of the pesticides being treated and the treatment conditions . In a different study, a sequential UV and biological degradation of a mixture of 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol were tested with an initial concentration of 50 mg/L . Under their reaction conditions, pentachlorophenol degraded faster compared with other phenolic compounds and 4-chlorophenol degraded the slowest. A combined biological and chemical procedure was also used as an ecologically and economically favorable remediation technique for 2,4,6-trinitrotoluene (TNT) reduction in contaminated ground and surface water . It was observed that the anaerobic transformation process resulted in a faster reduction of TNT due to significant change in the redox potential of the solutions under both aerobic and anaerobic conditions. Biodegradation of organic pollutants by halophilic bacteria was carried out by Le Borgne and co-workers .

In a very recent study, wastewater from a pharmaceutical formulation facility in Israel was treated with a biological activated-sludge system followed by ozonation. This work was aimed at reducing the concentrations of carbamazepine (CBZ) and venlafaxine (VLX), before their discharge into the municipal wastewater treatment plant, and they achieved efficient removal of the drugs by this collective method. The byproducts identified from the incomplete oxidation of ozonation were likely to be more biodegradable than the parent compounds; thus, a postozonation biological treatment was endorsed for the efficient removal of these toxic pharmaceuticals from the wastewater. A recent review has discussed the chemical and biological treatment technologies for leather tannery chemicals and wastewaters. It was concluded from the review that there has not been a full scale application of emerging technologies using AOP to remove xenobiotics present in tannery wastewater, and, thus, there is an opportunity for researchers to explore this aspect. In addition, adsorption process has been widely used as an efficient technique for the removal of a variety of toxic pollutants and this is discussed in Section.