Evaluation of Toxic Organics Removal by Simultaneous Adsorption and Biodegradation

Simultaneous adsorption and biodegradation processes were investigated. Three toxic organic compounds, nitrobenzene, aniline, and phenol were selected to be studied individually and in mixtures as a model of polluted toxic industrial wastewaters. Their behavior was assessed separately in adsorption, biotreatment, as well as in combined systems, by physicochemical and respirometric methods. Powdered activated carbon (PAC) was used as an adsorbent in these experiments. In the adsorption systems, in single, bi- and trisolute solutions, the limiting adsorption capacities, Q° and b, the energy of adsorption related constants, were determined from the linearized forms of Langmuir adsorption isotherms. Q° values for aniline and phenol were found to be similar and approximately 2.5 times higher for nitrobenzene. The energy related coefficient b, was similar for nitrobenzene and phenol, and almost 5 times higher for aniline. The presence of mineral nutrients, needed for biological processes, significantly decreased the energy related constants for phenol and aniline, but did not affect this parameter for nitrobenzene. Kinetic characteristics of those three compounds' biodegradation by acclimated microbial cultures were determined in biological systems. The degree of bioresistance of the organics was estimated. PAC addition to the biological systems affected differently the biooxidation of the three compounds. The presence of PAC considerably enhanced the microbial respiration in the bioreactor with nitrobenzene, distinctly intensified that of phenol, but reduced it in the reactor with aniline. Different organic removal mechanisms were suggested in simultaneous adsorption and biodegradation of each of the three compounds, due to their different adsorption characteristics. It was found that the strong inhibiting effect of the three compounds in highly concentrated mixture on microbial respiration was completely wiped out by adding PAC to the biological reactor. As a result, the initial COD 3350 mg O2/L was reduced to 27.6 mg O2/L. The optimal PAC dose was determined by using respirometric data. The results obtained can be used for the evaluation of simultaneous adsorption and biodegradation as a method for effective removal of toxic organics from industrial wastewaters, under appropriate conditions. The method can be applied for the industrial wastewater treatment alone as well as for pretreatment, before discharging to the municipal biological treatment plant. The process is expected to decrease the harmful effect on conventional activated sludge processes and to prevent the disposal of hazardous materials into the environment.