Characteristics of Organics Removal by Pact Simultaneous Adsorption and Biodegradation

-The use of powdered activated carbon treatment (PACT), based on simultaneous adsorption and biodegradation, is effective for treating organic toxic pollutants, present in industrial wastewaters. Removal of phenol and aniline from aqueous solutions by biological treatment alone, by adsorption on powdered activated carbon (PAC) alone and by simultaneous adsorption and biodegradation were compared. In the adsorption experiments, Langmuir adsorption isotherms were obtained, from which Qo, the limiting adsorption capacities, and b, the constant related to the energy of adsorption, were determined. Q° values of phenol and aniline were found to be similar, while the energy-related constant for aniline was five times higher than for phenol. Addition of mineral nutrients, needed for the biological treatment, and inactivated microbial cells increased the limiting adsorption capacities and significantly decreased the energy related constants. In biological treatment alone, kinetic studies showed that aniline was more resistant to biodegradation than phenol. In the simultaneous adsorption and biodegradation process, the PAC presence differently affected the biooxidation of phenol and aniline. While the PAC enhanced the microbial respiration in the phenol bioreactor, it significantly reduced the microbial respiration in the aniline bioreactor. Different organic removal mechanisms are suggested in PACT for phenol and aniline, due to their different energy of adsorption. The respirometric studies are recommended as an adequate tool for prediction of toxic organics removal capabilities from industrial wastewaters by PACT. © 1997 Elsevier Science Ltd. All rights reserved Key words--powdered activated carbon treatment (PACT), mechanisms, simultaneous adsorption and biodegradation, phenol, aniline NOMENCLATURE simultaneous adsorption and biodegradation. WasteAdsorption water purification, by powdered activated carbon treatment (PACT), which was introduced by DuPont b = energy related Langmuir constant (L/rag) C = liquid phase concentration of pollutant at (Hutton and Robertaccio, 1975) has been based equilibrium (mg/L) on these two processes. The mechanisms involved q~ = adsorbent phase concentration of pollutant at in the complicated simultaneous adsorption and equilibrium (mg/g) biodegradation process still need to be studied. Q" = maximum, or limiting, adsorption capacity (mg/g Two different PACT mechanisms are found in the PAC) literature. The first one (Kalinske, 1972; Perrotti and Biodegradation Rodman, 1974; Spetiel, 1989) suggests a mutual effect BODr**v = Respirometric Biochemical Oxygen Demand of the microbial cells and the powdered activated (mgO2 uptake/rag substrate removed) K, = Haldane inhibitor constant (rag/L) carbon (PAC). The presence of PAC increases the #ma~ = maximum specific biomass growth rate (h -~) liquid-solid surfaces, on which microbial cells, R = respirometric biomass equivalent (mgO2 uptake/ enzymes, organic materials and oxygen are adsorbed, mg biomass formed) providing an enriched environment for microbial Y = cell yield coefficient (mg biomass formed/mg metabolism. Surface catalysis o f physico-chemical substrate removed) reactions is also possible on the surface of activated carbon (Kalinske, 1972), Microbial enzymes, exINTRODUCTION creted into carbon micropores, bring about extraIn many natural ecosystems a combinat ion of cellular biodegradation of adsorbed organics and biological and adsorption processes is a common bioregeneration of the activated carbon. The carbon phenomenon. Organic pollutants, discharged from adsorption capacity, controlled by the bioregeneraindustries, are removed from the environment due to tion, is highly increased and the carbon adsorption column cycle is prolonged, as compared to pure *Author to whom all correspondence should be addressed adsorption systems alone. As a result, when [Fax: + 972 4 822 8898]. simultaneous biodegradation and adsorption occurs,