EFFECTS OF Cd AND Cu ON A BIOFILM TREATMENT SYSTEM
Shoou-Yuh Chang, Assistant Professor
Ju-Chang Huang, Professor
Yow-Chyun Liu, Graduate Student
Department of Civil Engineering
University of Missouri-Rolla
Rolla, Missouri 65401
INTRODUCTION
High concentrations of heavy metals have been known to be toxic to most microorganisms and
able to cause a serious upset in a biological waste treatment system. However, when the metal concentration is not too high and a proper acclimation process is allowed, a biological system may be used to
remove a certain amount of a given metal without itself being adversely affected. The effect of heavy
metals on the biological treatment efficiency is generally dependent upon the type, solubility, and
total concentration of each individual metal. It also depends upon the organic strength of wastewater
and the extent of system acclimation. It has been reported that only soluble metal ions cause toxicity
[1]. The toxicity of metals has also been found to decrease with an increasing organic strength of
wastewater [2]. The tolerance of a biological system for heavy metals can be greatly enhanced by acclimation. One theory of acclimation is that when a metallic cation causes damages or inactivation of
one or more critical enzymes, additional enzymes can be produced to replace the damaged ones. If the
damage becomes too severe, an alternate or a shunt metabolic pathway may be created. Because of the
narrow spectrum of life forms of the anaerobic and nitrifying microorganisms, they are more susceptible to the toxic effects of heavy metals than aerobic heterotrophic microorganisms [3]. As a matter of
fact, in an aerobic process, heavy metals may adversely affect several species of microorganisms without affecting the overall biological treatment efficiency.
Removals of heavy metals in a biological system are mainly attributed to the sorption of soluble
and finely-divided metal particulates by biological floes. It has been found that the microbial removal
of heavy metals consists of an initial rapid uptake followed by a long-term slow, but consistent uptake
phase. The rate of uptake is greatly affected by the pH of solution [4]. Sludge age as well as the extent
of acclimation can also affect the metal adsorption in an activated sludge system.
Most of the past research on the toxicity of heavy metals on biological systems has been directed
toward the suspend-growth activated sludge process. The effects of heavy metals on fixed-film biological system, such as a rotating biological contactor (RBC), remain relatively unexplored. The objective
of this study was to evaluate the effect of cadmium (Cd) and copper (Cu) on the stabilization efficiency of soluble organic carbon (SOC) in a laboratory scale, three-stage RBC unit treating a synthetic
sugar waste. Cadmium was studied at 5 and 20 mg/1 while copper was studied at 1,5, 10, 25 and 50
mg/I.
LITERATURE REVIEW
Numerous past research studies had been conducted to investigate the toxic effects of heavy metals
on biological treatment processes, but most of them were directed toward the suspended-growth activated sludge system. Since this study deals with only cadmium and copper, this literature review will
present information of the toxic effects of these two metals on various biological systems.
Sierp and Fransemeier [5] investigated the copper effect on an activated sludge system. They found
that copper at a concentration of 1 mg/1 had a detectable influence in increasing effluent turbidity and
decreasing the extent of nitrification but showed only a slight impact on the BOD removal efficiency.
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