72    ADSORPTION OF CADMIUM AND CHROMIUM FROM
WASTEWATER BY PEAT
T. Viraraghavan, Professor
Faculty of Engineering
University of Regina
Regina, Saskatchewan
Canada
Ganesh A.K. Rao, Graduate Student
Department of Civil Engineering
University of Akron
Akron, Ohio
INTRODUCTION
The heavy metals discharged in the wastewaters can be toxic to aquatic life and cause natural waters
to be unsuitable as potable water sources. Their extreme toxicity even in trace quantities and their
tendency for bioaccumulation in the food chain make it necessary to develop schemes for the removal
of heavy metals from wastewaters. Since adsorption is one of the more effective methods for removing heavy metals from wastewaters, an inexpensive and more easily available adsorbent would make
the removal of heavy metals from wastewaters by adsorption an economically viable alternative. The
abundance of peat and its easy availability makes it an economical adsorbent for removing heavy
metals from wastewaters.
Peat is defined as (1) a fibrous mass of organic matter in various stages of decomposition, generally
dark in color, and of spongy consistency; and (2) as unconsolidated, hydrophilic, carbonaceous
sediment formed by the accumulation of partially fragmented, decomposed and commonly heterogeneous plant remains which retain more than 75% inherent moisture, and less than 12% mineral matter
in saturated natural deposits. Peat can be described as fossilized plant matter which occurs in wet
areas where there is a lack of oxygen; the accumulation of plant matter is therefore more rapid than its
decomposition. Peat moss is a rather complex material containing lignin and cellulose as major
constituents. These constituents, especially lignin, contain polar functional groups, such as alcohols,
aldehydes, ketones, acids, phenolic hydroxides and ethers that can be involved in chemical bonding.'
Because of the very polar nature of this material, the specific adsorption for dissolved solids such as
transition metals and polar organic molecules is reported to be quite high. Peat has a greater cation
exchange capacity than mineral soil and research by several investigators has shown that peat is an
effective adsorbent for the removal of heavy metals from wastewater.1"9
This study was conducted to evaluate the effectiveness of locally available horticultural peat in the
removal of cadmium and chromium from municipal wastewater. Laboratory batch kinetic and isotherm studies were conducted to evaluate the adsorption capacity of peat in removing cadmium and
chromium from wastewater. The effects of contact time, pH and temperature on the adsorption
capacity of peat were also investigated. The study also included an investigation on the influence of
acid treatment of peat on the adsorption capacity of peat in removing cadmium and chromium from
municipal wastewater.
MATERIALS AND METHODS
Wastewater
The wastewater used in the study was collected from the City of Regina Municipal Wastewater
Treatment Plant located 20 km west of the City of Regina. The treatment plant receives mostly
residential wastewater and the effluent from a few industries in and around the city, of which an oil
refinery and a steel mill are the major contributors. The wastewater used in this study was the raw
wastewater collected at the bar screens before the wastewater enters the primary sedimentation tanks.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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