3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P46 bIOSORbENTS PREPARATION FOR hEAVy
METALS REMOVING FROM wATERS
JAnA JEnČáROVá and ALEnA LUPTáKOVá
Institute of Geotechnics of Slovak Academy of Sciences
Watsonova 45, 043 53 Kosice, Slovakia,
jencarova@saske.sk
Introduction
Heavy metals are very important pollutants in waters.
They are non-degradable and therefore continue to accumulate
in water bodies. Because of their toxic properties and the
tendency for bioaccumulation in the food chain, it is imperative
to take effective precautions and to reduce the concentration
levels of heavy metals in waters 1 .
Current methods in order to remove the toxic metal ions
from wastewater are: chemical precipitation, ion exchange,
extraction, adsorption, reverse osmosis techniques 2 .
Adsorption is understood to involve the interphase
accumulation or concentration of substances at a surface or
interface. Absorption is a process in which the molecules or
atoms of one phase interpenetrate nearly uniformly among
those of another phase to form a solution with it 3 . A specific
type of sorption based on the used solid phase that is derived
from various types of biomaterials or biomass is biosorption
4 .
Microbial biomass is frequently used for the bioremediation
of heavy metals polluted waters as the biomass capable
absorb, adsorb and in some cases precipitate the metals out
of solution 5 .
Sulphate reducing bacteria (SRB) are genera of dissimilatory
bacteria, which utilise sulphate as a terminal electron
acceptor and perform dissimilatory reduction of sulphate ions
(SO 4 2– ) to hydrogen sulphide (H2 S) gas. The hydrogen sulphide
produced by the SRB, as part of their metabolic processes
is capable to react with metal cations to form stable
sulphide precipitates 6 .
Microbial iron sulphide is well known as an adsorbent
for the treatment of metallic ion polluted wastewater 5 .
Material and Methods
C u l t i v a t i n g M e d i u m
For sulphate-reducing bacteria cultivation was modified
nutrient medium DSM-63 (ref. 7 ) with the addition of
Fe 2 (SO 4 ) 3 . 9H2 O used. This medium creates optimal conditions
for SRB growth genera Desulfovibrio and Desulfotomaculum.
S u l p h a t e - R e d u c i n g B a c t e r i a
Bacteria were isolated from a mixed culture obtained
from potable mineral water collected at Gajdovka spring
(Košice, Slovak republic) with pH 7.5 and H 2 S odour.
S o r b e n t s P r e p a r a t i o n
The iron sulphides preparation was realized in the bioreactor
filled with 500 ml of modified nutrient medium DSM-
s672
63 and inoculated with 100 ml of a culture of SRB during
21 days at 30 °C under anaerobic conditions. These conditions
were generated by introducing an inert gas (n 2 ) and chemically
with sodium thioglycollate. The pH of the medium
was adjusted to the value 6.8 with sodium hydroxide.
Preparation was realized under 2 different modes. During
first mode the bioreactor worked at 30 °C under anaerobic
conditions without addition of fresh nutrient medium during
21 days. During second process of preparation the bioreactor
worked 4 days in batch mode and then 3 days in continuous
mode (i.e. fresh medium was supplied into reactor for more
intensive SRB growth and iron sulphides production). We
realized 3 periods (21 days).
M o d e l S o l u t i o n s
Model solutions were prepared by dissolving
ZnSO 4 . 7H2 O and CuSO 4 . 5H2 O analytical grade salts. For
sorption experiments were solutions with contain of Zn 2+ and
Cu 2+ 100 mg dm –3 used.
S o r p t i o n E x p e r i m e n t s
Batch sorption experiments were realized in Erlenmeyer
flasks filled by 100 ml of model solution of Zn 2+ or Cu 2+ and
the sorbent. The sorbent dose was 0.1 g. For the best contact
between sorbent and model solution were samples agitated by
mechanical laboratory shaker at 250 oscillations per minute.
Sampling was conducted during 90 minutes. The concentration
of zinc and copper was determined by atomic absorption
spectrometry.
Results and Discussion
The process of the iron sulphides preparation by SRB
was successful in both modes, demonstrated by black precipitates
in Fig. 1. and the sensorial detection of H 2 S odour.
Fig. 1. bacterially produced iron sulphides
Sorption of Cu and Zn cations from model solutions by
biogenic sorbents prepared in batch-continuous mode was
studied. Fig. 2. shows removal of Zn 2+ and Cu 2+ during 90
minutes. All copper ions were removed. In the same time
only 50 % of zinc ions were removed.