Heavy metal removal using sodium alginate immobilized SRB was evaluated under batch and continuous mode. 7 FTIR spectra of the UFAR biomass obtained at the end of the metal removal experiments.
Sulfate
Therefore, the removal of metals from wastewater before it is released into the environment becomes inevitable. Therefore, the removal of metals from wastewater before it is released into the environment is extremely important.
Treatment Methods For Heavy Metal And Sulfate Containing Wastewater
Biological Sulfate Reduction For Heavy Metal Removal
Sources
Heavy metals occur in geological formations of the Earth and can therefore pass into streams, lakes, rivers and groundwater; very often these heavy metals are discharged into.
Environment and health effects of heavy metals
Low pH of the AMD streams directly causes toxic effects on the aquatic environment by increasing the solubility of toxic metals and affecting the natural mineral cycles (Johnson, 2000; Lens et al., 2002). AMD also affects ecological balance, biodiversity and the quality of water used for industrial, recreational and agricultural applications (Jarvis and Younger, 2000).
Heavy Metal Removal Methods
- Chemical precipitation
- Hydroxide precipitation
- Sulfide precipitation
- Chemical precipitation combined with other methods
- Heavy metal chelating precipitation
- Ion-exchange
- Adsorption
- Activated carbon
- Carbon nano-tubes
- Low-cost adsorbents
- Biosorption
- Membrane filtration
- Ultrafiltration
- Reverse osmosis
- Nano-filtration
- Electro-dialysis
- Coagulation and flocculation
- Flotation
- Electrochemical treatment
The following are some widely used adsorbents for the removal of heavy metals from wastewater. Conversion of carbon materials to AC for heavy metal remediation has been reported in the literature.
Sulfate
Effects of sulfate
High levels of sulfate in mine tailings from metal-bearing ores and some coal ores are easily oxidized by water and oxygen, resulting in acid discharge that disturbs the ecological balance (Masigol et al., 2012). The presence of sulfate ions increases the conductivity and corrosion potential of receiving water bodies and can contribute to water mineralization (Silva et al., 2010).
Sulfate Removal Methods
Membrane technologies, such as ED and RO, are known to be used to treat sulfate-containing wastewater (Silva et al., 2012). Sulfide generated thus helps to precipitate heavy metals as metal sulfides (Cabrera et al., 2006).
Heavy Metal Removal by Biological Sulfate Reduction
Biological sulfate removal is considered one of the most cost-effective alternatives to the expensive physicochemical removal methods for treating high-sulfate wastewater (Maree et al., 1991). The metal binding capacity of various microorganisms and several biomass sources has shown a very good potential to remove hazardous metals from wastewater (Darnall et al., 1986; Lembi and Waaland, 1988; Volesky, 1990).
Sulfate Reducing Bacteria
Classification of SRB
Acidophilic or acid-tolerant bacteria can grow in an acidic environment, and the use of these types of extremophiles will simplify the system and keep the process economy low (Kolmert et al., 2001; Kimura et al., 2006). These systems normally produce less sludge and are able to handle high organic load rates with high removal efficiency (Vallero, 2003; Pender et al., 2004).
Sulfate removal mechanism and its significance to heavy metal removal from
A low reaction rate of the sulfate reduction process at low temperatures could be compensated by an increased number of bacteria (Knoblauch et al., 1999; Sahm et al., 1999). The elimination of wastewater treatment sludge avoids the geotechnical costs of constructing ponds and the costs associated with making valuable land available for sludge ponds (Bratty et al., 2006).
SRB Based Treatment Systems
Passive biological treatment systems
- Anoxic ponds
- Wetland systems
- Substrate injection into subsurface
- Infiltration beds
- Permeable reactive barrier systems
- Other passive treatment systems
The choice of the reactive mixture affects the permeability and reactive nature of the barrier (Waybrant et al., 1998; Amos et al., 2003). Cadillac molybdenite passive bioreactor was operated with 5-day HRT using wood chips, limestone, hay and manure as substrates (Kuyucak et al., 2006).
Active bioreactor systems
- Upflow anaerobic sludge blanket (UASB) reactor
- Fluidized bed reactor (FBR)
- Anaerobic filter reactor (AFR)
- Anaerobic hybrid reactor (AHR)
- Continuously stirred tank reactor (CSTR)
- Anaerobic baffled reactor (ABR)
- Anaerobic contact process (ACP)
- Anaerobic packed bed reactor and column bioreactors
- Anaerobic fixed-film reactor
- Gas lift reactor (GLR)
- Membrane bioreactor (MBR)
Gas lift reactor (GLR) systems provide good mixing and increase mass transfer rates (Dijkman et al., 1999). Zinc sulfide precipitation on the effluent side of the membrane resulted in decreased HS mass transfer (Chuichulcherm et al., 2001).
Passive vs. active treatment systems
However, the latter requires more expenditure and skilled manpower for operation and maintenance (Gazea et al., 1996; Johnson, 2000; Kaksonen et al., 2004). 6 Main characteristics of active and passive systems for biological treatment of heavy metal-containing wastewater (Gazea et al., 1996; Johnson, 2000; Kaksonen and Puhakka, 2007).
Factors Affecting The Selection of Sulfidogenic Bioreactors For Heavy Metal Removal
6 Several factors determine the choice of sulfidogenic reactors for the removal of sulphate and heavy metals from wastewater (Andrea et al., 2014). In a one-stage process, sulfate reduction is performed by SRB to produce sulfide, promoting metal precipitation as metal sulfides in the reactor (Kaksonen et al., 2003a).
Effect of Different Parameters on The Performance of Sulfidogenic Bioreactors
Microbial composition
The microbial composition of biomass varies due to the ability of microbes to colonize and form biofilm. Therefore, it is essential to choose the best source of biomass for efficient wastewater treatment with a bioreactor.
Influent parameters
Reactor design and operational parameters
The high cost and high proportion of undissociated lactate in metal-containing wastewaters such as AMD, leading to SRB inhibition, are some of the drawbacks of lactate as a carbon source (Bruser et al., 2000). 8 Gibbs free energy change of different electron donors for sulfate reduction reactions (Stefanie et al., 1994).
Biofilm Composition in Attached Growth Sulfidogenic Bioreactors
Therefore, it is recognized as a resource-rich method to both remove and recover metals from contaminated wastewater (Cabrera et al., 2006). One such limitation is the inherent toxicity of metals on SRB growth and activity (Min et al., 2008).
Statistical Design of Experiments
It mainly focuses on the potential application of anaerobic RBC reactor systems immobilized with SRB for the treatment of synthetic wastewater containing sulfate and different heavy metals in single and mixture component systems. Furthermore, statistically valid experimental design, namely Plackett Burman and factorial designs, were applied to carry out the heavy metal removal experiments involving mixture component system.
Aim and Objectives
To identify key factors and their contribution to an observed response, the normal approach to using one-variable-at-a-time (OVAT) involves a large number of experiments to be performed that often fail to detect significant process interaction. elucidate. variables (Ryan et al., 2007). Statistical experimental designs are powerful tools to improve the efficiency of experiments and facilitate a better understanding of the system under investigation with a minimal number of experiments.
Presentation and Layout of the Thesis
Membrane filtered water (reverse osmosis (RO)) was used for performing all experiments in the study (Sartorious, Arium 61316RO . & 611UF, Germany).
Source of Anaerobic Biomass and Growth Conditions
Batch Heavy Metal Removal
Screening of heavy metals and anaerobic biomass
- Characterization of the metal precipitates
Simultaneous sulfate reduction and heavy metal removal experiments were conducted using 100 mL serum bottles equipped with a rubber stopper and aluminum shrink seal. Fourier transform infrared spectra were obtained to explain the changes in the functional groups of the biomass due to sulfate reduction for heavy metal removal.
Metal removal from multi-component system
- Characterization of the metal bio-precipitates
1 Plackett-Burman experimental design matrix showing different levels of heavy metal combination in the multicomponent study. Characterization of metal bio-precipitates formed due to SRB was performed by FTIR, TEM-EDS and FESEM-EDX spectroscopy.
Batch Heavy Metal Removal Using Immobilized SRB Beads
- Preparation and characterization of immobilized SRB beads
- Batch heavy metal removal
- Reusability and durability of the immobilized SRB beads
- Characterization of the immobilized SRB beads
Batch metal removal experiments using immobilized SRB beads were performed using 100 mL serum vials with rubber stoppers and aluminum crimp seals. After activation, the immobilized SRB beads were first washed with distilled water and two grams each of the beads (5%) were used as the inoculum source in the metal removal experiments.
Continuous Heavy Metal Removal Using Downflow Column Reactor (DFCR) With
DFCR setup
To ensure the reuse potential of the immobilized SRB beads for heavy metal removal, batch experiments were performed on the beads using 25 mg/L initial concentrations of Ni(II), Zn(II), Pb(II) , Cd(II). ), Fe(III) and 50 mg/L Cu(II), respectively. 4 Photograph of experimental setup showing down-flow column reactor with immobilized SRB granules for heavy metal removal in continuous mode of operation.
Single component system
- Metal removal experiments
Multi-component system
4 Fractional factorial experimental design matrix showing different levels of heavy metal combination in the mixture using DFCR. The statistical software, Minitab (Version 16, PA, USA) was used for the design of fractional factorial experiments and for the statistical analysis of the obtained results.
Continuous Heavy Metal Removal Using The Anaerobic Rotating Biological Contactor
- An-RBC reactor setup
- Biofilm development
- Characterization of the bio-support material
- Heavy metal removal experiments
- Single component system
- Identification and characterization of SRB
Photographs of the An-RBC reactor before and after immobilization with SRB are shown in Figs. 6 Photograph of the experimental setup showing the rotating biological contactor (RBC) reactor before immobilization with SRB.
Multi-component System
8 Fractional factorial design of experiments presenting different heavy metal combination levels tested in the mixture using the An-RBC reactor. The reactor was operated for a period of time to three steady state values of effluent heavy metal concentration.
Analytical Methods
Screening of biomass sources for heavy metal removal
- Effect of initial metal concentration
- Heavy metal removal mechanism
- Characterization of metal precipitates
3 Sulfate reduction in the presence of different heavy metals by biomass from: (a) WWTP, (b) UFAR and (c) APR. 4 Sulfate reduction in the presence of different heavy metals by biomass from: (a) WWTP, (b) UFAR and (c) APR.
Batch heavy metal removal from multi-component system
- Heavy metal and COD removal and sulfate reduction in the multi-component
- Statistical analysis
- Characterization of metal bioprecipitates
For a better interpretation and assessment of the significance of the individual heavy metals on each other's removal as well as on the sulphate and COD reduction by SRB, the results. Metal precipitates near the bacterial cell surface are clearly visible in Fig.
Sulfate reduction, metal and COD removal using immobilized SRB
- Heavy metal and COD removal and sulfate reduction
- Reusability and durability of immobilized SRB
- Characterization of immobilized beads
Based on the results of metal removal efficiency by immobilized SRB obtained at different initial metal concentrations (10 and 50 mg/L), reusability and durability of the immobilized biomass for heavy metal removal were tested with 25 mg/L initial concentration of Ni(II) ), Zn( II), Pb(II), Fe(III) and Cd(II); in the case of Cu(II), 50 mg/L initial concentration was chosen. Based on the results obtained, a schematic of metal removal mechanism by immobilized SRB beads is shown in Fig.
Continuous Metal Removal Using DFCR With Immobilized SRB Biomass
Single component system
- Heavy metal and COD removal and sulfate reduction
Performance of the DFCR in terms of metal removal rate with respect to inlet metal loading rate (ILR) is shown in Fig. 26 Heavy metal removal rate as a function of inlet metal loading rate obtained using the continuously operated DFCR with immobilized SRB beads: ( a) Cd(II), (b) Cu(II), (c) Ni(II), (d) Fe(III ), (e) Pb(II) and (f) Zn(II) (▲: Metal removal rate from single component system; ○: Metal removal rate from multimetal solution).
Heavy metal removal from multi-component system
- Heavy metal and COD removal and sulfate reduction
- Characterization of bio-precipitates formed in the mixture experiments
- Statistical analysis
27 (a) Continuous removal of mixed heavy metals, (b) Continuous removal of COD, sulfate reduction and sulfide generated in mixing experiments using DFCR. These values of COD removal, sulfate reduction and generated sulfide were lower than those obtained in the single-component system (Fig.
Heavy Metal Removal Using The Anaerobic Rotating Biological Contactor (An-RBC)
Single component system
- FSESM characterization of immobilized SRB onto the support material
- Heavy metal and COD removal and sulfate reduction
These results were slightly less than the metal removal results previously obtained with the DFCR (Fig. 4.22). In the present study, the metals at their respective low inlet metal concentrations did not inhibit the sulfate reduction by SRB (Fig. 4.30), which was also in good agreement with the results obtained using the DFCR.
Heavy metal removal from multi-component system
- Heavy metal and COD removal and sulfate reduction
- Statistical analysis
- Characterization of metal bio-precipitates formed in the reactor
A study of the effect of pH and dissolved heavy metals on the growth of sulfate-reducing bacteria using a fractional factorial design. Removal of Cu(II) and Fe(III) from aqueous solutions by dead sulfate-reducing bacteria.
Statistical design of experiments
Chemical precipitation of heavy metal by sodium sulfide
Identification of SRB culture
Analysis of variance of heavy metal removal from a multi-component system by
Analysis of variance of sulfate and COD removal in the presence different heavy
ANOVA of heavy metal removal using the DFCR
Student's t test for estimating the coefficients of individual and interaction effects of
ANOVA of heavy metal removal using the An-RBC reactor
Student's t test for estimating the coefficients of individual and interaction effects of
Table. Simple cost estimation of the An-RBC reactor set up
