Removal of Cr (VI) from aqueous solution and tannery effluent in sequence with Cr (VI) resistant microfungi (Aspergillus niger, Penicillium chrysogenum) and sawdust degraded by basidiomycete (Gloeophyllum sepiarium) was investigated in the laboratory. Initial or primary treatment with microfungi reduced 200 mg/l Cr (VI) in aqueous solution by 64.6% - 78.2% while a markedly lower 0.52 mg/l Cr (VI) in tannery effluent was reduced by 72.4% - 84.6%. However, the residual Cr (VI) in both aqueous solution and tannery effluent was reduced to a non-detectable level after secondary treatment by passage through basidiomycete-degraded sawdust column. The recovery of 65.4% - 87.7% of the Cr (VI) removed by treatment microfungi by elution indicated adsorption as the major mechanism for Cr (VI) removal. The microfungi reduced BOD in tannery effluent by 85.3 ± 5.6 - 92.7 ± 6.8 and concomitantly removed Cr (VI), hence it is hypothesized that non-Cr (VI) constituents of tannery effluent may have interfered with biosorption of Cr (VI) by treatment microfungi. It is concluded that the two-stage sequential treatment process may be of potential cost-saving stratagem for removal of chromium from industrial wastes.
The tanning industry generates wastes which include compounds such as chromium, phenol, chloride sulphide tannins and formaldehyde among others [
Despite their tolerance of metals, microorganisms are not always able to remove the metals completely from industrial wastes. For example [
Aromatic compounds produced by some wood rot fungi during wood decomposition, include carboxyl, methoxyl and hydroxyl groups [
The test P. chysogenum and A. niger were isolated from tannery effluent-contaminated soil in Kano, Northern Nigeria in preliminary studies. Both microfungi tolerated Cr (VI) concentrations of 500 mg/l in potato dextrose medium.
The test P.chrysogenum, A. niger and G. sepiarium were each propagated in 150 ml flasks containing potato dextrose broth made up to 50 ml level mark for uniformity. They were incubated statically at room temperature (30˚C ± 2˚C) till growth covered the entire surface of the medium in order to ensure that the same standard of mycelial inoculum was generated. The mycelia were subsequently harvested by filtration with Whatman filter paper No 1 and washed several times with sterile distilled water to remove any adhering growth medium. This was the standard inoculum used for the treatment tests.
The effluent used for the tests was collected from a tannery located in Kano, Northern Nigeria. The level of Cr (VI) in the effluent was determined by the atomic absorption spectrophotometer method of [
The ability of microfungal mycelia recovered from treated tannery effluent to remove Cr (VI) from aqueous solution was tested. The mycelia were recovered by filtration and washed with 0.1 M Tris-HCl buffer pH 7.8 [
Obeche wood (Triplochiton scleroxylon) sawdust was collected from sawmills, dried to constant weight at 105˚C, and dispensed at 50 g/250ml flask. The sawdust was moistened with 20 ml distilled water and autoclaved at 120˚C for 30 mins. On cooling, the flasks were inoculated with 10 ml Potato Dextrose Broth suspension of macerated mycelia of Gloeophyllum sepiarium (brown-rot basidiomycete) that was developed as described previously and manually turned over to effect sawdust/hyphal even mixture. The flasks were divided into 3 sets of 5 replicates bringing it to a total of 15 and set aside on the laboratory bench at room temperature for 3 months. They were moistened with 10 ml sterile distilled water/flask at weekly intervals to prevent desiccation. A set of 5 flasks were retrieved at intervals of 4 weeks, manually macerated to break the hyphae/sawdust entanglement and dried to 30% moisture content at 45˚C in a dessicator. This temperature was chosen to minimise any damage to potential Cr (VI) binding biomolecule that may be present. Thereafter they were aseptically packed into 5 replicate glass columns with an inner diameter of 4 cm and a height of 15 cm. The filtrates of effluents or aqueous solution from primary treatment were passed through the degraded sawdust column at a drop/second from a burette. The effluents collected from the outlet at the bottom of the column were analyzed for Cr (VI) concentration. For the purpose of control, the above experiment was repeated with un-degraded sawdust as substitute for the basidiomycete-degraded sawdust. The concentration of Cr (VI) removed was expressed as percentage of the residual concentration in the filtrates from the primary treatment.
Another set of microfungal mycelia were retrieved after primary treatment, dried overnight at 70˚C, and transferred to flasks containing 0.1 M Tris-HCl buffer solution (pH 7.8). They were shaken overnight at 200 rpm to allow desorption of Cr (VI) occur. The filtrates were subsequently analyzed for desorbed Cr (VI) and expressed as percentages of the concentrations adsorbed during primary treatment. The degraded sawdust in the glass column were also retrieved after secondary treatment and similarly desorbed.
The Cr (VI) removed from tannery effluent and aqueous solution by the microfungi peaked at the 36th hour of incubation (
The results of the primary treatment tests showed that the live microfungi removed over 70% of the chromium in the tannery effluent and aqueous solution and concomitantly reduced BOD by over 80% in the same effluent (
Treatment organisms | After treatment | ||
---|---|---|---|
Status | Organism | Cr (VI) removal (%) M ± SD | *BOD reduction (%) M ± SD |
Live in tannery effluent | As. niger P. chrysogenum G. sepiarium | 72.5 ± 4.2 84.6 ± 4.7 9.6 ± 1.2 | 85.3 ± 5.6 92.7 ± 6.8 18.5 ± 3.3 |
Dead in tannery effluent | As. niger P. chrysogenum G. sepiarium | 25.3 ± 2.0 32.1 ± 2.1 5.4 ± 1.0 | 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 |
Live in aqueous solution | As. niger P. chrysogenum G. sepiarium | 64.6 ± 4.5 78.2 ± 4.8 9.7 ± 1.5 | NA NA NA |
Dead in aqueous solution | As. niger P. chrysogenum G. sepiarium | 68.6 ± 3.4 71.7 ± 4.3 6.3 ± 1.2 | NA NA NA |
Concentration of Cr (V1) before primary treatment: tannery effluent, 0.52 ± 0.08 mg/l; aqueous solution 200 mg/l. *BOD concentration in tannery effluent before treatment = 1240.0 mg/l. NA. Not applicable.
removed Cr (VI) from aqueous solution to an extent that was not markedly different from the level it was reduced to by the live mycelia (
The BOD test results confirm the presence of compounds in the tannery effluent that can interfere with metal binding sites on the fungal mycelia. This inference is supported by the observation that despite the low concentration of Cr (VI) in tannery effluent, the microfungi were unable to achieve 100% removal rate. This contrasts sharply with the result showing the same fungal mycelia dead or alive, removing markedly higher concentrations of Cr (VI) in aqueous solution. Further evidence comes from the observation that the mycelia of A. niger and P. chysogenum recovered from primary treatment of tannery effluent was able to remove 115.4 ± 5.3 mg/l (57.7%) and 122.2 ± 5.8 mg/l (61.1%) Cr (VI), respectively from aqueous solution. This suggests that interfering tannery constituents may have been dislodged from the mycelia by the washings with Tris-HCL buffer and distilled deionised water. The limited Cr (VI) removal ability of dead mycelia in tannery effluent can be attributed to lack of metabolic activity that can degrade some of the tannery constituents that may have interfered with Cr (VI) binding sites on the mycelia.
The secondary treatment with G. sepiarium-degraded obeche wood sawdust removed the residual Cr (VI) in the tannery effluent and aqueous solution after primary treatment (with microfungi) to the extent that Cr (VI) could not be detected (
On the other hand, removal of Cr (VI) in tannery effluent or aqueous solution (with or without primary treatment) by un-degraded obeche sawdust was marginal (
The results presented in
Source of filtrate | Primary treatment organism | Removal of residual Cr (VI) (%) by degraded sawdust after: | ||
---|---|---|---|---|
4 | 8 | 12 weeks | ||
Tannery effluent | aA. niger bP. chrysogenum | 96.5 ± 5.3 97.4 ± 5.5 | ND ND | ND ND |
Aqueous solution | cA. niger dP. chrysogenum | 89.2 ± 4.7 92.5 ± 5.0 | ND ND | ND ND |
Untreated tannery effluent | Control | 59.3 ± 3.6 | 72.8 ± 4.5 | 75.2 ± 4.5 |
ND, Not detected. Cr (VI) in filtrate from primary treatment: a0.14 ± 0.03 mg/l; b0.08 ± 0.01 mg/l; c70.8 ± 3.6, mg/l; d44.5 ± 3.0 mg/l. Cr (VI) in: untreated tannery effluent, 0.52 ± 0.08 mg/l; aqueous solution, 200 mg/l.
Source of Cr (VI) | Primary treatment fungus | Removal of Cr (VI) in un-degraded sawdust (%) M ± SD |
---|---|---|
Tannery effluent | aA. niger bP. chrysogenum Not treated | 2.5 ± 0.10 2.8 ± 0.10 1.6 ± 0.10 |
Aqueous solution | cA. niger dP. chrysogenum Not treated | 5.4 ± 0.15 5.8 ± 0.15 2.3 ± 0.10 |
Cr (V1) in filtrate from primary treatment: a0.14 ± 0.03 mg/l; b0.08 ± 0.01 mg/l; c70.8 ± 3.6, mg/l; d44.5 ± 3.0 mg/l.
Source of Cr (VI) | *Fungal mycelia | Desorbed Cr (VI) (%) M ± SD |
---|---|---|
Tannery effluent | Aspergillus niger Penicillium chrysogenum | 86.5 ± 4.0 87.7 ± 4.2 |
Aqueous solution | Aspergillus niger Penicillium chrysogenum | 65.4 ± 3.6 69.6 ± 3.7 |
Biodegraded sawdust | NA | 52.5 ± 3.3 |
NA, Not applicable; *after primary treatment.
by desorption. However the percentage of Cr (VI) recovered from degraded sawdust was markedly lower than that recovered from fungal mycelia (
The main objective was to complement chromium biosorption capacity of microfungi with biosorption capability of brown-rot wood decomposition products in a sequential arrangement. This was achieved because Cr (VI) was reduced to non-detectable level at the end of the two-phase treatment sequence. The live mycelium possesses a better potential for initial treatment of tannery effluent than the dead mycelia. The reason was that in addition to removing Cr (VI) better than the dead mycelia, it also metabolized other tannery constituents as indicated by BOD reduction which was not possible with dead mycelia. This strategy may prove useful in a cost-effective treatment stratagem for chromium removal in industrial wastes if further tests with other wastes prove successful. Low-income countries that cannot afford the cost of the conventional treatment technology may find it attractive especially as sawdust is an abundant, but often wasted resource in many developing countries like Nigeria.
Bernard O. Ejechi,Olubunmi O. Akpomie, (2016) Removal of Cr (VI) from Tannery Effluent and Aqueous Solution by Sequential Treatment with Microfungi and Basidiomycete-Degraded Sawdust. Journal of Environmental Protection,07,771-777. doi: 10.4236/jep.2016.76069