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Biological nitrogen and organic matter removal from tannery wastewater in pilot plant operations in Ethiopia
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
2004 (English)In: Applied Microbiology and Biotechnology, ISSN 0175-7598, E-ISSN 1432-0614, Vol. 66, no 3, 333-339 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this study was to set-up a pilot plant and to evaluate its effectiveness for biological nitrogen and organic matter removal from tannery wastewater in Ethiopia. A pilot wastewater treatment plant consisting of a predenitrification-nitrification process was constructed and operated for 6 months. This was fed with a raw tannery wastewater obtained from the Modjo Tannery located 70 km south of the capital, Addis Ababa. Up to 98% total nitrogen and chemical oxygen demand, and 95% ammonium nitrogen removal efficiencies were achieved in the system. The average effluent ammonium nitrogen ranged from 8.4 mg l(-1) to 86.0 mg l(-1), whereas the average effluent for nitrate nitrogen ranged from 2.9 mg l(-1) to 4.4 mg l(-1). The average values of denitrification and nitrification rates determined by nitrate and ammonium uptake rates (NUR and AUR) were 8.0 mg NO3-N [g volatile suspended solids (VSS)](-1) h(-1) and 5.4 mg NH4-N (g VSS)(-1) h(-1), respectively, demonstrating that the treatment processes of the pilot plant were effective. Further studies of the effect of chromium III on AUR showed 50% inhibition at a concentration of 85 mg l(-1), indicating that this metal was not causing process inhibition during performance operations. Thus, the predenitrification-nitrification process was found to be efficient for simultaneous removal of nitrogen and organic substrates from tannery wastewaters.

Place, publisher, year, edition, pages
2004. Vol. 66, no 3, 333-339 p.
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5340DOI: 10.1007/s00253-004-1715-2ISI: 000225225300016PubMedID: 15316686Scopus ID: 2-s2.0-11244283455OAI: oai:DiVA.org:kth-5340DiVA: diva2:8972
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2017-11-30Bibliographically approved
In thesis
1. Developing and optimizing processes for biological nitrogen removal from tannery wastewaters in Ethiopia
Open this publication in new window or tab >>Developing and optimizing processes for biological nitrogen removal from tannery wastewaters in Ethiopia
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In Ethiopia industrial effluents containing high contents of organic matter, nitrogen and heavy metals are discharged into inland surface waters with little or no pre-treatment. Significant pollution concerns related to these effluents include dissolved oxygen depletion, toxicity and eutrophication of the receiving waters. This has not only forced the government to formulate regulations and standards for discharge limits but also resulted in an increasing interest and development of methods and systems by which wastewater can be recycled and used sustainably. The need for technologies for environmentally friendly treatment of industrial wastes such as tannery wastewaters is therefore obvious. Biological processes are not only cost effective but also environmentally sound alternatives to the chemical treatment of tannery wastewaters.

The aim of the research presented in this thesis was to develop and optimize processes for biological nitrogen removal from tannery wastewaters and to identify the most efficient denitrifying organisms in tannery wastewaters laden with toxic substances. A pilot plant consisting of a predenitrification anoxic system, aerated nitrification compartment and a sedimentation tank (clarifier) all arranged in series was developed and installed on the premises of Addis Ababa University, Ethiopia. In spite of high influent chromium and sulphide perturbations over the successive feeding phases, the performance of the pilot plant was encouraging. The overall removal efficiency of the pilot plant over the experimental feeding phases varied between 82-98% for total nitrogen, 95-98% for COD, 96-98% for BOD5, 46-95% for ammonia nitrogen, 95-99% for sulphide and 93-99% for trivalent Chromium. Six isolates from over 1000 pure cultures were identified as the most efficient denitrifying bacteria. From both cellular fatty acid profiles and 16S rRNA gene sequencing, the six selected strains were phylogenetically identified as Brachymonas denitrificans in the β-subdivision of the Proteobacteria. All the six strains contain cd1-type nitrite reductase. The efficient isolates characterized in this study are of great value because of their excellent denitrifying properties and high tolerance to the concentrations of toxic compounds prevailing in tannery wastewaters. Bio-augmentation of the pilot plant with this bacterium showed a clear correlation between in situ denitrifying activities measured by nitrate uptake rate, population dynamics of the introduced B.denitrificans monitored by fluorescent in situ hybridization and the pilot plant performance, suggesting that the strategy of introducing this species for enhancing process performance has potential applications.

Moreover, the nitrate-reducing, sulphur-oxidizing bacteria (NR-SOB) were also found in the pilot plant in abundance with steady sulphide removal efficiency during the study period. This could provide opportunities for the application of biologically mediated simultaneous removal of sulphide and nitrogen from tannery effluents. In addition to enriching high consortia of denitrifiers in the anoxic system to attain high denitrification efficiency and also improving the overall nitrification efficiency of the system, the predenitrification-nitrification pilot process plant stimulated the activity of indigenous NR-SOB to simultaneously remove sulphide from the system. Thus, the pilot plant was found to be operationally efficient for the removal of nitrogen, organic matter and other pollutants from tannery wastewaters.

Keywords: Biological nitrogen and sulphide removal, denitrifying bacteria, nitrate-reducing, sulphur-oxidizing bacteria, nitrate uptake rate, fluorescent in situ hybridization, pollution, tannery effluents.

Place, publisher, year, edition, pages
Bioteknologi, 2004
Keyword
Ecology, biological nitrogen and supphide removal, dntififying bacteria, nitrade-reducing, sulphuroxidizing bacteria, nitrate uptake rate, Ekologi
National Category
Ecology
Identifiers
urn:nbn:se:kth:diva-32 (URN)91-7283-830-2 (ISBN)
Public defence
2004-10-01, Kollegiesalen, KTH, Valhallavägen 79, Stockholm, 14:00
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Supervisors
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2012-03-21

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