Novel techniques for the recovery of sulphur as useful products from air pollutants using aerobic biofilters
Rabbani, Khondkar (2015) Novel techniques for the recovery of sulphur as useful products from air pollutants using aerobic biofilters. PhD thesis, Murdoch University.
Biofilters and biotrickling filters are popular for the removal of odorous pollutants like hydrogen sulphide and ammonia from gaseous emissions in wastewater treatment plants because of their low capital costs, low energy requirements and environmental performance. In an aerobic environment, the microbes in biofilters oxidize hydrogen sulphide to non-odorous sulphate. Despite several advantages over conventional chemical systems, one of the consequences of maintaining a suitable pH and moisture content for the microbes in the biofilter is the production of large volumes of weakly acidic leachate which needs to be treated or disposed safely. In this research, weakly acidic leachate was considered as a sulphur resource rather than a waste stream and strategies to utilise this resource were investigated.
A novel laboratory scale biofilter system removed hydrogen sulphide with a removal efficiency of 98.8% and produced small volumes (1 mL of solution/L of reactor/day) of sulphuric acid with concentrations greater than 6M after 150 days of continuous operation. This was achieved by compensating for the loss of moisture in the upflow biofilter by intermittently trickling a minimum amount of nutrient solution. This created a moisture and pH gradient within the biofilter resulting in an environment at the top for the bacterial conversion of hydrogen sulphide while sulphuric acid was accumulated at the base. The small volume of high concentration sulphuric acid is a more valuable resource than a large volume of weakly acidic leachate produced in conventional biofilters.
Simultaneous removal of hydrogen sulphide and ammonia in contaminated air can also be achieved by aerobic biofilters, with biological oxidation by microbes producing sulphate and nitrate in the leachate. A pilot scale biofilter was setup at a local wastewater treatment plant for the simultaneous removal of hydrogen sulphide and ammonia from gaseous emissions but instead of biological oxidation of both the pollutants, the sulphate produced from the biological conversion of hydrogen sulphide in a biofilter was allowed to accumulate in a concentrated form first. The ammonia was then subsequently removed, not by biological oxidation, but by the chemical reaction of ammonium ion with sulphate to form ammonium sulphate which was washed down and accumulated in the bottom. This biofilter, which had been in continuous operation for more than 150 days, removed both hydrogen sulphide and ammonia at an average removal efficiency of 91.96% and 100% respectively. Unlike conventional biofilters which convert hydrogen sulphide to sulphate and ammonia to nitrate, this biofilter produced a solution of ammonium sulphate which can be harvested for further use.
The novel techniques explored in this research provide an alternative to conventional biofilters that allows recovery of the sulphur as useful products rather than waste.
|Publication Type:||Thesis (PhD)|
|Murdoch Affiliation:||School of Engineering and Information Technology|
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