A comparative evaluation of dried activated sludge and mixed dried activated sludge with rice husk silica to remove hydrogen sulfide
© Mehdinia et al.; licensee BioMed Central Ltd. 2013
Received: 19 July 2012
Accepted: 6 March 2013
Published: 12 March 2013
The aim of this study was to investigate the effectiveness of dried activated sludge (DAS) and mixed dried activated sludge with rice husk silica (DAS & RHS) for removal of hydrogen sulfide (H2S). Two laboratory-scale filter columns (packed one litter) were operated. Both systems were operated under different conditions of two parameters, namely different inlet gas concentrations and different inlet flow rates. The DAS & RHS packed filter showed more than 99.96% removal efficiency (RE) with empty bed residence time (EBRT) of 45 to 90 s and 300 mg/L inlet concentration of H2S. However, the RE decreased to 96.87% with the EBRT of 30 s. In the same condition, the DAS packed filter showed 99.37% RE. Nonetheless, the RE was shown to have dropped to 82.09% with the EBRT of 30 s. The maximum elimination capacity (EC) was obtained in the DAS & RHS packed filter up to 52.32 g/m3h, with the RE of 96.87% and H2S mass loading rate of 54 g/m3h. The maximum EC in the DAS packed filter was obtained up to 44.33 g/m3h with the RE of 82.09% and the H2S mass loading rate of 54 g/m3h. After 53 days of operating time and 54 g/m3h of loading rates, the maximum pressure drop reached to 3.0 and 8.0 (mm H2O) for the DAS & RHS packed and DAS packed filters, respectively. Based on the findings of this study, the DAS & RHS could be considered as a more suitable packing material to remove H2S.
KeywordsHydrogen sulphide Rice husk silica Dried activated sludge Removal efficiency Elimination capacity Pressure drop
Waste gases containing reduced sulphur compounds, such as hydrogen sulfide (H2S), dimethyl sulphide (Me2S) and methyl mercaptan (MeSH), have an unpleasant odour even at extremely low concentrations . H2S is irritating, smelly substance with very low odour threshold number up to 1.1 parts per billion . This unwanted pollutant is emitted into the atmosphere from different industrial processes including leather manufacturing, food processing, livestock farming and wastewater treatment processes . Commonly used processes of H2S treatment include chemical and physico-chemical methods. However, these methods have high operating costs and produce chemical waste by-products that must be disposed . The application of biofiltration systems are more attractive because they are inexpensive and cause no environmental pollution [5–7]. Lately, the influence of even low concentrations of air pollutants on human health has re-emerged as an important scientific issue. Several studies have linked various acute and chronic health impacts to air pollution . It is important to note that biological treatment system is one of the earliest biological processes which has been developed for the elimination of gaseous compounds and used for odor removal in the wastewater treatment industry. At present, the biological treatment system is becoming more popular because it is a green technology which does not use chemicals and also does not produce wastes which are potentially dangerous for the environment. This process is essentially based on the ability of micro-organisms to transform both organic and inorganic pollutants into less toxic and odorless compounds .
The main goal of this study was to investigate the removal efficiency of hydrogen sulphide using two packing materials, namely dried activated sludge and mixed dried activated sludge with rice husk silica. Moreover, elimination capacity and pressure drop versus operating time, different empty bed residence time (EBRT) and different inlet concentration of H2S was investigated.
Materials and methods
Characterization of the packing materials
Some of the important characteristics of dried activated sludge and rice husk silica used in this study
Dried activated sludge
Rice husk silica
< 2 mm
Median pore radius
Cumulative pore volume
Analysis of elements:
Analysis of elements:
0.36 ± 0.05
Data analysis and performance of the filters
Where Q is the gas flow rate (m3/h), Vf is the volume of the filter bed (m3), CGi and CGo are the inlet and outlet hydrogen sulfide concentration (mg/L) [12–15]. In the Faculty of Chemistry University Putra Malaysia the chemical analysis including analysis of elements (CHNS) and chemical composition was carried out. Moreover, Brunauer-Emmett-Teller (BET) specific surface area was performed by using a ThermoFinnigan Sorptomatic apparatus using nitrogen adsorption at −196°C for rice husk silica.
The mixed rice husk silica with dried activated sludge packed filter showed greater than 99.96% removal efficiency (RE) with the EBRT of 45 to 90 s and 300 mg/L inlet concentrations of H2S. However, its RE was found to have decreased to 96.87% with the EBRT of 30 s. The dried activated sludge packed filter showed 99.37% of RE in the same condition. The RE, nevertheless, dropped to 82.09% with the EBRT of 30 s. Masoudinejad et al. reported 90% of RE with an inlet H2S concentration up to 93.34 mg/L, after three weeks of operating system. They used Thiobacillus thioparus on the seashell bed biofilter . Meanwhile, Lee et al. achieved stable RE of over 99%, with the EBRT ranging from 8.2 to 60 s at the 250 mg/L of H2S inlet concentration. They also found that the RE was reduced by about 10 percent when the retention time was reduced to 5.5 s. In their study, they used a biofilter packed with scoria, and inoculated with Bacillus sp. as H2S oxidizer .
The maximum EC was obtained in the mixed rice husk silica with dried activated sludge packed filter up to 52.32 (g/m3h) with the RE of 96.87% and the H2S mass loading rate of 54 (g/m3h). At the RE greater than 99.96%, however, the maximum EC was 26.99 (g/m3h) with H2S mass loading rate of 27 (g/m3h). The maximum EC in the dried activated sludge packed filter was obtained up to 44.33 (g/m3h) with the RE of 82.09% and H2S mass loading rate of 54 (g/m3h). Roshani et al. reported the maximum EC of about 22 g-S/m3 h for the biofilter during the operating time with the maximum inlet H2S concentration of 265 mg/L . Meanwhile, Kim et al. recorded the maximum EC of 8 g H2S g/m3h at a loading rate of 13 g H2S g/m3h. In their study, they used a bio filter packed with biomedia, encapsulated by sodium alginate and polyvinyl alcohol (PVA) . Ramirez et al. obtained a critical EC of 14.9 g/m3h with the RE of 99.8%. However, they found the maximum EC of 55.0 g/m3h with the RE of 79.8% and the EBRT of 150 s. The researchers also investigated the removal of H2S using immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam .
In the mixed rice husk silica with dried activated sludge packed filter, the maximum pressure drop reached 3.0 mm H2O after 53 days of operating time and 54 g/m3h of mass loading rates. The maximum pressure drop in the dried activated sludge packed filter reached up to 8.0 mm H2O in the same condition. McNevin and Barford reported an increasing pressure drop from less than 500 to greater than 2500 pa after 3 months of continuous operating time . Meanwhile, the maximum pressure drop of 18 mm H2O was reported in the study by Roshani et al. who evaluated the performance of biofiltration in the removal of H2S from gas stream .
Higher performance (higher removal efficiency, higher elimination capacity, and lower pressure drop) was obtained in the filter packed with mixed rice husk silica and dried activated sludge. Therefore, based on the results of this study, mixed rice husk silica with dried activated sludge could be considered as more suitable packing material for removal of hydrogen sulfide.
This research was financially supported by Research University Grant (RUGs) in University Putra Malaysia (UPM) through Project No: 91806. Therefore, the authors would like to acknowledge the University Putra Malaysia (UPM) for the research funding.
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