Removal Of Carbonyl Sulfide Using Compost Biofilter: Measurement Of Removal Rates And Elimination Capacity In Conjunction With Hydrogen Sulfide

A lab study using biofiltration was conducted using three PVC columns as biofilters, with hardwood chips and compost as the media. Previous research determined the removal efficiency of carbonyl sulfide alone. (Nawal, 2004) Typically, however H2S is present with COS in the air streams from wastewater treatment plant units. In the current study, different combinations of hydrogen sulfide and carbonyl sulfide gases were tested using H2S/COS ratios typical of the concentrations from wastewater treatment plants. Various runs were conducted using compost and hardwood chips individually and also with an 80:20 ratio by volume of wood chips to compost. \nThe specific research objectives of the study were: \n1.To find the critical mass loading for COS by studying the typical elimination capacity versus mass loading curve. \n2.To study the degradation of carbonyl sulfide in presence of hydrogen sulfide using compost and a mixture of hardwood chips and Compost as media. \nOne of the initial findings of the study was that the Interscan 1000 series sensor used for H2S interfered with International Sensor Technology Model IQ-350 sensor used for COS and had a negative impact on the COS gas concentration measurement. The setup was altered to avoid the interference of gases. More importantly, critical factors governing the process like moisture content, humidity, air flow rate and pH were carefully analyzed and maintained to obtain the best degradation rates for the combinations tested. The moisture content was maintained in the range of 50- 55% , relative humidity at 90-95% and an air flow rate was monitored to be in the range of 2-3 LPM to provide sufficient gas residence time during the experiment. \nA 60 ppm concentration of H2S, 1:6 and 1:2 ratios by ppm of COS to H2S respectively yielded 100% removal efficiency for both compounds when the biofilter was operated with compost medium. It was found that the critical load is atleast 9 g/m3-hr for COS with compost media.