landfill biocovers

Meet Gomathy Radhakrishna Iyer of SCS Engineers at GWMS 2020

January 24, 2020

Dr. Gomathy Radhakrishna Iyer

Dr. Iyer is a Staff Professional at SCS focusing on environmental research and engineering in water, wastewater, solid waste, and landfill design. Gomathy is another of our remarkably talented young professionals utilizing her expertise in leachate management and landfill design to support her clients.

We hope you will attend Gomathy’s presentation “Suitability of Un-Composted Grass Clippings and Biosolids as Biocovers for Biological Methane Removal from Landfills,” on Tuesday, February 25 at 8:30 am (Track B: Landfill Covers), at the 2020 Global Waste Management Symposium. Her presentation is based on a technical paper of the same name and co-authored with Melanie Sattler of the University of Texas at Arlington, and Darrin Dillah of SCS Engineers.

Landfill biocovers are widely used to oxidize methane emissions, a known greenhouse gas. The biocovers in use today are typically either fully or partially made of composts. However, the production of compost, although theoretically an aerobic process, also produces potentially substantial quantities of methane, from 3.2 to 362 kg carbon dioxide (CO2)-equivalents per ton of wet waste composted, depending on various factors, for example, the type of waste, and open or enclosed composting technology. This research explored the suitability of using uncomposted grass clippings as a biocover for methane removal from landfills, with the aim of reducing net greenhouse gas emissions.

Physical and chemical characteristics of grass clippings along with other components of yard waste were studied and compared. The use of biosolids and fly ash as potential bulking materials were considered since the physical and chemical characteristics of biosolids and fly ash complemented the grass clippings and biosolids were expected to provide a good inoculum of microbes for the biocover. Batch tests were performed on the grass clippings and combinations of grass, biosolids and fly ash mixtures for aerobic methane removal. Grass clippings were found to have a maximum methane removal rate of 2,121.7 nmol/kg/s, and a combination of grass and biosolids showed a maximum methane removal rate of 4,410.8 nmol/kg/s. Analyzing different proportions of grass, biosolids and fly ash mixtures, it was found that a 70% grass, 21% biosolids and 9% fly ash mixture exhibited the highest methane oxidation of 5,862.5 nmol/kg/s.

Column tests were performed on the grass clippings and on a combination of 70% grass, 21% biosolids and 9% fly ash by introducing a continuous flow of 50% methane and 50% carbon dioxide at the bottom of the column reactor containing 2 feet of biocover material. The column reactors with grass clippings showed a methane removal of 90-100% within the first 10 days, and the reactors with the combination of grass, biosolids and fly ash showed a methane removal of 90-100% within first 3 days. Biocover performance indexes were calculated based on the performance of each biocover. The biocover performance index for grass was found to be 20.8 µg/g/hr and that for the combination of 70% grass, 21% biosolids and 9% fly ash was found to be 43.3 µg/g/hr.

Representative samples were taken from the column reactors to analyze for the presence of methanotrophs involved in the methane removal process. A PCR (Polymerase Chain Reaction) analysis was performed on these samples with A189 (forward) and A682 (reverse) primers. The evidence of pMMO PCR amplification products was seen in all column reactor samples, indicating the presence of the pMMO gene, which is found in methanotrophs and hence confirmed the presence of methanotrophs. A BLAST (Basic Local Alignment Search Tool) was performed on the sequence obtained from the PCR analysis confirmed methalocystis and type 2 methanotrophs. Figure 1 shows the gel picture of the PCR analysis of the column reactor samples. #1

1&2: Column reactor with grass clipping, 3&4: Column reactor with 70% grass, 21% biosolids, and 9% fly ash, 5: Column reactor with yard waste compost (control), 7: Mock extract, 8: Primer negative control, Neg: PCR negative control.

LEAF testing was conducted to analyze the leachability of fly ash in the biocover. It was seen that silver, arsenic, cadmium, chromium and thallium exceeded the permissible level in drinking water. Hence, it was concluded that the grass clippings by itself or a combination of grass and biosolids can be used as a biocover for biological methane removal.

Global Waste Management Symposium 2020
February 23 @ 8:00 am – February 26 @ 5:00 pm
2020 GWMS Information





Posted by Diane Samuels at 6:01 am