Methane Stripping Trials

Experimental Methane Stripping Trials

1. Introduction

Over the last 15 years, our designer has carried out studies at a number of landfill sites in the UK and Ireland, to investigate the controlled stripping of methane from a variety of landfill leachates, using a purpose-built, pilot-scale system.

These studies have provided fundamental and practical data, which have been used by this designer to provide successful process designs for our full-scale stripping plants on landfill sites.

Trials were undertaken using a portable treatment system, which could be set up rapidly, and is capable of treating in excess of 20 litres of leachate per minute (>1 m3/hr), at accurately controlled and measured leachate and air flow rates.

The equipment laid out ready for a Methane Stripping Trial

2. The Test Equipment

The methane stripping test unit comprised of four identical reactors, each constructed from a standard wheeled bin. Each reactor contained a coarse aeration device in the base, that allows air to bubble through the contents at a rate which can be controlled and measured.

Leachate was pumped into the first chamber, by means of twin electric pumps, directly from a leachate sump at the landfill, and flow rate was determined accurately using a large measuring cylinder and stopwatch.

Effluent from chamber 1 overflows into chamber 2, and passes through the system in a similar manner, finally flowing by gravity into an effluent tank, from where it is pumped to discharge by a low level-controlled pump. When all of the chamber lids are closed, the concentration of methane in ‘off-gas’ from each individual chamber, can be determined, by testing the flow of gas within a horizontal vent in the lid of each reactor.

3. The Tests Carried Out

The system was operated for 2 – 3 hours for each leachate tested, to allow more than 4 volumes (approximately 3 m3) of leachate to pass through. Regular measurements were conducted to ensure that the system had achieved ‘steady state’ conditions before final samples are taken, and tested for dissolved methane.

If needed, small controlled amounts of a silicone-based anti-foam solution were added to the first reaction chamber, to calculate likely requirements of a full-scale system.

Concentrations of methane were measured regularly in leachate and liquid leaving each reactor using a rapid indirect method throughout the trial.

The measurement of methane in reactor off-gases also provided a good indication of the stability of the overall treatment system during the trials.

4. Trial Results

The stripping trial results for each leachate (mean values of several analyses taken after steady-state conditions) were summarised. Results were expressed as reductions in actual concentration of dissolved methane against cumulative volumes of air used to strip each volume of leachate.

The results in all tests were stable and consistent.

In all cases, effluents from the fourth treatment reactor were well below the sewer discharge limit of 0.14 mg/l dissolved methane. For those leachates containing lower initial levels of dissolved methane (< 3.2 mg/l) this limit was reached after passage through only 3 reactors, and use of five or less volumes of air per volume of leachate in total.

5. Conclusion

The trial results, from this method of data collection, from short (1 or 2 day) trials on landfill sites, therefore provide a scientifically based method of collecting data from each landfill site, and from that producing a process design for a wide range of leachates and methane concentrations.

It is this data which IPPTS Associates uses to provide our current designs for our methane stripping plant clients.