HYTECH WATER LTD

Methane Stripping Plants

When methane is generated within the heart of a landfill a proportion of the gas dissolves in the landfill leachate.

When leachate leaves the landfill this methane often comes out of solution and can form pockets of explosive gas within sewers and pumping stations.

In order to eliminate this potential problem at source, eight plants have been constructed in the North West of England by Hytech Water. Four were for the Greater Manchester Waste Disposal Authority (designed by Enviros Consulting of Shrewsbury). Hytech have designed and built two plants for Wigan C.C.

A further plant was construction in Blackpool for Lancashire C.C. (Enviros Consulting design). This plant was maintained and operated by Hytech Water. The treatment capacity is in excess of 1500 m³/day.

Hytech Water have also developed an in-line dissolved methane monitor. This allows the volume of air — used to agitate the leachate and strip out the methane — to be varied to suit both the rate of leachate inflow plus the strength of the incoming leachate.

The amount of methane dissolved in the raw leachate can vary from 15 mg/litre down to 2 mg/litre. If account is not taken of this variation, the excess air supplied at the lower levels of contamination causes a rapid and heavy calcification of the plant. This calcification will result in additional maintenance, a requirement for the dosing of anti-calcifying chemicals, and can eventually lead to a breakdown of the plant and the catastrophic failure of key components.

Careful control of the air supply will reduce and hopefully eliminate such calcification problems.

The level of methane in heavily contaminated leachate is currently being reduced in all plants to well below that permitted by the local Water Authority for direct discharge into their sewers (0.14 mg/litre).

These fully automatic plants avoid the high operating and maintenance costs associated with competitive plants by careful attention to air and water flowpath design so that potential blockage and sedimentation points are as far as possible eliminated.

Where the accumulation of deposits may be expected, the design permits easy access for de-sludging and de-scaling equipment and personnel.

The modular approach to the design of the plant permits units to be supplied utilising the same basic principle for stripping methane out of a wide range of daily leachate outflow volumes, whenever a site investigation and treatability study reveals a current or potential danger to public Health and Safety.