The case was brought after the Health and Safety Executive investigated the death of Dennis Krauesslar at the site in 2007.
According to media reports, 58-year-old Krauesslar was allegedly hit by the shovel of a mechanical digger as he deposited grass cuttings at the recycling centre.
When it appeared at West Berkshire Magistrates Court on 8 February, the waste management firm pleaded guilty to breaching a health and safety regulation which says that every employer should ensure that those not employed by him who may be affected are not exposed to risks or their health and safety.
Biffa also put in a guilty plea for not making a suitable and sufficient assessment of the risks to the health and safety of persons not in its employment but connected with Biffa’s conduct by it of its undertaking.
The case has been referred to Reading Crown Court for sentencing.