Managing director Brian McBride, who founded the Midlothian-based company in 1983, was the sole shareholder, and is believed to be in line for about £1 million after costs.
Both McBride and his son, James, will remain at the company, as group area manager and Scottish operations manager, respectively.
James McBride said that, after 21 years of family ownership, now was the right time to become part of a larger, national group.
"Weve reached a point where things are going very well, but the necessary expansion and growth is going to cost a lot," he said. "As part of Viridor, we can continue to do what we do well but with the backing of a lot more resources."
Mac Glass, which is likely to be rebranded as Viridor, specialises in recycling container glass, such as jars, bottles and glasses, and has a number of large commercial and industrial clients, including 12 local authorities in Scotland and two in England. It employs about 25 people and, according to the most records filed in Companies House, it posted income of about £700,000 to the end of November 2003.
Viridor, which is a subsidiary of water and waste management company the Pennon Group, focuses on plate glass, such as windscreen and window glass, for use in the fibre wool industry. It has had a strong presence in Scotland since it bought EnviroScot, the waste collection and recycling company, for £19m.
According to chief executive Colin Drummond, the acquisition is in line with the groups strategy of expanding its waste management activities particularly in the areas of waste treatment and materials recycling.
He said that Viridor will now relocate its existing recycling unit at Wishaw in North Lanarkshire to Mac Glasss base at Cockpen in Midlothian, with the aim of increasing throughput of waste glass five-fold within 12 months.
The group is also planning to invest in new "optical sorting equipment" for the site, with the aim of improving the quality of end product.