The Australian Department of Immigration and Citizenship said eight Sri Lankan men, including five from the processing center on Nauru Island, arrived in Colombo Sunday after having agreed to return voluntarily.
Some of the 332 returnees have been returned involuntarily and asylum seekers can request to be sent home at any time during their processing, a department spokesman said.
"Regular transfers to Nauru and more Sri Lankans returning home is further proof that there is no advantage engaging with people smugglers," the spokesman said.
Those who choose to depart voluntarily can apply for support from the International Organization for Migration in Switzerland.
All 332 have been sent back since the government announced Aug. 13 that "irregular maritime arrivals" would be liable for transfer to regional processing facilities in Nauru and Papua New Guinea.
Immigration Minister Chris Bowen said in a statement the departure of recent Sri Lankans "raised no issues that engaged Australia's international obligations."
A report by The Australian newspaper said Bowen's comment implied that the returned Sri Lankans weren't considered refugees.
"The government will continue to return people where they do not engage Australia's international obligations," Bowen said.
The Labor government ran into heavy criticism from opposition politicians when it announced it would reopen the two processing centers, one being on rugged and jungle-covered Manus Island, part of Papua New Guinea which lies north of Australia.
Opposition parties and humanitarian organizations say they are concerned asylum seekers in offshore centers won't have the same legal protection as people on the mainland.
Papua's government has had close relations with Australia, which governed it until independence in 1975.
Australia also reached an agreement with the government of Nauru -- a circular island in the South Pacific with a population of just more than 9,000 -- to reopen a processing center there.
Nauru, a former British Colony called Pleasant Island, has been independent since 1968 but is under the protection of Australia.
The centers are operated in exchange for financial aid to the governments.
In September, soon after the Nauru center opened, Iranian asylum seekers rioted, causing around $24,000 damage to facilities including kitchens and tents.
Australia continues to struggle with thousands of asylum seekers arriving in its waters in dangerously overcrowded and rickety boats. All have paid people smugglers hundreds or thousands of dollars for the sometimes fatal voyage.
Government figures estimate around more than 600 refugees have drowned in the past three years.
The centers were opened after a deal by the government of Prime Minister Julia Gillard with Malaysia floundered earlier this year over legal issues.
Australia was to accept bona fide refugees from Malaysia in return for sending asylum seekers there for processing.
Gillard decided in August to negotiate the reopening of the centers after an independent panel, led by former Air Chief Marshal Angus Houston, recommended offshore processing.
The panel saw offshore centers as part of a "hard-headed but not hardhearted" approach to the problem of increasing numbers of asylum seekers.