Founded in 2017, Duozhuayu now has a 6,000-square-meter warehouse in Tianjin to examine, refurbish and store used books.

Chen Qiulin, 24, a staff member at the warehouse, said a recycled used book must undergo a four-step refurbishing process before it goes back on the bookshelf.

"The first step is cleaning. Some 50 percent of the recycled books are in quite good condition, and 3 to 5 percent are brand new, so each of our workers can clean about 200 books an hour," Chen said.

The second step is polishing the edges, before the books are sent to a disinfection room. "They remain there for 60 to 85 minutes for ozone disinfection. This room can hold 2,000 books at a time," Chen said.

The final step is the addition of plastic packaging for each book before it is ready to be delivered to the reader.

"We have about 25 workers in all four processes, and they can now handle about 14,000 books a day," Chen added.

Yan Shen, 23, who works for a film company, enjoys receiving refurbished books from Duozhuayu, as she loves to read used ones.

"For some new books, it's not easy to flip the pages over, but for used books, it's usually smooth," Yan said. "Also, when you see remarks written on the pages, you feel connected to the previous owner, which seems romantic to me."

Yan places two to three orders with Duozhuayu each month, and as her collection of books mounts, she plans to sell some of them back to the platform.

Gao has already started to resell books, but has only selected those she thinks she won't reread. Using her phone, she scans the bar codes of those she wants to sell on Duozhuayu's WeChat progam, and it tells her whether a certain book has been recycled by the platform, and the purchasing price.

A courier visits her home to collect the books and take them to the warehouse in Tianjin. After a book is checked, Gao receives payment.

Chen is responsible for a book's final check. He said that three out of 100 books are rejected, mainly because they are pirated.

"We record different versions of pirated books and also trace the legitimate version so that we can identify pirated copies," Chen said. "Take Miracles of the Namiya General Store (a 2012 Japanese novel by Keigo Higashino) as an example. The inside cover of the legitimate version has a wrinkle effect, whilst the pirated version does not."