Shopping cart cleaning protocols vary by supermarket, and even by location within the same brand. At my local Walmart they use hot water and steam—you can feel both the temperature of the cart and the dampness when they've come fresh out of the sanitization station. Other supermarkets, like Hy-Vee, use systems like this Sterile Cart, which sprays disinfectant on the carts.

Not all supermarkets have the footprint to house a dedicated cleaning area. In those cases they can outsource the cleaning. A company called HealthyCart operates mobile trailers where they show up to the site, get the carts into their trailer and blast them clean.

Over in Europe, Germany's ShopBox Group also produces mobile shopping cart washing systems.

Those latter two solutions are fine for suburbs where there's room to get the truck ins, but such solutions are a no-go for space-tight urban areas. Therefore Dutch company CleanShopping has managed to cram an entire system into a Sprinter van.

In order to gain complete coverage within a limited amount of space, the engineers had to get creative. There's no room to install a 360-degree nozzle arrangement, so they instead created a rotary drum for the carts:

CleanShopping operates in the Netherlands, but has recently made a foray into Spain; the company is planning a Europe-wide expansion.